The objective and timing of drug disposition studies, appendix III. Diethylpropion and its metabolites in the blood plasma of the human after subcutaneous and oral administration.

Diethylpropion hydrochloride is an effective anorexiant at the recommended dose of 25 mg three times a day. Previous work in volunteers to evaluate the effects of much larger doses showed that 400 mg given orally was equipotent with 600 mg subcutaneously in terms of subjective and physiologic effects, i.e., the drug was more potent orally than subcutaneously. In one volunteer, blood level studies after a 600-mg subcutaneous dose showed concentrations of unchanged diethylpropion in the plasma about three times as high as those found after the equipotent 400 mg oral dose. In nine other volunteers, the plasma concentrations of unchanged diethylpropion found after a 75-mg oral dose was less than 1/100 of that observed after a 400-mg oral dose. These observations suggest a rapid but limited metabolic capacity for conversion of diethylpropion to its metabolites. The data indicate that the metabolites, rather than the parent drug, are responsible for the pharmacologic responses seen with doses much larger than those necessary for inducting anorexia.