API: Orphenadrine Citrate

What Is Orphenadrine Citrate and How Does It Work?

Orphenadrine Citrate is an anticholinergic drug that also has antihistamine properties. As an anticholinergic, the drug binds to and inhibits both muscarinic acetylcholine receptors as well as N-methyl-D-aspartate (NMDA) receptors in the central nervous system, which are ion channel proteins in the nerve cells that are responsible for synaptic plasticity and memory function. Although the exact mechanism of action is unclear, orphenadrine citrate is thought to interfere with the transmission of nerve impulses from the spinal cord to the muscles, thereby relaxing the muscles.1 The drug is effective for treating spasms and tremors due to Parkinson’s Disease. The drug also acts as an antagonist against histamine H1 receptors, and can be used to treat allergies.

For more information, including a MSDS sheet, please see PNA’s Orphenadrine Citrate page.

Approved Indications

  • Musculoskeletal pain or spasms: Orphenadrine citrate is used for short-term treatment of painful musculoskeletal spasms, usually alongside rest and physical therapy
  • Parkinson’s Disease: Orphenadrine citrate is used to control trembling due to Parkinson’s Disease, again as an adjunct therapy.
  • Allergies: Orphenadrine citrate is related to the structurally similar antihistamine Benadryl and has mild antihistamine effects against allergies

Side Effects and Drug Interactions

Common side effects in patients taking orphenadrine citrate include2:

  • Dry mouth
  • Drowsiness
  • Dizziness or lightheadedness
  • Upset stomach or vomiting
  • Constipation or problems urinating
  • Blurred vision
  • Headache

Patients who suffer from severity of these common side effects should contact their pharmacist or physician right away. Patients who experience rapid or irregular heartbeat, fainting, confusion, anxiety, tremors or seizures, hallucinations, or a skin rash should inform their physician immediately.3 In rare cases, some patients taking this drug have also experienced anaphylactic shock (skin reactions such as itchy hives, and flushed or pale skin, a sense of warmth, a lump in the throat or a swollen tongue that prevents breathing, a weak and rapid pulse, nausea, vomiting or diarrhea, and dizziness or fainting). These patients need immediate emergency intervention.

Patients who are allergic to orphenadrine citrate should not take this drug. Significant drug reaction has been seen with sodium oxybate delivered in oral form. Patients taking antihistamines, drugs for sleep or anxiety, muscle relaxants, narcotic pain relievers, or any medication that causes drowsiness should inform their physician before starting this medication. Patients who have or who have had glaucoma, myasthenia gravis, ulcers, a urinary tract blockage, intestinal blockage, an enlarged prostate, an irregular heartbeat, or liver, kidney, or heart disease should also inform their physician before taking this drug. This drug may be habit forming due to the euphoric nature of its activity.

Latest News and Research

Orphenadrine was first invented in the 1940s, both in a citrate form and as a hydrochloride. The former is used to treat muscle spasms whereas the latter has more significant activity against Parkinson’s Disease tremors. More recently, the drug has been investigated for its activity as an anti-spasmodic in patients who have suffered spinal cord injury. Initial results indicate that the drug could control spasms in as early as 30 minutes post delivery. However, more studies are needed to see if the drug is indicated as an effective treatment.4 Another pair of related condition that may benefit from the drug is restless leg syndrome and/or nocturnal cramps, both as second line treatments.5

Along different lines of research, orphenadrine citrate may also be used to treat the rare condition of middle-ear myoclonus is a rare condition. The condition is essentially continuous high-frequency tinnitus caused by spasms in the middle ear. In at least two cases, the condition was easily treated using orphenadrine citrate, although more studies are needed for optimal treatment.6

Buying Guide

PNA is a recommended bulk supplier of Orphenadrine Citrate and other APIs. You can learn more about Orphenadrine Citrate here.

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Show 6 footnotes

  1. “Orphenadrine,” http://pubchem.ncbi.nlm.nih.gov/compound/orphenadrine#section=Top
  2. “Orphenadrine,” January 13, 2016, https://www.nlm.nih.gov/medlineplus/druginfo/meds/a682162.html#side-effects
  3. “Norflex” 2016, http://www.rxlist.com/norflex-drug.htm
  4. “Spasticity following spinal cord injury,” 2012, http://amlar-res.com/wp-content/uploads/2012/02/spasticity.pdf
  5. “Management of restless legs syndrome and nocturnal cramps,” March 5, 2012, http://onlinelibrary.wiley.com/doi/10.1002/psb.875/epdf
  6. “Objective high-frequency tinnitus of middle-ear myoclonus,” April 2004, https://www.researchgate.net/publication/8632235_Objective_high-frequency_tinnitus_of_middle-ear_myoclonus