Increased risk of ALT elevations w/ ombitasvir/paritaprevir/ritonavir & dasabuvir, w/or w/o ribavirin. Decreased serum conc w/ drugs known to reduce GI transit time & absorption, rifampicin, rifabutin, barbiturates, primidone, phenylbutazone, phenytoin, dexamethasone, griseofulvin, topiramate, some PIs, modafinil, St. John's wort, ritonavir, certain antibiotics eg, ampicillin & other penicillins, tetracyclines. Increased serum conc w/ atorvastatin, ascorbic acid, paracetamol, indinavir, fluconazole, troleandomycin. Increased risk of intrahepatic cholestasis by troleandomycin. Increased plasma & tissue conc w/ cyclosporine, theophylline, corticosteroids. Decreased plasma & tissue conc w/ lamotrigine. Increased risk of galactorrhea w/ flunarizine. Increased risk of intrahepatic cholestasis w/ troleandomycin.