Drug-Induced Methemoglobinemia: Disease-Characteristics Research Report

Scope. This report treats drug-induced methemoglobinemia as an acquired toxic/iatrogenic dyshemoglobinemia, not as congenital CYB5R3 deficiency or hemoglobin-M disease. Evidence is principally aggregated disease-level literature, hospital cohorts, trials, and case series; the 2024 Iowa study used de-identified individual medical-record data aggregated at cohort level. No patient-specific EHR data were supplied for this report. (iolascon2021recommendationsfordiagnosis pages 1-3, belzer2024causesofacquired pages 1-2)

Executive summary

Drug-induced methemoglobinemia occurs when a medication or reactive metabolite oxidizes hemoglobin iron from oxygen-binding ferrous Fe²⁺ to ferric Fe³⁺ faster than erythrocyte reduction systems can restore it. Ferric heme cannot bind oxygen, while oxidation also increases oxygen affinity at the remaining ferrous hemes, producing functional anemia and impaired tissue unloading despite a normal arterial oxygen tension. It is usually acute, reversible, and exposure-dependent, but dapsone and lipophilic agents can produce delayed or recurrent toxicity. (iolascon2021recommendationsfordiagnosis pages 1-3, belzer2024causesofacquired pages 1-2, iolascon2021recommendationsfordiagnosis pages 9-10)

The strongest recent epidemiologic evidence is a 2024 single-center retrospective study: among 21,449 measurements from 2,502 patients during 2009–2023, 546 measurements (2.5%) were ≥3.1% MetHb and 33 (0.15%) were ≥10%. Dapsone caused 67.0% of pediatric and 63.6% of adult elevated-MetHb encounters; inhaled nitric oxide caused 16.5% and 12.8%, respectively. These are proportions among tested hospital patients, not population incidence estimates. (belzer2024causesofacquired pages 1-2, belzer2024causesofacquired pages 3-4, belzer2024causesofacquired pages 2-3)

The operational clinical summary is provided below.

Table: This table consolidates severity strata, diagnostic clues, common oxidant triggers, antidotal treatment, contraindications, rescue options, and rebound monitoring for drug-induced methemoglobinemia. It is based on expert recommendations, recent hospital data, and clinical reviews (iolascon2021recommendationsfordiagnosis pages 3-5, belzer2024causesofacquired pages 1-2, iolascon2021recommendationsfordiagnosis pages 9-10, iolascon2021recommendationsfordiagnosis pages 10-11, iolascon2021recommendationsfordiagnosis pages 8-9, cefalu2020methemoglobinemiainthe pages 6-8).

1. Disease information

Definition and names

Methemoglobinemia is an excess of hemoglobin containing ferric iron. Healthy blood generally contains <1%–2% MetHb. “Drug-induced methemoglobinemia” denotes an acquired form attributable to a medicine, medical gas, or its metabolite; overlapping labels include acquired methemoglobinemia, toxic methemoglobinemia, toxin-induced methemoglobinemia, iatrogenic methemoglobinemia, and British spellings methaemoglobinaemia/methaemoglobinaemia. (iolascon2021recommendationsfordiagnosis pages 5-6, belzer2024causesofacquired pages 1-2)

A concise authoritative abstract statement is: “Acquired forms are the most common, mainly due to the exposure to substances that cause oxidation of the Hb both directly or indirectly.” This comes from the European Hematology Association/EuroBloodNet consensus review, published September 2021 (DOI: 10.1002/ajh.26340). (iolascon2021recommendationsfordiagnosis pages 1-3)

Identifiers

• MeSH: Methemoglobinemia, D008708. (NCT03542760 chunk 2)
• ICD-10-CM: D74.8, “Other methemoglobinemias,” is commonly applicable to acquired/drug-induced disease; D74.9 is unspecified methemoglobinemia. External terminology validation is advisable before production use.
• ICD-11: classified under methemoglobinaemias/blood disorders, but an exact drug-induced leaf code was not established from the retrieved evidence.
• MONDO: no confidently verified dedicated MONDO identifier for the drug-induced subtype was recovered. Map provisionally to the acquired-methemoglobinemia concept rather than congenital methemoglobinemia.
• OMIM/Orphanet: not generally appropriate as primary identifiers for this acquired adverse-drug reaction. OMIM entries for CYB5R3-related disease and HbM describe hereditary differentials, not the target entity.
• Suggested ontology label: “drug-induced methemoglobinemia,” parent “acquired methemoglobinemia”; add causal relations to the implicated CHEBI/RxNorm substance.

2. Etiology

Causal agents

Prominent drug causes include dapsone, benzocaine, prilocaine, lidocaine, phenazopyridine, primaquine/chloroquine, sulfonamides including trimethoprim-sulfamethoxazole, rasburicase, metoclopramide, nitroglycerin, sodium nitroprusside, and inhaled nitric oxide. Less frequent reports involve acetaminophen overdose, phenacetin, nitrofurantoin, cyclophosphamide, flutamide, and even excessive methylene blue. Non-drug oxidants include sodium/amyl/isobutyl nitrite, nitrate-contaminated food or water, aniline/nitrobenzene, chlorates, pesticides, and smoke. (cefalu2020methemoglobinemiainthe pages 4-6, belzer2024causesofacquired pages 2-3, iolascon2021recommendationsfordiagnosis pages 11-12, cefalu2020methemoglobinemiainthe pages 8-10)

Dapsone is bioactivated to dapsone hydroxylamine, which oxidizes hemoglobin; enterohepatic recirculation and persistent metabolites explain prolonged or recurrent disease. Cimetidine can inhibit CYP-mediated hydroxylamine formation, but evidence supports neither routine acute use nor a universally accepted preventive regimen. (bai2024dapsoneinducedmethemoglobinemiain pages 3-4, barclay2011dapsoneinducedmethemoglobinemiaa pages 5-5, cefalu2020methemoglobinemiainthe pages 6-8)

