The influence of orphenadrine HCl in overdose alone and in combination with droperidol on respiration and circulation in the rat.

Orphenadrine HCL was intravenously administered to rats under urethane anesthesia to investigate whether the primary cause of death in orphenadrine intoxication is respiratory arrest or cardiac standstill. The spontaneously breathing animals died from apnoe after a mean dose of 63 + 11 mg/kg. The artificially ventilated animals died from cardiac arrest after a mean dose of 144 +/- 47 mg/kg. It was concluded that primary cause of death is respiratory insufficiency and that hypoventilation can mask the cardiotoxicity of orphenadrine. On the analogy of earlier experiments in dogs the ability of droperidol to counteract the influence of orphenadrine was investigated. Droperidol enhanced the influence of orphenadrine on respiration and had no influence on the cardiotoxic influence of orphenadrine in the rat.