Chemistry:Chlorphenesin carbamate
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| Trade names | Maolate, Musil |
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| Formula | C10H12ClNO4 |
| Molar mass | 245.66 g·mol−1 |
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| Melting point | 86–92 °C (187–198 °F) |
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Chlorphenesin carbamate (marketed as Maolate, Musil, and Rinlaxer) is a central nervous system skeletal muscle relaxant used to treat muscle pain and spasms. It is the carbamate ester of chlorphenesin.[1] Chlorphenesin carbamate has a longer biological half-life than the related muscle relaxant methocarbamol and produces central nervous system effects, including sedation, that methocarbamol does not at comparable doses.[2][3] It is no longer marketed in the United States; the FDA withdrew approval of the sole remaining new drug application in 2020 after the holder repeatedly failed to file required annual reports.[4]
Pharmacology
Chlorphenesin carbamate acts as a selective blocker of polysynaptic reflex pathways at both spinal and supraspinal levels.[5] In spinalized rats, intravenous administration inhibited both the monosynaptic and polysynaptic spinal reflex, with the polysynaptic reflex more strongly depressed; unlike mephenesin, it did not affect the dorsal root potential evoked by dorsal root stimulation, though both drugs reduced motoneuron excitability.[6]
Broader motor-system studies across species found the compound decreased grip strength and inhibited corneal and pinna reflexes in mice, produced longer-lasting protection than mephenesin against picrotoxin-, pentylenetetrazol-, and electroshock-induced convulsions, and suppressed oxotremorine-induced tremor; however, unlike mephenesin it showed no anti-strychnine effect.[7] The same study reported inhibition of spinal reflex activity in rats, chicks, and frogs with a longer duration of action than mephenesin, and depression of both intercollicular and ischemic decerebrate rigidity.[7]
Antinociception
In adjuvant-induced arthritic rats, chlorphenesin carbamate produced an antinociceptive effect distinct from its muscle-relaxant activity, suggesting a role in pain modulation independent of spasmolysis.[8]
Pharmacokinetics
A comparative pharmacokinetic study in humans found the mean biological half-life of chlorphenesin carbamate to be 3.14 hours, significantly longer than the 1.20 hours measured for methocarbamol.[2] A later randomized, single-dose, two-period crossover trial in healthy Korean volunteers assessed the relative bioavailability of generic and branded 250 mg and 500 mg oral chlorphenesin carbamate tablets, supporting continued generic manufacture and clinical use of the drug outside the United States.[9]
Clinical studies
A controlled clinical trial compared the effects of chlorphenesin carbamate and carisoprodol on psychological test scores in patients treated for musculoskeletal conditions.[10]
Regulatory history
Chlorphenesin carbamate was marketed in the United States as Maolate (400 mg tablets, NDA 014217), held by Pan American Laboratories, LLC.[4] In March 2020, the Food and Drug Administration withdrew approval of this application, along with two unrelated NDAs, on the grounds that the holders had repeatedly failed to submit required annual reports.[4] The drug's availability in the United States is now listed as discontinued.[11]
Current research
As of 2025, chlorphenesin carbamate is under investigation in combination with hydroxychloroquine and modified FOLFIRINOX chemotherapy in a clinical trial for locally advanced or metastatic pancreatic cancer, reflecting continued research interest beyond its original indication.[12]
References
- ↑ "Chlorphenesin Carbamate | Drug Information, Uses, Side Effects, Chemistry". https://www.pharmacompass.com/chemistry-chemical-name/chlorphenesin-carbamate.
- ↑ 2.0 2.1 "Comparative pharmacokinetics of chlorphenesin carbamate and methocarbamol in man". Journal of Pharmaceutical Sciences 60 (11): 1686–1688. 1971. doi:10.1002/jps.2600601121. PMID 5133920. Bibcode: 1971JPhmS..60.1686F.
- ↑ "[Electroencephalographic effects of chlorphenesin carbamate, a new central muscle relaxant, in rabbits]" (in ja). Nihon Yakurigaku Zasshi 73 (4): 479–496. May 1977. doi:10.1254/fpj.73.479. PMID 908544.
- ↑ 4.0 4.1 4.2 "Withdrawal of Approval of Three New Drug Applications". Federal Register. 2020-03-16. https://public-inspection.federalregister.gov/2020-05498.pdf.
- ↑ "Chlorphenesin carbamate (Maolate)". https://www.medchemexpress.com/chlorphenesin-carbamate.html.
- ↑ "Effect of a muscle relaxant, chlorphenesin carbamate, on the spinal neurons of rats". Japanese Journal of Pharmacology 36 (1): 7–13. September 1984. doi:10.1254/jjp.36.7. PMID 6503049.
- ↑ 7.0 7.1 "Pharmacological study on a centrally acting muscle relaxant (chlorphenesin carbamate) with special reference to the effects on motor systems". Folia Pharmacologica Japonica 70 (3): 341–358. 1974. doi:10.1254/fpj.70.341. https://www.jstage.jst.go.jp/article/fpj1944/70/3/70_3_341/_article.
- ↑ "Antinociceptive effect of chlorphenesin carbamate in adjuvant arthritic rats". Research Communications in Chemical Pathology and Pharmacology 55 (2): 147–160. February 1987. PMID 3823606.
- ↑ "Relative bioavailability of generic and branded 250-mg and 500-mg oral chlorphenesin carbamate tablets in healthy Korean volunteers: a single-dose, randomized-sequence, open-label, two-period crossover trial". Clinical Therapeutics 31 (11): 2735–2743. November 2009. doi:10.1016/j.clinthera.2009.11.036. PMID 20110015.
- ↑ "The influence of chlorphenesin carbamate and carisoprodol on psychological test scores". Current Therapeutic Research, Clinical and Experimental 11 (9): 553–560. September 1969. PMID 4980885.
- ↑ "Chlorphenesin Carbamate: Indications, Side Effects, Warnings". https://www.drugs.com/cdi/chlorphenesin-carbamate.html.
- ↑ Yoo, Changhoon (12 April 2025). Hydroxychloroquine and Chlorphenesin Carbamate in Combination With mFOLFIRINOX in Pancreatic Cancer. https://clinicaltrials.gov/study/NCT05083780. Retrieved 2026-07-13.
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