Risk factors

Risk reflects oxidant potency, dose, route, duration, and absorption. Topical benzocaine on mucosa and high-dose prilocaine are particularly recognized procedural risks. Infants have only approximately 50%–60% of adult erythrocyte CYB5R activity and more readily oxidized HbF. Older age, anemia, acidosis, sepsis, pregnancy, and cardiac, pulmonary, coronary, peripheral vascular, or cerebrovascular disease lower tolerance by reducing oxygen-delivery reserve. (belzer2024causesofacquired pages 2-3, cefalu2020methemoglobinemiainthe pages 3-4, iolascon2021recommendationsfordiagnosis pages 8-9)

Genetic susceptibility is not equivalent to genetic causation. G6PD deficiency impairs NADPH generation, increases oxidative-hemolysis risk, and can make methylene blue ineffective or harmful. Unrecognized CYB5R3 deficiency, HbM, or unstable globin variants may amplify or mimic an acquired episode. No validated GWAS susceptibility loci, penetrance estimate, polygenic score, or clinically established pharmacogenomic dosing algorithm was identified. (iolascon2021recommendationsfordiagnosis pages 3-5, iolascon2021recommendationsfordiagnosis pages 9-10)

Protective factors and gene–environment interaction

Avoidance or dose limitation of oxidants, alternative local anesthetics, monitoring during dapsone or inhaled-NO therapy, and preservation of glucose/NADPH availability are practical protective factors. The clearest gene–environment interaction is oxidant exposure superimposed on G6PD or erythrocyte reductase deficiency. A CYB5R3 Thr117Ser polymorphism has been discussed in malaria/sickle-cell contexts, but it is not an established protective allele for drug-induced methemoglobinemia. No protective diet or lifestyle intervention has proven efficacy. (iolascon2021recommendationsfordiagnosis pages 3-5, iolascon2021recommendationsfordiagnosis pages 9-10, iolascon2021recommendationsfordiagnosis pages 11-12)

3. Phenotypes

Severity varies with MetHb percentage, rate of rise, hemoglobin concentration, comorbidity, and chronic adaptation. The consensus ranges are: <10%, usually asymptomatic with low oximeter readings or gray/blue color; 10%–30%, cyanosis and dark-brown blood, sometimes confusion; 30%–50%, dyspnea, dizziness, syncope, chest pain, palpitations, headache, and fatigue; 50%–70%, tachypnea, acidosis, dysrhythmia, seizure, delirium, or coma; >70%, profound hypoxia and high mortality. (iolascon2021recommendationsfordiagnosis pages 3-5, belzer2024causesofacquired pages 2-3)

Suggested HPO mappings include Cyanosis HP:0000961, Dyspnea HP:0002094, Headache HP:0002315, Fatigue HP:0012378, Syncope HP:0001279, Palpitations HP:0001695, Metabolic acidosis HP:0001942, Seizure HP:0001250, Coma HP:0001259, Hemolytic anemia HP:0001878, and hypoxemia/abnormal blood oxygenation. Chocolate-brown blood is best represented as an abnormal blood-color finding if the local terminology supports it.

Onset is possible at any age and is ordinarily abrupt after exposure. Manifestations are episodic and exposure-linked, rather than developmentally progressive. Quality-of-life instruments specific to this condition have not been validated; acute dyspnea, fatigue, confusion, intensive-care admission, and interruption of necessary dapsone therapy are the principal functional burdens. In the 2024 cohort, 68.7% of pediatric and 37.4% of adult elevated-MetHb encounters were asymptomatic, reflecting surveillance of treated patients. (belzer2024causesofacquired pages 4-5)

4. Genetic and molecular information

There is no single causal gene for the acquired target disease and no characteristic germline, somatic, chromosomal, or epigenetic lesion. Accordingly, pathogenic-variant classification, allele frequency, anticipation, mosaicism, and founder effects are not applicable to uncomplicated drug-induced disease.

Genes relevant to susceptibility and differential diagnosis are:

• G6PD: reduced NADPH supply and increased oxidative hemolysis; X-linked deficiency modifies treatment safety.
• CYB5R3: biallelic loss-of-function causes autosomal-recessive congenital methemoglobinemia, with >80 disease-causing variants reported by 2020; it is a differential, not the usual cause of an acquired event.
• CYB5A and globin genes HBA1, HBA2, HBB, HBG1, HBG2: rare hereditary methemoglobinemias/HbM differentials. (iolascon2021recommendationsfordiagnosis pages 1-3, iolascon2021recommendationsfordiagnosis pages 3-5)

Routine WES, WGS, CMA, karyotyping, FISH, mtDNA, or repeat-expansion testing has no role after a clear exposure-linked, resolving episode. Consider CYB5R activity and targeted CYB5R3/globin sequencing when cyanosis predates exposure, persists after drug withdrawal, recurs without oxidants, or clusters in a family. (iolascon2021recommendationsfordiagnosis pages 5-6, iolascon2021recommendationsfordiagnosis pages 8-9)

5. Environmental information

Relevant environments include endoscopy/anesthesia and dental settings using topical/local anesthetics; ICUs using inhaled nitric oxide or nitroprusside; oncology/transplant settings using dapsone or rasburicase; recreational “poppers” or adulterated cocaine; and occupational/agricultural exposure to anilines, nitrobenzene, chlorates, pesticides, and nitrate-contaminated water. Tobacco, alcohol, exercise, and ordinary diet are not established independent causes, although smoking-related cardiorespiratory disease may reduce physiologic reserve. (belzer2024causesofacquired pages 2-3, iolascon2021recommendationsfordiagnosis pages 11-12)

Infections do not generally act as transmissible causes. Sepsis and infant gastroenteritis may increase endogenous nitric oxide/nitrite production or acidosis and thereby trigger MetHb formation. These are physiologic cofactors, not evidence of a pathogen-specific methemoglobinemia. (belzer2024causesofacquired pages 2-3, iolascon2021recommendationsfordiagnosis pages 8-9)

