Pharmacokinetics and biotransformation of hydralazine acetone hydrazone, a metabolite of hydralazine, in the rat.

The pharmacokinetics of hydralazine acetone hydrazone (HAH), which is a metabolite of hydralazine (HP), was investigated after iv administration to rats. Plasma concentrations of HAH, HP, and hydralazine pyruvic acid hydrazone (HPH) were simultaneously determined by a specific HPLC method. A five-compartment pharmacokinetic model was presented to elucidate the disposition of HAH and two products, HP and HPH. The parameters used in the model were obtained by administering each of the three compounds (10 mg/kg) separately. The proposed model described the experimental data well and the model parameters were close to the model-independent values. After HP administration, HPH appeared rapidly in plasma, but the HPH availability from HP amounted to only 17.8 +/- 3.7%, based on the comparison between the area under the plasma concentration curves of formed and iv HPH. The formation of HP from HAH in the systemic circulation was demonstrated, but formed HP disappeared rapidly. The fraction of HAH available to the systemic circulation as HPH was extremely low (7.8 +/- 2.2%), indicating that the conversion of HAH to HP was not so extensive. The present results support the hypotheses that HPH is formed via the direct reaction of HAH with pyruvic acid and that the secondary formation is mediated by conversion to HP.