Atevirdine (U-87201E) is a nonnucleoside inhibitor of HIV-1 reverse transcriptase, that has been studied for the treatment of HIV infection. Atevirdine mesylate is the first-generation member of the bisheteroarylpiperazine class of nonnucleoside inhibitors, which inhibits reverse transcriptase noncompetitively by binding near the catalytic site. The safety, tolerability, and antiviral activity of atevirdine were studied in phase I/II clinical trial. Rash was the most common adverse event, with a grade 3 or 4 rash. No significant change from baseline in HIV-1 plasma RNA mean copy number was detected.