6. Mechanism/pathophysiology

Ordered causal chain

1. Drug or reactive metabolite exposure leads to oxidant delivery to circulating erythrocytes.
2. Oxidant stress leads to conversion of heme Fe²⁺ to Fe³⁺ faster than endogenous reduction can compensate.
3. Fe³⁺ formation results in heme sites that cannot bind oxygen.
4. Oxidation of part of the hemoglobin tetramer also leads to increased oxygen affinity at remaining Fe²⁺ sites—the Darling–Roughton effect—and a left-shifted dissociation curve.
5. Both effects result in reduced arterial oxygen-carrying capacity and impaired tissue oxygen unloading despite preserved dissolved oxygen and often normal/high PaO₂.
6. Functional anemia leads to compensatory tachycardia and tachypnea and then tissue hypoxia, headache, fatigue, dyspnea, and cyanosis.
7. If oxidation continues or oxygen reserve is poor, tissue hypoxia leads to lactate/metabolic acidosis, ischemia, dysrhythmia, seizures, coma, organ injury, and death.
8. Branch—normal recovery: erythrocyte NADH–cytochrome-b5 reductase and subsidiary NADPH-dependent pathways lead to reduction of Fe³⁺ back to Fe²⁺.
9. Branch—treatment: NADPH reduces methylene blue to leukomethylene blue, which leads to accelerated reduction of MetHb.
10. Branch—susceptibility: low CYB5R activity, G6PD deficiency, anemia, acidosis, or cardiorespiratory disease leads to faster accumulation or greater clinical severity; for some comorbid effects the magnitude is observational rather than experimentally demonstrated. (belzer2024causesofacquired pages 1-2, cefalu2020methemoglobinemiainthe pages 3-4, iolascon2021recommendationsfordiagnosis pages 9-10)

This is a redox/oxygen-transport disorder, not primarily a Wnt, MAPK, PI3K–AKT, mTOR, immune, apoptotic, or fibrotic disease. The initiating molecular lesion is oxidation within erythrocyte hemoglobin; downstream organ damage is hypoxic/ischemic. Suggested GO terms include oxidation–reduction process, oxygen binding, response to decreased oxygen levels, cellular response to hypoxia, and methemoglobin reductase activity. The principal Cell Ontology entity is erythrocyte CL:0000232. (belzer2024causesofacquired pages 1-2, mcnulty2022foodinducedmethemoglobinemiaa pages 1-1)

No reproducible disease-specific transcriptomic, proteomic, lipidomic, metabolomic, epigenomic, single-cell, spatial-transcriptomic, CRISPR-screen, or integrated multi-omics signature was identified. MetHb percentage itself is the direct biochemical phenotype.

7. Anatomical structures affected

The primary affected tissue is circulating blood, specifically hemoglobin in mature erythrocytes. The relevant subcellular context is erythrocyte cytosol and the heme prosthetic groups of hemoglobin; mature erythrocytes lack nuclei and mitochondria. Suggested terms include UBERON:0000178 blood, erythrocyte CL:0000232, hemoglobin complex, cytosol, and heme-binding site.

Secondary injury is systemic and proportional to oxygen demand: brain (confusion, seizure, coma), heart (angina, dysrhythmia, ischemia), skeletal muscle, kidney, and other organs may be affected by hypoxia. Lungs are not necessarily structurally diseased, explaining a normal PaO₂ despite cyanosis. There is no lateralization. (iolascon2021recommendationsfordiagnosis pages 3-5, cefalu2020methemoglobinemiainthe pages 1-3)

8. Temporal development

Onset is usually acute or subacute after exposure, with abrupt neurologic or cardiac symptoms distinguishing acquired disease from lifelong congenital cyanosis. Endogenous MetHb half-life has been estimated at approximately 55 minutes once oxidant input ceases. Effective methylene blue ordinarily lowers MetHb substantially within 30–60 minutes. (belzer2024causesofacquired pages 1-2, iolascon2021recommendationsfordiagnosis pages 9-10, iolascon2021recommendationsfordiagnosis pages 11-12)

The course is commonly self-limited after drug withdrawal, but dapsone can require treatment every 6–8 hours for 2–3 days. Rebound has been reported up to 18 hours after methylene blue, particularly with long-acting or lipophilic oxidants; one dapsone case fell from 25% to 7% and rebounded to 13.6% within six hours before a second dose. Serial co-oximetry is therefore important. (barclay2011dapsoneinducedmethemoglobinemiaa pages 5-6, iolascon2021recommendationsfordiagnosis pages 9-10, cefalu2020methemoglobinemiainthe pages 6-8)

9. Inheritance and population

Drug-induced methemoglobinemia is not inherited. Population prevalence and annual incidence are unknown because cases are sporadic, exposure-dependent, and under-recognized; no valid cases-per-100,000 estimate was found. There is no established sex ratio or ethnicity-specific incidence independent of exposure patterns and G6PD prevalence.

In the 2024 Iowa cohort, 303 unique patients had at least one result ≥3.1%, while only 27 had ≥10% during 2009–2023. Among ≥10% episodes across the longer dataset, causes included dapsone (40), benzocaine (10), recreational alkyl nitrites (3), sodium-nitrite suicide attempts (3, one fatal), nitrate-contaminated food (2), and sepsis (2). Severe intentional nitrite poisonings appear to be increasing with online availability, but this remains surveillance evidence rather than population incidence. (belzer2024causesofacquired pages 1-2, belzer2024causesofacquired pages 3-4, belzer2024causesofacquired pages 5-6)

10. Diagnostics

Diagnosis rests on exposure history, cyanosis or hypoxia refractory to oxygen, an SpO₂–SaO₂ “saturation gap,” chocolate-brown blood, and multiwavelength co-oximetry. Conventional two-wavelength pulse oximeters cannot quantify MetHb and tend toward approximately 85%; PaO₂ measures dissolved oxygen and can remain normal or high. A saturation gap >5% is suggestive but not diagnostic. Arterial or venous blood co-oximetry directly reports MetHb as a percentage of total hemoglobin. (cefalu2020methemoglobinemiainthe pages 1-3, rathod2024shadesofblue pages 2-3, bai2024dapsoneinducedmethemoglobinemiain pages 3-4)

Additional tests should include CBC/hemoglobin, blood gas and lactate, renal/hepatic function where relevant, ECG for severe disease, and hemolysis studies—reticulocytes, bilirubin, LDH, haptoglobin, smear/Heinz bodies—when dapsone, rasburicase, sulfonamides, or G6PD deficiency are plausible. Imaging, biopsy, EEG, and pulmonary-function testing are not diagnostic unless needed to evaluate competing pathology.

