In vitro interactions of water-soluble garlic components with human cytochromes p450

Dietary supplements, cytochrome metabolism, and pharmacogenetic considerations

BACKGROUND

Dietary supplement use has continued to rise. In addition to supplement-drug interactions, it is prudent to consider how dietary supplements may interact with a patient's specific pharmacogenetics. Variations in genes associated with CYP 450 enzymes have evidence of impacting drug metabolism and adverse effects.

AIMS

This research was performed to evaluate CYP P450 enzyme activity of the top 15 dietary supplements used in the USA in order to initiate pharmacogenetic considerations specific to commonly used dietary supplements.

METHODS

The most common dietary supplements used in the USA were obtained from the National Health and Nutrition Examination Survey (NHANES). Primary literature detailing supplement CYP P450 activity was compiled from PubMed using MeSH search terms: supplement name(s), cytochrome P450 enzymes, metabolism, and pharmacokinetics. Additional resources utilized for documented CYP enzyme genotypes were the pharmacogenetic databases from Clinical Pharmacogenetics Implementation Consortium and The Pharmacogenomic Variation Consortium.

RESULTS

Of the 15 most common dietary supplements used in the USA, 53% (cranberry, echinacea, garlic, ginkgo biloba, ginseng, melatonin, milk thistle, and valerian) exhibit CYP P450 metabolism, with some having possible induction activity as well. Melatonin and garlic are substrates of CYP1A2 and CYP2C19, respectively. Additionally, there is evidence of echinacea having possible CYP3A4 induction activity.

CONCLUSION

CYP P450 activity is an important consideration for any patient but becomes increasingly critical if patients have certain CYP P450 phenotypes that impact metabolism. These popular supplements have the potential for changes in supplement exposure, and adverse effects based on pharmacogenetic profiles. Furthermore, these sites of metabolism are shared with many medications, setting the stage for possibly more profound interactions between medications and supplements. This paper highlights the mechanisms in which dietary supplements may constitute a risk for patients with certain CYP P450 phenotypes. Further research is needed in the area of dietary supplements and their pharmacogenomic implications.

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).

Potential inhibition of major human cytochrome P450 isoenzymes by selected tropical medicinal herbs-Implication for herb-drug interactions

BACKGROUND

Increasing use of medicinal herbs as nutritional supplements and traditional medicines for the treatment of diabetes, hypertension, hyperlipidemia, and malaria fever with conventional drugs poses possibilities of herb-drug interactions (HDIs). The potential of nine selected widely used tropical medicinal herbs in inhibiting human cytochrome P450 (CYP) isoenzymes was investigated.

MATERIALS AND METHODS

In vitro inhibition of eight major CYP isoenzymes by aqueous extracts of Allium sativum, Gongronema latifolium, Moringa oleifera, Musa sapientum, Mangifera indica, Tetracarpidium conophorum, Alstonia boonei, Bauhinia monandra, and Picralima nitida was estimated in human liver microsomes by monitoring twelve probe metabolites of nine probe substrates with UPLC/MS-MS using validated N-in-one assay method.

RESULTS

Mangifera indica moderately inhibited CYP2C8, CYP2B6, CYP2D6, CYP1A2, and CYP2C9 with IC 50 values of 37.93, 57.83, 67.39, 54.83, and 107.48 μg/ml, respectively, and Alstonia boonei inhibited CYP2D6 (IC 50 = 77.19 μg/ml). Picralima nitida inhibited CYP3A4 (IC 50 = 45.58 μg/ml) and CYP2C19 (IC 50 = 73.06 μg/ml) moderately but strongly inhibited CYP2D6 (IC 50 = 1.19 μg/ml). Other aqueous extracts of Gongronema latifolium, Bauhinia monandra, and Moringa oleifera showed weak inhibitory activities against CYP1A2. Musa sapientum, Allium sativum, and Tetracarpidium conophorum did not inhibit the CYP isoenzymes investigated.

CONCLUSION

Potential for clinically important CYP-metabolism-mediated HDIs is possible for Alstonia boonei, Mangifera indica, and Picralima nitida with drugs metabolized by CYP 2C8, 2B6, 2D6, 1A2, 2C9, 2C19, and 3A4. Inhibition of CYP2D6 by Picralima nitida is of particular concern and needs immediate in vivo investigations.

