The comparative pharmacokinetics of pentamethylmelamine in man, rat, and mouse.

The pharmacokinetics of pentamethylmelamine (PMM) have been investigated in mouse (Balb C-, CBA/LAC, nude), rat (Wistar), and man. In all three species, PMM was extensively demethylated to N2,N2,N4,N6-tetramethylmelamine and N2,N4,N6-trimethylmelamine, although marked species differences in the rate of metabolism were observed. PMM metabolism was more rapid in the mouse (plasma t1/2 = less than 15 min) than in the rat (plasma t1/2 = 40 min), and slower in man (plasma t1/2 = 102 min) than in either mouse or rat. Furthermore, the peak plasma concentrations of N-methylolmelamines, intermediates generated during oxidative N-demethylation, were correspondingly higher in the mouse (563-773 microM) than in the rat (211 microM), whilst in man they were undetectable (less than 50 microM). In view of the highly cytotoxic nature of N-methylolmelamines, we conclude that these pharmacokinetic differences may be related to the antitumour effectiveness of PMM in mouse, rat, and man.