Drowsiness, although rare, may occur and may affect the performance of skilled tasks. Occasional reports of convulsions in patients taking antihistamines suggest a need for caution in patients with epilepsy. Many antihistamines are excreted in the urine in the form of active metabolites so that dosage reduction may be necessary in renal impairment. Caution is also needed in hepatic impairment. Antihistamines should not be given to neonates because the latter is more susceptible to antimuscarinic effects. It also has been recommended that antihistamines should be avoided in young children. Elderly patients are also susceptible to many of the adverse of antihistamines and, in particular, their inappropriate use for postural giddiness should be avoided.
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