Time effects of food intake on the pharmacokinetics and pharmacodynamics of quazepam

AIMS: There is little information on interaction between food and the hypnotic agent quazepam. We therefore studied the effects of food and its time interval on the pharmacokinetics and pharmacodynamics of quazepam. METHODS: A randomized three-phase crossover study with 2-week intervals was conducted. Nine healthy male volunteers took a single oral 20 mg dose of quazepam under the following conditions: 1) after fasting overnight; 2) 30 min after eating standard meal; or 3) 3 h after eating the same meal. Plasma concentrations of quazepam and its metabolite, 2-oxoquazepam and psychomotor function using the Digit Symbol Substitute Test (DSST), Stanford Sleepiness Scale (SSS) and Visual Analogue Scale were measured up to 48 h. RESULTS: During the food treatments at 30 min and 3 h before dosing, the peak concentrations (Cmax) were 300% (95% CI 260, 340%; P < 0.001) and 250% (95% CI 210, 290%; P < 0.01) of the corresponding value during the fasting phase. For quazepam, the area under the plasma concentration-time curve from 0 to 8 h measured at 30 min and 3 h before dosing was significantly increased, with the food treatments by 2.4-fold (95% CI 2.0; 2.8-fold; P < 0.001) and 2.1-fold (95% CI 1.7; 2.4-fold; P < 0.01), respectively. In response to pharmacokinetic changes, some of the pharmacodynamics (DSST, P < 0.05; SSS, P < 0.05) differed significantly between fasted status and fed status. No difference was found in any pharmacokinetic or pharmacodynamic parameters between the two food treatment phases. CONCLUSIONS: A food effect on quazepam absorption is evident and continues at least until 3 h after food intake. The dosing of quazepam after a long period of ordinary fasting might reduce its efficacy because a 3 h interval between the timing of the evening meal and bedtime administration of hypnotics is regarded as normal in daily life.     

Interaction between grapefruit juice and hypnotic drugs: comparison of triazolam and quazepam

Objective: Grapefruit juice (GFJ) inhibits cytochrome P450 (CYP) 3A4 in the gut wall and increases blood concentrations of CYP3A4 substrates by the enhancement of oral bioavailability. The effects of GFJ on two benzodiazepine hypnotics, triazolam (metabolized by CYP3A4) and quazepam (metabolized by CYP3A4 and CYP2C9), were determined in this study. Methods: The study consisted of four separate trials in which nine healthy subjects were administered 0.25 mg triazolam or 15 mg quazepam, with or without GFJ. Each trial was performed using an open, randomized, cross-over design with an interval of more than 2 weeks between trials. Blood samples were obtained during the 24-h period immediately following the administration of each dose. Pharmacodynamic effects were determined by the digit symbol substitution test (DSST) and utilizing a visual analog scale. Results GFJ increased the plasma concentrations of both triazolam and quazepam and of the active metabolite of quazepam, 2-oxoquazepam. The area under the curve (AUC)(0–24) of triazolam significantly increased by 96% (p<0.05). The AUC(0–24) of quazepam (+38%) and 2-oxoquazepam (+28%) also increased; however, these increases were not significantly different from those of triazolam. GFJ deteriorated the performance of the subjects in the DSST after the triazolam dose (−11 digits at 2 h after the dose, p<0.05), but not after the quazepam dose. Triazolam and quazepam produced similar sedative-like effects, none of which were enhanced by GFJ. Conclusion These results suggest that the effects of GFJ on the pharmacodynamics of triazolam are greater than those on quazepam. These GFJ-related different effects are partly explained by the fact that triazolam is presystemically metabolized by CYP3A4, while quazepam is presystemically metabolized by CYP3A4 and CYP2C9.     

Single oral dose pharmacokinetics of quazepam is influenced by CYP2C19 activity

The effects of cytochrome P450 (CYP)2C19 activity and cigarette smoking on the single oral dose pharmacokinetics of quazepam were studied in 20 healthy Japanese volunteers. Twelve subjects were extensive metabolizers (EMs), and 8 subjects were poor metabolizers (PMs) by CYP2C19 as determined by the PCR-based genotyping. Nine subjects were smokers (>10 cigarettes/d), and 11 subjects were nonsmokers. The subjects received a single oral 20-mg dose of quazepam, and blood samplings and evaluation of psychomotor function were conducted up to 72 hours after dosing. Plasma concentrations of quazepam and its active metabolite 2-oxoquazepam (OQ) were measured by HPLC. There were significant differences between EMs and PMs in the peak plasma concentration (mean +/- SD: 34.5 +/- 16.6 versus 66.2 +/- 19.2 ng/mL, P < 0.01) and total area under the plasma concentration-time curve (490.1 +/- 277.5 vs 812.1 +/- 267.2 ng x h/mL, P < 0.05) of quazepam. The pharmacokinetic parameters of OQ and pharmacodynamic parameters were not different between the 2 groups. Smoking status did not affect the pharmacokinetic parameters of quazepam and OQ or pharmacodynamic parameters. The present study suggests that the single oral dose pharmacokinetics of quazepam are influenced by CYP2C19 activity but not by cigarette smoking.     

