Four drugs form the core of treatment regimens for drug-susceptible organisms: PZA, isoniazid (INH), rifampicin (RIF) and ethambutol (EMB). All of these first-line drugs can induce mild to severe adverse drug reactions (ADR), including: hepatotoxicity associated to INH, RIF and PZA; cutaneous reactions associated to INH, PZA and EMB; gastrointestinal intolerance to RIF; and retrobulbar neuritis related to EMB.