Greater Protective Potent of s-Methyl Cysteine and Syringic Acid Combination for NGF-differentiated PC12 Cells against Kainic acid-induced Injury

Objective: The effects of pre-treatments from s-methyl cysteine (SMC) alone, syringic acid (SA) alone and SMC plus SA against kainic acid (KA) induced injury in nerve growth factor (NGF) differentiated PC12 cells were investigated. Methods: NGF-differentiated PC12 cells were treated with 1 μM SMC, 1 μM SA or 0.5 μM SMC plus 0.5 μM SA for 2 days. Subsequently, cells were further treated by 150 μM KA. Results: KA suppressed Bcl-2 mRNA expression, enhanced Bax mRNA expression and casued cell death. SMC was greater than SA, and similar as SMC+SA in increasing Bcl-2 mRNA expression. SMC+SA led to greater increase in mitochondrial membrane potential and cell survival than SMC or SA alone. SMC+SA resulted in more reduction in reactive oxygen species and tumor necrosis factor-alpha generation, more increase in glutathione content and glutathione reductase activity than SMC or SA alone. KA up-regulated protein expression of nuclear factor kappa B (NF-κB) p65 and phosphorylated p38 (p-p38). SMC or SA pre-treatments alone limited protein expression of both factors. SMC+SA resulted in more suppression in NF-κB p65 and p-p38 expression. KA decreased glutamine level, increased glutamate level and stimulated calcium release. SMC pre-treatments alone reversed these alterations. SMC alone elevated glutamine synthetase (GS) activity and mRNA expression. SMC+SA led to greater GS activity and mRNA expression than SMC pre-treatments alone. Conclusion: These findings suggested that this combination, SMC+SA, might provide greater protective potent for neuronal cells.

Research and Development of Atractylodes lancea (Thunb) DC. as a Promising Candidate for Cholangiocarcinoma Chemotherapeutics

Treatment and control of cholangiocarcinoma (CCA): the bile duct cancer is limited by the lack of effective chemotherapeutic drugs and alternative drugs are needed, particularly those from natural sources. This article reviews steps of research and development of Atractylodes lancea (Thunb) DC. (AL) as potential candidate for CCA chemotherapy, with adoption of the reverse pharmacology approach. Major steps include (1) reviewing of existing information on its phytochemistry and pharmacological properties, (2) screening of its activities against CCA, (3) standardization of AL, (4) nonclinical studies to evaluate anti-CCA activities, (5) phytochemistry and standardization of AL extract, (6) development of oral pharmaceutical formulation of standardized AL extract, and (7) toxicity testing of oral pharmaceutical formulation of standardized AL extract. Results from a series of our study confirm anti-CCA potential and safety profiles of both the crude extract and the finished product (oral pharmaceutical formulation of the standardized AL extract). Phases I and II clinical trials of the product to confirm tolerability and efficacy in healthy subjects and patients with advanced stage CCA will be carried out soon.

Evaluation of the Effects of S-Allyl-L-cysteine, S-Methyl-L-cysteine, trans-S-1-Propenyl-L-cysteine, and Their N-Acetylated and S-Oxidized Metabolites on Human CYP Activities

Three major organosulfur compounds of aged garlic extract, S-allyl-L-cysteine (SAC), S-methyl-L-cysteine (SMC), and trans-S-1-propenyl-L-cysteine (S1PC), were examined for their effects on the activities of five major isoforms of human CYP enzymes: CYP1A2, 2C9, 2C19, 2D6, and 3A4. The metabolite formation from probe substrates for the CYP isoforms was examined in human liver microsomes in the presence of organosulfur compounds at 0.01-1 mM by using liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Allicin, a major component of garlic, inhibited CYP1A2 and CYP3A4 activity by 21-45% at 0.03 mM. In contrast, a CYP2C9-catalyzed reaction was enhanced by up to 1.9 times in the presence of allicin at 0.003-0.3 mM. SAC, SMC, and S1PC had no effect on the activities of the five isoforms, except that S1PC inhibited CYP3A4-catalyzed midazolam 1'-hydroxylation by 31% at 1 mM. The N-acetylated metabolites of the three compounds inhibited the activities of several isoforms to a varying degree at 1 mM. N-Acetyl-S-allyl-L-cysteine and N-acetyl-S-methyl-L-cysteine inhibited the reactions catalyzed by CYP2D6 and CYP1A2, by 19 and 26%, respectively, whereas trans-N-acetyl-S-1-propenyl-L-cysteine showed weak to moderate inhibition (19-49%) of CYP1A2, 2C19, 2D6, and 3A4 activities. On the other hand, both the N-acetylated and S-oxidized metabolites of SAC, SMC, and S1PC had little effect on the reactions catalyzed by the five isoforms. These results indicated that SAC, SMC, and S1PC have little potential to cause drug-drug interaction due to CYP inhibition or activation in vivo, as judged by their minimal effects (IC₅₀>1 mM) on the activities of five major isoforms of human CYP in vitro.

