Pharmacokinetic evaluation of two doxepin products.

The pharmacokinetics of two marketed formulations of doxepin HCl administered as a single 100-mg oral dose were compared. Sixteen healthy volunteers between the ages of 21 and 50 years participated in this crossover study. A one-week washout period intervened between doses. Blood samples were drawn before drug administration and at various times up to 48 hours after dosing. The concentrations of doxepin (DOX) and desmethyldoxepin (DDOX), the major active metabolite, were determined. Bioequivalence was determined by statistical comparisons of the area under the curve and maximum concentrations of DOX and DDOX. Statistical comparisons indicated no difference between the two formulations with respect to any of the parameters. The results of this study demonstrate that the two formulations of doxepin HCl are bioequivalent and would be expected to have similar clinical efficacy.