Different effects of St John's wort on the pharmacokinetics of simvastatin and pravastatin

Use of statin therapy to reduce cardiovascular risk in older patients

Background. Cardiovascular disease is the principal cause of mortality in older individuals, and more than 80% of deaths due to coronary heart disease or stroke occur in patients over 65 years of age. Hyperlipidemia is one of the main modifiable risk factors for cardiovascular disease. Current guidelines recommend the use of statins to reduce low-density lipoprotein cholesterol to appropriate targets based on an individual's cardiovascular risk, and clearly state that older age should not be a barrier to treatment. Despite extensive evidence demonstrating clear benefit with statin therapy in older individuals, this population remains chronically undertreated. Scope. This paper provides an overview of the current evidence available regarding the efficacy and safety of statin therapy to reduce cardiovascular risk in older patients. We use hypothetical case studies to address some of the questions frequently posed by physicians responsible for the cardiovascular health of older patients. Conclusions. Various factors may account for the failure to provide appropriate treatment, including a lack of awareness of clinical benefits and perceived safety issues. However, if current guidelines are followed and older patients treated to appropriate LDL-C goals, the likelihood of cardiovascular events will be reduced in this high-risk population. Employing an evidence-based approach to the management of cardiovascular risk in older patients is likely to yield benefits in terms of overall cardiovascular burden.

Use of herbal products and potential interactions in patients with cardiovascular diseases

More than 15 million people in the U.S. consume herbal remedies or high-dose vitamins. The number of visits to providers of complementary and alternative medicine exceeds those to primary care physicians, for annual out-of-pocket costs of $30 billion. Use of herbal products forms the bulk of treatments, particularly by elderly people who also consume multiple prescription medications for comorbid conditions, which increases the risk of adverse herb-drug-disease interactions. Despite the paucity of scientific evidence supporting the safety or efficacy of herbal products, their widespread promotion in the popular media and the unsubstantiated health care claims about their efficacy drive consumer demand. In this review, we highlight commonly used herbs and their interactions with cardiovascular drugs. We also discuss health-related issues of herbal products and suggest ways to improve their safety to better protect the public from untoward effects.

Dietary regulation of P-gp function and expression

Food-drug interactions have been associated with clinically important pharmacokinetic and pharmacodynamic changes of a drug. The aim of this paper is to review the regulation of P-glycoprotein (P-gp) by dietary components and to correlate the changes in cellular P-gp function and expression with drug bioavailability. In summary, the published literature has provided extensive data supporting the modulation of drug bioavailability through P-gp regulation by components in food groups such as fruit juices, spices, herbs, cruciferous vegetables and green tea. Most of these data were, however, derived from in vitro cell models and, except for the St John's wort, the clinical significance of most reported interactions remains to be clarified. Studies on piperine and capsaicin have underscored an often poor correlation between in vivo and in vitro data, whereas experiments involving curcumin highlighted differences between acute and chronic consumption of a dietary component on P-gp function and expression in vivo. A better understanding of the pharmacokinetic and pharmacodynamic profiles of the dietary components will aid in addressing these knowledge gaps.

St John's wort greatly reduces the concentrations of oral oxycodone

BACKGROUND

Chronic pain is associated with depression. Self-treatment of depression with herbal over-the-counter medicine St John's wort makes pain patients prone to drug interactions.

AIMS

The aim of this study was to assess the potential of St John's wort to alter the CYP3A-mediated metabolism of a mu-opioid receptor agonist, oxycodone.

METHODS

The study design was placebo-controlled, randomized, cross-over with two phases at intervals of 4 weeks and was conducted with 12 healthy participants. St John's wort (Jarsin) or placebo was administered t.i.d. for 15 days and oral oxycodone hydrochloride 15 mg on day 14. Oxycodone pharmacokinetics and pharmacodynamics were compared after St John's wort or placebo. Behavioural and analgesic effects were assessed with subjective visual analogue scales and cold pressor test. Plasma drug concentrations were measured from 0 to 48 h, behavioural and analgesic effects from 0 to 12 h.

RESULTS

Following St John's wort administration the oxycodone AUC decreased 50% (p<0.001). Oxycodone elimination half-life shortened from a mean+/-SD 3.8+/-0.7 to 3.0+/-0.4h (p<0.001). The self-reported drug effect of oxycodone as measured by AUEC(0-12) decreased significantly (p=0.004). Differences between St John's wort and placebo phases in cold pain threshold and intensity AUEC(0-12) were not observed.

CONCLUSIONS

St John's wort greatly reduced the plasma concentrations of oral oxycodone. The self-reported drug effect of oxycodone decreased significantly. This interaction may potentially be of some clinical significance when treating patients with chronic pain.

Evidence-based guidelines for cardiovascular risk reduction: the safety and efficacy of high-dose statin therapy

Current clinical guidelines for management of low-density lipoprotein cholesterol (LDL-C) have evolved to reflect the findings of numerous randomized clinical trials and represent an important opportunity to effectively improve the cardiovascular (CV) risk profile of a wide range of patients. Implementation of guideline-recommended LDL-C management strategies facilitates the appropriate use of all available treatments, including lifestyle and dietary changes and pharmacotherapy. Where intensive lowering of LDL-C is required, suboptimal use of statins is a major contributor to the significant number of patients who remain at an unnecessarily increased risk of CV disease as a consequence of failing to reach their guideline-recommended LDL-C goals. This underuse may be explained by concerns over the safety and efficacy of high-dose statin regimens in certain populations. These issues are explored in the context of current, evidence-based clinical guidelines for LDL-C management and, through 3 hypothetical case studies, selection of appropriate starting doses of statins, and titration to a higher dose or switching to a more potent statin, to ensure that patients reach their individual LDL-C goals and reduce their overall CV risk, is also examined.

Herb-drug interactions with St John's wort (Hypericum perforatum): an update on clinical observations

St John's wort (SJW) extracts, prepared from the aerial parts of Hypericum perforatum, contain numerous pharmacologically active ingredients, including naphthodianthrones (e.g., hypericin and its derivatives), phloroglucinols derivatives (e.g., hyperforin, which inhibits the reuptake of a number of neurotransmitters, including serotonin), and flavonoids. Such extracts are widely used for the treatment of mild-to-moderate depression. As a monotherapy, SJW has an encouraging safety profile. However, relevant and, in some case, life-threatening interactions have been reported, particularly with drugs which are substrate of cytochrome P450 and/or P-glycoprotein. Well-documented SJW interactions include (1) reduced blood cyclosporin concentration, as suggested by multiple case reports as well as by clinical trials, (2) serotonin syndrome or lethargy when SJW was given with serotonin reuptake inhibitors, (3) unwanted pregnancies in women while using oral contraceptives and SJW, and (4) reduced plasma drug concentration of antiretroviral (e.g., indinavir, nevirapine) and anticancer (i.e., irinotecan, imatinib) drugs. Hyperforin, which is believed to contribute to the antidepressant action of St John's wort, is also strongly suspected to be responsible of most of the described interactions.