The effect of St John's Wort on the pharmacodynamic response of clopidogrel in hyporesponsive volunteers and patients: increased platelet inhibition by enhancement of CYP3A4 metabolic activity

Clopidogrel is metabolically activated by cytochrome P450 (CYP) isoenzymes. We evaluated whether St. John's wort (SJW), a CYP2C19 and CYP3A4 inducer, enhances the pharmacodynamic response of clopidogrel. Volunteers (n = 45) were screened for clopidogrel hyporesponsiveness after a 300-mg load. After a 7-day washout, hyporesponders (n = 10) received 14 days of SJW (300 mg 3 times a day) followed by a second 300-mg clopidogrel. Platelet aggregation was measured at 0, 2, 4, and 6 hours postloading; hepatic CYP3A4 activity was simultaneously determined at 0 and 4 hours by the erythromycin breath test. A prospective, randomized, double-blind pilot study was conducted in postcoronary stent patients (n = 85) on clopidogrel 75 mg/d screened for clopidogrel hyporesponsiveness. Hyporesponders (n = 20) were randomized to SJW (n = 10) or placebo (n = 10); platelet aggregation was measured before and after 14 days of therapy. In volunteers, SJW decreased platelet aggregation (59% ± 14% vs. 40% ± 15% at 2 hours, P = 0.02; 56% ± 10% vs. 44% ± 13% at 4 hours, P < 0.03; and 55% ± 14% vs. 37% ± 14% at 6 hours, P = 0.01) and increased CYP3A4 activity (2.1% ± 0.4% CO2 exhaled per hour before vs. 2.9% ± 0.6% CO2 exhaled per hour after SJW, P = 0.002). In patients, SJW decreased platelet reactivity (226 ± 39 vs. 185 ± 49 P2Y12 reactivity units, P = 0.0002) and increased platelet inhibition (23% ± 11% vs. 41% ± 16%, P = 0.002). SJW may be a future therapeutic option to increase CYP metabolic activity and antiplatelet effect of clopidogrel in hyporesponders.     

The effects of an oral contraceptive containing ethinyloestradiol and norgestrel on CYP3A activity

AIMS: To examine the effects of an oral contraceptive containing ethinyloestradiol and norgestrel on intestinal and hepatic CYP3A activity using midazolam as a probe substrate. METHODS: In a nonblinded sequential study, nine healthy women received simultaneous doses of intravenous midazolam (0.05 mg kg(-1)) and oral 15N3-midazolam (3 mg) on days 0, 4, 6, 8, and 14. On study day 5, Ovral(50 microg ethinyloestradiol/500 microg norgestrel) was administered for 10 days. Serum and urine samples were assayed for midazolam, 15N3-midazolam and metabolites by liquid chromatography-mass spectrometry. A Digit Symbol Substitution Test (DSST) was used to assess changes in the pharmacodynamic activity of midazolam. RESULTS: Moderate (% CV 26-46) interindividual variability in the pharmacokinetics of midazolam were observed. Compared with baseline, AUC(0,infinity)iv ratios (95% CIs) after 2, 4, and 10 days treatment with OC were 89% (79, 101), 96% (85, 109), and 88% (77, 99), respectively. The AUC(0,infinity)oral ratios (95% CIs) were 101% (82, 125), 105% (85, 130), and 114% (92, 141), respectively, after 2, 4, and 10 days OC treatment compared with baseline. Concomitant administration of the oral contraceptive, Ovral for 2, 4 or 10 days did not significantly alter the area under the curve, clearance, or half-life of midazolam after either oral or intravenous administration. No alterations in pharmacodynamic effects of midazolam were observed between treatment days. Mean DSST scores strongly correlated with mean total midazolam blood concentrations (r = -0.936). CONCLUSIONS: Administration of Ovral for 10 days had no impact on intestinal or hepatic CYP3A activity as determined by midazolam metabolism.     

