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.