AIM Step 10
3rd Year MBBS
Pharmacology
3rd Year MBBS
Pharmacology
Student Memory Support
Sympatholytic Drugs: Alpha, Beta and Mixed Adrenoceptor Antagonists
High-yield memory reinforcement and last-minute KMU revision.
1. High-Yield Flashcards
Tap each question to reveal the answer.
Which drug is the prototype non-selective alpha-adrenoceptor blocker?
Phenoxybenzamine.
Which alpha blocker has greater specificity for prostatic smooth muscle?
Tamsulosin, through preferential α1A blockade.
What is the main vascular effect of α1-adrenoceptor blockade?
Vasodilation with reduced peripheral vascular resistance.
What is epinephrine reversal?
After alpha blockade, adrenaline produces a fall in blood pressure because β2-mediated vasodilation becomes dominant.
Why can non-selective alpha blockers cause more reflex tachycardia?
They also block presynaptic α2 receptors, increasing noradrenaline release.
Which drug is the prototype non-selective beta blocker?
Propranolol.
Which beta blockers have intrinsic sympathomimetic activity?
Pindolol, acebutolol, carteolol and penbutolol.
Which beta blocker is a classic example of membrane-stabilizing sodium-channel activity?
Propranolol.
Which beta blockers are established for stable chronic heart failure?
Carvedilol, bisoprolol and appropriate long-acting metoprolol.
Which beta blockers are relatively safer when beta blockade is necessary in asthma?
β1-selective agents such as metoprolol, atenolol and bisoprolol.
What are the main cardiac effects of β1 blockade?
Reduced heart rate, contractility and AV conduction.
How does beta blockade reduce renin release?
By blocking β1 receptors on juxtaglomerular cells.
Which beta blocker is classically used for stage fright?
Propranolol.
Which beta blockers are used in glaucoma?
Timolol, betaxolol and carteolol.
What is the classic antidote for severe beta-blocker toxicity?
Glucagon.
Which two drugs are mixed alpha- and beta-adrenoceptor antagonists?
Labetalol and carvedilol.
2. Mnemonics
Mnemonic Title: Beta Blockers with ISA
PAC-P
Meaning: Pindolol, Acebutolol, Carteolol, Penbutolol.
Mnemonic Title: Stable Heart Failure Beta Blockers
CBM
Meaning: Carvedilol, Bisoprolol, long-acting Metoprolol.
Mnemonic Title: Mixed Adrenoceptor Antagonists
LC
Meaning: Labetalol and Carvedilol block β receptors plus α1 receptors.
3. Memory Tables
Alpha vs Beta vs Mixed Adrenoceptor Antagonists
| Feature | Alpha blockers | Beta blockers | Mixed blockers |
|---|---|---|---|
| Main receptor | α1 ± α2 | β1 ± β2 | α1 + β |
| Main effect | Vasodilation | Reduced cardiac activity | Both effects |
| Key example | Phenoxybenzamine | Propranolol | Labetalol / carvedilol |
| Key caution | Postural hypotension | Bradycardia / bronchospasm | Combined α/β effects |
Selective vs Non-Selective Beta Blockade
| Feature | β1-selective | Non-selective |
|---|---|---|
| Examples | Metoprolol, atenolol, bisoprolol | Propranolol, timolol, nadolol |
| Bronchial effect | Less β2 blockade | Greater bronchospasm risk |
| Asthma | Relatively safer if required | More problematic |
| Selectivity | Not absolute | β1 + β2 blockade |
4. Rapid Revision Points — Last-Minute Revision
Must Remember:
- Phenoxybenzamine is the classic prototype non-selective alpha blocker.
- Tamsulosin preferentially blocks α1A receptors in prostate and bladder-neck smooth muscle.
- Alpha blockade can cause postural hypotension because reflex vasoconstriction is impaired.
- Propranolol is the prototype non-selective beta blocker.
- β1 blockade reduces heart rate, contractility, AV conduction and renin release.
- Non-selective beta blockade can precipitate bronchospasm by blocking β2 receptors.
- Beta blockers may mask tachycardia during hypoglycemia in diabetic patients.
- Timolol reduces aqueous humor production in glaucoma.
- Propranolol suppresses peripheral sympathetic features of stage fright.
- Glucagon is the classic antidote for severe beta-blocker toxicity.
KMU Trap: Beta blockers are useful in stable chronic heart failure, but acute negative inotropy can worsen acute decompensated heart failure.
5. Clinical Memory Hooks
Urinary hesitancy in BPH → α1A blockade with tamsulosin → relaxation of prostate and bladder neck.
Dizziness after standing on prazosin → impaired α1-mediated reflex vasoconstriction → postural hypotension.
Wheezing after a non-selective beta blocker → β2 blockade → bronchoconstriction.
Palpitations and tremor before public speaking → propranolol → reduced peripheral sympathetic manifestations.
Bradycardia and hypotension after beta-blocker overdose → severe β blockade → glucagon.
6. High-Yield Exam Points
- ⭐ Epinephrine reversal: alpha blockade removes vasoconstriction, leaving β2-mediated vasodilation dominant.
- ⭐ Tamsulosin is the key alpha blocker with greater specificity for prostatic smooth muscle.
- ⭐ Propranolol is the prototype non-selective beta blocker and the classic drug for stage fright.
- ⭐ Carvedilol, bisoprolol and long-acting metoprolol are important beta blockers in stable chronic heart failure.
- ⭐ Non-selective beta blockers can worsen bronchial asthma through β2 blockade.
- ⭐ Beta blockers may mask tachycardia during hypoglycemia and interfere with β2-mediated glucose recovery.
- ⭐ Glucagon is the classic antidote for severe beta-blocker toxicity.