<prompt> A middle aged old man, with chronic renal failure is diagnosed to have sputum-positive pulmonary tuberculosis. His creatinine clearance is 25mlmin. All of the following drugs need modification in doses except:IsoniazideStreptomycinRifampicinEthambutol  <response>: Ans. is c i.e. Rifampicin This question has been repeated several times. Its advised to go through tables in C.M.D.T. and in Harrison mentioned above in Ref.More question related to this topic.Most nephrotoxic cephalosporin - cephaloridineMost nephrotoxic aminoglycoside - GentamycinLeast nephrotoxic aminoglycoside - TobramycinOnly tetracycline safe in Renal failure- DoxycyclineLeast nephrotoxic antitubercular - Rifampicin 