Assessment of cytochrome P450 activity by a five-drug cocktail approach.

OBJECTIVES: Our goal was to establish and validate a modified cocktail approach including probe drugs caffeine, chlorzoxazone, mephenytoin, metoprolol, and midazolam for simultaneous phenotyping of CYP1A2, CYP2E1, CYP2C19, CYP2D6, and CYP3A. METHODS: The study was conducted in 14 healthy, nonsmoking male volunteers with a cocktail of 5 drugs consisting of 100 mg caffeine, 200 mg chlorzoxazone, 100 mg mephenytoin, 100 mg metoprolol, and 7.5 mg midazolam in a randomized manner with a 7 x 7 Latin square design. Plasma was obtained at 1, 4, and 6 hours, and urine was collected from 0 to 8 hours after oral drug administration. RESULTS: The phenotypic indexes determined for caffeine, chlorzoxazone, mephenytoin, metoprolol, and midazolam were not significantly different when the drugs were given in different combinations. There were no metabolic interactions or analytic interference of these probe drugs. CONCLUSIONS: This cocktail approach can simultaneously provide independent in vivo phenotypic measures for the cytochrome P450 (CYP) enzymes CYP1A2, CYP2E1, CYP2C19, CYP2D6, and CYP3A.     

Isozyme-specific induction of low-dose aspirin on cytochrome P450 in healthy subjects

OBJECTIVE: This study was designed to define the effect of low-dose aspirin administration on the activity of cytochrome P450 (CYP) in normal human subjects. METHODS: Aspirin, 50 mg daily, was given for 14 days to 18 nonsmoking healthy male volunteers. A modified 5-drug cocktail procedure consisting of caffeine, mephenytoin, metoprolol, chlorzoxazone, and midazolam was performed to simultaneously assess in vivo activity of CYP1A2, CYP2C19, CYP2D6, CYP2E1, and CYP3A, respectively. The activities were assessed on 4 occasions including at baseline, after 7 and 14 daily doses of aspirin, and at 7 days after discontinuation of aspirin. Concentrations of parent drugs and corresponding metabolites in biologic samples were assayed by reversed-phase HPLC. RESULTS: Both 7-day and 14-day aspirin intake increased the activity of CYP2C19 significantly, as indicated by 4-hydroxymephenytoin urinary recovery (P <.001). Induction of low-dose aspirin on CYP2C19 was time-dependent. CYP3A activity indices increased moderately but significantly by both 7-day and 14-day aspirin treatment (P <.05), but the percentage changes in CYP3A activity indices were not significant. Low-dose aspirin had no effect on CYP1A2, CYP2D6, and CYP2E1 in vivo activity by either 7-day or 14-day treatment. CONCLUSIONS: The effect of low-dose aspirin on CYPs was enzyme-specific. Both 7-day and 14-day low-dose aspirin induced the in vivo activities of CYP2C19 but did not affect the activities of CYP1A2, CYP2D6, and CYP2E1. The effect of low-dose aspirin on CYP3A activity awaits further confirmation. When low-dose aspirin is used in combination with drugs that are substrates of CYP2C19, doses of the latter should be adjusted to ensure their efficacy.     

Effect of cytochrome P450 3A4 inhibitor ketoconazole on risperidone pharmacokinetics in healthy volunteers

