[Relation of dose, serum concentration and side effects in intravenous aminophylline therapy]

Routine intravenous aminophylline therapy was monitored by drug level measurements in 45 hospitalized patients with chronic obstructive bronchitis. Only 44% had theophylline serum concentrations (Cp) in the optimum range (10-20 mg/l), while in 36% of patients potentially toxic Cp values were observed. The incidence of side effects was related to theophylline serum concentration: 78% in cases with Cp greater than 30 mg/l against 24% in cases with Cp less than 20 mg/l. Theophylline toxicity occurred most frequently in elderly patients with cardiac failure, who had markedly reduced theophylline clearances. To avoid excessive drug accumulation the usual aminophylline dose should be reduced by 50% when clinical signs of cardiac failure are present. In addition, measurement of theophylline serum concentration is often necessary for optimum dosage adjustment.