Adult: As orphenadrine hydrochloride: Initially, 150 mg daily in divided doses, gradually increase by 50 mg every 2-3 days until maximum benefits is attained. Usual maintenance dose: 150-300 mg daily. Max: 400 mg daily in divided doses. Elderly: Dose reduction may be required.
Oral Painful muscle spasm associated with musculoskeletal conditions
Adult: As orphenadrine citrate: 100 mg bid. Elderly: Dose reduction may be required.
Administration
May be taken with or without food. May be taken w/ meals if GI upset occurs.
Patient with CV disease (e.g. heart failure, cardiac decompensation, coronary insufficiency, tachycardia, cardiac arrhythmias), thyrotoxicosis, hypertension, history of drug abuse or acute alcoholism, porphyria, micturition difficulties. Avoid abrupt withdrawal. Some products or formulations are not interchangeable; refer to specific product guideline for further information. Renal and hepatic impairment. Elderly. Pregnancy and lactation.
Adverse Reactions
Significant: CNS depression, euphoria (increased risk for drug abuse and dependence). Blood and lymphatic system disorders: Very rarely, aplastic anaemia. Cardiac disorders: Palpitation, tachycardia. Eye disorders: Disturbance of visual accommodation. Gastrointestinal disorders: Dry mouth, gastrointestinal disturbances, nausea, constipation. Immune system disorders: Hypersensitivity reaction. Rarely, anaphylaxis (IM). Nervous system disorders: Dizziness, drowsiness, restlessness. Psychiatric disorders: Confusion, hallucination. Renal and urinary disorders: Micturition difficulties.
This drug may cause blurred vision, dizziness or slight euphoria, if affected, do not drive or operate machinery.
Monitoring Parameters
If for prolonged use, monitor blood, urine, and LFTs.
Overdosage
Symptoms: Nausea, vomiting, flushing, dilated pupils, dry mouth and tongue, hot dry skin, fever, hypertension, sinus tachycardia, ataxia, nystagmus, drowsiness, delirium, agitation and visual hallucinations. Management: Administer activated charcoal or perform gastric lavage within 1 hour of ingestion. Establish patient airway and provide oxygen or ventilation to correct hypoxia or hypercapnia; administer intravascular volume expander or dopamine for hypo- or hyperthermia, hypotension; treat skin blisters as burns; administer diazepam for convulsions or delirium. Administer Na bicarbonate (even in the absence of acidosis) and correct hypoxia for cardiac dysrhythmias.
Drug Interactions
May enhance the sedative effect with other sedatives. May cause anxiety, confusion, tremors with propoxyphene. May increase the antimuscarinic effects with antihistamines, antispasmodics, TCAs, phenothiazines, dopaminergic antiparkinsonian drugs (e.g. amantadine), antiarrhythmics (e.g. disopyramide). Enhanced effect with anticholinergic drugs.
Food Interaction
Alcohol may potentiate the CNS depressant effect of this drug.
Action
Description: Orphenadrine, a tertiary amine antimuscarinic, is an indirect skeletal muscle relaxant that is believed to work by central atropine-like effects. Additionally, it has weak antihistaminic and local anaesthetic properties. Onset: 2-4 hours (oral). Duration: 4-6 hours. Pharmacokinetics: Absorption: Readily absorbed from the gastrointestinal tract and after an IM inj. Distribution: Rapidly distributed to tissues. Plasma protein binding: 20% Metabolism: Extensively metabolised in the liver into approx 8 metabolites. Excretion: Mainly via urine (8% as unchanged drug). Elimination half-life: 14-16 hours.
Chemical Structure
Orphenadrine Source: National Center for Biotechnology Information. PubChem Database. Orphenadrine, CID=4601, https://pubchem.ncbi.nlm.nih.gov/compound/Orphenadrine (accessed on Jan. 22, 2020)
Storage
Store below 30°C. Protect from light, moisture, and heat.
N04AB02 - orphenadrine (chloride) ; Belongs to the class of anticholinergic agents, ethers chemically close to antihistamines. Used in the management of Parkinson's disease.
References
Anon. Orphenadrine. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 27/05/2021.Buckingham R (ed). Orphenadrine Citrate. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 27/05/2021.iNova Pharmaceuticals (New Zealand) Limited. Norflex 100 mg Slow Release Tablets data sheet 11 December 2018. Medsafe. http://www.medsafe.govt.nz. Accessed 27/05/2021.Joint Formulary Committee. Orphenadrine Hydrochloride. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 27/05/2021.Norflex Tablet 100 mg (Adcock Ingram Ltd). National Pharmaceutical Regulatory Agency - Ministry of Health Malaysia. https://www.npra.gov.my. Accessed 27/05/2021.Orphenadrine Citrate Injection (A-S Medication Solutions). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 27/05/2021.Orphenadrine Citrate Tablet, Extended Release (Bryant Ranch Prepack). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 27/05/2021.Orphenadrine Hydrochloride 50 mg Tablets (Teva UK Limited). MHRA. https://products.mhra.gov.uk. Accessed 27/05/2021.Orphenadrine Hydrochloride 50 mg/5 mL Oral Solution (Rosemont Pharmaceuticals Ltd.). MHRA. https://products.mhra.gov.uk. Accessed 27/05/2021.
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