The Analgesic Interaction of Misoprostol with Nonsteroidal Anti-Inflammatory Drugs

Abstract

The purpose of this project was to evaluate the analgesic efficacy of misoprostol when combined with ibuprofen or diclofenac Na. Animal experiments using the inflamed rat paw formalin model suggested that misoprostol potentiates the analgesic effect of some NSAIDs (nonsteroidal anti-inflammatory drugs) including diclofenac Na but not propionic acid derivatives or opiates. The dental pain model was used to evaluate the clinical relevance of this interaction. Patients received a single oral dose of study medication following surgical removal of impacted teeth. Patients were medicated for moderate to severe postsurgical pain and then filled in an analgesic diary for a 6-h observation period. Several blood samples were taken over the observation period. In addition, microdialysis samples were taken directly from the extraction socket and were analyzed for immunoreactive prostaglandin E(2) levels. The studies were single-dose, parallel group and double-blind assays. In the first study, 70 patients received an oral dose of either placebo (n = 13), misoprostol 200 &mgr;g (n = 18), ibuprofen 200 mg (n = 19), or the combination of misoprostol + ibuprofen (n = 20). Misoprostol alone demonstrated a small analgesic effect compared to placebo. Both the ibuprofen and combination groups were substantially more effective than placebo but not different from each other. The combination group had higher ibuprofen blood levels during the first 45 min but had a lower C(max) and longer time to T(max). The second study evaluated oral doses of placebo (n = 11), misoprostol 200 &mgr;g (n = 21), diclofenac Na 50 mg (n = 18), and the combination of misoprostol + diclofenac Na (n = 20). Relative to placebo, misoprostol performance was similar to the first study. When the results of the two studies were combined, there was a small, but statistically significant, analgesic effect for misoprostol. Diclofenac Na was superior to both placebo and to misoprostol alone. The combination was the most effective treatment, and for hours 4--6 it was significantly better than diclofenac Na alone. Analysis of the blood samples showed an earlier and higher peak effect for the diclofenac Na group compared to the combination, and the combination again had a lower C(max). The microdialysis probe assays demonstrated that misoprostol depressed PGE(2) levels at the peripheral site of trauma over the first 2 h after surgery. These pilot studies used small samples, and the results only suggest trend effects. Both studies demonstrated that misoprostol 200 &mgr;g, a prostaglandin analog, does have an analgesic effect. When combined with ibuprofen, there was no potentiation of analgesia. In contrast, the combination of misoprostol + diclofenac Na demonstrated an enhanced peak effect, total effect for pain intensity difference and pain relief (sum pain intensity difference [SPID] and total pain relief [TOTPAR]), and