Pharmacology
The mode of therapeutic action has not been clearly identified but may be related to its analgesic properties. Orphenadrine citrate also possesses anticholinergic actions. Norflex is an extended release formulation that gives a peak level of 60 ng/mL at 8 hours following a 100 mg dose, as opposed to an immediate release product that gives a peak of 100 ng/mL at 3 hours following the same dose. The apparent half-life of Norflex is 18 hours.
Indications
Acute skeletal muscle spasm.
Precautions
Some patients may experience transient episodes of light-headedness, dizziness or syncope. Orphenadrine may impair the ability of the patient to engage in potentially hazardous activities such as operating machinery or driving a motor vehicle; ambulatory patients should therefore be cautioned accordingly.
Safety and effectiveness in children have not been established; therefore, this drug is not recommended for use in the pediatric age group.
Safe use of orphenadrine has not been established with respect to adverse effects upon fetal development. Therefore, orphenadrine should be used in women of childbearing potential and particularly during early pregnancy only when the potential benefits outweigh the possible hazards.
Supplied
Each white, unscored tablet, imprinted with “3M” on one side and “221” imprinted on the other side, contains: orphenadrine citrate 100 mg in an extended release formulation. Nonmedicinal ingredients: calcium stearate, ethylcellulose and lactose. Tartrazine-free. Bottles of 100 and 500.
Store at controlled room temperature (15 to 30°C).
Each 2 mL ampul contains: orphenadrine citrate 60 mg. Nonmedicinal ingredients: sodium bisulfite, sodium chloride, sodium hydroxide and water for injection, USP. Ampuls of 2 mL, boxes of 6.
Contraindications
Stenosing peptic ulcers, prostatic hypertrophy, glaucoma, pyloric or duodenal obstruction, bladder neck obstruction, cardiospasm and myasthenia gravis. Hypersensitivity to orphenadrine.
Warnings
No data supplied by the manufacturer.
Adverse Effects
Mainly due to the mild anticholinergic action of orphenadrine, and are usually associated with higher dosage. Dryness of the mouth is the first untoward effect to appear. When the daily dose is increased, possible adverse effects include: tachycardia, palpitation, urinary hesitancy or retention, blurred vision, dilatation of the pupil, increased ocular tension, weakness, nausea, vomiting, headache, dizziness, constipation and drowsiness and rarely, urticaria and other dermatoses. Infrequently, an elderly patient may experience some degree of mental confusion. These adverse effects can usually be eliminated by reduction in the dosage. Two cases of aplastic anemia associated with the use of orphenadrine citrate tablets have been reported. No causal relationship has been established.
Overdose
For management of a suspected drug overdose, CPhA recommends that you contact your regional Poison Control Centre. See the eCPS Directories section for a list of Poison Control Centres.
No data supplied by the manufacturer.
Dosage
Average adult dose, 60 mg i.v. or i.m. Orally, 100 mg twice daily.
