Ketotifen (KT) was encapsulated into poly(D,L-lactide) (PLA) and poly(D,Llactide-co-glycolide) (PLGA 50/50) by spray-drying to investigate the use of biodegradable drug-loaded microspheres as delivery systems in the intraperitoneal cavity. Ketotifen stability was evaluated by HPLC, and degradation was not observed. Drug entrapment efficiency was 74 AE 7% (82 AE 8 mg KT/mg for PLA) and 81 AE 6% (90 AE 7 mg KT/mg for PLGA 50/50). PLA microspheres released ketotifen (57% of encapsulated KT) in 350 h at two release rates (221 mg/h, 15 min to 2 h; 1.13 mg/h, 5-350 h). A quicker release of ketotifen took place from PLGA 50/50 microspheres (67.4% of encapsulated KT) in 50 h (322 mg/h, 15 min to 2 h; 16.18 mg/h, 5-50 h). After intraperitoneal administration (10 mg KT/kg b.w.), microsphere aggregations were detected in adipose tissue. Ketotifen concentration was determined in plasma by HPLC. The drug released from PLA and PLGA 50/50 microspheres was detected at 384 and 336 h, respectively. Noncompartmental analysis was performed to determine pharmacokinetic parameters. The inclusion of ketotifen in PLGA and PLA microspheres resulted in significant changes in the plasma disposition of the drug. Overall, these ketotifen-loaded microspheres yielded an intraperitoneal drug release that may be suitable for use as delivery systems in the treatment of inflammatory response in portal hypertension. ß 2007 Wiley-