Ans. is 'a' Rifampicin * Go through the following interactions of antiretroviral drugs and the answer will be clear.DrugsInteracting drugMechanism effectIndinavirSaquinavirRitonavirRifampinInduction of metabolism marked decrease in protease inhibitor drug levels.So the concomitant use should be avoidedZalcitabineStavudineDidanosineDrugs that cause peripheral neuropathyINH, d4T, ddl, ddCPotential for increased risk of peripheral neuropathy so monitor signs and symptoms such as numbness and tingling in extremitieszidovudineDrugs causing bone marrow suppression (i.e. TMP/SMZ, ganciclovir) sulfadiazineIncreased bone marrow suppression, Monitor for anaemia, neutropenia may require supportive therapy.