19) ANSWER 

D) Cimetidine (Tagamet)

Explanation

Cimetidine decreases metabolism of beta blockers, phenytoin, procainamide, quinidine, benzodiazepines, metronidazole, tricyclic antidepressants, and warfarin, leading to increased risk of drug toxicity. Ranitidine, famotidine, and nizatidine are histamine blockers that are newer than cimetidine, and have fewer side effects. The core issue of the question is knowledge of histamine antagonists that are highest in side or adverse effects. Specific medication knowledge is needed to answer the question. Use medication knowledge and the process of elimination to make a selection.