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Orphenadrine
See also Adrenoceptor agonists
General information
Orphenadrine is related to an antihistamine (diphenhydramine), and appears to have been developed in the hope of producing a greater effect in Parkinson’s disease by combining both anticholinergic and antihistaminic effects in a single molecule.
In the doses commonly used, any of the well-recognized anticholinergic effects can occur. Some patients become drowsy, whilst others are stimulated. With increasing dosages, some patients go into coma; others have agitation, convulsions, and marked euphoria, perhaps with hallucinations and disorientation.
Organs and systems
Cardiovascular
Non-sustained ventricular tachycardia has been attributed to orphenadrine [ ].
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A 57-year-old woman had been taking a formulation containing orphenadrine 15 mg and paracetamol 450 mg bd for musculoskeletal pain. She was also taking propafenone 600 mg/day for paroxysmal atrial fibrillation. After 5 days she developed severe palpitation. Holter monitoring showed frequent brief episodes not only of atrial fibrillation but also of non-sustained ventricular tachycardia. After the orphenadrine was withdrawn the palpitation ceased.
The authors pointed out the potential problems of anticholinergic drugs like orphenadrine in patients taking antidysrhythmic drugs.
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