Chlorphenamine
A sedating first-generation antihistamine for hay fever, hives, itchy skin and other allergic reactions.
Also called chlorpheniramine (US name).
Drug card
- How it works
- Blocking H1 receptors in body and brain, so they also sedate
- Used for
- Hay fever and allergic rhinitis
- Hives and angioedema
- Food, drug and insect-bite allergies
- Itchy skin in eczema
- Known for
- Drowsiness and sedation
- Dry mouth
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does chlorphenamine work?
An alkylamine that competitively and reversibly blocks histamine H1 receptors, reducing histamine's effects on smooth muscle and on capillary permeability, so swelling and wheals shrink in allergic reactions. It also has anticholinergic activity and mild sedative effects.
Like other first-generation antihistamines: First-generation antihistamines competitively and reversibly block histamine H1 receptors, so histamine released in allergy can no longer make small vessels leak and swell, cause itch or contract smooth muscle. They enter the brain readily and block its H1 receptors, which causes sedation, and they also block muscarinic receptors, giving anticholinergic effects such as dry mouth and blurred vision.
Uses
What is chlorphenamine used for?
- Hay fever and allergic rhinitis
- Hives and angioedema
- Food, drug and insect-bite allergies
- Itchy skin in eczema
Side effects
Side effects of chlorphenamine
- Drowsiness and sedationKnown for
- Dry mouthKnown for
- Dizziness, poor concentration and coordination
- Blurred vision
- Difficulty passing urine
- Headache
- Nausea
- Restlessness and excitement in children
- Confusion in older people
- Hemolytic anemia and other blood disordersSerious
- Hepatitis and jaundiceSerious
- Sensitivity to sunlight
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Contraindicated within 14 days of an MAO inhibitor, which intensifies its anticholinergic effects.
- Alcohol, anxiolytics and hypnotics add to its sedation; driving can be impaired.
- Care in glaucoma, prostate enlargement, epilepsy, severe heart disease, asthma and bronchitis.
- It slows phenytoin metabolism and can cause phenytoin toxicity.
Good to know: Children and older people are the most prone to its anticholinergic effects and to paradoxical excitement.
Remember it
A way to remember it
Old antihistamines get into your head.
First-generation drugs enter the brain, so they cause drowsiness (and in children sometimes excitement), and they block muscarinic receptors too, drying the mouth and holding back urine; the newer ones mostly stay out.
Written for biofideX
Its class
First-generation antihistamines
Other first-generation antihistamines with a card:
Easily mixed up with second-generation antihistamines, H2 receptor antagonists and antimuscarinics.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- Chlorpheniramine maleate tablets: label (DailyMed)
- Chlorphenamine allergy tablets: SmPC (emc)
- Chlorpheniramine maleate (NCI Thesaurus)
- Chlorphenamine (NHS)
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Lungs and allergy
Chlorphenamine is one of 16 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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