Placebo-controlled study of the analgesic efficacy of an effervescent formulation of 500 mg paracetamol in arthritis of the knee or the hip

The analgesic efficacy and safety of an effervescent formulation of paracetamol were studied in 60 patients with chronic pain due to arthritis of the knee or the hip. This double-blind randomized study was designed to compare paracetamol(P) (500 mg x 2; three times daily) with a placebo (PL) for 7 days in two parallel groups of 30 patients. Efficacy was assessed by the patient every evening by: 1. pain scores rated on a 100-mm visual analog scale (VAS), 2. discomfort scores defining the activity level reduction (none, mild, moderate, severe) and 3. number of awakenings caused by the pain during the previous night. At the end of the study overall efficacy was assessed by the patient on a verbal scale (none, poor, moderate, good, very good) and by the desire to continue the treatment (yes, no). Any side-effects were recorded continuously during the study and overall safety was assessed at the end of the study. Twenty-three men and 37 women were included (extremes 20-70 years, mean 56 years). Analgesic efficacy was significantly better with paracetamol than with placebo for the main criteria except the number of awakenings: overall efficacy (p<0.05), desire to continue (p<0.05), SPID (Sum of Pain Intensity Differences) on VAS daily pain scores (p<0.05). The evolution of pain on standing was significantly different from baseline with paracetamol, and not with placebo. The number of side-effects (P:4, PL:7) the number of side-effects which induced cessation of treatment (P:2, PL:2) and the overall safety assessment(P:82% vs PL:71% good or excellent) were not significantly different. This paracetamol formulation has been found to be an effective and safe analgesic treatment in arthritis of the knee or the hip, with 64% of the patients wishing to continue this treatment (vs 37% with placebo: difference is significant).