Pseudomembranous colitis in a patient on rifampicin and ethambutol.

A fifty-seven year old male with renal tuberculosis developed pseudomembranous colitis on rifampicin and ethambutol. Diarrhoea occurred within a week, and six weeks after commencing these antituberculous agents he developed typical sigmoidoscopic and biopsy findings. Withdrawal of the drugs led to rapid recovery. Repeated challenge testing indicated that the symptoms were worse when rifampicin was given, but a test dose of ethambutol also produced temporary aggravation of the diarrhoea.