Interaction of drugs and Chinese herbs: pharmacokinetic changes of tolbutamide and diazepam caused by extract of Angelica dahurica

Cytochrome P450 3A4 suppression by epimedium and active compound kaempferol leads to synergistic anti-inflammatory effect with corticosteroid

Introduction: Cytochrome P450 (CYP) 3A4 is a major drug metabolizing enzyme for corticosteroids (CS). Epimedium has been used for asthma and variety of inflammatory conditions with or without CS. It is unknown whether epimedium has an effect on CYP 3A4 and how it interacts with CS. We sought to determine the effects of epimedium on CYP3A4 and whether it affects the anti-inflammatory function of CS and identify the active compound responsible for this effect. Methods: The effect of epimedium on CYP3A4 activity was evaluated using the Vivid CYP high-throughput screening kit. CYP3A4 mRNA expression was determined in human hepatocyte carcinoma (HepG2) cells with or without epimedium, dexamethasone, rifampin, and ketoconazole. TNF-α levels were determined following co-culture of epimedium with dexamethasone in a murine macrophage cell line (Raw 264.7). Active compound (s) derived from epimedium were tested on IL-8 and TNF-α production with or without corticosteroid, on CYP3A4 function and binding affinity. Results: Epimedium inhibited CYP3A4 activity in a dose-dependent manner. Dexamethasone enhanced the expression of CYP3A4 mRNA, while epimedium inhibited the expression of CYP3A4 mRNA and further suppressed dexamethasone enhancement of CYP3A4 mRNA expression in HepG2 cells (p < 0.05). Epimedium and dexamethasone synergistically suppressed TNF-α production by RAW cells (p < 0.001). Eleven epimedium compounds were screened by TCMSP. Among the compounds identified and tested only kaempferol significantly inhibited IL-8 production in a dose dependent manner without any cell cytotoxicity (p < 0.01). Kaempferol in combination with dexamethasone showed complete elimination of TNF-α production (p < 0.001). Furthermore, kaempferol showed a dose dependent inhibition of CYP3A4 activity. Computer docking analysis showed that kaempferol significantly inhibited the catalytic activity of CYP3A4 with a binding affinity of -44.73kJ/mol. Discussion: Inhibition of CYP3A4 function by epimedium and its active compound kaempferol leads to enhancement of CS anti-inflammatory effect.

Inhibitory effect of Selaginella doederleinii hieron on human cytochrome P450

Introduction: Selaginella doederleinii Hieron is a traditional Chinese herbal medicine, the ethyl acetate extract from Selaginella doederleinii (SDEA) showed favorable anticancer potentials. However, the effect of SDEA on human cytochrome P450 enzymes (CYP450) remains unclear. To predict the herb-drug interaction (HDI) and lay the groundwork for further clinical trials, the inhibitory effect of SDEA and its four constituents (Amentoflavone, Palmatine, Apigenin, Delicaflavone) on seven CYP450 isoforms were investigated by using the established CYP450 cocktail assay based on LC-MS/MS. Methods: Appropriate substrates for seven tested CYP450 isoforms were selected to establish a reliable cocktail CYP450 assay based on LC-MS/MS. The contents of four constituents (Amentoflavone, Palmatine, Apigenin, Delicaflavone) in SDEA were determined as well. Then, the validated CYP450 cocktail assay was applied to test the inhibitory potential of SDEA and four constituents on CYP450 isoforms. Results: SDEA showed strong inhibitory effect on CYP2C9 and CYP2C8 (IC₅₀ ≈ 1 μg/ml), moderate inhibitory effect against CYP2C19, CYP2E1 and CYP3A (IC₅₀ < 10 μg/ml). Among the four constituents, Amentoflavone had the highest content in the extract (13.65%) and strongest inhibitory effect (IC₅₀ < 5 μM), especially for CYP2C9, CYP2C8 and CYP3A. Amentoflavone also showed time-dependent inhibition on CYP2C19 and CYP2D6. Apigenin and Palmatine both showed concentration-dependent inhibition. Apigenin inhibited CYP1A2, CYP2C8, CYP2C9, CYP2E1 and CYP3A. Palmatine inhibited CYP3A and had a weak inhibitory effect on CYP2E1. As for Delicaflavone, which has the potential to develop as an anti-cancer agent, showed no obvious inhibitory effect on CYP450 enzymes. Conclusion: Amentoflavone may be one of the main reasons for the inhibition of SDEA on CYP450 enzymes, the potential HDI should be considered when SDEA or Amentoflavone were used with other clinical drugs. On the contrast, Delicaflavone is more suitable to develop as a drug for clinical use, considering the low level of CYP450 metabolic inhibition.

The Angelica dahurica: A Review of Traditional Uses, Phytochemistry and Pharmacology

Angelica dahurica (A. dahurica) root is a famous edible medicinal herb that has been used in China for thousands of years. To date, more than 300 chemical constituents have been discovered from A. dahurica. Among these ingredients, coumarins and volatile oils are the major active compounds. Moreover, a few other compounds have also been isolated from the root of A. dahurica, such as alkaloids, phenols, sterols, benzofurans, polyacetylenes and polysaccharides. Modern pharmacological studies demonstrated that the root of A. dahurica and its active components displayed various bioactivities such as anti-inflammation, anti-tumor, anti-oxidation, analgesic activity, antiviral and anti-microbial effects, effects on the cardiovascular system, neuroprotective function, hepatoprotective activity, effects on skin diseases and so on. Based on these studies, this review focused on the research publications of A. dahurica and aimed to summarize the advances in the traditional uses, phytochemistry and pharmacology which will provide reference for the further studies and applications of A. dahurica.

Status analysis of herbal drug therapies in epilepsy: advancements in the use of medicinal plants with anti-inflammatory properties

BACKGROUND

Use of plants and plant products in health care has shown exponential increase in past two decades.

INTRODUCTION

In-spite of the availability of well-established pharmacotherapy for epilepsy, a large no of population still explores alternative treatments due to refractory seizures, adverse effects of drugs, chronic treatment, inaccessibility of standard therapies in rural areas and the social stigma attached to the disease. Various studies on medicinal plants showed the protective effect of herbals in animal models of epilepsy.

METHOD

In the present review, a status analysis of the traditional use of various medicinal plants in epilepsy with a special focus on plats having anti-inflammatory potential is recorded.

