Inhibition of oral midazolam clearance by boosting doses of ritonavir, and by 4,4-dimethyl-benziso-(2H)-selenazine (ALT-2074), an experimental catalytic mimic of glutathione oxidase.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: * The viral protease inhibitor ritonavir is known to inhibit clearance of intravenous midazolam. * ALT-2074, a catalytic mimic of glutathione oxidase, inhibits human cytochrome P450 3A (CYP3A) isoforms in vitro. WHAT THIS STUDY ADDS: * Short-term administration of low-dose ritonavir increases area under the plasma concentration curve following oral midazolam by a factor of 28. * Therefore ritonavir is an appropriate positive control inhibitor for clinical drug interaction studies involving CYP3A substrates. * Midazolam clearance is weakly inhibited by ALT-2074, consistent with its in vitro profile. AIMS: We evaluated whether 'boosting' doses of ritonavir can serve as a positive control inhibitor for pharmacokinetic drug-drug interaction studies involving cytochrome P450 3A (CYP3A). The study also determined whether 4,4-dimethyl-benziso-(2H)-selenazine (ALT-2074), an investigational organoselenium compound that acts as a catalytic mimic of glutathione oxidase, inhibits CYP3A metabolism in vivo. METHODS: Thirteen healthy volunteers received single 3-mg oral doses of midazolam on three occasions: in the control condition, during co-treatment with low-dose ritonavir (three oral doses of 100 mg over 24 h), and during co-treatment with ALT-2074 (three oral doses of 80 mg over 24 h). RESULTS: Ritonavir increased mean (+/-SE) total area under the curve (AUC) for midazolam by a factor of 28.4 +/- 4.2 (P < 0.001), and reduced oral clearance to 4.2 +/- 0.5% of control (P < 0.001). In contrast, ALT-2074 increased midazolam AUC by 1.25 +/- 0.11 (P < 0.05), and reduced oral clearance to 88 +/- 8% of control. CONCLUSIONS: Low-dose ritonavir produces extensive CYP3A inhibition exceeding that of ketoconazole (typically 10- to 15-fold midazolam AUC enhancement), and is a suitable positive control index inhibitor for drug-drug interaction studies. ALT-2074 inhibits CYP3A metabolism to a small degree that is of uncertain clinical importance.

Sitagliptin, an dipeptidyl peptidase-4 inhibitor, does not alter the pharmacokinetics of the sulphonylurea, glyburide, in healthy subjects.

AIMS: Sitagliptin, a dipeptidyl peptidase-4 inhibitor, is an incretin enhancer that is approved for the treatment of Type 2 diabetes. Sitagliptin is mainly renally eliminated and not an inhibitor of CYP450 enzymes in vitro. Glyburide, a sulphonylurea, is an insulin sensitizer and mainly metabolized by CYP2C9. Since both agents may potentially be co-administered, the purpose of this study was to examine the effects of sitagliptin on glyburide pharmacokinetics. METHODS: In this open-label, randomized, two-period crossover study, eight healthy normoglycaemic subjects, 22-44 years old, received single 1.25-mg doses of glyburide alone in one period and co-administered with sitagliptin on day 5 following a multiple-dose regimen for sitagliptin (200-mg q.d. x 6 days) in the other period. RESULTS: The geometric mean ratios and 90% confidence intervals [(glyburide + sitagliptin)/glyburide] for AUC(0-infinity) and C(max) were 1.09 (0.96, 1.24) and 1.01 (0.84, 1.23), respectively. CONCLUSION: Sitagliptin does not alter the pharmacokinetics of glyburide in healthy subjects.

Effect of food on the pharmacokinetics of a vildagliptin/metformin (50/1000 mg) fixed-dose combination tablet in healthy volunteers.

