Variations in absorption of theophylline from two sustained-release products

The intrasubject variability in the absorption of two sustained-release theophylline products was investigated in eight healthy volunteers, aged 27 to 38 years. Each subject randomly received 500 mg of Somophyllin-CRT on two days and 600 mg of Theo-Dur on two other days. At least one week separated each of the study days. Blood samples were collected at frequent intervals after each dose over a 24-hour period. Serum theophylline concentrations were assayed in duplicate by means of an enzyme immunoassay. The serum theophylline concentration-time curves were used to calculate the peak serum concentrations, the time to peak concentration, and the area under the curves for each subject. The intrasubject variability of these values was great with both drugs, but Theo-Dur demonstrated greater variability than did Somophyllin-CRT.