Inhibitory Activities of Thai Medicinal Plants with Promising Activities Against Malaria and Cholangiocarcinoma on Human Cytochrome P450

Malaria and cholangiocarcinoma remain important public health problems in tropical countries including Southeast Asian nations. Newly developed chemotherapeutic and plant-derived drugs are urgently required for the control of both diseases. The aim of the present study was to investigate the propensity to inhibit cytochrome P450-mediated hepatic metabolism (CYP1A2, CYP2C19, CYP2D6 and CYP3A4) of the crude ethanolic extract of eight Thai medicinal plants with promising activities against malaria and cholangiocarcinoma, using human liver microsomes in vitro. Piper chaba Linn. (PC) and Atractylodes lancea (thung.) DC. (AL) exhibited the most potent inhibitory activities on CYP1A2-mediated phenacetin O-deethylation with mean IC50 of 0.04 and 0.36 µg/mL, respectively. Plumbago indica Linn. (PI) and Dioscorea membranacea Pierre. (DM) potently inhibited CYP2C19-mediated omeprazole 5-hydroxylation (mean IC50 4.71 and 6.92 µg/mL, respectively). DM, Dracaena loureiri Gagnep. (DL) and PI showed the highest inhibitory activities on dextromethorphan O-demethylation (mean IC50 2.93-9.57 µg/mL). PC, DM, DL and PI exhibited the most potent inhibitory activities on CYP3A4-mediated nifedipine oxidation (mean IC50 1.54-6.43 µg/mL). Clinical relevance of the inhibitory potential of DM, PC and PI is of concern for the further development of these plants for the treatment of malaria and/or cholangiocarcinoma.

The use of plants in the traditional management of diabetes in Nigeria: pharmacological and toxicological considerations

ETHNOPHARMACOLOGICAL RELEVANCE

The prevalence of diabetes is on a steady increase worldwide and it is now identified as one of the main threats to human health in the 21st century. In Nigeria, the use of herbal medicine alone or alongside prescription drugs for its management is quite common. We hereby carry out a review of medicinal plants traditionally used for diabetes management in Nigeria. Based on the available evidence on the species׳ pharmacology and safety, we highlight ways in which their therapeutic potential can be properly harnessed for possible integration into the country׳s healthcare system.

MATERIALS AND METHODS

Ethnobotanical information was obtained from a literature search of electronic databases such as Google Scholar, Pubmed and Scopus up to 2013 for publications on medicinal plants used in diabetes management, in which the place of use and/or sample collection was identified as Nigeria. 'Diabetes' and 'Nigeria' were used as keywords for the primary searches; and then 'Plant name - accepted or synonyms', 'Constituents', 'Drug interaction' and/or 'Toxicity' for the secondary searches.

RESULTS

The hypoglycemic effect of over a hundred out of the 115 plants reviewed in this paper is backed by preclinical experimental evidence, either in vivo or in vitro. One-third of the plants have been studied for their mechanism of action, while isolation of the bioactive constituent(s) has been accomplished for twenty three plants. Some plants showed specific organ toxicity, mostly nephrotoxic or hepatotoxic, with direct effects on the levels of some liver function enzymes. Twenty eight plants have been identified as in vitro modulators of P-glycoprotein and/or one or more of the cytochrome P450 enzymes, while eleven plants altered the levels of phase 2 metabolic enzymes, chiefly glutathione, with the potential to alter the pharmacokinetics of co-administered drugs.

