Effect of caffeine on acetaminophen analgesia

Abstract

The value of caffeine in combination with acetaminophen in the relief of pain from uterine cramping, episiotomy and 3rd molar extraction was studied. In the dental study, 173 patients received 2 or 4 tablets of 500 mg acetaminophen or the combination of 500 mg acetaminophen and 65 mg caffeine. In the 3 postpartum studies, 1345 patients received 1-3 tablets of acetaminophen, the combination or a placebo. The mean scores for the summary variable percent sum of the pain intensity differences (% SPID) were higher in all for the combination than for acetaminophen alone, and in 2 studies the null hypothesis of no differences was rejected. The relative potency estimates for % SPID were 1.9, 1.8 and 1.3 for the 3 studies in which bioassays could be performed and the pooled relative potency was 1.7% with a 95% confidence interval of 1.1-3.1. The results were essentially the same among pain models and among patient groups with similar habitual caffeine consumption. Onset of analgesia was also faster with the combination. Apparently, caffeine enhances the analgesic efficacy of acetaminophen.