A 42-year-old man with hypertension and benign prostatic hyperplasia is started on doxazosin. Thirty minutes after the first dose, he experiences dizziness and syncope upon standing. Vital signs show BP 92/58 mmHg, HR 108 bpm, RR 16, temp 37.2°C, and SpO2 98% on room air. His wife notes facial flushing. He denies chest pain or shortness of breath. Recent labs show normal electrolytes and creatinine. Which of the following best explains this adverse effect?
- A)β-adrenergic receptor antagonism causing reflex tachycardia
- B)Muscarinic receptor blockade producing anticholinergic effects
- C)Unopposed α2-adrenergic agonism leading to vasoconstriction
- D)Inhibition of phosphodiesterase leading to cAMP accumulation
- E)First-dose effect causing profound vasodilation and orthostatic hypotensionGABARITO
Explicação
α1-adrenergic antagonists cause vasodilation by blocking α1 receptors on vascular smooth muscle. The first dose effect occurs because acute, unopposed vasodilation causes profound peripheral vasodilation and orthostatic hypotension, especially when transitioni... Ver explicação completa e trilha adaptativa →