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Acetazolamide (molecular mass (MM), 222) belongs to the class of sulfonamides (R-SO2-NH2) and is one of the strongest pharmacological inhibitors of carbonic anhydrase activity. Acetazolamide is excreted unchanged in the urine. Here, we report on the development, validation and biomedical application of a stable-isotope dilution GC-MS method for the reliable quantitative determination of acetazolamide in human urine. The method is based on evaporation to dryness of 50 μL urine aliquots, base-catalyzed derivatization of acetazolamide (d0-AZM) and its internal standard [acetylo-2H3]acetazolamide (d3-AZM) in 30 vol% pentafluorobenzyl (PFB) bromide in acetonitrile (60 min, 30 °C), reconstitution in toluene (200 μL) and injection of 1-μL aliquots. The negative-ion chemical ionization (NICI) mass spectra (methane) of the PFB derivatives contained several intense ions including [M]‒ at m/z 581 for d0-AZM and m/z 584 for d3-AZM, suggesting derivatization of their sulfonamide groups to form N,N-dipentafluorobenzyl derivatives (R-SO2-N(PFB)2), i.e., d0-AZM-(PFB)2 and d3-AZM-(PFB)2, respectively. Quantification was performed by selected-ion monitoring of m/z 581 and 83 for d0-AZM-(PFB)2 and m/z 584 and 86 for d3-AZM-(PFB)2. The limits of detection and quantitation of the method were determined to be 300 fmol (67 pg) and 1 μM of acetazolamide, respectively. Intra- and inter-assay precision and accuracy for acetazolamide in human urine samples in pharmacologically relevant concentration ranges were determined to be 0.3%–4.2% and 95.3%–109%, respectively. The method was applied to measure urinary acetazolamide excretion after ingestion of a 250 mg acetazolamide-containing tablet (Acemit®) by a healthy volunteer. Among other tested sulfonamide drugs, methazolamide (MM, 236) was also found to form a N,N-dipentafluorobenzyl derivative, whereas dorzolamide (MM, 324) was hardly detectable. No GC-MS peaks were obtained from the PFB bromide derivatization of hydrochlorothiazide (MM, 298), xipamide (MM, 355), indapamide and metholazone (MM, 366 each) or brinzolamide (MM, 384). We demonstrate for the first time that sulfonamide drugs can be derivatized with PFB bromide and quantitated by GC-MS. Sulfonamides with MM larger than 236 are likely to be derivatized by PFB bromide but to lack thermal stability. Keywords: Acetazolamide, Derivatization, Quantification, Sulfonamides, Validation

Our objective was to examine the effects of N-methylacetazolamide (NMA), a non‑carbonic anhydrase inhibitor, on ischemia-reperfusion injury. Isolated rat hearts were assigned to the following groups: 1) Non-ischemic control (NIC):110 min of perfusion and 2) Ischemic control (IC): 30 min of global ischemia and 60 min of reperfusion (R). Both groups were repeated in presence of NMA (5 μM), administered during the first 10 min of R. Infarct size (IS) was measured by TTC staining. Developed pressure (LVDP) and end-diastolic pressure (LVEDP) of the left ventricle were used to assess systolic and diastolic function, respectively. The content of P-Akt, P-PKCε, P-Drp1 and calcineurin Aβ were measured. In cardiomyocytes the L-type Ca

Methazolamide (MTZ) has been occasionally linked to the lethal Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), which are associated with HLA-B*59:01. However, some MTZ-induced SJS/TEN (MTZ-SJS/TEN) cases are negative for HLA-B*59:01, implying that other genetic factors besides HLA-B*59:01 are contributing to MTZ-SJS/TEN.To comprehensively identify HLA and non-HLA genetic susceptibility to MTZ-SJS/TEN in Han Chinese.Eighteen patients with MTZ-SJS/TEN, 806 subjects of the population control and 74 MTZ-tolerant individuals were enrolled in this study. Both exome-wide and HLA-based association studies were conducted. Molecular docking analysis was employed to simulate the interactions between MTZ and risk HLA proteins.We found a strong signal in the major histocompatibility complex region on chromosome 6 with 22 SNPs reaching exome-wide significance. Compared with MTZ-tolerant controls, a significant association of HLA-B*59:01 with MTZ-SJS/TEN was validated [odds ratio (OR) = 146.00, 95% confidence interval (CI): 16.12-1321.98; P = 6.19 × 10This study confirmed the association of HLA-B*59:01 with MTZ-SJS/TEN and identified HLA-B*55:02 as a novel risk allele in Han Chinese with the largest sample size to date. Notably, the rs41562914(A)-rs12697944(A) haplotype, encoding E45-L116, is capable of serving as a powerful genetic predictor for MTZ-SJS/TEN with a sensitivity of 89% and specificity of 96%.

