Effects of Low-dose Intramuscular Ketorolac on Experimental Pain in the Masseter Muscle of Healthy Women

Aims: To investigate the effect of a low dose of intramuscular (im) ketorolac compared with lidocaine (LA) in a double-blinded, randomized, and controlled trial. Methods: Twelve healthy women participated in three sessions and received two injections into their right masseter muscle per session. The first injections contained hypertonic saline (HS, 5% in 0.2 mL) to induce muscle pain. The second injections were given 30 minutes later and contained, together with HS, either ketorolac (3 mg in 0.2 mL), LA (2% lidocaine in 0.2 ml), or HS alone (control). HS-evoked pain intensity was scored on a 0 to 10 electronic visual analog scale (VAS) measuring peak, duration, and area under the curve (AUC). Pressure pain thresholds (PPT), pressure pain tolerance levels (PPTOL), and pain on palpation (POP) were determined bilaterally on the masseter muscle before and 5, 15, and 25 minutes after the injections. Maximum jaw opening (MJO) was measured at baseline and every 10 minutes after. McGill Pain Questionnaire (MPQ) scores and the extent of the HS-evoked pain (pain drawings) were recorded at baseline, 2 minutes after the first and second injections, and every 10 minutes during the entire experimental session. Results: There were no differences between the three sessions in HS-evoked pain measures from the first injection (P > .05). During the second injection, HS + LA demonstrated significantly lower VAS peak, duration, and AUC scores than control and HS + ketorolac (P .001). In the HS + ketorolac session, the VAS AUC was significantly lower than in the control session (P .005). The sessions had no main effect on PPT, PPTOL, POP, MJO, or pain drawings (P > .05). Conclusion: A low dose of im ketorolac has a significant and immediate analgesic effect on HS-evoked jaw muscle pain but significantly less than LA. A local anesthetic-like effect may be the underlying mechanism. Keywords: experimental muscle pain, ketorolac, local anesthetics, NSAIDs, trigeminal nociception