Absorption and dosage of theophylline in the horse after single and repeated administration of a microencapsulated preparation.

The kinetics of 2 formulations of theophylline were studied in horses. In an initial cross-over study (Phase I) serum concentration-time curves were determined for granulated and microencapsulated theophylline after a single oral administration (5 mg/kg bwt). In Phase II microencapsulated theophylline was administered at 5 mg/kg bwt/12 h for 10 days at feeding time, as in normal clinical practice. Although no significant differences between the 2 preparations were found with respect to the main kinetic parameters, the microencapsulated form was more evenly and completely absorbed from the digestive tract; furthermore, after the repeated treatment, its trough-peak serum concentrations were always within the therapeutic window and no toxic effects were observed in treated animals.