RESULT AND CONCLUSION

The shortcomings of research on medicinal plants which needs to be explored further in order to tackle the growing need of safer and effective drugs for epilepsy are discussed. Overall, there is a huge scope of herbal drugs in CNS disorders especially epilepsy, either as an adjunct by reducing the dose and thus side effects of standard anti-epileptic drugs or as standalone agent . Although, there is still an urgent need of well planned randomized controlled clinical trials to validate their efficacy and safety.

Use of Herbal Medicine by Pregnant Women: What Physicians Need to Know

About 80% of the consumers worldwide use herbal medicine (HMs) or other natural products. The percentage may vary significantly (7%-55%) among pregnant women, depending upon social status, ethnicity, and cultural traditions. This manuscript discusses the most common HMs used by pregnant women, and the potential interactions of HMs with conventional drugs in some medical conditions that occur during pregnancy (e.g., hypertension, asthma, epilepsy). It also includes an examination of the characteristics of pregnant HM consumers, the primary conditions for which HMs are taken, and a discussion related to the potential toxicity of HMs taken during pregnancy. Many cultures have used HMs in pregnancy to improve wellbeing of the mother and/or baby, or to help decrease nausea and vomiting, treat infection, ease gastrointestinal problems, prepare for labor, induce labor, or ease labor pains. One of the reasons why pregnant women use HMs is an assumption that HMs are safer than conventional medicine. However, for pregnant women with pre-existing conditions like epilepsy and asthma, supplementation of conventional treatment with HMs may further complicate their care. The use of HMs is frequently not reported to healthcare professionals. Providers are often not questioning HM use, despite little being known about the HM safety and HM-drug interactions during pregnancy. This lack of knowledge on potential toxicity and the ability to interact with conventional treatments may impact both mother and fetus. There is a need for education of women and their healthcare professionals to move away from the idea of HMs not being harmful. Healthcare professionals need to question women on whether they use any HMs or natural products during pregnancy, especially when conventional treatment is less efficient and/or adverse events have occurred as herbal-drug interactions could be the reason for these observations. Additionally, more preclinical and clinical studies are needed to evaluate HM efficacy and toxicity.

Caffeine/Angelica dahurica and caffeine/Salvia miltiorrhiza metabolic inhibition in humans: In vitro and in vivo studies

BACKGROUND

caffeine is a major constituent in numerous foods, beverages, dietary supplements and medications.Angelica dahurica (Hoffm.) Benth. & Hook.f. ex Franch. & Sav, and Salvia miltiorrhiza Bunge are traditional medicines commonly used in Asia.

OBJECTIVES

to compare the pharmacokinetics of caffeine in humans before and after consuming an aqueous extract of A. dahurica or S. miltiorrhiza, and to propose a mechanistic explanation for in vivo caffeine metabolism inhibition based on in vitro data obtained with human liver microsomes.

METHODS

Each of the four human volunteers was given a single oral dose of caffeine before and after consuming an A. dahurica or S. miltiorrhiza extract. Saliva samples were collected from the volunteers at pre-determined time points after receiving caffeine. The saliva samples were analyzed for unchanged caffeine using liquid chromatography.

RESULTS

A. dahurica and S. miltiorrhiza extracts were capable of inhibiting caffeine metabolism in the human volunteers. In a separate study, cytochrome (CYP) 1A2-mediated caffeine demethylase activity was studied in incubation containing human liver microsomes, β-nicotinamide adenine dinucleotide phosphate, and an herbal extract (or a pure bioactive chemical from the herbs). In all cases, CYP1A2 activity was decreased with an increasing inhibitor concentration, confirming the inhibition of caffeine metabolism in vivo. Caffeine metabolism inhibition most likely involved the competitive and/or non-competitive mechanism.

CONCLUSION

Because a high level of caffeine in the plasma may result in adverse health effects in humans, care must be exercised when caffeine is consumed together with A. dahurica or S. miltiorrhiza.

Understanding the relevance of herb-drug interaction studies with special focus on interplays: a prerequisite for integrative medicine

Integrative medicine refers to the blending of conventional and evidence-based complementary medicines and therapies with the aim of using the most appropriate of either or both modalities for ultimate patient benefits. One of the major hurdles for the same is the chances of potential herb–drug interactions (HDIs). These HDIs could be beneficial or harmful, or even fatal; therefore, a thorough understanding of the eventualities of HDIs is essential so that a successful integration of the modern and complementary alternative systems of medicine could be achieved. Here, we summarize all the important points related to HDIs, including types, tools/methods for study, and prediction of the HDIs, along with a special focus on interplays between drug metabolizing enzymes and transporters. In addition, this article covers future perspective, with a focus on background endogenous players of interplays and approaches to predict the drug–disease–herb interactions so as to fetch the desired effects of these interactions.

Shenmai-Yin decreased the clearance of nifedipine in rats: The involvement of time-dependent inhibition of nifedipine oxidation

The traditional Chinese herbal formula Shenmai-Yin (SY) and nifedipine have both been used to treat patients with cardiovascular disorders. Nifedipine is primarily oxidized by cytochrome P450 (CYP) 3A. The oxidation and pharmacokinetics of nifedipine were studied in rats in vitro and in vivo to illustrate the interaction of SY with nifedipine. Schisandrol A, schisandrin A and schisandrin B were identified as the main lignans in SY. In the study in vitro, the ethanolic extract of SY was used due to the solubility and the extract inhibited nifedipine oxidation (NFO) activity in a time-dependent manner. Among lignans, schisandrin B caused the most potent inhibition. According to the time-dependent inhibition behavior, rats were treated with SY 1 h before nifedipine administration. After oral treatment with 1.9 g/kg SY, nifedipine clearance decreased by 34% and half-life increased by 142%. SY treatment decreased hepatic NFO activity by 49%. Compared to the change caused by ketoconazole, the SY-mediated reduction of nifedipine clearance was moderate. These findings demonstrate that SY causes a time-dependent inhibition of NFO and schisandrin B contributes to the inhibition. The decreased nifedipine clearance by SY in rats warrants further human study to examine the clinical impact of this decrease.

