A 58-year-old man with benign prostatic hyperplasia (BPH) and hypertension presents with dizziness and syncope 30 minutes after taking his first dose of doxazosin 2 mg. Blood pressure is 88/54 mmHg, heart rate 102/min. He denies chest pain or dyspnea. What is the most appropriate immediate next step?

Explanation

## Clinical Recognition: First-Dose Effect **Key Point:** The constellation of syncope, hypotension, and tachycardia occurring within 30 minutes of the first dose of an alpha blocker is pathognomonic for the **first-dose effect** — a sudden, transient drop in systemic vascular resistance due to unopposed α~1~-adrenergic blockade. **High-Yield:** First-dose syncope occurs in 0.5–1% of patients starting alpha blockers and is most pronounced with doxazosin and terazosin (longer-acting agents). Prazosin and alfuzosin carry lower risk. ## Pathophysiology 1. **Acute α~1~ blockade** → loss of peripheral vasoconstriction 2. **Baroreceptor reflex** → compensatory tachycardia (explains HR 102) 3. **Transient hypotension** → cerebral hypoperfusion → syncope 4. **Self-limited** → usually resolves within 1–2 hours as compensatory mechanisms engage ## Management Algorithm ```mermaid flowchart TD A[First-dose syncope on alpha blocker]:::outcome --> B{Hemodynamically stable?}:::decision B -->|Yes, SBP > 80| C[Supine position + IV fluids]:::action B -->|No, SBP < 80| D[IV fluids + consider vasopressor]:::action C --> E[Observe 1–2 hours]:::action D --> E E --> F[Counsel on first-dose effect]:::action F --> G[Restart at LOWER dose after 24 hrs]:::action G --> H[Titrate slowly over weeks]:::action ``` **Clinical Pearl:** Taking the first dose at bedtime and instructing the patient to remain supine for 2–3 hours significantly reduces symptomatic first-dose syncope. **Tip:** This patient is hemodynamically responsive (BP 88/54 is low but not cardiogenic shock). Fluid resuscitation and observation are sufficient; no need for inotropes or ICU admission. [cite:KD Tripathi 8e Ch 10]