Muscle Relaxants May Not Always Cause Drowsiness When Effective: A Post-Hoc Analyisis of Cyclobenzaprine ER

AUSTIN, TXApproximately half of patients treated for acute, painful muscle spasm responded to 15mg and 30mg oral doses of cyclobenzaprine extended-release (CER) with little to no drowsiness, challenging the common medical belief that sedation is integral to efficacy of skeletal muscle relaxants. That's the conclusion of a study assessing the association between drowsiness and efficacy with once-daily dosing of the agents, as reported during the American Pain Society's 30th Annual Scientific Meeting.

Bill H. McCarberg, MD, of Kaiser Permanente, Escondido, CA, and colleagues noted that the assumption is frequently made that the efficacy of skeletal muscle relaxants requires some degree of sedation. To test that hypothesis, they conducted a post-hoc analysis on pooled data from two identically designed, randomized, double-blind, placebo-controlled, parallel-group studies in patients with acute, painful muscle spasm.

Patients were randomized to receive CER 15mg once daily, CER 30mg once daily, or placebo. Daily assessments of daytime drowsiness were recorded by patients in a diary each day (1=no drowsiness, 5=extreme drowsiness). At Day 4, patients were stratified into two categories based on reported daytime drowsiness—“little to none” or “some to extreme.” Patients were analyzed for a positive efficacy response, defined as good to excellent improvement on the patient's rating of medication helpfulness at Day 4. The relationship between drowsiness and efficacy at Day 4 was also assessed by a correlation analysis (Kendall's tau b).

In the CER 15mg group, of the 59 patients with very little to no drowsiness, 32 (54%) reported good to excellent medication helpfulness, which was also noted by 33 of 57 of those (58%) who reported some to extreme drowsiness. In the CER 30mg group, of 50 patients with little to no drowsiness, 27 (54%) reported good to excellent medication helpfulness, as did 41 of 70 (59%) with some to extreme drowsiness. Correlation analysis showed only a very weak association between Day 4 drowsiness and medication helpfulness for CER 15mg (tau=0.115, 95% CI -0.050–0.280) and CER 30mg (tau=0.126, 95% CI -0.036–0.288).

The authors concluded these results demonstrated a lack of clear association between efficacy of CER and degree of drowsiness reported by patients. The study was sponsored by Cephalon, Inc.