- Chlorphenamine tablets 4mg; syrup 2mg/5mL; injection 10mg/mL: orally, 4mg every 4-6 hours, max 24mg daily. Subcutaneous or intramuscular injection: 10-20mg repeated if required, max 40mg in 24 hours. Slow intravenous injection: 10-20mg over 1 minute.
- Cetirizine tablets 10mg; oral solution 5mg/5mL: 10mg daily or 5mg twice daily.
- Loratadine tablets 10mg: 10mg daily.

• 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.

• 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.

• Cetirizine and loratadine cause less sedation than chlorphenamine but are more expensive; they are available over-the-counter.

• Loratadine may be a suitable alternative for patients who develop sedation with cetirizine.

• First choice preparation for allergic rhinitis is beclometasone nasal spray (see section 12.2.1).

- Adrenaline 1 in 1000 (1mg/mL) injection: intramuscularly, 0.5mL repeated if necessary at 5-minute intervals according to blood pressure, pulse and respiratory function.
- Adrenaline for self-administration: EpiPen® Auto-injector 0.3mg consists of a fully assembled syringe and needle delivering adrenaline 300micrograms by intramuscular injection; repeated after 15 minutes as necessary.
- Chlorphenamine injection 10mg/mL: 10-20mg by slow intravenous injection over 1 minute.
- Hydrocortisone sodium succinate injection 100mg: 100-300mg intravenously.

• Adrenaline should be given immediately for an acute anaphylactic reaction (laryngeal oedema, bronchospasm and hypotension).

• Chlorphenamine injection is a useful adjunctive treatment given after adrenaline injection and continued for 24-48 hours to prevent relapse.

• Hydrocortisone injection is of secondary value in the initial management of anaphylactic shock because the onset of action is delayed for several hours, but should be given to prevent further deterioration in severely affected patients.

• Atopic individuals are particularly at risk of anaphylactic reactions; patients with known severe allergy to insect stings, foods or peanuts should carry, and receive instruction for the use of, prefilled syringes (e.g. EpiPen®) for self-administration. Patients should usually be prescribed two.