Medical residents' knowledge of dietary supplements

INTRODUCTION

The widespread use of complementary and alternative medicine modalities such as dietary supplements has prompted many medical schools to offer courses covering such topics. To date, little is known about the impact of these courses on medical graduates' knowledge. This study was designed to evaluate resident physicians' level of understanding of popular dietary supplement regulation and to determine whether an interactive online curriculum could aid in improving such knowledge.

METHODS

A multicenter online educational intervention was developed and administered to physicians at 15 internal medicine residency programs throughout the United States, between March 1, 2006 and June 30, 2006. Pretest performance was used to measure baseline knowledge of commonly used dietary supplements. Posttest performance compared with pretest performance measured the effectiveness of the educational intervention.

RESULTS

A total of 335 physicians completed the module. Baseline knowledge of dietary supplements was low (average pretest score 59.7%). More than one-third of respondents were unaware of the reasons for use of saw palmetto and black cohosh. Results for questions on safety and drug-supplement interactions were similarly low. Only 57% of physicians knew that kava kava has been associated with hepatitis. Only 15% were aware that St. John's Wort can lower cyclosporine levels. With regards to knowledge of efficacy, only 36% were aware that fish oil has been shown to lower triglyceride levels. After completion of the curriculum, scores improved significantly (P < 0.001) in all question/content areas.

CONCLUSIONS

Residents' knowledge of dietary supplements is poor. An online didactic module may improve knowledge and potentially enhance patient-physician communication regarding the use of such products.

Clinical assessment of CYP2D6-mediated herb-drug interactions in humans: effects of milk thistle, black cohosh, goldenseal, kava kava, St. John's wort, and Echinacea

Cytochrome P450 2D6 (CYP2D6), an important CYP isoform with regard to drug-drug interactions, accounts for the metabolism of approximately 30% of all medications. To date, few studies have assessed the effects of botanical supplementation on human CYP2D6 activity in vivo. Six botanical extracts were evaluated in three separate studies (two extracts per study), each incorporating 16 healthy volunteers (eight females). Subjects were randomized to receive a standardized botanical extract for 14 days on separate occasions. A 30-day washout period was interposed between each supplementation phase. In study 1, subjects received milk thistle (Silybum marianum) and black cohosh (Cimicifuga racemosa). In study 2, kava kava (Piper methysticum) and goldenseal (Hydrastis canadensis) extracts were administered, and in study 3 subjects received St. John's wort (Hypericum perforatum) and Echinacea (Echinacea purpurea). The CYP2D6 substrate, debrisoquine (5 mg), was administered before and at the end of supplementation. Pre- and post-supplementation phenotypic trait measurements were determined for CYP2D6 using 8-h debrisoquine urinary recovery ratios (DURR). Comparisons of pre- and post-supplementation DURR revealed significant inhibition (approximately 50%) of CYP2D6 activity for goldenseal, but not for the other extracts. Accordingly, adverse herb-drug interactions may result with concomitant ingestion of goldenseal supplements and drugs that are CYP2D6 substrates.

Effects of St John's wort and CYP2C9 genotype on the pharmacokinetics and pharmacodynamics of gliclazide

BACKGROUND AND PURPOSE

Patients commonly take complementary medicines in conjunction with conventional drugs without clear evidence of safety or the risk of herb-drug interactions. The aim of this study was to assess potential pharmacokinetic (PK) and pharmacodynamic (PD) interactions between St John's wort and gliclazide in healthy subjects with different cytochrome P450 2C9 (CYP2C9) genotypes.

EXPERIMENTAL APPROACH

A crossover controlled study was conducted in 21 healthy subjects. Each received gliclazide (80 mg) either alone or during 15 days treatment with St John's wort. The area under the plasma concentration-time curve (AUC(0-infinity)), apparent clearance (CL/F) and elimination half-life (t 1/2) of gliclazide and incremental changes in glucose and insulin AUC(0-4) were compared. CYP2C9*2 and CYP2C9*3 alleles were identified using PCR followed by restriction enzyme digestion analysis.

KEY RESULTS

St John's wort significantly altered gliclazide pharmacokinetics in all except for four healthy subjects. The mean ratio and 90% confidence interval (CI) of gliclazide AUC(0-infinity) and CL/F were 0.67 (0.55-0.81) and 1.50 (1.24-1.81), respectively, after St John's wort treatment. St John's wort decreased gliclazide t (1/2), with mean ratio and 90% CI of 0.85 (0.74-0.93). There were no significant changes in glucose or insulin AUC(0-4) after St John's wort treatment and no significant differences according to CYP2C9 genotype.

CONCLUSIONS AND IMPLICATIONS

Treatment with St John's wort significantly increases the apparent clearance of gliclazide which is independent of CYP2C9 genotype. People with diabetes receiving this combination should be closely monitored to evaluate possible signs of reduced efficacy.

The recovery time-course of CYP3A after induction by St John's wort administration

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

St John's wort causes the induction of CYP3A. Little is known about how long the effect remains after cessation of St John's wort.

WHAT THIS STUDY ADDS

The in vivo CYP3A activity returns progressively to the basal level approximately 1 week after cessation of St John's wort administration

AIMS

To examine the recovery time course of CYP3A after enzyme induction by St John's wort administration.

METHODS

The subjects were 12 healthy men, aged 20-33 years. On the first day, they received an oral dose of midazolam 5 mg without St John's wort (day -14). From the next day, they took St John's wort for 14 days. On the last day of St John's wort treatment (day 0) and 3 and 7 days after completion of St John's wort treatment (days 3 and 7), they received the same dose of midazolam. On each day, blood samples were obtained until 8 h after midazolam administration. Plasma concentrations of midazolam were measured by HPLC. Pharmacokinetic parameters of midazolam were determined using noncompartmental analysis.

RESULTS

Apparent oral clearance of midazolam was significantly increased after St John's wort administration from 65.3 +/- 8.4 l h(-1) (day -14) to 86.8 +/- 17.3 l h(-1) (day 0). It returned to the control level 7 days after the completion of St John's wort (day 7, 59.7 +/- 3.8 l h(-1)). No significant difference in the elimination half-life between the four periods of the study was observed. The changes in apparent oral clearance after St John's wort discontinuation indicated that CYP3A activity recovers from enzyme induction with an estimated half-life of 46.2 h.

CONCLUSIONS

CYP3A activity induced by St John's wort administration progressively returns to the basal level after approximately 1 week. This finding may provide useful information to avoid clinically significant interactions of St John's wort with CYP3A substrates.

Advising patients who use dietary supplements

Public use of dietary supplements is quite prevalent, with an estimated 1 of 5 patients using such substances in an effort to maintain or promote their health. Despite their popularity, patients and physicians are often unaware of the limited regulation of these products as well as their potential risks and benefits. Lack of physician knowledge in these areas has the potential to strain the doctor-patient relationship. In this review, we present a 6-step approach to advising patients who are considering use of dietary supplements. Our framework includes a discussion of regulatory issues, efficacy and safety, potential supplement-drug interactions, and monitoring for adverse events and therapeutic effects.

Effects of treatment with a commercially available St John's Wort product (Movina) on cholesterol levels in patients with hypercholesterolemia treated with simvastatin

OBJECTIVE

To assess the effect of treatment with a St John's Wort product (Movina) on cholesterol levels (total cholesterol, LDL-cholesterol, and HDL-cholesterol) in patients with hypercholesterolemia on treatment with a stable dose of simvastatin.