A Metabolism-Based Synergy for Total Coumarin Extract of Radix Angelicae Dahuricae and Ligustrazine on Migraine Treatment in Rats

Radix Angelicae dahuricae, containing coumarins, which might affect cytochrome P450 enzyme (CYP450) activity, has been co-administered with ligustrazine, a substrate of CYP450s, for the clinical treatment of migraine. However, whether a pharmacokinetic-based synergy exists between Radix Angelicae dahuricae and ligustrazine is still unknown. In this study, the total coumarin extract (TCE) of Radix Angelicae dahuricae (50 mg/kg, orally) reinforced the anti-migraine activity of ligustrazine by declining head scratching, plasma calcitonin gene-related peptide, and serum nitric oxide, as well as increasing plasma endothelin levels in rats (p < 0.05). Moreover, the pharmacokinetic study reflected that TCE potentiated the area under the concentration⁻time curve of ligustrazine and prolonged its mean retention time in rats (p < 0.05). Besides, the IC₅₀ for TCE, imperatorin and isoimperatorin inhibiting ligustrazine metabolism were 5.0 ± 1.02, 1.35 ± 0.46, 4.81 ± 1.14 µg/mL in human liver microsomes, and 13.69 ± 1.11, 1.19 ± 1.09, 1.69 ± 1.17 µg/mL in rat liver microsomes, respectively. Moreover, imperatorin and isoimperatorin were CYP450s inhibitors with IC₅₀ < 10 µM for CYP1A2, 2C9, 2D6, and 3A4. Therefore, this study concluded that Radix Angelicae dahuricae could increase ligustrazine plasma concentration and then reinforce its pharmacological effect by inhibiting its metabolism through interference with CYP450s. This could be one mechanism for the synergy between Radix Angelicae dahuricae and ligustrazine on migraine treatment.

Effects of Ojeok-san on the Pharmacokinetics of Celecoxib at Steady-state in Healthy Volunteers

Ojeok-san is a frequently used herbal medication for the management of osteoarthritic pain. We evaluated the effect of Ojeok-san on the pharmacokinetics of celecoxib at steady-state in healthy individuals. An open-label, fixed-sequence, two-period, two-treatment cross-over study was conducted. In period I, the individuals received celecoxib capsule 200 mg once daily for 4 days. In period II, only Ojeok-san (14.47 g/pack, three times daily) was administered for 4 days, followed by co-administration with celecoxib for 4 days. On the fourth (final) day of administration, Ojeok-san was administered as a single dose. The blood samples for pharmacokinetic evaluation were collected for up to 48 hr after the administration of celecoxib in each study period. Of the 22 enrolled individuals, 20 individuals completed the study. In the presence of Ojeok-san, the systemic exposure of celecoxib was decreased. The geometric mean ratios ([celecoxib + Ojeok-san]/celecoxib) and the 90% confidence intervals for the maximum plasma concentration (C_max ) and the area under the plasma concentration-time curve during dosing interval (AUC_τ ) of celecoxib at steady-state were 0.725 (0.620-0.848) and 0.885 (0.814-0.962), respectively. The changes in the mean of the C_max and AUC_τ of celecoxib were greater in intermediate metabolizers of cytochrome 2C9 (CYP2C9) than in normal metabolizers. Our results suggested that the C_max and AUC_τ of celecoxib were reduced by Ojeok-san co-administration. This finding may be beneficial to determine the required adjustment of celecoxib dosage when co-administered with Ojeok-san.

High hepatic exposure of furanocoumarins in Radix Angelica dahuricae is associated with transporter mediated active uptake

ETHNOPHARMACOLOGICAL RELEVANCE

Radix Angelica dahuricae (RAD), the roots of Angelica dahurica (Hoffm.) Benth. & Hook.f. ex Franch. & Sav, is a well-known traditional Chinese medicine (TCM) and has been used for centuries to treat headaches, toothaches, nose congestion, abscesses, furunculoses, and acne. This herb is also one of frequently reported TCMs showing the herb-drug interaction potential. Furanocoumarins are main bioactive components of RAD.

AIM OF THE STUDY

This study is designed to characterize the tissue distribution profiles of furanocoumarins after oral administration of RAD extract in rats and to explore the mechanism underlying the high hepatic exposure of the major furanocoumarins.

MATERIALS AND METHODS

The tissue distribution of nine furanocoumarins was determined in rats after an oral dose of 0.46g/kg RAD extract using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Unbound fractions (ƒ_u) of major furanocoumarins, including imperatorin (IM), isoimperatorin (IIM), bergapten (BER) and oxypeucedanin hydrate (OXYH), were measured in rat plasma and selected tissue homogenates (liver, kidney, lung and brain) with Rapid Equilibrium Dialysis (RED) method. The temperature dependent hepatic uptake of IM, IIM, BER and OXYH were evaluated in suspended rat primary hepatocytes at 4°C or 37°C by the oil-spin method. The uptake kinetics was conducted in the cells over a wide concentration range. The furanocoumarins were co-incubated with a panel of transporter inhibitors to investigate the involvement of uptake transporters in the hepatic uptake. The transcellular transport characteristics of IM, IIM, BER and OXYH were further assessed using Caco-2 cell monolayer model.

RESULTS

IM, IIM, BER and OXYH were found to be the major bioactive furanocoumarins in rat plasma and tissues, representing more than 90% exposure for all the detected furanocoumarins. The most concentrative organ of major furanocoumarins was the liver, with liver-to-plasma exposure ratio (K_p,_AUC) of 5.1, 6.5 and 4.7 for IM, IIM and BER, and 2.3 for OXYH, respectively. IM, IIM and BER also showed higher concentrations in the kidney with K_p above 2.2. The higher protein binding of the furanocoumarins partially contributed to their higher tissue exposure. In suspended rat primary hepatocyte, the hepatic uptake of IM, IIM, BER and OXYH was temperature-dependent, with considerably higher uptake at 37°C than at 4°C. Uptake kinetics indicated that the hepatic uptake of IM, IIM, BER and OXYH involved both active transport and passive diffusion processes. For IM, IIM and BER, the contribution of the active transport was greater than the passive process, with the CL_active/CL_uptake > 72%. Ritonavir (RTN) and cyclosporine A (CsA), the known inhibitors of organic anion transporting polypeptide (Oatp) significantly inhibited the hepatic uptake of IM and BER, while the inhibitor of the organic anion transporters (Oat) probenecid (PBC) remarkably reduced IIM uptake. In the Caco-2 cell model, the furanocoumarins were highly permeable in the apical to basolateral direction without notable active efflux.