What is known and objective: Risperidone is an atypical antipsychotic agent used for the treatment of schizophrenia. It is mainly metabolized by human cytochrome P450 CYP2D6 and partly by CYP3A4 to 9‐hydroxyrisperidone. Ketoconazole is used as a CYP3A4 inhibitor probe for studying drug–drug interactions. We aim to investigate the effect of ketoconazole on the pharmacokinetics of risperidone in healthy male volunteers. Methods: An open‐label, randomized, two‐phase crossover design with a 2‐week washout period was performed in 10 healthy male volunteers. The volunteers received a single oral dose of 2 mg of risperidone alone or in combination with 200 mg of ketoconazole, once daily for 3 days. Serial blood samples were collected at specific periods after ingestion of risperidone for a period of 96 h. Plasma concentrations of risperidone and 9‐hydroxyrisperidone were determined using a validated HPLC–tandem mass spectrometry method. Results and discussion: After pretreatment with ketoconazole, the clearance of risperidone decreased significantly by 34·81 ± 15·10% and the T_1/2 of risperidone increased significantly by 28·03 ± 40·60%. The AUC_0–96 and AUC_0–∞ of risperidone increased significantly by 66·61 ± 43·03% and 66·54 ± 39·76%, respectively. The Vd/f of risperidone increased significantly by 39·79 ± 53·59%. However, the C_max and T_max of risperidone were not significantly changed, indicating that ketoconazole had minimal effect on the absorption of risperidone. The C_max, T_max and T_1/2 of 9‐hydroxyrisperidone did not decrease significantly. However, the Cl/f of 9‐hydroxyrisperidone increased significantly by 135·07 ± 124·68%, and the Vd/f of 9‐hydroxyrisperidone decreased significantly by 29·47 ± 54·64%. These changes led to a corresponding significant decrease in the AUC_0–96 and AUC_0–∞ of 9‐hydroxyrisperidone by 47·76 ± 22·39% and 48·49 ± 20·03%, respectively. Ketoconazole significantly inhibited the metabolism of risperidone through the inhibition of hepatic CYP3A4. Our results suggest that besides CYP2D6, CYP3A4 contributes significantly to the metabolism of risperidone. What is new and Conclusion: The pharmacokinetics of risperidone was affected by the concomitant administration of ketoconazole. If a CYP3A4 inhibitor is used concomitantly with risperidone, it is necessary for the clinicians to monitor their patients for signs of adverse drug reactions.     

Safety,tolerability, and pharmacokinetics of oral baicalein tablets in healthy Chinese subjects: A single‐center,randomized, double‐blind,placebo‐controlled multiple‐ascending‐dose study

Baicalein is a biologically important flavonoid in extracted from the Scutellaria baicalensis Georgi, which can effectively inhibit the influenza virus. This study aimed to analyze the safety and pharmacokinetic (PK) characteristics of baicalein tablets in healthy Chinese subjects and provide more information for phase II clinical trials. In this multiple‐ascending‐dose placebo‐controlled trial, 36 healthy subjects were randomized to receive 200, 400, and 600 mg of baicalein tablet or placebo once daily on day 1 and day 10, 3 times daily on days 4–9. All groups were intended to produce safety and tolerability outcomes (lowest dose first). Blood and urine samples were collected from subjects in the 600 mg group for baicalein PK analysis. Our study had shown that Baicalein tablet was generally safe and well‐tolerated. All adverse events were mild and resolved without any intervention except one case of fever reported in the 600 mg group, which was considered as moderate but not related with baicalein as judged by the investigator. Oral baicalein tablets were rapidly absorbed with peak plasma levels being reached within 2 h after multiple administration. The highest urinary excretion of baicalein and its metabolites peaked in 2 h, followed by 12 h, with a double peak trend.

Study Highlights

• WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC?

Many studies have shown that baicalin has an anti‐influenza effect in cell and animal experiments. The primary mechanism of action is that baicalein has a strong inhibitory effect on the sialidase of the influenza virus.

• WHAT QUESTION DID THIS STUDY ADDRESS?

This study aimed to analyze the safety and pharmacokinetic (PK) characteristics of baicalein tablets in healthy Chinese subjects and provide more information for phase II clinical trials.

• WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE?

Our study results have shown that baicalein tablets were administered multiple times within the studied dose range were safe and well‐tolerated in healthy Chinese subjects with no serious or severe adverse effects. The highest urinary excretion of baicalein and its metabolites peaked in 2 h, followed by 12 h, with a double peak trend. Oral baicalein tablets were rapidly absorbed with peak plasma levels reached within 2 h after multiple administration.

• HOW MIGHT THIS CHANGE CLINICAL PHARMACOLOGY OR TRANSLATIONAL SCIENCE?

Our study addresses the safety outcomes of baicalein tablets and emphasizes the PKs of baicalein, which provides a better understanding and a scientific basis of the clinical application of baicalein for further evaluation.     