Alterations in cyclosporin A pharmacokinetics and metabolism during treatment with St John's wort in renal transplant patients

AIM: This study investigated the effects of St John's wort extract (SJW) on the pharmacokinetics and metabolism of the immunosuppressant cyclosporin A (CSA). METHODS: In an open-label study, 11 renal transplant patients received 600 mg SJW extract daily for 14 days in addition to their regular regimen of CSA. Blood concentrations of CSA and its metabolites AM1, AM1C, AM9, AM19, and AM4N were measured by HPLC. RESULTS: After 2 weeks of SJW coadministration, dose-corrected AUC0-12, Cmax and Ctrough values for CSA decreased significantly by 46%[geometric mean ratio baseline/SJW (95% CI): 1.83 (1.63-2.05)], 42%[1.72 (1.42-2.08)], and 41%[1.70 (1.17-2.47)], respectively. CSA doses were increased from a median of 2.7 mg day(-1) kg(-1) at baseline to 4.2 mg day(-1) kg(-1) at day 15, with the first dose adjustment required only 3 days after initiation of SJW treatment. Additionally, the metabolite pattern of CSA was substantially altered during SJW treatment. Whereas dose-corrected AUC values for AM1, AM1c and AM4N significantly decreased by 59%, 61%, and 23% compared with baseline, AUC values for AM9 and AM19 were unchanged. Following the increase in CSA dose, observed AUC and Cmax values for AM9, AM19, and AM4N increased by 20-51% and 43-90%, respectively. CONCLUSION: Administration of SJW extract to patients receiving CSA treatment resulted in a rapid and significant reduction of plasma CSA concentrations. Additionally, the substantial alterations in CSA metabolite kinetics observed may affect the toxicity profile of the drug.     

Effect of dietary fat content in meals on pharmacokinetics of quazepam

Dietary fat content in meals has been reported to increase the absorption of several drugs proportionately. However, there is no information about the effects of dietary fat in meals on the sedative hypnotic agent quazepam, although limited data suggest that food intake alters quazepam absorption. Therefore, the authors measured and compared pharmacokinetic parameters of quazepam taken in a fasted state and taken 30 minutes after consuming meals containing different amounts of dietary fat. A three-arm randomized crossover study was conducted. Nine healthy male volunteers took a single oral 20-mg dose of quazepam under the following conditions: (1) after fasting overnight for at least 12 hours, (2) 30 minutes after consuming a low-fat meal (two slices of bread and 200 ml of apple juice), or (3) 30 minutes after consuming high-fat meal (two slices of bread with 30 gm of butter and 200 ml of apple juice). Plasma concentrations of quazepam and its metabolite, 2-oxoquazepam, were monitored up to 48 hours after the dosing. In comparison with corresponding plasma values for quazepam taken in a fasting state, the peak concentrations (Cmax) of quazepam taken 30 minutes after consuming a low-fat meal and high-fat meal were 243% (90% confidence interval [CI] = 161%-325%) and 272% (90% CI = 190%-355%), respectively. Area under the plasma concentration-time curve from 0 to 8 hours (AUC(0-8)) and 0 to 48 hours (AUC(0-48)) of quazepam was increased with the low-fat meal by 2-fold (90% CI = 1.5- to 2.7-fold) and 1.4-fold (90% CI = 1.0- to 1.7-fold), respectively, and with the high-fat meal by 2.2-fold (90% CI = 1.3- to 3-fold) and 1.5-fold (90% CI = 0.7- to 2.4-fold), respectively. The pharmacokinetic change in 2-oxoquazepam to the parent compound was similar. Quazepam was well tolerated, with no significant difference in the Stanford Sleepiness Scale between fasted and fed conditions. These findings show that food intake has an evident effect on quazepam absorption, but further studies are needed to clarify a determinant factor of this alteration (2.5-fold for Cmax and 2.1-fold for AUC(0-8), on average). It might not be necessary to do dose adjustment with meal content because quazepam is well tolerated.     

