[Evaluation of drug concentration in tissues after percutaneous administration of non-steroidal antirheumatics].

For some 10 years it has been usual practice to determine tissue drug concentrations following the application of topical antirheumatic agents. However, testing the measured drug concentrations for their therapeutic relevance continues to be difficult. An appropriate reference parameter is, for example, the IC50 of the inhibition of the prostaglandin synthesis. Moreover, tissue concentrations should be compared with those achieved following oral administration of clinically effective doses. Based upon practical experience with ibuprofen (CAS 15687-27-1) following both topical and oral administrations, it is illustrated how such studies and the tissue concentrations found could be evaluated and interpreted taking into particular consideration the sample size calculation and the therapeutic relevance of the results.