Common Herbal Dietary Supplement-Drug Interactions.

Nearly 25% of U.S. adults report concurrently taking a prescription medication with a dietary supplement. Some supplements, such as St. John's wort and goldenseal, are known to cause clinically important drug interactions and should be avoided by most patients receiving any pharmacologic therapy. However, many other supplements are predicted to cause interactions based only on in vitro studies that have not been confirmed or have been refuted in human clinical trials. Some supplements may cause interactions with a few medications but are likely to be safe with other medications (e.g., curcumin, echinacea, garlic, Asian ginseng, green tea extract, kava kava). Some supplements have a low likelihood of drug interactions and, with certain caveats, can safely be taken with most medications (e.g., black cohosh, cranberry, ginkgo, milk thistle, American ginseng, saw palmetto, valerian). Clinicians should consult reliable dietary supplement resources, or clinical pharmacists or pharmacologists, to help assess the safety of specific herbal supplement-drug combinations. Because most patients do not disclose supplement use to clinicians, the most important strategy for detecting herb-drug interactions is to develop a trusting relationship that encourages patients to discuss their dietary supplement use.

Role of UDP-Glucuronosyltransferase 1A1 in the Metabolism and Pharmacokinetics of Silymarin Flavonolignans in Patients with HCV and NAFLD.

Silymarin is the most commonly used herbal medicine by patients with chronic liver disease. Silymarin flavonolignans undergo rapid first-pass metabolism primarily by glucuronidation. The aims of this investigation were: (1) to determine the association of UGT1A1*28 polymorphism with the area under the plasma concentration-time curves (AUCs) for silybin A (SA) and silybin B (SB); (2) to evaluate the effect of UGT1A1*28 polymorphism on the profile of flavonolignan glucuronide conjugates found in the plasma; and (3) to investigate the role of UGT1A1 enzyme kinetics on the pharmacokinetics of SA and SB. AUCs and metabolic ratios for thirty-three patients with chronic liver disease administered oral doses of silymarin were compared between different UGT1A1*28 genotypes. The AUCs, metabolic ratios, and the profiles of major SA and SB glucuronides did not differ significantly among the three UGT1A1 genotypes. In contrast, an increase in the proportion of sulfated flavonolignan conjugates in plasma was observed in subjects with UGT1A1*28/*28 genotype compared to subjects carrying wild type alleles. Differences in SA and SB in vitro intrinsic clearance estimates for UGTIA1 correlated inversely with SA and SB exposures observed in vivo indicating a major role for UGT1A1 in silymarin metabolism. In addition, a significant difference in the metabolic ratio observed between patients with NAFLD and HCV suggests that any effect of UGT1A1 polymorphism may be obscured by a greater effect of liver disease on the pharmacokinetics of silymarin. Taken together, these results suggest the presence of the UGT1A1*28 allele does not contribute significantly to a large inter-subject variability in the pharmacokinetics of silybin A and silybin B which may obscure the ability to detect beneficial effects of silymarin in patients with liver disease.

Randomized Pharmacokinetic Crossover Study Comparing 2 Curcumin Preparations in Plasma and Rectal Tissue of Healthy Human Volunteers.

Curcumin is poorly absorbed, which is interest in new preparations. However, little is known about variations in its pharmacokinetics and tissue bioavailability between formulations. In this randomized, crossover study we evaluated the relationship between steady-state plasma and rectal tissue curcuminoid concentrations using standard and phosphatidylcholine curcumin extracts. There was no difference in the geometric mean plasma AUCs when adjusted for the 10-fold difference in curcumin dose between the 2 formulations. Phosphatidylcholine curcumin extract yielded only 20% to 30% plasma demethoxycurcumin and bisdemethoxycurcumin conjugates compared to standard extract, yet yielded 20-fold greater hexahydrocurcumin. When adjusting for curcumin dose, tissue curcumin concentrations were 5-fold greater for the phosphatidylcholine extract. Improvements in curcuminoid absorption due to phosphatidylcholine are not uniform across the curcuminoids. Furthermore, curcuminoid exposures in the intestinal mucosa are most likely due to luminal exposure rather than to plasma disposition. Finally, once-daily dosing is sufficient to maintain detectable curcuminoids at steady state in both plasma and rectal tissues.

Medication use and medical comorbidity in patients with chronic hepatitis C from a US commercial claims database: high utilization of drugs with interaction potential.

