Examination of the in vitro degradation of [14C] pentaerythritol tetranitrate in rat and human blood with an improved thin-layer radiochromatographic procedure.

Improvements were made on a reported thin-layer radiochromatographic assay for the determination of [14C]pentaerythritol tetranitrate (PETN) and its metabolites in whole blood, using methanol instead of dioxane as the extracting solvent. Recovery of total radioactivity for the entire work-up procedure was greater than 90%, and the distribution of PETN and its metabolites in degraded blood samples was found to be reproducible. This modified method appeared simpler and yielded better recovery of radioactivity than the literature method. In vitro metabolism of [14C]PETN in rat and human blood was examined by incubation of the drug with fresh blood at 37 degrees C for 60 min. In rat blood, the half-life of PETN degradation was about 15 min producing the trinitrate, dinitrate and mononitrate metabolites. Human blood was also capable of degrading PETN in vitro, but at a lower rate than rat blood, yielding only the trinitrate metabolite in quantifiable amounts during the incubation period. Equilibrium of PETN between plasma and red blood cells was observed within 1 min after PETN addition to both rat and human blood. The apparent plasma/red blood cells partition ratios of PETN were 1.1 and 1.7 for rat and human blood, respectively. PETN degradation was approximately ten times slower in rat plasma than in rat blood, suggesting that enzymes in erythrocytes are important for PETN metabolism in rat whole blood.