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Chlorphenamine(Chlorpheniramine)
📖 About
Always check the BNF link here.
- 🌙 First-generation sedating antihistamine.
- Widely used in allergy and emergency settings (e.g. anaphylaxis protocols).
⚙️ Action
- Antagonist at Histamine H1 receptors.
- Blocks the effects of histamine released from mast cells and basophils.
- Has additional mild antimuscarinic effects (explains side effects).
💉 Indications / Dose
- 🤧 Allergy (hay fever, urticaria, insect bites): 4 mg PO every 4–6 hours (max 24 mg/day).
- 🚑 Anaphylaxis / acute allergy (adjunct to adrenaline): 10 mg slow IV injection over 1 minute (can also be given IM).
- Paediatric dosing differs → check BNF carefully.
🔄 Interactions
- 🍷 Alcohol → increases sedation.
- 💊 MAOIs & TCAs → increase antimuscarinic effects.
- ⬆️ May increase phenytoin plasma levels.
⚠️ Cautions
- 👴 BPH / prostatism → risk of urinary retention.
- 👁️ Glaucoma.
- ⚡ Epilepsy, severe hypertension, cardiovascular disease.
- 🚗 Sedation → caution with driving or operating machinery.
⛔ Contraindications
- 🚫 Known hypersensitivity to chlorphenamine or excipients.
💥 Side Effects
- 😴 Sedation, drowsiness, fatigue (less than older antihistamines, but still significant).
- 🤢 Antimuscarinic effects: dry mouth, blurred vision, constipation, urinary retention, nausea, dizziness.
- ❤️ Palpitations, tachycardia.
- 🧠 Rare: paradoxical CNS stimulation (especially in children, can cause irritability or insomnia).
- 🩺 Rare: liver dysfunction, allergic skin reactions.
| The content on this website is provided for educational and informational purposes only to support exam preparation (e.g., MLA, MRCP, USMLE) and learning. This is NOT medical advice, diagnosis, treatment, or professional guidance. It does not replace consultation with a qualified healthcare professional, official guidelines (e.g., NICE, GMC, BNF), or supervised clinical practice. Always verify information with current, authoritative sources. Makindo and its contributors accept no liability for any reliance on this content, including errors, omissions, or any resulting harm, loss, or consequences. By using this site, you agree to these terms. |
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