CONCLUSION

This review, therefore, provides a useful resource to enable a thorough assessment of the profile of plants used in diabetes management so as to ensure a more rational use. By anticipating potential toxicities or possible herb-drug interactions, significant risks which would otherwise represent a burden on the country׳s healthcare system can be avoided.

Herbal-drug interaction induced rhabdomyolysis in a liposarcoma patient receiving trabectedin

BACKGROUND

Rhabdomyolysis is an uncommon side effect of trabectedin which is used for the second line therapy of metastatic sarcoma after anthracycline and ifosfamide failure. This side effect may be due to pharmacokinetic interactions caused by shared mechanisms of metabolism involving the cytochrome P450 (CYP) system in the liver. Here, for the first time in literature, we describe the unexpected onset of heavy toxicity, including rhabdomyolysis, after the fourth course of trabectedin in a patient with retroperitoneal liposarcoma who at the same time was taking an alternative herbal medicine suspected of triggering this adverse event.

CASE PRESENTATION

This is the case of a 56 year old Caucasian man affected by a relapsed de-differentiated liposarcoma who, after the fourth cycle of second-line chemotherapy with trabectedin, complained of sudden weakness, difficulty walking and diffuse muscle pain necessitating complete bed rest. Upon admission to our ward the patient showed grade (G) 4 pancytopenia and a marked increase in liver lytic enzymes, serum levels of myoglobin, creatine phosphokinase (CPK) and lactate dehydrogenase. No cardiac or kidney function injuries were present. Based on these clinical and laboratory features, our conclusive diagnosis was of rhabdomyolysis induced by trabectedin.The patient did not report any trauma or muscular overexertion and no co-morbidities were present. He had not received any drugs during treatment with trabectedin, but upon further questioning the patient informed us he had been taking a folk medicine preparation of chokeberry (Aronia melanocarpa) daily during the last course of trabectedin and in the 2 subsequent weeks.One week after hospitalization and cessation of intake of chokeberry extract, CPK and other markers of myolysis slowly returned to standard range, and the patient noted a progressive recovery of muscle strength.The patient was discharged on day 14 when a blood transfusion and parenteral hydration gradually lowered general toxicity. Progressive mobilization of the patient was obtained as well as a complete normalization of the laboratory findings.

CONCLUSIONS

The level of evidence of drug interaction leading to the adverse event observed in our patient was 2 (probable). Thus our case underlines the importance of understanding rare treatment-related toxicities such as trabectedin-induced rhabdomyolysis and the possible role of the drug-drug interactions in the pathogenesis of this rare side effect. Furthermore, this report draws attention to a potential problem of particular concern, that of nutritional supplements and complementary and alternative drug interactions. These are not widely recognized and can cause treatment failure.

Garlic and cardioprotection: insights into the molecular mechanisms

Garlic is widely recognized for its immense therapeutic potential. Garlic has been shown to exert its beneficial effects against a wide spectrum of diseases, including cancer, diabetes, and microbial infections, as well as immunological and cardiovascular disorders. Most of the research on garlic has indicated that garlic and its active compounds are effective in reducing cardiovascular and metabolic risk by normalizing abnormal plasma lipids, oxidized low density lipoproteins, abnormal platelet aggregation, high blood pressure, and cardiac injury. Some of the beneficial effects of dietary garlic against cardiovascular disorders are mediated via the generation of hydrogen sulfide and nitric oxide in cardiomyocytes and endothelial cells. Garlic has the potential to protect the heart against myocardial infarction, doxorubicin-induced cardiotoxicity, arrhythmia, hypertrophy, and ischemia-reperfusion injury. The induction of cardiac endogenous antioxidants and the reduction of lipid peroxidation by garlic has been reported by several different groups. Other mechanisms, such as regulating ion channels, modulating Akt signaling pathways, histone deacetylase inhibition, and cytochrome P450 inhibition, could be responsible for the cardioprotective effect of garlic. Although several mechanisms have been identified for the cardioprotective effect of garlic, there is a need for further research to identify the specific molecular mechanism of cardioprotection in different cardiac diseases.

The effect of garlic supplements and phytochemicals on the ADMET properties of drugs

INTRODUCTION

Garlic supplements have received wide public attention because of their health-beneficial effects. Although these products are considered as innocuous, several case reports and studies have shown the capacity of individual garlic phytochemicals/supplements to interfere with drug pharmacokinetics.

