Influence of Goldenseal Root on the Pharmacokinetics of Indinavir

An Integrative Approach to Elucidate Mechanisms Underlying the Pharmacokinetic Goldenseal-Midazolam Interaction: Application of In Vitro Assays and Physiologically Based Pharmacokinetic Models to Understand Clinical Observations

The natural product goldenseal is a clinical inhibitor of CYP3A activity, as evidenced by a 40%-60% increase in midazolam area under the plasma concentration versus time curve (AUC) after coadministration with goldenseal. The predominant goldenseal alkaloids berberine and (-)-β-hydrastine were previously identified as time-dependent CYP3A inhibitors using human liver microsomes. Whether these alkaloids contribute to the clinical interaction, as well as the primary anatomic site (hepatic vs. intestinal) and mode of CYP3A inhibition (reversible vs. time-dependent), remain uncharacterized. The objective of this study was to mechanistically assess the pharmacokinetic goldenseal-midazolam interaction using an integrated in vitro-in vivo-in silico approach. Using human intestinal microsomes, (-)-β-hydrastine was a more potent time-dependent inhibitor of midazolam 1'-hydroxylation than berberine (KI and kinact: 8.48 μM and 0.041 minutes-1, respectively, vs. >250 μM and ∼0.06 minutes-1, respectively). Both the AUC and Cmax of midazolam increased by 40%-60% after acute (single 3-g dose) and chronic (1 g thrice daily × 6 days) goldenseal administration to healthy adults. These increases, coupled with a modest or no increase (≤23%) in half-life, suggested that goldenseal primarily inhibited intestinal CYP3A. A physiologically based pharmacokinetic interaction model incorporating berberine and (-)-β-hydrastine successfully predicted the goldenseal-midazolam interaction to within 20% of that observed after both chronic and acute goldenseal administration. Simulations implicated (-)-β-hydrastine as the major alkaloid precipitating the interaction, primarily via time-dependent inhibition of intestinal CYP3A, after chronic and acute goldenseal exposure. Results highlight the potential interplay between time-dependent and reversible inhibition of intestinal CYP3A as the mechanism underlying natural product-drug interactions, even after acute exposure to the precipitant. SIGNIFICANCE STATEMENT: Natural products can alter the pharmacokinetics of an object drug, potentially resulting in increased off-target effects or decreased efficacy of the drug. The objective of this work was to evaluate fundamental mechanisms underlying the clinically observed goldenseal-midazolam interaction. Results support the use of an integrated approach involving established in vitro assays, clinical evaluation, and physiologically based pharmacokinetic modeling to elucidate the complex interplay between multiple phytoconstituents and various pharmacokinetic processes driving a drug interaction.

Potential Cytochrome P450-mediated pharmacokinetic interactions between herbs, food, and dietary supplements and cancer treatments

Herbs, food and dietary supplements (HFDS), can interact significantly with anticancer drug treatments via cytochrome p450 isoforms (CYP) CYP3A4, CYP2D6, CYP1A2, and CYP2C8. The objective of this review was to assess the influence of HFDS compounds on these cytochromes. Interactions with CYP activities were searched for 189 herbs and food products, 72 dietary supplements in Web of Knowledge® databases. Analyses were made from 140 of 3,125 clinical trials and 236 of 3,374 in vitro, animal model studies or case reports. 18 trials were found to report direct interactions between 9 HFDS with 8 anticancer drugs. 21 HFDS were found to interact with CYP3A4, a major metabolic pathway for many anticancer drugs. All 261 HFDS were classified for their interaction with the main cytochromes P450 involved in the metabolism of anticancer drugs. We provided an easy-to-use colour-coded table to easily match potential interactions between 261 HFDS and 117 anticancer drugs.

