Early H.I.V. med

AZT

This antiretroviral, first approved in 1987, was originally developed as a cancer treatment before becoming a landmark therapy for a different condition. Its three-letter name stands for azidothymidine.

Early H.I.V. med" points to AZT, short for azidothymidine, one of the first drugs approved to treat HIV in the 1980s. The clue keeps it simple by focusing on its historical role as an early medication, avoiding scientific jargon. Since AZT is a well-known abbreviation in medical history, solvers familiar with HIV treatment would recognize it right away. The brevity of the answer (just three letters) also fits classic crossword style.