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Taurolidine is an experimental antibacterial and antiendotoxic compound whose clinical utility as an antitumor agent is being investigated in human clinical trials. Taurolidine in aqueous solution exists in equilibrium with taurultam. Taurultam is subsequently transformed to taurinamide. The pharmacokinetic profiles of these metabolites are not well established. In this study, 18 healthy volunteers were administered 5.0 g of taurolidine in 250 mL of 5% polyvinylpyrrolidone in water over 2, 1, or 0.5 hours by intravenous infusion in a parallel-group design. All subjects noted discomfort at the infusion site, although there were no serious adverse events. t(max) generally occurred at the end of infusion for taurinamide, whereas that of taurultam was reached before completion of infusion. The taurolidine metabolite taurultam demonstrated a shorter half-life and lower systemic exposure than taurinamide. Shortening of infusion duration increased the C(max) and AUC of taurultam. Changes in infusion rate did not substantially change the pharmacokinetic parameters of taurinamide.

Aprepitant is the first NK1 receptor antagonist approved for use with corticosteroids and 5HT3 receptor antagonists to prevent chemotherapy-induced nausea and vomiting (CINV). The effective dose to prevent CINV is a 125-mg capsule on day 1 followed by an 80-mg capsule on days 2 and 3. Study 1 evaluated the bioavailability of the capsules and estimated the effect of food. The mean (95% confidence interval [CI]) bioavailabilities of 125-mg and 80-mg final market composition (FMC) capsules, as assessed by simultaneous administration of stable isotope-labeled intravenous (i.v.) aprepitant (2 mg) and FMC capsules, were 0.59 (0.53, 0.65) and 0.67 (0.62, 0.73), respectively. The geometric mean (90% CI) area under the plasma concentration time curve (AUC) ratios (fed/fasted) were 1.2 (1.10, 1.30) and 1.09 (1.00, 1.18) for the 125-mg and 80-mg capsule, respectively, demonstrating that aprepitant can be administered independently of food. Study 2 defined the pharmacokinetics of aprepitant administered following the 3-day regimen recommended to prevent CINV (125 mg/80 mg/80 mg). Consistent daily plasma exposures of aprepitant were obtained following this regimen, which was generally well tolerated.

To investigate the influence of modifying in vivo cytochrome P450 3A (CYP3A) activity on the pharmacokinetics of etoricoxib, a selective inhibitor of cyclooxygenase-2, and of etoricoxib administration on CYP3A activity, a 3-part, randomized, crossover study was conducted in 3 panels of healthy volunteers. In part I, 8 subjects were administered a single dose of 60 mg etoricoxib alone and following daily doses of 400 mg ketoconazole, a known strong inhibitor of CYP3A. In part II, 8 different subjects were administered a single dose of 60 mg etoricoxib alone and following daily doses of 600 mg rifampin, a known strong inducer of CYP3A. In parts I and II, plasma samples were collected following each etoricoxib dose and analyzed for etoricoxib. In part III, 8 different subjects were administered 120 mg etoricoxib or placebo once daily for 11 days, and the erythromycin breath test was administered on day 11 of each period. Coadministration of etoricoxib with daily doses of ketoconazole resulted in an average 43% increase in etoricoxib AUC; based on previous studies, this increase would not be expected to have any clinically meaningful effect. In contrast, coadministration of etoricoxib with daily doses of rifampin had a potentially clinically important effect on etoricoxib pharmacokinetics (average 65% decrease in etoricoxib AUC). Etoricoxib had no effect on hepatic CYP3A activity, as assessed by the erythromycin breath test.

