Piroxicam serum levels in patients treated for rheumatic diseases.

Serum levels of piroxicam were observed for periods of one to 15 months in patients who had a variety of rheumatic diseases. At a dose of 20 mg per day, patients' serum levels ranged from undetectable (less than 0.5) to 24.8 micrograms/mL. Mean serum levels did not vary with age or body weight and remained relatively constant in individual subjects during the period of follow-up. Thus, there is no justification for altering the recommended dose of 20 mg based solely on patient age or weight. Concomitant administration of salicylate or acetaminophen was associated with decreased serum levels of piroxicam, but other drugs, such as diuretics, prednisone, and cimetidine, had no discernible effect on piroxicam levels. Gastrointestinal toxicity, requiring discontinuance of piroxicam therapy, occurred in only four patients, and there was no association between serum levels of piroxicam and gastrointestinal toxicity.