A 52-year-old man with hypertension and benign prostatic hyperplasia (BPH) presents to the clinic. He has been on doxazosin 4 mg daily for 6 months with good blood pressure control (BP 128/82 mmHg) and improved urinary symptoms. However, he now complains of persistent orthostatic dizziness on standing, particularly in the morning, and occasional syncope during exertion. Vital signs show BP 145/88 mmHg supine and 118/70 mmHg standing (drop of 27 mmHg systolic). Heart rate is 88 bpm supine and 102 bpm standing. What is the most appropriate next step in management?

Explanation

## Clinical Context This patient has symptomatic orthostatic hypotension (>20 mmHg systolic drop with symptoms) secondary to α₁-adrenergic blockade by doxazosin. The drug is working for both hypertension and BPH, but the dose-related adverse effect (vasodilation via α₁ antagonism on vascular smooth muscle) is causing harm. ## Mechanism of Adverse Effect **Key Point:** α₁-adrenergic receptors on peripheral vasculature mediate vasoconstriction and maintain blood pressure during postural changes. Non-selective α₁ antagonists (doxazosin, terazosin, prazosin) block these receptors, causing vasodilation and orthostatic hypotension, especially with initial dosing or dose escalation. ## Management Algorithm ```mermaid flowchart TD A[Patient on α₁ antagonist with orthostatic hypotension]:::outcome --> B{Drug working for primary indication?}:::decision B -->|Yes| C[Reduce dose, not discontinue]:::action B -->|No| D[Switch to alternative agent]:::action C --> E[Counsel on non-pharmacological measures]:::action E --> F[Slow positional changes, hydration, salt intake, compression stockings]:::action F --> G[Reassess in 2 weeks]:::outcome D --> H[Consider selective α₁A antagonist or alternative class]:::action ``` **High-Yield:** Dose reduction is preferred over discontinuation when the drug is otherwise efficacious. Non-pharmacological measures (slow position changes, adequate hydration, increased salt intake, compression stockings) are first-line adjuncts and often sufficient to prevent syncope. ## Why This Answer 1. **Preserve efficacy:** The drug is controlling both BP and BPH symptoms. 2. **Reduce adverse effect:** Lowering the dose decreases α₁ blockade intensity while maintaining therapeutic benefit. 3. **Non-pharmacological support:** Lifestyle modifications address orthostatic stress without additional drugs. 4. **Avoid polypharmacy:** Adding a beta-blocker would compound hypotension risk. **Clinical Pearl:** Morning orthostatic symptoms are classic for α₁ antagonists due to overnight volume depletion and loss of compensatory vasoconstriction. Bedtime dosing and increased morning fluid intake can also help.