Methazolamide (MTZ), a carbonic anhydrase inhibitor, has been shown to inhibit cardiomyocyte hypertrophy and exert a hypoglycemic effect in patients with type 2 diabetes mellitus and diabetic db/db mice. However, whether MTZ has a cardioprotective effect in the setting of diabetic cardiomyopathy is not clear. We investigated the effects of MTZ in a mouse model of streptozotocin-induced type 1 diabetes mellitus (T1DM). Diabetic mice received MTZ by intragastric gavage (10, 25, or 50 mg/kg; daily for 16 weeks). In the diabetic group, MTZ significantly reduced both random and fasting blood glucose levels and improved glucose tolerance in a dose-dependent manner. MTZ ameliorated T1DM-induced changes in cardiac morphology and dysfunction. Mechanistic analysis revealed that MTZ blunted T1DM-induced enhanced expression of β-catenin. Similar results were observed in neonatal rat cardiomyocytes (NRCMs) and adult mouse cardiomyocytes treated with high glucose or Wnt3a (a β-catenin activator). There was no significant change in β-catenin mRNA levels in cardiac tissues or NRCMs. MTZ-mediated β-catenin downregulation was recovered by MG132, a proteasome inhibitor. Immunoprecipitation and immunofluorescence analyses showed augmentation of AXIN1–β-catenin interaction by MTZ in T1DM hearts and in NRCMs treated with Wnt3a; thus, MTZ may potentiate AXIN1–β-catenin linkage to increase β-catenin degradation. Overall, MTZ may alleviate cardiac hypertrophy by mediating AXIN1–β-catenin interaction to promote degradation and inhibition of β-catenin activity. These findings may help inform novel therapeutic strategy to prevent heart failure in patients with diabetes mellitus.

Carbonic anhydrases (CAs) catalyze the synthesis of HCO3- from H2O and CO2. The dysfunction of CAs leads to aqueous humor secretion and high intraocular pressure to cause glaucoma pathogenesis. Methazolamide (MTZ), a CA inhibitor, can effectively treat glaucoma by reducing aqueous humor secretion. We previously reported that carbonic anhydrase I (CA1), a CA family member, was highly expressed in atherosclerotic tissues of the aorta and stimulated atherosclerosis (AS) by promoting calcification. MTZ showed therapeutic and preventive effects on AS in a mouse model. The above findings suggest a relationship between AS and glaucoma. This study explored the possible association between AS prevalence and glaucoma prevalence and the therapeutic effect of MTZ on AS by analyzing medical records. Among 10,751 patients with a primary diagnosis of glaucoma, 699 (6.5%) were also diagnosed with AS. However, the incidences of AS in patients with keratitis and scleritis, which are also ophthalmic diseases, were 2.5% (206/8383 patients) and 3.5% (46/1308 patients), respectively. In the population without ophthalmic records, the AS prevalence was only 1.9% (99,416/5,168,481 patients) (all p values between each group were below 0.001). Among 152,425 patients with a primary diagnosis of AS, 1245 (0.82%) were also diagnosed with glaucoma. Among 199,782 patients with a primary diagnosis of hypertension (excluding AS), 1149 (0.57%) were diagnosed with glaucoma, and among 5,313,433 patients without AS or hypertension, 9513 (0.18%) were diagnosed with glaucoma (all p values between each group were below 0.001). Additionally, among 14 patients who suffered from both AS and glaucoma and were treated with MTZ to cure their glaucoma, 9 of them showed reduced low-density lipoprotein (LDL) levels, the main index of AS, within 3 months after medication use (2.81 ± 0.61 mmol/L vs. 2.38 ± 0.58 mmol/L, p = 0.039). The above findings demonstrated a strong relation between AS and glaucoma and suggested that AS patients with glaucoma were more likely to suffer from angle-closure glaucoma.

