Chlorphenamine
Also known as: chlorpheniramine
A first-generation antihistamine, sold over the counter, that relieves hay fever, hives and allergic reactions within an hour but causes drowsiness because it enters the brain; also given by injection for severe allergic reactions.
- Generic name
- Chlorphenamine
- Active ingredient
- Chlorphenamine (variants: chlorphenamine maleate, chlorpheniramine maleate)
- Product type
- Small-molecule medicine
- Drug class
- Antihistamines
- Brand names
- UK Piriton, Allerief · US Chlor-Trimeton
- Routes
- Oral, Intramuscular, Intravenous (Oral (tablets, oral solution); injection)
- Dosage forms
- Tablet, Solution, Injection
- Also known as
- chlorpheniramine
- Forms
- Tablets 4 mg every 4-6 hours (maximum daily dose applies), oral solution for children over the licensed age; injection in hospital
- Onset and duration
- Within 30-60 minutes; lasts 4-6 hours.
- Terminology
- RxNorm RxCUI 2400 · ATC R06AB04 · FDA EPC Histamine-1 Receptor Antagonist [EPC]
- Monitoring
- No tests; drowsiness, urinary symptoms and confusion are reviewed, especially in older people.
Availability by country
| Country | Status | Note | Source |
|---|---|---|---|
| UK | Over the counter | Tablets and liquid in small packs; larger packs from pharmacies | UK |
| UK | Prescription only | Injection and use in children under the over-the-counter age | UK |
Legal status differs between countries and can change; each row cites the document it was taken from and applies only to the country named.
What it is used for
- Hay fever and other allergic rhinitis
- Hives (urticaria), itchy rashes and insect bites
- Symptom relief in allergic reactions and, by injection, as an adjunct in anaphylaxis after adrenaline
- Some cold and flu remedies contain it for its drying effect
How it works in the body
Chlorphenamine blocks H1 histamine receptors, so the histamine released by mast cells in an allergic reaction can no longer widen small blood vessels, make them leaky or trigger itch and sneezing. Because it crosses into the brain and also blocks some muscarinic receptors, it causes drowsiness, dry mouth and blurred vision, which newer antihistamines largely avoid.
Common side effects
- Drowsiness and slowed reactions
- Dry mouth, blurred vision, difficulty passing urine
- Headache, feeling sick
Serious: seek help
- Confusion, agitation or falls, particularly in older people
- Palpitations or a fast heartbeat
- Signs of an allergic reaction to the medicine itself
Cautions and interactions
- Do not drive, cycle or operate machinery if drowsy; alcohol and other sedatives add to the effect
- Avoided in older people where possible (falls, confusion) and in glaucoma, prostate enlargement and urinary retention
- Not for children under the licensed age without medical advice
- Adds sedation to opioids, benzodiazepines and some antidepressants
Interactions
Check interactions
Taking Chlorphenamine with other medicines? Add them to the checker to see what the official sources say about each pair: the mechanism, general management and monitoring, never a bare "safe".
Interactions documented in the official sources cited on each card. The list covers the medicines represented on this site and is not exhaustive; how the interaction data is compiled.
No pair records for this medicine are in the sources currently represented by Anatomy Nexus. Absence from this list does not mean no interaction exists.
Same-class and related medicines
Same class: Antihistamines
Medicines that share the class of Chlorphenamine. They are separate medicines with their own licences, doses and interactions, not alternative names for Chlorphenamine.
Related medicines
Medicines often discussed alongside Chlorphenamine: used together, compared with it, or acting on the same problem by a different route.