Drug-induced colitis is most frequently associated with

Clindamycin: This potent lincosamide antibiotic is similar in mechanism of action (inhibits protein synthesis by binding to 50S ribosome) and spectrum of activity to erythromycin with which it exhibits paial cross resistance. Modification of the ribosomal binding site by constitutive methylase enzyme confirs resistance to both. It inhibits most gram-positive cocci (including penicillinase producing Staph., but not MRSA), C. diphtheriae, Nocardia, Actinomyces, Toxoplasma, but the distinctive feature is its high activity against a variety of anaerobes, especially Bact. fragilis. Aerobic gram-negative bacilli, spirochetes, Chlamydia, Mycoplasma and Rickettsia are not affected. Side effects are rashes, uicaria, abdominal pain, but the major problem is diarrhoea and pseudomembranous enterocolitis due to Clostridium difficile superinfection which is potentially fatal. The drug should be promptly stopped and metronidazole (alternatively vancomycin) given to treat it. ESSENTIALS OF MEDICAL PHARMACOLOGY K.D.TRIPATHI SIXTH EDITION PAGE NO:731