AREAS COVERED

This review covers recently published literature on garlic chemistry and composition, and provides a thorough review of published studies evaluating drug-garlic interactions. The authors illustrate the mechanisms underlying pharmacokinetic interactions, which could serve as important highlights in further research to explain results for drugs with narrow therapeutic indices or for drugs, utilizing multiple absorption, distribution and metabolism pathways.

EXPERT OPINION

To increase the relevance of further research on safety and efficacy of garlic supplements and phytochemicals, their composition should be addressed before conducting in vitro or in vivo research. It is also strongly recommended to characterize in vitro formulation performance to assess the rate and extent of garlic phytochemical release in order to anticipate the in vivo impact on the pharmacokinetics of concomitantly consumed drugs. The main conclusion of this review is that the impact of garlic on different stages of pharmacokinetics, especially on drug absorption and metabolism, is drug specific and dependent on the type/quality of utilized supplement.

Effects of Garlic on Cytochromes P450 2C9- and 3A4-Mediated Drug Metabolism in Human Hepatocytes

Several reports suggest garlic supplements may inhibit the metabolism of cytochrome P450 (CYP) 2C9 and CYP3A4 substrates, such as warfarin and saquinavir. To characterize the effects of garlic extract on CYP2C9 and CYP3A4 enzyme activity immortalized human hepatocytes (Fa2N-4 cells) were exposed to garlic extract (0-200 μg/mL). CYP2C9 and CYP3A4 enzyme activities were evaluated in parallel with enzymatic activities, expression of respective RNA transcripts was also assessed.Exposure to increasing concentrations of garlic extract led to progressive reduction in Fa2N-4 CYP2C9 activity as detected by diclofenac hydroxylation. CYP2C9 mRNA expression also revealed a concentration-dependent reduction. Greater than 90% reduction in CYP2C9 activity was observed following four days of exposure to 50 μg/mL garlic extract. In contrast, exposure to garlic extract had no effect on the CYP3A4 enzymatic activity or RNA transcript concentration in Fa2N-4. Therefore, suppression of CYP2C9 expression and activity is a heretofore unrecognized mechanism by which garlic extract may modulate CYP activity. Exposure of hepatocytes to garlic extract may reduce the expression and activity of CYP2C9 with no detectible effects on CYP3A4.

Drug-botanical interactions: a review of the laboratory, animal, and human data for 8 common botanicals

Many Americans use complementary and alternative medicine (CAM) to prevent or alleviate common illnesses, and these medicines are commonly used by individuals with cancer.These medicines or botanicals share the same metabolic and transport proteins, including cytochrome P450 enzymes (CYP), glucuronosyltransferases (UGTs), and P-glycoprotein (Pgp), with over-the-counter and prescription medicines increasing the likelihood of drug-botanical interactions.This review provides a brief description of the different proteins, such as CYPs, UGTs, and Pgp.The potential effects of drug-botanical interactions on the pharmacokinetics and pharmacodynamics of the drug or botanical and a summary of the more common models used to study drug metabolism are described.The remaining portion of this review summarizes the data extracted from several laboratory, animal, and clinical studies that describe the metabolism, transport, and potential interactions of 8 selected botanicals. The 8 botanicals include black cohosh, Echinacea, garlic, Gingko biloba, green tea, kava, milk thistle, and St John's wort; these botanicals are among some of the more common botanicals taken by individuals with cancer.These examples are included to demonstrate how to interpret the different studies and how to use these data to predict the likelihood of a clinically significant drug-botanical interaction.

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.

