Eperisone HCl has very low bioavailability after oral administration in rats and extensively high oral clearance in humans. It undergoes extensive first-pass metabolism after oral administration in rats and humans because absorption of the drug is very high. The bioavailabilities in the intestine were 0.176 and 0.0879 at administration rates of 100 and 25 mg/h/kg, respectively, whereas those in the liver were 0.532 and 0.486, respectively. Eperisone has high metabolic clearance in the small intestine.