Effect of an oral contraceptive preparation containing ethinylestradiol and gestodene on CYP3A4 activity as measured by midazolam 1'-hydroxylation

AIMS: To characterize the effect of an oral contraceptive (OC) containing ethinylestradiol and gestodene on the activity of CYP3A4 in vivo as measured by the 1'-hydroxylation of midazolam. METHODS: In this randomised, double-blind, cross-over trial nine healthy female subjects received either a combined OC (30 microg ethinylestradiol and 75 microg gestodene) or placebo once daily for 10 days. On day 10, a single 7.5 mg dose of midazolam was given orally. Plasma concentrations of midazolam and 1'-hydroxymidazolam were determined up to 24 h and the effects of midazolam were measured with three psychomotor tests up to 8 h. RESULTS: The combined OC increased the mean AUC of midazolam by 21% (95% CI 2% to 40%; P = 0.03) and decreased that of 1'-hydroxymidazolam by 25% (95% CI 10% to 41%; P = 0.01), compared with placebo. The metabolic ratio (AUC of 1'-hydroxymidazolam/AUC of midazolam) was 36% smaller (95% CI 19% to 53%; P = 0.01) in the OC phase than in the placebo phase. There were no significant differences in the Cmax, tmax, t(1/2) or effects of midazolam between the phases. CONCLUSIONS: A combined OC preparation caused a modest reduction in the activity of CYP3A4, as measured by the 1'-hydroxylation of midazolam, and slightly increased the AUC of oral midazolam. This study suggests that, at the doses used, ethinylestradiol and gestodene have a relatively small effect on CYP3A4 activity in vivo.     

Effect of grapefruit juice on the disposition of manidipine enantiomers in healthy subjects

AIM: To examine the effect of grapefruit juice, an inhibitor of CYP3A4 in the small intestine, on the disposition of manidipine enantiomers in healthy subjects. METHODS: A randomized cross-over study with at least a 2-week wash-out period was performed. Seven healthy male volunteers received an oral 40-mg dose of racemic manidipine after an overnight fast with either grapefruit juice (GFJ) or water, as a control study. Plasma concentrations of (S)- and (R)-manidipine were monitored up to 10 h after the dosing. RESULTS: The plasma concentrations of (S)-manidipine were significantly higher (P<0.001) than those of (R)-manidipine in the control phase with an S/R ratio for the AUC0-infinity of 1.62 (95% confidence interval 1.52, 1.73). GFJ significantly increased Cmax and AUC0-infinity of (S)-manidipine by 2.4-fold (P<0.01) and 2.3-fold (P<0.01), respectively, and Cmax and AUC0-infinity of (R)-manidipine were increased by 3.4-fold (P<0.01) and 3.0-fold (P<0.01), respectively. There were significant differences (P<0.01) in GFJ-mediated percentage increases in Cmax and AUC0-infinity of (S)-manidipine compared with those of (R)-manidipine. The S/R ratio for AUC0-infinity was significantly decreased from 1.6 to 1.2 during the GFJ phase (P<0.01). CONCLUSION: These results indicate that the stereoselective disposition of manidipine was altered by GFJ, as an inhibitor of CYP3A4. GFJ appears to affect this metabolic disposal of (R)-manidipine to a greater extent than that of (S)-manidipine.     

复方银杏叶胶囊对肝损伤大鼠CYP2E1、CYP3A4的影响

目的研究复方银杏叶胶囊(CGB)对酒精性肝损伤大鼠CYP2E1、CYP3A4活性的影响。方法正常组和酒精性肝损伤模型组均以CGB[(250 mg/(kg.d)]灌胃,分别在灌胃CGB前及灌胃1周后,灌胃探针药氯唑沙宗(50 mg/kg)及氨苯砜(20 mg/kg),于探针药灌后24 h内不同时间点采血,测定各探针药血药浓度。结果灌胃CGB前,模型组氯唑沙宗和氨苯砜的AUC0-24、Cmax均显著低于正常组(P<0.05或P<0.01)。灌胃CGB后,模型组氯唑沙宗和氨苯砜的AUC0-24、Cmax均较灌胃前显著升高(P<0.05或P<0.01);且氯唑沙宗的t1/2灌胃CGB后明显高于灌胃前(P<0.05)。结论 CGB能够明显抑制酒精性肝损伤大鼠CYP2E1、CYP3A4酶活性。     

No relevant interaction with alprazolam, caffeine, tolbutamide, and digoxin by treatment with a low-hyperforin St John's wort extract

