Which of the listed medications can affect the efficacy of clopidogrel?

Clopidogrel is an antiplatelet medication that works by inhibiting the activation of platelets, thereby preventing blood clot formation. Its efficacy can be significantly influenced by certain medications that affect the metabolism of clopidogrel. Omeprazole, a proton pump inhibitor (PPI), has been shown to reduce the effectiveness of clopidogrel when used concurrently. This occurs because omeprazole inhibits the enzyme CYP2C19, which is essential for the conversion of clopidogrel into its active metabolite. When this conversion is impaired, the antiplatelet effect of clopidogrel diminishes, potentially leading to an increased risk of cardiovascular events in patients relying on this medication for its protective effects.

In contrast, other medications such as calcium citrate, famotidine, and lansoprazole do not have the same significant impact on clopidogrel's metabolism or efficacy. While they may affect gastrointestinal pH or calcium absorption, they do not interfere with the CYP2C19 enzyme in the manner that omeprazole does, making omeprazole a standout choice in terms of its interaction with clopidogrel.