Goldenseal (Hydrastis canadensis L.) and its active constituents: A critical review of their efficacy and toxicological issues

Goldenseal (Hydrastis canadensis L.) is a medicinal plant widely used in various traditional systems of medicine and as a food supplement. It has been traditionally used by Native Americans as a coloring agent and as medicinal remedy for common diseases and conditions like wounds, digestive disorders, ulcers, skin and eye ailments, and cancer. Over the years, goldenseal has become a popular food supplement in the USA and other regions. The rhizome of this plant has been used for the treatment of a variety of diseases including, gastrointestinal disorders, ulcers, muscular debility, nervous prostration, constipation, skin and eye infections, cancer, among others. Berberine is one of the most bioactive alkaloid that has been identified in different parts of goldenseal. The goldenseal extract containing berberine showed numerous therapeutic effects such as antimicrobial, anti-inflammatory, hypolipidemic, hypoglycemic, antioxidant, neuroprotective (anti-Alzheimer's disease), cardioprotective, and gastrointestinal protective. Various research finding suggest the health promoting effects of goldenseal components and their extracts. However, few studies have also suggested the possible neurotoxic, hepatotoxic and phototoxic activities of goldenseal extract and its alkaloids. Thus, large randomized, double-blind clinical studies need to be conducted on goldenseal supplements and their main alkaloids to provide more evidence on the mechanisms responsible for the pharmaceutical activity, clinical efficacy and safety of these products. Thus, it is very important to review the scientific information about goldenseal to understand about the current scenario.

Pharmacokinetic Interactions between Herbal Medicines and Drugs: Their Mechanisms and Clinical Relevance

The therapeutic efficacy of a drug or its unexpected unwanted side effects may depend on the concurrent use of a medicinal plant. In particular, constituents in the medicinal plant extracts may influence drug bioavailability, metabolism and half-life, leading to drug toxicity or failure to obtain a therapeutic response. This narrative review focuses on clinical studies improving knowledge on the ability of selected herbal medicines to influence the pharmacokinetics of co-administered drugs. Moreover, in vitro studies are useful to anticipate potential herbal medicine-drug interactions. In particular, they help to elucidate the cellular target (metabolic or transporter protein) and the mechanism (induction or inhibition) by which a single constituent of the herbal medicine acts. The authors highlight the difficulties in predicting herbal–drug interactions from in vitro data where high concentrations of extracts or their constituents are used and pharmacokinetics are missed. Moreover, the difficulty to compare results from human studies where different kinds of herbal extracts are used is discussed. The herbal medicines discussed are among the best sellers and they are reported in the “Herbal Medicines for Human Use” section of the European Medicinal Agency (EMA).

Interactions between antiretroviral therapy and complementary and alternative medicine: a narrative review

BACKGROUND

The use of complementary and alternative medicine including herbal medicine (phytotherapy), vitamins, minerals and food supplements is frequent among people living with HIV/AIDS (PLWHAs) who take antiretroviral (ARV) drugs, but is often not known by their prescribing physicians. Some drug-supplement combinations may result in clinically meaningful interactions.

AIMS

In this literature review, we aimed to investigate the evidence for complementary and alternative medicine interactions with ARVs.

SOURCES

A bibliographic search of all in vitro, human studies and case reports of the PubMed database was performed to assess the risk of interactions between complementary and alternative self-medication products and ARVs. The 'HIV drug interaction' (https://www.hiv-druginteractions.org) and 'Natural medicines comprehensive database' (https://naturalmedicines.therapeuticresearch.com) interaction checkers were also analysed.

CONTENT

St John's wort, some forms of garlic, grapefruit and red rice yeast are known to have significant interaction and thus should not be co-administered, or should be used with caution with certain ARV classes. Data on other plant-based supplements come from in vitro studies or very small size in vivo studies and are thus insufficient to conclude the real in vivo impact in case of concomitant administration with ARVs. Some polyvalent minerals such as calcium, magnesium, and iron salts can reduce the absorption of integrase inhibitors by chelation. Potential interactions with vitamin C and quercetin with some ARVs should be noted and efficacy and tolerance of the treatment should be monitored.

IMPLICATIONS

This review shows the importance of screening all PLWHAs for complementary and alternative medicine use to prevent treatment failure or adverse effects related to an interaction with ARVs. Further human studies are warranted to describe the clinical significance of in vitro interactions between numerous complementary and alternative medicine and ARVs.