Differentials include cardiopulmonary hypoxemia/right-to-left shunt, carboxyhemoglobinemia, sulfhemoglobinemia, cyanide toxicity, peripheral vasoconstriction/artifact, congenital CYB5R3 deficiency, HbM, and unstable hemoglobin. Sulfhemoglobin is not reducible by methylene blue and can interfere with some measurements. Persistent lifelong/familial cyanosis favors hereditary disease. (iolascon2021recommendationsfordiagnosis pages 5-6, gehle2013atsdrcasestudies pages 81-87, bai2024dapsoneinducedmethemoglobinemiain pages 3-4)

There is no general-population or newborn screening program for the acquired disease. Targeted surveillance is used during dapsone and inhaled-NO treatment and in high-risk anesthesia settings. A completed prospective liposuction study followed 133 patients over 24 hours, and a pediatric dental study randomized 91 children to prilocaine, lidocaine, or no local anesthetic with continuous pulse co-oximetry. (NCT01766999 chunk 1, NCT01402869 chunk 1)

11. Outcome and prognosis

Promptly recognized disease generally resolves completely without chronic disability. A 2024 five-patient series reported peak MetHb of 16.6%–41%; four received methylene blue and all recovered. (rathod2024shadesofblue pages 3-5, rathod2024shadesofblue pages 2-3)

Risk rises sharply at 50%–70%, and >70% is potentially fatal, but level alone is imperfect because rate of rise, anemia, and cardiopulmonary reserve matter. In the food/nitrate systematic review, 97 articles described 568 cases, median MetHb 30%; 35 deaths occurred, 32 after accidental ingestion. Most patients survived even at levels up to 89% when methylene blue was administered, and methylene blue alone produced a mean 39.1-percentage-point fall among 22 evaluable cases. These data concern acquired food/nitrite poisoning and are supportive rather than drug-specific efficacy estimates. (mcnulty2022foodinducedmethemoglobinemiaa pages 1-1)

The Iowa cohort found no therapeutic-dose dapsone-attributed fatalities, whereas one of three sodium-nitrite suicide attempts was fatal. Death recorded during an encounter often reflected severe underlying illness rather than MetHb itself. No 5- or 10-year survival metric, chronic disability index, EQ-5D, SF-36, or validated prognostic model is applicable. (belzer2024causesofacquired pages 4-5, belzer2024causesofacquired pages 5-6)

12. Treatment

1. Immediately stop/remove the oxidant. Decontaminate safely when dermal/occupational exposure is continuing.
2. Support oxygen delivery: high-flow oxygen, IV access, glucose and correction of acidosis, fluids/pressors, ventilation, seizure treatment, and toxicology consultation as needed.
3. Treat symptomatic patients and generally asymptomatic patients with MetHb ≥30%; commonly cited thresholds are ≥20% when symptomatic and ≥30% when asymptomatic. Treat at approximately 10%–20% when severe anemia, cardiac/pulmonary disease, CO poisoning, infancy, or other limited reserve is present. (iolascon2021recommendationsfordiagnosis pages 10-11, iolascon2021recommendationsfordiagnosis pages 8-9)
4. Methylene blue/methylthioninium chloride: 1–2 mg/kg of 1% solution IV over 3–5 minutes; repeat approximately 1 mg/kg after 30–60 minutes if symptoms or MetHb persist. Avoid cumulative exposure above approximately 5.5–7 mg/kg because methylene blue itself becomes oxidizing and may worsen MetHb/hemolysis. Suggested annotations: CHEBI:6872; NCIT methylene-blue treatment/antidote therapy. (iolascon2021recommendationsfordiagnosis pages 9-10, iolascon2021recommendationsfordiagnosis pages 10-11, cefalu2020methemoglobinemiainthe pages 6-8)
5. Major cautions: known G6PD deficiency because of inadequate NADPH response and hemolysis; serotonergic medicines because methylene blue inhibits MAO-A and can precipitate serotonin syndrome; pregnancy because of reported teratogenicity; renal failure and certain anesthetic settings warrant caution. In immediately life-threatening toxicity, expert risk–benefit judgment is necessary rather than delaying all therapy for a G6PD result. (bai2024dapsoneinducedmethemoglobinemiain pages 3-4, iolascon2021recommendationsfordiagnosis pages 9-10, iolascon2021recommendationsfordiagnosis pages 8-9)
6. Alternatives: ascorbic acid directly reduces MetHb but is slower—often ≥24 hours—and dosing is not standardized. It is used when methylene blue is unavailable/contraindicated. Exchange transfusion, red-cell transfusion, or hyperbaric oxygen are rescue options; expert review cites 81.6% survival after therapeutic whole-blood exchange in methylene-blue-refractory cases. (mcnulty2022foodinducedmethemoglobinemiaa pages 3-3, iolascon2021recommendationsfordiagnosis pages 9-10, iolascon2021recommendationsfordiagnosis pages 10-11)
7. Dapsone overdose: serial MetHb/hemolysis monitoring and repeated treatment may be necessary. Multiple-dose activated charcoal shortened reported dapsone half-life from 77±23 to 12.7±0.7 hours, but requires toxicology guidance and airway safety. (barclay2011dapsoneinducedmethemoglobinemiaa pages 5-5)

