An open-label, noncomparative study of the efficacy and tolerability of a once-daily piroxicam fast-dissolving dosage form (FDDF) comprised 157 patients aged 15 to 76 years (56.7% men) with acute low back pain of not more than 48 hours' duration. Patients received 40-mg piroxicam FDDF once daily for the first 2 days and 20 mg once daily for up to a total of 14 days of treatment. Fifteen investigators in three countries examined patients at baseline and at follow-up visits on days 4, 8, and 15. All efficacy assessments-including general low back pain; pain on sitting, standing, and walking; overall severity of night pain; duration of morning stiffness; lumbosacral tenderness on moderate pressure; modified Schober test of ability to bend forward; restriction of passive motion; length of time to resumption of an activity impaired by back pain; and overall restriction of back motion-demonstrated statistically significant improvements from baseline at each follow-up visit. Relief of pain, noted 30 minutes after the first dose, was maintained for the 24-hour dosing interval during the first 3 days. At visit 4, after piroxicam FDDF treatment had been completed, the number of patients being assessed had declined by half, principally because the resolution of symptoms had prompted discontinuation of the study drug. At the end of the treatment, 82.9% of patients evaluated the efficacy of piroxicam FDDF as good or excellent and investigators rated efficacy as good or excellent in 85.6% of patients. Tolerability was also rated highly, with 91% of patients characterizing piroxicam FDDF treatment as good or excellent, and investigators rating the treatment as good or excellent in 92% of patients. In all, 12.7% of the patients experienced drug-related adverse events, most frequently involving the gastrointestinal system. Drug-related adverse experiences prompted discontinuation of the study medication in five (3.2%) patients. These results suggest that the newly developed dosage form, piroxicam FDDF, administered in a dosage of 40 mg/d for the first 2 days and 20 mg/d thereafter (for up to 14 days), is effective and well tolerated in the treatment of patients with acute low back pain.