Therapeutic Risk and Benefits of Concomitantly Using Herbal Medicines and Conventional Medicines: From the Perspectives of Evidence Based on Randomized Controlled Trials and Clinical Risk Management

Despite increased awareness of the potential of herb-drug interactions (HDIs), the lack of rigorous clinical evidence regarding the significance provides a challenge for clinicians and consumers to make rational decisions about the safe combination of herbal and conventional medicines. This review addressed HDIs based on evidence from randomized controlled trials (RCTs). Literature was identified by performing a PubMed search till January 2017. Risk description and clinical risk management were described. Among 74 finally included RCTs, 17 RCTs (22.97%) simply addressed pharmacodynamic HDIs. Fifty-seven RCTs (77.03%) investigated pharmacokinetic HDIs and twenty-eight of them showed potential or actual clinical relevance. The extent of an HDI may be associated with the factors such as pharmacogenomics, dose of active ingredients in herbs, time course of interaction, characteristics of the object drugs (e.g., administration routes and pharmacokinetic profiles), modification of herbal prescription compositions, and coexistence of inducers and inhibitors. Clinical professionals should enhance risk management on HDIs such as increasing awareness of potential changes in therapeutic risk and benefits, inquiring patients about all currently used conventional medicines and herbal medicines and supplements, automatically detecting highly substantial significant HDI by computerized reminder system, selecting the alternatives, adjusting dose, reviewing the appropriateness of physician orders, educating patients to monitor for drug-interaction symptoms, and paying attention to follow-up visit and consultation.

Drug interactions in HIV treatment: complementary & alternative medicines and over-the-counter products

INTRODUCTION

Use of complementary and alternative medicines (CAMs) and over-the-counter (OTC) medications are very common among HIV-infected patients. These products can cause clinically significant drug-drug interactions (DDIs) with antiretroviral (ARV) medications, thereby increasing risk for negative outcomes such as toxicity or loss of virologic control. Areas covered: This article provides an updated review of the different mechanisms by which CAM and OTC products are implicated in DDIs with ARV medications. Expert commentary: Much of the literature published to date involves studies of CAMs interacting with older ARV agents via the cytochrome P450 (CYP450) system. However, the HIV treatment and prevention arsenal is continually evolving. Furthermore, our elucidation of the role of non-CYP450 mediated DDIs with ARV medications is greatly increasing. Therefore, clinicians are well served to understand the various mechanisms and extent by which new ARV therapies may be involved in drug interactions with CAMs and OTC medications.

Dietary supplement interactions with antiretrovirals: a systematic review

Many patients who take antiretroviral drugs also take alternative therapies including dietary supplements. Some drug-supplement combinations may result in clinically meaningful interactions. We aimed to investigate the evidence for dietary supplement interactions with antiretrovirals. A systematic review was conducted using multiple resources including PubMed, Natural Medicine Comprehensive Database, The Review of Natural Products, and Google Scholar. All human studies or case reports evaluating an interaction between a dietary supplement and an antiretroviral were selected for inclusion. Twenty-eight pharmacokinetic studies and case-series/case reports were selected for inclusion. Calcium carbonate, ferrous fumarate, some forms of ginkgo, some forms of garlic, some forms of milk thistle, St. John's wort, vitamin C, zinc sulfate, and multivitamins were all found to significantly decrease the levels of selected antiretrovirals and should be avoided in patients taking these antiretrovirals. Cat's claw and evening primrose oil were found to significantly increase the levels of antiretrovirals and patients should be monitored for adverse effects while taking these dietary supplements with antiretrovirals. This systematic review shows the importance of screening all human immunodeficiency virus patients for dietary supplement use to prevent treatment failure or adverse effects related to an interaction.

A Review of the Toxicity of HIV Medications II: Interactions with Drugs and Complementary and Alternative Medicine Products