DESIGN

Controlled, randomized, open, crossover pharmacodynamic study.

SETTING

Two primary healthcare centres. Intervention. Patients were treated with Movina one tablet (containing 300 mg of Hypericum perforatum) twice daily and control (a commercially available multivitamin tablet, Vitamineral). The trial started with a run-in period of 4 weeks. Then the treatment order between control and active treatment was decided (randomization using sealed envelopes). The duration of each treatment period was 4 weeks and simvastatin treatment was kept unchanged during the whole study period (12 weeks).

SUBJECTS

Twenty-four patients with hypercholesterolemia treated with a stable dose of simvastatin (10-40 mg daily) for at least three months.

MAIN OUTCOME MEASURES

Assessments of total cholesterol, HDL- cholesterol, LDL-cholesterol, and triglycerides were performed in the morning with the patients in a fasting condition.

RESULTS

All patients completed the study. LDL-cholesterol was significantly increased during active treatment compared with control. Thus, the mean LDL-cholesterol after 4 weeks' active treatment was 2.72 mmol/L compared with 2.30 mmol/L after treatment with control (p <0.0001). An increase in total-cholesterol was also observed (5.08 mmol/L compared with 4.56 mmol/L, p <0.0001).

CONCLUSION

Products containing St John's Wort should not be given to patients with hypercholesterolemia who are on treatment with simvastatin.

Interaction between a commercially available St. John’s wort product (Movina) and atorvastatin in patients with hypercholesterolemia

OBJECTIVE

The aim of this study was to assess the effect of treatment with a St. John's wort product (Movina) on cholesterol [total cholesterol, low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol] and triglyceride levels in patients with hypercholesterolemia on treatment with a stable dose of atorvastatin in a controlled, randomised, open, crossover interaction study.

METHODS

Sixteen patients with hypercholesterolemia treated with a stable dose of atorvastatin (10-40 mg/daily) for at least 3 months were treated with Movina one tablet (containing 300 mg of hypericum perforatum) twice daily and control (a commercially available multivitamin tablet Vitamineral). After a run-in period of 4 weeks, patients were randomised to treatment with either Movina or control for 4 weeks in a crossover design. The atorvastatin dose was kept unchanged during the study period (12 weeks), and assessments of total cholesterol, HDL cholesterol, LDL cholesterol and triglycerides were performed in the morning with the patients in the fasting condition. The difference between control and active treatment in LDL cholesterol after 4 weeks of treatment was the primary endpoint.

RESULTS

All patients completed the study. The St. John's wort product significantly increased the serum level of LDL cholesterol compared with control (2.66 mmol/l compared with 2.34 mmol/l, p = 0.004). A significant increase in total cholesterol was also observed (5,10 mmol/l compared with 4.78 mmol/l, p = 0.02). No statistically significant change was observed in HDL cholesterol (1.59 mmol/l and 1.56 mmol/l, p = 0.49) or in triglycerides (1.87 mmol/l and 1.94 mmol/l, p = 0.60). No product-related side effects were reported

CONCLUSION

An interaction was observed between the studied St.-John's-wort-containing product and atorvastatin. Physicians and patients should be aware of this interaction and if treatment with a St. John's wort product is considered necessary, then there may be a need for increasing the dose of atorvastatin.

Drug-herb interaction: effect of St John's wort on bioavailability and metabolism of procainamide in mice

CONTEXT

St John's wort induces the activity of the cytochrome P450 enzyme system causing treatment failure because of increased metabolism of many drugs. Procainamide is metabolized by a different pathway to N-acetyl procainamide.

OBJECTIVE

To study St John's wort-procainamide interaction using a mouse (Swiss Webster) model.

DESIGN

One group of mice (group A, 4 mice in each group) was fed St John's wort each day for 2 weeks (last dose 1 day before administration of procainamide); another group (group B) received the same dose of St John's wort for 1 week. The third group (group C) received only a single dose 1 hour before administration of procainamide, and the control group (group D) received no St John's wort. All groups later received a single oral dose of procainamide. Blood was drawn 1, 4, and 24 hours after administration of procainamide and concentrations in serum of procainamide as well as N-acetyl procainamide were measured using immunoassays.

RESULTS

The procainamide concentrations 1 hour after administration was highest in group C (mean, 11.59 microg/mL) followed by group A (9.92 microg/mL), whereas group B (7.44 microg/mL) and control group D (7.36 microg/mL) showed comparable values. The concentration in group C was significantly greater than the control group D (P = .03, 2-tailed independent t test). N-Acetyl procainamide concentrations and estimated half-life of procainamide among groups were comparable. In a separate experiment when mice were fed purified hypericin, the active component of St John's wort, a significant increase in bioavailability (53%) of procainamide was observed compared with the control group.

CONCLUSIONS

St John's wort has an acute effect to increase bioavailability of procainamide but has no effect on its metabolism.

St. John's wort does not interfere with therapeutic drug monitoring of 12 commonly monitored drugs using immunoassays

St. John's wort, a popular herbal remedy for depression, is known to interact with many Western drugs because of the ability of its components to induce liver enzymes. Lower concentrations of various drugs due to increased clearance have been reported. Because immunoassays are commonly used in clinical laboratories for therapeutic drug monitoring, we studied the potential interference of St. John's wort with commonly monitored therapeutic drugs. Drug-free serum pools were supplemented with St. John's wort to achieve in vitro St. John's wort concentrations mimicking in vivo concentrations after both recommended use and overdose. Concentrations of digoxin, tricyclic antidepressants (TCAs), phenytoin, carbamazepine, theophylline, valproic acid, quinidine, phenobarbital, procainamide, and N-acetyl procainamide were measured in serum. Pooled serum specimens from patients who were taking a particular drug were also supplemented in vitro with concentrations of St. John's wort to investigate whether observed concentrations changed after supplementation with St. John's wort. The effect of St. John's wort on cyclosporine and tacrolimus (FK 506) was studied in whole blood. We found no significant interference from St. John's wort with any assay studied. Moreover, when drug-free serum was supplemented with very high concentrations of hypericin (2 microg/mL) and hyperforin (2 microg/mL) pure standard, we observed no apparent drug level with any immunoassay. The presence of both hypericin and hyperforin was also confirmed by thin layer chromatography (TLC) in both preparations of St. John's wort. We conclude that immunoassays may be used to measure levels of therapeutic drugs in patients who self-medicate with St. John's wort.

Role of P-glycoprotein in statin drug interactions

Understanding the mechanisms of drug interactions with 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) has become increasingly important because of the potential for serious adverse effects, most notably myopathy. Most of the evidence supports the role of cytochrome P450 (CYP) isoenzymes in many of these drug interactions. However, P-glycoprotein (P-gp), an efflux protein located in the gastrointestinal tract, placenta, kidneys, brain, and liver, may also play a role. Results of several studies with in vitro models have shown that lovastatin, simvastatin, and atorvastatin are inhibitors for P-gp and may be substrates for this transporter as well. Pravastatin and fluvastatin consistently demonstrate no significant inhibition of P-gp. Drug interaction studies involving statins and digoxin support a role for P-gp. Many additional drugs such as diltiazem, verapamil, itraconazole, ketoconazole, and cyclosporine, as well as dietary supplements such as St. John's wort and grapefruit juice, interact with statins and are modulators of both CYP3A4 and P-gp. However, the role of P-gp in these specific drug interactions remains unclear.

