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Tweetable abstract Layered double hydroxide nanocarriers are capable of intercalating hydrophobic NSAIDs, such as mefenamic acid, which improves their pharmacokinetics and bioavailability.

The sodium-glucose cotransporter 2 inhibitor ertugliflozin is metabolized by the uridine 5'-diphospho-glucuronosyltransferase (UGT) isozymes UGT1A9 and UGT2B4/2B7. This analysis evaluated the drug-drug interaction (DDI) following co-administration of ertugliflozin with the UGT inhibitor mefenamic acid (MFA) using physiologically-based pharmacokinetic (PBPK) modeling. The ertugliflozin modeling assumptions and parameters were verified using clinical data from single-dose and multiple-dose studies of ertugliflozin in healthy volunteers, and the PBPK fraction metabolized assignments were consistent with human absorption, distribution, metabolism, and excretion results. The model for MFA was developed using clinical data, and in vivo UGT inhibitory constant values were estimated using the results from a clinical DDI study with MFA and dapagliflozin, a UGT1A9 and UGT2B4/2B7 substrate in the same chemical class as ertugliflozin. Using the verified compound files, PBPK modeling predicted an ertugliflozin ratio of area under the plasma concentration-time curves (AUC R ) of 1.51 when co-administered with MFA. ClinicalTrials.gov identifier: NCT00989079., (© 2020 Pfizer Inc. CPT: Pharmacometrics & Systems Pharmacology published by Wiley Periodicals LLC on behalf of American Society for Clinical Pharmacology and Therapeutics.)

This analysis reports a quantitative modeling and simulation approach for oral dapagliflozin, a primarily uridine diphosphate-glucuronosyltransferase (UGT)-metabolized human sodium-glucose cotransporter 2 selective inhibitor. A mechanistic dapagliflozin physiologically based pharmacokinetic (PBPK) model was developed using in vitro metabolism and clinical pharmacokinetic (PK) data and verified for context of use (e.g., exposure predictions in pediatric subjects aged 1 month to 18 years). Dapagliflozin exposure is challenging to predict in pediatric populations owing to differences in UGT1A9 ontogeny maturation and paucity of clinical PK data in younger age groups. Based on the exposure-response relationship of dapagliflozin, twofold acceptance criteria were applied between model-predicted and observed drug exposures and PK parameters (area under the curve and maximum drug concentration) in various scenarios, including monotherapy in healthy adults (single/multiple dose), monotherapy in hepatically or renally impaired patients, and drug-drug interactions with UGT1A9 modulators, such as mefenamic acid and rifampin. The PBPK model captured the observed exposure within twofold of the observed monotherapy data in adults and adolescents and in special population. As a guide to determining dosing regimens in pediatric studies, the verified PBPK model, along with UGT enzyme ontogeny maturation understanding, was used for predictions of dapagliflozin monotherapy exposures in pediatric subjects aged 1 month to 18 years that best matched exposure in adult patients with a 10-mg single dose of dapagliflozin., (© 2021 The Authors. CPT: Pharmacometrics & Systems Pharmacology published by Wiley Periodicals LLC on behalf of American Society for Clinical Pharmacology and Therapeutics.)

Ertugliflozin (ERTU) is a novel, potent, and highly selective sodium glucose cotransporter 2 inhibitor that has been recently approved for the treatment of type 2 diabetes mellitus. We describe a novel bioanalytical method using high-performance liquid chromatography (HPLC) coupled with fluorescence detection for quantitative determination of ERTU in rat plasma. Acetonitrile-based protein precipitation method was used for sample preparation, and chromatographic separation was performed on a Kinetex® C18 column with an isocratic mobile phase comprising acetonitrile and 10 mM potassium phosphate buffer (pH 6.0). The eluent was monitored by a fluorescence detector at an optimized excitation/emission wavelength pair of 277/320 nm. The method was validated to demonstrate the selectivity, linearity (ranging from 4 to 2000 ng/mL), precision, accuracy, recovery, matrix effect, and stability in line with the current FDA guidelines. The newly developed method was successfully applied to investigate the pharmacokinetic interactions of ERTU with mefenamic acid (MEF) and ketoconazole (KET). The findings of the present study revealed that the pharmacokinetics of ERTU may be altered by concurrent administration of MEF and KET in rats. To our knowledge, the present study is the first to develop a validated bioanalytical method for quantification of ERTU using HPLC coupled with fluorescence detection and to assess the drug interaction potential of ERTU with non-steroidal anti-inflammatory (MEF) and azole antifungal (KET) drugs., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The purpose of this work was to investigate the use of the dimethylaminoethyl methacrylate-copolymer Eudragit EPO (EPO) in oral solubility-enabling formulations for anionic lipophilic drugs, aiming to guide optional formulation design and maximize oral bioavailability. We have studied the solubility, the permeability, and their interplay, using the low-solubility nonsteroidal anti-inflammatory drug mefenamic acid as a model drug. Then, we studied the biorelevant solubility enhancement of mefenamic acid from EPO-based formulations throughout the gastrointestinal tract (GIT), using the pH-dilution dissolution method. EPO allowed a profound and linear solubility increase of mefenamic acid, from 10 μg/mL without EPO to 9.41 mg/mL in the presence of 7.5% EPO (∼940-fold; 37 °C); however, a concomitant decrease of the drug permeability was obtained, both in vitro and in vivo in rats, indicating a solubility-permeability trade-off. In the absence of an excipient, the unstirred water layer (UWL) adjacent to the GI membrane was found to hinder the permeability of the drug, accounting for this UWL effect and revealing that the true membrane permeability allowed good prediction of the solubility-permeability trade-off as a function of EPO level using a direct relationship between the increased solubility afforded by a given EPO level and the consequent decreased permeability. Biorelevant dissolution studies revealed that EPO levels of 0.05 and 0.1% were insufficient to dissolve mefenamic acid dose during the entire dissolution time course, whereas 0.5 and 1% EPO allowed complete solubility with no drug precipitation. In conclusion, EPO may serve as a potent solubility-enabling excipient for BCS class II/IV acidic drugs; however, it should be used carefully. It is prudent to use the minimal EPO amounts just sufficient to dissolve the drug dose throughout the GIT and not more than that. Excess amounts of EPO provide no solubility gain and cause further permeability loss, jeopardizing the overall success of the formulation. This work may help the formulator to hit the optimal solubility-permeability balance, maximizing the oral bioavailability afforded by the formulation.

Aim: The current investigation is focused on solid self-microemulsifying drug-delivery systems (S-SMEDDS) of mefenamic acid (MFA) for improving pharmacodynamic activity. Methodology & results: Solubility assessment in various lipid excipients and optimization of pseudoternary plots were carried out for development of liquid SMEDDS. The optimized liquid SMEDD formulation was spray dried to solid dosage form and observed with enhanced amorphization or molecular dispersion of MFA in S-SMEDDS, as evident from x-ray diffractometry and differential scanning calorimetry studies. Enhanced in vitro dissolution rate of optimized formulation was observed, resulting in multifold enhancement in absorption profile of MFA, as compared with pure drug and marketed product. These studies further substantiate the dose reduction in SMEDDS by gaining equivalent therapeutic profile with marketed product. Enhanced analgesic and anti-inflammatory activity was observed with S-SMEDD formulations in acetic acid-induced writhings and carrageenan-induced paw edema models, respectively., Conclusion: The optimized S-SMEDD formulation holds great promise for enhancement of its physiochemical and biological attributes.

