Induction of Cytochrome P450 3A4 and P-Glycoprotein by the Isoxazolyl- Penicillin Antibiotic Flucloxacillin

Abstract

Clinical findings indicate that co-administration of the isoxazolyl-penicillin flucloxacillin with cyclosporine may reduce the plasma concentrations of cyclosporine. We have explored in the present study if induction of cytochrome P450 3A4 or P-glycoprotein may offer a mechanistic explanation of the observed effects. Flucloxacillin is neither an inhibitor nor a substrate of drug metabolizing cytochrome P450 isoenzymes (CYP3A4, 1A2, 2C9, 2C19 and 2D6) or P-glycoprotein as shown by an in vitro assay for CYP inhibition, a fluorescent indicator assay for P-glycoprotein inhibition and a functional P-glycoprotein ATPase assay. However, incubation of human LS 180 colorectal adenocarcinoma cells with flucloxacillin led to a dose-dependent induction of MDR1 as well as of CYP3A4 mRNA, which was also confirmed in primary human hepatocytes. At high concentrations, flucloxacillin activated the human Pregnane-X-Receptor, PXR, a ligand-dependent transcription factor that is the target of many drugs that induce CYP3A4, with consequences for the metabolism of other drugs. Liver microsomes from control rats or rats, which received for 3 consecutive days 100 mg/kg of oral flucloxacillin, were used to study the metabolism and metabolite pattern of midazolam, a model substrate of CYP 3A4. There was a trend towards a higher intrinsic microsomal clearance of midazolam using microsomes from flucloxacillin treated rats. In addition, there was a significant increase in the formation of the principal midazolam metabolites 1-hydroxy midazolam, 4-hydroxy midazolam and 1,4-dihydroxy midazolam as compared to controls. These findings indicate that flucloxacillin has the potential to induce expression of both CYP3A4 as well as P-glycoprotein, most likely through activation of the nuclear hormone receptor PXR. This would offer an explanation for the observed clinical drug-drug interactions between the antibiotic and cyclosporine.

Interaction of flucloxacillin and quinidine

“…Flucloxacillin is also a known substrate of Pgp and is capable of inducing Pgp and CYP3a4 [14,15]. Previously published case reports have shown that the AUC of quinidine can be decreased by 60-80% through induction by the concomitant use of rifampicin [9].…”

“…Previously published case reports have shown that the AUC of quinidine can be decreased by 60-80% through induction by the concomitant use of rifampicin [9]. Alternatively, flucloxacillin has been shown to reduce the plasma levels of cyclosporine through the induction of Pgp and CYP3a4 [15,16]. This is very relevant, as quinidine, like cyclosporine, is a mixed Pgp and CYP3a4 substrate.…”

Prediction of Drug-Drug Interactions From in Vitro Induction Data

“…CYP3A4 is predominantly expressed in the liver and the small intestine and is known to metabolize the majority of drugs whose biotransformation is known (Guengerich, 1996;Rendic and Di Carlo, 1997). Induction of CYP3A activity in the clinic can result in therapeutic failure such as tissue rejection in transplant patients caused by increased clearance of cyclosporine or unwanted pregnancy caused by increased clearance of oral contraceptive agents, among others (Mannel, 2004;Huwyler et al, 2006). Therefore, different models to study CYP3A4 induction have been developed to allow the selection and development of safer compounds and aid in the design of more efficient clinical trials.…”

The far and distal enhancers in the CYP3A4 gene co-ordinate the proximal promoter in responding similarly to the pregnane X receptor but differentially to hepatocyte nuclear factor-4α

“…For example, the antidepressant herbal remedy St John's wort is a potent inducer of CYP3A4, and concurrent use of this remedy increases the clearance of the anticancer agent imatinib mesylate by as much as 43 % [6]. Induction of CYP3A4 is largely due to transcriptional activation [7,8]. The PXR (pregnane X receptor) is recognized as a key regulator that mediates the induction [9,10].…”