OBJECTIVE: Vildagliptin is an orally active, potent and selective DPP-4 inhibitor that improves glycemic control in patients with type 2 diabetes by increasing alpha- and beta-cell responsiveness to glucose. RESEARCH DESIGN AND METHODS: This open-label, single-center, randomized, two-period crossover study in healthy subjects (n=23) ages 18-45 years investigated the effect of food on the pharmacokinetics of vildagliptin and metformin following administration of a vildagliptin/metformin (50/1000 mg) fixed-dose combination tablet. RESULTS: Administration of the fixed-dose combination tablet following a high-fat meal had no effect on vildagliptin AUC(0-infinity) (ratio of geometric mean for fed:fasted state, 1.10 [90% CI 1.03, 1.18]), C(max) (ratio of means 0.98 [90% CI 0.85, 1.13]) or median t(max) (2.5 h in fed and fasted states). The rate of absorption of metformin was decreased when given with food, as reflected by the prolonged t(max) (2-4 h) and reduction in C(max) (by 26%), but the extent of absorption was not changed. The food effect on the metformin component of the fixed-dose combination tablets was consistent with, but of a lesser magnitude compared with data stated. CONCLUSIONS: The vildagliptin/metformin (50/1000 mg) fixed-dose combination tablet can be administered in the same manner as metformin, and can be recommended to be taken with meals to reduce the gastrointestinal symptoms associated with metformin.

Pomegranate juice does not impair clearance of oral or intravenous midazolam, a probe for cytochrome P450-3A activity: comparison with grapefruit juice.

The effect of pomegranate juice (PJ) or grapefruit juice (GFJ) on CYP3A activity was studied in vitro and in healthy human volunteers. In human liver microsomes, the mean 50% inhibitory concentrations (IC(50)) for PJ and GFJ versus CYP3A (triazolam alpha-hydroxylation) were 0.61% and 0.55%, (v/v) respectively, without preincubation of inhibitor with microsomes. After preincubation, the IC(50) for PJ increased to 0.97% (P < .05), whereas the IC(50) for GFJ decreased to 0.41% (P < .05), suggesting mechanism-based inhibition by GFJ but not PJ. Pretreatment of volunteer subjects (n = 13) with PJ (8 oz) did not alter the elimination half-life, volume of distribution, or clearance of intravenous midazolam (2 mg). Administration of PJ also did not affect C(max), total area under the curve (AUC), or clearance of oral midazolam (6 mg). However, GFJ (8 oz) increased midazolam C(max) and AUC by a factor of 1.3 and 1.5, respectively, and reduced oral clearance to 72% of control values. Thus, PJ does not alter clearance of intravenous or oral midazolam, whereas GFJ impairs clearance and elevates plasma levels of oral midazolam.

Interaction of flurbiprofen with cranberry juice, grape juice, tea, and fluconazole: in vitro and clinical studies.

OBJECTIVES: Recent anecdotal, unvalidated case reports have suggested potentiation of warfarin-induced anticoagulation by cranberry juice, possibly through inhibition of human cytochrome P450 (CYP) 2C9, the enzyme responsible for the clearance of the active S-enantiomer of warfarin. To address this question, the effect of cranberry juice and other beverages on CYP2C9 activity was evaluated in vitro and in vivo. METHODS: The effects of 4 beverages on CYP2C9 activity were studied in human liver microsomes, by use of flurbiprofen hydroxylation as the index reaction. In a clinical study 14 healthy volunteers received 100 mg flurbiprofen on 5 occasions in a crossover fashion, with at least 1 week separating the 5 trials. Flurbiprofen was preceded in random sequence by the following: (1) cranberry juice placebo (8 oz), (2) cranberry juice (8 oz), (3) brewed tea (8 oz), (4) grape juice (8 oz), and (5) fluconazole, a CYP2C9 inhibitor serving as a positive control, with 8 oz of water. RESULTS: Flubiprofen hydroxylation in vitro was reduced to 11% +/- 8% of control by 2.5% (vol/vol) brewed tea, to 10% +/- 7% of control by grape juice, to 56% +/- 16% of control by cranberry juice, to 85% +/- 5% of control by cranberry juice placebo, and to 21% +/- 6% of control by the index inhibitor sulfaphenazole (2.5 micromol/L) (P <.01 for all comparisons versus control). Flurbiprofen clearance (29-33 mL/min) and elimination half-life (3.3-3.4 hours) did not differ significantly among trials 1, 2, 3, and 4. However, clearance in the fluconazole treatment condition (trial 5) was significantly reduced compared with the placebo control (17 +/- 5 mL/min versus 31 +/- 8 mL/min, P <.05), and the half-life was prolonged (5.3 +/- 1.6 hours versus 3.3 +/- 0.8 hours, P <.05). Formation of 4-hydroxyflurbiprofen was correspondingly reduced by fluconazole (P <.05). CONCLUSIONS: Although grape juice and tea impaired CYP2C9 activity in vitro, none of the 3 beverages altered CYP2C9-mediated clearance of flurbiprofen in humans, making a pharmacokinetic interaction with warfarin highly unlikely.