The activities of hundreds, perhaps thousands, of metabolites are regulated by human cytosolic sulfotransferases (SULTs) - a 13-member family of disease relevant enzymes that catalyze transfer of the sulfuryl moiety (-SO 3 ) from PAPS (3'-phosphoadenosine 5'-phosphosulfonate) to the hydroxyls and amines of acceptors. SULTs harbor two independent allosteric sites, one of which, the focus of this work, binds non-steroidal anti-inflammatory drugs (NSAIDs). The structure of the first NSAID-binding site - that of SULT1A1 - was elucidated recently and homology modeling suggest that variants of the site are present in all SULT isoforms. The objective of the current study was to assess whether the NSAID-binding site can be used to regulate sulfuryl transfer in humans in an isoform specific manner. Mefenamic acid (Mef) is a potent (K i 27 nM) NSAID-inhibitor of SULT1A1 - the predominant SULT isoform in small intestine and liver. Acetaminophen (APAP), a SULT1A1 specific substrate, is extensively sulfonated in humans. Dehydroepiandrosterone (DHEA) is specific for SULT2A1, which we show here is insensitive to Mef inhibition. APAP and DHEA sulfonates are readily quantified in urine and thus the effects of Mef on APAP and DHEA sulfonation could be studied non-invasively. Compounds were given orally in a single therapeutic dose to a healthy, adult male human with a typical APAP-metabolite profile. Mef profoundly decreased APAP sulfonation during first pass metabolism and substantially decreased systemic APAP sulfonation without influencing DHEA sulfonation; thus, it appears the NSAID site can be used to control sulfonation in humans in a SULT-isoform specific manner., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Mefenamic Acid (MFA) is a widely-used non-steroidal anti-inflammatory drug. MFA presents four possible crystal forms; Form I and Form II being the only two pure crystals that have been isolated and fully characterized. Both Form I and Form II were prepared following the literature and completely characterized by middle (MIR) and near (NIR) infrared spectroscopy, digital optical microscopy, differential scanning calorimetry, melting point and dissolution properties. In order to develop quantitative models to assess Form I in formulated products, two sets of samples, training (n=10) and validation (n=8) sets, were prepared by mixing both polymorphs and the matrix of excipient (simulating commercial tablets). The particle size of the samples was homogenized by sieving and samples were mechanically mixed. A batch of commercial tablets was gently disaggregated, sieved and mechanically mixed for further analysis. For each sample, full MIR and NIR spectra were acquired and used as input of partial least squares (PLS) algorithm separately. Method optimization and internal validation were performed by leave one out procedure. Full spectra and 5 PLS-factors were used for MIR; while, 5 PLS-factors and mean center spectra of full spectra were the optimal conditions for NIR. Accuracy and precision were assessed by evaluation of the actual vs. predicted curve of validation set; and by calculating validation set recoveries and deviations (104.3±8.2% and 100.4±1.0% for MIR and NIR respectively). Only NIR-PLS yielded acceptable results and low deviations during commercial samples evaluation (102.8±0.1%). The same behavior was observed when spiked tablets were analyzed (103.5±0.5%). Additionally, for the calibration set ten dissolution profiles (average of 6 curves each), were obtained under optimized test conditions (900 ml of buffer phosphate pH 9 with surfactant, apparatus II USP, 100rpm, detection at 342nm). A multiple linear regression (MLR) was carried out using dissolution profiles and Form I content. The developed MLR model could correlate dissolution profiles and polymorphic richness. This approach, coupled to previously developed NIR-PLS, may act as a valid tool to estimate dissolution profiles from solid forms., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Drug load plays an important role in the development of solid dosage forms, since it can significantly influence both processability and final product properties. The percolation threshold of the active pharmaceutical ingredient (API) corresponds to a critical concentration, above which an abrupt change in drug product characteristics can occur. The objective of this study was to identify the percolation threshold of a poorly water-soluble drug with regard to the dissolution behavior from immediate release tablets. The influence of the API particle size on the percolation threshold was also studied. Formulations with increasing drug loads were manufactured via roll compaction using constant process parameters and subsequent tableting. Drug dissolution was investigated in biorelevant medium. The percolation threshold was estimated via a model dependent and a model independent method based on the dissolution data. The intragranular concentration of mefenamic acid had a significant effect on granules and tablet characteristics, such as particle size distribution, compactibility and tablet disintegration. Increasing the intragranular drug concentration of the tablets resulted in lower dissolution rates. A percolation threshold of approximately 20% v/v could be determined for both particle sizes of the API above which an abrupt decrease of the dissolution rate occurred. However, the increasing drug load had a more pronounced effect on dissolution rate of tablets containing the micronized API, which can be attributed to the high agglomeration tendency of micronized substances during manufacturing steps, such as roll compaction and tableting. Both methods that were applied for the estimation of percolation threshold provided comparable values.

Purpose: The anionic form of the drug mefenamic acid intercalated into the nanocarrier layered double hydroxide (LDH-Mef) was evaluated by anti-inflammatory and antinociceptive assays., Methods: The LDH-Mef material was characterized by a set of physicochemical techniques, which was supported by Density Functional Theory calculations. The pharmacological effects of LDH-Mef (40 wt% of drug) were evaluated by hemolytic, anti-inflammatory activity and antinociceptive assays., Results: In vivo assays were conducted for the first time in order to assess the LDH-Mef potential. The hemolytic effects decreased for the intercalated Mef as demonstrated by the higher tolerated hemolytic concentration (1.83 mM) compared to mefenamic acid (MefH), 0.48 mM. Pretreatment of animals with MefH or LDH-Mef reduced carrageenan-, dextran sulfate- and PGE2-induced paw edema. MefH or LDH-Mef also decrease total leucocytes and neutrophil counts of the peritoneal cavity after inflammation induction with carrageenan. In the nociception model, oral pretreatment with LDH-Mef reduced mechanical hypernociception carrageenan-induced after 3-4h and also the number of writhings induced by acetic acid., Conclusions: This work shows the increase of the anti-inflammatory and antinociceptive potential of the drug confined into the LDH, as well as, its hemolytic effect., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Background: Non steroidal anti-inflammatory drugs are the most widely prescribed drugs to manage pain and inflammatory conditions, but their long term use is associated with gastrointestinal toxicity., Objectives: The study aimed to synthesize an ester-based prodrug of a non steroidal anti-inflammatory agent, mefenamic acid in order to improve the therapeutic index vis a vis to overcome the side effects such as gastrointestinal irritation and bleeding associated with the use of mefenamic acid., Methods: The ester prodrug (MA-NH) was prepared by condensing mefenamic acid with N-hydroxymethylsuccinimide in the presence of Phosphorus oxychloride. The pharmacokinetic profile, including stability and release of mefenamic acid and N-hydroxymethylsuccinimide from the ester prodrug (MA-NH) was studied by RP- HPLC in acidic medium (pH 1.2), basic medium (pH 7.4), 80 % v/v human plasma, 10 % w/v rat intestinal homogenate and 10 % w/v rat liver homogenate (pH 7.4)., Results: The chemical structure of the title compound was characterized by using modern spectroscopic techniques. The prodrug was found to be stable in acid medium, but it hydrolyzed and released sufficient quantities of the drug in alkaline medium. The prodrug produced lesser number of ulcers and showed improved analgesic and anti-inflammatory activity as compared to the parent drug., Conclusion: The results indicate that the synthesized prodrug (MA-NH) is better in terms of analgesic and antiinflammatory activities and with less GI toxicity than the parent drug.

