3.4.1 Antihistamines

Prescribing Notes

• Encourage self-care and advise patients that antihistamines can be purchased OTC.
• Refer to bulletin on the management of hayfever in primary care for further information.
• Antihistamines may be of value in the treatment of nasal allergies, especially hay fever and vasomotor rhinitis. They reduce rhinorrhoea and sneezing but are usually less effective for nasal congestion.
  • First choice preparation for allergic rhinitis is beclometasone nasal spray (see BNF Chapter 12).
• Oral antihistamines are of value in preventing urticaria and are used to treat urticarial rashes, pruritus and insect bites and stings; they are also used in drug allergies.
  • Antihistamines are sometimes used at above licensed dosage for the management of chronic urticaria under specialist advice.
• Promethazine is sometimes used (prescribed or purchased OTC) as a perceived ‘safer’ alternative to benzodiazepines in the short-term management of insomnia. It can cause severe anticholinergic effects, particularly in elderly patients and when taking other anticholinergic drugs in combination (anticholinergic burden). Refer to SPPG bulletin on ‘Anticholinergic Drugs in Older People’. Prescribers should be aware that use may lead to hangover drowsiness the following day and its sedative effects may diminish after a few days of continued treatment.

Cautions

Older Patients – antihistamines

• Older sedating antihistamines e.g. chlorphenamine, promethazine are more liable to cause drowsiness, urinary retention or blurred vision in older patients.