II. Indications
III. Contraindications
- Older patients
- Sleep Apnea
- Severe COPD
IV. Efficacy
V. Precautions
- Maximize Analgesics (NSAIDs and Acetaminophen) as they are generally more effective
- Dose as needed and primarily at night to assist sleep (primary effect is sedation)
- Limit to adjunctive (primarily bedtime use) in Acute Low Back Pain (and avoid in Chronic Low Back Pain)
- Avoid concurrent use of CNS Depressants (e.g. Alcohol, Benzodiazepines, Opioids)
- Risk of respiratory depression and death
VI. Agents: Preferred
-
Cyclobenzaprine (Flexeril) 5 mg (up to 10 mg) orally at bedtime up to three times daily
- Best studied of all antispasmodic agents, appears consistently effective, and is inexpensive
- Anticholinergic adverse effects (related to Tricyclic Antidepressants)
- Methocarbamol (Robaxin) 750 to 1500 mg four times daily
- Significantly less expensive than Flexeril
- Warn about Urine Color change
VII. Agents: Higher risk of Adverse Effects
- Chlorzoxazone (Parafon Forte) 250-750 mg 3-4 times daily
- Risk of liver abnormalities and GI upset
- Metaxalone (Skelaxin) 800 mg 3-4 times daily
- Risk of liver, hematologic abnormalities and GI upset
- Less effective and expensive
- Orphenadrine (Norflex) 100 mg twice daily
- Risk of Tachycardia, hematologic abnormalities and GI upset
- Orphenadrine with 770 mg Aspirin and 60 mg Caffeine (Orphengesic Forte)
- Very expensive ($25/tab) rebranding of an older Muscle relaxant
- Unclear if any Muscle relaxant is indicated (low efficacy) and risk of falls and Fractures in older adults
- Aspirin adds additional bleeding risk including Gastrointestinal Bleeding
- (2020) presc lett 27(9): 51
VIII. Agents: Higher risk of dependence
-
Carisoprodol (Soma) 350 mg up to four times daily
- Schedule IV drug in U.S. as of January 2012
- Risk of transient neurologic changes, serious Allergic Reactions, Substance Abuse, and fatal Overdoses
- Metabolized to Meprobamate, a Sedative and FDA controlled substance similar to Barbiturates
- See Carisoprodol Poisoning
- Benzodiazepines
IX. References
- (2017) Presc Lett 24(2): 9-10
- (2012) Presc Lett 19(1): 6
- Beebe (2005) Am J Ther 12(2): 151-71 [PubMed]
- Chou (2004) J Pain Symptom Manage 28(2):140-75 [PubMed]
- See (2008) Am Fam Physician 78: 365-70 [PubMed]
Images: Related links to external sites (from Bing)
Related Studies
| methocarbamol (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing) | ||
| METHOCARBAMOL 500 MG TABLET | Generic | $0.04 each |
| METHOCARBAMOL 750 MG TABLET | Generic | $0.05 each |
| chlorzoxazone (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing) | ||
| CHLORZOXAZONE 500 MG TABLET | Generic | $0.23 each |
| metaxalone (on 9/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing) | ||
| METAXALONE 400 MG TABLET | Generic | $3.85 each |
| METAXALONE 800 MG TABLET | Generic | $0.60 each |
| orphenadrine (on 12/21/2022 at Medicaid.Gov Survey of pharmacy drug pricing) | ||
| ORPHENADRINE ER 100 MG TABLET | Generic | $0.46 each |
Ontology: Chlorzoxazone (C0008296)
| Definition (NCI) | A benzoxazolone derivative with mild sedative and centrally-acting muscle relaxant activities. Although its exact mechanism of action is unknown, chlorzoxazone (CZ) appears to act at the spinal cord and subcortical levels of the brain to inhibit multisynaptic reflex arcs involved in producing and maintaining muscle spasms. This agent is extensively hydroxylated by cytochrome P450 2E1 (CYP2E1) to 6-hydroxychlorzoxazone (HCZ),11,12 which is subsequently glucuronidated and eliminated renally. Highly selective for CYP2E1, CZ may be used as a selective probe for phenotyping CYP2E1 in humans; the ratio of HCZ-to-CZ plasma concentrations obtained 2 to 4 hours after oral administration of CZ may be used as a phenotypic measure of CYP2E1 enzymatic activity. |
