A66-year-old man suffering from benign prostatic hyperplasia was admitted to the hospital because of severe suprapubic pain and an inability to pass urine for the past 24 hours. On questioning, he said he had been taking diphenhydramine for a few days to relieve itching. Which of the following actions most likely mediated the adverse effect of the drug in this patient?

Correct Answer: A

Rationale: The correct answer is A: Relaxation of the detrusor muscle. Diphenhydramine, an anticholinergic drug, causes relaxation of the detrusor muscle, leading to urinary retention. In benign prostatic hyperplasia, the enlarged prostate already causes obstruction, exacerbating the urinary retention. Therefore, the relaxation of the detrusor muscle due to diphenhydramine worsens the situation by further impairing bladder emptying. Explanation for other choices: B: Constriction of the bladder external sphincter - This would lead to urinary retention, not relieve it. C: Constriction of the prostate capsule - Constriction of the prostate capsule would not relieve urinary retention in benign prostatic hyperplasia. D: Relaxation of the bladder internal sphincter - Relaxation of the bladder internal sphincter would promote bladder emptying, which is opposite to the clinical presentation of urinary retention in this case.

Correct Answer: C

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: C

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: A

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: C

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.