Plasma levels and bioavailability of cyclobenzaprine in human subjects

Cyclobenzaprine was extensively metabolized in man, less than 1% of the dose being excreted unchanged in the urine. Comparison of areas under plasma level curves (AUC) after oral and intravenous doses suggests that the drug may be partly metabolized in the lumen or during its first passage through the gut wall and/or liver. Average plasma levels of the drug increased with increasing dosage, but the AUC increased less rapidly with increasing dose, possibly because of dose-dependent absorption.