Orphenadrine citrate

What is orphenadrine citrate?

Orphenadrine citrate is a centrally acting muscle relaxant. In the product information for a combination tablet, it is described as a compound that acts on the brain stem and selectively blocks facilitatory functions of the reticular formation.^[2] It is not a painkiller by itself; in the registered clinical trial it is studied as part of fixed combinations with paracetamol and diclofenac.^[1]

Orphenadrine citrate is already authorised as a medicine. In the product records linked to the trial, it appears in authorised fixed combinations, including a product named Norgesic 35 mg / 450 mg tablets and a triple combination product with diclofenac and paracetamol.^[1] It is an oral medicine formulated as film-coated tablets or tablets.^[1]

How does orphenadrine citrate work?

Orphenadrine citrate works centrally in the nervous system. According to the product label, it is a centrally acting compound that in animals selectively blocks facilitatory functions of the reticular formation in the brain stem.^[2] It does not produce a myoneural block, meaning it does not stop nerve signals at the junction between nerve and muscle.^[2] This central action is different from that of pain relievers such as paracetamol or non-steroidal anti-inflammatory drugs such as diclofenac, which act mainly on pain and inflammation pathways.

Which conditions is orphenadrine citrate used or studied for?

• Acute severe low back pain — the registered Phase 3 trial studies a triple combination containing orphenadrine in people with acute severe low back pain.^[1]
• Muscle spasm associated with acute painful musculoskeletal conditions — the product information describes orphenadrine citrate as a muscle relaxant used in combination with aspirin and caffeine, a combination used for musculoskeletal pain relief.^[2]

How is orphenadrine citrate given?

Orphenadrine citrate is given by mouth. The trial product records list oral film-coated tablets and tablets.^[1] In the registered trial, the orphenadrine-containing comparator is Norgesic 35 mg / 450 mg tablets, which contain orphenadrine citrate and paracetamol.^[1] A separate authorised combination product contains orphenadrine citrate 50 mg together with aspirin 770 mg and caffeine 60 mg per tablet.^[2]

What do the clinical trials show?

The EU Clinical Trials Information System lists one interventional Phase 3 trial that includes orphenadrine citrate.^[1] The trial is registered as authorised and plans to enrol 224 participants with acute severe low back pain.^[1]

The study compares three oral treatments: a fixed-dose combination of diclofenac, orphenadrine and paracetamol as the test product, diclofenac alone (Cataflam 50 mg tablets), and an orphenadrine-paracetamol combination (Norgesic 35 mg / 450 mg tablets).^[1] Placebo arms are also included.^[1]

The primary endpoint is the cumulative, time-weighted sum of pain intensity differences, expressed as the sum of seven daily SPID values from 0 to 6 hours after each dose across the 7-day treatment period.^[1] In plain words, researchers measure how much pain intensity drops after each daily dose and add up those differences over a week to compare the treatment groups.

Orphenadrine citrate appears in the trial both as part of the test product and as part of an active comparator.^[1] This means the trial tests whether adding diclofenac to the orphenadrine-paracetamol combination improves pain relief compared with the combination without diclofenac.

What side effects are known?

The supplementary source used for this page does not provide a side-effect section for orphenadrine citrate. The product label describes its pharmacological action but does not list adverse reactions in the excerpt available here.^[2] Therefore no side-effect frequencies are reported on this page.