Reduced plasma conc w/ rifampicin. May increase plasma conc of bosentan, ciclosporin, midazolam, nevirapine, amitriptyline, nortriptyline, phenytoin, rifabutin, sulfonylurea, hypoglycaemics & nateglinide, selective COX-2-inhibitors (eg, celecoxib & parecoxib), tacrolimus, triazolam, warfarin, & zidovudine. May inhibit the formation of toxic metabolite of sulfamethoxazole. Increased terfenadine & astemizole conc associated w/ ECG abnormalities following high doses of fluconazole. Increased cisapride conc associated w/ toxicity. Syncope attributed to increased amitriptyline conc. Reduce clearance of theophylline. May increase or decrease conc of contraceptive steroids & efficacy of OCs may be affected.
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