Artemisinin antimalarials moderately affect cytochrome P450 enzyme activity in healthy subjects

The aim of this study was to investigate which principal human cytochrome P450 (CYP450) enzymes are affected by artemisinin and to what degree the artemisinin derivatives differ with respect to their respective induction and inhibition capacity. Seventy-five healthy adults were randomized to receive therapeutic oral doses of artemisinin, dihydroartemisinin, arteether, artemether or artesunate for 5 days (days 1-5). A six-drug cocktail consisting of caffeine, coumarin, mephenytoin, metoprolol, chlorzoxazone and midazolam was administered orally on days -6, 1, 5 and 10 to assess the activities of CYP1A2, CYP2A6, CYP2C19, CYP2D6, CYP2E1 and CYP3A, respectively. Four-hour plasma concentrations of parent drugs and corresponding metabolites and 7-hydroxycoumarin urine concentrations were quantified by liquid chromatography-tandem mass spectrometry. The 1-hydroxymidazolam/midazolam 4-h plasma concentration ratio (CYP3A) was increased on day 5 by artemisinin [2.66-fold (98.75% CI: 2.10-3.36)], artemether [1.54 (1.14-2.09)] and dihydroartemisinin [1.25 (1.06-1.47)] compared with day -6. The S-4'-hydroxymephenytoin/S-mephenytoin ratio (CYP2C19) was increased on day 5 by artemisinin [1.69 (1.47-1.94)] and arteether [1.33 (1.15-1.55)] compared with day -6. The paraxanthine/caffeine ratio (CYP1A2) was decreased on day 1 after administration of artemisinin [0.27 (0.18-0.39)], arteether [0.70 (0.55-0.89)] and dihydroartemisinin [0.73 (0.59-0.90)] compared with day -6. The alpha-hydroxymetoprolol/metoprolol ratio (CYP2D6) was lower on day 1 compared with day -6 in the artemisinin [0.82 (0.70-0.96)] and dihydroartemisinin [0.83 (0.71-0.96)] groups, respectively. In the artemisinin-treated subjects this decrease was followed by a 1.34-fold (1.14-1.58) increase from day 1 to day 5. These results show that intake of artemisinin antimalarials affect the activities of several principal human drug metabolizing CYP450 enzymes. Even though not significant in all treatment groups, changes in the individual metrics were of the same direction for all the artemisinin drugs, suggesting a class effect that needs to be considered in the development of new artemisinin derivatives and combination treatments of malaria.     

Effect of cytochrome P450 3A4 inhibition on the pharmacokinetics of docetaxel

OBJECTIVE: In vitro studies indicate that the anticancer drug docetaxel is primarily eliminated by cytochrome P450 (CYP) 3A4-mediated metabolism. Coadministration of drugs that modulate the activity of CYP3A4 is, therefore, likely to have undesirable clinical consequences. We investigated the effects of the potent CYP3A4 inhibitor ketoconazole on the pharmacokinetics of docetaxel in patients with cancer. METHODS: Seven patients were treated in a randomized crossover design with docetaxel (100 mg/m(2)), followed 3 weeks later by docetaxel (10 mg/m(2)) given in combination with orally administered ketoconazole (200 mg once daily for 3 days), or the reverse sequence. Plasma concentration-time data were analyzed by noncompartmental analysis. RESULTS: Ketoconazole coadministration resulted in a 49% decrease in clearance of docetaxel (P =.018). The mean (+/-SD) clearance values were 35.0 +/- 11.8 L/h (95% confidence interval, 24.1-45.9 L/h) for docetaxel alone and 18.2 L/h (95% confidence interval, 9.22-27.1 L/h) in the presence of ketoconazole, respectively. The docetaxel clearance ratio in the presence and absence of ketoconazole was weakly related to the area under the curve of ketoconazole (R(2) = 0.529, P =.064). CONCLUSION: Inhibition of CYP3A4 by ketoconazole in vivo results in docetaxel clearance values that have previously been shown to be associated with a several-fold increase in the odds for febrile neutropenia at standard doses. Caution should be taken and substantial dose reductions are required if docetaxel has to be administered together with potent inhibitors of CYP3A4.     

