The correct answer is A. Cimetidine is an H2 blocker associated with P-450 inhibition, anti- androgenic effects, decreased renal excretion of creatinine, and arrhythmias. As a result of P-450 inhibition, cimetidine decreases hepatic metabolism of many drugs oxidized by the P-450 system, including warfarin, increasing their systemic toxicities. This results in a prolonged prothrombin time.
Answer B is incorrect. Insulin lispro can cause hypoglycemia.
Answer C is incorrect. Metoprolol can be associated with decreased perception of hypoglycemia in diabetics. However, it does not affect warfarin levels.
Answer D is incorrect. NPH insulin can cause hypoglycemia or idiopathic allergic and anaphylactoid reactions.
Answer E is incorrect. Omeprazole is a proton pump inhibitor that is relatively free of adverse effects.