Gastrointestinal Drugs and Medications Q 17
Which histamine-2 antagonist is associated with the most drug interactions?
A. ranitidine
B. cimetidine
C. Prilosec
D. nizatidine
Correct Answer: B. cimetidine
Cimetidine was the first histamine-2 antagonist developed and is associated with the most toxic drug interactions of the group. High doses of cimetidine (over 5 g/day) can cause reversible impotence or gynecomastia. This effect appears to be the result of the antiandrogenic potential of cimetidine, which depends on an increase in prolactin levels secondary to histamine H2 receptor blockade. Also, cimetidine has non-specific actions that stimulate prolactin secretion, causing galactorrhea in men in a dose-related pattern. The effects could also be related to a blockade of the 2-hydroxylation of estradiol. However, gynecomastia in men is not an adverse effect with the other H2 receptor blockers (ranitidine, famotidine, and nizatidine).
Option A: Severe toxicity to ranitidine is rare, and there currently is no antidote for ranitidine overdose. Patients may present with CNS depression or severe hypotension. Supportive treatment and monitoring based on the presenting symptoms may be warranted.
Option C: Omeprazole is considered a benign drug; however, the primary adverse effects of omeprazole include headache, abdominal pain, nausea, diarrhea, vomiting, and flatulence in adults. The major adverse effects in the pediatric population are similar to adults; the most frequent events were reportedly fever and respiratory. Proton pump inhibitors (PPI) therapy may correlate with an increased risk of Clostridioides difficile (C. diff) associated diarrhea.
Option D: H2RAs are generally well-tolerated. Mild side effects may include headache, drowsiness, fatigue, abdominal pain, constipation, or diarrhea. The use of H2RAs in patients with renal impairment, hepatic impairment, or who are over 50 years of age has correlated with central nervous system side effects such as delirium, confusion, hallucinations, or slurred speech.