Mefenamic acid (MEF) is a widely prescribed non-steroidal anti-inflammatory drug that has been found associated with rare but severe cases of hepatotoxicity, nephrotoxicity and gastrointestinal toxicity. The formation of protein-reactive acylating metabolites such as 1-O-acyl-MEF glucuronide (MEFG) and 3'-hydroxymethyl-MEF 1-O-acyl-glucuronide is one proposed cause. In addition to the well-reported 3'-hydroxymethyl-MEF, two mono-hydroxyl-MEF (OH-MEFs) were recently identified in vitro. However, in vivo evidence is lacking and whether these OH-MEFs would be further glucuronidated to the potentially reactive 1-O-acyl-glucuronides (OH-MEFGs) is unknown. Utilizing UPLC-Q-TOF/MS and LC-MS/MS, the current study identified, for the first time, four OH-MEFs and their corresponding OH-MEFGs from plasma after a single oral administration of MEF (40 mg/kg) to rats, including an OH-MEF that has not been reported previously. The systemic exposure of these identified metabolites was high, with metabolic to parent AUC0 → 24 h ratios reaching 23-52% (OH-MEFs) and 8-29% (OH-MEFGs). These metabolites also had a long systemic exposure time in both single and 5 day multiple oral MEF-treated rats, with elimination half-lives between 9 h and > 24 h. In addition to these novel metabolites, the previously reported MEFG was also identified and its systemic exposure was found to be doubled after multiple MEF administrations. These pharmacokinetic results suggest that systemic toxicities caused by the potentially reactive MEFG and OH-MEFGs could be considerable, especially after repeated MEF treatment. Nevertheless, MEFG and OH-MEFGs had negligible uptake in the brain, indicating a minimal risk of brain toxicities. Furthermore, an in situ intestinal perfusion study revealed that during MEF absorption, it was extensively metabolized to MEFG while < 5% was metabolized to OH-MEFs and OH-MEFGs., (Copyright © 2015 John Wiley & Sons, Ltd.)

Ethnopharmacological Relevance: Scutellariae Radix (SR), the dried root of Scutellariae baicalensis Georgi, has a lot in common with non-steroidal anti-inflammatory drugs (NSAIDs). Their similarities in therapeutic action (anti-inflammation) and metabolic pathways (phase II metabolisms) may lead to co-administration by patients with the potential of pharmacokinetic and/or pharmacodynamic interactions. The current study aims to investigate the potential interactions between SR and an NSAID, mefenamic acid (MEF), on the overall pharmacokinetic dispositions, anti-inflammatory effects and adverse effects in rats., Materials and Methods: The current study simultaneously monitored the pharmacokinetic and pharmacodynamic interactions in a single animal. Four groups of Sprague-Dawley rats (n=7 each) received oral doses of a standardized SR extract (300mg/kg, twice daily), MEF (40mg/kg, daily), combination of SR extract and MEF, and vehicle control, respectively, for 5 days. On Day 5, blood samples were collected after first dose over 24h for the determination of (1) plasma concentrations of SR bioactive components, MEF and its metabolites by LC-MS/MS, and (2) prostaglandin E2 (PGE2) production and cyclooxygenase-2 (COX-2) gene expression by ex vivo analyses using LPS-stimulated RAW264.7 macrophage cells, ELISA and real time-PCR. After the rats were sacrificed, stomachs were isolated to assess their gross mucosal damage. Statistical comparisons were conducted using ANOVA and t-test., Results: Minimal pharmacokinetic interaction between SR extract and MEF was observed. Co-administration of SR extract and MEF did not significantly alter the plasma concentration-time profile or the pharmacokinetic parameters such as Cmax, AUC0→24, Tmax or clearance. Pharmacodynamic interaction via the COX-2 pathway was observed. The PGE2 level in LPS-stimulated RAW264.7 cells treated with plasma collected from control group over the 24h sampling (AUC0→24[PGE2]) was 191981±8789pg/mlhr, which was significantly reduced to 174,780±6531 and 46,225±1915pg/mlhr by plasma collected from rats administered with SR extract and MEF, respectively. Co-administration of SR extract and MEF further potentiated the PGE2 inhibition, with an AUC0→24[PGE2] of 37013±2354pg/mlhr (p<0.05, compared to SR or MEF group). By analyzing the COX-2 gene expression, SR extract significantly prolonged the COX-2 inhibitory effect of MEF over the 24h (p<0.05). Furthermore, the MEF-induced stomach ulcer after the 5-day treatment, as evidenced by the increased gross ulcer index and sum of lesion length (p<0.05, compared to control), could be alleviated by co-administration with SR extract (p<0.05)., Conclusions: Co-administration of SR extract and MEF potentiated the anti-inflammatory effects, alleviated the MEF-induced stomach adverse effect while having minimal pharmacokinetic interactions. Our findings provide insight for combination therapy of SR extract and MEF against inflammatory diseases., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

Mefenamic acid (MFA) has been associated with rare but severe cases of hepatotoxicity, nephrotoxicity, gastrointestinal toxicity, and hypersensitivity reactions that are believed to result from the formation of reactive metabolites. Although formation of protein-reactive acylating metabolites by phase II metabolism has been well-studied and proposed to be the cause of these toxic side effects, the oxidative bioactivation of MFA has not yet been competely characterized. In the present study, the oxidative bioactivation of MFA was studied using human liver microsomes (HLM) and recombinant human P450 enzymes. In addition to the major metabolite 3'-OH-methyl-MFA, resulting from the benzylic hydroxylation by CYP2C9, 4'-hydroxy-MFA and 5-hydroxy-MFA were identified as metabolites resulting from oxidative metabolism of both aromatic rings of MFA. In the presence of GSH, three GSH conjugates were formed that appeared to result from GSH conjugation of the two quinoneimines formed by further oxidation of 4'-hydroxy-MFA and 5-hydroxy-MFA. The major GSH conjugate was identified as 4'-OH-5'-glutathionyl-MFA and was formed at the highest activity by CYP1A2 and to a lesser extent by CYP2C9 and CYP3A4. Two minor GSH conjugates resulted from secondary oxidation of 5-hydroxy-MFA and were formed at the highest activity by CYP1A2 and to a lesser extent by CYP3A4. Additionally, the ability of seven human glutathione S-transferases (hGSTs) to catalyze the GSH conjugation of the quinoneimines formed by P450s was also investigated. The highest increase of total GSH conjugation was observed with hGSTP1-1, followed by hepatic hGSTs hGSTA2-2 and hGSTM1-1. The results of this study show that, next to phase II metabolites, reactive quinoneimines formed by oxidative bioactivation might also contribute to the idiosyncratic toxicity of MFA.

