Pseudomembranous colitis is associated mostly with which drug?

Ans. b (Ampicilin). (Ref. Harrison's principles of internal medicine, 18th/Chapter 129.)Pseudomembranous colitis/Clostridium difficile-associated disease (CDAD)# It is a unique colon infection that is acquired almost exclusively in association with antimicrobial use and the consequent disruption of the normal colonic flora.# C. difficile is an obligately anaerobic, gram+, spore-forming bacillus whose spores are found wide in nature.# The agents responsible include:- Most frequently 2nd and 3rdgeneration cephalosporins (cefotaxime, ceftriaxone, cefuroxime, and ceftazidime).- Clindamycin, ampicillin, and other cephalosporins- Penicillin/b-lactamase-inhibitor combinations such as ticarcillin/ clavulanate and piperacillin/tazobactam pose significantly less risk.- However, all antibiotics, including vancomycin and metronidazole (the agents most commonly used to treat CDAD), have been found to carry a risk of subsequent CDAD.# Spores of toxigenic C. difficile are ingested, survive gastric acidity, germinate in the small bowel, and colonize the lower intestinal tract, where they elaborate two large toxins:- Toxin A, an enterotoxin , and a potent neutrophil chemoattractant- Toxin B, a cytotoxin.# The diagnosis of CDAD is based on a combination of clinical criteria:- (1) diarrhea (>3 unformed stools per 24 h for >2 days), with no other recognized cause; plus- (2) toxin A or B detected in the stool, toxin-producing C. difficile detected by stool culture, or pseudomembranes seen in the colon.# Rx:- Metronidazole is the drug of first choice and the least expensive agent.- Vancomycin as first-line treatment is discouraged as it may increase the incidence of vancomycin-resistant enterococci in hospitals.