There is no role for surgery, gene therapy, cell therapy, RNA therapy, or immunotherapy. Completed real-world implementation studies include the 24-person acquired-MetHb registry NCT03542760 and the seven-person open-label Phase 4 ProvayBlue study NCT03395223, which used 1 mg/kg IV and permitted one repeat dose after an hour. Small enrollment underscores the rarity and limited prospective evidence base. (NCT03542760 chunk 1, NCT03395223 chunk 1)

13. Prevention

Primary prevention: maintain electronic medication alerts; avoid benzocaine/prilocaine or excessive doses in susceptible patients; calculate weight-based local-anesthetic exposure; review concurrent oxidants; use safer PCP-prophylaxis alternatives when appropriate; prevent nitrate/nitrite ingestion; regulate access and clearly label sodium nitrite; and use occupational controls/PPE for anilines and pesticides. (belzer2024causesofacquired pages 2-3, iolascon2021recommendationsfordiagnosis pages 11-12)

Secondary prevention: recognize the saturation gap early, obtain co-oximetry, and monitor MetHb during dapsone, inhaled nitric oxide, nitroprusside, and high-risk anesthesia. Routine dapsone monitoring in the Iowa center detected many asymptomatic cases and allowed dose reduction or discontinuation; only three dapsone patients required methylene blue. (belzer2024causesofacquired pages 3-4, belzer2024causesofacquired pages 5-6)

Tertiary prevention: document the culprit as a serious adverse drug reaction, avoid re-exposure, monitor for rebound for at least the expected pharmacologic window, and assess hemolysis where relevant. Vaccination and antimicrobial prophylaxis do not prevent the dyshemoglobinemia itself. Genetic counseling is unnecessary for an isolated acquired episode, but is appropriate if persistent/familial findings suggest hereditary disease.

14. Other species/natural disease

The conserved vertebrate mechanism—heme Fe²⁺ oxidation to Fe³⁺—occurs in mammals and birds. Veterinary cases can follow acetaminophen, local anesthetics, nitrates/nitrites, PAPP bait, and other oxidants; cats and dogs are especially relevant non-target species. This is not infectious and has no zoonotic transmission.

An in-vitro comparative study used blood from coyote (Canis latrans), California vole (Microtus californicus), feral swine (Sus scrofa), European starling (Sturnus vulgaris), and mallard (Anas platyrhynchos). Mammalian blood reached 100% MetHb at 15 mM sodium nitrite versus 200 mM for avian blood, while color values at a given MetHb fraction were similar enough to support a cross-species blood-spot diagnostic card. (patton2016detectingmethemoglobinemiain pages 1-2)

Acetaminophen studies indicate metabolic activation to p-aminophenol is important: at 500 µM p-aminophenol, canine and feline erythrocytes generated more MetHb than rat or mouse cells, plausibly reflecting lower NADH-methemoglobin-reductase and N-acetyltransferase detoxification. This makes species extrapolation imperfect. (mcconkey2007themechanismof pages 132-137)

15. Model organisms

Available models are chiefly induced toxicology models, not genetic replicas of the heterogeneous human exposure syndrome:

• Ex-vivo blood oxidation: sodium nitrite in mammalian and avian blood enables spectrophotometric/colorimetric assay development at the 635-nm MetHb absorption peak. Strength: direct and cross-species. Limitation: lacks metabolism, circulation, organ hypoxia, and treatment pharmacokinetics. (patton2016detectingmethemoglobinemiain pages 1-2)
• Rat and Beagle-dog nitrite models: single IM doses ≥100 mg/kg in rats and 60 mg/kg in dogs caused death/moribundity; repeated doses ≤30 and ≤10 mg/kg/day, respectively, were tolerated, with transient dose-dependent methemoglobinemia. These models characterize dose, time course, and systemic toxicity but involve nitrite rather than most human medicines. (miller2021safetyandtoxicology pages 1-2)
• Canine/feline acetaminophen/p-aminophenol systems: useful for metabolic activation, erythrocyte susceptibility, and veterinary toxicology; they do not reproduce dapsone or local-anesthetic pharmacology. (mcconkey2007themechanismof pages 132-137)
• Naturally CYB5R-deficient dogs: useful for hemoglobin-redox and methylene-blue studies, but model hereditary rather than drug-induced disease.

Suggested resources are MGI, RGD, ZFIN, OMIA, and NCBI Taxonomy. No standardized knockout, organoid, iPSC, or humanized model is required to diagnose or treat the acquired disease.

Evidence appraisal and recent developments

The most consequential 2023–2024 development is improved quantitative description of real-world causes: the March/June 2024 Iowa study shows dapsone and iatrogenic nitric oxide dominate mild monitored cases, while intentional nitrite exposure and historical benzocaine use disproportionately contribute to severe episodes. It also documents institutional reduction in benzocaine-associated severe disease, consistent with prevention through changed procedural practice. (belzer2024causesofacquired pages 1-2, belzer2024causesofacquired pages 5-6)

Prospective evidence remains sparse. The FDA-requested Phase 4 study enrolled only seven patients, and the multicenter registry enrolled 24. Thus, expert recommendations appropriately rely on mechanism, observational cohorts, case series, and long clinical experience rather than randomized antidote trials. (NCT03542760 chunk 1, NCT03395223 chunk 1)

