The Analgesic Efficacy of Intra-Articular Acetaminophen in an Experimental Model of Carrageenan-Induced Arthritis

BACKGROUND: Acetaminophen is one of the most common drugs used for the treatment of pain and fever. OBJECTIVES: To examine the effects of intra-articular (IA) acetaminophen on carrageenan-induced arthritic pain-related behaviour and spinal c-Fos expression in rats. METHODS: The present study was performed using 20 Sprague Dawley rats. Forty microlitres of IA 0.9% NaCl was injected in the control group, and 40 mu L of IA carrageenan was injected in the carrageenan group. One hour after carrageenan injection, 400 mu g of IA acetaminophen was injected in the IA acetaminophen group, and 400 mu g of intraperitoneal (IP) acetaminophen was injected in the IP acetaminophen group. One day before injection, and 4 h and 8 h after injection, diameters of both knee joints, motility of the rat, paw loading and joint mobility were assessed. After the rats were euthanized, L3 and L4 spinal segments were excised for c-Fos assessment. RESULTS: IA acetaminophen decreased both the severity and distribution of c-Fos expression. IP acetaminophen decreased only the distribution of c-Fos expression. IA acetaminophen decreased knee diameter at 8 h. IA and IP acetaminophen increased rat motility and paw loading scores. Joint mobility scores of IP acetaminophen were similar to saline at 8 h. CONCLUSIONS: Results of the present study indicate an analgesic and/or possible anti-inflammatory effect of IA acetaminophen and provide further evidence on the efficacy of systemic acetaminophen injection in reducing arthritic pain.Wo