For many patients today, HIV has become a chronic disease. For those patients who have access to and adhere to lifelong antiretroviral (ARV) therapy, the potential for drug-drug interactions has become a real and life-threatening concern. It is known that most ARV drug interactions occur through the cytochrome P450 (CYP) pathway. Medications for comorbid medical conditions, holistic supplements, and illicit drugs can be affected by CYP inhibitors and inducers and have the potential to cause harm and toxicity. Protease inhibitors (PIs) tend to inhibit CYP3A4, while most non-nucleoside reverse transcriptase inhibitors (NNRTIs) tend to induce the enzyme. As such, failure to adjust the dose of co-administered medications, such as statins and steroids, may lead to serious complications including rhabdomyolysis and hypercortisolism, respectively. Similarly, gastric acid blockers can decrease several ARV absorption, and warfarin doses may need to be adjusted to maintain therapeutic concentrations. Illicit drugs such as methylenedioxymethamphetamine (MDMA, "ecstasy") in combination with PIs lead to increased toxicity, while the concomitant administration of sedative drugs such as midazolam and alprazolam in patients taking PIs can result in prolonged sedation, delayed recovery, and increased length of stay. Even supplements like St. John's Wort can alter PI concentrations. In theory, any drug that is metabolized by CYP has potential for a pharmacokinetic drug-drug interaction with all PIs, cobicistat, and most NNRTIs. When adding a new medication to an ARV regimen, use of a drug-drug interaction software and/or consultation with a clinical pharmacist/pharmacologist or HIV specialist is recommended.

Potential pharmacokinetic interactions between antiretrovirals and medicinal plants used as complementary and African traditional medicines

The use of traditional/complementary/alternate medicines (TCAMs) in HIV/AIDS patients who reside in Southern Africa is quite common. Those who use TCAMs in addition to antiretroviral (ARV) treatment may be at risk of experiencing clinically significant pharmacokinetic (PK) interactions, particularly between the TCAMs and the protease inhibitors (PIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs). Mechanisms of PK interactions include alterations to the normal functioning of drug efflux transporters, such as P-gp and/or CYP isoenzymes, such a CYP3A4 that mediate the absorption and elimination of drugs in the small intestine and liver. Specific mechanisms include inhibition and activation of these proteins and induction via the pregnane X receptor (PXR). Several clinical studies and case reports involving ARV-herb PK interactions have been reported. St John's Wort, Garlic and Cat's Claw exhibited potentially significant interactions, each with a PI or NNRTI. The potential for these herbs to induce PK interactions with drugs was first identified in reports of in vitro studies. Other in vitro studies have shown that several African traditional medicinal (ATM) plants and extracts may also demonstrate PK interactions with ARVs, through effects on CYP3A4, P-gp and PXR. The most complex effects were exhibited by Hypoxis hemerocallidea, Sutherlandia frutescens, Cyphostemma hildebrandtii, Acacia nilotica, Agauria salicifolia and Elaeodendron buchananii. Despite a high incidence of HIV/AIDs in the African region, only one clinical study, between efavirenz and Hypoxis hemerocallidea has been conducted. However, several issues/concerns still remain to be addressed and thus more studies on ATMs are warranted in order for more meaningful data to be generated and the true potential for such interactions to be determined.

Interactions between herbs and conventional drugs: overview of the clinical data

This article provides an overview of the clinical evidence of interactions between herbal and conventional medicines. Herbs involved in drug interactions--or that have been evaluated in pharmacokinetic trials--are discussed in this review. While many of the interactions reported are of limited clinical significance and many herbal products (e.g. black cohosh, saw palmetto, echinacea, hawthorn and valerian) seem to expose patients to minor risk under conventional pharmacotherapy, a few herbs, notably St. John's wort, may provoke adverse events sufficiently serious to endanger the patients' health. Healthcare professionals should remain vigilant for potential interactions between herbal medicines and prescribed drugs, especially when drugs with a narrow therapeutic index are used.

Clinically based evidence of drug-herb interactions: a systematic review

IMPORTANCE OF THE FIELD

Healthcare practitioners are deeply concerned about drug-herb interactions and how concurrent administration may affect both the safety and effectiveness of prescribed drugs. Interactions between botanical medicines and synthetic drugs can be clinically relevant and it is important to understand what kinds of interactions are possible. Better knowledge in this area will help avoid negative interactions and may also help enable synergistic interactions.

AREAS COVERED IN THIS REVIEW

Includes articles related to the investigation of Western botanicals or whole herbal extracts in human subjects, investigating either the impact on Cytochrome P450 isoenzymes or an assessment of specific drug-herb interactions within a clinical trial. Searches were conducted in both Pubmed and EMBASE from inception to March 2009.