Solid lipid nanoparticles and nanostructured lipid carriers showed promising results for enhancement of ocular bioavailability of drugs with poor corneal permeability. One of these drugs is methazolamide, which is an orally administered carbonic anhydrase inhibitor for glaucoma treatment. However, sterilization by autoclaving may result in loss of the physical properties of lipid nanoparticles such as particle size and surface charge. Here, we evaluated gamma radiation as an alternative sterilization method. Methazolamide loaded nanostructured lipid carriers were optimized using 23 factorial design. Optimized formulations contained 6% lipid (85% solid lipid (Cetostearyl alcohol and glyceryl behenate) and 15% oil either medium chain triglycerides or isopropyl myristate) stabilized by 2% polysorbate 80 and 0.15% stearylamine. Nanoparticles were cationic, smaller than 500 nm, and had an entrapment efficiency of about 30%. They released methazolamide within 8 hours and showed a 5-fold enhanced reduction in intraocular pressure compared to methazolamide solution. Gamma sterilization was superior to autoclaving in preserving entrapped methazolamide, size, and surface charge of lipid nanoparticles. These findings demonstrate that gamma radiation is a viable alternative to autoclaving for sterilizing lipid nanoparticles. Moreover, this proves that nanostructured lipid carriers enhance pharmacological response of topically administered methazolamide for treating glaucoma.

Carbonic anhydrases (CAs) catalyze the synthesis of HCO3− from H2O and CO2. The dysfunction of CAs leads to aqueous humor secretion and high intraocular pressure to cause glaucoma pathogenesis. Methazolamide (MTZ), a CA inhibitor, can effectively treat glaucoma by reducing aqueous humor secretion. We previously reported that carbonic anhydrase I (CA1), a CA family member, was highly expressed in atherosclerotic tissues of the aorta and stimulated atherosclerosis (AS) by promoting calcification. MTZ showed therapeutic and preventive effects on AS in a mouse model. The above findings suggest a relationship between AS and glaucoma. This study explored the possible association between AS prevalence and glaucoma prevalence and the therapeutic effect of MTZ on AS by analyzing medical records. Among 10751 patients with a primary diagnosis of glaucoma, 699 (6.5%) were also diagnosed with AS. However, the incidence of AS in patients with keratitis and scleritis, which are ophthalmic diseases, was 2.5% (206/8383 patients) and 3.5% (46/1308 patients), respectively. In the population without ophthalmic records, the AS prevalence was only 1.9% (99416/5168481 patients). Among 152425 patients with a primary diagnosis of AS, 1245 (0.82%) were also diagnosed with glaucoma. Among 199782 patients with a primary diagnosis of hypertension (excluding AS), 1149 (5.7‰) were diagnosed with glaucoma, and among 5313433 patients without AS or hypertension, 9513 (1.8‰) were diagnosed with glaucoma. Our study also found that AS patients with glaucoma were more likely to suffer from angle-closure glaucoma, Additionally, Among 14 patients who suffered from both AS and glaucoma and were treated with MTZ to cure their glaucoma, 9 people showed reduced low-density lipoprotein (LDL) levels, the main index of AS, within 3 months after medication use (2.81 ± 0.61 mmol/L VS 2.38 ± 0.58 mmol/L, p = 0.039). The above findings show a strong relation between AS and glaucoma and support that MTZ can be considered a potential therapy to treat AS.

Stevens-Johnson syndrome (SJS) /toxic epidermal necrolysis (TEN) are life-threatening severe cutaneous adverse drug reactions characterized by widespread epidermal necrosis. Recent studies have indicated that SJS/TEN is a specific immune reaction regulated by T cells. Certain drug serves as foreign antigens that are presented by major histocompatibility complex (MHC) and recognized by T cell receptors (TCRs), inducing adaptive immune responses. However, few studies have performed detailed characterization of TCR repertoire in SJS/TEN, and it remains unclear whether the particular types of TCRs expanded clonally are drug-specific, which would provide a potential underlying mechanism of SJS/TEN. In this study, using high-throughput sequencing, we comprehensively assessed the diversity, composition and molecular characteristics of the TCRβ repertoires in 17 SJS/TEN patients associated with three different causative drugs including methazolamide (MZ), carbamazepine (CBZ) and allopurinol (ALP). Systematic analysis of the TCRβ sequences revealed that SJS/TEN patients had more highly expanded clones and less TCR repertoire diversity, and the TCR repertoire diversity of these patients showed certain associations with the clinical severity of disease. Similar predominant clonotypes, shared-usage TRBV/TRBJ subtypes and combinations thereof were observed among different subjects with the same causative agent. Our observations provide enhanced understanding of the role of T lymphocytes in the pathogenesis of SJS/TEN and enumerate potential therapeutic targets.

