A clinical case and pharmacokinetic analysis of an inadvertent overdose of dipyrone (metamizole) without clinical toxicity: A case report.

Dipyrone (metamizole) is a widely used non-opioid analgesic. Its use is restricted due to the risk of side effects such as liver toxicity. We report the case of a patient who accidentally received an oral dose of 12.5 g (132 mg/kg) dipyrone. The patient was monitored for the next 62 days and remained asymptomatic, showing no signs of gastrointestinal, hepatic, or other toxicity. Dipyrone was not detectable in the plasma, while the plasma concentrations of its active metabolites 4-methylaminoantipyrine and 4-aminoantipyrine were elevated. The pharmacokinetics were best described by nonlinear one-compartment models with Michaelis-Menten elimination. The terminal half-life of both metabolites was 2.9 h. These results demonstrate the rapid absorption of dipyrone and the extremely short window for effective gastric decontamination. Due to its specific pharmacokinetic profile, the high systemic exposure to active dipyrone metabolites did not result in acute organ toxicity in this case. Therefore, intensive medical monitoring may not always be mandatory after dipyrone overdose in otherwise clinically stable patients, although agranulocytosis remains as idiosyncratic long-term risk.