[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › Skeletal muscle relaxants and spasmolytics # 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). Updated Nov 1, 2026 ## 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) ## Key points - Baclofen, especially intrathecal, must never be stopped abruptly: withdrawal causes fever, altered mental state, rebound spasticity and rhabdomyolysis. - Dantrolene is the specific treatment of malignant hyperthermia; long-term oral use can cause hepatitis. - Tizanidine is a short-acting alpha-2 agonist cleared by CYP1A2: ciprofloxacin and fluvoxamine are contraindicated; watch blood pressure and liver tests. - Cyclobenzaprine is a tricyclic relative: no MAO inhibitors, caution in heart disease, glaucoma and urinary retention, and short courses only. - Botulinum toxin type A cleaves SNAP-25; its boxed warning is distant spread with swallowing and breathing problems. ## Drugs in this class - [**Baclofen** A 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)](https://durgical.com/en/pharmacology/baclofen/) - [**Dantrolene** Relaxes 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](https://durgical.com/en/pharmacology/dantrolene/) - [**Botulinum toxin type A** A 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](https://durgical.com/en/pharmacology/botulinum-toxin-type-a/) - [**Cyclobenzaprine** A 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)](https://durgical.com/en/pharmacology/cyclobenzaprine/) - [**Tizanidine** A short-acting alpha-2 agonist, related to clonidine, that relieves spasticity; it lowers blood pressure, sedates and… Alpha-2A adrenergic receptor](https://durgical.com/en/pharmacology/tizanidine/) - [**Methocarbamol** An older muscle relaxant whose effect seems to come from general sedation; used briefly for acute musculoskeletal pain. No specific target known (general CNS depression)](https://durgical.com/en/pharmacology/methocarbamol/) - [**Carisoprodol** A centrally acting muscle relaxant for short-term muscle injuries. Its metabolite meprobamate is sedating and… Central nervous system (sedative action; metabolite meprobamate)](https://durgical.com/en/pharmacology/carisoprodol/) ## 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. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/classes/skeletal-muscle-relaxants-and-spasmolytics/) [More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology) [← All of pharmacology](https://durgical.com/en/pharmacology/) 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](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d63af5f0-c275-480b-89b5-6cf1ad55ab63) (DailyMed (U.S. National Library of Medicine), 2026); [DailyMed - DANTROLENE injection, powder, for solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ab0efc75-0598-4f4e-91ad-6195bb2661fe) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=M03BX) (WHO Collaborating Centre for Drug Statistics Methodology, 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/classes/skeletal-muscle-relaxants-and-spasmolytics/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/classes/skeletal-muscle-relaxants-and-spasmolytics/