Orphenadrine

Orphenadrine is a prescription skeletal muscle relaxant used to relieve pain and muscle spasm associated with acute musculoskeletal conditions such as strains, sprains, and other minor injuries. It is available orally as the citrate salt in tablet form, and in some countries as an injectable preparation. It is generally prescribed for short courses, typically a few days to a couple of weeks, as part of a treatment plan that may include rest, ice, and physical therapy.

The exact mechanism of action is not fully understood. Orphenadrine has central anticholinergic effects and acts as a central muscle relaxant. It is chemically related to diphenhydramine and may have antihistamine-like properties, which can contribute to sedating effects.

Common adverse effects include drowsiness, dizziness, dry mouth, blurred vision, constipation, and urinary retention. Because of its anticholinergic activity, it can worsen glaucoma, urinary retention in prostatic enlargement, and cognitive impairment in susceptible individuals, especially in older adults. Caution is advised in the elderly and in those with liver or kidney impairment, or with concurrent use of other central nervous system depressants.

Contraindications include hypersensitivity to orphenadrine and conditions in which anticholinergic effects are problematic, such as glaucoma or myasthenia gravis. Pregnancy and breastfeeding are typically considered for limited use only. Interactions can occur with alcohol, sedatives, and other anticholinergic drugs, and care is advised when combining with monoamine oxidase inhibitors.

Pharmacokinetically, orphenadrine is absorbed from the gut, distributed widely, metabolized in the liver, and excreted in the urine. Reported elimination half-life in adults is variable, commonly cited around several hours to over a day, depending on individual factors. Brand names include Norflex in the United States and other names in different countries.