Should Cytochrome P450 Inducers be Used to Accelerate Clearance of Brodifacoum from Poisoned Patients?

A recent multi-state outbreak of life-threatening bleeding following inhalation of synthetic cannabinoids has been attributed to contamination with the long-acting anticoagulant rodenticide (LAAR) brodifacoum, a second-generation, highly potent, long-acting derivative of the commonly used blood thinner warfarin. While long-term treatment with high-dose vitamin K1 restores coagulation, it does not affect brodifacoum metabolism or clearance, and, consequently, brodifacoum remains in the human body for several months, thereby predisposing to risk of bleeding recurrence and development of coagulation-independent injury in extrahepatic tissues and fetuses. This has prompted the evaluation of pharmacological measures that accelerate brodifacoum clearance from poisoned patients. Since the induction of certain cytochrome P450 (CYP) enzymes accelerates warfarin metabolism, using CYP inducers, such as phenobarbital, to accelerate brodifacoum clearance seems plausible. However, unlike warfarin, brodifacoum does not undergo significant metabolism in the liver, nor have the effects of phenobarbital on vitamin K1 metabolism been previously determined. In addition, the safety of phenobarbital in brodifacoum-poisoned patients has not been established. Therefore, we propose that CYP inducers should not be used to accelerate the clearance of brodifacoum from poisoned patients, but that alternative approaches such as reducing enterohepatic recirculation of brodifacoum, or using lipid emulsions to scavenge brodifacoum throughout the body, be considered.

Evaluation of cynomolgus monkeys for the identification of endogenous biomarkers for hepatic transporter inhibition and as a translatable model to predict pharmacokinetic interactions with statins in humans.

Inhibition of hepatic transporters such as organic anion transporting polypeptides (OATPs) 1B can cause drug-drug interactions (DDIs). Determining the impact of perpetrator drugs on the plasma exposure of endogenous substrates for OATP1B could be valuable to assess the risk for DDIs early in drug development. As OATP1B orthologs are well conserved between human and monkey, we assessed in cynomolgus monkeys the endogenous OATP1B substrates that are potentially suitable to assess DDI risk in humans. The effect of rifampin (RIF), a potent inhibitor for OATP1B, on plasma exposure of endogenous substrates of hepatic transporters was measured. From the 18 biomarkers tested, RIF (18 mg/kg, oral) caused significant elevation of plasma unconjugated and conjugated bilirubin, which may be attributed to inhibition of cOATP1B1 and cOATP1B3 based on in vitro to in vivo extrapolation analysis. To further evaluate whether cynomolgus monkeys are a suitable translational model to study OATP1B-mediated DDIs, we determined the inhibitory effect of RIF on in vitro transport and pharmacokinetics of rosuvastatin (RSV) and atorvastatin (ATV). RIF strongly inhibited the uptake of RSV and ATV by cOATP1B1 and cOATP1B3 in vitro. In agreement with clinical observations, RIF (18 mg/kg, oral) significantly decreased plasma clearance and increased the area under the plasma concentration curve (AUC) of intravenously administered RSV by 2.8- and 2.7-fold, and increased the AUC and maximum plasma concentration of orally administered RSV by 6- and 10.3-fold, respectively. In contrast to clinical findings, RIF did not significantly increase plasma exposure of either intravenous or orally administered ATV, indicating species differences in the rate-limiting elimination pathways.

Evaluation of in vitro inhibition and induction of cytochrome P450 activities by hydrolyzed ginkgolides.

ETHNOPHARMACOLOGICAL RELAVANCE: The extracts of Ginkgo biloba leaves are effective in treating cerebral infarction, of which ginkgolides have been demonstrated to be the active ingredients. The purpose of this study was to determine whether hydrolyzed ginkgolides would cause potential drug-drug interactions (DDI) during its clinical use via inhibition or induction of the major human cytochrome P450s (CYPs). MATERIALS AND METHODS: The inhibition (direct and metabolism-dependent inhibiton on CYP activities) and induction (mRNA expression level and activity of CYPs) by the hydrolyzed ginkgolides were evaluated in human liver microsomes and cryopreserved human hepatocytes, respectively. RESULTS: Within 0.1 to 10µg/mL, the hydrolyzed ginkgolides showed negligible direct inhibition against CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4m (midazolam as substrate) and 3A4t (testosterone as substrate), with IC50 values determined to be >10µg/mL (concentrations expressed as the sum of equivalent concentrations of ginkgolide A, B and K). For the metabolism-dependent inhibition studies, the preincubation of 30min did not substantially alter the IC50 values when compared with the corresponding values in the direct inhibition studies. The activities and mRNA expression levels for CYP1A2 and 2B6 within each drug-treated group (0.1, 1 and 10µg/mL) were not affected after the 48-h incubation. For CYP3A4, the activity and mRNA expression level were not altered when incubated with 0.1 and 1µg/mL of hydrolyzed ginkgolides. When incubated with hydrolyzed ginkgolides at 10µg/mL, the relative activity and relative mRNA expression level of CYP3A4 remarkably increased to 4.59±3.67 and 17.2±9.16-fold of the corresponding vehicle control values, respectively. CONCLUSIONS: The hydrolyzed ginkgolides is not likely to cause DDI via inhibition of the major human CYPs. However, the CYP3A4 induction might be clinically relevant.

Dose-response of oridonin on hepatic cytochromes P450 mRNA expression and activities in mice.

ETHNOPHARMACOLOGICAL RELEVANCE: Oridonin, the major terpene found in Rabdosia rubescens, is widely used as a dietary supplement or therapeutic drug. The effects of oridonin on drug processing genes, such as cytochrome P450 and nuclear receptors, were still unclear. Therefore, the present study investigated the influence of oridonin on the hepatic drug metabolizing system to evaluate the safety through its drug interaction potential. MATERIALS AND METHODS: In this study, eight-week-old male C57BL/6 mice were treated oridonin orally (0, 25, 50, 100, 200 mg/kg, i.g.) for 15 days. The effects of oridonin on major Cyps in mice livers were examined at both the mRNA and enzyme activity levels. RESULTS: In general, there are no significant influence of various dose of oridonin on mice liver function. However, oridonin significantly increased Cyps (1a, 2a, 2d, 2e, 2c and 3a family) mRNA expression. In addition, it could induce Cyps activity in microsome incubation at maximum dosage. To our knowledge, it is the first time to identify oridonin as a Cyps inducer in vivo. It also promotes the expression of CAR, PXR and POR. CONCLUSION: These results indicate that, if studies in mice extrapolate to humans by orthologous genes, oridonin appears to be a risk to herb-drug interactions due to its induction effects on drug processing genes expression and activation.