Increased conc & toxicity w/ CYP450 isoenzyme CYP3A4 inhibitors eg, ketoconazole. Reduced conc & efficacy w/ CYP3A4 inducers eg, rifampicin. Increased exposure w/ ciprofloxacin or potent inhibitors of CYP1A2. Altered distribution or elimination w/ ciclosporin & verapamil. Impaired absorption w/ antacids, proton pump inhibitors, or H
2-receptor antagonists. Reduced exposure in smokers.