Relationship between saliva levels of metamizol metabolites, bioavailability and analgesic efficacy.

Salivary levels of the metabolites of metamizol (N-methyl-, N-acetyl- and 4-aminoantipyrine) were determined after the intake of film-coated metamizol (Novalgin) tablets and metamizol (Novalgin) solution. Cortical evoked potentials, pain ratings and thresholds of sensation were monitored following tooth pulp stimulation after administration of metamizol tablets. Within the different groups of subjects a remarkable degree of reproducibility was obtained for the metabolite concentrations in saliva. At 20 min after drug intake a more rapid absorption was demonstrable for the solution in comparison to the tablets. The metabolite levels were correlated to the simultaneously recorded pain response demonstrating that the analgesic efficacy can only be attributed to the two metabolites N-methyl- and -4-amino-antipyrine.