Nad(p)h: quinone oxidoreductase 1 (NQO1) is an enzyme capable of reducing a broad range of chemically reactive quinones and quinoneimines (QIs) and can be strongly upregulated by Nrf2/Keap1-mediated stress responses. Several commonly used drugs implicated in adverse drug reactions (ADRs) are known to form reactive QI metabolites upon bioactivation by P450, such as acetaminophen (APAP), diclofenac (DF), and mefenamic acid (MFA). In the present study, the reductive activity of human NQO1 toward the QI metabolites derived from APAP and hydroxy-metabolites of DF and MFA was studied, using purified bacterial P450 BM3 (CYP102A1) mutant M11 as a bioactivation system. The NQO1-catalyzed reduction of the QI metabolites was quantified relative to spontaneous glutathione (GSH) conjugation. Addition of NQO1 to the incubations strongly reduced the formation of all corresponding GSH conjugates, and this activity could be prevented by dicoumarol, a selective NQO1 inhibitor. The GSH conjugation was strongly increased by adding human GSTP1-1 in a wide range of GSH concentrations. Still, NQO1 could effectively compete with the GST catalyzed GSH conjugation by reducing the QIs. In conclusion, we identified the QI metabolites of the 4'- and 5-hydroxy-metabolites of DF and MFA as novel substrates for human NQO1. NQO1-mediated reduction proves to be an effective pathway to detoxify these QI metabolites in addition to GSH conjugation. Genetically determined deficiency of NQO1 therefore might be a risk factor for ADRs induced by reactive QI drug metabolites.

Many pharmaceutically active compounds are weak electrolytes and are ionizable in the pH range experienced throughout the gastrointestinal tract. Changes in protonation state due to pH changes in the gut can have dramatic effects on solubility, dissolution, and permeation through biological barriers. Preclinical assessment of the pH-dependence of oral absorption is critical for compounds possessing pH-dependent solubility. Here we examine pH-dependent solubility and oral exposure in rat for three model compounds, dasatinib, ketoconazole, and mefenamic acid. Dasatinib and ketoconazole are both weak bases, while mefenamic acid is a carboxylic acid. The effects of gastric pH modulators, pentagastrin and famotidine, were investigated in rat PK studies to assess the applicability of using the rat to evaluate the risk of pH-dependent oral exposure for ionizable compounds. Dasatinib showed similar exposure between control and pentagastrin-pretreated groups, and 4.5-fold lower AUC in famotidine-pretreated rats. Ketoconazole showed a 2-fold increase in AUC in pentagastrin-treated rats relative to control, and 4.5-fold lower AUC in famotidine treated rats, relative to the pentagastrin group. Mefenamic acid showed highly similar exposures among control, pentagastrin-pretreated, and famotidine-pretreated groups. The rat model was shown to be useful for compounds displaying pH-dependent solubility and oral absorption that may be affected by gastric pH modulators.

In the present study, the development and validation of an LC-MS/MS method for quantifying mefenamic acid in human plasma is described. The method involves liquid-liquid extraction using diclofenac as an internal standard (IS). Chromatographic separation was achieved on a Thermo Hypurity C(18) , 50 × 4.6 mm, 5 µm column with a mobile phase consisting of 2 m m ammonium acetate buffer and methanol (pH 4.5 adjusted with glacial acetic acid; 15:85, v/v) at a flow-rate of 0.75 mL/min and the total run time was 1.75 min. Analyte was introduced to the LC-MS/MS using an atmospheric pressure ionization source. Both the drug and IS were detected in negative-ion mode using multiple reaction monitoring m/z 240.0 → 196.3 and m/z 294.0 → 250.2, respectively, with a dwell time of 200 ms for each of the transitions. The standard curve was linear from 20 to 6000 ng/mL. This assay allows quantification of mefenamic acid at a concentration as low as 20 ng/mL in human plasma. The observed mean recovery was 73% for the drug. The applicability of this method for pharmacokinetic studies has been established after successful application during a 12-subject bioavailabity study., (Copyright © 2012 John Wiley & Sons, Ltd.)

Carboxylic acid-containing nonsteroidal anti-inflammatory drugs (NSAIDs) can be metabolized to chemically reactive acyl glucuronide and/or S-acyl-CoA thioester metabolites capable of transacylating GSH. We investigated the metabolism of the NSAID mefenamic acid (MFA) to metabolites that transacylate GSH, leading to MFA-S-acyl-GSH thioester (MFA-SG) formation in incubations with rat and human hepatocytes and in vivo in rat bile. Thus, incubation of MFA (1-500 μM) with rat hepatocytes led to the detection of MFA-1-β-O-acyl glucuronide (MFA-1-β-O-G), MFA-S-acyl-CoA (MFA-SCoA), and MFA-SG by liquid chromatography-tandem mass spectrometric analysis. The C(max) of MFA-SG (330 nM; 10-min incubation with 100 μM MFA) was 120- to 1400-fold higher than the C(max) of drug S-acyl-GSH adducts detected from studies with other carboxylic acid drugs to date. MFA-SG was also detected in incubations with human hepatocytes, but at much lower concentrations. Inhibition of MFA acyl glucuronidation in rat hepatocytes had no effect on MFA-SG formation, whereas a 58 ± 1.7% inhibition of MFA-SCoA formation led to a corresponding 66 ± 3.5% inhibition of MFA-SG production. Reactivity comparisons with GSH in buffer showed MFA-SCoA to be 80-fold more reactive than MFA-1-β-O-G forming MFA-SG. MFA-SG was detected in MFA-dosed (100 mg/kg) rat bile, where 17.4 μg was excreted after administration. In summary, MFA exhibited bioactivation in rat and human hepatocytes and in vivo in rat, leading to reactive acylating derivatives that transacylate GSH. The formation of MFA-SG in hepatocytes was shown not to be mediated by reaction with MFA-1-β-O-G, and not solely by MFA-SCoA, but perhaps also by intermediary MFA-acyl-adenylate formation, which is currently under investigation.

Objectives: The objectives of this study were to assess the bioavailability of an optimized mephenamic acid (MFA) microspheres (test) against a Ponstan® capsule (reference) in healthy volunteers, and to establish a correlation with in vitro parameters., Subjects and Methods: Four subjects received the test and reference (250 mg MFA each) in a randomized crossover design, separated by a 1-week washout period. The drug was analyzed in plasma by a specific high-performance liquid chromatographic method. The relevant pharmacokinetic parameters [maximum plasma concentration (C(max)), time of peak concentration (T(max)), area under plasma concentration-time curves from 0 to 12 h (AUC(0-12)) and area under plasma concentration-time curves from zero to ∞ (AUC(0-)∞)] were calculated from the plasma drug concentration-time data., Results: The test product exhibited faster absorption (T(max) of 1.87 ± 0.482 vs. 2.14 ± 0.20 h; C(max) of 5.91 ± 0.604 vs. 3.58 ± 0.671 μg/ml) when compared to the reference. The relative bioavailability of the test compared to the reference capsule was 172%. Good correlations were established between the in vitro 90% dissolution (T90) and each of the AUC(0-12) and T(max), as well as between the percentage of drug released and plasma concentrations., Conclusion: The formulation of MFA microsphere with polyethylene glycol improved the dissolution rate and bioavailability of MFA, as evidenced by a higher C(max), AUC(0-12) and AUC(0-)∞, and shorter T(max) values. Good correlations between T90 and both AUC(0-12) and T(max) as well as between the percentage of drug released and plasma concentrations were achieved., (Copyright © 2011 S. Karger AG, Basel.)

