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Pyrazinoylguanidine (PZG), 3-aminopyrazinoylguanidine (NH2PZG) and their pyrazinoic acid metabolites were measured by a new reverse-phase HPLC method in the serum of dogs and humans after administration of PZG, NH2PZG or 2-pyrazinoic acid (PZA). Kinetic properties of PZG and its principal metabolite, PZA, were studied in normal humans and also in azotemic patients, since PZG acts on renal tubules of patients with kidney failure to increase urea elimination. In humans and dogs, PZG was rapidly hydrolyzed to PZA. The serum half-life (t1/2) of PZG was 1 h. In turn, PZA was metabolized to 5-hydroxy-PZA, but no evidence appeared for conjugation of PZA with glycine. The apparent volume of distribution of PZG and its 3-amino analog, NH2PZG, exceeded that of total body water. In the dog the serum t1/2 for NH2PZG was twice that of PZG. Compared to PZG, NH2PZG and its metabolite, 3-aminopyrazinoic acid, were much stabler in vitro in serum and water.
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