Chemical formula: C₁₈H₂₃NO Molecular mass: 269.381 g/mol PubChem compound: 4601
Orphenadrine interacts in the following cases:
Care should be taken when using in patients with concomitant hepatic dysfunction.
Care should be taken when using in patients with concomitant renal dysfunction.
As with other similar agents, the anti-muscarinic effects of orphenadrine may be enhanced by the concomitant administration of other medications with anti-muscarinic properties, such as antihistamines, antispasmodics, tricyclic antidepressants, phenothiazines, dopaminergic anti parkinsonian drugs including amantadine, and anti-arrhythmics such as disopyramide.
Confusion, anxiety and tremors have been reported in few patients receiving propoxyphene and orphenadrine concomitantly. As these symptoms may be simply due to an additive effect, reduction of dosage and/or discontinuation of one or both agents is recommended in such cases.
Orphenadrine should be used with caution in patients with tachycardia, cardiac decompensation, coronary insufficiency, cardiac arrhythmias.
Use with caution in conditions characterised by tachycardia. Anti-muscarinic agents, such as orphenadrine, should be used with caution in patients with pre-existing tachycardia (e.g. in heart failure, thyrotoxicosis) as they may cause further acceleration of the heart rate.
Care should be taken when using orphenadrine in patients with concomitant hypertension.
There is inadequate evidence of safety in human pregnancy, and, although it has been widely used for many years without apparent ill consequence, if considered necessary orphenadrine should be used with caution during pregnancy. Animal studies have not revealed any hazard.
Pregnancy Category C.
Animal reproduction studies have not been conducted with orphenadrine citrate. It is also not know whether orphenadrine citrate can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Orphenadrine citrate should be given to a pregnant woman only if clearly needed.
It is probably excreted in milk during lactation. Although the quantity is unlikely to be significant at normal therapeutic doses, if considered necessary orphenadrine should be used with caution during breast feeding.
It is not known whether orphenadrine is excreted in human milk. Caution should be exercised when orphenadrine citrate is administered to a nursing woman.
Orphenadrine may cause blurred vision or slight euphoria. If patients experience these side effects, driving or operating machinery is not recommended.
Common >1/100 <1/10, Uncommon >1/1000 <1/100, Rare >1/10,000 <1/1000
Uncommon: Hypersensitivity
Common: Dizziness, restlessness
Uncommon: Sedation, confusion, nervousness, hallucinations, convulsions, insomnia, euphoria, co-ordination disturbances, light-headedness
Rare: Memory disturbances
Common: Accommodation disorders
Uncommon: Tachycardia
Common: Dry mouth, nausea, gastrointestinal disturbances
Uncommon: Constipation
Uncommon: Urinary retention
Adverse reactions of orphenadrine are mainly due to the mild anticholinergic action of orphenadrine, and are usually associated with higher dosage. Dryness of the mouth is usually the first adverse effect to appear. When the daily dose is increased, possible adverse effects include: tachycardia, palpitation, urinary hesitancy or retention, blurred vision, dilatation of pupils, increased ocular tension, weakness, nausea, vomiting, headache, dizziness, constipation, drowsiness, hypersensitivity reactions, pruritus, hallucinations, agitation, tremor, gastric irritation, and rarely urticaria and other dermatoses. Infrequently, an elderly patient may experience some degree of mental confusion.
These adverse reactions can usually be eliminated by reduction in dosage. Very rare cases of aplastic anemia associated with the use of orphenadrine tablets have been reported. No causal relationship has been established.
Rare instances of anaphylactic reaction have been reported associated with the intramuscular injection of orphenadrine citrate.
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