Quantitation of dose and concentration-effect relationships for fenclofenac in rheumatoid arthritis.

Response to non-steroidal anti-inflammatory drugs (NSAIDs) is not usually assessed on the basis of concentration measurements: identification of a concentration-effect relationship has proved difficult to achieve. Dose and concentration-effect relationships of fenclofenac have been determined in a group of 18 patients with rheumatoid arthritis at three dose levels (600, 1200 and 1800 mg day-1). The study was double-blind and treatments were randomised according to a Latin square design. A multiple linear regression technique (GLIM) was used in the analysis. The best model to describe the change in effect in terms of dose and concentration incorporated an average slope and an individual subject intercept for each effect measurement. On average, an improvement in grip strength of 20 mm Hg could be obtained with an increase in fenclofenac (trough) concentration of 100 micrograms ml-1.