In vitro inhibition of CYP3A4 by herbal remedies frequently used by cancer patients

The herbal remedies Natto K2, Agaricus, mistletoe, noni juice, green tea and garlic, frequently used by cancer patients, were investigated for their in vitro inhibition potential of cytochrome P-450 3A4 (CYP3A4) metabolism. To our knowledge, only garlic and green tea had available data on the possible inhibition of CYP3A4 metabolism. Metabolic studies were performed with human c-DNA baculovirus expressed CYP3A4. Testosterone was used as a substrate and ketoconazole as a positive quantitative inhibition control. The formation of 6-beta-OH-testosterone was quantified by a validated HPLC methodology. Green tea was the most potent inhibitor of CYP3A4 metabolism (IC(50): 73 microg/mL), followed by Agaricus, mistletoe and noni juice (1324, 3594, >10 000 microg/mL, respectively). All IC(50) values were high compared with those determined for crude extracts of other herbal remedies. The IC(50)/IC(25) ratios for the inhibiting herbal remedies ranged from 2.15 to 2.67, indicating similar inhibition profiles of the herbal inhibitors of CYP3A4. Garlic and Natto K2 were classified as non-inhibitors. Although Agaricus, noni juice, mistletoe and green tea inhibited CYP3A4 metabolism in vitro, clinically relevant systemic or intestinal interactions with CYP3A4 were considered unlikely, except for a probable inhibition of intestinal CYP3A4 by the green tea product.

Identification and Exploration of Herb-Drug Combinations Used By Cancer Patients

Introduction: This survey aims to identify herb-chemotherapeutic drug combinations in a defined group of cancer patients and to explore possible clinical consequences of these combinations. Methods: Herb-chemotherapeutic drug combinations were identified among adult cancer patients, and clinical consequences of the combinations were explored by literature searches in medical databases on possible mutual effects on similar cytochrome P-450 metabolising enzymes (CYPs) and/or the P-glycoprotein (P-gp) transporter. Results: Among 42 cancer patients using herbal remedies concurrently with chemotherapy, 136 two-agent herb-drug combinations were registered and 47 different potential herb-drug interactions were identified on the level of CYP metabolism and P-gp transport in vitro. Garlic, ginger, green tea and noni juice were the herbal remedies most frequently used in such combinations. For 48 % of the herbal remedies identified no literature data exist on their interaction potentials. Clinical studies were available for four herbal remedies only. Minor clinical potential for CYP interactions in humans was indicated for green tea and Echinacea. P-gp interactions were only investigated for garlic, which showed a significant interaction potential both in vivo and in vitro. Conclusion: The large number of in vitro potential herb-drug interactions identified urge for more clinical pharmacokinetic interaction studies in humans.

Potential of pharmacokinetic profiling for detecting herbal interactions with drugs

The issue of herb-drug interactions has generated significant concern within the pharmaceutical industry and among regulatory authorities in recent years. Therefore, accurate models of predicting metabolic herb-drug interactions would be useful tools in efforts to avoid toxic adverse events. However, the majority of pharmacokinetic interactions listed for herbal medicinal products are based on theoretical predictions of the in vitro pharmacological effects of known constituents, which do not necessarily have to be the active ingredients. The prediction of herb-drug interactions is further complicated by the fact that pharmacokinetic data on active or (at least) known ingredients are often not available. The present article discusses the potential of pharmacokinetic profiling for detecting herb-drug interactions, using the most frequently cited interactions in the literature as examples. In particular, common mechanisms of herb-drug interactions are summarized, and the available experimental methods for detecting such interactions, as well as the limitations of these models, are critically evaluated. In addition, we discuss the question of whether the existing methods of detecting herb-drug interactions correlate with the clinical relevance. Effective screening tools that accurately predict metabolic herb-drug interactions would offer a tremendous advantage because it is not possible to study all potential herb-drug interactions in clinical trials.

Garlic (Allium sativum L.): adverse effects and drug interactions in humans

Garlic (Alllium sativum L., Fam Liliaceae) is used medicinally mainly for the treatment of hypercholesterolemia and prevention of arteriosclerosis. Clinical trials have consistently shown that "garlic breath" and body odor are the most common (and well-documented) complaints associated to garlic intake. Case reports have highlighted the possibility that garlic use may cause allergic reactions (allergic contact dermatitis, generalized urticaria, angiedema, pemphigus, anaphylaxis and photoallergy), alteration of platelet function and coagulation (with a possible risk of bleeding), and burns (when fresh garlic is applied on the skin, particularly under occlusive dressings). Consumption of garlic by nursing mothers modifies their infant's behavior during breast-feeding. Finally, garlic may enhance the pharmacological effect of anticoagulants (e. g. warfarin, fluindione) and reduce the efficacy of anti-AIDS drugs (i. e. saquinavir).