Impaired intrinsic chiral inversion activity of ibuprofen in rats with adjuvant-induced arthritis

Stereoselective Pharmacokinetics and Chiral Inversion of Ibuprofen in Adjuvant-induced Arthritic Rats

2-Arylpropionic acid (2-APA) nonsteroidal anti-inflammatory drugs are commonly used in racemic mixtures (rac) for clinical use. 2-APA undergoes unidirectional chiral inversion of the in vivo inactive R-enantiomer to the active S-enantiomer. Inflammation causes the reduction of metabolic activities of drug-metabolizing enzymes such as cytochrome P450 (P450) and UDP-glucuronosyltransferase. However, it is unclear whether inflammation affects the stereoselective pharmacokinetics and chiral inversion of 2-APA such as ibuprofen (IB). We examined the effects of inflammation on the pharmacokinetics of R-IB and S-IB after intravenous administration of rac-IB, R-IB, and S-IB to adjuvant-induced arthritic (AA) rats, an animal model of inflammation. The plasma protein binding of rac-IB, glucuronidation activities for R-IB and S-IB, and P450 contents of liver microsomes in AA rats were determined. Total clearance (CL_tot) of IB significantly increased in AA rats, although the glucuronidation activities for IB, and P450 contents of liver microsomes decreased in AA rats. We presumed that the increased CL_tot of IB in AA rats was caused by the elevated plasma unbound fraction of IB due to decreased plasma albumin levels in AA rats. Notably, CL_tot of R-IB but not S-IB significantly increased in AA rats after intravenous administration of rac-IB. These results suggested that AA could affect drug efficacies after stereoselective changes in the pharmacokinetics of R-IB and S-IB.