<prompt> A 45 yr old male presents with fever, cough, and anorexia. Sputum is positive for AFB. He is staed on isoniazid, rifampicin, pyrazinamide and ethambutol. What is the reason for administering multidrug therapy in tuberculosis?To broaden antimicrobial spectrumTo delay development of resistanceTo prevent toxin release from the organismTo reduce toxicity  <response>: The reason for administering muti-drug therapy in tuberculosis is to prevent develompment of resistance. Resistance to individual drugs in Mycobacterium tuberculosis occurs by spontaneous point mutations that occur at a low but predictable rate 10 to 10 . The development of drug-resistant tuberculosis TB is almost invariably the result of monotherapy, i.e., the failure of the health care provider to prescribe at least 2 drugs to which the tubercle bacilli are susceptible. Hence, multi-drug therapy is recommended for tuberculosis. Common point mutations in M.tuberculosis which cause drug resistance Rifampin : rpoB gene Isoniazid : katG gene inhA Pyrazinamide : pncA gene Ethambutol : embB gene Aminoglycosides : rrs gene fluoroquinolones : gyrA-gyrB genes Reference: Ananthanarayan and Paniker;s Textbook of Microbiology Tenth edition 