We evaluated the pharmacokinetic interaction between a low-hyperforin St John's wort (SJW) extract and alprazolam, caffeine, tolbutamide, and digoxin. Previous reports on other SJW products had shown remarkably decreased plasma concentrations of certain co-medicated drugs, which was attributed to an inducing effect of SJW on cytochrome P-450 (CYP) and p-glycoprotein (p-gp) activity. Two randomised, placebo-controlled studies were performed with 28 healthy volunteers (age 18 - 55 years) in each study. In study A, single doses of alprazolam (1 mg; substrate of CYP3A4) and caffeine (100 mg; CYP1A2) were given on days 1 and 11. In study B, single doses of tolbutamide (500 mg, days 1 and 11; CYP2C9) and multiple doses of digoxin (0.75 mg on days -2 and -1, 0.25 mg/die on days 1 to 11; p-gp) were given. The participants received SJW (Esbericum capsules; 240 mg/die of extract, 3.5 mg hyperforin) or placebo on days 2 to 11. Blood for pharmacokinetic analysis was drawn on days 1 and 11. No statistically significant differences were found in the primary kinetic parameter, AUC0 - 24, of alprazolam, caffeine (AUC0 - 12), paraxanthine, tolbutamide, 4-hydroxytolbutamide, and digoxin between the placebo group and the SJW group at the end of the study. The SJW-induced change in AUCs was less than 12 % of the initial median AUC of the participants in studies A and B, thus clinically irrelevant. On day 11, trough concentrations were 2.0 (range 0.6 - 4.1) microg/L and 1.0 (0.2 - 3.9) microg/L for hypericin and pseudohypericin, respectively, whereas hyperforin concentrations were below the quantification limit (< 1 microg/L). Kinetics of investigated probe drugs were only marginally influenced by concomitant treatment with Esbericum capsules. This may be due in particular to the low hyperforin plasma concentration as this SJW component has been shown to activate the PXR receptor which regulates expression of CYP3A4 and p-gp. Our findings corroborate the view that reports about interactions of other SJW extracts seem not to be predictive for the product we studied.     

Effect of rifampin on plasma concentrations of mefloquine in healthy volunteers

Mefloquine is a 4-quinolinemethanol compound structurally related to quinine. Quinine is mainly metabolized by the cytochrome P450 3A4 isozyme (CYP3A4), whereas rifampin, a potent inducer of CYP3A4, is known to markedly decrease plasma quinine concentration. Our aim was to study the effect of rifampin on the pharmacokinetics of mefloquine, and explore a possible role of CYP3A4 on mefloquine metabolism. In an open, two-phase crossover study, seven healthy Thai male volunteers received a single oral dose of 500 mg mefloquine alone, or 500 mg mefloquine plus a long-term administration of 600 mg rifampin. Blood samples were collected at specific time points over a 56-day period. Plasma mefloquine and its carboxylic acid metabolite were measured by HPLC for pharmacokinetic analysis. The results indicate that rifampin significantly decreased the area under the plasma concentration-time curve (AUC0 - infinity) of mefloquine by 68% (P < 0.01), maximum plasma concentration (Cmax) by 19% (P < 0.001), and elimination half-life (t1/2) by 63% (P < 0.01), whereas the time to reach Cmax (t(max)) of mefloquine was unaffected. The apparent oral clearance (CL) of mefloquine was significantly increased by 281% (P < 0.01). After administration of rifampin, the Cmax of the carboxylic acid metabolite of mefloquine was significantly increased by 47% (P < 0.05), whereas the t1/2 was significantly decreased by 39% (P < 0.01), and t(max) by 76% (P < 0.01). The AUC0 - infinity and CL of the mefloquine metabolite were increased by 30% and 25%, respectively, but were not significantly different from the control phase. The results indicate that rifampin reduces the plasma concentration of a single oral dose of 500 mg mefloquine by increasing metabolism of mefloquine in the liver and gut wall. The CYP3A4 isozyme most likely plays an important role in the enhanced metabolism of mefloquine. Simultaneous use of rifampin and mefloquine should be avoided to optimize the therapeutic efficacy of mefloquine and prevent the risk of Plasmodium falciparum resistance in malarial treatment.     

Induction and inhibition of cytochromes P450 by the St. John's wort constituent hyperforin in human hepatocyte cultures.