A suitable topical formulation of mefenamic acid was developed in order to eliminate the gastrointestinal disorders associated with its oral administration. Drug coprecipitates prepared with different polymers at various drug-to-polymer ratios improved drug solubility and dissolution compared to pure drug and physical mixtures. PVP polymers (ratio 1:4) produced the best results. Aqueous ionic cream, ointments of absorption and water soluble bases and gels of methylcellulose, carboxymethylcellulose sodium, HPMC, Carbopol® 934 and 940, and Pluronic® F127 bases containing 1-10% drug as coprecipitates of PVP polymers (1:4) were prepared. The highest drug release was achieved at 1% drug concentration from water soluble base and methylcellulose among cream/ointment and gel bases, respectively. Gels, in general yielded better release than creams/ointments. All tested medicated creams/ointments exhibited plastic flow while all gels conformed to pseudoplasticity. Most of them showed thixotropy, a desired property of topical preparations. Stability studies revealed that HPMC and methylcellulose had the smallest changes in drug content, viscosity, and pH among the formulations. Considering drug release, rheological properties, and stability, methylcellulose gel containing 1% drug as coprecipitates of PVP K90 was the best among the studied formulations, was promising for improving bioavailability of mefenamic acid and can be used in future studies.

Mephenamic acid is characterized by low solubility, which affects its dissolution rate and bioavailability. The objective of this study was to develop fast-release microspheres of ammonium salt of the drug (AMM) by emulsion congealing.The effect of polymer, drug to polymer ratio, surfactant, type and volume of oil phase, stirring rate, microsphere size, encapsulation efficiency and stability of the microspheres were investigated. The results pointed out a good yield (69&#x2013;98%) and encapsulation efficiency (71&#x2013;100%). Optimum conditions include moderate molecular weight PEG, inclusion of Tween 20 and/or Span 80, high ratio of PEG (1 : 4, drug : PEG), use of mineral oil and high stirring rate (2000 rpm). Dissolution efficiency ranged between 57% and 90%. Effect of ageing on drug content and release revealed that the microspheres prepared remained stable throughout 1 year of storage. The described method was simple, efficient and resulted in stable microspheres with enhanced drug release.

The permeation enhancement of mefenamic acid by ethanol across full-thickness porcine skin, heat-separated epidermal membrane and heat-separated dermal membrane has been probed. Three donor phases saturated with mefenamic acid were used: (1) PEG400; (2) PEG400 with 10% ethanol; (3) mefenamic acid in PEG 400 with 30 mg ml(-1) cetrimide; these were applied to membranes mounted in Franz diffusion-type cells with 30 mg ml(-1) cetrimide as receptor phase (n > or =5). Across full-thickness skin, the flux was below the limit of detection from PEG400, but with the inclusion of 10% ethanol was 0.83 microg cm(-2)h(-1). When cetrimide was present in the donor (and receptor) phase the flux was very low 0.1 microg cm(-2)h(-1). Across heat-separated epidermal membrane the flux from PEG was 11.9+/-2.4 microg cm(-2)h(-1) with a 2.42 x increase in flux observed when 10% ethanol was present (p=0.0095). Across heat-separated dermal membrane the flux from PEG400 was 0.62+/-0.13 microg cm(-2)h(-1), with a 2.34 x increase in flux observed when 10% ethanol was present (p=0.0027). To conclude, complexation and co-permeation with ethanol via a pull effect was confirmed as the mechanism of enhanced skin permeation of mefenamic acid. Full thickness skin provides a more effective barrier than either isolated dermis or epidermis, casting doubt over the use of heat-separated epidermal membranes to model skin permeation and penetration. There was evidence that cetrimide does not cause skin barrier modulation, supporting its use as an effective receptor phase.

Profiling of rat plasma using a highly sensitive LC-ARC-MS technique showed that [(3)H] mefenamic acid was metabolized to several products, including a sulfate conjugate and a hydroxylated analogue as major metabolites. This technique of detecting low levels of radioactivity in plasma was superior to previously used methods, such as beta-RAM detectors.

Acyl glucuronides have been implicated in the toxicity of many xenobiotics and marketed drugs. These toxicities are hypothesized to be a consequence of covalent binding of the reactive forms of the acyl glucuronide to proteins. Reactive intermediates of the acyl glucuronide arise from the migration of the aglycone leading to other positional and stereoisomers under physiological conditions. In order to screen for the potential liabilities of these metabolites during the early phase of pharmaceutical development, an NMR method based on the disappearance of the anomeric resonance of the O-1-acyl glucuronide was used to monitor the degradation kinetics of 11 structurally diverse acyl glucuronides, including those produced from the known nonsteroidal anti-inflammatory drugs (NSAIDs). The acyl glucuronides were either chemically synthesized or were isolated from biological matrices (bile, urine, and liver microsomal extracts). The half-lives attained utilizing this method were found to be comparable to those reported in the literature. NMR analysis also enabled the delineation of the two possible pathways of degradation: acyl migration and hydrolytic cleavage. The previously characterized 1H resonances of acyl migrated products are quite distinguishable from those that arise from hydrolysis. The NMR method described here could be used to rank order acyl glucuronide forming discovery compounds based on the potential reactivity of the conjugates and their routes of decomposition under physiological conditions. Furthermore, we have shown that in vitro systems such as liver microsomal preparations can be used to generate sufficient quantities of acyl glucuronides from early discovery compounds for NMR characterization. This is particularly important, as we often have limited supply of early discovery compounds to conduct in vivo studies to generate sufficient quantities of acyl glucuronides for further characterization.

The simultaneous skin permeation of drug and penetration enhancer have been studied in vitro. Simple formulations of mefenamic acid in PEG400 incorporating various proportions of ethanol or 1,8-cineole were prepared and applied to porcine ear skin in diffusion cells under infinite conditions. Receptor phases were assayed for mefenamic acid by HPLC and ethanol or 1,8-cineole by GC. Concentration-dependent permeation profiles were obtained for both ethanol or 1,8-cineole, in addition to concentration-dependent enhancement of mefenamic acid. When the steady state flux of mefenamic acid was plotted against ethanol or 1,8-cineole, linear relationships were observed with r2 values of 0.988 and 0.999, respectively. The close connection between rates of excipient and solute permeation is generally referred to as the 'pull' (or 'drag') effect, where in this case permeation of the enhancer facilitated permeation of the solute. This appears to be sufficient to account for the enhancing activity of ethanol and 1,8-cineole, notwithstanding initial modulations that may occur within the stratum corneum.

It is well accepted that bacterial and virus infections elevate the levels of cytokines in serum and cerebrospinal fluids. Such high levels of cytokines might alter the integrity of the blood-brain barrier (BBB) and/or blood-cerebrospinal fluid barrier (BCSFB), subsequently affecting brain penetration of drugs. However, few reports have addressed this issue. Thus, we investigated brain penetration of cyclooxygenase (COX) inhibitors, commonly used as antipyretics, in mice treated with Shiga-like toxin II (SLT-II) derived from E. coli O157:H7, which significantly elevates cytokine levels. As antipyretics, we used diclofenac, mefenamic acid, and acetaminophen. We found that SLT-II significantly increased the brain-to-plasma concentration ratio (Kp) of diclofenac and mefenamic acid, but not of acetaminophen. Moreover, the Kp of diclofenac and mefenamic acid was increased by probenecid, an anionic compound. These results suggest that efflux anion transporters might be involved in the transport of diclofenac and mefenamic acid. Western blot analysis revealed that SLT-II decreased the expression of organic anion transporter-3, an efflux transporter located on the BBB and/or BCSFB. Taken together, these results suggest that SLT-II and/or SLT-II-stimulated cytokines might change brain penetration of drugs and could possibly increase the risk of their side-effects by altering the expression of transporters.

