Methemoglobinemia due to topical pharyngeal anesthesia during endoscopic procedures

Figures & data

Figure 1 Methemoglobin levels are tightly controlled in the human body by an intricate balance between mechanisms that produce and reduce methemoglobin.

Table 1 List of medications commonly used in clinical practice that have been linked to methemoglobinemia^17,20

Antimalarials – Primaquine, chloroquine

Antineoplastic agents – Cyclophosphamide, flutamide

Antibiotics – Sulfonamides, dapsone, nitrofurantoin

Local anesthetics – Benzocaine, lidocaine, prilocaine, bupivacaine

Antianginal agents – Nitroglycerin, nitrates

Antihypertensives – Sodium nitroprusside

Anti-inflammatory/analgesics – Acetaminophen, celecoxib, sulfasalazine, phenazopyridine

Other agents – Rasburicase, zopiclone, metoclopramide

Table 2 Clinical symptoms and signs of methemoglobinemia in relation to the level of methemoglobin

Level of methemoglobin	Clinical symptoms and signs
<10%	Frequently asymptomatic, occasionally grayish skin
10%–20%	Skin changes such as cyanosis
20%–30%	Dyspnea, headache, anxiety
30%–50%	Dizziness, palpitations, confusion, tachypnea
50%–70%	Seizures, cardiac arrhythmias, metabolic acidosis, coma
>70%	Death

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