A phase I,randomized, double‐blind,placebo‐controlled,single‐ and multiple dose escalation study evaluating the safety,pharmacokinetics and pharmacodynamics of VX‐128, a highly selective Nav1.8 inhibitor,in healthy adults

Selective inhibition of certain voltage‐gated sodium channels (Na_vs), such as Na_v1.8, is of primary interest for pharmacological pain research and widely studied as a pharmacological target due to its contribution to repetitive firing, neuronal excitability, and pain chronification. VX‐128 is a highly potent and selective Na_v1.8 inhibitor that was being developed as a treatment for pain. We evaluated the safety, tolerability, and pharmacokinetics of VX‐128 in healthy subjects in a single‐ and multiple‐ascending dose (MAD) first‐in‐human study. Pharmacodynamics were evaluated in the MAD part using a battery of evoked pain tests. Overall, single doses of VX‐128 up to 300 mg were well‐tolerated, although adverse effect (AE) incidence was higher in subjects receiving VX‐128 (41.7%) compared with placebo (25.0%). After multiple dosing of up to 10 days, skin rash events were observed at all dose levels (up to 100 mg once daily [q.d.]), in five of 26 (19.2%) subjects, including one subject receiving VX‐128 (100 mg q.d.) who had a serious AE of angioedema. A trend in pain tolerance were observed for cold pressor‐ and pressure pain, which was dose‐dependent for the latter. VX‐128 was rapidly absorbed (median time to maximum plasma concentration between 1 and 2 h) with a half‐life of ~80 h at 10 mg q.d., and approximately two‐fold accumulation ratio after 10 and 30 mg q.d. Although VX‐128, when given in a multiple dose fashion, resulted in early study termination due to tolerability issues, effects were observed on multiple pain tests that may support further investigation of Na_v1.8 inhibitors as pain treatments.

Study Highlights

• WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC?

Selective sodium channel (Na_v) inhibitors have been proposed as an alternative to opioids for pain management. Their potential, however, has yet to be confirmed, as none of the multiple selective Na_v inhibitors that have been investigated for pain management has reached the market.

• WHAT QUESTION DID THIS STUDY ADDRESS?

We investigated the safety, tolerability, and initial analgesic effects of VX‐128, a novel and highly selective Na_v1.8 inhibitor, in healthy volunteers.

• WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE?

This is the first study to describe clinical data obtained on the highly selective Na_v1.8 inhibitor VX‐128, and the first to report analgesic effects of this selective Na_v inhibitor in humans. VX‐128 administered as a single dose was well‐tolerated, but dose‐limiting skin rashes occurred after multiple doses resulting in a premature study halt. Although the study had a parallel design and was not necessarily powered to detect pharmacodynamic effects, nociceptive test results suggest that VX‐128 leads to dose‐dependent analgesic effects.

• HOW MIGHT THIS CHANGE CLINICAL PHARMACOLOGY OR TRANSLATIONAL SCIENCE?

Our findings substantiate research that is performed on evaluating selective Na_v1.8 inhibitors as treatment for pain, and suggests that the cold pressor‐ and pressure pain models are suitable to evaluate selective Na_v1.8 inhibitors.     

Effect of growth hormone on hepatic cytochrome P450 activity in healthy elderly men

OBJECTIVE: Our objective was to study the effect of recombinant human growth hormone (rhGH) on hepatic cytochrome P450 (CYP) activity in 30 healthy elderly men. METHODS: The study was carried out as a randomized, double-blind, placebo-controlled parallel-group study. rhGH or placebo was administered for a period of 12 weeks. CYP activity was measured before, after 12 weeks of rhGH and placebo administration, and at 4 weeks after termination of rhGH and placebo administration with use of the biomarker reactions of CYP1A2 (caffeine), CYP2C19 (mephenytoin), CYP2D6 (sparteine), CYP3A4 (endogenous cortisol metabolism), and antipyrine clearance as common markers of CYP activity. RESULTS: The metabolic ratio of caffeine increased significantly in the group that received growth hormone compared with placebo (median difference, 4.55; 95% confidence interval (CI), 1.64 to 8.60; versus -0.90; 95% CI, -5.70 to 1.36), indicating an induction of CYP1A2. Moreover, the S/R ratio of mephenytoin showed a small but significant increase (median difference, 0.02; 95% CI, 0 to 0.31; versus 0; 95% CI, -0.01 to 0.06), indicating an inhibition of CYP2C19. There were no significant changes of the metabolic ratios of cortisol and sparteine or the antipyrine clearance compared with placebo. CONCLUSIONS: These results indicate that growth hormone induces CYP1A2 and, to a lesser extent, inhibits CYP2C19 in elderly men, but it exerts no effects on CYP2D6 and CYP3A4. Although the induction of CYP1A2 may be of some clinical relevance, the small inhibition of CYP2C19 is probably unimportant.     

