Effect of continuous silymarin administration on oral talinolol pharmacokinetics in healthy volunteers

Current perspectives in herbal and conventional drug interactions based on clinical manifestations

Background

Herbs are an important source of pharmaceuticals. Herbs are traditionally used by millions of peoples for medicine, food and drink in developed and developing nations considering that they are safe. But, interaction of herbs with other medicines may cause serious adverse effects or reduces their efficacy. The demand for “alternative” medicines has been increased significantly, which include medicine derived from plant or herbal origin. The objective of this review article mainly focuses on drug interactions of commonly used herbs along with possible mechanisms. The method adopted for this review is searching of herb-drug interactions in online database.

Main text

Herb-drug interaction leads to pharmacological modification. The drug use along with herbs may show pharmacodynamic and pharmacokinetic interactions. Pharmacokinetic interaction causes alteration in absorption, distribution, metabolism and elimination. Similarly, pharmacodynamic interaction causes additive or synergistic or antagonist effect on the drugs or vice versa. Researchers had demonstrated that herbs show the toxicities and drug interactions like other pharmacologically active compounds. There is lack of knowledge amongst physician, pharmacist and consumers related to pharmacological action and mechanism of herb-drug interaction. This review article focuses on the herb-drug interaction of danshen (Salvia miltiorrhiza), Echinacea (Echinacea purpurea), garlic (Allium sativum), ginkgo (Ginkgo biloba), goldenseal (Hydrastis canadensis), green tea (Camellia sinensis), kava (Piper methysticum), liquorice (Glycyrrhiza glabra), milk thistle (Silybum marianum) and St. John’s wort (Hypericum perforatum) along with probable mechanisms and clinical manifestation based on case studies reported in literature.

Conclusion

Herb-drug interactions may lead to serious side effects. Physician, pharmacist and patients must be more cautious while prescribing and or consuming these herbs.

Systematic review of pharmacokinetics and potential pharmacokinetic interactions of flavonolignans from silymarin

Silymarin is an extract from the seeds (fruits) of Silybum marianum that contains flavonolignans and flavonoids. Although it is frequently used as a hepatoprotective agent, its application remains somewhat debatable, in particular, due to the low oral bioavailability of flavonolignans. Moreover, there are claims of its potential interactions with concomitantly used drugs. This review aims at a systematic summary and critical assessment of known information on the pharmacokinetics of particular silymarin flavonolignans. There are two known major reasons for poor systemic oral bioavailability of flavonolignans: (1) rapid conjugation in intestinal cells or the liver and (2) efflux of parent flavonolignans or formed conjugates back to the lumen of the gastrointestinal tract by intestinal cells and rapid excretion by the liver into the bile. The metabolism of phase I appears to play a minor role, in contrast to extensive conjugation and indeed the unconjugated flavonolignans reach low plasma levels after common doses. Only about 1%-5% of the administered dose is eliminated by the kidneys. Many in vitro studies tested the inhibitory potential of silymarin and its components toward different enzymes and transporters involved in the absorption, metabolism, and excretion of xenobiotics. In most cases, effective concentrations are too high to be relevant under real biological conditions. Most human studies showed no silymarin-drug interactions explainable by these suggested interferences. More interactions were found in animal studies, likely due to the much higher doses administered.

Triglyceride-induced cardiac lipotoxicity is mitigated by Silybum marianum

BACKGROUND AND AIMS

Silybum marianum (SM) is an herbal product with cytoprotective and antioxidant properties. We have previously demonstrated that SM ameliorates ventricular remodeling and improves cardiac performance. Here, we evaluated whether SM could exert beneficial effects against cardiac lipotoxicity in a pig model of closed-chest myocardial infarction (MI).

METHODS

Study 1 investigated the effect of SM administration on lipid profile and any potential SM-related adverse effects. Animals received SM or placebo during 10 days and were afterward sacrificed. Study 2 evaluated the effectiveness of SM daily administration in reducing cardiac lipotoxicity in animals subjected to a 1.5h myocardial infarction (MI), who were subsequently reperfused for 2.5h and euthanized or kept under study for three weeks and then sacrificed.

