Metabolism of metamizol in early stages of the incubated hen's egg.

In a previous paper we introduced a model for studying the metabolism of xenobiotics in the incubated hen's egg. This model is characterized by application of the xenobiotic into the yolk sac and identification of metabolites in the allantoic fluid (AF). Depending on the stage of development, the incubated hen's egg can be used both conservatively--in the sense of an animal experiment--and alternatively as a complementary method (appr. first half of incubation period). In the present investigation we used the sodium salt of [(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-lH-pyrazol-4-yl)-N-methylamino] methanesulfonic acid (1; metamizol, dipyrone) as model substance. Concentrations of 1 up to 32 mg/egg did not affect the viability of the incubated eggs. After inoculation of 1 (10 mg/egg) on the sixth day of incubation (DI) eight compounds were identified in the AF on DI 11 (TLC, GC, GC-MS, synthesis, MS, 13C NMR): 4-methylamino-(2), 4-amino-(3), 4-hydroxy-(4), 4-acetylamino-(5), 4-N-acetyl-N-methylamino-(6), 4-N-hydroxyacetyl-N-methylamino-(7), 4-N-hydroxyoxalyl-N-methylamino-(8) and 4-N-formyl-N-methylamino-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol- 3-one (-antipyrine; 9), respectively. Main metabolites are 2 and 5; 4 and 7 occur as sulfate or glucuronide conjugates. Compound 7 is also eliminated in it's free form. To our knowledge 7 has been detected as a new metabolite of 1 for the first time. The metabolic route of 7 was elucidated after application of 6. Compounds 8 and 9 are artefacts of 7. The data presented here demonstrate the usefulness of the developed model also in early stages of the incubated hen's egg. Consequently, the model is suitable as a complementary method for xenobiotic metabolism.