In order to reduce the gastrointestinal side effect, of mefenamic acid, its carboxylic group was condensed with the hydroxyl group of 1,2,3-trihydroxy propane 1,3-dipalmitate/stearate to give 3a and 3b. These compounds were evaluated for their gastric toxicity, anti-inflammatory activity by the carageenan induced paw oedema test and analgesic activity by the acetic acid induced writhing method. The release of mefenamic acid from the esters 3a and 3b was studied at pH 3, 4, 5 and 7.4 with direct analysis by reverse phase HPLC using acetonitrile:acetate buffer (0.1 M, pH 3.5): methanol (40:25:35) at 1 mL/min. The prodrugs showed less hydrolysis at pH 5 compared to pH 7.4 indicating that the prodrugs do not dissociate at stomach pH but release mefenamic acid at pH 7.4 in adequate amounts. The hydrolysis studies were also performed in rat plasma. A higher plasma concentration of mefenamic acid was observed in animals treated with 3a and 3b compared to the animals treated with the parent drug, and even after 8 h the concentration of mefenamic acid was 2 times higher. The peak plasma concentration of mefenamic acid in animals treated with mefenamic acid was attained in 1.5 h compared with 2 h in the case of prodrugs treated animals. The prodrugs showed less gastric ulceration compared to mefenamic acid at 100 mg/kg, a severity index of 1.10, 1.22 being observed with 3a, 3b and with mefenamic acid a severity index of 2.37 was observed. The prodrugs showed better anti-inflammatory activity compared to the parent drug and analgesic activity comparable to the parent drug. These findings suggest that the prodrugs 3a and 3b synthesized might be used as biolabile prodrugs of mefenamic acid with increased bioavailability and less gastrointestinal side effects.

A simple, rapid and specific method for analysis of mefenamic acid (I) in serum by a sensitive high-performance liquid chromatography is described. Only 70 microl of serum and a little sample work-up is required. A simple procedure of extraction by dichloromethane followed by evaporation to dryness under gentle stream of nitrogen and dissolving the dried residue in mobile phase was used. The mefenamic acid peak was separated from endogenous peaks on a C(8) column by a mobile phase of acetonitrile-water (50:50, v/v, pH 3). Mefenamic acid and internal standard (IS) (diclofenac) were eluted at 7.4 and 5.4 min, respectively. The limit of quantitation of mefenamic acid in serum was 25 ng/ml at 280 nm. The method was linear over the range of 25-2000 ng/ml with r(2) of 0.998. Mean recovery for mefenamic acid was 110%.

The preparation of mefenamic acid (MH)-alkanolamine [monoethanolamine, diethanolamine, triethanolamine and propanolamine] complexes was attempted to increase the transdermal flux of MH. A lipophilic enhancer system consisting of isopropyl myristate (IPM) and ethanol (9:1; EI system) produced a marked enhancement of MH flux from the alkanolamine complexes through hairless rat skin membrane. Among the alkanolamines examined, the propanolamine complex had the greatest enhancing effect on the permeation of MH. The observed permeation enhancement of MH-alkanolamine complexes by the EI system was explained by an analysis based on a two-layer diffusion model. The stratum corneum immersed in IPM forms a continuous phase of vehicle and stratum corneum and, from the phase, ethanol transport the MH-alkanolamine complexes to the epidermis and dermis, and the complexes, which are more water soluble than MH, exhibit increased partition into the epidermis and dermis, as the flux increases.

Phenytoin (pulverized powder), mefenamic acid (capsule), and sulpiride (film-coated tablet) are currently available on the Japanese market. For absorption of these drugs from their pharmaceutical preparations, they must disintegrate and dissolve during passage through the gastrointestinal tract. The bioavailability of these drugs differ among different pharmaceutical preparations and even for the same preparation. This led to a review of the influence of the features of pharmaceutical preparations and the physicochemical properties of film coating materials as well as the physiologic factors affecting drug bioavailability. The influence of coadministered drugs and concomitant intake of beverages and food on the bioavailability of drugs from pharmaceutical preparations is also described.

Purpose: Prodrug of non-steroidal anti-inflammatory drugs (NSAIDs) or NSAIDs linked with guaiacol have been reported to suppress gastrointestinal (GI) toxicity or induce GI protective effect. In this study. mefenamic-guaiacol ester was synthesized and its physicochemical properties. stability, and transport across Caco-2 monolayers were investigated., Methods: Synthesis of the ester was carried out using mefenamic acid, guaiacol. N. N'-dimethylaminopyridine, and N,N'dicyclohexylcarbodiimide. The hydrolysis of the ester was investigated in aqueous buffer solutions pH 1-12 as well as in Caco-2 homogenate, human plasma, and porcine liver esterase. Caco-2 cell monolayers were utilized for transport studies. Due to the high lipophilicity of the ester with a calculated logP of 6.15, bovine serum albumin (BSA, 4%) was included in the receiver compartment to obtain a good in vitro-in vivo correlation. Permeation of the ester was assessed with or without the exposure of cells to PMSF, an inhibitor of esterase., Results: The ester was stable at a wide pH range from 1-10. However, it was hydrolyzed by enzymes from porcine liver esterase and Caco-2 homogenate. With the PMSF exposure on the apical (AP) side and in the presence of 4% BSA on the basolateral (BL) side, the transported amount of the ester from AP-to-BL direction was 14.63% after 3 hr with a lag time of 23 min. The Papp for the ester was 4.72 x 10(-6) cm s(-1)., Conclusion: The results from hydrolysis studies indicate that this ester is a prodrug. The Papp value suggests the moderate absorption characteristic of the compound. The accumulation of this highly lipophilic ester in Caco-2 cells is reduced in the presence of BSA.

Mefenamic acid is a problematic drug in granulation, tableting, and dissolution due to its poor solubility, hydrophobicity, and tendency to stick to surfaces. In most cases, the specifications of a drug by the pharmacopoeia include identification and purity, but they do not describe the physicochemical drug properties precisely. To characterize the mefenamic acid particle size, surface area measurements, X-ray pattern, differential scanning calorimetry (DSC), wettability, crystal habit, and compression behavior of different batches from two manufacturers were investigated. Due to larger particle size and better wettability, mefenamic acid of Il Yang type was easier to handle in a granulation process. The compression behavior of both types was nearly the same, although particle size, crystal habit, and wettability were very different.

The objectives of these studies were, first, to determine the effect of elevated luminal viscosity on the gastrointestinal absorption of four model drugs and, second, to identify the key processes influencing drug absorption under elevated viscosity conditions. Studies were conducted in vitro and in healthy female mongrel dogs under fasting conditions. In the canine model, both the rate and extent of paracetamol and hydrochlorothiazide absorption were significantly decreased by the coadministration of 15 g guar gum dissolved in 500 ml normal saline. In the case of cimetidine, the rate but not extent of absorption was decreased. Owing to the high variability in the data, no statistically based conclusion could be drawn about the effects of coadministered guar gum on the oral absorption of the poorly soluble mefenamic acid. Based on the in vitro data, it appears that substantial reductions in the dissolution rate of paracetamol, hydrochlorothiazide and cimetidine account for the effects observed in vivo. It is concluded that the effect of an elevation in the intraluminal viscosity on drug absorption is greatest for highly soluble drugs, and results from a combination of a decrease in dissolution rate and gastric emptying rate.

The bioavailability and pharmacokinetics of mefenamic acid was studied in alloxan-diabetic rabbits. Mefenamic acid in plasma was assayed by high performance liquid chromatography. A paired t-test for normal and alloxan treated rabbits revealed a significant decrease in all the bioavailability and disposition kinetic parameters of mefenamic acid during diabetes was observed in the present study. The altered bioavailability and disposition of mefenamic acid in the diabetic state will require adjustment of the dosage regimen prescribed for diabetics in a clinical setting.