法罗培南钠片剂在健康志愿者中药动学研究

目的研究健康志愿者单剂量口服法罗培南钠片剂的药动学特点。方法10名受试者在2个周期内分别空腹单剂量口服法罗培南钠片剂300mg、600mg，以高效液相色谱-紫外线（HPLC—UV）法测定其血液、尿液法罗培南浓度，并用Win-Nonlin专业版计算药动学参数。结果单次口服300mg、600mg法罗培南后的主要药动学参数AUC（0-x）分别为（7．612±3．296）和（15.539±7．395）mg·h／L，AUC（0-∞）分别为（7.737±3．328）和（15．716±7．368）mg·h／l，Cmax分别为（3．815±1．053）和（6.885±2．256）mg／L，Tmax分别为1．00和1．00h，t（1／2）分别为1．006和1．055h，CL／F分别为（46．980±22．247）和（46．996±22．475）L／h，V／F分别为（70．151±38.281）和（73．535±40.439）L。尿药浓度测定结果表明，法罗培南12h尿累积排出率分别为（5．96±3.15）和（4．35±1．48）％。结论法罗培南在300～600mg范围内Cmax和AUC随剂量呈比例增加，单剂量给药在健康人体耐受性良好。     

Cytochrome P450 induction by rifampicin in healthy subjects: determination using the Karolinska cocktail and the endogenous CYP3A4 marker 4beta-hydroxycholesterol

The Karolinska cocktail, comprising caffeine, losartan, omeprazole, and quinine, was given before and after administration of rifampicin (20, 100, or 500 mg daily) to measure induction of cytochrome P450 (P450) enzymes. Rifampicin was given for 14 days to eight healthy subjects (all of whom possessed at least one wild-type CYP2C9 and one wild-type CYP2C19 gene) in each dose group. 4beta-hydroxycholesterol was assessed as an endogenous marker of CYP3A4 induction. A fourfold induction of CYP3A4 was seen at the highest dose by both quinine:3'-hydroxyquinine and 4beta-hydroxycholesterol measurements (P < 0.001). CYP3A4 was also induced at the two lower doses of rifampicin when measured by these two markers (P < 0.01 or P < 0.001). CYP1A2, CYP2C9, and CYP2C19 were induced after 500 mg rifampicin daily (1.2-fold, P < 0.05; 1.4-fold, P < 0.05; and 4.2-fold, P < 0.01, respectively). In conclusion, we have shown that the Karolinska cocktail and 4beta-hydroxycholesterol can be used for an initial screening of the induction properties of a drug candidate.     

Safety,tolerability, and pharmacokinetics of single‐ and multiple‐dose administration of islatravir (MK‐8591) in adults without HIV

Islatravir (MK‐8591) is a nucleoside analogue in development for the treatment and prevention of HIV‐1. Two phase 1 trials were conducted during initial evaluation of islatravir: rising single doses (Study 1) and rising multiple doses (Study 2) of oral islatravir in male and female participants without HIV (aged 18–60 years). Safety, tolerability, and pharmacokinetics of islatravir (plasma) and islatravir‐triphosphate (peripheral blood mononuclear cells) were assessed. In Study 1, 24 participants, assigned to 1 of 3 panels, received alternating single doses of islatravir in a fasted state from 5 mg to 400 mg, or placebo, over 3 dosing periods; a 30 mg dose was additionally assessed following a high‐fat meal. In Study 2, 8 participants per dose received 3 once‐weekly doses of 10, 30, or 100 mg islatravir or placebo in a fasted state. For each panel in both trials, 6 participants received active drug and 2 received placebo. Islatravir was generally well‐tolerated, with no serious adverse events or discontinuations due to adverse events. Islatravir was rapidly absorbed (median time to maximum plasma concentration 0.5 hours); plasma half‐life was 49–61 h; intracellular islatravir‐triphosphate half‐life was 118–171 h. Plasma exposure increased in an approximately dose‐proportional manner; there was no meaningful food effect. There was a modest degree of intracellular islatravir‐triphosphate accumulation after multiple weekly dosing. After single oral doses of islatravir greater than or equal to 5 mg, intracellular islatravir‐triphosphate levels were comparable to levels associated with efficacy in preclinical studies. These results warrant continued clinical investigation of islatravir.