BACKGROUND: With the advent of the direct-acting antiviral agents, significant drug-drug interaction (DDI) potential now exists for patients treated for chronic hepatitis C virus (HCV) infection. However, little is known about how often patients with HCV infection use medications that may interact with newer HCV treatments, especially those with cytochrome P450 3A (CYP3A) DDI potential. METHODS: Using a large US commercial insurance database, medication use and comorbidity burden were examined among adult patients with a chronic HCV diagnosis from 2006 to 2010. Medications were examined in terms of total number of prescription claims, proportion of patients exposed, and DDI potential with the prototypical CYP3A direct-acting antiviral agents boceprevir and telaprevir, for which data were available. RESULTS: Patient comorbidity burden was high and increased over the study period. Medication use was investigated in 53 461 patients with chronic HCV. Twenty-one (53%) of the top 40 most utilized medications were classified as having interaction potential, with 62% of patients receiving at least one of the top 22 interacting medications by exposure. Of these, 59 and 41% were listed in a common DDI resource but not in medication-prescribing information, 77 and 77% had not been investigated in DDI studies, 41 and 36% did not have clear recommendations for DDI management, and only 14 and 23% carried a recommendation to avoid coadministration for boceprevir and telaprevir, respectively. CONCLUSION: Practitioners may expect a medication with CYP3A DDI potential in two-thirds of patients with HCV and may expect almost one-half of the most frequently used medications to have CYP3A DDI potential. However, DDI potential may not be reflected in prescribing information.

Interaction of silymarin flavonolignans with organic anion-transporting polypeptides.

Organic anion-transporting polypeptides (OATPs) are multispecific transporters mediating the uptake of endogenous compounds and xenobiotics in tissues that are important for drug absorption and elimination, including the intestine and liver. Silymarin is a popular herbal supplement often used by patients with chronic liver disease; higher oral doses than those customarily used (140 mg three times/day) are being evaluated clinically. The present study examined the effect of silymarin flavonolignans on OATP1B1-, OATP1B3-, and OATP2B1-mediated transport in cell lines stably expressing these transporters and in human hepatocytes. In overexpressing cell lines, OATP1B1- and OATP1B3-mediated estradiol-17ß-glucuronide uptake and OATP2B1-mediated estrone-3-sulfate uptake were inhibited by most of the silymarin flavonolignans investigated. OATP1B1-, OATP1B3-, and OATP2B1-mediated substrate transport was inhibited efficiently by silymarin (IC50 values of 1.3, 2.2 and 0.3 µM, respectively), silybin A (IC50 values of 9.7, 2.7 and 4.5 µM, respectively), silybin B (IC50 values of 8.5, 5.0 and 0.8 µM, respectively), and silychristin (IC50 values of 9.0, 36.4, and 3.6 µM, respectively). Furthermore, silymarin, silybin A, and silybin B (100 µM) significantly inhibited OATP-mediated estradiol-17ß-glucuronide and rosuvastatin uptake into human hepatocytes. Calculation of the maximal unbound portal vein concentrations/IC50 values indicated a low risk for silymarin-drug interactions in hepatic uptake with a customary silymarin dose. The extent of silymarin-drug interactions depends on OATP isoform specificity and concentrations of flavonolignans at the site of drug transport. Higher than customary doses of silymarin, or formulations with improved bioavailability, may increase the risk of flavonolignan interactions with OATP substrates in patients.

The influence of sex, ethnicity, and CYP2B6 genotype on bupropion metabolism as an index of hepatic CYP2B6 activity in humans.