Pharmacokinetic behavior of single dose of 2 mefenamic acid capsule formulations was studied in a randomized crossover design in 22 healthy male volunteers. Following ingestion of 250 mg of either of the products, blood samples were obtained over a 14-hour period and the serum drug concentrations were determined by an HPLC assay with ultraviolet detection at 280 nm. The parametric 90% confidence intervals of the mean value of the ratio (fendol (test)/ponstan (reference)) of pharmacokinetic parameters were 0.88-1.07, 0.94-1.19, and 0.89-1.16 for AUC zero-infinity, Cmax and T1/2. In each case values were within the acceptable bioequivalence range of 0.8-1.25. Distribution-free point estimate for the difference in expected medians of Tmax of the 2 formulations (fendol-ponstan) was -0.5 hours with a 90% confidence interval of -1.0 to -0.25 which overlaps with the stipulated bioequivalence range of +/-0.48. The kinetic parameters a comparable to what is reported for mefenamic acid and there were no statistically significant differences in any of them when comparing the 2 products by ANOVA on log-transformed data. Although the 2 products are not equivalent regarding the secondary parameter Tmax, still the data indicate that they could be considered bioequivalent regarding rate of absorption (Cmax), extent of absorption (Cmax and AUC), and elimination (t1/2).

Urinary excretion of mefenamic acid (MA) and its two oxidative metabolites, M-I (3'-hydroxymethyl derivative) and M-II (3'-carboxyl derivative), and their glucuronides was investigated in preterm infants undergoing MA therapy. MA was given orally at a dose of 2 mg/kg and the dose was repeated every 24 h a maximum of three times. Urine was collected for up to 5 d after the last dose, and MA and the metabolites were determined by a newly developed HPLC. The cumulative amounts of MA and the metabolites excreted in the urine varied from 7 to 46% of the total dose administered, and were less than those reported in adults and children. Significant correlation was observed between the plasma half-life of MA and the cumulative amount of MA and the metabolites excreted in the urine. These results suggest that long plasma half-lives of MA observed in preterm infants are due mainly to low activity of drug metabolizing enzyme(s). In an infant who received the two regimens of MA therapy about 2 weeks apart, the plasma half-life of MA was shortened and the urinary excretion of the MA metabolites including their glucuronides was greatly increased during this period. It is suggested that the activities of both cytochrome P-450(s) and glucuronyltransferase(s) related to MA metabolism rapidly increased during the first month of the infant's life.

Various acyloxyethyl mefanamates were synthesized and evaluated for potential application as prodrugs. Their kinetics of hydrolysis were examined in aqueous solutions of pH 1.0 and 7.4 and in human plasma at 37 degrees C. Among the synthesized compounds, the beta-carboxypropionylethyl mefenamate and the pivaloyloxyethyl mefenamate show high stability against enzymatic and non enzymatic hydrolysis. On the other hand the acetyloxyethyl mefenamate shows t1/2s of 1.4 h, 1.41 h and 3.61 h in human plasma, solutions of pH 7.4 and pH 1.0 respectively; However, its hydrolysis to mefenamic acid in plasma was not quantitative. Preliminary in vivo study shows that acetyloxyethyl mefenamate gave plasma concentration of mefenamic acid lower than that of control after oral administration. The calculated AUC0-inf for the acetyloxyethyl and control were 45 and 85 micrograms.h/ml respectively.

The bioequivalence of three different formulations of mefenamic acid was tested using the index zeta 2 previously defined by Rescigno. This index is a measure of the distance in Hilbert space of two concentration vs time functions; unlike the approach of Westlake which assumes a multiplicative model for the AUC and Cmax characteristics, this approach does not imply any hypotheses on the structure of the data and no particular model of the absorption or of the elimination processes. The index zeta 2 is simply an indication of how similar two formulations are. Results for this new test were compared with those obtained with two other tests, namely 90 and 95% symmetrical confidence intervals of Westlake and two one-sided t-tests of Shuirmann through the 90% confidence intervals in the ranges 80-125% for AUC and 70-143% for Cmax. Results of the new test are fully comparable with those obtained using the other two tests.

Mefenamic acid is a nonsteroidal anti-inflammatory drug commonly used in analgesia. The use of this drug has been implicated in several cases of nephrotoxicity including acute renal failure and tubulointerstitial nephritis. One theory of drug-induced tubulointerstitial nephritis is that the drug or a derivative of the drug becomes irreversibly bound to certain sites in renal tissue and an immune response is directed against the hapten-host conjugate. Previous studies have shown that in humans the nonsteroidal anti-inflammatory drug mefenamic acid is metabolized by both phase I enzymes and the phase II enzyme family UDP-glucuronosyltransferase. Indeed, three glucuronides were identified and isolated from human urine by semipreparative HPLC after oral administration of mefenamic acid. This study focuses on mefenamic acid glucuronide and further characterizes this acyl glucuronide in terms of stability and its ability to bind irreversibly to proteins. Stability studies of mefenamic acid glucuronide in aqueous buffer highlighted the relative stability of this acyl glucuronide at physiological pH. The half-life at 37 degrees C, pH 7.4, was 16.5 +/- 3.1 hr, which is considerably longer than those reported for many acyl glucuronides. The degradation of mefenamic acid glucuronide was accelerated under alkaline conditions, decreasing the half-life to 5 +/- 1.6 hr at pH 8.0. Mefenamic acid glucuronide, although extremely stable in buffer at physiological pH, was found to bind irreversibly to human serum albumin in vitro. Irreversible binding to cellular proteins in culture was also evident with the addition of mefenamic acid to the heterologous Chinese hamster lung fibroblast cell line V79 expressing the human UDP-glucuronosyltransferase isoenzyme UGT1*02. This binding was directly related to glucuronide formation, because irreversible binding was not evident in the untransfected cell line V79.

The pharmacokinetics of mefenamic acid (MA), 2 mg/kg, were studied in 17 preterm infants with symptomatic patent ductus arteriosus. They were given this dosage orally at 24 h intervals. There were marked inter-individual differences in some of the pharmacokinetic parameters after the first dose; peak plasma concentration (Cmax) varied from 1.2 to 6.1 micrograms/mL with a mean of 3.8 micrograms/mL, time to reach Cmax (tmax) varied from 2 to 18 h with a mean of 7.7 h and plasma half-life (t1/2) varied from 3.8 to 43.6 h with a mean of 18.7 h. The group of infants (10/17) who had ductus closure after the first dose had significantly lower clearance (P < 0.01), longer t1/2 (P < 0.01) and higher 24 h plasma concentration (P < 0.001) compared to the group of infants (7/17) who had no ductus closure after the first dose. It appeared that the plasma concentration of MA had to be above 2.0 micrograms/mL and maintained at this concentration for at least 12 h for MA associated with ductus closure in preterm infants to take effect. In view of the inter-individual variation of plasma MA concentration and the effective plasma concentration, we suggest that measurement of the plasma concentration should be done 24 h after the first dose. This might be useful for safe and effective therapy for infants with ductus closure failure after the first dose.

Three major metabolites of mefenamic acid were isolated from the urine of a normal adult man receiving mefenamic acid orally. The structures of those metabolites were determined as glucuronides of mefenamic acid, its hydroxymethyl derivative, and its carboxylic acid derivative on the basis of spectral data.

