Clinical experience with theophylline. A case for monitoring serum concentrations.

Administration of theophylline has often been associated with serious serum concentration-related side-effects and toxicity as well as lack of efficacy. A therapeutic drug monitoring programme which enables individualisation of dosage on the basis of pharmacokinetic principles is described. Patients taking a standard dose of a slow-release theophylline preparation equivalent to 256, 1 mg anhydrous theophylline 12-hourly were monitored. Of 44 patients, 68% had theophylline serum concentrations below the generally accepted therapeutic range. Four case reports illustrate the use of pharmacokinetic principles to determine optimum doses in the individual patient. The clinical improvement observed confirms the axiom: 'Drugs don't have doses--people have doses!'