Pharmacology and toxicology of Bupleurum root-containing Kampo medicines in clinical use

Kampo (Japanese traditional herbal) medicines have been produced by combining multiple crude drugs, almost all of plant origin but with some of animal or mineral origin, and contain a great many substances. Their effect is a combination of the various interactions of the constituent substances, whether they are enhancing, synergistic or suppressive. Kampo medicine has an overall effect that is different from the combined effects of individual crude drugs, and several side effects such as anorexia, slight fever and nausea have been reported in the treatment of certain disorders and disease states with Kampo medicines. Among 210 medical formulations used in Japan, some relevant information on the clinical uses, pharmacology and toxicology of six manufactured Kampo medical formulations, Shosaikoto, Daisaikoto, Saikokeishito, Hochuekkito, Saibokuto and Saireito, containing Bupleurum root are reviewed. Studies of some potential interactions between Kampo medicine and western drugs are also considered.

The effect of St John's wort extracts on CYP3A: a systematic review of prospective clinical trials

AIM

The aim of this systematic review was to assess the quality and outcomes of clinical trials investigating the effect of St John's wort extracts on the metabolism of drugs by CYP3A.

METHODS

Prospective clinical trials assessing the effect of St John's wort (SJW) extracts on metabolism by CYP3A were identified through computer-based searches (from their inception to May 2005) of Medline, Cinahl, PsycINFO, AMED, Current Contents and Embase, hand-searches of bibliographies of relevant papers and consultation with manufacturers and researchers in the field. Two reviewers selected trials for inclusion, independently extracted data and recorded details on study design.

RESULTS

Thirty-one studies met the eligibility criteria. More than two-thirds of the studies employed a before-and-after design, less than one-third of the studies used a crossover design, and only three studies were double-blind and placebo controlled. In 12 studies the SJW extract had been assayed, and 14 studies stated the specific SJW extract used. Results from 26 studies, including all of the 19 studies that used high-dose hyperforin extracts (>10 mg day(-1)), had outcomes consistent with CYP3A induction. The three studies using low-dose hyperforin extracts (<4 mg day(-1)) demonstrated no significant effect on CYP3A.

CONCLUSION

There is reasonable evidence to suggest that high-dose hyperforin SJW extracts induce CYP3A. More studies are required to determine whether decreased CYP3A induction occurs after low-dose hyperforin extracts. Future studies should adopt study designs with a control phase or control group, identify the specific SJW extract employed and provide quantitative analyses of key constituents.

Pharmacokinetic and pharmacodynamic alterations of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors: drug-drug interactions and interindividual differences in transporter and metabolic enzyme functions

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) are widely used for the treatment of hypercholesterolemia. Their efficacy in preventing cardiovascular events has been shown by a large number of clinical trials. However, myotoxic side effects, sometimes severe, including myopathy or rhabdomyolysis, are associated with the use of statins. In some cases, such toxicity is associated with pharmacokinetic alterations. In this review, the pharmacokinetic aspects and physicochemical properties of statins are reviewed in order to understand the mechanism governing their pharmacokinetic alterations. Among the statins, simvastatin, lovastatin and atorvastatin are metabolized by cytochrome P450 3A4 (CYP3A4) while fluvastatin is metabolized by CYP2C9. Cerivastatin is subjected to 2 metabolic pathways mediated by CYP2C8 and 3A4. Pravastatin, rosuvastatin and pitavastatin undergo little metabolism. Their plasma clearances are governed by the transporters involved in the hepatic uptake and biliary excretion. Also for other statins, which are orally administered as open acid forms (i.e. fluvastatin, cerivastatin and atorvastatin), hepatic uptake transporter(s) play important roles in their clearances. Based on such information, pharmacokinetic alterations of statins can be predicted following coadministration of other drugs or in patients with lowered activities in drug metabolism and/or transport. We also present a quantitative analysis of the effect of some factors on the pharmacokinetics of statins based on a physiologically based pharmacokinetic model. To avoid a pharmacokinetic alteration, we need to have information about the metabolizing enzyme(s) and transporter(s) involved in the pharmacokinetics of statins and, along with such information, model-based prediction is also useful.

Herbal remedies: effects on clinical laboratory tests

CONTEXT

Complementary and alternative medicine (herbal medicines) can affect laboratory test results by several mechanisms.

OBJECTIVE

In this review, published reports on effects of herbal remedies on abnormal laboratory test results are summarized and commented on.

DATA SOURCES

All published reports between 1980 and 2005 with the key words herbal remedies or alternative medicine and clinical laboratory test, clinical chemistry test, or drug-herb interaction were searched through Medline. The authors' own publications were also included. Important results were then synthesized.

DATA SYNTHESIS

Falsely elevated or falsely lowered digoxin levels may be encountered in a patient taking digoxin and the Chinese medicine Chan Su or Dan Shen, owing to direct interference of a component of Chinese medicine with the antibody used in an immunoassay. St John's wort, a popular herbal antidepressant, increases clearance of many drugs, and abnormally low cyclosporine, digoxin, theophylline, or protease inhibitor concentrations may be observed in a patient taking any of these drugs in combination with St John's wort. Abnormal laboratory results may also be encountered owing to altered pathophysiology. Kava-kava, chaparral, and germander cause liver toxicity, and elevated alanine aminotransferase, aspartate aminotransferase, and bilirubin concentrations may be observed in a healthy individual taking such herbal products. An herbal product may be contaminated with a Western drug, and an unexpected drug level (such as phenytoin in a patient who never took phenytoin but took a Chinese herb) may confuse the laboratory staff and the clinician.

CONCLUSIONS

Use of alternative medicines may significantly alter laboratory results, and communication among pathologists, clinical laboratory scientists, and physicians providing care to the patient is important in interpreting these results.

Evidence-based drug–herbal interactions

Due to the growing use of herbals and other dietary supplements healthcare providers and consumers need to know whether problems might arise from using these preparations in combination with conventional drugs. However, the evidence of interactions between natural products and drugs is based on known or suspected pharmacologic activity, data derived from in vitro or animal studies, or isolated case reports that frequently lack pertinent information. The usefulness of such information is questionable. More recently an increasing number of documented case reports, in vivo studies, and clinical trials have evaluated herbal-drug interactions. Results have sometimes been contradictory and more research is needed. Since there is a lack of rigorous studies that can establish the clinical significance of herb-drug interactions, an evidence-based evaluation of the current literature concerning commonly used herbal-drug interactions, as well as other dietary supplements, was conducted.