Two studies examined the pharmacokinetics of indinavir and rifabutin when coadministered in healthy subjects. Rifabutin, which induces the expression of cytochrome P450 (CYP) 3A, and indinavir, which inhibits that enzyme system, are frequently coadministered in patients infected with HIV. The second study was undertaken to determine if altering the dose of rifabutin coadministered with indinavir would minimize the drug interaction observed in the first study. Two studies, each with a three-period crossover design, were performed. In study 1, standard doses of rifabutin and indinavir (300 mg of rifabutin qd and 800 mg indinavir q8h) were administered as monotherapy (with placebo to the other drug) or in combination to 10 volunteers for 10 days. In study 2, 150 mg qd of rifabutin together with 800 mg q8h of indinavir, 300 mg qd of rifabutin alone, or 800 mg q8h of indinavir alone was administered to 14 volunteers for 10 days. In study 1, the geometric mean ratio (GMR) (90% confidence interval [CI]) of the AUC ( 0 - 8 h ) of indinavir, coadministered with rifabutin 300 mg qd compared to indinavir alone (with rifabutin placebo), was 0.66 (0.56, 0.77), while that of the AUC ( 0 - 2 4 ) of rifabutin, coadministered with indinavir compared to rifabutin alone (with indinavir placebo), was 2.73 (1.99, 3.77). In study 2, the GMR (90% CI) of the AU ( 0 - 8 h ) of indinavir, coadministered with rifabutin 150 mg qd compared to indinavir alone, was 0.68 (0.60, 0.76), while that of the AUC ( 0 - 2 4 h ) of rifabutin, when rifabutin 150 mg qd was coadministered with indinavir compared to rifabutin 300 mg qd alone, was 1.54 (1.33, 1.79). For both studies 1 and 2, indinavir and rifabutin administered alone or in combination were generally well tolerated. No clinical or laboratory adverse experience was serious. These data demonstrate the important pharmacokinetic interactions between indinavir and rifabutin when they are coadministered. Indeed, these observations formed the basis for the subsequent ACTG 365 study that explored dose adjustments for these agents in combination regimens to preserve the sustained antiviral activites of indinavir in the absence of adverse events as a result of elevated circulating levels of rifabutin.

Mibefradil, a calcium channel blocker, was removed from the market because of adverse drug interactions with coadministered CYP3A4 substrates. This study examined the effect of mibefradil on the activity of hepatic and intestinal CYP3A4 in vivo, employing the erythromycin breath test (EBT) and oral midazolam pharmacokinetics. This was a two-period, single-blind, placebo-controlled crossover study in which 8 male volunteers were randomized to the order of receiving placebo and a single 100-mg oral dose of mibefradil. Oral midazolam was coadministered with intravenous [14C N-methyl] erythromycin 1 hour after mibefradil/placebo administration. The EBT was performed 20 minutes following erythromycin administration. Blood and urine were collected during the 36 hours following probe drug administration for analysis of midazolam pharmacokinetics. Coadministration of mibefradil increased the Cmax of midazolam 3-fold, the AUC 8- to 9-fold, and the t1/2 4-fold. Mibefradil coadministration decreased the amount of exhaled 14CO2 in 6 of 8 subjects, with a mean decrease of 25%. It was concluded that a single oral dose of mibefradil significantly inhibits CYP3A4 in intestine and liver. These data support that adverse drug interactions involving mibefradil reflect inhibition of CYP3A4 in intestine and liver. Also, they suggest that the EBT, while a valid probe of in vivo hepatic CYP3A4 activity, is a single time point measurement and may be less sensitive than oral midazolam pharmacokinetics in detecting CYP3A4 inhibition.

Inhibition of ex vivo arachidonic acid (AA)-induced aggregation is a biomarker for the isotype selectivity of cyclooxygenase (COX) inhibitors since platelets express COX-1 but not COX-2. At low concentrations, there is broad inter- and intrasubject variability in AA-induced aggregation of platelets ex vivo. This study defined a concentration that reliably induces aggregation without overcoming inhibition by therapeutic aspirin therapy (ASA, 81-mg) treatment. Logistic regression analysis of ex vivo aggregation, induced with increasing concentrations of AA in platelet-rich plasma (PRP), estimated that platelets from > or = 90% of subjects would aggregate at > or = 1.5 mM AA (95% confidence interval [CI], 1.1, 2.1). A concentration of 1.6 mM AA failed to aggregate platelets from 26 healthy volunteers, who had previously aggregated at this concentration, following six daily oral doses of 81 mg of ASA. These data demonstrate that 1.6 mM AA reproducibly induces platelet aggregation in PRP from healthy volunteers without overcoming the antiplatelet effect of daily low-dose aspirin therapy.