RESULTS

Animals administered a 10-day SM regime presented a sharp decline in plasma triglyceride levels vs. controls, with no other modifications in lipid profile. The decrease in triglyceride concentration was accompanied by a marked reduction in triglyceride intestinal absorption and glycoprotein-P expression. Three weeks post-MI the triglyceride content in the ischemic myocardium of the SM-treated animals was significantly lower than in the ischemic myocardium of placebo-controls. This effect was associated with an enhanced cardiac expression of PPARγ and triglyceride clearance receptors. This long-term SM-administration induced a lower expression of lipid receptors in subcutaneous adipose tissue. No SM-related side-effects were registered.

CONCLUSION

SM administration reduces plasma triglyceride levels through attenuation of triglyceride intestinal absorption and modulates cardiac lipotoxicity in the ischemic myocardium, likely contributing to improve ventricular remodeling.

Effects of breviscapine and C3435T MDR1 gene polymorphism on the pharmacokinetics of fexofenadine, a P-glycoprotein substrate, in healthy volunteers

Breviscapine (BRE) is usually used for long-term use in patients with cardiovascular diseases such as coronary heart disease, angina pectoris, and cerebral thrombosis. It is possible to combine it with P-glycoprotein (P-gp) substrates in clinic. At present, little is known about whether the simultaneous use of BRE affects the disposal of P-gp substrates. The aim of this study was to evaluate the effect of BRE on the pharmacokinetics of fexofenadine (FEX), a P-gp probe substrate and its associations with the MDR1 C3435T genetic polymorphism in healthy volunteers. In this randomised, open-label, placebo-controlled, two-phase crossover clinical study, drug interactions were evaluated in healthy volunteers. FEX was used as a phenotypic probe for P-gp. In each phase, 18 volunteers were given daily doses of 120 mg (40 mg, three times a day) of BRE tablet or a placebo for 14 days. On day 15, a single oral dose of 120 mg FEX hydrochloride was given orally. Blood samples were collected at predefined time intervals, and plasma levels of FEX were determined by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The pharmacokinetic parameters were calculated by non-compartmental method, and bioequivalence was evaluated. Results showed that BRE pretreatment did not significantly affect the pharmacokinetics of FEX. The peak maximum plasma concentration (C _max) and the area under the plasma concentration-time curve from zero to infinity (AUC_inf) mean value of FEX with BRE and placebo-treated groups were 699 ng/mL vs. 710 ng/mL and 2972.5 ng⋅h/mL vs. 3460.5 ng⋅h/mL, respectively. The geometric mean ratios (90% confidence intervals) for FEX C _max and AUC_inf were within the pre-specified range of 0.8-1.25, indicating that FEX in the two pretreatment phases were bioequivalent. Pharmacokinetic parameters of FEX showed no statistically significant difference between MDR1 C3435T CC, CT and TT genotype, revealing that BRE and MDR1 C3435T gene polymorphisms did not affect the pharmacokinetics of FEX in healthy volunteers.

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).

Recent insight on improving the iron chelation efficacy of deferasirox by adjuvant therapy in transfusion dependent beta thalassemia children with sluggish response

Background: Deferasirox is the first line of treatment in iron overload. In spite of the many studies concerning the efficacy of deferasirox, some patients remain unresponsive to deferasirox.Methods: One hundred and sixty patients were enrolled in stratified-randomized controlled study. Patients were randomly divided into four regimens, group I (n = 40) received 30 mg/kg deferasirox, group II (n = 40) received 20 mg omeprazole and 30 mg/kg deferasirox, group III (n = 40) received 400 mg vitamin E and 30 mg/kg deferasirox and group IV (n = 40) received 420 mg silymarin and 30 mg/kg deferasirox. Blood specimens were collected from each patient for up to 24 h, and then plasma deferasirox concentrations were inspected.Results: Silymarin, Vitamin E, and omeprazole significantly increased the peak plasma concentration of deferasirox (P < 0.001) by 27.9, 14.9 and 2.4 fold, respectively, as compared to deferasirox alone. The bioavailability of deferasirox was improved up to 3.03, 3.57, and 4.98-fold, respectively, following administration of omeprazole, vitamin E, and silymarin compared to deferasirox alone.Conclusion: Silymarin, vitamin E, and omeprazole represent promising adjuvant therapy to improve the chelation efficacy of deferasirox that might also be further applied to enhance the pharmacokinetics of deferasirox to overcome the lack of response.

