Which of the following adverse effects is characteristic of non-selective alpha blockers like prazosin and doxazosin but NOT seen with uroselective agents like tamsulosin?

Explanation

## Adverse Effects Profile: Selective vs. Non-selective Alpha Blockers **Key Point:** First-dose syncope and orthostatic hypotension are hallmark adverse effects of **non-selective α1 antagonists** due to their potent vascular α1B blockade. Uroselective agents (tamsulosin, alfuzosin) spare vascular receptors and thus avoid these hemodynamic complications. ### Mechanism of First-Dose Syncope 1. **Non-selective agents** block α1B receptors on arteriolar and venous smooth muscle 2. **Acute vasodilation** occurs, reducing peripheral vascular resistance and venous return 3. **Orthostatic hypotension** develops, especially upon standing after initial dose 4. **Syncope** may occur within 30–90 minutes of the first dose 5. **Tolerance** develops over days to weeks, reducing severity **Clinical Pearl:** Patients starting prazosin or doxazosin must be counseled to take the first dose at bedtime to minimize syncope risk. Uroselective agents do not require this precaution. ### Adverse Effects Comparison | Adverse Effect | Non-selective (Prazosin, Doxazosin) | Uroselective (Tamsulosin, Alfuzosin) | Mechanism | | --- | --- | --- | --- | | **First-dose syncope** | **Common** | **Rare** | Vascular α1B blockade | | **Orthostatic hypotension** | **Frequent** | **Minimal** | Vascular α1B blockade | | **Tachycardia** | **Yes** | **No** | Reflex sympathetic activation | | **Retrograde ejaculation** | Yes | Yes | α1A blockade in bladder neck | | **Urinary retention** | No | Rare | Not a class effect | **High-Yield:** The **distinction between non-selective and uroselective agents hinges on vascular effects**. Non-selective agents cause troublesome hemodynamic side effects; uroselective agents do not. **Mnemonic:** **VASCULAR = Non-selective** — **V**asodilation, **A**rthostatic hypotension, **S**yncope (first-dose), **C**ardiac reflex tachycardia, **U**nwanted hemodynamic effects, **L**arge blood pressure drop, **A**void in elderly, **R** = Reflex activation. **Warning:** Tachycardia and palpitations occur as a **reflex sympathetic response** to acute vasodilation in non-selective blockade. This is NOT a direct α-adrenergic effect but a baroreceptor-mediated compensation. [cite:KD Tripathi 8e Ch 12]