This is not surprising since cyclopentolate is structurally similar to atropine but contains a dimethylated side group also found in some tranquillisers and hallucinogenic drugs. CNS toxicity induced by cyclopentolate is especially prominent in children and the elderly. This seems to indicate that CNS immaturity or ageing is necessary for its potent psychotomimetic action to become manifest. As with atropine, there is increased incidence of systemic toxic reactions in children with brain damage. The peripheral signs and symptoms of cylopentolate toxicity are variable and frequently absent. Gastrointestinal toxicity consisting of ileus or gastroenteritis which has been observed with cyclopentolate concentrations of 0.5% or greater in pre-term infants due reduced gastric acid secretion and volume.