Consumption of typical quantities of grapefruit juice (GFJ) increases the oral bioavailability of several CYP3A4 substrates without affecting their elimination, consistent with selective inhibition of intestinal but not hepatic CYP3A4. However, increases in the AUCs of CYP3A4 substrates recently associated with the consumption of large amounts of GFJ were similar to those observed with potent inhibitors of hepatic CYP3A4. The current study compared the effects of consuming large quantities and more typical amounts of GFJ on the activity of hepatic and intestinal cytochrome P450 3A4 in vivo, employing the erythromycin breath test (EBT) and oral midazolam pharmacokinetics. This was a two-phase, randomized, placebo-controlled crossover study, with each phase conducted with a separate panel of subjects. In Phase I, 8 male volunteers were randomized to the order of receiving one glass (240 mL) of water (placebo) or double-strength (DS) GFJ tid for 2 days and then 90, 60, and 30 minutes prior to administration of probe drugs on the 3rd day. In Phase II, 16 male volunteers were randomized to the order of receiving one glass of (1) single-strength (SS) GFJ, (2) DS GFJ, and (3) water (placebo). All treatments were administered in a fasted state. There was at least a 7-day washout period between treatments. Probe drugs, administered 30 minutes or 1 hour following each treatment in Phase I or II, respectively, consisted of oral midazolam (2 mg) coadministered with IV [14G N-methyl] erythromycin (0.03 mg). The EBT was performed 20 minutes following erythromycin administration. Blood was collected during the 24 hours following probe drug administration for the analysis of midazolam pharmacokinetics. In Phase I, consumption of one glass of DS GFJ tid for 3 days increased the Cmax of midazolam 3-fold, the AUC 6-fold, and the t1/2 2-fold and decreased the amount of exhaled 14CO2 in all 8 subjects, with a mean decrease in EBT of 18%. In Phase II, consumption of one glass of DS GFJ significantly increased the AUC and Cmax of midazolam approximately 2-fold without a significant effect on the t1/2 of midazolam or the EBT. The effects of consuming one glass of SS GFJ on midazolam pharmacokinetics and the EBT were not significantly different from those of one glass of DS GFJ. It was concluded that consumption of one glass of DS GFJ tid for 3 days significantly increased the AUC, Cmax, and t1/2 of midazolam and reduced EBT values, reflecting inhibition of both hepatic and intestinal CYP3A4. In contrast, consumption of one glass of SS or DS GFJ increased midazolam AUC and Cmax, with little effect on the midazolam t1/2 and EBT values, reflecting preferential inhibition of intestinal CYP3A4. Alterations of midazolam AUC and Cmax induced by nine glasses of DS GFJ were significantly greater than those produced by one glass of SS or DS GFJ. These data suggest that GFJ inhibits intestinal and hepatic CYP3A4 in an exposure-dependent fashion and that patients taking medications that are CYP3A4 substrates are at risk for developing drug-related adverse events if they consume large amounts of grapefruit juice.

Potential for inhibition of CYP3A activity by simvastatin, an HMG-CoA reductase inhibitor, was evaluated in 12 healthy male subjects who received placebo or 80 mg of simvastatin, the maximal recommended dose, once daily for 7 consecutive days. On day 7, an intravenous injection of 3 microCi [14C N-methyl]erythromycin for the erythromycin breath test (EBT) was coadministered with a 2 mg oral solution of midazolam. The values for percent 14C exhaled during the first hour (for EBT) and the pharmacokinetic parameters of midazolam (AUC, Cmax, t1/2) were not affected following multiple once-daily oral doses of simvastatin 80 mg. The 95% confidence interval was 0.97 to 1.18 for EBT and 0.99 to 1.23 for midazolam AUC. In addition, the total urinary recoveries of midazolam and its 1'-hydroxy metabolites (free plus conjugate) obtained from both treatments were not statistically different (p > 0.200). These data demonstrate that multiple dosing of simvastatin, at the highest recommended clinical dose, does not significantly alter the in vivo hepatic or intestinal CYP3A4/5 activity as measured by the commonly used EBT and oral midazolam probes.

The erythromycin breath test (EBT), which measures 14 CO 2 produced from [ 14 CN-methyl] erythromycin, is one of the most frequently employed measures to examine drug interactions involving cytochrome P450 3A4 (CYP3A). However, the reproducibility and reliability of this test, and the effects of drugs that alter CYP3A activity, continue to be defined. In this study, the reproducibility of the EBT was evaluated in eight healthy volunteers before and after oral administration of 600 mg of rifampin daily for 8 days. Two sequential EBT determinations performed 5 days apart before rifampin administration were highly reproducible. Rifampin induced CYP3A, reflected in a mean percent (± standard deviation) increase in EBT values of 86 ± 30%. Recovery of enzyme function after discontinuation of rifam pin for 17 days was manifested as a return of EBT values to preinduction levels. These results support the utility of EBT as a valid, reproducible, and reliable measure of CYP3A activity in vivo.