CONCLUSION

The furanocoumarins rapidly and widely distributed into various tissues after oral dose of the RAD extract. IM, IIM, BER and OXYH were the major components detected in both plasma and tissues. Liver was the most distributed tissue of the total and free furanocoumarins. Non-specific protein binding contributed partially to the higher tissue exposures of these bioactive components. The Oatp and Oat mediated active uptake played the primal role in the high hepatic exposure of the furanocoumarins.

Simultaneous Determination of Three Furanocoumarins by UPLC/MS/MS: Application to Pharmacokinetic Study of Angelica dahurica Radix after Oral Administration to Normal and Experimental Colitis-Induced Rats

In traditional oriental medicine, Angelica dahurica Radix (ADR) is used in the treatment of gastrointestinal, respiratory, neuromuscular, and dermal disorders. We evaluated the pharmacokinetic profiles of oxypeucedanin, imperatorin, and isoimperatorin, major active ingredients of ADR, in normal and 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis rats. A rapid, sensitive, and validated UPLC/MS/MS method was established for evaluating the pharmacokinetics of three furanocoumarins. After oral administration of ADR (0.5 and 1.0 g/kg), blood samples were collected periodically from the tail vein. In colitis rats, the time to reach the peak concentration (T_max) of imperatorin and isoimperatorin was significantly delayed (p < 0.05). Lower peak plasma concentrations (C_max) and longer mean residence times for all furanocoumarins were also observed (p < 0.05) compared with normal rats. There was no significant difference in the area under the plasma concentration-time curve or elimination half-lives. Thus, the delayed T_max and decreased C_max, with no influence on the elimination half-life, could be colitis-related changes in the drug-absorption phase. Therefore, the prescription and use of ADR in colitis patients should receive more attention.

Natural Health Product Interactions with Medication

Natural health products (or dietary supplements) refer to those products found in oral dosage forms, containing 1 or more active ingredients considered to be a nutrient, an herbal product, or any other nonnutrient/nonherbal substance. Their use continues to increase in the general population and in patients seen by nutrition support clinicians. Aside from an appraisal of product safety and effectiveness, attention should be paid to the potential for these product ingredients to interact with medication. Estimates are that at least 15 million adults in the United States are at risk for supplement-drug interactions. These can occur through both pharmacokinetic and pharmacodynamic mechanisms. This review describes the influence of dietary supplements on both the disposition and the effect of medication and provides numerous examples. Patients at greatest risk for interactions are those with chronic disease, who use multiple medications-particularly those with a narrow therapeutic range-have genetic variants in drug metabolism, impaired organ function, and are at either end of the age spectrum. Knowledge of the specific effects on drug absorption, metabolism, and effect is still incomplete. Relative to the large number of possible interactions between supplements and medication, only a small number of combinations have been examined or reported. The greatest limiting factor remains the quality or reliability of the existing evidence, as many widely accepted interactions are only theoretical based either on in vitro data or known pharmacology. A distinction needs to be clearly drawn between "documented" interactions and "potential" interactions. Although drug-drug interactions have been widely recognized, supplement-drug interactions may be as important to recognize, report, and manage.

Inhibitory and inductive effects of Phikud Navakot extract on human cytochrome P450

Effects of the hydroethanolic extract of Phikud Navakot (PN), a Thai traditional remedy, on human cytochrome P450s (CYPs) were investigated in vitro. Selective substrates of CYPs were used to investigate the effects and kinetics of PN on CYP inhibition using human liver microsomes. Primary human hepatocytes were used to assess the inductive effects of PN on CYP enzyme activities and protein expressions. The results showed that PN inhibited the activities of CYP1A2, CYP2C9, CYP2D6, and CYP3A4 with half maximal inhibitory concentration (IC50) values of 13, 62, 67, and 88 μg/mL, respectively. Meanwhile, it had no effect on the activities of CYP2C19 and CYP2E1 (IC50 > 1 mg/mL). PN exhibited competitive inhibition of CYP1A2 (Ki = 34 μg/mL), mixed type inhibition of CYP2C9 and CYP2D6 (Ki = 80 and 12 μg/mL, respectively), and uncompetitive inhibition of CYP3A4 (Ki = 150 μg/mL). PN did not have an inductive effect on CYP1A2, CYP2C9, CYP2C19 and CYP3A4 in primary human hepatocytes, which is an advantageous characteristic of the extract. However the extract may cause herb-drug interactions via inhibition of CYP1A2, CYP2C9, CYP2D6 and CYP3A4, and precautions should be taken when PN is coadministered with drugs that are metabolized by these CYP enzymes.

Separation and simultaneous quantification of nine furanocoumarins from Radix Angelicae dahuricae using liquid chromatography with tandem mass spectrometry for bioavailability determination in rats

Radix Angelicae dahuricae is a well-known medicinal herb in a number of herb preparations for medical uses. In this study, a rapid and selective method using liquid chromatography with tandem mass spectrometry was developed for the separation and simultaneous quantitation of nine furanocoumarins from Radix A. dahuricae, namely imperatorin, isoimperatorin, oxypeucedanin hydrate, bergapten, oxypeucedanin, xanthotoxol, xanthotoxin, isopimpinellin, and psoralen. Chromatographic separation was achieved on a CAPCELL PAK MG II C18 analytical column. Detection was performed using positive electrospray ion source in the multiple reaction monitoring mode. The method was fully validated for analyzing these principles in rat plasma with a lower limit of quantification from 0.5 to 5 ng/mL. The intra- and interbatch precisions were less than 10%, and the accuracies ranged from -7.5 to 8.0%. The extraction recovery of the analytes was above 70% without a significant matrix effect. The method was used to determine the oral and intravenous pharmacokinetic profiles of these furanocoumarins after dosing with Radix A. dahurica extract. The bioavailability of these furanocoumarins ranged from 10.1 to 82.8%. These data provide critical information for a better understanding of the pharmacological mechanisms and herb-drug interaction potential of Radix A. dahurica.

Effects of Nigella sativa, Lepidium sativum and Trigonella foenum-graecum on sildenafil disposition in beagle dogs

The present study was conducted to investigate the effects of some commonly used herbs namely Nigella sativa, Lepidium sativum and Trigonella foenum-graecum on the pharmacokinetics of sildenafil in beagle dogs. The study design involved four treatments in a non-balanced crossover design. Sildenafil was given one tablet 100 mg orally to each dog and blood samples were obtained. After a suitable washout period, animals were commenced on a specific herb treatment for 1 week. Blood samples were withdrawn at different time intervals and sildenafil was analyzed by HPLC method. Oral administration of Nigella sativa resulted in reduction of AUC0-∞, C max and t 1/2 as compared to the control. Treatment of Lepidium sativum resulted in a significant reduction in the C max and AUC. There were no significant differences between the rests of the pharmacokinetic parameters relative to those of the control. For Trigonella foenum-graecum, the effects were similar to those obtained in case of Lepidium sativum. It was concluded that concurrent use of investigated herbs alters the pharmacokinetics of sildenafil. Co-administration of investigated herbs should be cautious since their concomitant use might result in decrease in sildenafil bioavailability.