Mefenamic acid (MA) is a nonsteroidal antiinflammatory analgesic agent widely used clinically. A simple and sensitive liquid-chromatographic assay has been developed for the quantitative determination of MA in human plasma. A reverse phase, 10-microns cyano column (25 x 0.4 cm), a mobile phase of water-acetonitrile-methanol-17 M acetic acid (69:15:15:1 by volume), and an ultraviolet detection (290 nm) are used for the separation of MA and internal standard (methyl-clonazepam). MA and internal standard are extracted from acidified plasma into diethyl ether and after evaporation of the organic phase, the residue is redissolved in methanol. Calibration curves are linear in the range 0.05-3.20 micrograms/ml, and at the plasma level corresponding to the quantification limit (0.05 microgram/ml) coefficients of variation are 7.5% and 10.2% for repeatability and reproducibility studies, respectively. This assay was successfully used in the study of pharmacokinetics of MA in human plasma after a single oral administration of a low MA dose.

The dissolution behavior and absorption of mefenamic acid following oral and rectal administration from drug:egg albumin solid dispersions have been studied in comparison with those of the drug alone. The interaction of drug with egg albumin in aqueous solution and solid state were examined by solubility analysis, dialysis experiments, and X-ray diffractometry. The results showed that the dissolution rate of mefenamic acid, and also the release of drug from witepsol H-15 suppositories, were significantly increased by using egg albumin:drug solid dispersions. Although egg albumin:drug solid dispersion enhanced the mean serum levels and the area under serum concentration-time curves after oral and rectal administration compared with those of the drug alone, no significant differences were found between the mean residence time values of drug and its solid dispersion. It was also noted that the extent of bioavailability of mefenamic acid and its solid dispersion following oral administration was significantly greater than that following rectal administration.

Optimum conditions for the preparation of non-magnetic and magnetic microspheres of albumin-globulin mix (alglomix) containing mefenamic acid have been standardized. The effect of various parameters has been investigated with regard to the appearance, yield, drug content and encapsulation efficiency. The physicochemical parameters of the microspheres such as density, particle size distribution, surface topography and wall thickness, as well as the magnetite contained within the magnetic microspheres, have been determined. The infrared spectroscopic analysis confirmed the encapsulation of the drug and absence of free drug on the surface of the microspheres. The X-ray diffraction analysis confirmed that the crystallinity of the drug remained unchanged indicating thereby that no complex formation had taken place between core and coat materials. The in vitro release profiles of the microspheres have been studied. An attempt has also been made to check the in vivo efficacy in rats.

Encapsulation of mefenamic acid (MFA), a potent non-steroidal anti-inflammatory drug with cationic acrylic resin, Eudragit E, was carried out using a fluidized-bed granulator (Glatt AG). Three drug:polymer ratios were prepared using 50 ml of 1, 2.5 and 5 per cent w/v aqueous suspension of Eudragit to coat 100 mg powdered drug. The bioavailability of the coated and uncoated drug was studied using four groups of animals, each consisting of six male rabbits (2-2.5 kg). Investigations were performed using the rabbits to examine the effects of prolonged administration of the coated and the uncoated MFA with Eudragit E(1 and 5 per cent) in a dose of 100 mg filled in hard gelatin capsules. One capsule was given daily for 30 days. Plasma levels of MFA with Eudragit E were significantly higher than those of drug only. Meanwhile, 5 per cent w/v polymer coating afforded higher drug availability than 2.5 per cent w/v which induced a higher level than 1 per cent w/v. Chronic gastric ulcers with different severities were found in the internal mucosa of all animals. In addition, there were multiple erosions in the glandular mucosa of stomachs of rabbits receiving MFA within the treatment period. IN the control group the gastric photograph was normal in every instance. Despite the extensive morphological damage at the end of treatment, the observed changes in the stomach of rabbits given coated drug is less deleterious than that treated with uncoated drug. The results of this study indicate that the coating of MFA with cationic Eudragit E increases its bioavailability and decreases the probability of ulceration.(ABSTRACT TRUNCATED AT 250 WORDS)

Mefenamic acid suppository 500 mg was administered by rectum to eight healthy adult volunteers followed by either activated charcoal 5 g orally at hourly intervals for 7 h or an equal volume of water on two separate occasions 7 days apart. Administration of charcoal did not significantly affect the pharmacokinetic variables of mefenamic acid. Thus the beneficial effects of charcoal in the treatment of mefenamic acid overdose are largely due to interference with absorption, rather than enhancement of elimination of the drug.

A quantitative method for the analysis of flunixin, 2-(2-methyl-3-trifluoromethylanilino) nicotinic acid, in equine urine by gas chromatography with nitrogen-phosphorus detection has been developed. Flunixin and the internal standard, mefenamic acid, N-(2,3-xylyl) anthranilic acid, were analysed after extractive methylation of the carboxylic acid group using methyl iodide. The extraction and alkylation conditions of flunixin and mefenamic acid have been studied. The detection limit of the method was 0.25 mumol/l flunixin in urine (74 ng/ml). Flunixin was found to be conjugated to 96.5% in equine urine, and the conjugate was spontaneously hydrolysed to free flunixin. This approach can also be used to confirm the presence of flunixin or mefenamic acid in horse urine in the doping control of racehorses.

The effect of various antacids on the absorption of tolfenamic and mefenamic acids has been investigated in three separate crossover studies, each consisting of four phases. Single doses of magnesium hydroxide (85 mg, 425 mg and 1700 mg) or of water (150 ml) were given by mouth to 6 healthy volunteers immediately after tolfenamic acid 400 mg (Study 1), and, using an identical study design, after mefenamic acid 500 mg (Study 3). In Study 2 sodium bicarbonate 1 g, aluminium hydroxide 1 g, an antacid preparation containing both aluminium and magnesium hydroxides, or water alone were ingested with tolfenamic acid 400 mg. Plasma concentrations of tolfenamic and mefenamic acids and their cumulative excretion in urine were determined up to 24 h. Magnesium hydroxide greatly accelerated, in a dose-dependent manner the absorption of both tolfenamic and mefenamic acids. The peak times in plasma were shortened by about 1 h by 425 mg and 1700 mg magnesium hydroxide, and the peak plasma concentrations of both fenamates were elevated up to 3-fold. The area under the plasma concentration-time curve between 0 and 1 h of tolfenamic acid was increased up to 7-fold and that of mefenamic acid up to 3-fold. The total bioavailability of tolfenamic and mefenamic acids was only slightly increased. Aluminium hydroxide alone and in combination with magnesium hydroxide significantly retarded the absorption and lowered the peak plasma concentration of tolfenamic acid. Sodium bicarbonate had no significant effect on its absorption. The interaction with magnesium hydroxide leads to higher and earlier peak plasma concentrations of the fenamates.(ABSTRACT TRUNCATED AT 250 WORDS)

Using improved techniques in a study of faecal blood loss no significant change over control level occurred during administration of mefenamic acid 500 mg t.i.d. for six days. This lack of gastro-intestinal bleeding is at variance with earlier findings for this compound. Studies of two mefenamic acid formulations (250 mg capsule and 500 mg filmseal tablet) showed no significant difference in area under blood level curves or in urinary output data, indicating equivalent total absorption. The 500 mg film-coated tablet gave significantly higher serum levels at 0.5 hours, whereas the 250 mg capsule gave significantly higher serum levels at 6 and 8 hours.