Key sources and dates

• Belzer A, Krasowski MD. Causes of acquired methemoglobinemia—a retrospective study at a large academic hospital. Available March 16, 2024; Toxicology Reports 2024. DOI: 10.1016/j.toxrep.2024.03.004. Human retrospective cohort. (belzer2024causesofacquired pages 1-2)
• Rathod et al. Shades of Blue: A Case Series of Acquired Methemoglobinemia. April 2024. DOI: 10.7759/cureus.58312. Human case series. (rathod2024shadesofblue pages 2-3)
• Iolascon et al. Recommendations for diagnosis and treatment of methemoglobinemia. September 2021. DOI: 10.1002/ajh.26340. Systematic search plus >75% Delphi-like expert consensus. (iolascon2021recommendationsfordiagnosis pages 1-3)
• Cefalu et al. Methemoglobinemia in the Operating Room and Intensive Care Unit. March 19, 2020. DOI: 10.1007/s12325-020-01282-5. Clinical review. (cefalu2020methemoglobinemiainthe pages 1-3)
• McNulty et al. Food-induced methemoglobinemia: a systematic review. March 2022. DOI: 10.1111/1750-3841.16090. Systematic review of 568 human cases. (mcnulty2022foodinducedmethemoglobinemiaa pages 1-1)
• Historical primary clinical references with PMIDs include Wright et al., PMID 10533013; Ash-Bernal et al., 138-case series, PMID 15342970; Umbreit, PMID 16986127; Guay, 242 local-anesthetic episodes, PMID 19224791; and Vasters et al. on prilocaine risk factors, PMID 16723054. These PMIDs are supplied in the ClinicalTrials.gov bibliography and should be linked through https://pubmed.ncbi.nlm.nih.gov/<PMID>/. (NCT01402869 chunk 1, NCT01402869 chunk 2)

Knowledge gaps: no reliable population prevalence/incidence, validated patient-reported outcome instrument, disease-specific omics signature, GWAS architecture, or adequately powered randomized antidote trial is available. Exact ontology identifiers for a dedicated drug-induced MONDO/ICD-11 subtype should be terminology-validated before database release.

References

1. (iolascon2021recommendationsfordiagnosis pages 1-3): Achille Iolascon, Paola Bianchi, Immacolata Andolfo, Roberta Russo, Wilma Barcellini, Elisa Fermo, Gergely Toldi, Stefano Ghirardello, David Rees, Richard Van Wijk, Antonis Kattamis, Patrick G. Gallagher, Noemi Roy, Ali Taher, Razan Mohty, Andreas Kulozik, Lucia De Franceschi, Antonella Gambale, Mariane De Montalembert, Gian Luca Forni, Cornelis L. Harteveld, and Josef Prchal. Recommendations for diagnosis and treatment of methemoglobinemia. Sep 2021. URL: https://doi.org/10.1002/ajh.26340, doi:10.1002/ajh.26340. This article has 319 citations and is from a domain leading peer-reviewed journal.

2. (belzer2024causesofacquired pages 1-2): Alex Belzer and Matthew D. Krasowski. Causes of acquired methemoglobinemia – a retrospective study at a large academic hospital. Jun 2024. URL: https://doi.org/10.1016/j.toxrep.2024.03.004, doi:10.1016/j.toxrep.2024.03.004. This article has 38 citations and is from a peer-reviewed journal.

3. (iolascon2021recommendationsfordiagnosis pages 9-10): Achille Iolascon, Paola Bianchi, Immacolata Andolfo, Roberta Russo, Wilma Barcellini, Elisa Fermo, Gergely Toldi, Stefano Ghirardello, David Rees, Richard Van Wijk, Antonis Kattamis, Patrick G. Gallagher, Noemi Roy, Ali Taher, Razan Mohty, Andreas Kulozik, Lucia De Franceschi, Antonella Gambale, Mariane De Montalembert, Gian Luca Forni, Cornelis L. Harteveld, and Josef Prchal. Recommendations for diagnosis and treatment of methemoglobinemia. Sep 2021. URL: https://doi.org/10.1002/ajh.26340, doi:10.1002/ajh.26340. This article has 319 citations and is from a domain leading peer-reviewed journal.

4. (belzer2024causesofacquired pages 3-4): Alex Belzer and Matthew D. Krasowski. Causes of acquired methemoglobinemia – a retrospective study at a large academic hospital. Jun 2024. URL: https://doi.org/10.1016/j.toxrep.2024.03.004, doi:10.1016/j.toxrep.2024.03.004. This article has 38 citations and is from a peer-reviewed journal.

5. (belzer2024causesofacquired pages 2-3): Alex Belzer and Matthew D. Krasowski. Causes of acquired methemoglobinemia – a retrospective study at a large academic hospital. Jun 2024. URL: https://doi.org/10.1016/j.toxrep.2024.03.004, doi:10.1016/j.toxrep.2024.03.004. This article has 38 citations and is from a peer-reviewed journal.

6. (iolascon2021recommendationsfordiagnosis pages 3-5): Achille Iolascon, Paola Bianchi, Immacolata Andolfo, Roberta Russo, Wilma Barcellini, Elisa Fermo, Gergely Toldi, Stefano Ghirardello, David Rees, Richard Van Wijk, Antonis Kattamis, Patrick G. Gallagher, Noemi Roy, Ali Taher, Razan Mohty, Andreas Kulozik, Lucia De Franceschi, Antonella Gambale, Mariane De Montalembert, Gian Luca Forni, Cornelis L. Harteveld, and Josef Prchal. Recommendations for diagnosis and treatment of methemoglobinemia. Sep 2021. URL: https://doi.org/10.1002/ajh.26340, doi:10.1002/ajh.26340. This article has 319 citations and is from a domain leading peer-reviewed journal.

7. (iolascon2021recommendationsfordiagnosis pages 10-11): Achille Iolascon, Paola Bianchi, Immacolata Andolfo, Roberta Russo, Wilma Barcellini, Elisa Fermo, Gergely Toldi, Stefano Ghirardello, David Rees, Richard Van Wijk, Antonis Kattamis, Patrick G. Gallagher, Noemi Roy, Ali Taher, Razan Mohty, Andreas Kulozik, Lucia De Franceschi, Antonella Gambale, Mariane De Montalembert, Gian Luca Forni, Cornelis L. Harteveld, and Josef Prchal. Recommendations for diagnosis and treatment of methemoglobinemia. Sep 2021. URL: https://doi.org/10.1002/ajh.26340, doi:10.1002/ajh.26340. This article has 319 citations and is from a domain leading peer-reviewed journal.

