Step 1: A co-infected patient (HIV plus active TB) needs both diseases treated, but the order of drugs matters because of immune reconstitution risk.
Step 2: The safer strategy is to bring the tuberculosis under control before reviving the immune system. So anti-tubercular drugs go in first, typically about two weeks ahead of antiretrovirals.
Step 3: If you reverse the order and start antiretrovirals first, the rapidly rising CD4 count can attack the still-active TB bacilli with an overwhelming inflammatory reaction. This is IRIS, and it makes the patient appear clinically worse even though treatment is working.
Step 4: Hence the recommended approach is to begin ATT first, then layer cART on top.
\[\boxed{\text{Start ATT first}}\]