Orphenadrine is a skeletal muscle relaxant.[2][3] It is used to relieve pain caused by muscle injuries such asstrains andsprains, in combination with rest and physical therapy.[3] A 2004 review found fair evidence that orphenadrine is effective for acute back or neck pain, but found insufficient evidence to establish the relative efficacy of the drug in relation to other drugs in the study.[4]
Orphenadrine and other muscle relaxants are sometimes used to treat pain arising fromrheumatoid arthritis but there is no evidence they are effective for that purpose.[5]
In 2003, aCochrane Review of the use ofanticholinergic drugs to improve motor function inParkinson's disease found that as a class, the drugs are useful for that purpose; it identified one single-site randomised, cross-over study of orphenadrine vs placebo.[6] Although orphenadrine and other anticholinergics have largely been superseded by other drugs; they have a use in alleviating motor function symptoms, and appear to help about 20% of people with Parkinson's.[7]
Orphenadrine has the side effects of the other common antihistamines in large part. Stimulation is somewhat more common than with other related antihistamines, and is especially common in the elderly. Common side effects include dry mouth, dizziness, drowsiness, constipation, urine retention, blurred vision, and headache.[3] Its use in Parkinson's is especially limited by these factors.[6]
Continuous and/or cumulative use ofanticholinergic medications, including first-generation antihistamines, is associated with higher risk of cognitive decline and dementia in older people.[9][10]
Orphenadrine is known to have these pharmacological properties:
NonselectivemACh receptorantagonist (anticholinergic, 58% as potent as atropine)[11] Various monographs and package inserts, nursing manuals, journal articles and so forth have proposed the theory that this anticholinergic (atropine-like) activity, NMDA antagonism and possible local anaesthetic and miscellaneous analgesic effects may be the reason for orphenadrine's efficacy against muscle and other pain.[12] These reasons are behind the use of orphenadrine and other drugs of a number of types which are used with paracetamol, aspirin, naproxen, and similar agents with or without opioid analgesics to more effectively manage pain of various types.[13]
George Rieveschl was a professor of chemistry at theUniversity of Cincinnati and led a research program working onantihistamines. In 1943, one of his students, Fred Huber, synthesizeddiphenhydramine. Rieveschl worked withParke-Davis to test the compound, and the company licensed the patent from him. In 1947 Parke-Davis hired him as their Director of Research. While he was there, he led the development of orphenadrine, an analog of diphenhydramine.[21]
Prior to the development ofamantadine in the late 1960s and then other drugs, anticholinergics like orphenadrine were the mainstay of Parkinson's treatment.[7]
Orphenadrine has been available as a citrate salt and a hydrochloride salt; in the US as of February 2016 the citrate form was available in tablets, extended release tablets, compounding powder and by injection for acute use in a hospital setting.[2][22]
^Labout JJ, Thijssen C, Keijser GG, Hespe W (1982). "Difference between single and multiple dose pharmacokinetics of orphenadrine hydrochloride in man".European Journal of Clinical Pharmacology.21 (4):343–50.doi:10.1007/BF00637624.PMID7056281.S2CID24631265.
^abc"Orphenadrine".Drugs.com international listings. Retrieved5 February 2016.
^abc"Orphenadrine".Medline Plus. 1 December 2010. Retrieved6 February 2016.
^Syvälahti EK, Kunelius R, Laurén L (February 1988). "Effects of antiparkinsonian drugs on muscarinic receptor binding in rat brain, heart and lung".Pharmacology & Toxicology.62 (2):90–4.doi:10.1111/j.1600-0773.1988.tb01852.x.PMID3353357.
^Scholz EP, Konrad FM, Weiss DL, Zitron E, Kiesecker C, Bloehs R, et al. (December 2007). "Anticholinergic antiparkinson drug orphenadrine inhibits HERG channels: block attenuation by mutations of the pore residues Y652 or F656".Naunyn-Schmiedeberg's Archives of Pharmacology.376 (4):275–84.doi:10.1007/s00210-007-0202-6.PMID17965852.S2CID20049051.
^Rote Liste Service GmbH (Hrsg.) (2017).Rote Liste 2017 Arzneimittelverzeichnis für Deutschland (einschließlich EU-Zulassungen und bestimmter Medizinprodukte). Vol. 57. Frankfurt/Main: Rote Liste Service GmbH. p. 207.ISBN978-3-946057-10-9.
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