Therapy for hyperthermia-induced seizures in Scn1a mutant rats

PURPOSE

Mutations in the SCN1A gene, which encodes the α1 subunit of voltage-gated sodium channels, cause generalized epilepsy with febrile seizures plus (GEFS+) and severe myoclonic epilepsy of infancy (SMEI). N1417H-Scn1a mutant rats are considered to be an animal model of human FS+ or GEFS+. To assess the pharmacologic validity of this model, we compared the efficacies of eight different antiepileptic drugs (AEDs) for the treatment of hyperthermia-induced seizures using N1417H-Scn1a mutant rats.

METHODS

AEDs used in this study included valproate, carbamazepine (CBZ), phenobarbital, gabapentin, acetazolamide, diazepam (DZP), topiramate, and potassium bromide (KBr). The effects of these AEDs were evaluated using the hot water model, which is a model of experimental FS. Five-week-old rats were pretreated with each AED and immersed in water at 45°C to induce hyperthermia-induced seizures. The seizure manifestations and video-electroencephalographic recordings were evaluated. Furthermore, the effects of each AED on motor coordination and balance were assessed using the balance-beam test.

KEY FINDINGS

KBr significantly reduced seizure durations, and its anticonvulsant effects were comparable to those of DZP. On the other hand, CBZ decreased the seizure threshold. In addition, DZP and not KBr showed significant impairment in motor coordination and balance.

SIGNIFICANCE

DZP and KBr showed potent inhibitory effects against hyperthermia-induced seizures in the Scn1a mutant rats, whereas CBZ exhibited adverse effects. These responses to hyperthermia-induced seizures were similar to those in patients with GEFS+ and SMEI. N1417H-Scn1a mutant rats may, therefore, be useful for testing the efficacy of new AEDs against FS in GEFS+ and SMEI patients.

A pharmacodynamic-pharmacokinetic (PD-PK) study on the effects of Danshen (Salvia miltiorrhiza) on midazolam, a model CYP3A probe substrate, in the rat

This study investigated the effect of Danshen on the pharmacodynamic-pharmacokinetic (PD-PK) effects of midazolam, a model CYP3A probe substrate. The effects of acute and 3-day Danshen treatment on the pharmacokinetics of a low dose midazolam (10 mg/kg, i.p.) were determined in vivo in the rat. Danshen (200 mg/kg, i.p.) treatment decreased midazolam clearance by 16%, with increases in the AUC by 22% and the half-life by 14%. 3-Day Danshen treatment (200 mg/kg/day, i.p.) for 3 days decreased the clearance, with increases in the T(1/2) and AUC. The effects of acute and 3-day Danshen on midazolam-induced hypnosis, serum 1'-hydroxy-midazolam to midazolam ratio and hepatic CYP3A protein expression were determined in the rat. Danshen treatments (100-200 mg/kg, i.p. and 200-500 mg/kg, p.o.) increased the sleeping time (p<0.001) produced by a hypnotic dose of midazolam (50 mg/kg, i.p.) without affecting the sleep latency. Serum 1'-hydroxy-midazolam to midazolam ratio after the hypnotic dose of midazolam was decreased after intraperitoneal Danshen treatment (200 mg/kg) but not after oral treatment at up to 500 mg/kg. All the treatment groups with Danshen, after intraperitoneal and oral administration, decreased hepatic CYP3A protein expression (p<0.05) by about 25%. The results confirmed that Danshen had no enzyme inducing effects on rat CYP3A.

Effects of some commonly used Saudi folk herbal medications on the metabolic activity of CYP2C9 in human liver microsomes

OBJECTIVE

To investigate the potential effects of eleven of the most commonly used Saudi folk herbal medications on the metabolic activity of CYP2C9 in human liver microsomes.

METHOD

CYP2C9-mediated 4'-hydroxylation of tolbutamide (TB) to 4'-hydroxytolbutamide (4-OH-TB) was utilized to assess the metabolic activity of CYP2C9. In the present study, an initial screening of the eleven herbs was carried out by incubating TB with microsomes and NADPH in absence or presence of a fixed concentration (25 μg/ml) of alcoholic extracts of different herbs and the metabolite formed was measured by HPLC. Herbs that showed significant effects were further investigated at a lower range of concentration.

RESULTS

Among the investigated herbal extracts, only aniseed and curcuma showed statistically significant effects on the formation of 4-OH-TB in human liver microsomes. Curcuma produced a potent inhibition on the metabolite formation and its maximum (about 45% inhibition) was observed at the highest extract concentrations (10 and 25 μg/ml). On the other hand, aniseed significantly activates the formation of 4-OH-TB and the maximum activation (about 55%) was observed at 2.5 μg/ml of aniseed extract.

CONCLUSION

The results of this study have shown that alcoholic extracts of curcuma and aniseed were capable of inhibiting and activating; respectively, the CYP2C9-mediated 4-OH-TB formation in human liver microsomes, suggesting that these herbs have the potential to interact with CYP2C9 drug substrates. None of the other nine investigated herbs was able to produce any statistically significant effect.

Pharmacokinetics of drugs in rats with diabetes mellitus induced by alloxan or streptozocin: comparison with those in patients with type I diabetes mellitus

Objectives

In rats with diabetes mellitus induced by alloxan (DMIA) or streptozocin (DMIS), changes in the cytochrome P450 (CYP) isozymes in the liver, lung, kidney, intestine, brain, and testis have been reported based on Western blot analysis, Northern blot analysis, and various enzyme activities. Changes in phase II enzyme activities have been reported also. Hence, in this review, changes in the pharmacokinetics of drugs that were mainly conjugated and metabolized via CYPs or phase II isozymes in rats with DMIA or DMIS, as reported in various literature, have been explained. The changes in the pharmacokinetics of drugs that were mainly conjugated and mainly metabolized in the kidney, and that were excreted mainly via the kidney or bile in DMIA or DMIS rats were reviewed also. For drugs mainly metabolized via hepatic CYP isozymes, the changes in the total area under the plasma concentration–time curve from time zero to time infinity (AUC) of metabolites, AUCmetabolite/AUCparent drug ratios, or the time-averaged nonrenal and total body clearances (CLNR and CL, respectively) of parent drugs as reported in the literature have been compared.