Study Highlights

• WHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC?

​Current HIV treatment and prevention strategies have limitations, and novel agents that offer improved safety and tolerability, a high barrier to HIV resistance, and more convenient dosing regimens are required.

• WHAT QUESTION DID THIS STUDY ADDRESS?

Two phase 1 studies in participants without HIV assessed safety and pharmacokinetics of rising single and multiple doses of oral islatravir, a nucleoside analogue, to support continued development for the treatment and prevention of HIV‐1 infection.

• WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE?

Islatravir was generally well‐tolerated at single doses up to 400 mg. Oral doses of islatravir greater than or equal to 10 mg resulted in intracellular peripheral blood mononuclear cell levels of the active form, islatravir‐triphosphate, comparable to those associated with antiviral efficacy in preclinical studies.

• HOW MIGHT THIS CHANGE CLINICAL PHARMACOLOGY OR TRANSLATIONAL SCIENCE?

These studies provide important safety and pharmacokinetic information about islatravir in adults without HIV, which will be used to support further clinical investigation of islatravir for the treatment and prevention of HIV‐1 infection.     

Organization of multiple cytochrome P450s with NADPH-cytochrome P450 reductase in membranes

Microsomal P450-mediated monooxygenase activity supported by NADPH requires an interaction between flavoprotein NADPH-cytochrome P450 reductase and cytochrome P450. These proteins have been identified as the simplest system (with the inclusion of a phospholipid (PL) component) that possesses monooxygenase function; however, little is known about the organization of these proteins in the microsomal membrane. Although reductase and P450 are known to form a 1:1 functional complex, there exists a 10- to 20-fold excess of P450 over the reductase. This raises several questions including "How are the enzymes of the P450 system organized in the microsomal membrane?" and "Can one P450 enzyme affect the functional characteristics of another P450?" This review summarizes evidence supporting the potential for enzymes involved in the P450 system to interact, focusing on the interactions between reductase and P450 and interactions between multiple P450 enzymes. Studies on the aggregation characteristics of P450 as well as on rotational diffusion are detailed, with a special emphasis on the potential for P450 enzymes to produce oligomeric complexes and to suggest the environment in which P450 exists in the endoplasmic reticulum. Finally, more recent studies describing the potential for multiple P450s to exist as complexes and their effect on P450 function are presented, including studies using reconstituted systems as well as systems where two P450s are coexpressed in the presence of reductase. An understanding of the interactions among reductase and multiple P450s is important for predicting conditions where the drug disposition may be altered by the direct effects of P450-P450 complex formation. Furthermore, the potential for one P450 enzyme to affect the behavior of another P450 may be extremely important for drug screening and development, requiring metabolic screening of a drug with reconstituted systems containing multiple P450s rather than simpler systems containing only a single form.     

