Multicentre evaluation of the adenosine agonist GR79236X in patients with dental pain after third molar extraction

Background. Adenosine is analgesic in humans, and the selective adenosine A1 receptor agonist GR79236X has significant anti-nociceptive activity in an animal pain model of inflammatory pain. Methods. Seventy-nine patients with moderate pain after third molar extraction under general anaesthesia were randomized to receive a 15 min double-blind infusion containing either GR79236X 4 μg kg^-1, GR79236X 10 μg kg^-1, diclofenac 50 mg, or saline placebo. Rescue analgesia was promptly available to all patients. Results. Meaningful pain relief (mild or no pain) was attained by 9 (47%) patients in the placebo group, 12 (63%) patients in the GR79236 4 μg kg ^-1 group, 10 (48%) patients in the 10 μg kg^-1 group, and 16 (80%) patients in the diclofenac 50 mg group. Neither dose of GR79236 produced a significant improvement over placebo, but diclofenac was superior to both placebo (P=0.036) and GR79236 10 μg kg^-1 (P=0.034). Median times to rescue or additional analgesia were 62, 100, 60, and 363 min for patients receiving placebo, GR79236 4 μg kg^-1, 10 μg kg^-1, and diclofenac 50 mg, respectively (diclofenac significantly longer than placebo, P=0.002 log-rank test). Pain control was poor in the placebo group and in both GR79236 groups, with between 79 and 86% of patients having good pain control (i.e. mild or no pain) for <20% of the time compared with only 30% of patients who received diclofenac. Conclusion. We found no evidence of efficacy of GR79236 compared with placebo, but the active control diclofenac was effective. It is possible that a higher dose of GR79236 might have been effective or that i.v. administration of this drug does not achieve appropriate concentrations in the brain or peripheral nerves.