A single-dose comparison of three slow-release theophylline oral preparations in healthy Thai volunteers.

The study was done to compare the pharmacokinetic characteristics of three slow-release theophylline (SRT) preparations. Twelve healthy nonsmokers were randomly assigned a single dose of the following treatments at weekly intervals: Theo-Dur, Theo-24 or Xanthium orally, or aminophylline intravenously. Serially collected serum samples were analyzed for theophylline with use of fluorescence polarization immunoassay (FPIA). All three SRT preparations showed reliable absorption characteristics, but Theo-Dur had a shorter Tmax and MRT and a higher Ka. The pharmacokinetic characteristics of Theo-24 and Xanthium were similar except that Xanthium had lower bioavailability. Using single dose data for simulation of steady state pharmacokinetics, we found that a once-a-day dosage regimen with either Theo-24 or Xanthium would maintain serum levels within the therapeutic range for average non-smoking young adults whereas more frequent dosing intervals with Theo-Dur would be more appropriate. Our results argue against open substitution of SRT preparations without, close monitoring of the serum theophylline concentrations when a change is made.