Orphenadrine is a muscarinic acetylcholine receptor (mAChR) antagonist (Kds = 48, 213, 120, 170, and 129 nM for M1-M5 receptors, respectively).1 Orphenadrine (2-5 mg/kg, i.v.) decreases muscle activity induced by the mAChR agonist oxotremorine in rabbits.2 It is also an NMDA receptor antagonist with a Ki value of 6 ?M in a radioligand binding assay in human postmortem frontal cortex and an IC50 value of 16.2 ?M for inhibiting steady state currents in cultured superior colliculus neurons.3 Formulations containing orphenadrine have been used in the treatment of acute painful musculoskeletal conditions, including muscle spasms.
1.Stanton, T., Bolden-Watson, C., Cusack, B., et al.Antagonism of the five cloned human muscarinic cholinergic receptors expressed in CHO-K1 cells by antidepressants and antihistaminicsBiochem. Pharmacol.45(11)2352-2354(1993) 2.Ban, T., and Hojo, M.A comparative study of the effects of anti-parkinson drugs on the oxotremorine-induced EEG and muscular activitiesPsychopharmacologia19(1)1-15(1971) 3.Kornhuber, J., Parsons, C.G., Hartmann, S., et al.Orphenadrine is an uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist: Binding and patch clamp studiesJ. Neural Transm. Gen. Sect.102(3)237-246(1995)