St. John's wort extract (SJW) (Hypericum perforatum L.) is among the most commonly used herbal medications in the United States. The predominance of clinical reports indicates that SJW increases the activity of cytochrome P450 3A4 (CYP3A4) enzyme and reduces plasma concentrations of certain drugs. Although the inductive effect of SJW on CYP3A4 is clear, other reports indicate that SJW constituents may have, to a small degree, some enzyme inhibitory effects. Therefore, we sought to study the induction and inhibition effects of the constituents of SJW on CYP3A4 in the human hepatocyte model. Moreover, most research has focused on the induction of CYP3A4 by SJW with little attention paid to other prominent drug-metabolizing enzymes such as CYP1A2, CYP2C9, and CYP2D6. To examine the effects of SJW on CYP1A2, CYP2C9, CYP2D6, as well as CYP3A4, hepatocytes were exposed to hyperforin and hypericin, the primary constituents of SJW extract. Hepatocytes treated with hypericin or hyperforin were exposed to probe substrates to determine enzyme activity and protein and RNA harvested. Hyperforin treatment resulted in significant increases in mRNA, protein, and activity of CYP3A4 and CYP2C9, but had no effect on CYP1A2 or CYP2D6. Acute administration of hyperforin at 5 and 10 microM 1 h before and along with probe substrate inhibited CYP3A4 activity. Hypericin had no effect on any of the enzymes tested. These results demonstrate that with chronic exposure, the inductive effect of SJW on drug-metabolizing enzymes predominates, and human hepatocyte cultures are a versatile in vitro tool for screening the effect of herbal products on cytochrome P450 enzymes.     

A mechanistic study on altered pharmacokinetics of irinotecan by St. John's wort

Irinotecan (CPT-11) is an important anticancer drug in management of advanced colon cancer. A marked protective effect on CPT-11-induced blood and gastrointestinal toxicity is obtained by combination of St. John's wort (SJW) in recent clinical and rat studies. However, the mechanism is unclear. This study aimed to explore the effects of SJW on the pharmacokinetics of CPT-11 and its major metabolites (SN-38 and SN-38 glucuronide) in rats and the underlying mechanisms using several in vitro models. Short-term (3 days) and long-term (14 days) pretreatment with SJW were conducted in rats to examine the effects of co-administered SJW on the plasma pharmacokinetics of CPT-11, SN-38 and SN-38 glucuronide. Rat liver microsomes and a rat hepatoma cell line, H4-II-E cells, were utilized to study the effects of aqueous and ethanolic extracts (AE and EE) and major active components (hyperforin, hypericin and quercetin) of SJW on CPT-11 and SN-38 metabolism and intracellular accumulation. Co-administered SJW for consecutive 14 days significantly decreased the initial plasma concentration (C0) of CPT-11, the area under the concentration-time curve (AUC(0-10hr)) and maximum plasma concentration (Cmax) of SN-38. The ethanolic extracts (EE) of SJW at 5 microg/ml significantly decreased SN-38 glucuronidation by 45% (P < 0.05) in rat hepatic microsomes. Pre-incubation of aqueous SJW extracts (AE) at 10 microg/ml, SJW EE at 5 microg/ml, and quercetin at 10 microM significantly increased the glucuronidation of SN-38 in H4-II-E cells. A 2-hr pre-incubation of quercetin (100 microM) significantly increased the intracellular accumulation of CPT-11 (P < 0.05). However, pre-incubation of hypericin (20 nM and 200 nM) and hyperforin (1 microM) significantly decreased the intracellular accumulation of CPT-11. In addition, pre-incubation of hypericin, SJW EE and quercetin significantly increased the intracellular accumulation of SN-38. Aqueous and ethanolic SJW extracts and its major active components did not alter the plasma protein binding of CPT-11 and SN-38. These results indicated that the aqueous and ethanolic extracts of SJW and its major active components could markedly alter glucuronidation of SN-38 and intracellular accumulation of CPT-11 and SN-38, which probably provides partial explanation for the altered plasma pharmacokinetics of CPT-11 and SN-38 and the antagonizing effects on the toxicities of CPT-11. Further studies are needed to explore the role of both pharmacokinetic and pharmacodynamic components in the protective effect of SJW against the toxicities of CPT-11.     

Effect of itraconazole on the pharmacokinetics and pharmacodynamics of a single oral dose of brotizolam

AIMS: To assess the effect of itraconazole, a potent inhibitor of cytochrome P450 (CYP)3A4, on the single oral dose pharmacokinetics and pharmacodynamics of brotizolam. METHODS: In this randomized, double-blind, cross-over trial 10 healthy male subjects received either itraconazole 200 mg or matched placebo once daily for 4 days. On day 4, a single 0.5 mg dose of brotizolam was administered orally. Plasma concentrations of brotizolam were followed up to 24 h, together with assessment of psychomotor function measured by the digit symbol substitution test (DSST), visual analogue scales and UKU side-effect rating scale. RESULTS: Itraconazole significantly (P < 0.001) decreased the apparent oral clearance (CL/F) (16.47 +/- 4.3 vs 3.91 +/- 2.1), increased the area under the concentration-time curves (AUC) from 0 h to 24 h (28.37 +/- 10.8 vs 68.71 +/- 24.1 ng ml h(-1)), and prolonged the elimination half-life (4.56 +/- 1.4 vs 23.27 +/- 10.3 h) of brotizolam. The AUC(0,24 h) of the DSST (P < 0.001) and the item 'sleepiness' of UKU (P < 0.05) were significantly decreased. CONCLUSIONS: Itraconazole increases plasma concentrations of brotizolam probably via its inhibitory effect on CYP3A4 brotizolam metabolism.     

