Interaction of cimetidine and theophylline in two infants.

Theophylline has such a narrow safety margin that a small reduction in clearance may result in toxic effects. In adults cimetidine has decreased the clearance of theophylline and toxic effects have resulted.' Weinberger and associates2 recently reported an increase in the serum theophylline concentration to a potentially toxic level in a 15-year-old girl given theophylline and cimetidine concurrently. Because children metabolize theophylline more rapidly than adults, they need larger doses and may therefore be at greater risk of a cimetidine-theophylline interaction. The risk may be further increased by the saturation kinetics previously reported in children.3 We report two cases in which an infant's theophylline clearance was impaired by cimetidine.

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