The effects of sex, ethnicity, and genetic polymorphism on hepatic CYP2B6 (cytochrome P450 2B6) expression and activity were previously demonstrated in vitro. Race/ethnic differences in CYP2B6 genotype and phenotype were observed only in women. To identify important covariates associated with interindividual variation in CYP2B6 activity in vivo, we evaluated these effects in healthy volunteers using bupropion (Wellbutrin SR GlaxoSmithKline, Research Triangle Park, NC) as a CYP2B6 probe substrate. A fixed 150-mg oral sustained-release dose of bupropion was administered to 100 healthy volunteers comprising four sex/ethnicity cohorts (n = 25 each): Caucasian men and Caucasian, African American, and Hispanic women. Blood samples were obtained at 0 and 6 hours postdose for the measurement of serum bupropion (BU) and hydroxybupropion (HB) concentrations. Whole blood was obtained at baseline for CYP2B6 genotyping. To characterize the relationship between CYP2B6 activity and ethnicity, sex, and genotype when accounting for serum BU concentrations (dose-adjusted log(10)-transformed), analysis of covariance model was fitted in which the dependent variable was CYP2B6 activity represented as the log(10)-transformed, metabolic ratio of HB to BU concentrations. Several CYP2B6 polymorphisms were associated with CYP2B6 activity. Evidence of dependence of CYP2B6 activity on ethnicity or genotype-by-ethnicity interactions was not detected in women. These results suggest that CYP2B6 genotype is the most important patient variable for predicting the level of CYP2B6 activity in women, when measured by the metabolism of bupropion. The bupropion metabolic ratio appears to detect known differences in CYP2B6 activity associated with genetic polymorphism, across different ethnic groups. Prospective studies will be needed to validate the use of bupropion as a probe substrate for clinical use.

Limited sampling estimates of epigallocatechin gallate exposures in cirrhotic and noncirrhotic patients with hepatitis C after single oral doses of green tea extract.

BACKGROUND: Epigallocatechin-3-gallate (EGCG) has antiangiogenic, antioxidant, and antifibrotic properties that may have therapeutic potential for the treatment of cirrhosis induced by hepatitis C virus (HCV). However, cirrhosis might affect EGCG disposition and augment its reported dose-dependent hepatotoxic potential. OBJECTIVE: The safety, tolerability, and disposition of a single oral dose of EGCG in cirrhotic patients with HCV were examined in an exploratory fashion. METHODS: Eleven patients with hepatitis C and detectable viremia were enrolled. Four had Child-Pugh (CP) class A cirrhosis, 4 had Child-Pugh class B cirrhosis, and 3 were noncirrhotic. After a single oral dose of green tea extract 400 mg containing 94% pure EGCG, blood for EGCG levels and safety parameters was ascertained at 2, 4, and 10 hours. RESULTS: C(max) and AUC to EGCG overlapped among the 3 groups, which suggests that the disposition of EGCG was not significantly altered in these patients with cirrhosis. CONCLUSIONS: A single 400-mg oral dose of EGCG was safe and well tolerated by all of the patients in the study. These results provide guidance for the continued investigation of the long-term safety and antitumor potential of EGCG in cirrhotic patients with HCV.

Effect of silymarin (milk thistle) on liver disease in patients with chronic hepatitis C unsuccessfully treated with interferon therapy: a randomized controlled trial.

CONTEXT: The botanical product silymarin, an extract of milk thistle, is commonly used by patients to treat chronic liver disease, despite scant and conflicting evidence of its efficacy. OBJECTIVE: To determine the effect of silymarin on liver disease activity in patients with chronic hepatitis C virus (HCV) infection unsuccessfully treated with interferon-based therapy. DESIGN, SETTING, AND PARTICIPANTS: Multicenter, double-blind, placebo-controlled trial conducted at 4 medical centers in the United States. Participants included 154 persons with chronic HCV infection and serum alanine aminotransferase (ALT) levels of 65 U/L or greater who were previously unsuccessfully treated with interferon-based therapy. Enrollment began in May 2008 and was completed in May 2010, with the last follow-up visit completed in March 2011. INTERVENTION: Participants were randomly assigned to receive 420-mg silymarin, 700-mg silymarin, or matching placebo administered 3 times per day for 24 weeks. MAIN OUTCOME MEASURES: The primary outcome measure was serum ALT level of 45 U/L or less (considered within the normal range) or less than 65 U/L, provided this was at least a 50% decline from baseline values. Secondary outcomes included changes in ALT levels, HCV RNA levels, and quality-of-life measures. RESULTS: After 24 weeks of treatment, only 2 participants in each treatment group (P ≥ .99) met the primary outcome measure (3.8% [95% CI, 0.5% to 13.2%] for placebo, 4.0% [95% CI, 0.5% to 13.7%] for 420-mg silymarin, and 3.8% [95% CI, 0.5% to 13.2%] for 700-mg silymarin). The mean decline in serum ALT activity at the end of treatment did not differ significantly (P = .75) across the 3 treatment groups (mean decline, -4.3 [95% CI, -17.3 to 8.7] U/L for placebo, -14.4 [95% CI, -41.6 to 12.7] U/L for 420-mg silymarin, -11.3 [95% CI, -27.9 to 5.4] U/L for 700-mg silymarin); there likewise were no significant differences in HCV RNA levels (mean change, 0.07 [95% CI, -0.05 to 0.18] log10 IU/mL for placebo, -0.03 [95% CI, -0.18 to 0.12] log10 IU/mL for 420-mg silymarin, 0.04 [95% CI, -0.08 to 0.16] log10 IU/mL for 700-mg silymarin; P = .54) or quality-of-life measures. The adverse event profile of silymarin was comparable with that of placebo. CONCLUSION: Higher than customary doses of silymarin did not significantly reduce serum ALT levels more than placebo in participants with chronic HCV infection unsuccessfully treated with interferon-based therapy. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00680342.