Effect of cyclosporine on the pharmacokinetics of colchicine in healthy subjects

Objective: Colchicine and cyclosporine are often administered together, particularly in patients who have undergone solid-organ transplantation. However, the potential for drug-drug interactions between these agents resulting in colchicine toxicity is high. Methods: This study sought to determine the effect of cyclosporine (100-mg capsule) on the pharmacokinetics of the US Food and Drug Administration-approved formulation of colchicine (0.6-mg tablet) after single oral-dose administration in 24 healthy subjects under fasted conditions in a phase 1, single-sequence, 2-period drug-drug interaction trial. Results: Coadministration of cyclosporine increased colchicine maximum observed plasma concentration, area under the plasma concentration-time curve to the last measurable time point, and area under the plasma concentration-time curve to time infinity on average by 224%, 216%, and 215% (ie, almost doubled), respectively, and decreased colchicine oral clearance on average by 72% (from 48.24 to 13.42 L/h), indicating substantially higher colchicine exposures when combined with cyclosporine, compared with colchicine alone. Conclusion: The dose of colchicine should be reduced by ≥ 50% when colchicine and cyclosporine are administered concurrently for treatment and prophylaxis of gout flares or treatment of patients with familial Mediterranean fever. Health care professionals should be vigilant for potential adverse events during colchicine/cyclosporine coadministration, notably in patients who have undergone solid-organ transplantation.Trial registration: www.ClinicalTrials.gov identifier NCT00983931 (http://clinicaltrials.gov/ct2/show/NCT00983931).     

Effect of rifampin on the pharmacokinetics of rosiglitazone in healthy subjects

BACKGROUND AND OBJECTIVE: Rifampin (INN, rifampicin) causes several drug interactions with coadministered antidiabetic drugs. Rosiglitazone is a novel thiazolidinedione antidiabetic drug, but little is known about the drug interaction between rifampin and rosiglitazone. Our objective was to investigate the effect of rifampin on the pharmacokinetics of rosiglitazone in humans. METHOD: In an open-label, randomized, 2-way crossover study, 10 healthy Korean male subjects were treated once daily for 6 days with 600 mg rifampin or with placebo. On day 7, a single dose of 8 mg rosiglitazone was administered orally. Plasma rosiglitazone concentrations were measured. RESULTS: Rifampin significantly decreased the mean area under the plasma concentration-time curve for rosiglitazone by 65% (2947.9 ng. h/mL versus 991.5 ng. h/mL, P <.001) and the mean elimination half-life from 3.9 to 1.5 hours (P <.001). The peak plasma concentration of rosiglitazone was significantly decreased by rifampin (537.7 ng/mL versus 362.3 ng/mL, P <.01). The apparent oral clearance of rosiglitazone increased about 3-fold after rifampin treatment (2.8 L/h versus 8.5 L/h, P <.001). CONCLUSION: This study showed that rifampin affected the disposition of rosiglitazone in humans, probably by the induction of cytochrome P450 (CYP) 2C8 and, to a lesser extent, CYP2C9. Therefore caution should be exercised during the coadministration of rifampin and rosiglitazone.     

Evaluation of the relationship between polymorphisms in CYP2C19 and the single‐dose pharmacokinetics of omeprazole in healthy Chinese volunteers: A multicenter study

The aim of this study was to evaluate the relationship between polymorphisms in CYP2C19 and the single‐dose pharmacokinetics (PKs) of omeprazole in healthy Chinese volunteers. A 20 mg single dose of omeprazole (Losec) enteric‐coated capsules or tablets was orally administered to 656 healthy subjects from eight subcenters. The polymorphic alleles of CYP2C19*2, *3, and *17 were determined by Sanger sequencing and Agena mass array. Plasma concentrations of omeprazole were determined by high‐performance liquid‐chromatography tandem mass spectrometry. PK parameters of area under the concentration versus time curve (AUC)_0‐t, AUC from zero to infinity (AUC_0‐∞), maximum plasma concentration (C_max), and terminal half‐life (t_1/2) were significantly influenced by CYP2C19 phenotype (all p < 0.001) and diplotype (all p < 0.001), and the same results were obtained in the subgroup analysis of the effects of diet and dosage form. The polymorphisms of CYP2C19*2(rs4244285; all PK parameters p < 0.001) and *3(rs4986893; p _Cmax = 0.020, and the p values of other PK parameters were less than 0.001) were significantly associated with the PKs of omeprazole. For CYP2C19*17 (rs12248560), only t_1/2 showed a significant correlation (p = 0.032), whereas other PK parameters did not. The present study demonstrated that the Pks of omeprazole is greatly influenced by CYP2C19.     

