Mecamylamine
Ganglionic blockers
Ganglionic blockers
An oral ganglionic blocker for severe hypertension. Blocking both autonomic divisions causes orthostatic hypotension, ileus and urinary retention.
Quick facts
- Group
- Ganglionic blockers
- Target
- Neuronal nicotinic acetylcholine receptor of autonomic ganglia (channel blocker)
- Key effects
- Orthostatic hypotension · Constipation
- Monitor
- Lying and standing blood pressure · Urine output
- ATC
- C02BB01
No doses: the clinician sets them by the current guideline.
Mechanism of action
Mecamylamine blocks the ion channel of the neuronal nicotinic receptor in autonomic ganglia, so acetylcholine released by preganglionic fibres can no longer fire the postganglionic neuron. Loss of sympathetic tone dilates arterioles and veins and lowers blood pressure, mostly on standing. Loss of parasympathetic tone causes tachycardia, dilated pupils, blurred near vision, dry mouth, constipation and urinary retention. As a secondary amine it also enters the brain.
- Blocks the nicotinic channel in autonomic ganglia
- Sympathetic ganglia off: vessels dilate, pressure falls on standing
- Parasympathetic ganglia off: dry mouth, ileus, urinary retention
- Enters the brain: tremor or mental changes are possible
Indications
- Moderately severe to severe essential hypertension and uncomplicated malignant hypertension Arterial hypertension →
Adverse effects
Common
- Orthostatic hypotension, dizziness and fainting
- Constipation, dry mouth
- Blurred vision and dilated pupils
- Urinary retention
Contraindications
- Mild, moderate or labile hypertension
- Coronary insufficiency or recent myocardial infarction
- Uraemia
- Glaucoma
- Organic pyloric stenosis
- Concomitant antibiotics and sulfonamides (generally avoided)
Key interactions
- Other antihypertensives, alcohol and anaesthesia
- Stronger fall in blood pressure
- Antibiotics and sulfonamides
- Patients receiving them generally should not be treated with ganglionic blockers
- Diuretics, vomiting, diarrhoea or heavy sweating (salt depletion)
- Potentiated hypotension
What is monitored
- Lying and standing blood pressure
- Bowel habit and abdominal distension
- Urine output
- Kidney function
Administration and safety
- Stopped gradually, with another antihypertensive usually taking its place
- Heat, fever, exercise, bleeding and surgery can increase its effect
Pregnancy and breastfeeding
No animal or human reproduction data; used only if clearly needed.
Nursing care
- Measures blood pressure lying and standing
- Teaches the patient to rise slowly and that alcohol, exercise and hot weather worsen dizziness
- Asks daily about bowel movements, distension and urination; reports loose stools with a swollen abdomen at once
- Watches for tremor, confusion or abnormal movements
Pharmacokinetics
- Absorption
- Almost completely absorbed by mouth
- Elimination
- Slowly, unchanged in urine; alkaline urine slows and acidic urine speeds its excretion
- Onset and duration
- Gradual, within half an hour to 2 hours; the effect usually lasts 6 to 12 hours or more
Test yourself
Think of the answer, then tap the question to see it.
Where does mecamylamine act?
On neuronal nicotinic receptors of autonomic ganglia, blocking their ion channel.
Why does mecamylamine cause urinary retention and constipation?
Bladder and gut are under predominant parasympathetic tone, which is blocked at the ganglia.
How does urine pH change its elimination?
Alkaline urine reduces and acidic urine increases its renal excretion.
Why can mecamylamine cause tremor or seizures, unlike hexamethonium?
It is a secondary amine that crosses into the brain; quaternary blockers stay out.
Connections
← Back to the class: Ganglionic blockers
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - MECAMYLAMINE HYDROCHLORIDE tablet (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.