Hyperforin in St. John's wort drug interactions

Recently, interactions of herbal medicines with synthetic drugs came into focus of particular interest. In the past 3 years, more than 50 papers were published regarding interactions between St. John's wort (Hypericum perforatum L.; SJW) and prescription drugs. Co-medication with SJW resulted in decreased plasma concentrations of a number of drugs including amitriptyline, cyclosporine, digoxin, indinavir, irinotecan, warfarin, phenprocoumon, alprazolam, dextrometorphane, simvastatin, and oral contraceptives. Sufficient evidence from interaction studies and case reports indicate that SJW is a potent inducer of cytochrome P450 enzymes (particularly CYP3A4) and/or P-glycoprotein. Recent studies could show that the degree of enzyme induction by SJW correlates strongly with the amount of hyperforin found in the product. Products that do not contain substantial amounts of hyperforin (<1%) have not been shown to produce clinically relevant enzyme induction. On the other hand, some evidence suggests that hyperforin may also contribute to the antidepressant activity of SJW. However, clinical studies using SJW preparations with a low hyperforin amount (<1%) clearly demonstrated the superiority of this plant extract over placebo and its equivalence to imipramine and fluoxetine in the treatment of mild to moderate forms of depression. In the present paper clinical significant SJW interactions are critically evaluated against the background of hyperforin.

Assessing the clinical significance of botanical supplementation on human cytochrome P450 3A activity: comparison of a milk thistle and black cohosh product to rifampin and clarithromycin

Phytochemical-mediated modulation of cytochrome P450 enzymes (CYPs) may underlie many herb-drug interactions. This study's purpose was to assess the effects of milk thistle and black cohosh supplementation on CYP3A activity and compare them to a clinically recognized inducer, rifampin, and inhibitor, clarithromycin. Healthy volunteers were randomly assigned to receive a standardized milk thistle (900 mg) or black cohosh (80 mg) supplement for 14 days. Subjects also received rifampin (600 mg) and clarithromycin (1000 mg) for 7 days as positive controls for CYP3A induction and inhibition, respectively. Midazolam was administered orally before and after each supplementation and control period. The effects of milk thistle, black cohosh, rifampin, and clarithromycin on midazolam pharmacokinetics were determined using noncompartmental techniques. Unlike those observed for rifampin and clarithromycin, midazolam pharmacokinetics was unaffected by milk thistle or black cohosh. Milk thistle and black cohosh appear to have no clinically relevant effect on CYP3A activity in vivo.

Effect of milk thistle (Silybum marianum) and black cohosh (Cimicifuga racemosa) supplementation on digoxin pharmacokinetics in humans

Phytochemical-mediated modulation of P-glycoprotein (P-gp) and other drug transporters may underlie many herb-drug interactions. Serial serum concentration-time profiles of the P-gp substrate, digoxin, were used to determine whether supplementation with milk thistle or black cohosh modified P-gp activity in vivo. Sixteen healthy volunteers were randomly assigned to receive a standardized milk thistle (900 mg daily) or black cohosh (40 mg daily) supplement for 14 days, followed by a 30-day washout period. Subjects were also randomized to receive rifampin (600 mg daily, 7 days) and clarithromycin (1000 mg daily, 7 days) as positive controls for P-gp induction and inhibition, respectively. Digoxin (Lanoxicaps, 0.4 mg) was administered orally before and at the end of each supplementation and control period. Serial digoxin serum concentrations were obtained over 24 h and analyzed by chemiluminescent immunoassay. Comparisons of area under the serum concentration time curves from 0 to 3 h (AUC(0-3)), AUC(0-24), Cmax, apparent oral clearance of digoxin (CL/F), and elimination half-life were used to assess the effects of milk thistle, black cohosh, rifampin, and clarithromycin on digoxin pharmacokinetics. Rifampin produced significant reductions (p < 0.01) in AUC(0-3), AUC(0-24), and Cmax, whereas clarithromycin increased these parameters significantly (p < 0.01). Significant changes in digoxin half-life and CL/F were also observed with clarithromycin. No statistically significant effects on digoxin pharmacokinetics were observed following supplementation with either milk thistle or black cohosh, although digoxin AUC(0-3) and AUC(0-24) approached significance (p = 0.06) following milk thistle administration. When compared with rifampin and clarithromycin, supplementation with these specific formulations of milk thistle or black cohosh did not appear to affect digoxin pharmacokinetics, suggesting that these supplements are not potent modulators of P-gp in vivo.

A similarity measure for case based reasoning modeling with temporal abstraction based on cross-correlation

Adverse drug events (ADEs) are a major limitation of drug safety. They are often caused by inappropriate selection of dose and the concurrent use of drugs modulating each other (drug interaction). Risk assessment and prevention strategies must therefore consider co-administered drugs, individual doses, and their timing. In a new approach we evaluated the performance of cross correlation, commonly used in signal processing, to determine similarities in patient treatments. To achieve this, patient treatments were modeled as groups of vectors representing discrete time intervals. These vectors were cross-correlated and the results evaluated to find clusters in time courses indicating similarity in treatment of different patients. To evaluate our algorithm, we then created a number of test cases. The focus of this article is on each treatment, and its pattern in time and dosage. The algorithm successfully produces a relatively low similarity score for cases that are completely different with respect to their pattern of time and dosage but high scores when they are equal (score of 0.699) or similar (score of 0.528) in their therapies, and thus succeeds in having a relatively high specificity (27/30). Such an approach might help to considerably reduce the problem of false alarms which hampers most existing alerting systems for medication errors or impending ADEs.

Effect of St John's wort (Hypericum perforatum) on cytochrome P-450 activity in perfused rat liver

St. John's wort (Hypericum perforatum) is a popular over-the-counter dietary supplement and a herbal antidepressant that has been implicated in drug interactions with substrates of several cytochrome P-450 (CYP) isozymes. The effects of the St. John's wort extract (100 mg/kg, i.p., once daily for 10 days) on metabolic activity of CYP450 were assessed in the system of isolated perfused rat liver. The substrates used in this study were tolbutamide (CYP2C6), dextromethorphan (CYP2D2) and midazolam (CYP3A2). Validated HPLC method was used to quantify all compounds of interest. St. John's wort administration affected CYP activity, causing a significant decline in AUC of dextromethorphan [F(4,31)=1511, p<0.001; PLSD, p<0.001] and AUC of midazolam [F(3,25)=221, p<0.001; PLSD, p=0.035] and a significant increase in AUC of tolbutamide [F(3,26)=200, p<0.001; PLSD, p<0.001]. St. John's wort administration resulted in a significant induction of CYP2D2 and CYP3A2, and in a significant inhibition of CYP2C6 metabolic activities.

An overview of psychotropic drug-drug interactions

The psychotropic drug-drug interactions most likely to be relevant to psychiatrists' practices are examined. The metabolism and the enzymatic and P-glycoprotein inhibition/induction profiles of all antidepressants, antipsychotics, and mood stabilizers are described; all clinically meaningful drug-drug interactions between agents in these psychotropic classes, as well as with frequently encountered nonpsychotropic agents, are detailed; and information on the pharmacokinetic/pharmacodynamic results, mechanisms, and clinical consequences of these interactions is presented. Although the range of drug-drug interactions involving psychotropic agents is large, it is a finite and manageable subset of the much larger domain of all possible drug-drug interactions. Sophisticated computer programs will ultimately provide the best means of avoiding drug-drug interactions. Until these programs are developed, the best defense against drug-drug interactions is awareness and focused attention to this issue.

