Are you on an HIV protease inhibitor (PI) and erythromycin? If so, read on: Some meds—including ritonavir and other PIs—raise blood levels of erythromycin and may lead to life-threatening arrhythmias (irregular heartbeat) when taken with the commonly prescribed antibiotic. Other erythro-level boosters: heart meds diltiazem and verapamil and antifungals ending in -conazole. Erythro’s sister drugs Zithromax (azithromycin) and Biaxin (clarithromycin) may affect heart rhythms, too.