Key findings

After intravenous administration of drugs that were mainly metabolized via hepatic CYP isozymes, their hepatic clearances were found to be dependent on the in-vitro hepatic intrinsic clearance (CLint) for the disappearance of the parent drug (or in the formation of the metabolite), the free fractions of the drugs in the plasma, or the hepatic blood flow rate depending on their hepatic extraction ratios. The changes in the pharmacokinetics of drugs that were mainly conjugated and mainly metabolized via the kidney in DMIA or DMIS rats were dependent on the drugs. However, the biliary or renal CL values of drugs that were mainly excreted via the kidney or bile in DMIA or DMIS rats were faster.

Summary

Pharmacokinetic studies of drugs in patients with type I diabetes mellitus were scarce. Moreover, similar and different results for drug pharmacokinetics were obtained between diabetic rats and patients with type I diabetes mellitus. Thus, present experimental rat data should be extrapolated carefully in humans.

Pharmacovigilance: effects of herbal components on human drugs interactions involving cytochrome P450

Cytochrome P450 (CYP P450) enzymes are a superfamily of mono-oxygenases that are found in all kingdoms of life. The CYP P450 enzymes constitute a large superfamily of haem-thiolate proteins involved in the metabolism of a wide variety of both exogenous and endogenous compounds. The CYP activities have been shown to be involved in numerous interactions especially between drugs and herbal constituents. The majority of serious cases of drug interactions are as a result of the interference of the metabolic clearance of one drug by yet another co-administered drug, food or natural product. Gaining mechanistic knowledge towards such interactions has been accepted as an approach to avoid adverse reactions. The inductions and inhibition of CYP enzymes by natural products in the presence of a prescribed drug has led to adverse effects. Herbal medicines such as St. John's wort (Hypericum perforatum), garlic (Allium sativa), piperine (from Piper sp.), ginseng (Ginseng sp.), gingko (Gingko biloba), soya beans (Glycine max), alfalfa (Medicago sativa) and grape fruit juice show clinical interactions when co-administered with medicines. This review documents the involvement of CYP enzymes in the metabolism of known available drugs and herbal products. We also document the interactions between herbal constituents & CYP enzymes showing potential drug-herb interactions. Data on CYP450 enzymes in activation (i.e. induction or inhibition) with natural constituents is also reviewed.

Evolution of medical treatment for endometriosis: back to the roots?

Experimental evidence is accumulating to suggest that medicinal botanicals have anti-inflammatory and pain-alleviating properties and hold promise for treatment of endometriosis. Herein, we present a systematic review of clinical and experimental data on the use of medicinal herbs in the treatment of endometriosis. Although there is a general lack of evidence from clinical studies on the potential efficacy of medicinal herbs for the treatment of endometriosis-associated symptoms, our review highlights the anti-inflammatory and pain-alleviating mechanisms of action of herbal remedies. Medicinal herbs and their active components exhibit cytokine-suppressive, COX-2-inhibiting, antioxidant, sedative and pain-alleviating properties. Each of these mechanisms of action would be predicted to have salutary effects in endometriosis. Better understanding of the mechanisms of action, toxicity and herb-herb and herb-drug interactions permits the optimization of design and execution of complementary alternative medicine trials for endometriosis-associated pain. A potential benefit of herbal therapy is the likelihood of synergistic interactions within individual or combinations of plants. In this sense, phytotherapies may be analogous to nutraceuticals or whole food nutrition. We encourage the development of herbal analogues and establishment of special, simplified registration procedures for certain medicinal products, particularly herbal derivates with a long tradition of safe use.

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

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

Herbal interactions involving cytochrome p450 enzymes: a mini review

The metabolism of a drug can be altered by another drug or foreign chemical, and such interactions can often be clinically significant. Cytochrome P450 (CYP) enzymes, a superfamily of enzymes found mainly in the liver, are involved in the metabolism of a plethora of xenobiotics and have been shown to be involved in numerous interactions between drugs and food, herbs and other drugs. The observed induction and inhibition of CYP enzymes by natural products in the presence of a prescribed drug has (among other reasons) led to the general acceptance that natural therapies can have adverse effects, contrary to the popular beliefs in countries where there is an active practice of ethnomedicine. Herbal medicines such as St. John's wort, garlic, piperine, ginseng, and gingko, which are freely available over the counter, have given rise to serious clinical interactions when co-administered with prescription medicines. Such adversities have spurred various pre-clinical and in vitro investigations on a series of other herbal remedies, with their clinical relevance remaining to be established. Although the presence of numerous active ingredients in herbal medicines, foods and dietary supplements complicate experimentation, the observable interactions with CYP enzymes warrant systematic studies, so that metabolism-based interactions can be predicted and avoided more readily. This article highlights the involvement of CYP enzymes in metabolism-related drug-herb interactions and the importance of gaining a mechanism-based understanding to avoid potential adverse drug reactions, in addition to outlining other contributory factors, such as pharmacogenetics and recreational habits that may compound this important health issue.

The Influence of the Sennosides on Absorption of Glycyrrhetic Acid in Rats

In the course of our clinical studies of Kampo medicine (traditional Japanese medicines), we observed the pharmacokinetic interactions between two herbs. When Onpito (TJ-8117, Kampo medicine) containing licorice and rhubarb was administered orally to human subjects, we observed that the AUC(0-lim) and Cmax of glycyrrhetic acid (GA) in plasma were lower than those treated with other Kampo medicines containing licorice. In this study, we demonstrate the pharmacokinetic interactions of GA derived from glycyrrhizinic acid (GL) in licorice and anthraquinones derived from rhubarb. To our knowledge, this is the first report to investigate the pharmacokinetic interactions between two herbs. When GL was orally co-administrated to rats with a non-effective dose of sennoside A having purgative activity, the AUC(0-lim) and Cmax of GA decreased. In addition, sennoside A did not affect the metabolism of GL by the intestinal bacteria in vitro. In the examination using an in situ loop of rat colon, the remaining ratio of GA rose drastically by the co-administration of sennoside A, sennidin A and rhein. Observed inhibition activity of these anthraquinones on GA absorption depended on the concentration of the components added. The maximum inhibition ratio was approximately 75% by rhein, 60% by sennoside A and 25% by sennidin A. We conclude that the decrease of the pharmacokinetic parameters of GA in human plasma observed in the clinical study of TJ-8117 is attributable to an interactive action of absorption from the intestinal tract by anthraquinones contained in or derived from rhubarb.