Toxicity and drug interactions associated with herbal products: ephedra and St. John's Wort

Health care providers are being increasingly confronted with the use of herbal medications by their patients. It is imperative that patients be questioned regarding herbal preparation use and that health care providers become familiar with these agents. Research into the active components and mechanisms of action of various herbals is ongoing [350]. Long-range studies need to be performed to follow patients for efficacy or toxicity in chronic use [351,352]. Adverse reactions to herbal remedies should be reported to the FDA MedWatch at http://www.fda.gov/medwatch. As withany therapeutic agent, risk of use must always be weighed against potential benefits.

Prediction of herb-drug metabolic interactions: a simulation study

In vitro and in vivo studies have indicated that the induction or inhibition of cytochrome P450 (CYP) is one of the major mechanisms for some clinically important pharmacokinetic herb-drug interactions. An attempt was made to simulate the effects of herbal preparation with single or multiple CYP-inhibiting constituents on the area of the plasma concentration-time curve (AUC) of coadministered drug that was either a low clearance drug by intravenous (i.v.) injection or a high clearance drug by oral route. Our simulation studies indicated that the expected increase (Rc) in the AUC of the coadministered drug by inhibiting herbal constituent(s) was dependent on the route of administration. For low clearance drug by i.v. injection, Rc was generally determined by inhibition constant (Ki), unbound inhibitor concentration ([I]), hepatic fraction (fh), number of inhibitory herbal constituents (n) and metabolic pathway fraction in hepatic metabolism (fm), while Rc for a high clearance drug by oral route, Rc was determined by Ki, [I], n and fm. By varying these parameters, Rc changed accordingly. It appeared likely to predict a herb-drug metabolic interaction, if the inhibiting herbal constituents could be quantitatively determined. However, many herb- and drug-related factors may cause difficulties with the prediction, and thus in vivo animal and human studies are always necessary.

Natural health product-drug interactions: a systematic review of clinical trials

Interactions between natural health products (NHP) and prescription medications are of increasing concern. This paper aims to identify all clinical trials of NHP-drug interactions. To determine the prevalence and outcomes of clinical investigations of NHP-drug pharmacokinetic interactions, electronic databases were searched from inception through March 2004, as well as reference lists from published reports and experts in the field for unpublished studies. Eligible studies were clinical investigations of the interaction between a NHP and the metabolism of a regulated medication in humans. Studies were excluded that only investigated the metabolism of an NHP or examined food-drug or NHP-NHP interactions. Two reviewers selected studies for inclusion and independently extracted data. Forty-seven trials were identified, studying an average of 14 participants/study (95% confidence interval [CI] 11-18), examined drug interactions with 19 different herbal preparations. All trials were pharmacokinetic studies, 41 of healthy volunteers and 6 of patients. Ten different herbal medicines as well as 5 different traditional herbal concoctions were studied. Potentially clinically significant drug interactions were observed with St. John wort (16/24 studies), garlic (2/5 studies), and American ginseng (1 study). Research on NHP-drug interactions is limited in number and scope. With the exception of St. John wort, clinicians and the public do not have information that permits strong inferences about interactions between NHPs and conventional medications.

Usefulness of studies on the molecular mechanism of action of herbals/botanicals: The case of St. John's wort

The use of herbals/botanicals has been gaining wide popularity in recent years in the United States as well as in other parts of the world. The mechanism of action of most of these herbals/botanicals has not been subjected to thorough scientific investigations. St. John's wort (Hypericum perforatum) represents a useful case study in this sense. Traditionally, it is used as a natural treatment for depression; however, in recent years its molecular mechanism of action has been elucidated by a number of laboratories across the world. Such studies have helped understand potential interactions of St. John's wort with drugs and other xenobiotics. St. John's wort activates a nuclear receptor called pregnane X receptor (PXR). PXR is a ligand-activated transcription factor that induces a number of xenobiotic-metabolizing enzymes and transporters including cytochrome P4503A4 (CYP3A4) in humans. Because CYP3A4 alone metabolizes about 60% of all clinically relevant drugs, induction of CYP3A4 may result in the rapid elimination of these drugs and a consequent reduction in drug efficacy. Ironically, such enzyme-inducing effects may not produce any immediate adverse symptomatology in the person taking St. John's wort. Therefore, the case of St. John's wort should serve as a good example of the usefulness and importance of studies on the mechanism of action of the herbals/botanicals, particularly those with widespread use. Scientists, physicians, and other health professionals can make use of the knowledge from such studies as an additional risk management tool.

Herbs and alternative therapies: Relevance to hypertension and cardiovascular diseases

Herbal remedies, supplements, and alternative therapeutic items are used by many patients with hypertension and cardiovascular diseases. Scientific knowledge about their efficacy and safety is lacking, and unfortunately, physicians are frequently not aware that patients are using these nontraditional forms of medical care. Patients may anticipate physicians' disapproval of their use, or not realize that it is important for the physician to know what they are taking. Therefore, it is imperative that patients are asked nonjudgmental questions about current and past use of herbals and alternative therapies. Even when physicians are aware of such use, they feel poorly trained to identify the constituents and effects. Although many such therapies are innocuous, several herbal or alternative therapeutic items can significantly elevate blood pressure or cause interactions with cardiovascular drugs. Practitioners in cardiovascular medicine should be competent and know current scientific evidence for the benefits and adverse effects of herbal supplements and provide patients reasonable advice. In this brief article, we review the epidemiology of alternative therapy use, and select several important herbal or other supplements that patients with hypertension and cardiovascular diseases may be taking. We discuss the therapies considered biological in nature as opposed to mind-body interventions or manipulative body or energy therapies.

Adverse drug interactions and reactions in dermatology: current issues of clinical relevance

This article highlights several adverse drug interactions and reactions relevant to current dermatologic practice. Absorption interactions between drugs and compounds containing polyvalent cations, potential interactions between herbal and conventional medicines, the meaning of sulfa allergy, and adverse cutaneous reactions caused by epidermal growth factor receptor inhibitors are discussed.

Herb-drug interactions: an overview of the clinical evidence

Herbal medicines are mixtures of more than one active ingredient. The multitude of pharmacologically active compounds obviously increases the likelihood of interactions taking place. Hence, the likelihood of herb-drug interactions is theoretically higher than drug-drug interactions, if only because synthetic drugs usually contain single chemical entities. Case reports and clinical studies have highlighted the existence of a number of clinically important interactions, although cause-and-effect relationships have not always been established. Herbs and drugs may interact either pharmacokinetically or pharmacodynamically. Through induction of cytochrome P450 enzymes and/or P-glycoprotein, some herbal products (e.g. St John's wort) have been shown to lower the plasma concentration (and/or the pharmacological effect) of a number of conventional drugs, including cyclosporine, indinavir, irinotecan, nevirapine, oral contraceptives and digoxin. The majority of such interactions involves medicines that require regular monitoring of blood levels. To date there is less evidence relating to the pharmacodynamic interaction. However, for many of the interactions discussed here, the understanding of the mechanisms involved is incomplete. Taking herbal agents may represent a potential risk to patients under conventional pharmacotherapy.

