Affected drug	Interacting drugs	Mechanism/effect	Recommendation
Atovaquone	Rifampin	Induction of metabolism—decreased drug levels	Concentrations might not be therapeutic; avoid combination or increase atovaquone dose.
Clarithromycin	Ritonavir	Inhibition of metabolism—increased drug levels by 77%	No adjustment needed in normal renal function; adjust if creatinine clearance is < 30.
Clarithromycin	Nevirapine	Induction of metabolism—decrease in clarithromycin area under the curve (AUC) by 35%, increase in AUC of 14-OH clarithromycin by 27%	Effect on Mycobacterium avium prophylaxis might be decreased; monitor closely.
Ketoconazole	Antacids, didanosine, histamine H2-receptor blockers, proton pump inhibitors	Increase in gastric pH that impairs absorption of ketoconazole	Avoid use of ketoconazole with pH-raising agents or use alternative antifungal drug.
Quinolone antibiotics (ciprofloxacin, levofloxacin, ofloxacin)	Didanosine, antacids, iron products, calcium products, sucralfate	Chelation that results in marked decrease in quinolone drug levels	Administer interacting drug at least 2 hours after quinolone.
Rifabutin	Fluconazole	Inhibition of metabolism—marked increase in rifabutin drug levels	Monitor for rifabutin toxicity such as uveitis, nausea and neutropenia.
Rifabutin	Efavirenz	Induction of metabolism—significant decrease in rifabutin AUC	Increase rifabutin dosage to 450 mg daily.
Rifabutin	Ritonavir, saquinavir, indinavir, nelfinavir, amprenavir, delavirdine	Inhibition of metabolism—marked increase in rifabutin drug levels	Contraindicated with hard-gel saquinavir (caution also advised with soft-gel saquinavir) and delavirdine; use 1/2 dosage (150 mg daily) with indinavir, nelfinavir, amprenavir; use 1/4 dosage (150 mg every other day) with ritonavir.