Chlorphenamine (chlorpheniramine)
A sedating antihistamine, useful at night for itch (chickenpox). Not first-line for urticaria or anaphylaxis.
On this page
How it works
Chlorphenamine is a first-generation antihistamine. It blocks H1 receptors, reducing itch, sneezing, wheals and swelling caused by histamine. Because it crosses into the brain it causes drowsiness, and it also has anticholinergic effects (dry mouth, urinary retention). Newer non-sedating antihistamines such as cetirizine do not cross into the brain to the same extent.
When it is used
- Itch at night, where sedation is useful: chickenpox, insect bites, eczema flares.
- Allergic reactions: as an add-on for skin symptoms once airway, breathing and circulation are stable.
- Occasionally for allergic rhinitis or transfusion reactions with itch and hives.
It is not a treatment for anaphylaxis: it does not open the airway or raise blood pressure, and it must never delay adrenaline. For daytime urticaria and hay fever, a non-sedating antihistamine such as cetirizine is better. It should not be used to make children sleep.
Dose
| Age | Oral dose |
|---|---|
| 1–23 months | 1 mg twice daily |
| 2–5 years | 1 mg every 4–6 hours (max 6 mg/day) |
| 6–11 years | 2 mg every 4–6 hours (max 12 mg/day) |
| 12 years and over | 4 mg every 4–6 hours (max 24 mg/day) |
| IV or IM (adult) | 10 mg (adjunct in allergic reactions after adrenaline) |
Cautions
- Drowsiness, dry mouth, urinary retention.
- Avoid in young infants where possible; non-sedating antihistamines are preferred for urticaria.
Contraindications
- Hypersensitivity to chlorphenamine.
- Use of an MAO inhibitor within the previous 14 days.
- Use with great care, if at all, in epilepsy, angle-closure glaucoma, prostatic enlargement or urinary retention, and severe liver disease.
Side effects
- Common: drowsiness, poor concentration, dizziness, headache, dry mouth, blurred vision.
- Elderly: confusion, falls and urinary retention from anticholinergic effects.
- Children: paradoxical excitement, restlessness and poor sleep.
- IV use: transient low BP, stinging and dizziness, especially if given too fast.
Interactions
- Alcohol, opioids, benzodiazepines, gabapentinoids and other sedatives: additive drowsiness and breathing depression.
- Other anticholinergic drugs (tricyclics, oxybutynin): more dry mouth, constipation, confusion and retention.
- It may raise phenytoin levels.
Monitoring
- Level of sedation, especially in the elderly or when combined with other sedatives.
- BP and pulse after IV doses.
- Urine output in older men.
Pregnancy and breastfeeding
It has been used for many years in pregnancy, but should be given only when needed; use near delivery can cause drowsiness or other effects in the newborn. In breastfeeding it may make the baby drowsy or irritable and can reduce milk supply; a non-sedating antihistamine such as loratadine is generally preferred.
Practical tips
- IV: give slowly over about 1 minute. Fast injection causes dizziness and low BP. IM is an alternative.
- Advise patients not to drive or operate machinery and to avoid alcohol after taking it.
- For itch in chickenpox, give a single dose at night in children over 1 year and use a non-sedating antihistamine in the day if needed.
- Chlorphenamine is in many cough and cold mixtures sold over the counter in Pakistan; ask about these to avoid double dosing, and do not use them in children under 6.
- Elderly patients: prefer a non-sedating antihistamine to reduce falls.
Frequently asked questions
Is chlorphenamine used in anaphylaxis?
Only as an adjunct for skin symptoms after adrenaline; it doesn't treat airway or circulation problems.
Can chlorphenamine be given to a baby?
Oral chlorphenamine is not used under 1 year of age, and in older infants and toddlers only at the low doses in the table. Seek senior advice for babies.
Chlorphenamine or cetirizine for urticaria?
Cetirizine (or another non-sedating antihistamine) is preferred because it lasts longer and causes less drowsiness. Chlorphenamine is mainly useful at night.
How should IV chlorphenamine be given?
Slowly over about 1 minute, or IM. A rapid push can cause dizziness and a fall in BP.
Used in these guides
Sources
Doses on this page are typical doses from the sources above. Always confirm with a current drug reference, the product leaflet and your hospital protocol, especially in children, pregnancy and kidney or liver disease.
For FCPS Part 1
Revising for FCPS Part 1? Chlorphenamine is covered in our textbook chapter Asthma drugs and antihistamines, with practice MCQs.