Ethoxzolamide (EZA), acetazolamide, and methazolamide are clinically used sulphonamide drugs designed to treat non-bacteria-related illnesses (e.g. glaucoma), but they also show antimicrobial activity against the gastric pathogen Helicobacter pylori. EZA showed the highest activity, and was effective against clinical isolates resistant to metronidazole, clarithromycin, and/or amoxicillin, suggesting that EZA kills H. pylori via mechanisms different from that of these antibiotics. The frequency of single-step spontaneous resistance acquisition by H. pylori was less than 5 × 10−9, showing that resistance to EZA does not develop easily. Resistance was associated with mutations in three genes, including the one that encodes undecaprenyl pyrophosphate synthase, a known target of sulphonamides. The data indicate that EZA impacts multiple targets in killing H. pylori. Our findings suggest that developing the approved anti-glaucoma drug EZA into a more effective anti-H. pylori agent may offer a faster and cost-effective route towards new antimicrobials with a novel mechanism of action.

Several studies has been reported on1,3,4- thiadiazole and their derivatives because of their wide range of therapeutic activities. Many drugs containing thiadiazole derivatives are available in market such as acetazolamide, methazolamide, sulphamethazole, cefazoline. This review article highlights the recently synthesized 1,3,4-thiadiazole possessing important therapeutic activities and Computational Studies.

Coronavirus disease 2019 (COVID-19) represents a systemic disease that may cause severe metabolic complications in multiple tissues including liver, kidney, and cardiovascular system. However, the underlying mechanisms and optimal treatment remain elusive. Our study shows that impairment of ACE2 pathway is a key factor linking virus infection to its secondary metabolic sequelae. By using structure-based high-throughput virtual screening and connectivity map database, followed with experimental validations, we identify imatinib, methazolamide, and harpagoside as direct enzymatic activators of ACE2. Imatinib and methazolamide remarkably improve metabolic perturbations in vivo in an ACE2-dependent manner under the insulin-resistant state and SARS-CoV-2-infected state. Moreover, viral entry is directly inhibited by these three compounds due to allosteric inhibition of ACE2 binding to spike protein on SARS-CoV-2. Taken together, our study shows that enzymatic activation of ACE2 via imatinib, methazolamide, or harpagoside may be a conceptually new strategy to treat metabolic sequelae of COVID-19.

Methazolamide-induced Stevens-Johnson syndrome and toxic epidermal necrolysis (SJS/TEN) are life-threatening adverse drug reactions. Based on previous studies, HLA genotypes may play an important role in methazolamide-induced SJS/TEN. Therefore, to identify the associations between HLA genotypes and methazolamide-induced cutaneous adverse drug reactions (cADRs) (i.e., SJS/TEN and hypersensitivity syndrome), a systematic review and meta-analysis were performed. Two studies (one study in Korean and another in Han Chinese) met the inclusion criteria. The studies included 13 patients with methazolamide-induced SJS/TEN, 30 methazolamide-tolerant, and 768 population controls. Associations between HLA-B*5901, HLA-B*5901-Cw*0102 haplotype, and methazolamide-induced SJS/TEN were identified in methazolamide-tolerant and population controls. Overall ORs were 305.0 (95% CI = 11.3-8, 259.4) in methazolamide-tolerant and 715.3 (95% CI = 83.1-6,158.5) in population control. In addition, statistically significant associations between the HLA-Cw*0102 and methazolamide-induced SJS/TEN were found in methazolamide-tolerant (OR = 12.1; 95% CI = 1.3-111.7) and population control (OR = 17.5; 95% CI = 3.2-96.6). Since HLA-B*5901 and HLA-B*5901-Cw*0102 haplotype are associated with methazolamide-induced SJS/TEN, genetic screening prior to methazolamide therapy in Asian populations is warranted.

