Drug use to treat mysthenia gravis D rubocurarine Hexamethonium Ambenonium Gallamine
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Answer: C. Ambenonium
The correct answer is Ambenonium.
Why Ambenonium?
Ambenonium is a reversible anticholinesterase (anti-ChE) inhibitor used in the symptomatic treatment of myasthenia gravis (MG). It works by inhibiting acetylcholinesterase (AChE) at the neuromuscular junction, preventing the breakdown of acetylcholine (ACh). This increases the concentration of ACh available to bind to the remaining functional nicotinic receptors on the motor end plate, thereby improving muscle strength.
As stated in Goodman & Gilman's Pharmacological Basis of Therapeutics:
"Pyridostigmine, neostigmine, and ambenonium are the standard anti-ChE drugs used in the symptomatic treatment of myasthenia gravis."
Why the Other Options Are Wrong?
| Drug | Class | Action | Use |
|---|---|---|---|
| d-Tubocurarine | Non-depolarizing NMJ blocker | Competitive antagonist at nicotinic receptors | Surgical muscle relaxant - WORSENS MG |
| Hexamethonium | Ganglionic blocker | Blocks nicotinic receptors at autonomic ganglia (NN) | Used historically for hypertension - not for MG |
| Ambenonium | Anticholinesterase (carbamate) | Inhibits AChE → increases ACh at NMJ | TREATS MG |
| Gallamine | Non-depolarizing NMJ blocker | Competitive antagonist at nicotinic receptors | Surgical muscle relaxant - WORSENS MG |
Key Concept
Myasthenia gravis is an autoimmune disease where antibodies attack nicotinic ACh receptors (NM) at the neuromuscular junction, reducing the number of functional receptors. The result is progressive, fatigable muscle weakness.
The treatment strategy is to inhibit AChE so that ACh stays in the synapse longer and can activate the remaining receptors more effectively. The drugs used are:
- Pyridostigmine (most commonly used, first-line)
- Neostigmine
- Ambenonium
Drugs like d-tubocurarine and gallamine are neuromuscular blocking agents that compete with ACh at the same receptors - they would dramatically worsen MG symptoms and are contraindicated. Hexamethonium blocks ganglionic nicotinic receptors (NN) and has no therapeutic role in MG.
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