Toxicological considerations of Kampo medicines in clinical use

Kampo (Japanese herbal) medicines, produced by combining multiple crude drugs, almost all of plant origin but with some of animal or mineral origin, contain great many substances. Since Kampo medicine results from the combination of many substances, their effect is a combination of the various interactions of the constituent substances. It has been demonstrated that several potential side effects such as allergic reactions, diarrhea and vomiting may be experienced when administering Kampo medicine. In addition, it has been reported that Kampo medicine may have antagonistic or synergistic interactions with western drugs or with some foods such as grapefruit juice. Among the 210 medicinal prescriptions used in present-day Japan, the clinical uses and the acute, chronic and mutagenic toxicity of some Kampo medicines are described. Studies of some potential interaction between Kampo medicines and western drugs are also considered.

Effects of the aqueous extract from Salvia miltiorrhiza Bge on the pharmacokinetics of diazepam and on liver microsomal cytochrome P450 enzyme activity in rats

The aim of this study was to determine the effects of the aqueous extract of Salvia miltiorrhiza Bge (danshen in Chinese) on the pharmacokinetics of diazepam and on liver microsomal cytochrome P450 enzyme activity in rats. Rats (n = 5) were pretreated with danshen extract (100 mg kg(-1) per day, p.o.) for 15 consecutive days. Control rats (n = 5) received saline at the same time. Each rat was then administered a single oral dose of 15 mg kg(-1) diazepam. The pharmacokinetic parameters of diazepam were significantly different between the two groups. In the danshen pretreated group, the maximum concentration of diazepam and the area under the plasma concentration-time curve were reduced to about 72.7% and 44.4%, respectively, while the total body clearance was markedly increased by 2-fold. To help explain the results, liver microsomal suspensions were obtained from rats that were randomly divided into the control group (n = 10), and the low- (20 mg kg(-1) for 15 days, p.o., n = 10) and high-dose groups (100 mg kg(-1) for 15 days, p.o., n = 10) pretreated with danshen extract. Compared with the control rats, the microsomal protein content, cytochrome P450 enzyme level and erythromycin N-demethylase activity of pretreated rats were significantly increased. These results indicate that danshen extract can stimulate the activity of cytochrome P450 isoforms, and changes in the pharmacokinetics of diazepam resulting from danshen extract are related to an increase in metabolic activity of cytochrome P450.

Toxicological aspects of Kampo medicines in clinical use

Among 210 medicinal prescriptions used in present-day Japan, the clinical uses and the acute, chronic and mutagenic toxicity study of 16 Kampo (Japanese herbal) medicines are summarized. These Kampo medicines are classified into two categories; eight prescriptions containing Bupleurum root (Bupleurum falcatum L.) such as Sho-saiko-to and Saiko-keishi-to, and eight prescriptions not containing Bupleurum root such as Juzen-taiho-to and Ninjin-yoei-to. Studies of some potential interaction between herbal medicine and western drugs are also described.

Interactions of herbs with cytochrome P450

A resurgence in the use of medical herbs in the Western world, and the co-use of modern and traditional therapies is becoming more common. Thus there is the potential for both pharmacokinetic and pharmacodynamic herb-drug interactions. For example, systems such as the cytochrome P450 (CYP) may be particularly vulnerable to modulation by the multiple active constituents of herbs, as it is well known that the CYPs are subject to induction and inhibition by exposure to a wide variety of xenobiotics. Using in vitro, in silico, and in vivo approaches, many herbs and natural compounds isolated from herbs have been identified as substrates, inhibitors, and/or inducers of various CYP enzymes. For example, St. John's wort is a potent inducer of CYP3A4, which is mediated by activating the orphan pregnane X receptor. It also contains ingredients that inhibit CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4. Many other common medicinal herbs also exhibited inducing or inhibiting effects on the CYP system, with the latter being competitive, noncompetitive, or mechanism-based. It appears that the regulation of CYPs by herbal products complex, depending on the herb type, their administration dose and route, the target organ and species. Due to the difficulties in identifying the active constituents responsible for the modulation of CYP enzymes, prediction of herb-drug metabolic interactions is difficult. However, herb-CYP interactions may have important clinical and toxicological consequences. For example, induction of CYP3A4 by St. John's wort may partly provide an explanation for the enhanced plasma clearance of a number of drugs, such as cyclosporine and innadivir, which are known substrates of CYP3A4, although other mechanisms including modulation of gastric absorption and drug transporters cannot be ruled out. In contrast, many organosulfur compounds, such as diallyl sulfide from garlic, are potent inhibitors of CYP2E1; this may provide an explanation for garlic's chemoproventive effects, as many mutagens require activation by CYP2E1. Therefore, known or potential herb-CYP interactions exist, and further studies on their clinical and toxicological roles are warranted. Given that increasing numbers of people are exposed to a number of herbal preparations that contain many constituents with potential of CYP modulation, high-throughput screening assays should be developed to explore herb-CYP interactions.

Drug Interactions Between Herbal and Prescription Medicines

Until reports of interactions between St John's wort and drugs such as digoxin, warfarin, protease inhibitors and oral contraceptives began to appear, very few herb-drug interactions were documented. These are now becoming more common, although still rare compared with drug-drug interactions. In the absence of hard data, potential interactions are being highlighted, and this review attempts to distinguish between the speculative and the proven. The subject is approached from a therapeutic point of view since in most cases the patient is already taking one or more prescription drugs, and the question is whether or not it is safe for a particular herb to be added to the regimen. Although many of the examples of herb-drug interactions are minor or theoretical at present, the fact remains that some are serious and life threatening, and these almost exclusively concern cyclosporin, anticoagulants, digoxin, antidepressants and protease inhibitors, taken with the herb St John's wort. Ginkgo and ginseng are implicated in a number of reports, but many of these are unsubstantiated. To date, the cardiovascular, central nervous and immune systems are the most common therapeutic categories cited in the literature and other than those, examples are very limited. Although many herbal drugs have good safety profiles, it must be borne in mind that herbal supplements are intended to be taken over an extended period of time, which provides the opportunity for enzyme induction and other mechanisms of interaction to take effect.