| Definition (MSH) | A centrally acting central muscle relaxant with sedative properties. It is claimed to inhibit muscle spasm by exerting an effect primarily at the level of the spinal cord and subcortical areas of the brain. (From Martindale, The Extra Pharmacopoea, 30th ed, p1202) |
| Concepts | Pharmacologic Substance (T121) , Organic Chemical (T109) |
| MSH | D002753 |
| SnomedCT | 400361007, 44908000 |
| LNC | LP18103-9, MTHU003391 |
| English | Chlorzoxazone, 2(3H)-Benzoxazolone, 5-chloro-, chlorzoxazone, muscle relaxants skeletal chlorzoxazone, chlorzoxazone (medication), Chlorzoxazone [Chemical/Ingredient], CHLORZOXAZONE, chlorzoxozone, Chlorzoxozone, Chlorzoxozone (product), Chlorzoxozone (substance) |
| Swedish | Klorzoxazon |
| Czech | chlorzoxazon |
| Finnish | Klooritsoksatsoni |
| Russian | KHLORZOKSAZON, ХЛОРЗОКСАЗОН |
| Japanese | クロルゾキサゾン |
| Spanish | clorzoxozona (producto), clorzoxazona (producto), clorzoxazona, clorzoxozona (sustancia), clorzoxozona, Clorzoxazona |
| Polish | Chlorzoksazon |
| French | Chlorzoxazone |
| German | Chlorzoxazon |
| Italian | Clorozossazone |
| Portuguese | Clorzoxazona |
Ontology: Methocarbamol (C0025659)
| Definition (NCI) | A carbamate with centrally acting muscle relaxant properties. Though the exact mechanism of action of methocarbamol was not established, it's postulated to be via a mechanism similar of carbamate, inhibition of acetylcholinesterase at synapses in the autonomic nervous system, neuromuscular junction, and central nervous system. Methocarbamol has no direct effect on the contractile mechanism of striated muscle, the motor end plate or the nerve fiber. |
| Definition (MSH) | A centrally acting muscle relaxant whose mode of action has not been established. It is used as an adjunct in the symptomatic treatment of musculoskeletal conditions associated with painful muscle spasm. (From Martindale, The Extra Pharmacopoeia, 30th ed, p1206) |
| Concepts | Pharmacologic Substance (T121) , Organic Chemical (T109) |
| MSH | D008721 |
| SnomedCT | 387486000, 83973001 |
| LNC | LP16197-3, MTHU007392 |
| English | Carbamate, Guaiphenesin, Guaiphenesin Carbamate, Methocarbamol, 1,2-Propanediol, 3-(2-methoxyphenoxy)-, 1-carbamate, methocarbamol, methocarbamol (medication), muscle relaxants skeletal methocarbamol, METHOCARBAMOL, Methocarbamol [Chemical/Ingredient], Methocarbamol (product), Methocarbamol (substance) |
| Swedish | Metokarbamol |
| Czech | methokarbamol |
| Finnish | Metokarbamoli |
| Russian | GVAIFENEZINKARBAMAT, METOKARBAMOL, ГВАЙФЕНЕЗИНКАРБАМАТ, МЕТОКАРБАМОЛ |
| Japanese | メトカルバモル, ロバキシン, メトカルバモール, グアイフェネシンカルバメート |
| Polish | Robaksyna, Metokarbamol |
| Spanish | metocarbamol (producto), metocarbamol (sustancia), metocarbamol, Carbamato de Guaifenesina, Metocarbamol |
| French | Méthocarbamol |
| German | Guaiphenesincarbamat, Methocarbamol |
| Italian | Metocarbammolo |
| Portuguese | Carbamato de Guaifenesina, Metocarbamol |
Ontology: Orphenadrine (C0029309)
| Definition (NCI) | A muscarinic antagonist with muscle relaxant activity. Although the mechanism of action has not been determined, orphenadrine appears to block muscarinic acetylcholine receptors as well as N-methyl-D-aspartate (NMDA) receptors in the central nervous system (CNS). This may interfere with the transmission of nerve impulses from the spinal cord to the muscles and may help relax muscles. In addition, orphenadrine exerts antagonistic effects on histamine H1 receptors. |