Rationale, challenges, and participants in a Phase II trial of a botanical product for chronic hepatitis C.

BACKGROUND: Chronic hepatitis C is associated with significant morbidity and mortality as a consequence of progression to cirrhosis, hepatocellular carcinoma, and liver failure. Current treatment for chronic hepatitis C with pegylated interferon (IFN) and ribavirin is associated with suboptimal responses and numerous adverse effects. A number of botanical products have been used to treat hepatic disorders. Silymarin, extracted from the milk thistle plant, Silybum marianum (L) Gaertn. (Asteraceae), has been most widely used for various liver disorders, including chronic hepatitis C, B, and alcoholic liver disease. However, the safety and efficacy of silymarin have not been studied systematically in chronic hepatitis C. PURPOSE: We describe our strategy for a phased approach for studying the impact of silymarin in hepatitis C, in the context of the unique challenges of botanical product clinical trials and the development of specific and curative antiviral therapy. METHODS: This multicenter, randomized, double-masked, placebo-controlled trial was conducted with four clinical centers and a data-coordinating center in the United States, to assess the impact of silymarin therapy in patients with chronic hepatitis C who failed conventional antiviral therapy. RESULTS: Key aspects relevant to performing clinical trials of botanical products include early identification of an appropriate product with standard product chemistry, acquisition of pharmacokinetic and dosing information, selection of the appropriate study group, and choosing rigorous outcome variables. POTENTIAL LIMITATIONS: Trial participants were chronic hepatitis C patients who were nonsustained virologic responders to IFN-based therapy; therefore, the findings are not generalizable to all hepatitis C populations. Further, alanine aminotransferase, a biochemical liver test, rather than hepatitis viral RNA or liver histology was the primary end point. CONCLUSIONS: The challenges identified and addressed during development of this United States multicenter Phase II trial to evaluate silymarin for treatment of patients with chronic hepatitis C infection who had failed to respond successfully to previous IFN-based therapy are common and must be addressed to conduct rigorous trials of botanical products.

Differences in the disposition of silymarin between patients with nonalcoholic fatty liver disease and chronic hepatitis C.

Silymarin, derived from the milk thistle plant Silybum marianum and widely used for self-treatment of liver diseases, is composed of six major flavonolignans including silybin A and silybin B, which are the predominant flavonolignans quantified in human plasma. The single- and multiple-dose pharmacokinetics of silymarin flavonolignans were examined in patients with nonalcoholic fatty liver disease (NAFLD) or hepatitis C virus (HCV) to determine whether the disposition of silymarin and therefore its potential efficacy vary among liver disease populations. Cohorts of eight subjects with noncirrhotic liver disease were randomized 3:1 to oral silymarin or placebo (280 or 560 mg) every 8 h for 7 days. Forty-eight-hour blood sampling was conducted after the first and final doses. In general, plasma concentrations of silybin A and silybin B were higher, whereas concentrations of conjugates were lower in NAFLD compared with HCV. After adjustment of the area under plasma concentration-time curve from 0 to 8 h (AUC(0-8 h)) for weight and dose, only silybin B and silybin B conjugates differed significantly between disease types. For NAFLD, the adjusted mean AUC(0-8 h) was higher for silybin B (p < 0.05) but lower for silybin B conjugates (p < 0.05) compared with that for HCV. At the 280-mg dose, steady-state plasma concentrations of silybin B conjugates for NAFLD subjects were characterized by 46% lower AUC(0-8 h) (p < 0.05) and 42% lower C(max) (p < 0.05) compared with HCV subjects. Evidence of enterohepatic cycling of flavonolignans was only observed in NAFLD subjects. In summary, the efficacy of silymarin may be more readily observed in NAFLD patients because of their higher flavonolignan plasma concentrations and more extensive enterohepatic cycling compared with those in HCV patients.

