Tenoxicam and ketoprofen level monitoring with high performance liquid chromatography in patients affected by rheumatoid arthritis.

A new reversed-phase high-performance liquid chromatography (HPLC) technique was employed in order to monitor the plasma Tenoxicam (TNX) levels in 13 patients affected by rheumatoid arthritis who were participating in a short-term, controlled, randomized, double-blind TNX (20 mg once a day) vs Ketoprofen (KPF) study. The HPLC method described by Sutterwhite was used to measure the KPF levels in plasma samples from 10 rheumatoid patients assigned to the treatment with this drug (100 mg twice a day). The mean (+/- 1 SD) steady-state plasma TNX concentration was 11.138 +/- 3.55 micrograms/ml. Twelve out of 13 patients had a drug level within the steady-state range and 8 out of these 12 patients showed clinical improvement. A synovial fluid TNX concentration slightly lower than plasma levels (11.04 vs 13.58 micrograms/ml), and TNX synovial tissue levels remarkably lower than plasma levels (1.02 vs 3.5 and 0.85 vs 4.1 micrograms/ml) were observed in three further rheumatoid patients. The mean plasma concentration of KPF (+/- 1 SD) was 3.23 +/- 2.68 micrograms/ml and only two patients showed drug levels within the therapeutic range. In some cases the lack of compliance with the treatment regimen was proved in both groups, and an explanation for the poor efficacy of the drug was provided. A positive clinical result was reached in some of the patients with low drug plasma levels, in both the TNX and KPF groups. Gastrointestinal side-effects were observed in 4 patients from both groups, 2 within the therapeutic range and 2 below. This finding confirms that several variables, in addition to the plasma drug concentration, condition the efficacy and side-effects of an NSAID.