WHAT THE READER WILL GAIN

Knowledge regarding specific interactions to consider in clinical practice. The reader will also gain an appreciation of the complexities associated with the area of drug-herb interactions. Summary tables of relevant drug-herb interactions are presented both for the individual herbs included and at the level of the CYP450 enzymes.

TAKE HOME MESSAGE

Knowledge of drug-herb interactions is limited and much more research needs to be done to further document clinically relevant interactions. Even though preclinical data are often poorly generalizable to the human situation, caution must be taken in the absence of clinical evidence especially where drugs with narrow therapeutic windows are concerned.

Antiviral drug disposition and natural health products: risk of therapeutic alteration and resistance

The HIV/AIDS patient population is known to use natural health products (NHPs) in addition to the several antiretroviral drugs that constitute the treatment regimen for this disease. This review focuses on NHPs and their potential for interactions with antiretroviral agents resulting in therapeutic alterations or resistance. There are conflicting published medical literature reports and very few well-documented human clinical studies that unequivocally demonstrate if this concomitant use increases the risk of interaction/adverse reaction with these therapeutic products. This article outlines some findings from the Canadian domestic adverse reaction case reports associated with the use of antiretrovirals and NHPs. These adverse reaction case reports were specifically examined for patients taking NHPs together with their highly active antiretroviral therapy during or around the time when the adverse reaction developed. Together, the case reports and limited human clinical studies suggest that the risk for therapeutic alterations and resistance can exist due to changes in pharmacokinetic parameters with concomitant use of these therapeutic 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.

Modulation of human cytochrome P450 3A4 (CYP3A4) and P-glycoprotein (P-gp) in Caco-2 cell monolayers by selected commercial-source milk thistle and goldenseal products

In this study, we used an in vitro Caco-2 cell monolayer model to evaluate aqueous extracts of commercial-source goldenseal (Hydrastis canadensis) and milk thistle (Silybum marianum) capsule formulations, their marker phytochemicals (berberine and silibinin, respectively), as well as dillapiol, vinblastine, and the HIV protease inhibitor saquinavir for their ability to modulate CYP3A4 and ABCB1 expression after short-term exposure (48 h). Both upregulation and downregulation of CYP3A4 expression was observed with extracts of varying concentrations of the two natural health products (NHPs). CYP3A4 was highly responsive in our system, showing a strong dose-dependent modulation by the CYP3A4 inhibitor dillapiol (upregulation) and the milk thistle flavonolignan silibinin (downregulation). ABCB1 was largely unresponsive in this cellular model and appears to be of little value as a biomarker under our experimental conditions. Therefore, the modulation of CYP3A4 gene expression can serve as an important marker for the in vitro assessment of NHP-drug interactions.

Supplementation With Goldenseal (Hydrastis canadensis), but not Kava Kava (Piper methysticum), Inhibits Human CYP3A Activity In Vivo

The effects of goldenseal (Hydrastis canadensis) and kava kava (Piper methysticum) supplementation on human CYP3A activity were evaluated using midazolam (MDZ) as a phenotypic probe. Sixteen healthy volunteers were randomly assigned to receive either goldenseal or kava kava for 14 days. Each supplementation phase was followed by a 30-day washout period. MDZ (8 mg, per os) was administered before and after each phase, and pharmacokinetic parameters were determined using standard non-compartmental methods. Comparisons of pre- and post-supplementation MDZ pharmacokinetic parameters revealed significant inhibition of CYP3A by goldenseal (AUC(0-infinity), 107.9+/-43.3 vs 175.3+/-74.8 ng x h/ml; Cl/F/kg, 1.26+/-0.59 vs 0.81+/-0.45 l/h/kg; T(1/2), 2.01+/-0.42 vs 3.15+/-1.12 h; Cmax, 50.6+/-26.9 vs 71.2+/-50.5 ng/ml). MDZ disposition was not affected by kava kava supplementation. These findings suggest that significant herb-drug interactions may result from the concomitant ingestion of goldenseal and CYP3A substrates.