Key points Carbonic anhydrase (CA) inhibitors such as acetazolamide inhibit hypoxic pulmonary vasoconstriction (HPV) in humans and other mammals, but the mechanism of this action remains unknown. It has been postulated that carbonic anhydrase may act as a nitrous anhydrase in vivo to generate nitric oxide (NO) from nitrite and that this formation is increased in the presence of acetazolamide. Acetazolamide reduces HPV in pigs without evidence of any NO generation, whereas nebulized sodium nitrite reduces HPV by NO formation; however; combined infusion of acetazolamide with sodium nitrite inhalation did not further increase exhaled NO concentration over inhaled nitrite alone in pigs exposed to alveolar hypoxia. We conclude that acetazolamide does not function as either a nitrous anhydrase or a nitrite reductase in the lungs of pigs, and probably other mammals, to explain its vasodilating actions in the pulmonary or systemic circulations. Abstract The carbonic anhydrase (CA) inhibitors acetazolamide and its structurally similar analogue methazolamide prevent or reduce hypoxic pulmonary vasoconstriction (HPV) in dogs and humans in vivo, by a mechanism unrelated to CA inhibition. In rodent blood and isolated blood vessels, it has been reported that inhibition of CA leads to increased generation of nitric oxide (NO) from nitrite and vascular relaxation in vitro. We tested the physiological relevance of augmented NO generation by CA from nitrite with acetazolamide in anaesthetized pigs during alveolar hypoxia in vivo. We found that acetazolamide prevents HPV in anaesthetized pigs, as in other mammalian species. A single nebulization of sodium nitrite reduces HPV, but this action wanes in the succeeding 3 h of hypoxia as nitrite is metabolized and excreted. Pulmonary artery pressure reduction and NO formation as measured by exhaled gas concentration from inhaled sodium nitrite were not increased by acetazolamide during alveolar hypoxia. Thus, our data argue against a physiological role of carbonic anhydrase as a nitrous anhydrase or nitrite reductase as a mechanism for its inhibition of HPV in the lung and blood in vivo.

The rationale of this study was to formulate topically effective sustained release ophthalmic Methazolamide (MTA) liposomal in-situ gel. Lipid film hydration method was employed for the preparation of MTA liposomes consisting of lecithin and cholesterol. Optimization of the MTA liposomes by Design-Expert software was done to evaluate the effect of cholesterol and drug in varying concentrations using a 32 factorial design. Encapsulation efficiency and particle size were considered as dependent variables. Drug encapsulation was increased by increasing cholesterol as well as drug concentration. The optimized batch showed encapsulation efficiency of 74.12 ± 0.52% and particle size was found 193.2 ± 1.34 nm. The liposomal gel was prepared by incorporating MTA liposomes in Carbopol 934 gel.The final formulation showed a pH of 7.1 ± 0.05, spreadability of 0.8 ± 0.1. In vitro release studies of MTA liposomes and MTA liposomal gel were compared. In comparison to MTA solution, MTA liposomal gel showed a significant reduction (p

The two β-carbonic anhydrases (CAs, EC 4.2.1.1) recently cloned and purified from the ascomycete fungus Sordaria macrospora, CAS1 and CAS2, were investigated for their inhibition with a panel of 39 aromatic, heterocyclic, and aliphatic sulfonamides and one sulfamate, many of which are clinically used agents. CAS1 was efficiently inhibited by tosylamide, 3-fluorosulfanilamide, and 3-chlorosulfanilamide (KIs in the range of 43.2–79.6 nM), whereas acetazolamide, methazolamide, topiramate, ethoxzolamide, dorzolamide, and brinzolamide were medium potency inhibitors (KIs in the range of 360–445 nM). CAS2 was less sensitive to sulfonamide inhibitors. The best CAS2 inhibitors were 5-amino-1,3,4-thiadiazole-2-sulfonamide (the deacetylated acetazolamide precursor) and 4-hydroxymethyl-benzenesulfonamide, with KIs in the range of 48.1–92.5 nM. Acetazolamide, dorzolamide, ethoxzolamide, topiramate, sulpiride, indisulam, celecoxib, and sulthiame were medium potency CAS2 inhibitors (KIs of 143–857 nM). Many other sulfonamides showed affinities in the high micromolar range or were ineffective as CAS1/2 inhibitors. Small changes in the structure of the inhibitor led to important differences of the activity. As these enzymes may show applications for the removal of anthropically generated polluting gases, finding modulators of their activity may be crucial for designing environmental-friendly CO2 capture processes.