| Definition (MSH) | A muscarinic antagonist used to treat drug-induced parkinsonism and to relieve pain from muscle spasm. |
| Concepts | Pharmacologic Substance (T121) , Organic Chemical (T109) |
| MSH | D009966 |
| SnomedCT | 35035001, 372714007 |
| LNC | LP15175-0, MTHU002564 |
| English | Methyldiphenylhydramine, Orphenadrine, Ethanamine, N,N-dimethyl-2-((2-methylphenyl)phenylmethoxy)-, orphenadrine (medication), Orphenadrine [Chemical/Ingredient], ORPHENADRINE, orphenadrine, Orphenadrine (product), Orphenadrine (substance) |
| Swedish | Orfenadrin |
| Czech | orfenadrin |
| Finnish | Orfenadriini |
| Russian | ORFENADRIN, METILDIFENILGIDRAMIN, МЕТИЛДИФЕНИЛГИДРАМИН, ОРФЕНАДРИН |
| Japanese | オルフェナドリン, メチルジフェニルヒドラミン |
| Polish | Orfenandryna, Metylodifenylohydramina |
| Spanish | orfenadrina (producto), orfenadrina (sustancia), orfenadrina, Metildifenilhidramina, Orfenadrina |
| French | Orphénadrine |
| German | Methyldiphenylhydramin, Orphenadrin |
| Italian | Orfenadrina |
| Portuguese | Metildifenilidramina, Orfenadrina |
Ontology: skeletal muscle relaxants (C0037250)
| Concepts | Pharmacologic Substance (T121) |
| MSH | D009465 |
| SnomedCT | 17893001, 372666009 |
| English | Muscle Relaxants, Skeletal, Relaxants, Skeletal Muscle, SKELETAL MUSCLE RELAXANTS, skeletal muscle relaxants (medication), muscle relaxants skeletal, [MS200] SKELETAL MUSCLE RELAXANTS, skeletal muscle relaxant, skeletal muscle relaxants, Skeletal muscle relaxant, Skeletal muscle relaxant (product), Skeletal muscle relaxant (substance), Skeletal muscle tone depressant, Skeletal muscle relaxant, NOS, Skeletal muscle tone depressant, NOS, Skeletal Muscle Relaxants |
| French | Myorelaxants, Décontracturants des muscles striés, Relaxants musculaires, Myorésolutifs, Décontracturants, Décontracturants musculaires, Relaxants des muscles squelettiques |
| Czech | myorelaxancia |
| Spanish | Relajantes del Musculo Esquelético, depresor del tono muscular esquelético, miorrelajante esquelético, relajante de músculo esquelético (sustancia), relajante de músculo esquelético, relajante del músculo esquelético (producto), relajante del músculo esquelético (sustancia), relajante del músculo esquelético |
| German | Skelettmuskelrelaxanzien |
| Portuguese | Relaxantes de Musculo Esquelético |
| Italian | Rilassanti muscolo scheletrici |
Ontology: metaxalone (C0163055)
| Definition (NCI) | An oxazolidinone with centrally-acting skeletal muscle relaxant properties. Although the exact mechanism through which metaxalone exerts its effect is largely unknown, it might be due to general central nervous system (CNS) depression. Metaxalone has no direct effect on the contractile mechanisms of striated muscle, the motor end plate, or the nerve fiber. |
| Concepts | Pharmacologic Substance (T121) , Organic Chemical (T109) |
| MSH | C011301 |
| SnomedCT | 87599003, 404863006 |
| LNC | LP100044-9, MTHU035865 |
| English | 5-((3,5-dimethylphenoxy)methyl)-2-oxazolidinone, metaxalone, Zorane, 2-Oxazolidinone, 5-((3,5-dimethylphenoxy)methyl)-, metaxalone (medication), muscle relaxants skeletal metaxalone, METAXALONE, metaxalone [Chemical/Ingredient], Metaxalone, Metaxalone (substance), Metaxalone (product) |
| Spanish | metaxalona (sustancia), metaxalona, metaxalona (producto) |