Potentiation by saiboku-to of diazepam-induced decreases in hippocampal and striatal acetylcholine release in rats

Effects of saiboku-to, a traditional oriental herbal medicine, on diazepam-induced changes in cerebral acetylcholine (ACh) were investigated in rat striatum and hippocampus. Diazepam (10 mg/kg, i.p.) increased tissue concentrations of the ACh in both regions. The increase was enhanced in rats subacutely treated with saiboku-to (2.0 g/kg, p.o., once a day) for 7 days. Diazepam also decreased release levels of ACh in both regions. The release levels were further decreased in saiboku-to-treated rats. On the other hand, no significant changes in ACh synthesizing and the hydrolyzing enzyme activities in either brain region were observed in saiboku-to-, diazepam- and combination-treated rats. These results suggest that not only is the diazepam-induced increase in tissue ACh due to the inhibition of ACh release but also that saiboku-to potentiates diazepam-induced inhibition of ACh release.

Effects of Kampo extracts on drug metabolism in rat liver microsomes: Rhei Rhizoma extract and Glycyrrhizae Radix extract inhibit drug oxidation

In the present study, the effects on drug oxidations in rat liver microsomes in vitro using 126 Kampo extracts were investigated. Although the effects of inhibition on drug oxidations were dependent on the Kampo extracts and probe reactions studied, most of the Kampo extracts showed inhibitory effects on both N-demethylations of aminopyrine and erythromycin in rat liver microsomes. Among the Kampo extracts studied herein, Daio-kanzo-to exhibited the most remarkable inhibitory effect on both reactions. The Rhei Rhizoma extract inhibited not only aminopyrine and erythromycin N-demethylations, but also phenacetin O-deethylation, 7-ethoxycoumarin O-deethylation, ethanol oxidation and tolbutamide 4-hydroxylation in rat liver microsomes. The Glycyrrhizae Radix extract also showed a remarkable inhibitory effect on phenacetin O-deethylation as well as aminopyrine and erythromycin N-demethylations. In contrast, the Glycyrrhizae Radix extract virtually showed no effect on ethanol oxidation.

Pharmacokinetic interactions between herbal remedies and medicinal drugs

1. The use of herbal products to treat a wide range of conditions is rising rapidly, leading to increased intake of phytochemicals. Recent studies revealed potentially fatal interactions between herbal remedies and traditional drugs. 2. In transplant patients, self-medication with St John's wort (Hypericum perforatum) has led to a drop in plasma levels of the immunosuppressant drug cyclosporine, causing tissue rejection. 3. Intake of St John's wort increases the expression of intestinal P-glycoprotein and the expression of CYP3A4 in the liver and intestine. The combined up-regulation in intestinal P-glycoprotein and hepatic and intestinal CYP3A4 impairs the absorption and stimulates the metabolism of cyclosporine, leading to subtherapeutic plasma levels. The St John's wort component, hyperforin, contributes to the induction of CYP3A4. 4. St John's wort also enhances the metabolism of other CYP3A4 substrates including the protease inhibitors indinavir and nevirapine, oral contraceptives, and tricyclic antidepressants such as amitriptyline. 5. Other herbal remedies with the potential to modulate cytochrome P450 activity and thus participate in interactions with conventional drugs include Milk thistle, Angelica dahurica, ginseng, garlic preparations, Danshen and liquorice. 6. Herbal products are currently not subject to the rigorous testing indispensable for conventional drugs. However, if potential drug interactions are to be predicted, it is essential that the ability of herbal products to interfere with drug-metabolizing enzyme systems is fully established.

Inhibitory potential of herbal medicines on human cytochrome P450-mediated oxidation: properties of umbelliferous or citrus crude drugs and their relative prescriptions

To investigate the possible drug interaction with herbal medicine, hot water decoctions or 40% ethanol infusions of several Umbelliferous or Citrus crude drugs and their prescriptions were examined in vitro for their abilities to inhibit human cytochrome P450 3A (CYP3A). Addition of each decoction or infusion from Baizhi (Angelica dahurica and varieties), Qianghuo (Notopterygium incisum or N. forbesii), Duhuo (Angelica biserrata), Fangfeng (Saposhnikovia divaricata), Danggui (Angelicasinensis), Zhishi or Zhiqiao (Citrus aurantium) resulted in various degrees of human CYP3A inhibition as determined by microsomal testosterone 6beta-hydroxylation. The inhibitory potency was consistent with the abundance of the hydrophobic components for each sample. Experiments on the infusion of a Japanese Baizhi (BZ1) showed the major role of furanocoumarins on human CYP3A inhibition. Some of the crude drugs and a related prescription showed increased inhibition after the preincubation, suggesting the involvement of a mechanism-based inhibition. Some formulated prescriptions, however, showed intense inhibition with their hydrophobic fractions rather than with their hydrophobic fractions, suggesting that components other than furanocoumarins in herbal prescriptions may also cause CYP3A inhibition. These results indicate the necessity of intensive investigations on the possible drug interaction with traditional medicines.

Effects of subacutely administered saiboku-to, an oriental herbal medicine, on pharmacodynamics and pharmacokinetics of diazepam in rodents

Subacute treatment with saiboku-to (2000 mg/kg, p.o., once a day) for 7 days induced an anxiolytic-like effect in rats. It did not, however, produce any other effects, such as sedative and hypnotic effects, anticonvulsive and muscle relaxant effects except for anxiolytic effect observed in diazepam-injected rats or mice. Diazepam (1.0 mg/kg, s.c.) induced anxiolytic-like effect was enhanced in saiboku-to treated rats as an additional effect of that induced by saiboku-to. To elucidate whether the enhancement of the anxiolytic-like effect following combined administration of diazepam and saiboku-to is due to the inhibition of hepatic drug-metabolizing enzymes, the pharmacokinetics of diazepam were further investigated in saiboku-to treated rats. The pharmacokinetic studies clearly demonstrated that subacute treatment with saiboku-to did not affect plasma concentration and protein binding rate of diazepam, and the activities of hepatic drug-metabolizing enzymes related to diazepam metabolism. These results, taken together, suggest that the enhancement of diazepam-induced anxiolytic-like effect observed in saiboku-to-treated rats is not due to an inhibition of diazepam metabolism.