Beta Blockers USMLE Step 1 Practice Question
A 28-year-old man with a 10-year history of ulcerative colitis undergoes total proctocolectomy with ileostomy after an acute perforation. Three weeks postoperatively, he is started on propranolol 80 mg orally twice daily for essential tremor. His family reports that unlike his previous treatment with intravenous propranolol in the hospital, the oral medication produces minimal reduction in his tremor. Laboratory studies show normal creatinine and liver function tests. Serum propranolol levels are significantly lower than expected for his oral dose. Which of the following pharmacokinetic parameters best explains the reduced clinical effect observed in this patient?
Answer choices
- ADecreased volume of distribution due to reduced total body water
- BDecreased bioavailability secondary to reduced intestinal absorption surface areaCorrect answer
- CDecreased half-life resulting in rapid drug elimination
- DDecreased hepatic clearance due to portosystemic shunting
- EIncreased first-pass metabolism by residual colonic tissue
- FDecreased therapeutic index narrowing the therapeutic window
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