Commonly Available Generic Muscle Relaxants
Generic muscle relaxants available in clinical practice include both antispasticity agents (baclofen, tizanidine, dantrolene) and antispasmodic agents (cyclobenzaprine, carisoprodol, methocarbamol, metaxalone, chlorzoxazone, orphenadrine). 1
Antispasticity Agents
These medications are primarily used for spasticity from upper motor neuron syndromes:
Baclofen - A GABA-B agonist available as 10 mg and 20 mg oral tablets, with documented efficacy for muscle spasm and spasticity particularly in CNS injury and neuromuscular disorders 2, 3, 4
Tizanidine - A centrally acting alpha-2 adrenoceptor agonist with both antispastic and antispasmodic activity, showing efficacy across common indications for skeletal muscle relaxants 3, 5
Dantrolene - Acts by affecting the contractile response of muscle beyond the myoneural junction, interfering with calcium release from the sarcoplasmic reticulum 6, 4
Antispasmodic Agents
These medications are primarily used for peripheral musculoskeletal conditions:
Cyclobenzaprine - The most heavily studied antispasmodic agent, consistently shown to be effective for various musculoskeletal conditions including acute back and neck pain 1, 4, 7
Carisoprodol - Effective compared to placebo for musculoskeletal conditions, though it is metabolized to meprobamate and carries risks for abuse and overdose 1, 4
Methocarbamol - Less sedating option, though effectiveness evidence is limited and elimination is significantly impaired in patients with liver and kidney disease 3, 4, 7
Metaxalone - Less sedating alternative with limited effectiveness data, contraindicated in patients with significant hepatic or renal dysfunction 3, 4, 7
Chlorzoxazone - Limited or inconsistent data regarding effectiveness, associated with hepatotoxicity that is generally reversible 1, 4
Orphenadrine - Available as 60 mg per 2 mL injection (30 mg/mL) for intravenous or intramuscular use, with anticholinergic properties that can cause confusion and cardiovascular instability 8, 3, 4
Neuromuscular Blocking Agents (Anesthesia Use)
For perioperative use, distinct from the above skeletal muscle relaxants:
Succinylcholine - Fast-acting depolarizing muscle relaxant recommended at 1-2 mg/kg for rapid sequence induction 1
Rocuronium - Non-depolarizing agent recommended at 0.9-1.2 mg/kg for rapid sequence induction, mainly eliminated in urine and bile 1
Atracurium - Benzylisoquinoline muscle relaxant with organ-independent elimination (Hofmann reaction and ester hydrolysis), recommended for patients with renal or hepatic failure 1
Cisatracurium - One of ten isomers of atracurium with overwhelmingly non-enzymatic elimination, also recommended for renal or hepatic failure 1
Important Clinical Distinctions
The term "skeletal muscle relaxants" encompasses two pharmacologically distinct groups that are often confused in clinical practice. 4, 9 Antispasticity agents (baclofen, tizanidine, dantrolene) treat upper motor neuron syndromes, while antispasmodic agents treat peripheral musculoskeletal conditions. 4, 9
No skeletal muscle relaxant has been proven superior to another for efficacy in comparative trials. 1, 4, 7 Choice should be based on adverse-effect profile, tolerability, cost, and specific patient factors rather than efficacy differences. 9, 7
Critical Safety Considerations
All skeletal muscle relaxants are associated with central nervous system adverse effects, primarily sedation and dizziness. 1, 7
Dantrolene carries a black box warning for potentially fatal hepatotoxicity, and chlorzoxazone is also associated with hepatotoxicity. 1, 4
Carisoprodol is classified as a controlled substance with substantial abuse and addiction potential. 3
Most muscle relaxants have not been proven superior to acetaminophen or NSAIDs for low back pain. 7