Metabolism, Transport and Drug-Drug Interactions of Silymarin

Silymarin, the extract of milk thistle, and its major active flavonolignan silybin, are common products widely used in the phytotherapy of liver diseases. They also have promising effects in protecting the pancreas, kidney, myocardium, and the central nervous system. However, inconsistent results are noted in the different clinical studies due to the low bioavailability of silymarin. Extensive studies were conducted to explore the metabolism and transport of silymarin/silybin as well as the impact of its consumption on the pharmacokinetics of other clinical drugs. Here, we aimed to summarize and highlight the current knowledge of the metabolism and transport of silymarin. It was concluded that the major efflux transporters of silybin are multidrug resistance-associated protein (MRP2) and breast cancer resistance protein (BCRP) based on results from the transporter-overexpressing cell lines and MRP2-deficient (TR-) rats. Nevertheless, compounds that inhibit the efflux transporters MRP2 and BCRP can enhance the absorption and activity of silybin. Although silymarin does inhibit certain drug-metabolizing enzymes and drug transporters, such effects are unlikely to manifest in clinical settings. Overall, silymarin is a safe and well-tolerated phytomedicine.

Interaction of herbal products with prescribed medications: A systematic review and meta-analysis

Although several studies on pharmacokinetic and/or pharmacodynamic herb-drug interactions (HDI) have been conducted in healthy volunteers, there is large uncertainty on the validity of these studies. A qualitative review and a meta-analysis were performed to establish the clinical evidence of these interaction studies. Out of 4026 screened abstracts, 32 studies were included into the qualitative analysis. The meta-analysis was performed on eleven additional studies. St. John's wort (SJW) significantly decreased the AUC (p < 0.0001) and clearance (p = 0.007) of midazolam. Further subgroup analysis identified age to affect C_max of midazolam (p < 0.01) in the presence of SJW. Echinacea purpurea (EP) significantly increased the clearance of midazolam (p = 0.01). Evidence of publication bias (p > 0.001) was shown on the effect of the herbal products o half-life of midazolam. Green tea (GT) showed significant 85% decrease in plasma concentration of nadolol. The study findings suggest that GT, SJW and EP perpetuate significant interactions with prescribed medications via CYP3A4 or OATP1A2. Our studies show that meta-analyses are important in the area of natural products to provide necessary information on their use in overall medication plans in order to avoid unintended interactions.

A regulatory science viewpoint on botanical-drug interactions

There is a continued predisposition of concurrent use of drugs and botanical products. Consumers often self-administer botanical products without informing their health care providers. The perceived safety of botanical products with lack of knowledge of the interaction potential poses a challenge for providers and both efficacy and safety concerns for patients. Botanical–drug combinations can produce untoward effects when botanical constituents modulate drug metabolizing enzymes and/or transporters impacting the systemic or tissue exposure of concomitant drugs. Examples of pertinent scientific literature evaluating the interaction potential of commonly used botanicals in the US are discussed. Current methodologies that can be applied to advance our efforts in predicting drug interaction liability is presented. This review also highlights the regulatory science viewpoint on botanical–drug interactions and labeling implications.

Phytotherapeutics: The Emerging Role of Intestinal and Hepatocellular Transporters in Drug Interactions with Botanical Supplements

In herbalism, botanical supplements are commonly believed to be safe remedies, however, botanical supplements and dietary ingredients interact with transport and metabolic processes, affecting drug disposition. Although a large number of studies have described that botanical supplements interfere with drug metabolism, the mode of their interaction with drug transport processes is not well described. Such interactions may result in serious undesired effects and changed drug efficacy, therefore, some studies on interaction between botanical supplement ingredients and drug transporters such as P-gp and OATPs are described here, suggesting that the interaction between botanical supplements and the drug transporters is clinically significant.