Silymarin ascending multiple oral dosing phase I study in noncirrhotic patients with chronic hepatitis C.

Silymarin, derived from the milk thistle plant Silybum marianum, is widely used for self-treatment of liver diseases, including hepatitis C virus (HCV), and its antiviral activity has been demonstrated in vitro and in HCV patients administered an intravenous formulation of the major silymarin flavonolignans, silybin A and silybin B. The safety and dose-exposure relationships of higher than customary oral doses of silymarin and its acute effects on serum HCV RNA were evaluated in noncirrhotic HCV patients. Four cohorts of 8 patients with well-compensated, chronic noncirrhotic HCV who failed interferon-based therapy were randomized 3:1 to silymarin or placebo. Oral doses of 140, 280, 560, or 700 mg silymarin were administered every 8 hours for 7 days. Steady-state exposures for silybin A and silybin B increased 11-fold and 38-fold, respectively, with a 5-fold increase in dose, suggesting nonlinear pharmacokinetics. No drug-related adverse events were reported, and no clinically meaningful reductions from baseline serum transaminases or HCV RNA titer were observed. Oral doses of silymarin up to 2.1 g per day were safe and well tolerated. The nonlinear pharmacokinetics of silybin A and silybin B suggests low bioavailability associated with customary doses of silymarin may be overcome with doses above 700 mg.

Hepatic metabolism and biliary excretion of silymarin flavonolignans in isolated perfused rat livers: role of multidrug resistance-associated protein 2 (Abcc2).

Silymarin, an extract from seeds of Silybum marianum, is used by 8 to 33% of patients to self-treat chronic viral hepatitis C in the United States. Studies in humans and rodents suggest that biliary excretion of glucuronide and sulfate conjugates is the major route for silymarin's elimination. To determine the role of multidrug resistance-associated protein 2 (Mrp2) (Abcc2) in the biliary excretion of silymarin, the hepatobiliary disposition of the six major silymarin flavonolignans was studied using isolated perfused livers (IPRLs) from wild-type (WT) and Mrp2-deficient (TR(-)) Wistar rats. For all the flavonolignans, approximately 96% of the dose was cleared from perfusate within 30 min in both WT and TR(-) livers, and <5% of parent was recovered in bile or perfusate by the end of the perfusion. In WT livers, the percentage of dose excreted as conjugates into bile varied for each flavonolignan (silychristin, 51.6 +/- 9.3%; silydianin, 101.5 +/- 28.3%; silybin A, 21.0 +/- 8.3%; silybin B, 31.7 +/- 13.2%; isosilybin A, 50.5 +/- 23.6%; isosilybin B, 42.8 +/- 19.3%). Among the flavonolignans, only silydianin was primarily glucuronidated and almost completely recovered in bile. In TR(-) livers, biliary excretion of flavonolignan conjugates was reduced 80 to 92%, with 30 to 83% of each flavonolignan conjugate recovered in perfusate compared with only 5 to 30% at 90 min. Biliary excretion of glucuronide and sulfate conjugates of all the flavonolignans were reduced by 94 to 98% and 73 to 84%, respectively, in TR(-) IPRLs. These data indicate a primary role for Mrp2 in the biliary elimination of silymarin flavonolignan conjugates.

The pharmacokinetics of silymarin is altered in patients with hepatitis C virus and nonalcoholic Fatty liver disease and correlates with plasma caspase-3/7 activity.

Silymarin, used by 30 to 40% of liver disease patients, is composed of six major flavonolignans, each of which may contribute to silymarin's hepatoprotective properties. Previous studies have only described the pharmacokinetics for two flavonolignans, silybin A and silybin B, in healthy volunteers. The aim of this study was to determine the pharmacokinetics of the major silymarin flavonolignans in liver disease patients. Healthy volunteers and three patient cohorts were administered a single, 600-mg p.o. dose of milk thistle extract, and 14 blood samples were obtained over 24 h. Silybin A and B accounted for 43% of the exposure to the sum of total silymarin flavonolignans in healthy volunteers and only 31 to 38% in liver disease cohorts as a result of accumulation of silychristin (20-36%). Area under the curve (AUC(0-24h)) for the sum of total silymarin flavonolignans was 2.4-, 3.3-, and 4.7-fold higher for hepatitis C virus (HCV) noncirrhosis, nonalcoholic fatty liver disease (p

The influence of CYP3A5 genotype on dexamethasone induction of CYP3A activity in African Americans.

