Generic Name : Orphenadrine.

Trade Name    : Norflex.

Drug Class      :  Skeletal Muscle Relaxants.

Forms of The Drug

  1. Injectable solution: 30mg/mL.
  2. Tablet: 

Mechanism of Action

Orphenadrine is a medication primarily used as a muscle relaxant and analgesic to relieve discomfort associated with musculoskeletal conditions such as muscle spasms, strains, and sprains. Its mechanism of action involves multiple pharmacological effects on the central nervous system (CNS) and peripheral tissues.

  1. Anticholinergic Activity: Orphenadrine exerts its effects in part through its anticholinergic properties. It acts as a competitive antagonist at muscarinic acetylcholine receptors in the CNS and peripheral tissues. By blocking these receptors, orphenadrine inhibits the actions of acetylcholine, a neurotransmitter involved in various physiological processes, including muscle contraction. This antagonism contributes to the muscle relaxant effects of orphenadrine.
  2. NMDA Receptor Antagonism: Orphenadrine also exhibits N-methyl-D-aspartate (NMDA) receptor antagonist activity. NMDA receptors play a crucial role in the transmission of pain signals in the CNS. By blocking NMDA receptors, orphenadrine modulates pain perception and transmission, contributing to its analgesic effects.
  3. Sodium Channel Blockade: Orphenadrine has been shown to block voltage-gated sodium channels in neurons. By inhibiting sodium influx through these channels, orphenadrine stabilizes the neuronal membrane and reduces the generation and propagation of action potentials. This sodium channel blockade may contribute to the muscle relaxant properties of orphenadrine by dampening excitability in motor neurons and reducing muscle spasms.
  4. Alpha-1 Adrenergic Receptor Blockade: Orphenadrine exhibits antagonist activity at alpha-1 adrenergic receptors, which are G protein-coupled receptors found in various tissues, including smooth muscle cells. By blocking alpha-1 adrenergic receptors, orphenadrine can induce smooth muscle relaxation, contributing to its muscle relaxant effects.
  5. Histamine H1 Receptor Antagonism: Orphenadrine acts as a histamine H1 receptor antagonist, blocking the effects of histamine, a neurotransmitter involved in allergic reactions and inflammatory responses. While the significance of histamine receptor blockade in the therapeutic effects of orphenadrine is not fully elucidated, it may contribute to its antispasmodic and antihistaminic properties.


  1. Muscle Spasms.
  2. Musculoskeletal Pain: such as strains, sprains, and other injuries to the muscles or bones.
  3. Musculoskeletal Disorders: such as fibromyalgia, myofascial pain syndrome, or tension headaches.
  4. Adjunctive Therapy: such as physical therapy, rest, and analgesic medications.
  5. Postoperative Pain.


  1. Hypersensitivity
  2. Glaucoma
  3. Urinary Retention.
  4. Gastrointestinal Obstruction.
  5. Severe Liver or Kidney Impairment.
  6. Myasthenia Gravis.

Side Effects

  1. Dry mouth, blurred vision, and urinary retention.
  2. Drowsiness and Dizziness.
  3. Confusion and Cognitive Impairment.
  4. Nausea, vomiting, constipation, or abdominal discomfort.
  5. Tachycardia and Palpitations.
  6. Urinary Retention.
  7. Sweating
  8. Rash, itching, swelling, or difficulty breathing.
  9. Headache, tremor, or agitation.

Drug Interaction

  1. Central Nervous System Depressants: such as opioids, benzodiazepines, alcohol, and certain antipsychotic medications.
  2. Anticholinergic Medications: such as tricyclic antidepressants, antihistamines, and antipsychotics.
  3. Monoamine Oxidase Inhibitors (MAOIs).
  4. Quinidine
  5. Antihypertensive Medications: such as beta-blockers, calcium channel blockers, and alpha-blockers.
  6. Urinary Alkalizers: such as sodium bicarbonate.


  1. Pregnancy: Category C.
  2. Lactation: Orphenadrine is excreted into human breast milk. Therefore, caution is advised when considering its use in lactating women.

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