BNF for Children 2011-2012

BNFC 2011–2012 3.4 Antihistamines, immunotherapy, and allergic emergencies 153Indication and doseProphylaxis of asthma see notes above and Managementof Chronic Asthma, p. 135. By mouthChild 12–18 years 20 mg twice dailyAccolate c (AstraZeneca) ATablets, f/c, zafirlukast 20 mg, net price 56-tab pack =£17.75. Label: 233.4 Antihistamines,immunotherapy, andallergic emergencies3.4.1 Antihistamines3.4.2 Allergen immunotherapy3.4.3 Allergic emergencies3.4.1 AntihistaminesAntihistamines (histamine H 1 -receptor antagonists) areclassified as sedating or non-sedating, according to theirrelative potential for CNS depression. Antihistaminesdiffer in their duration of action, incidence of drowsiness,and antimuscarinic effects; the response to anantihistamine may vary from child to child (see Sideeffects,below). Either a sedating or a non-sedatingantihistamine may be used to treat an acute allergicreaction; for conditions with more persistent symptomswhich require regular treatment, a non-sedating antihistamineshould be used to minimise the risk of sedationand psychomotor impairment associated withsedating antihistamines.Oral antihistamines are used in the treatment of nasalallergies, particularly seasonal allergic rhinitis (hayfever), and may be of some value in vasomotor rhinitis;rhinorrhoea and sneezing is reduced, but antihistaminesare usually less effective for nasal congestion. Antihistaminesare used topically to treat allergic reactions inthe eye (section 11.4.2) and in the nose (section 12.2.1).Topical application of antihistamines to the skin is notrecommended (section 13.3).An oral antihistamine may be used to prevent urticaria,and for the treatment of acute urticarial rashes, pruritus,insect bites, and stings. Antihistamines are also used inthe management of nausea and vomiting (section 4.6),of migraine (section 4.7.4.1), and the adjunctive managementof anaphylaxis and angioedema (section 3.4.3).The non-sedating antihistamine cetirizine is safe andeffective in children. Other non-sedating antihistaminesthat are used include acrivastine, desloratadine (anactive metabolite of loratadine), fexofenadine (anactive metabolite of terfenadine), levocetirizine (anisomer of cetirizine), loratadine, mizolastine, andrupatadine. Most non-sedating antihistamines arelong-acting (usually 12–24 hours). There is little evidencethat desloratadine or levocetirizine confer anyadditional benefit—they should be reserved for childrenwho cannot tolerate other therapies.Sedating antihistamines are occasionally useful wheninsomnia is associated with urticaria and pruritus (section4.1.1). Most of the sedating antihistamines arerelatively short-acting, but promethazine may be effectivefor up to 12 hours. Alimemazine and promethazinehave a more sedative effect than chlorphenamineand cyclizine (section 4.6). Chlorphenamine isused as an adjunct to adrenaline (epinephrine) in theemergency treatment of anaphylaxis and angioedema(section 3.4.3).Cautions and contra-indications Antihistaminesshould be used with caution in children with epilepsy.Most antihistamines should be avoided in acute porphyria,but some are thought to be safe (see section9.8.2). Sedating antihistamines have significant antimuscarinicactivity—they should not be used in neonatesand should be used with caution in children withurinary retention, glaucoma, or pyloroduodenalobstruction. Phenothiazine sedating antihistamines,such as alimemazine and promethazine, should not begiven to children under 2 years, except on specialistadvice, because the safety of such use has not beenestablished. See also MHRA/CHM advice, p. 167.Interactions: see Appendix 1 (antihistamines).Hepatic impairment Sedating antihistamines shouldbe avoided in children with severe liver disease—increased risk of coma.Pregnancy Most manufacturers of antihistaminesadvise avoiding their use during pregnancy; howeverthere is no evidence of teratogenicity, except forhydroxyzine where toxicity has been reported withhigh doses in animal studies. The use of sedating antihistaminesin the latter part of the third trimester maycause adverse effects in neonates such as irritability,paradoxical excitability, and tremor.Breast-feeding Most antihistamines are present inbreast milk in varying amounts; although not known tobe harmful, most manufacturers advise avoiding theiruse in mothers who are breast-feeding.Side-effects Drowsiness is a significant side-effectwith most of the older antihistamines although paradoxicalstimulation may occur rarely in children, especiallywith high doses. Drowsiness may diminish after afew days of treatment and is considerably less of aproblem with the newer antihistamines (see also notesabove). Side-effects that are more common with theolder antihistamines include headache, psychomotorimpairment, and antimuscarinic effects such as urinaryretention, dry mouth, blurred vision, and gastro-intestinaldisturbances. Other rare side-effects of antihistaminesinclude hypotension, palpitation, arrhythmias,extrapyramidal effects, dizziness, confusion, depression,sleep disturbances, tremor, convulsions, hypersensitivityreactions (including bronchospasm, angioedema,anaphylaxis, rashes, and photosensitivity reactions),blood disorders, and liver dysfunction.Non-sedating antihistaminesSkilled tasks Although drowsiness is rare, childrenand their carers should be advised that it can occur andmay affect performance of skilled tasks (e.g. cycling ordriving); alcohol should be avoided.3 Respiratory system