The CYP3A5(*)1 allele has been associated with differences in the metabolism of some CYP3A substrates. CYP3A5 polymorphism may also influence susceptibility for certain drug interactions. We have previously noted a correlation between basal CYP3A activity and the inductive effects of dexamethasone using the erythromycin breath test (ERBT). To determine whether CYP3A5 polymorphism influences induction of CYP3A activity, we examined the effect of an antiemetic regimen of dexamethasone, and the prototypical inducer rifampin, on the ERBT in African American volunteers prospectively stratified by CYP3A5(*)1 allele carrier status. Mean basal ERBTs were significantly higher in CYP3A5(*)1 carriers (2.71 +/- 0.53%) versus noncarriers (2.12 +/- 0.37%, P = 0.006). Rifampin increased ERBTs in CYP3A5(*)1 carriers (4.68 versus 2.60%, P = 0.0008) and noncarriers (3.55 versus 2.11%, P = 0.0017), whereas dexamethasone increased ERBTs only in CYP3A5(*)1 noncarriers (3.03 versus 2.14%, P = 0.031). CYP3A5 polymorphism appears to influence susceptibility to induction-type drug interactions for some inducers, and CYP3A5(*)1 noncarriers may be more susceptible to the inductive effects of dexamethasone as a result of lower basal CYP3A activity.

Pharmacokinetics and metabolic profile of free, conjugated, and total silymarin flavonolignans in human plasma after oral administration of milk thistle extract.

Silymarin, a mixture of polyphenolic flavonoids extracted from milk thistle (Silybum marianum), is composed mainly of silychristin, silydianin, silybin A, silybin B (SB(B)), isosilybin A (ISB(A)), and isosilybin B. In this study, the plasma concentrations of free (unconjugated), conjugated (sulfated and glucuronidated), and total (free and conjugated) silymarin flavonolignans were measured using liquid chromatography-electrospray ionization-mass spectrometry, after a single oral dose of 600 mg of standardized milk thistle extracts to three healthy volunteers. Pharmacokinetic analysis indicated that silymarin flavonolignans were rapidly eliminated with short half-lives (1-3 and 3-8 h for free and conjugated, respectively). The AUC(0-->infinity) values of the conjugated silymarin flavonolignans were 4- to 30-fold higher than those of their free fractions, with SB(B) (mean AUC(0-->infinity) = 51 and 597 microg x h/l for free and conjugated, respectively) and ISB(A) (mean AUC(0-->infinity) = 30 and 734 microg x h/l for free and conjugated, respectively) exhibiting higher AUC(0-->infinity) values in comparison with other flavonolignans. Near the plasma peak times (1-3 h), the free, sulfated, and glucuronidated flavonolignans represented approximately 17, 28, and 55% of the total silymarin, respectively. In addition, the individual silymarin flavonolignans exhibited quite different plasma profiles for both the free and conjugated fractions. These data suggest that, after oral administration, silymarin flavonolignans are quickly metabolized to their conjugates, primarily forming glucuronides, and the conjugates are primary components present in human plasma.

The influence of CYP3A5 expression on the extent of hepatic CYP3A inhibition is substrate-dependent: an in vitro-in vivo evaluation.

Despite several studies suggesting that CYP3A5 expression can influence the extent of hepatic CYP3A-mediated inhibition, a systematic in vitro-in vivo evaluation of this potential clinically important issue has not been reported. Using representative probes from two distinct CYP3A substrate subgroups (midazolam, erythromycin), the inhibitory potency of fluconazole was evaluated in pooled human liver microsomes (HLM) with a low or high specific CYP3A5 content, in recombinant CYP3A enzymes (rCYP3A), and in healthy volunteers lacking or carrying the CYP3A5(*)1 allele. Fluconazole was a slightly more potent inhibitor of CYP3A activity in CYP3A5-HLM than in CYP3A5+ HLM with midazolam (K(i) of 15 and 25 microM, respectively) but not with erythromycin (IC(50) of 70 and 54 microM, respectively). In comparison, fluconazole was a much more potent inhibitor of rCYP3A4 than rCYP3A5 with both midazolam (K(i) of 7.7 and 54 microM, respectively) and erythromycin (IC(50) of 100 and 350 microM, respectively). As predicted from HLM, with i.v. midazolam, the average (+/- S.D.) in vivo K(i) (K(i,iv)) was significantly higher in CYP3A5(*)1 carriers (24 +/- 17 and 17 +/- 8 microM for homozygous and heterozygous groups, respectively) than in noncarriers (13 +/- 6 microM) (p = 0.02). With the erythromycin breath test, the average K(i,iv) was not different between homozygous CYP3A5(*)1 carriers (30 +/- 12 microM) and noncarriers (58 +/- 53 microM). In conclusion, the effect of CYP3A5 on hepatic CYP3A-mediated inhibitory drug-drug interactions is substrate-dependent, and HLM, rather than rCYP3A, are the preferred in vitro system for predicting these interactions in vivo.

