Orphenadrine was introduced in the 1950s (around 1959 in the U.S.) and is a centrally acting muscle relaxant used for short-term relief of muscle spasms and musculoskeletal pain. It works in the brain and spinal cord to reduce muscle tension and pain signals rather than directly acting on muscles. It is commonly prescribed for conditions like back pain, strains, and sprains, but it should be used only for a short period due to possible side effects such as drowsiness, dry mouth, and dizziness.
BRAND NAMES
Norflex: The primary, most common brand name for orphenadrine citrate.
Norgesic / Norgesic Forte: A common combination of orphenadrine, aspirin, and caffeine.
Orfenace: A brand name used in some regions.
MECHANISM OF ACTION
Orphenadrine is a centrally acting skeletal muscle relaxant that works primarily as an anticholinergic (antimuscarinic) agent to relieve pain from muscle spasms. It works in the CNS, likely by blocking NMDA receptors and histamine H1 receptors, reducing motor nerve impulses and providing mild analgesic and sedative effects.
PHARMACOKINETICS
Absorption: Orphenadrine is well absorbed from the gastrointestinal tract after oral administration, with peak blood levels typically reached within a few hours.
Distribution: It is widely distributed throughout body tissues, including the central nervous system, and it can cross the blood-brain barrier due to its lipophilic nature.
Metabolism: Orphenadrine is mainly metabolized in the liver through processes such as N-demethylation and hydroxylation, producing active and inactive metabolites.
Elimination: It is primarily eliminated through the kidneys in the urine, both as unchanged drug and metabolites, with a relatively long half-life that allows prolonged action.
PHARMACODYNAMICS
Orphenadrine acts as a centrally acting skeletal muscle relaxant with anticholinergic and mild antihistaminic properties. It does not directly act on skeletal muscles but instead blocks nerve signals involved in muscle contraction and pain transmission, leading to relaxation and reduced discomfort.
ADMINISTRATION
Orphenadrine is given orally as tablets, usually taken once or in divided doses as prescribed by a doctor. It can be taken with or without food and should be swallowed with water for short-term relief of muscle spasms.
DOSAGE AND STRENGTH
Orphenadrine is commonly available in tablet form with strengths of 100 mg (immediate-release) and 100 mg or 200 mg (extended-release). The usual adult dose is 100 mg taken 2–3 times dailyor 200 mg extended-release once or twice daily, depending on the severity of symptoms and the doctor’s prescription. The exact dosage is individualized and should not exceed the maximum recommended daily limit set by a healthcare provider.
DRUG INTERACTIONS
Orphenadrine can interact with alcohol, sedatives, opioids, antihistamines, and antidepressants, increasing drowsiness and anticholinergic side effects like dry mouth and confusion. It should be avoided with MAO inhibitors due to risk of serious reactions.
FOOD INTERACTIONS
Orphenadrine has no major clinically significant food interactions. It can generally be taken with or without food, but taking it with food may help reduce stomach upset or irritation in some people. However, alcohol should be avoided because it can increase drowsiness, dizziness, and impairment of coordination
CONTRAINDICATIONS
Orphenadrine is contraindicated in patients with hypersensitivity to the drug or its components. It should not be used in individuals with conditions such as narrow-angle glaucoma, urinary retention or enlarged prostate, myasthenia gravis, or obstructive gastrointestinal diseases. It is also generally avoided in patients with severe heart rhythm disorders or significant tachycardia, and in those who are unable to tolerate its anticholinergic effects.
SIDE EFFECTS
Dry mouth, nose, or throat
Dizziness or lightheadedness
Drowsiness or sedation
Blurred vision or dilated pupils
Constipation
Nausea or vomiting
Weakness
OVER DOSE
An overdose of Orphenadrine may cause severe anticholinergic effects such as confusion, hallucinations, dry mouth, fast heartbeat, urinary retention, and dilated pupils. In serious cases, it can lead to seizures, coma, or respiratory problems, requiring urgent medical treatment.
TOXICITY
Orphenadrine toxicity is mainly due to anticholinergic and central nervous system effects. Toxic levels can cause confusion, agitation, hallucinations, severe dry mouth, blurred vision, flushing, tachycardia, urinary retention, hyperthermia, and reduced sweating. In severe poisoning, it may progress to seizures, coma, cardiac arrhythmias, and respiratory depression.