Effects of genetic polymorphism of cytochrome P450 enzymes on the pharmacokinetics of benzodiazepines

Pharmacogenetic studies have shown that several cytochrome P450 (CYP) enzymes exhibit genetic polymorphisms. Several benzodiazepines (BZPs) are metabolized predominantly or partly by polymorphic CYP2C19 and CYP3A4/5. The pharmacokinetics of diazepam, etizolam, quazepam and desmethylclobazam have been shown to be affected by CYP2C19 polymorphism. The CYP3A5 polymorphism has been reported to affect the pharmacokinetics of alprazolam, but its effect on midazolam kinetics has been inconclusive. For etizolam and desmethylclobazam, some data suggest that CYP2C19 deficiency leads to side-effects or toxicity. For the remaining BZPs the clinical significance of the observed pharmacokinetic changes remains unclear. Further studies on the effects of genetic polymorphisms of CYP enzymes on the pharmacokinetics and pharmacodynamics of BZPs are necessary to guide treatment individualization and optimization.     

Effect of eslicarbazepine acetate on the pharmacokinetics of digoxin in healthy subjects

Eslicarbazepine acetate (ESL) is a new-generation voltage-gated sodium channel blocker, which has been demonstrated to be effective and well tolerated in the treatment of epilepsy. The primary objective of this study was to investigate the effect of ESL on the pharmacokinetics of digoxin. This study was a randomized, double-blind, placebo-controlled, two-way crossover study of 12 healthy subjects (six men and six women). The study included two 8-day treatment periods with a washout of ≥10 days. In each period, subjects received either ESL 1200 mg once-daily or placebo, concomitantly with a loading oral dose of digoxin 0.5 mg on days 1 and 2, followed by a once-daily maintenance dose of 0.25 mg on days 3–8. Maximum serum digoxin plasma concentrations ( C _max) were reached ( t _max) at 0.5–2.0 h post-dose (median = 1.0 h) and at 0.5–4.0 h post-dose (median = 1.0 h) with Reference (digoxin plus placebo) and Test (digoxin plus ESL) treatments, respectively. The Test/Reference digoxin geometric mean ratios and 90% confidence intervals (90% CI) were 0.96 and 0.90–1.03 for the area under the plasma concentration–time curve over the dosing interval (AUC_0–24) and 0.85 and 0.68–1.07 for C _max. The 90% CI was within the bioequivalence range (0.80–1.25) for AUC_0–24, thus demonstrating bioequivalence. The 90% CI was outside the 0.80–1.25 range for digoxin C _max, but it appeared to be caused by a higher variability in digoxin C _max following co-administration of digoxin with placebo than with ESL. Co-administration of ESL and digoxin was well tolerated. Concomitant administration of ESL has no clinically relevant effect in the systemic exposure to digoxin.     

Effect of sinomenine on human cytochrome P450 activity

BACKGROUND: Cytochrome P450s superfamily expressed widely in organisms are known to play an important role in the biotransformation of many endogenous and exogenous substances. Inhibition or induction of cytochrome P450 isozymes is one of the major causes for clinical drug-drug interactions. Sinomenine can be metabolized to at least 2 metabolites in human, rat in vivo and in human liver microsomes. The major metabolite was identified to be N-demethylsinomenine. However, which CYP450 isozymes mediated by sinomenine in vivo and in vitro is not known. METHOD: In vitro study, 6 probe drugs were incubated with or without sinomenine respectively to study the effect of sinomenine on different cytochrome P450s activities in human microsomes. In vivo study, a 5-drug cocktail approach was used to study the inhibitive and inducing effect of sinomenine at normal clinical dose on cytochrome P450s activities. RESULTS: Sinomenine (50 micromol/l) had no significant effects on the activities of CYP1A2, CYP3A4, CYP2C9, CYP2E1, and CYP2D6, but it decreased the activity of CYP2C19 by 69% (p=0.012) in human microsomes. In vivo, sinomenine showed almost no significant effects on the activities of CYP1A2, CYP3A4, CYP2E1, and CYP2D6, but enhanced the elimination of mephenytoin by 73% (p=0.032). CONCLUSION: Sinomenine (50 micromol/l) inhibited the activity of CYP2C19 in human microsomes, but in vivo sinomenine at normal clinical dose enhanced the elimination of mephenytoin.