Martha A. Hubbard

Cytochrome P450 phenotypic ratios for predicting herb-drug interactions in humans.

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 St Johns wort, garlic oil, Panax ginseng, and Ginkgo biloba affected CYP1A2, CYP2D6, CYP2E1, or CYP3A4 activity.

Clinical assessment of effects of botanical supplementation on cytochrome P450 phenotypes in the elderly: St John's wort, garlic oil, Panax ginseng and Ginkgo biloba.

ObjectivesElderly patients are more likely to ingest prescription medications concurrently with botanical supplements, and may therefore be vulnerable to herb-drug interactions. Phytochemical-mediated modulation of cytochrome P450 (CYP) activity may underlie many herb-drug interactions. Some evidence suggests that CYP activity may decrease in the elderly. If so, herb-mediated changes in CYP activity may take on greater clinical relevance in this population. In this study, single timepoint, phenotypic metabolic ratios were used to determine whether long-term supplementation of St John’s wort, garlic oil, Panax ginseng, and Ginkgo biloba affected CYP1A2, CYP2D6, CYP2E1 or CYP3A4 activity in elderly subjects.MethodsTwelve healthy volunteers between the ages of 60 and 76 years (mean age 67 years) were randomly assigned to receive each botanical supplement for 28 days followed by a 30-day washout period. Probe drug cocktails of midazolam, caffeine, chlorzoxazone and debrisoquine were administered before and at the end of supplementation. Pre- and post-supplementation phenotypic ratios were determined for CYP3A4, CYP1A2, CYP2E1 and CYP2D6 using 1-hydroxymidazolam/midazolam serum ratios (1-hour), paraxanthine/caffeine serum ratios (6-hour), 6-hydroxychlorzoxazone/chlorzoxazone serum ratios (2-hour) and debrisoquine urinary recovery ratios (8-hour), respectively. The content of purported ‘active’ phytochemicals was determined for each supplement.ResultsComparisons of pre- and post-St John’s wort phenotypic ratios revealed significant induction of CYP3A4 (≈140%) and CYP2E1 activity (≈28%). Garlic oil inhibited CYP2E1 activity by approximately 22%. P. ginseng inhibition of CYP2D6 was statistically significant, but the magnitude of the effect (≈7%) did not appear to be clinically relevant. None of the supplements tested in this study appeared to affect CYP1A2 activity.ConclusionsElderly subjects, like their younger counterparts, are susceptible to herb-mediated changes in CYP activity, especially those involving St John’s wort. Pharmacokinetic herb-drug interactions stemming from alterations in CYP activity may adversely affect drug efficacy and/or toxicity. When compared with earlier studies that employed young subjects, the data suggest that some age-related changes in CYP responsivity to botanical supplementation may exist. Concomitant ingestion of botanical supplements with prescription medications, therefore, should be strongly discouraged in the elderly.

In vivo assessment of botanical supplementation on human cytochrome P450 phenotypes: Citrus aurantium, Echinacea purpurea, milk thistle, and saw palmetto

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 Citrus aurantium, Echinacea purpurea, milk thistle (Silybum marianum), or saw palmetto (Serenoa repens) extracts affected CYP1A2, CYP2D6, CYP2E1, or CYP3A4 activity.

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. Johns 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.

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.

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 studys 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.

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–∞), 107.9±43.3 vs 175.3±74.8 ng·h/ml; Cl/F/kg, 1.26±0.59 vs 0.81±0.45 l/h/kg; T1/2, 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.

