Aim: We did a prospective study to investigate pharmacokinetics of a single intramuscularly (i.m.) administered Valdecoxib (VC) polymeric microparticles in New Zealand white rabbits. Method: Poly[lac(glc-leu)] microparticles encapsulating a potent cyclooxygenase-2- selective inhibitor, VC, were prepared by emulsion and solvent evaporation technique and administered i.m. to rabbits for pharmacokinetic study. Results: A single i.m. dose of drug-loaded poly[lac(glc-leu)] microparticles resulted in sustained therapeutic drug levels in the plasma for 49 days. The relative bioavailability was increased severalfold as compared with unencapsulated drug. Conclusions: Injectable poly[lac(glc-leu)] microparticles hold promise for increasing drug bioavailability and reducing dosing frequency for better management of rheumatoid arthritis. © Informa UK, Ltd.