Causative Agents in Clinically Significant Methemoglobinemia: A National Poison Data System Study.

BACKGROUND: Recognition of the agents most commonly implicated in causing methemoglobinemia can provide context for making therapeutic decisions and inform the diagnostic process. We evaluated the etiologic agents most commonly implicated in clinically significant methemoglobinemia using data from the National Poison Data System (NPDS).

STUDY QUESTION: What are the most frequent etiologic agents associated with clinically significant methemoglobinemia.

STUDY DESIGN: This was a retrospective cross-sectional chart review using electronic data from the NPDS. The NPDS database was queried to identify cases from July 1, 2007, to June 30, 2017, that were coded as methylene blue treatment recommended and/or performed. Cases were excluded if the substance(s) have never been known to cause methemoglobin or the substances suggested methylene blue was used adjunctively for refractory shock (eg, calcium channel or beta blocker). Multiple substance exposures were reviewed and substances not known to cause methemoglobinemia were excluded.

MEASURES AND OUTCOMES: The primary end point was to summarize the most frequent etiologic agents associated with the administration of methylene blue for clinically significant methemoglobinemia.

RESULTS: There were 2563 substances reported in 1209 cases. After excluding coingestants and cases not associated with methemoglobinemia, there were 1236 substances. The top 4 substance categories were benzocaine, phenazopyridine, dapsone, and nitrates/nitrites.

CONCLUSIONS: This study reveals the relative contribution of various drugs and chemicals associated with methylene blue administration. Over two-thirds of all cases were associated with benzocaine, phenazopyridine, dapsone, and nitrates/nitrites.