Effect of Goldenseal (Hydrastis canadensis) and Kava Kava (Piper methysticum) Supplementation on Digoxin Pharmacokinetics in Humans

Phytochemical-mediated modulation of P-glycoprotein (P-gp) and other drug transporters may give rise to many herb-drug interactions. Serial plasma concentration-time profiles of the P-gp substrate, digoxin, were used to determine whether supplementation with goldenseal or kava kava modified P-gp activity in vivo. Twenty healthy volunteers were randomly assigned to receive a standardized goldenseal (3210 mg daily) or kava kava (1227 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 (Lanoxin, 0.5 mg) was administered p.o. before and at the end of each supplementation and control period. Serial digoxin plasma concentrations were obtained over 24 h and analyzed by chemiluminescent immunoassay. Comparisons of area under the curve (AUC)(0–3), AUC(0–24), Cmax, CL/F, and elimination half-life were used to assess the effects of goldenseal, kava kava, rifampin, and clarithromycin on digoxin pharmacokinetics. Rifampin produced significant reductions (p < 0.01) in AUC(0–3), AUC(0–24), CL/F, t1/2, and Cmax, whereas clarithromycin increased these parameters significantly (p < 0.01). With the exception of goldenseals effect on Cmax (14% increase), no statistically significant effects on digoxin pharmacokinetics were observed following supplementation with either goldenseal or kava kava. When compared with rifampin and clarithromycin, supplementation with these specific formulations of goldenseal or kava kava did not appear to affect digoxin pharmacokinetics, suggesting that these supplements are not potent modulators of P-gp in vivo.

Validation of a liquid chromatography-tandem mass spectrometric assay for the quantitative determination of hydrastine and berberine in human serum

A high throughput liquid chromatography/tandem mass spectrometry (LC-MS/MS) method for the simultaneous determination of berberine and hydrastine in human serum, after oral administration of goldenseal (Hydrastis canadensis L.), was developed using simple acetonitrile treatment of serum samples. Noscapine served as the internal standard. Lower limit of quantification for both analytes was 0.1 ng mL(-1) using positive ion electrospray tandem mass spectrometry (MS/MS). The intra-day (n=5) accuracy and precision of the method for hydrastine was 82+/-8.8%, 97.9+/-2.4% and 96.2+/-3.3%, respectively. The inter-day (n=4) accuracy and precision for hydrastine was 90.0+/-15.17%, 99.9+/-7.1% and 98+/-6.54%, respectively. For berberine quantitation intra-day accuracy and precision was 96.0+/-8.4%, 92.5+/-4.7% and 94.4+/-3.7%, respectively. The respective values for inter-day quantitation were 91.0+/-8.4%, 94.3+/-4.7% and 94.4+/-3.7%. The analytical recovery for hydrastine was 82.4-96.2% and for berberine it was 94.4-96.0%. The analytes and noscapine were stable for 24h at room temperature (CV 5-10%). Matrix ion effects were studied by post-column infusion of hydrastine and berberine, calculation of calibration curve slope precision was obtained using serum from five different subjects, and by comparison of the response of methanol standards and extracted serum samples. The method was further validated by determination of serum pharmacokinetics of hydrastine and berberine after administration of a single oral dose of goldenseal extract containing 77 mg of hydrastine and 132 mg of berberine.

Multiple dosing of ephedra-free dietary supplements: hemodynamic, electrocardiographic, and bacterial contamination effects.

Four popular ephedra‐free dietary supplements were evaluated for their effects on heart rate (HR), blood pressure (BP), and electrocardiographic (ECG) parameters. Twelve healthy men participated in a study randomized for product sequence, with a 21‐day washout period between supplement‐administration phases. Throughout the study, Holter monitors were used to assess ECG and HR activity. BP was assessed automatically on multiple occasions. The supplements were ingested three times daily for 3 days. Caffeine content, microbial load, and serum caffeine concentrations were determined. Mean systolic (SBP) and diastolic BP (DBP) readings showed significant increases relative to baseline (10.8 ± 2.5 and 5.3 ± 3.1 mm Hg, respectively; P < 0.05). All supplements significantly increased HR and decreased bradycardia runs; abnormal atrial/ventricular events were frequently noted. Gastrointestinal and sympathomimetic symptoms were also common. Two supplements were heavily contaminated with Bacillus species. In light of these findings, the use of ephedra‐free dietary supplements should be discouraged in individuals with hypertension, diabetes, or other cardiovascular diseases.