Effect of St John's wort on the activities of CYP1A2, CYP3A4, CYP2D6, N-acetyltransferase 2, and xanthine oxidase in healthy males and females

AIMS: To investigate the influence of St. John's wort (SJW) on CYP3A4, CYP1A2, CYP2D6, N-acetyltransferase 2 (NAT2), and xanthine oxidase (XO) activities in healthy males and females. METHODS: Eight males and eight females were treated with SJW extract (3 x 300 mg day(-1)) for 14 days. Assessment of CYP1A2, NAT2, XO, CYP2D6, and CYP3A4 activities was performed before and at the end of the study period, using caffeine, dextromethorphan, and endogenous cortisol as probes. The corresponding metabolic ratios measured were 17MX/137MX in saliva and (AFMU+1MX+1MU)/17MU in urine for CYP1A2, AFMU/1MX for NAT2, 1MU/1MX for XO, DOR/DMO for CYP2D6, 3MM/DMO and 6OHC/C for CYP3A4, all determined in urine. RESULTS: The ratios of the treatment to baseline values for CYP3A4 using cortisol as the probe were 1.5 [95% confidence interval (CI) 1.3, 1.9] for males, and 1.9 (1.1, 3.0) for females. The corresponding ratios using dextromethorphan as the probe for CYP2D6 were 0.9 (95% CI 0.5, 2.1) for males and 1.9 (1.3, 3.2) for females. For CYP1A2, a significant increase in the metabolic ratios was found only for females (ratio of values 1.2; 95% CI 1.1, 1.4). No influence of SJW on CYP2D6, NAT2, and XO activities was observed. CONCLUSIONS: An induction of CYP3A4 by SJW was confirmed. CYP1A2 appears to be induced by SJW only in females. The activities of CYP2D6, NAT2, and XO were not affected by SJW.     

Rofecoxib is a potent inhibitor of cytochrome P450 1A2: studies with tizanidine and caffeine in healthy subjects

AIMS: Case reports suggest an interaction between rofecoxib and the CYP1A2 substrate tizanidine. Our objectives were to explore the extent and mechanism of this possible interaction and to determine the CYP1A2 inhibitory potency of rofecoxib. METHODS: In a randomized, double-blind, two-phase cross-over study, nine healthy subjects took 25 mg rofecoxib or placebo daily for 4 days and, on day 4, each ingested 4 mg tizanidine. Plasma concentrations and the urinary excretion of tizanidine, its metabolites (M) and rofecoxib, and pharmacodynamic variables were measured up to 24 h. On day 3, a caffeine test was performed to estimate CYP1A2 activity. RESULTS: Rofecoxib increased the area under the plasma concentration-time curve (AUC(0-infinity)) of tizanidine by 13.6-fold [95% confidence interval (CI) 8.0, 15.6; P < 0.001), peak plasma concentration (C(max)) by 6.1-fold (4.8, 7.3; P < 0.001) and elimination half-life (t(1/2)) from 1.6 to 3.0 h (P < 0.001). Consequently, rofecoxib markedly increased the blood pressure-lowering and sedative effects of tizanidine (P < 0.05). Rofecoxib increased several fold the tizanidine/M-3 and tizanidine/M-4 ratios in plasma and urine and the tizanidine/M-5, tizanidine/M-9 and tizanidine/M-10 ratios in urine (P < 0.05). In addition, it increased the plasma caffeine/paraxanthine ratio by 2.4-fold (95% CI 1.4, 3.4; P = 0.008) and this ratio correlated with the tizanidine/metabolite ratios. Finally, the AUC(0-25) of rofecoxib correlated with the placebo phase caffeine/paraxanthine ratio (r = 0.80, P = 0.01). CONCLUSIONS: Rofecoxib is a potent inhibitor of CYP1A2 and it greatly increases the plasma concentrations and adverse effects of tizanidine. The findings suggest that rofecoxib itself is also metabolized by CYP1A2, raising concerns about interactions between rofecoxib and other CYP1A2 substrate and inhibitor drugs.     

