Cyproheptadine
Related FACEM curriculum (2022) learning objectives:
- ME 3.8.1.6(e) Principles of management of toxicological presentations including: Indications for antidotes
- ME 3.8.2.4 Identify the appropriate antidote or antivenom.
Presentation
- 4 mg tablets (50, 100).
Indications
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Mild-to-moderate serotonin syndrome.
Contraindications
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Known hypersensitivity.
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Acute asthma.
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Closed-angle glaucoma.
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Bladder neck obstruction.
Mechanism of Action
- Competitive antagonist at histamine H1 and serotonin 5-HT1A and 5-HT2 receptors.
- Inhibits ACTH centrally, likely via serotonin antagonism.
- Moderate local anaesthetic and mild peripheral anticholinergic effects.
Pharmacokinetics
- Well absorbed orally, with peak plasma levels at 1–3 hours.
- Eliminated primarily by hepatic glucuronidation; metabolites excreted in urine.
Administration
- Initial dose: 8 mg orally.
- Maintenance: 8 mg every 8 hours for 24 hours if effective.
- Therapy may extend with irreversible MAO inhibitor-associated serotonin syndrome.
Therapeutic Endpoints
- Improvement or resolution of serotonin syndrome features within 1–2 hours of the initial dose.
Adverse Drug Reactions
- Insignificant at therapeutic doses.
Specific Considerations
- Pregnancy: No restriction on use.
- Paediatrics: Suggested dose for 7–14 years: Initial 4 mg, then 4 mg every 8 hours for 24 hours.
Handy Tips
- Not a life-saving antidote; supports symptom management in mild-to-moderate cases.
- Simple supportive care and mild benzodiazepine sedation usually suffice.
- Not effective in severe serotonin syndrome; prioritise early intubation and neuromuscular paralysis.
Pitfalls
- Failure to evaluate response to the initial dose.
- Over-reliance on cyproheptadine at the expense of supportive care.