Skeletal muscle relaxants and spasmolytics
Drugs that ease spasticity or muscle spasm: in the spinal cord (baclofen, tizanidine), in muscle (dantrolene) or at the nerve ending (botulinum toxin).
What they are
Two different problems share this group. Spasticity comes from upper motor neuron lesions (multiple sclerosis, spinal cord injury, stroke, cerebral palsy) and responds to baclofen, tizanidine, dantrolene, benzodiazepines and botulinum toxin. Acute muscle spasm after a musculoskeletal injury is treated briefly with centrally acting sedative relaxants such as cyclobenzaprine and methocarbamol, which do not help spasticity. Neuromuscular blockers used in anaesthesia are a separate class.
Mechanism of action
Baclofen activates GABA-B receptors and tizanidine alpha-2 receptors in the spinal cord, both reducing excitatory drive to motor neurons. Dantrolene blocks calcium release through the ryanodine receptor RyR1 inside the muscle fibre. Botulinum toxin cleaves SNARE proteins at the nerve terminal so acetylcholine is not released. Cyclobenzaprine and methocarbamol act in the brain, largely through sedation.
Target: GABA-B and alpha-2 receptors (spinal cord), RyR1 (muscle), SNAP-25 (nerve terminal)
Drugs in this class
- BaclofenA GABA-B agonist that eases spasticity from multiple sclerosis or spinal cord injury, by mouth or into the spinal…GABA-B receptor (GABA-B1 subunit)
- DantroleneRelaxes skeletal muscle from inside the fibre by blocking calcium release. Given intravenously, it is the specific…Ryanodine receptor 1 (RyR1), the calcium-release channel of the sarcoplasmic reticulum
- Botulinum toxin type AA bacterial toxin injected in tiny amounts into a muscle, gland or the bladder; it blocks acetylcholine release for…SNAP-25, a SNARE protein needed for acetylcholine release
- CyclobenzaprineA centrally acting muscle relaxant related to tricyclic antidepressants, used for a short time for painful muscle…Brainstem serotonin and noradrenaline pathways (5-HT2 receptors; exact target uncertain)
- TizanidineA short-acting alpha-2 agonist, related to clonidine, that relieves spasticity; it lowers blood pressure, sedates and…Alpha-2A adrenergic receptor
- MethocarbamolAn older muscle relaxant whose effect seems to come from general sedation; used briefly for acute musculoskeletal pain.No specific target known (general CNS depression)
- CarisoprodolA centrally acting muscle relaxant for short-term muscle injuries. Its metabolite meprobamate is sedating and…Central nervous system (sedative action; metabolite meprobamate)
Others in the class
- Carisoprodol
- Metaxalone
- Orphenadrine
- Botulinum toxin type B (rimabotulinumtoxinB)
Test yourself
Think of the answer, then tap the question to see it.
Which relaxant acts inside the muscle fibre?
Dantrolene (it blocks RyR1 calcium release).
Which two spinal receptors are targeted by antispasticity drugs?
GABA-B (baclofen) and alpha-2 adrenergic (tizanidine).
Is cyclobenzaprine a good choice for spasticity after spinal cord injury?
No; it is for short-term musculoskeletal spasm, not spasticity of central origin.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - BACLOFEN injection (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - DANTROLENE injection, powder, for solution (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.