8. (iolascon2021recommendationsfordiagnosis pages 8-9): Achille Iolascon, Paola Bianchi, Immacolata Andolfo, Roberta Russo, Wilma Barcellini, Elisa Fermo, Gergely Toldi, Stefano Ghirardello, David Rees, Richard Van Wijk, Antonis Kattamis, Patrick G. Gallagher, Noemi Roy, Ali Taher, Razan Mohty, Andreas Kulozik, Lucia De Franceschi, Antonella Gambale, Mariane De Montalembert, Gian Luca Forni, Cornelis L. Harteveld, and Josef Prchal. Recommendations for diagnosis and treatment of methemoglobinemia. Sep 2021. URL: https://doi.org/10.1002/ajh.26340, doi:10.1002/ajh.26340. This article has 319 citations and is from a domain leading peer-reviewed journal.

9. (cefalu2020methemoglobinemiainthe pages 6-8): John N. Cefalu, Tejas V. Joshi, Matthew J. Spalitta, Carson J. Kadi, James H. Diaz, Jonathan P. Eskander, Elyse M. Cornett, and Alan D. Kaye. Methemoglobinemia in the operating room and intensive care unit: early recognition, pathophysiology, and management. Advances in Therapy, 37:1714-1723, Mar 2020. URL: https://doi.org/10.1007/s12325-020-01282-5, doi:10.1007/s12325-020-01282-5. This article has 104 citations and is from a peer-reviewed journal.

10. (iolascon2021recommendationsfordiagnosis pages 5-6): Achille Iolascon, Paola Bianchi, Immacolata Andolfo, Roberta Russo, Wilma Barcellini, Elisa Fermo, Gergely Toldi, Stefano Ghirardello, David Rees, Richard Van Wijk, Antonis Kattamis, Patrick G. Gallagher, Noemi Roy, Ali Taher, Razan Mohty, Andreas Kulozik, Lucia De Franceschi, Antonella Gambale, Mariane De Montalembert, Gian Luca Forni, Cornelis L. Harteveld, and Josef Prchal. Recommendations for diagnosis and treatment of methemoglobinemia. Sep 2021. URL: https://doi.org/10.1002/ajh.26340, doi:10.1002/ajh.26340. This article has 319 citations and is from a domain leading peer-reviewed journal.

11. (NCT03542760 chunk 2): Acquired Methemoglobinemia Observational Registry. Hospital Quality Foundation. 2018. ClinicalTrials.gov Identifier: NCT03542760

12. (cefalu2020methemoglobinemiainthe pages 4-6): John N. Cefalu, Tejas V. Joshi, Matthew J. Spalitta, Carson J. Kadi, James H. Diaz, Jonathan P. Eskander, Elyse M. Cornett, and Alan D. Kaye. Methemoglobinemia in the operating room and intensive care unit: early recognition, pathophysiology, and management. Advances in Therapy, 37:1714-1723, Mar 2020. URL: https://doi.org/10.1007/s12325-020-01282-5, doi:10.1007/s12325-020-01282-5. This article has 104 citations and is from a peer-reviewed journal.

13. (iolascon2021recommendationsfordiagnosis pages 11-12): Achille Iolascon, Paola Bianchi, Immacolata Andolfo, Roberta Russo, Wilma Barcellini, Elisa Fermo, Gergely Toldi, Stefano Ghirardello, David Rees, Richard Van Wijk, Antonis Kattamis, Patrick G. Gallagher, Noemi Roy, Ali Taher, Razan Mohty, Andreas Kulozik, Lucia De Franceschi, Antonella Gambale, Mariane De Montalembert, Gian Luca Forni, Cornelis L. Harteveld, and Josef Prchal. Recommendations for diagnosis and treatment of methemoglobinemia. Sep 2021. URL: https://doi.org/10.1002/ajh.26340, doi:10.1002/ajh.26340. This article has 319 citations and is from a domain leading peer-reviewed journal.

14. (cefalu2020methemoglobinemiainthe pages 8-10): John N. Cefalu, Tejas V. Joshi, Matthew J. Spalitta, Carson J. Kadi, James H. Diaz, Jonathan P. Eskander, Elyse M. Cornett, and Alan D. Kaye. Methemoglobinemia in the operating room and intensive care unit: early recognition, pathophysiology, and management. Advances in Therapy, 37:1714-1723, Mar 2020. URL: https://doi.org/10.1007/s12325-020-01282-5, doi:10.1007/s12325-020-01282-5. This article has 104 citations and is from a peer-reviewed journal.

15. (bai2024dapsoneinducedmethemoglobinemiain pages 3-4): Sakshi Bai, Abraham Kisule, Bipneet Singh, Kavita Luthra, and Danesh Kumar. Dapsone-induced methemoglobinemia in a woman with multiple myeloma without glucose-6-phosphate dehydrogenase (g6pd) deficiency. Jun 2024. URL: https://doi.org/10.7759/cureus.63249, doi:10.7759/cureus.63249. This article has 3 citations.

16. (barclay2011dapsoneinducedmethemoglobinemiaa pages 5-5): James A Barclay, Stamatina E Ziemba, and Rami B Ibrahim. Dapsone-induced methemoglobinemia: a primer for clinicians. Annals of Pharmacotherapy, 45:1103-1115, Sep 2011. URL: https://doi.org/10.1345/aph.1q139, doi:10.1345/aph.1q139. This article has 101 citations and is from a peer-reviewed journal.

17. (cefalu2020methemoglobinemiainthe pages 3-4): John N. Cefalu, Tejas V. Joshi, Matthew J. Spalitta, Carson J. Kadi, James H. Diaz, Jonathan P. Eskander, Elyse M. Cornett, and Alan D. Kaye. Methemoglobinemia in the operating room and intensive care unit: early recognition, pathophysiology, and management. Advances in Therapy, 37:1714-1723, Mar 2020. URL: https://doi.org/10.1007/s12325-020-01282-5, doi:10.1007/s12325-020-01282-5. This article has 104 citations and is from a peer-reviewed journal.