An update on clinical drug interactions with the herbal antidepressant St. John's wort

St. John's wort (Hypericum perforatum, SJW) is one of the most commonly used herbal antidepressants for the treatment of minor to moderate depression. Limited clinical trials suggest that hypericum and standard antidepressants have similar beneficial effects, but current evidence regarding the antidepression effects of SJW extracts is inconsistent. A major safety concern about SJW is its ability to alter the pharmacokinetics and/or clinical response of a variety of clinically important drugs. This review highlights and updates the knowledge regarding drug interactions with SJW by a systematic review of all the available evidence, including worldwide published literature and spontaneous case reports. A number of clinically significant interactions of SJW have been identified with conventional drugs. These interactions often result in a decrease in the concentration or effect of the combined drug, most probably due to the induction of cytochrome P450s (CYPs) and the key drug transporter P-glycoprotein (P-gp) by the major active constituents in SJW. SJW is a potent inducer of human CYP3A4 and P-gp in vitro and in vivo. In addition, pharmacodynamic interactions of SJW with some drugs (e.g. selective serotonin re-uptake inhibitors) have been identified, which are associated with an increased risk of adverse reactions. Since potential interactions of SJW with conventional drugs is a major safety concern, it is important to minimize and avoid these interactions by taking appropriate approaches. These include systematic research to identify SJW-drug interaction; close therapeutic drug monitoring when SJW is combined with conventional drugs with a narrow therapeutic window; proper dose and regimen adjustment; patient education and communication between the patient and physician; design of new preparations of SJW without inducing ability of CYP3A4 and P-gp while retaining its bioactivity; and appropriate regulation in herbal safety and efficacy. Further clinical and mechanistic studies are warranted to explore the interaction of SJW with other important drugs and clinical significance.     

No correlations between the urinary ratio of 6beta-hydroxycortisol to free cortisol and pharmacokinetics of alprazolam

OBJECTIVE: The urinary ratio of 6beta-hydroxycortisol to cortisol is known as a possible marker of CYP3A4 activity. We investigated the correlation between this ratio and the disposition of alprazolam, which is a substrate of CYP3A4. METHODS: Twelve healthy volunteers took a single dose (0.8 mg) of alprazolam at 0800 hours. Blood samplings were conducted up to 48 h after the dosing. Urine was collected during the 24 h prior to dosing. Quantification of alprazolam in plasma and that of cortisol and 6beta-hydroxycortisol in urine was performed using high-performance liquid chromatography. RESULTS: Mean (+/-SD) values of peak plasma concentration (Cmax), time to Cmax (tmax), area under the plasma concentration-time curve [AUC(0-48)] and elimination half-life (tl/2) of alprazolam were 12.0+/-3.0 ng/ml, 1.5+/-0.9 h, 200+/-41 ng/ml h and 16.0+/-4.3 h, respectively. Mean (+/-SD) urinary ratio of 6beta-hydroxycortisol to cortisol was 3.28+/-0.67. No significant correlations were found between urinary ratio of 6beta-hydroxycortisol to cortisol and any pharmacokinetic parameters of alprazolam (Cmax: rs= -0.06; tmax: r(s)= 0.34; AUC(0-48): rs=0.08; t1/2: r(s)= -0.36). CONCLUSION: This study suggests that the urinary ratio of 6beta-hydroxycortisol to cortisol is unlikely to predict pharmacokinetics of alprazolam.     

Effects of itraconazole on the plasma kinetics of quazepam and its two active metabolites after a single oral dose of the drug

The effects of itraconazole, a potent inhibitor of cytochrome P450 (CYP) 3A4, on the plasma kinetics of quazepam and its two active metabolites after a single oral dose of the drug were studied. Ten healthy male volunteers received itraconazole 100 mg/d or placebo for 14 days in a double-blind randomized crossover manner, and on the fourth day of the treatment they received a single oral 20-mg dose of quazepam. Blood samplings and evaluation of psychomotor function by the Digit Symbol Substitution Test and Stanford Sleepiness Scale were conducted up to 240 h after quazepam dosing. Itraconazole treatment did not change the plasma kinetics of quazepam but significantly decreased the peak plasma concentration and area under the plasma concentration-time curve of 2-oxoquazepam and N-desalkyl-2-oxoquazepam. Itraconazole treatment did not affect either of the psychomotor function parameters. The present study thus suggests that CYP 3A4 is partly involved in the metabolism of quazepam.