HIV/AIDS: Interactions between Natural Health Products and Antiretroviral Drugs: Pharmacokinetic and Pharmacodynamic Effects

Concurrent use of natural health products (NHPs) with antiretroviral drugs (ARVs) is widespread among human immunodeficiency virus-infected patients. This article reviews the clinical pharmacokinetic and pharmacodynamic interactions between NHPs and ARVs. Many NHPs are complex mixtures and are likely to contain organic compounds that may induce and/or inhibit drug metabolizing enzymes and drug transporters. Although the weight of evidence for the effects of certain NHPs varies and many studies of these products lack scientific rigor, it has been observed that St. John's wort clearly induces cytochrome P450 3A4 and P-glycoprotein and reduces protease inhibitor and nonnucleoside reverse-transcriptase inhibitor concentrations, thereby increasing the likelihood of therapeutic failure. Limited clinical research suggests that intake of garlic and vitamin C results in reductions in ARV concentrations. The intake of milk thistle, Echinacea species, and goldenseal inhibits cytochrome P450 enzymes in vitro and may increase ARV concentrations, but by clinically unimportant amounts. Intake of fish oil reduces ARV-induced hypertriglyceridemia without significantly affecting lopinavir concentrations. Before recommending the use of NHPs as adjuncts to ARV use, studies should first exclude significant pharmacokinetic interactions and ensure that ARV efficacy is maintained.

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.

NATURAL HEALTH PRODUCTS AND DRUG DISPOSITION

Botanicals such as herbal products (HPs) and nutraceuticals (NCs) are often regarded as low risk because of their long history of human use. Anecdotal and literature reports of adverse drug events (ADEs) and clinical studies with HPs are increasing, but many of the reports are incomplete and contradictory. These reports need to identify confounding factors and explain contradictory findings if they are to help health care professionals or patients understand what risks are involved. HPs are complex botanicals, not single-active ingredient (SAI) products. Studies can be confounded by different manufacturing processes and formulations, including cosmetics and food supplements; environment; chemotypes; misidentification or adulteration; and factors associated with the patient or user population such as use, total drug load, and genetics. Future studies need to be conducted with characterized product that includes all commercially available related products. Clinical trials should be relevant to the user population and take into account the confounding factors that may influence the interpretation of the findings.

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.

Capillary zone electrophoresis as a tool for the quality control of goldenseal extracts

The root extracts of goldenseal (Hydrastis canadensis L.) are popular phytomedicines for the treatment of gastrointestinal disorders and upper respiratory tract infections. Here we describe a simple and fast capillary zone electrophoresis (CZE) method with ultraviolet detection at 225 nm for the quantification of the major goldenseal constituents, berberine and hydrastine, in herbal remedies containing goldenseal root extracts. Tritoqualine, an antihistaminic drug with a hydrastine-like phthalidisoquinoline structure, was applied as an internal standard. The running buffer was a 1:5 mixture of 500 mM ammonium acetate (adjusted to pH 3.4 with acetic acid) and methanol. Our newly developed CZE method was validated regarding limit of detection (LOD), limit of quantification, linearity, accuracy and precision. For both berberine and hydrastine, the LOD was 1.0 microg/mL and the linearity was obtained between 2.5 and 500 microg/mL. Using our newly developed method, both the alkaloids could be analysed in herbal remedies containing goldenseal root extracts within 8 min.

Drug interactions in the management of HIV infection

The availability of antiretroviral therapy has significantly reduced the morbidity and mortality of HIV infection. In addition, improved treatment of opportunistic infections and comorbidities common to patients with HIV is further prolonging the lives of patients. Improvement in the treatment of HIV has led to a significant increase in the number of medications which caregivers are able to utilise to manage HIV/AIDS. Antiretroviral medications, as well as many of the drugs used in the management of opportunistic infections and primary care (e.g., macrolide antibiotics, azole antifungals, cholesterol-lowering medications), are particularly prone to drug interactions. The interpretation of clinically significant interactions is complicated by the rate at which new information on drug metabolism and transport is becoming available. Management of drug interactions in HIV is further confounded by conflicting study results and differences between documented and theoretical inter-actions. The mechanisms and significance of interactions involving antiretrovirals, drugs used for opportunistic infections, and other medications commonly used in HIV patients will be reviewed.