A new β-class carbonic anhydrase was cloned and purified from the filamentous ascomycete Sordaria macrospora, CAS3. This enzyme has a higher catalytic activity compared to the other two such enzymes from this fungus, CAS1 and CAS2, which were reported earlier, with the following kinetic parameters: kcat of (7.9 ± 0.2) × 105 s−1, and kcat/Km of (9.5 ± 0.12) × 107 M−1∙s−1. An inhibition study with a panel of sulfonamides and one sulfamate was also performed. The most effective CAS3 inhibitors were benzolamide, brinzolamide, dichlorophnamide, methazolamide, acetazolamide, ethoxzolamide, sulfanilamide, methanilamide, and benzene-1,3-disulfonamide, with KIs in the range of 54–95 nM. CAS3 generally shows a higher affinity for this class of inhibitors compared to CAS1 and CAS2. As S. macrospora is a model organism for the study of fruiting body development in fungi, these data may be useful for developing antifungal compounds based on CA inhibition.

NEW FINDINGS What is the central question of this study? Does the combination of methazolamide and theophylline reduce symptoms of acute mountain sickness (AMS) and improve aerobic performance in acute hypobaric hypoxia? What is the main finding and its importance? The oral combination of methazolamide (100 BID) and theophylline (300 BID) improved arterial oxygen saturation but did not reduce symptoms of AMS and impaired aerobic performance. We do not recommend this combination of drugs for prophylaxis against the acute negative effects of hypobaric hypoxia. ABSTRACT A limited number of small studies have suggested that methazolamide and theophylline can independently reduce symptoms of acute mountain sickness (AMS) and, if taken together, can improve aerobic exercise performance in normobaric hypoxia. We performed a randomized, double-blind, placebo-controlled, cross-over study to determine if the combination of oral methazolamide and theophylline could provide prophylaxis against AMS and improve aerobic performance in hypobaric hypoxia (∼4875 m). Volunteers with histories of AMS were screened at low altitude (1650 m) and started combined methazolamide (100 mg BID) and theophylline (300 mg BID) treatment, or placebo, 72 h prior to decompression. Baseline AMS (Lake Louise Questionnaire), blood (haemoglobin, haematocrit), cognitive function, ventilatory and pulse oximetry ( SpO2 ) measures were assessed at low altitude and repeated between 4 and 10 h of exposure to hypobaric hypoxia (PB = 425 mmHg). Aerobic exercise performance was assessed during a 12.5 km cycling time trial (TT) after 4 h of hypobaric hypoxia. Subjects repeated all experimental procedures after a 3-week washout period. Differences between drug and placebo trials were evaluated using repeated measures ANOVA (α = 0.05). The drugs improved resting SpO2 by ∼4% (P

In-cell NMR can investigate protein conformational changes at atomic resolution, such as those changes induced by drug binding or chemical modifications, directly in living human cells, and therefore has great potential in the context of drug development as it can provide an early assessment of drug potency. NMR bioreactors can greatly improve the cell sample stability over time and, more importantly, allow for recording in-cell NMR data in real time to monitor the evolution of intracellular processes, thus providing unique insights into the kinetics of drug-target interactions. However, current implementations are limited by low cell viability at >24 h times, the reduced sensitivity compared to "static" experiments and the lack of protocols for automated and quantitative analysis of large amounts of data. Here, we report an improved bioreactor design which maintains human cells alive and metabolically active for up to 72 h, and a semiautomated workflow for quantitative analysis of real-time in-cell NMR data relying on Multivariate Curve Resolution. We apply this setup to monitor protein-ligand interactions and protein oxidation in real time. High-quality concentration profiles can be obtained from noisy 1D and 2D NMR data with high temporal resolution, allowing further analysis by fitting with kinetic models. This unique approach can therefore be applied to investigate complex kinetic behaviors of macromolecules in a cellular setting, and could be extended in principle to any real-time NMR application in live cells.

As a carbonic anhydrase inhibitor and a methylated lipophilic analogue of acetazolamide, Methazolamide has higher lipid solubility, less plasma protein binding and renal excretion, and fewer side effects, compared to acetazolamide. Methazolamide can increase systemic metabolic acidosis and sequentially improve ventilation and oxygenation level. The increased oxygenation level leads to reduced reactive oxygen species (ROS) production, relived cerebral edema, mitigated hypoxic pulmonary vasoconstriction, abrogated hypoxic fatigue, and decreased excessive erythrocytosis. In addition to the effect as a carbonic anhydrase inhibitor, methazolamide directly activates the transcription factor anti-oxidative nuclear factor-related factor 2 (Nrf2) and inhibits interleukin-1β (IL-1β) release. These pharmacological functions of methazolamide are beneficial for the prevention and treatment of high-altitude illnesses. Besides, methazolamide causes less fatigue side effects than acetazolamide does. It is also worth noting that several studies suggested that a lower dose of methazolamide has similar prophylaxis and treatment efficacy in acute mountain sickness (AMS) to a higher dose of acetazolamide. Given methazolamide's advantages over acetazolamide, methazolamide may thus represent an alternative for acetazolamide when taken for high-altitude illnesses prophylaxis and treatment. However, more in-depth clinical trials are needed to fully evaluate this efficacy of methazolamide.

