Are there different types of antihistamines?
Generally, antihistamines have been classified into two groups:
- First-generation or sedating antihistamines can cause significant drowsiness and are generally more associated with the antimuscarinic side-effects mentioned above. These include alimemazine, chlorphenamine, clemastine, cyproheptadine, hydroxyzine, ketotifen and promethazine. These medicines may be used for their sedative effects should your sleep be disturbed by itching.
- Non-sedating or second-generation antihistamines are newer medicines which generally cause less drowsiness. However, anyone taking these medicines while performing skilled tasks - for example, driving - should be aware that a sedative effect may still occur and, in particular, in combination with alcohol. Second-generation antihistamines include acrivastine, cetirizine, desloratadine, fexofenadine, levocetirizine and loratadine.
Which is the best one?
All antihistamines work pretty well to reduce symptoms of allergy. Your doctor or pharmacist may advise or prescribe a particular antihistamine depending on the cause of your allergy and on whether you require a sedating or non-sedating medicine. For example:
- In general, antihistamines are probably roughly equally effective in reducing the symptoms of hay fever (seasonal allergic rhinitis) and hives (urticaria). However, non-sedating antihistamines tend to be used more commonly as they cause less drowsiness.
- Second-generation antihistamines are generally advised for most allergic situations as they cause less drowsiness.
- Cetirizine, fexofenadine, or loratadine are often recommended for urticaria.
- Antihistamine eye drops may be advised when itchy eyes are a particular problem - for example, azelastine eye drops or ketotifen drops.
- A sedating antihistamine may be particularly helpful at bedtime for children who have allergic symptoms. Cough medicines containing sedating antihistamines are not suitable for children under the age of 6 years, and a pharmacist's advice is needed for children between the ages of 6 and 12 years.
For other conditions, specific antihistamines may be used. For example, cyclizine and promethazine teoclate are used for feeling sick (nausea) and being sick (vomiting), not for hay fever. Chlorphenamine is the antihistamine most used in an emergency situation such as anaphylaxis, and may be given by injection in this situation. Diphenhydramine (Nytol®) is sold over the counter as a sleep remedy.
What preparations are there?
Antihistamines come as:
- Tablets (most commonly).
- Liquid medicine (for those who can't swallow tablets - for example, children).
- Injections (for serious allergic reactions where immediate treatment is necessary).
- In eye drops.
- In nose drops and spray.
- In creams and ointments.
Further reading and references
British National Formulary; NICE Evidence Services (UK access only)
Allergic Rhinitis; NICE CKS, October 2015 (UK access only)
Urticaria; NICE CKS, May 2016 (UK access only)
Guidelines for the management of allergic and non-allergic rhinitis; British Society for Allergy and Clinical Immunology (January 2008)
Primary Care Rhinitis algorithm; British Society for Allergy and Clinical Immunology (BSACI)
Over-the-counter cough and cold medicines for children; Medicines and Healthcare products Regulatory Agency (MHRA), 2009
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