Objective. - To evaluate the efficacy of intramuscular injection of thiocolchicoside (4 mg-2 ml) compared to placebo administered twice daily for 5 days in patients suffering from acute low back pain.

Patients and methods. - Multicenter, randomized, double-blinded, placebo-controlled trial. The study was conducted between July 1998 and March 2000 in five centers. Hospitalized patients with acute low back pain were included. The primary evaluation criterion was spontaneous pain at rest assessed by visual analog scale (VAS). Hand-to-floor distance, muscle spasm intensity, patients' global evaluation and analgesic tablet (paracetamol) consumption were used as secondary evaluation criteria.

Results. - One hundred and forty nine patients were included. Both groups showed improvement on spontaneous pain assessed by VAS at the end of day 1; however, improvement was statistically significant in thiocolchicoside group on day 3 (P < 0.001). Hand-to-floor distance and muscle spasm determined by palpation decreased significantly on day 5 in thiocolchicoside group (P < 0.0005 for both). According to the patients' global evaluation, 76.8% of patients in thiocolchicoside group evaluated the treatment as very good/good (P < 0.0005). Also a significant difference was observed in favor of the thiocolchicoside group in the total paracetamol consumption (P < 0.001). Treatment was well tolerated in both groups and none of the patients was withdrawn from the study due to an adverse effect.

Conclusion. - Twice daily administration of 4 mg thiocolchicoside for 5 days provides an efficient and safe treatment for patients with acute low back pain accompanied by muscle spasm.