Clonazepam pharmacokinetics: comparison of subcutaneous microsphere injection with multiple-dose oral administration.

Nine healthy volunteers participated in a 3-phase clinical pharmacokinetic study of the benzodiazepine derivative clonazepam. During phases I and II, subjects received the conventional oral dosage form of clonazepam, 0.5 mg 3 times daily, for 7 days. Multiple plasma samples were drawn on day 1 and day 7 of the trial and once daily during the washout period after the final dose. Based on nonlinear regression, mean kinetic variables for clonazepam were: absorption half-life, 24 minutes; elimination half-life, 40 hours; apparent oral clearance, 72 mL/min. The extent of accumulation at steady state relative to the first day of treatment averaged 3.3-fold, and was consistent with values predicted based on the elimination half-life. This finding suggests that once-daily dosage with clonazepam would be appropriate for many patients. In phase III of the study, subjects received a single 2.7 mg subcutaneous injection of a microsphere formulation of clonazepam, designed to produce a sustained-release profile. The maximum average plasma clonazepam concentration was 3.0 ng/mL, reached at 72 hours after dosage. Thereafter, plasma concentrations fell slowly over the 13-day sampling period, remaining above 1 ng/mL for 12 days. Overall systemic availability of clonazepam from the microsphere injection, relative to the conventional oral dosage form, was 1.05. Thus, the microsphere preparation of injectable clonazepam provides complete absorption from the injection site, with the intended slow-release pharmacokinetic profile.

Time course of recovery of cytochrome p450 3A function after single doses of grapefruit juice.

BACKGROUND: Components of grapefruit juice may impair the activity of intestinal cytochrome P450 (CYP) 3A enzymes, sometimes resulting in clinically important drug interactions. The time course of recovery from CYP3A inhibition after a single exposure to grapefruit juice is not clearly established. METHODS: Healthy volunteer subjects (N = 25) received a single 6-mg oral dose of the CYP3A substrate midazolam in the control condition without exposure to grapefruit juice. Two days later, midazolam was administered 2 hours after 300 mL of regular-strength grapefruit juice. Subjects were then randomly assigned to 3 different groups, receiving a third midazolam challenge at 26, 50, or 74 hours after exposure to grapefruit juice. The capacity of 6'7'-dihydroxybergamottin and bergamottin to inhibit human CYP3A was studied in vitro using human liver microsomes. RESULTS: The area under the plasma concentration curve (AUC) for midazolam increased by a factor of 1.65 (ratio compared with control) when midazolam was given 2 hours after grapefruit juice. At 26, 50, and 74 hours after grapefruit juice, the AUC ratios (mean AUC value at the indicated time divided by the mean control AUC on day 1) were 1.29, 1.29, and 1.06, respectively. The relationship of time after grapefruit juice exposure versus AUC increase over control indicated a recovery half-life estimated at 23 hours. The midazolam elimination half-life did not change significantly from the control value at any time after grapefruit juice exposure. 6'7'-Dihydroxybergamottin inhibited midazolam alpha-hydroxylation in vitro, with a mean 50% inhibitory concentration of 4.7 micro mol/L; preincubation of microsomes with 6'7'-dihydroxybergamottin greatly reduced the 50% inhibitory concentration to 0.31 micro mol/L, consistent with mechanism-based inhibition. Bergamottin itself had much weaker inhibitory potency compared to 6'7'-dihydroxybergamottin. CONCLUSIONS: A usual single exposure to grapefruit juice appears to impair the enteric, but not the hepatic, component of presystemic extraction of oral midazolam. Recovery is largely complete within 3 days, consistent with enzyme regeneration after mechanism-based inhibition. 6'7'-Dihydroxybergamottin was verified as a potent mechanism-based inhibitor of midazolam alpha-hydroxylation by CYP3A in vitro.