Warfarin dosing and the promise of pharmacogenomics.

Due to its narrow therapeutic index and substantial inter-patient variability in clinical response, warfarin represents an ideal drug candidate to benefit from the promise of pharmacogenomic-guided dosing strategies. Consistent with in vitro data, clinical studies have demonstrated that CYP2C9 polymorphisms significantly influence warfarin pharmacokinetics by reducing (S)-warfarin metabolic clearance, consequently lowering maintenance dose requirements and increasing the risk over-anticoagulation during the initiation phase of therapy. Recent data suggest that polymorphisms in genes encoding several pharmacodynamic determinants of the coagulation cascade may also influence warfarin's antithrombotic dose-response. Of these, VKORC1 polymorphisms account for a significant proportion of the inter-individual variability in warfarin dose requirements in all populations evaluated. Collectively, these data suggest that assessment of genetic polymorphisms affecting both warfarin pharmacokinetics and pharmacodynamics could help to predict warfarin dose requirements in patients. Therefore, the promise of pharmacogenomic-guided dosing as a useful strategy to improve clinical outcomes with warfarin therapy appears credible and warrants further investigation.

Antimycotic drug discovery in the age of genomics.

Genomic-based methodologies are increasingly used at all stages of drug development. The most extensive applications have occurred in early drug discovery stages due to advances in technologies that allow for automated synthesis and characterization of organic compounds, and for high-throughput screening of these molecules against known drug targets. The adaptation of genomic-based methodologies in later stages of drug development presents a more difficult task. In this review we describe how genomics can be used to identify previously uncharacterized pharmacologic actions that provide a basis for the development of new classes of antimycotic agents or for adverse event aversion. Clinically, novel antimycotics are gravely needed. This review provides a perspective on new technologies that will bridge the gap between drug discovery and development that may enable more rapid access to new antimycotic agents.

Kupffer cell-mediated IL-2 suppression of CYP3A activity in human hepatocytes.

Interleukin (IL)-2 administration has been shown to decrease CYP3A enzyme activity in vivo. To determine whether IL-2 suppression of human hepatocyte CYP3A activity is direct or whether it is facilitated by the presence of Kupffer cells, primary human hepatocytes were cultured alone or cocultured with primary human Kupffer cells at physiologic hepatocyte/Kupffer cell ratios of 10:1 or 10:4. Using proinflammatory cytokines as positive controls, IL-1 (0.2-20 ng/ml) and IL-6 (2-200 ng/ml) exposure resulted in a 70 to 90% decrease in CYP3A activity after 72 h in hepatocyte cultures. In the hepatocyte/Kupffer cell cocultures, an 80% decrease in CYP3A activity was observed with IL-1 (2 ng/ml) or IL-6 (20 ng/ml), suggesting that direct suppressive effects of proinflammatory cytokines on hepatocyte CYP3A activity are not substantially altered by Kupffer cells. In contrast to the effects of these proinflammatory cytokines, no sustained suppression of CYP3A activity was observed with IL-2 (2-200 ng/ml) in hepatocyte cultures. However, in hepatocyte/Kupffer cell cocultures, a concentration-dependent 50 to 70% suppression of CYP3A activity was observed with IL-2 at 72 h. In summary, these data suggest that Kupffer cells are required to reconstitute the suppressive effects of IL-2 on CYP3A activity that are observed in vivo and that hepatocyte/Kupffer cell cocultures may provide a useful model for investigating mechanisms of CYP3A4 regulation by cytokines. Of particular relevance to certain hepatic diseases, these findings suggest potential mechanisms whereby cytokines released from infiltrating blood mononuclear cells might modulate intercellular signaling and controls on hepatocyte function by various cell types that reside in liver.