Alpha-Adrenergic Receptor Blockers Classification, Key differences, Clinical uses, Side Effects
Find out the notes on Alpha-Adrenergic Receptor Blockers
Alpha-Adrenergic Receptor Blockers
These drugs block alpha-adrenergic receptors, leading to vasodilation and reduced blood pressure.
🔹 Classification of Alpha Blockers
1. Non-selective Alpha Blockers
Block both α₁ and α₂ receptors
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Examples:
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Phentolamine (reversible)
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Phenoxybenzamine (irreversible)
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2. Selective α₁ Blockers
Block only α₁ receptors → vasodilation without increased NE release
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Examples:
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Prazosin
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Terazosin
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Doxazosin
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Tamsulosin (uroselective – α₁A selective)
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3. Selective α₂ Blockers
Rare; mainly experimental or research use
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Example:
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Yohimbine (↑ sympathetic outflow)
- Important Books for GPAT
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🔹 Key Differences
| Feature | Non-selective | Selective α₁ |
|---|---|---|
| Action | Blocks α₁ & α₂ | Blocks only α₁ |
| Reflex Tachycardia | ↑↑ (due to α₂ block) | Less |
| Duration | Phentolamine (short) < Phenoxybenzamine (long) | Moderate to long |
| Use in Pheochromocytoma | Yes | No (not preferred) |
🔹 Important Clinical Uses
| Drug | Use |
|---|---|
| Phenoxybenzamine | Pheochromocytoma (pre-op) |
| Phentolamine | Hypertensive crisis (e.g., MAOI + tyramine), diagnosis of pheochromocytoma |
| Prazosin, Terazosin, Doxazosin | Hypertension, BPH |
| Tamsulosin, Alfuzosin | BPH (selective for prostate, fewer BP effects) |
🔹 Adverse Effects
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Orthostatic hypotension (especially first-dose effect in α₁ blockers)
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Reflex tachycardia (notably with non-selective)
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Nasal congestion
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Dizziness, headache
🔹 Important Points to Remember
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First-dose phenomenon: Sudden hypotension — start with low dose at bedtime (esp. Prazosin).
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Phenoxybenzamine is irreversible — useful in long-term blockade (pheochromocytoma).
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Tamsulosin is α₁A-selective — fewer cardiovascular side effects.
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Blocking α₂ receptors increases norepinephrine release → reflex tachycardia.