Is Baclofen a Skeletal Muscle Relaxant?
Yes, baclofen is classified as a skeletal muscle relaxant and antispastic agent by the FDA, but it is specifically indicated for spasticity from upper motor neuron conditions (multiple sclerosis, spinal cord injuries), not for skeletal muscle spasm from musculoskeletal disorders like back pain. 1
FDA-Approved Classification and Indications
- Baclofen is officially described by the FDA as "a muscle relaxant and antispastic" agent 1
- The FDA specifically approves baclofen for alleviating signs and symptoms of spasticity resulting from multiple sclerosis and spinal cord diseases 1
- Baclofen is explicitly NOT indicated for skeletal muscle spasm resulting from rheumatic or musculoskeletal disorders 1
Mechanism and Clinical Context
- Baclofen works as a GABA-B agonist, acting centrally in the CNS to reduce spasticity 2
- The term "muscle relaxant" is somewhat of a misnomer for all these drugs, as they don't directly relax skeletal muscle but likely work through sedative and central nervous system properties 3
- Baclofen demonstrates efficacy specifically for spasticity of spinal origin (80% response rate) and muscle spasms (87% reduction), but has limited evidence for musculoskeletal conditions like low back pain 3, 4
Important Clinical Distinction
- Skeletal muscle relaxants are divided into two categories: antispasticity agents (baclofen, tizanidine, dantrolene) for upper motor neuron conditions, and antispasmodic agents (cyclobenzaprine, carisoprodol) for peripheral musculoskeletal conditions 5
- For lumbar radiculopathy and acute back pain, guidelines recommend tizanidine over baclofen due to sparse evidence supporting baclofen's use in these conditions (only 2 trials) 3
- When muscle relaxation is needed for musculoskeletal pain, baclofen is not the preferred choice despite its classification as a muscle relaxant 3, 1
Safety Profile
- Baclofen can be used at high doses (exceeding 80 mg daily) with adequate safety monitoring, though conventional dosing remains lower 6
- Side effects requiring dose reduction occur in approximately 20% of patients 4
- Baclofen requires dose adjustment in renal insufficiency, as impaired renal clearance can lead to gradual accumulation of drug levels over time 3, 6