This study was conducted to examine the pharmacokinetics and pharmacodynamics of tepoxalin in healthy volunteers, an antiinflammatory compound that inhibits cyclooxygenase and lipoxygenase. Tepoxalin was absorbed after oral administration of single doses from 35 to 300 mg, after which it was rapidly converted to an acidic metabolite, RWJ 20142, which inhibits cyclooxygenase but not lipoxygenase. The areas under the concentration-time curve (AUC) of tepoxalin and RWJ 20142 in plasma increased in a dose-dependent fashion. Administration of the lowest dose of tepoxalin completely inhibited whole blood cyclooxygenase for the entire period of observation. This inhibition correlated closely with that of secretion and aggregation induced by collagen of platelets obtained from these subjects. Similarly, administration of tepoxalin was associated with significant inhibition of lipoxygenase in whole blood. Lipoxygenase was inhibited a maximum of 60% in a time-dependent fashion, and the duration of inhibition was dose-dependent. These studies demonstrate that tepoxalin inhibits whole blood cyclooxygenase, lipoxygenase, and platelet function after oral administration in humans.

Amifostine, a chemo- and radioprotective agent developed as adjunctive therapy for malignancies, induces hypotension after approximately 20% of patient administrations. This study examines the molecular mechanisms underlying hypotension induced by amifostine. Amifostine and its metabolite, WR-1065, induced dose-dependent hypotension in anesthetized rats that was not blocked by N(G)-methyl L arginine (L-NAME), an NO synthase inhibitor. WR-1065 but not amifostine induced concentration-dependent relaxation of isolated rat aortic rings in an endothelium-independent fashion. Relaxation was not associated with increases in cGMP or cAMP and could not be blocked by L-NAME or indomethacin. Similarly, neither amifostine or WR-1065 activated adenylyl, particulate guanylyl, or soluble guanylyl cyclases. WR-1065 relaxed rat aortic rings precontracted with norepinepherine, suggesting alpha-adrenergic blocking activity. However, neither amifostine nor WR-1065 altered the ability of prazosin or phentolamine to bind to alpha-adrenergic receptors. Further, WR-1065 had no effect on receptor-mediated increases in intracellular calcium in BAL 17 murine B lymphocytes in vitro. Thus, hypotension after administration of amifostine is mediated by WR-1065 and appears to result from direct relaxation of vascular smooth muscle. Smooth muscle relaxation induced by WR-1065 is not related to production of nitric oxide, prostaglandins, or cyclic nucleotides; alpha-adrenergic receptor antagonism; or interference with receptor-dependent increases in intracellular calcium. Administration of ephedrine, an efficacious adrenergic agonist, attenuated hypotension induced by amifostine in anesthetized rats and may be useful in alleviating hypotension associated with amifostine administration in patients.

Previously, clinical studies comparing generic and reference formulations of sustained-release (SR) verapamil tablets revealed significant increases in the PR interval in subjects given the generic formulation in the presence of food. To determine the mechanisms underlying these differences in pharmacodynamics, the present analyses examined the pharmacokinetics of these formulations in the presence and absence of food. After single or multiple doses in fasting subjects, AUCs, Cmaxs, and tmaxs were similar, suggesting that these formulations were bioequivalent in the fasted state. However, the generic formulation exhibited a higher AUC(0-6) in fed subjects, suggesting that this formulation may be absorbed more rapidly than the reference formulation when given with food. Analysis of AUC(0-6) showed that 34% of the subjects receiving the generic formulation exhibited rapid absorption, compared with only 8% receiving the reference formulation. Significant increases in the PR interval were seen in nine fed subjects receiving the generic formulation compared with two receiving the reference formulation. Similarly, three fed subjects receiving the generic drug who were rapid absorbers exhibited first-degree heart block, whereas this conduction disturbance was seen in only one fed subject receiving the reference formulation. Thus, increased conduction disturbances seen in subjects given the generic formulation with a meal likely reflect more rapid absorption of this formulation in the presence of food, resulting in an increase in the ratio of more potent to less potent enantiomers of verapamil in the systemic circulation.