Herb-drug interactions: challenges and opportunities for improved predictions

Supported by a usage history that predates written records and the perception that "natural" ensures safety, herbal products have increasingly been incorporated into Western health care. Consumers often self-administer these products concomitantly with conventional medications without informing their health care provider(s). Such herb-drug combinations can produce untoward effects when the herbal product perturbs the activity of drug metabolizing enzymes and/or transporters. Despite increasing recognition of these types of herb-drug interactions, a standard system for interaction prediction and evaluation is nonexistent. Consequently, the mechanisms underlying herb-drug interactions remain an understudied area of pharmacotherapy. Evaluation of herbal product interaction liability is challenging due to variability in herbal product composition, uncertainty of the causative constituents, and often scant knowledge of causative constituent pharmacokinetics. These limitations are confounded further by the varying perspectives concerning herbal product regulation. Systematic evaluation of herbal product drug interaction liability, as is routine for new drugs under development, necessitates identifying individual constituents from herbal products and characterizing the interaction potential of such constituents. Integration of this information into in silico models that estimate the pharmacokinetics of individual constituents should facilitate prospective identification of herb-drug interactions. These concepts are highlighted with the exemplar herbal products milk thistle and resveratrol. Implementation of this methodology should help provide definitive information to both consumers and clinicians about the risk of adding herbal products to conventional pharmacotherapeutic regimens.

Effects of single or repeated silymarin administration on pharmacokinetics of risperidone and its major metabolite, 9-hydroxyrisperidone in rats

1. The interactions between herbal dietary supplements and therapeutic drugs have emerged as an important issue and P-glycoprotein (P-gp) has been reported as one of the significant factors of these interactions. 2. The objective of this article is to examine the effects of single and repeated administrations of silymarin on pharmacokinetics of a P-gp substrate, risperidone, and its major metabolite, 9-hydroxyrisperidone, in rats. 3. To determine the plasma levels of risperidone and 9-hydroxyrisperidone in rats, a HPLC method was developed using a liquid-liquid acid back extraction. When risperidone (6 mg/kg) was co-administered with silymarin (40 mg/kg) to rats orally, the C(max) of 9-hydroxyrisperidone was significantly increased to1.3-fold (p < 0.05), while the other pharmacokinetic parameters did not show any significant differences. Expanding the experiment where rats were repeatedly administered with silymarin for 5 days prior to giving risperidone, the C(max) of risperidone and 9-hydroxyrisperidone were significantly increased to 2.4-fold (p < 0.001) and 1.7-fold (p < 0.001), respectively, and the AUC(0-t), as well to 1.7-fold (p < 0.05) and 2.1-fold (p < 0.01), respectively. 4. The repeated exposures of silymarin, compared to single administration of silymarin, increased oral bioavailability and affected the pharmacokinetics of risperidone and 9-hydroxyrisperidone, by inhibiting P-gp.

In vivo probes of drug transport: commonly used probe drugs to assess function of intestinal P-glycoprotein (ABCB1) in humans

Intestinal P-glycoprotein (P-gp, ABCB1) may significantly influence drug absorption and elimination. Its expression and function is highly variable, regio-selective and influenced by genetic polymorphisms, drug interactions and intestinal diseases. An in vivo probe drug for intestinal P-gp should a registered, safe and well tolerated nonmetabolized selective substrate with low protein binding for which P-gp is rate-limiting during absorption. Other P-gp dependent processes should be of minor influence. The mechanism(s) and kinetics of intestinal uptake must be identified and quantified. Moreover, the release properties of the dosage form should be known. So far, the cardiac glycoside digoxin and the ß₁-selective blocker talinolol have been used in mechanistic clinical studies, because they meet most of these criteria. Digoxin and talinolol are suitable in vivo probe drugs for intestinal P-gp under the precondition, that they are used as tools in carefully designed pharmacokinetic studies with adequate biometrically planning of the sample size and that several limitations are considered in interpreting and discussion of the study results.