The bioavailability of orphenadrine hydrochloride after intramuscular and oral administration

The bioavailability of orphenadrine hydrochloride after a single intramuscular injection was compared to that after a single oral dose by following serial plasma concentration estimations of the unchanged drug. Eight subjects received 40 mg orphenadrine HCl intramuscularly and 50 mg orally on separate occasions 1 week apart. The bioavailability of orphenadrine from the intramuscular dosage form proved to be equal to or even greater than that from the tablet. The first hour plasma concentrations after intramuscular doses were significantly higher than those after oral doses, supporting the clinical use of the intramuscular route in those indications where rapid effects of the drug are required.