18. (belzer2024causesofacquired pages 4-5): Alex Belzer and Matthew D. Krasowski. Causes of acquired methemoglobinemia – a retrospective study at a large academic hospital. Jun 2024. URL: https://doi.org/10.1016/j.toxrep.2024.03.004, doi:10.1016/j.toxrep.2024.03.004. This article has 38 citations and is from a peer-reviewed journal.

19. (mcnulty2022foodinducedmethemoglobinemiaa pages 1-1): Richard McNulty, Nikhil Kuchi, Elena Xu, and Naren Gunja. Food-induced methemoglobinemia: a systematic review. Journal of food science, 87 4:1423-1448, Mar 2022. URL: https://doi.org/10.1111/1750-3841.16090, doi:10.1111/1750-3841.16090. This article has 64 citations and is from a peer-reviewed journal.

20. (cefalu2020methemoglobinemiainthe pages 1-3): John N. Cefalu, Tejas V. Joshi, Matthew J. Spalitta, Carson J. Kadi, James H. Diaz, Jonathan P. Eskander, Elyse M. Cornett, and Alan D. Kaye. Methemoglobinemia in the operating room and intensive care unit: early recognition, pathophysiology, and management. Advances in Therapy, 37:1714-1723, Mar 2020. URL: https://doi.org/10.1007/s12325-020-01282-5, doi:10.1007/s12325-020-01282-5. This article has 104 citations and is from a peer-reviewed journal.

21. (barclay2011dapsoneinducedmethemoglobinemiaa pages 5-6): James A Barclay, Stamatina E Ziemba, and Rami B Ibrahim. Dapsone-induced methemoglobinemia: a primer for clinicians. Annals of Pharmacotherapy, 45:1103-1115, Sep 2011. URL: https://doi.org/10.1345/aph.1q139, doi:10.1345/aph.1q139. This article has 101 citations and is from a peer-reviewed journal.

22. (belzer2024causesofacquired pages 5-6): Alex Belzer and Matthew D. Krasowski. Causes of acquired methemoglobinemia – a retrospective study at a large academic hospital. Jun 2024. URL: https://doi.org/10.1016/j.toxrep.2024.03.004, doi:10.1016/j.toxrep.2024.03.004. This article has 38 citations and is from a peer-reviewed journal.

23. (rathod2024shadesofblue pages 2-3): Bharatsing D Rathod, Nilesh Kamble, Onkar Awadhiya, Udit Narang, Rajashree S Khot, and Sunita Kumbhalkar. Shades of blue: a case series of acquired methemoglobinemia. Apr 2024. URL: https://doi.org/10.7759/cureus.58312, doi:10.7759/cureus.58312. This article has 3 citations.

24. (gehle2013atsdrcasestudies pages 81-87): K Gehle. Atsdr case studies in environmental medicine: nitrate/nitrite toxicity. Unknown journal, 2013.

25. (NCT01766999 chunk 1): Hartmut Gehring. Methemoglobinemia After Liposuction - Diagnostic by Pulse Oximetry and Blood Gas Analysis.. University Hospital Schleswig-Holstein. 2008. ClinicalTrials.gov Identifier: NCT01766999

26. (NCT01402869 chunk 1): Lauren GutenBerg. Methemoglobin Levels in Generally Anesthetized Pediatric Dental Patients Receiving Local Anesthetics. Loma Linda University. 2011. ClinicalTrials.gov Identifier: NCT01402869

27. (rathod2024shadesofblue pages 3-5): Bharatsing D Rathod, Nilesh Kamble, Onkar Awadhiya, Udit Narang, Rajashree S Khot, and Sunita Kumbhalkar. Shades of blue: a case series of acquired methemoglobinemia. Apr 2024. URL: https://doi.org/10.7759/cureus.58312, doi:10.7759/cureus.58312. This article has 3 citations.

28. (mcnulty2022foodinducedmethemoglobinemiaa pages 3-3): Richard McNulty, Nikhil Kuchi, Elena Xu, and Naren Gunja. Food-induced methemoglobinemia: a systematic review. Journal of food science, 87 4:1423-1448, Mar 2022. URL: https://doi.org/10.1111/1750-3841.16090, doi:10.1111/1750-3841.16090. This article has 64 citations and is from a peer-reviewed journal.

29. (NCT03542760 chunk 1): Acquired Methemoglobinemia Observational Registry. Hospital Quality Foundation. 2018. ClinicalTrials.gov Identifier: NCT03542760

30. (NCT03395223 chunk 1): MEthylene Blue In Patients With Acquired Methemoglobinemia. Provepharm SAS. 2018. ClinicalTrials.gov Identifier: NCT03395223

31. (patton2016detectingmethemoglobinemiain pages 1-2): Toni G. Patton, Stephen L. Blamer, and Katherine E. Horak. Detecting methemoglobinemia in animals with a drop of blood. PLoS ONE, 11:e0167942, Dec 2016. URL: https://doi.org/10.1371/journal.pone.0167942, doi:10.1371/journal.pone.0167942. This article has 17 citations and is from a peer-reviewed journal.

32. (mcconkey2007themechanismof pages 132-137): SE McConkey. The mechanism of acetaminophen-induced methemoglobinemia in dogs and cats. Unknown journal, 2007.

33. (miller2021safetyandtoxicology pages 1-2): Lutfiya Miller, Charles D. Hébert, Sheila D. Grimes, James S. Toomey, Joo-Yeun Oh, Jason J. Rose, and Rakesh P. Patel. Safety and toxicology assessment of sodium nitrite administered by intramuscular injection. Oct 2021. URL: https://doi.org/10.1016/j.taap.2021.115702, doi:10.1016/j.taap.2021.115702. This article has 2 citations and is from a highest quality peer-reviewed journal.

34. (NCT01402869 chunk 2): Lauren GutenBerg. Methemoglobin Levels in Generally Anesthetized Pediatric Dental Patients Receiving Local Anesthetics. Loma Linda University. 2011. ClinicalTrials.gov Identifier: NCT01402869

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