Human carbonic anhydrase-II (hCA-II) is the most dominant physiologic isoform amongst the sixteen reported hCA isoforms. Because of its high availability in the different anatomical, and cellular sites of the eye like retina and lens, it plays a more prominent role in the regulation of intraocular pressure than the other twelve catalytically active hCA isoforms. This isoform is also located in the brain, kidney, gastric mucosa, osteoclasts, RBCs, skeletal muscle, testes, pancreas, lungs, etc. Earlier, hCA-II inhibitors were designed based on the sulfonamides e.g. acetazolamide, dichlorphenamide, methazolamide, ethoxzolamide, etc. and they were used systemically in antiglaucoma therapy. Many successful attempts have been made by the researchers in order to design more potent and effective inhibitors by incorporating various moieties in sulphonamides. Some novel scaffolds like chalcones, thiophenes, organotellurium compounds, dithiocarbamate, selenide, and 2-benzylpyrazine, etc. were also designed as hCA-II inhibitors and their inhibitory efficacy was proved in the nanomolar range. In order to obtain relevant information from the insights of their structure-activity relationship, the reported hCA-II inhibitors from the year 1989 to 2019 were critically analysed. It gave a complete insight into the relationship between their structure-activity and hCA-II inhibition. The broad spectrum of our investigation may help researchers to summarize all the crucial structural information required for the development of more potent hCA-II inhibitors for glaucoma.

New findings What is the central question of this study? Acetazolamide and methazolamide both reduce hypoxic pulmonary vasoconstriction equally, but methazolamide does not impair skeletal muscle function. The effect of methazolamide on respiratory control in humans is not yet known. What is the main finding and its importance? Similar to acetazolamide after chronic oral administration, methazolamide causes a metabolic acidosis and shifts the ventilatory CO2 response curve leftwards without reducing O2 sensitivity. The change in ventilation over the change in log P O 2 provides a more accurate measure of hypoxic sensitivity than the change in ventilation over the change in arterial oxyhaemoglobin saturation. Abstract Acetazolamide is used to prevent/treat acute mountain sickness and both central and obstructive sleep apnoea. Methazolamide, like acetazolamide, reduces hypoxic pulmonary vasoconstriction, but has fewer side-effects, including less impairment of skeletal muscle function. Given that the effects of methazolamide on respiratory control in humans are unknown, we compared the effects of oral methazolamide and acetazolamide on ventilatory control and determined the ventilation-log P O 2 relationship in humans. In a double-blind, placebo-controlled, randomized cross-over design, we studied the effects of acetazolamide (250 mg three times daily), methazolamide (100 mg twice daily) and placebo in 14 young male subjects who were exposed to 7 min of normoxic hypercapnia and to three levels of eucapnia and hypercapnic hypoxia. With placebo, methazolamide and acetazolamide, the CO2 sensitivities were 2.39 ± 1.29, 3.27 ± 1.82 and 2.62 ± 1.79 l min-1 mmHg-1 (n.s.) and estimated apnoeic thresholds 32 ± 3, 28 ± 3 and 26 ± 3 mmHg, respectively (P V I ) and log P O 2 (using arterialized venous P O 2 in hypoxia) was linear, and neither agent influenced the relationship between hypoxic sensitivity ( Δ V I / Δ log P O 2 ) and arterial [H+ ]. Using Δ V I / Δ log P O 2 rather than Δ V I /Δ arterial oxyhaemoglobin saturation enables a more accurate estimation of oxygenation and ventilatory control in metabolic acidosis/alkalosis when right- or leftward shifts of the oxyhaemoglobin saturation curve occur. Given that acetazolamide and methazolamide have similar effects on ventilatory control, methazolamide might be preferred for indications requiring the use of a carbonic anhydrase inhibitor, avoiding some of the negative side-effects of acetazolamide.