Two specific skeletal muscle relaxants, orphenadrine and methocarbamol, are each used in more than 250,000 U.S. ED visits for low back pain annually, although scant evidence exists to determine the appropriateness of this approach.(7) Orphenadrine is a centrally acting medication with prominent anti-cholinergic and antihistaminic properties. The mechanism of action is not understood. Efficacy in low back pain may be related to non-specific analgesic properties. The mechanism of action of methocarbamol has also not been established. Its efficacy is thought to be related to CNS effects rather than direct effects on skeletal muscles.