In vivo effects of goldenseal, kava kava, black cohosh, and valerian on human cytochrome P450 1A2, 2D6, 2E1, and 3A4/5 phenotypes

OBJECTIVES

Phytochemical-mediated modulation of cytochrome P450 (CYP) activity may underlie many herb-drug interactions. Single-time point phenotypic metabolic ratios were used to determine whether long-term supplementation of goldenseal ( Hydrastis canadensis ), black cohosh ( Cimicifuga racemosa ), kava kava ( Piper methysticum ), or valerian ( Valeriana officinalis ) extracts affected CYP1A2, CYP2D6, CYP2E1, or CYP3A4/5 activity.

METHODS

Twelve healthy volunteers (6 women) were randomly assigned to receive goldenseal, black cohosh, kava kava, or valerian for 28 days. For each subject, a 30-day washout period was interposed between each supplementation phase. Probe drug cocktails of midazolam and caffeine, followed 24 hours later by chlorzoxazone and debrisoquin (INN, debrisoquine), were administered before (baseline) and at the end of supplementation. Presupplementation and postsupplementation phenotypic trait measurements were determined for CYP3A4/5, CYP1A2, CYP2E1, and CYP2D6 by use of 1-hydroxymidazolam/midazolam serum ratios (1-hour sample), paraxanthine/caffeine serum ratios (6-hour sample), 6-hydroxychlorzoxazone/chlorzoxazone serum ratios (2-hour sample), and debrisoquin urinary recovery ratios (8-hour collection), respectively. The content of purported "active" phytochemicals was determined for each supplement.

RESULTS

Comparisons of presupplementation and postsupplementation phenotypic ratio means revealed significant inhibition (approximately 40%) of CYP2D6 (difference, -0.228; 95% confidence interval [CI], -0.268 to -0.188) and CYP3A4/5 (difference, -1.501; 95% CI, -1.840 to -1.163) activity for goldenseal. Kava produced significant reductions (approximately 40%) in CYP2E1 only (difference, -0.192; 95% CI, -0.325 to -0.060). Black cohosh also exhibited statistically significant inhibition of CYP2D6 (difference, -0.046; 95% CI, -0.085 to -0.007), but the magnitude of the effect (approximately 7%) did not appear to be clinically relevant. No significant changes in phenotypic ratios were observed for valerian.

CONCLUSIONS

Botanical supplements containing goldenseal strongly inhibited CYP2D6 and CYP3A4/5 activity in vivo, whereas kava inhibited CYP2E1 and black cohosh weakly inhibited CYP2D6. Accordingly, serious adverse interactions may result from the concomitant ingestion of goldenseal supplements and drugs that are CYP2D6 and CYP3A4/5 substrates. Kava kava and black cohosh may interact with CYP2E1 and CYP2D6 substrates, respectively. Valerian appears to be less likely to produce CYP-mediated herb-drug interactions.

Pharmacokinetic properties of pravastatin in Mexicans: An open-label study in healthy adult volunteers

BACKGROUND

The pharmacokinetic properties of pravastatin, particularlyAUC and Cmax, are variable by population. A description of the pharmacokinetic properties of pravastatin in Mexican mestizos was not found in a search of MEDLINE/PubMed (key terms: pravastatin, Mexican, and pharmacokinetics; years: 1966-2005). Because Mexicans and Japanese have common ancestors (Mongoloid group), they also have a common gene pool. This gene pool was modified by genetic "bottlenecks" that occurred when these populations migrated to the Americas and when the Mexican population mixed with the Spanish population during the 16th and 17th centuries. Previous studies in Japanese subjects showed 5 main mutations on the hepatic drug transporter OATP-C, resulting in higher Cmax and AUC values compared with whites. In the Japanese population, the rates of expression of the (*) 1b and (*) 15 alleles were 46% and 15%, respectively.

OBJECTIVE

The aim of this study was to evaluate the pharmacokinetic propertiesof pravastatin in healthy Mexican mestizo volunteers and to compare them with those in white and Japanese populations described in the literature.

METHODS

This open-label, uncontrolled pilot study of the pharmacokineticproperties of pravastatin was conducted at the Division of Pharmacology, Center for Research and Advanced Studies, Mexico City, Mexico. Healthy, adult, Mexican volunteers received a single dose of pravastatin 10 mg PO (tablet). High-performance liquid chromatography was used to determine plasma pravastatin concentrations between 15 minutes and 12 hours after dosing.

RESULTS

Twenty-four subjects (15 women, 9 men; mean age, 30.6 years)participated in the study. The mean (SD) Cmax was 9.5 (2.4) ng/mL; Tmax, 0.8 (0.3) hours; AUC0-∞ 35.7 (19.7) ng/mL - h; t1/2, 2.7 (1.1) hours; and mean residence time, 3.1 (1.1) hours. One volunteer (4%) had an AUC value that differed substantially from the rest of the study population, producing a bimodal distribution of the pharmacokinetic parameters. No adverse events were observed or reported during the trial.

CONCLUSIONS

In this small pilot study of the pharmacokinetic properties of pravastatin in Mexican mestizos, AUC was not statistically significantly different from previous studies, either in a white or Japanese population. However, we did not find the high values reported for Cmax in some Japanese subjects carrying recently reported mutations on the pravastatin transporter.

Interactions between herbal and conventional medicines

Herb-drug interactions are subject to much interest at present, but for various reasons reports may be unreliable or unsubstantiated. Herbal medicines are variable in composition and quality, which may affect their interaction profile as well as the reliability of reports concerning them. In this review, clinical and experimental reports have been collated, evaluated and summarised, and the theoretical and clinical evidence presented. There is an explanation of the particular issues involved with herbal medicines as compared with conventional drugs, and reasons why comparisons may or may not be valid, which is intended for those without specialist experience in herbal products. It has become apparent that only a few herbal drugs have so far been cited in interaction reports, for example St John's Wort, Ginkgo biloba, Dan Shen, liquorice, Ma huang and garlic, and that the main drugs involved are those which are already susceptible to interactions with many other conventional drugs, such as warfarin, protease inhibitors and anti-cancer drugs. An attempt has been made to put the matter into perspective and recommendations have been given for health professionals to advise or develop strategies to safeguard patients, without resorting to speculation or scaremongering.

Interactions between aqueousHypericum perforatumextracts and drugs:in vitrostudies

Physico-chemical interactions between drugs and plant extracts can result in the formation of nanoparticles, microparticles and precipitates. The extraction method may have an influence on the components of the plant preparations and the interactions between drugs and plant extracts. In this study the particle formation in different drug-containing preparations of Hypericum perforatum L. was compared. The formation of nanoparticles was investigated by PCS and scanning electron microscopy. Precipitates were separated from nanoparticles by centrifugation or filtration. The particle formation in drug-containing infusions and reconstituted methanolic extracts of Hypericum perforatum L. was different. In reconstituted dry extracts 21.5% 17alpha-ethinylestradiol and 36.6% levonorgestrel was bound to precipitates, in aqueous Hypericum infusions less than 4% of the hormones was bound. In infusions containing desipramine nanoparticles were formed while the formation of nanoparticles in desipramine-containing reconstituted extracts was negligible. Up to 10% of desipramine was bound to precipitates in reconstituted extracts, but only 4% was associated with the precipitate of infusions. The interactions between extracts of Hypericum perforatum L. and drugs depended on the extraction method. Reconstituted methanolic extracts showed a more intensive binding with oral contraceptives than aqueous infusions.

