The purpose of this study was to determine the dose requirements and dose interval of a sustained-release theophylline sprinkle preparation (Somophyllin-12) necessary to maintain therapeutic serum theophylline concentrations in children with asthma. Eighteen patients aged 3-7 years (subgroup 1) and 21 patients aged 8-12 years (subgroup 2), who had been on continuous theophylline therapy with Somophyllin-12, completed the study. Prior to entry into the study, each patient's dosage of Somophyllin-12 was titrated to achieve predose and peak (4-hour postdose) theophylline levels in the therapeutic range (8-20 mg/L). The patients subsequently had predose and peak serum theophylline levels determined at baseline (week 0) and at weeks 2 and 4 of the study. The majority of children maintained theophylline levels in the therapeutic range throughout the 4-week trial, and t-tests showed no significant change from baseline in mean values of peak, trough, or peak-trough theophylline differences in either patient subgroup at weeks 2 and 4. Nevertheless, some individual patients had considerable variation from baseline in peak and trough theophylline levels at follow-up visits. Dosage requirements standardized for weight were significantly higher in patients in subgroup 1 than in subgroup 2 (21.3 +/- 4.5 mg/kg per day versus 17.5 +/- 4.7 mg/kg per day; p less than 0.05). The majority of the patients required 12-hourly administration of Somophyllin-12, but seven of 39 patients required 8-hour dosing.(ABSTRACT TRUNCATED AT 250 WORDS)