Drug interaction between St John's Wort and quazepam

AIM

St John's Wort (SJW) enhances CYP3A4 activity and decreases blood concentrations of CYP3A4 substrates. In this study, the effects of SJW on a benzodiazepine hypnotic, quazepam, which is metabolized by CYP3A4, were examined.

METHODS

Thirteen healthy subjects took a single dose of quazepam 15 mg after treatment with SJW (900 mg day(-1)) or placebo for 14 days. The study was performed in a randomized, placebo-controlled, cross-over design with an interval of 4 weeks between the two treatments. Blood samples were obtained during a 48 h period and urine was collected for 24 h after each dose of quazepam. Pharmacodynamic effects were determined using visual analogue scales (VAS) and the digit symbol substitution test (DSST) on days 13 and 14.

RESULTS

SJW decreased the plasma quazepam concentration. The Cmax and AUC(0-48) of quazepam after SJW were significantly lower than those after placebo [Cmax; -8.7 ng ml(-1) (95% confidence interval (CI) -17.1 to -0.2), AUC0-48; -55 ng h ml(-1) (95% CI -96 to -15)]. The urinary ratio of 6beta-hydroxycortisol to cortisol, which reflects CYP3A4 activity, also increased after dosing with SJW (ratio; 2.1 (95%CI 0.85-3.4)). Quazepam, but not SJW, produced sedative-like effects in the VAS test (drowsiness; P < 0.01, mental slowness; P < 0.01, calmness; P < 0.05, discontentment; P < 0.01). On the other hand, SJW, but not quazepam impaired psychomotor performance in the DSST test. SJW did not influence the pharmacodynamic profile of quazepam.

CONCLUSIONS

These results suggest that SJW decreases plasma quazepam concentrations, probably by enhancing CYP3A4 activity, but does not influence the pharmacodynamic effects of the drug.

Cardiovascular pharmacotherapy and herbal medicines: the risk of drug interaction

Use of herbal medicines among patients under cardiovascular pharmacotherapy is widespread. In this paper, we have reviewed the literature to determine the possible interactions between herbal medicines and cardiovascular drugs. The Medline database was searched for clinical articles published between January 1996 and February 2003. Forty-three case reports and eight clinical trials were identified. Warfarin was the most common cardiovascular drug involved. It was found to interact with boldo, curbicin, fenugreek, garlic, danshen, devil's claw, don quai, ginkgo, papaya, lycium, mango, PC-SPES (resulting in over-anticoagulation) and with ginseng, green tea, soy and St. John's wort (causing decreased anticoagulant effect). Gum guar, St. John's wort, Siberian ginseng and wheat bran were found to decrease plasma digoxin concentration; aspirin interactions include spontaneous hyphema when associated with ginkgo and increased bioavailability if combined with tamarind. Decreased plasma concentration of simvastatin or lovastatin was observed after co-administration with St. John's wort and wheat bran, respectively. Other adverse events include hypertension after co-administration of ginkgo and a diuretic thiazide, hypokalemia after liquorice and antihypertensives and anticoagulation after phenprocoumon and St. John's wort. Interaction between herbal medicine and cardiovascular drugs is a potentially important safety issue. Patients taking anticoagulants are at the highest risk.

Simultaneous determination of hypericin and hyperforin in human plasma with liquid chromatography–tandem mass spectrometry

A selective and sensitive method for the simultaneous determination of hypericin and hyperforin--the two main active ingredients of St. John's Wort (SJW) extract--in human plasma depending on liquid/liquid-extraction and LC/MS/MS detection has been developed, validated after specifying the stability of the photosensitive hypericin in plasma samples during light exposure and applied to samples of a patient. After extraction with ethyl acetate/n-hexane in the darkness, sample extracts were chromatographed isocratically within 6 min on a Kromasil RP-18 column. The analytes were detected with tandem mass spectrometry in the selected reaction monitoring mode using an electrospray ion source. The limit of quantification was 0.05 ng/mL for hypericin and 0.035 ng/mL for hyperforin. The accuracy of the method varied between 101.9 and 114.2% and the precision ranged from 4.7 to 15.4% (S.D., batch-to-batch) for both analytes. The method was linear at least between 0.05 and 10 ng/mL for hypericin and between 0.035 and 100 ng/mL for hyperforin. Using this method hypericin and hyperforin were determined successfully in a patient over seven days following discontinuation of exposure with therapeutic doses of St. John's Wort extract.

Herbal modulation of P-glycoprotein

P-glycoprotein (Pgp) is a 170 kDa phosphorylated glycoprotein encoded by human MDR1 gene. It is responsible for the systemic disposition of numerous structurally and pharmacologically unrelated lipophilic and amphipathic drugs, carcinogens, toxins, and other xenobiotics in many organs, such as the intestine, liver, kidney, and brain. Like cytochrome P450s (CYP3A4), Pgp is vulnerable to inhibition, activation, or induction by herbal constituents. This was demonstrated by using an ATPase assay, purified Pgp protein or intact Pgp-expressing cells, and proper probe substrates and inhibitors. Curcumin, ginsenosides, piperine, some catechins from green tea, and silymarin from milk thistle were found to be inhibitors of Pgp, while some catechins from green tea increased Pgp-mediated drug transport by heterotropic allosteric mechanism, and St. John's wort induced the intestinal expression of Pgp in vitro and in vivo. Some components (e.g., bergamottin and quercetin) from grapefruit juice were reported to modulate Pgp activity. Many of these herbal constituents, in particular flavonoids, were reported to modulate Pgp by directly interacting with the vicinal ATP-binding site, the steroid-binding site, or the substrate-binding site. Some herbal constituents (e.g., hyperforin and kava) were shown to activate pregnane X receptor, an orphan nuclear receptor acting as a key regulator of MDR1 and many other genes. The inhibition of Pgp by herbal constituents may provide a novel approach for reversing multidrug resistance in tumor cells, whereas the stimulation of Pgp expression or activity has implication for chemoprotective enhancement by herbal medicines. Certain natural flavonols (e.g., kaempferol, quercetin, and galangin) are potent stimulators of the Pgp-mediated efflux of 7,12-dimethylbenz(a)-anthracene (a carcinogen). The modulation of Pgp activity and expression by these herb constituents may result in altered absorption and bioavailability of drugs that are Pgp substrates. This is exemplified by increased oral bioavailability of phenytoin and rifampin by piperine and decreased bioavailability of indinavir, tacrolimus, cyclosporine, digoxin, and fexofenadine by coadministered St. John's wort. However, many of these drugs are also substrates of CYP3A4. Thus, the modulation of intestinal Pgp and CYP3A4 represents an important mechanism for many clinically important herb-drug interactions. Further studies are needed to explore the relative role of Pgp and CYP3A4 modulation by herbs and the mechanism for the interplay of these two important proteins in herb-drug interactions.