eMedicine Specialties > Pediatrics: General Medicine > Hematology
Methemoglobinemia: Treatment & Medication
Updated: Oct 6, 2009
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Treatment
Medical Care
Once the diagnosis of methemoglobinemia has been confirmed and appropriate treatment has been initiated, the underlying etiology should be sought.
- In acquired methemoglobinemia, the toxin or drug may be identified by obtaining blood levels, performing gastric lavage, or both. In asymptomatic patients with low levels of methemoglobin, monitoring serial serum levels is all that may be necessary. The levels normalize over time unless recurrent or chronic exposure to the offending agent occurs.
- If the methemoglobin levels are more than 30%, methylene blue should be intravenously administered at 1-2 mg/kg (up to 50 mg/dose in adults, adolescents, and older children) as a 1% solution over 5 minutes; repeat in 1 hour, if necessary. Methylene blue is an oxidant at levels of more than 7 mg/kg and, therefore, may cause methemoglobinemia in susceptible patients; thus, care must be taken in administration of this drug. Methylene blue is contraindicated in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency because it can lead to severe hemolysis.
- Ascorbic acid is an antioxidant that may also be administered in patients with methemoglobin levels of more than 30%.
- N -acetylcysteine has been shown to reduce methemoglobin in recent studies but is not yet an approved treatment for methemoglobinemia.
- No pharmaceutical treatment for hereditary forms of methemoglobinemia exists.
- Oral ascorbic acid (200-500 mg) has been found to be partially effective, if continued on an ongoing basis; however, this therapy has the potential risk of renal stones and hyperoxaluria. Methylene blue has also been used in these patients.
- In severe cases, exchange transfusion may be necessary.
Consultations
- Consultation with other specialists, such as hematologists, cardiologists, and pulmonologists, may be required to assist in the search for the cause of the methemoglobinemia.
Diet
- Some vegetables (eg, beets, spinach, and carrots) are high in nitrite content and may need to be avoided in susceptible patients.
- Well water can be contaminated with nitrites, nitrates, and oxidants and could lead to methemoglobinemia, especially in small infants (<4 mo) when well water is used to prepare formula or is given alone.
Activity
- No change in activity is indicated.
Medication
Unless the methemoglobinemia is severe or symptomatic, the treatment is purely for cosmetic and/or psychological reasons. Various agents can reduce the methemoglobin levels to within the reference range or to acceptable levels (5-10%). Methylene blue, ascorbic acid, and, rarely, exchange transfusion may be used. N -acetylcysteine has been shown to reduce levels of methemoglobin in studies but is not yet approved for the treatment of methemoglobinemia.
Antidotes
These agents are used in the management of poisoning or overdose to prevent toxic effects or in metabolic disorders in which toxic substances accrue. Mechanisms of action are variable (eg, antagonists, toxin transformation, altered metabolism, chelation, directed antibodies).
Methylene blue (Urolene blue)
Increases the activity of NADH-methemoglobin reductase in RBCs, assisting in the conversion of ferric (Fe3+) to ferrous (Fe2+) iron.
Adult
1-2 mg/kg (up to 25-50 mg/dose) IV as a single dose over 5 min can rapidly reduce the methemoglobin level by approximately 50%
As noted above, methylene blue is an oxidant at doses >7 mg/kg and must be administered with care
Pediatric
Acute cases: 1-2 mg/kg/dose IV over 5 minutes; not to exceed 25-50 mg/dose; may be repeated hourly, not to exceed a cumulative dose of 7 mg/kg
Chronic cases: 100-300 mg PO qd
None reported
Documented hypersensitivity; renal insufficiency; G6PD deficiency
Pregnancy
C - Safety for use during pregnancy has not been established.
Precautions
Can cause profound anemia in G6PD deficiency; do not inject into the CNS; secretions, such as urine and feces, may be stained blue to greenish blue; contact with clothing should be avoided; may cause urinary irritation; safety for long-term use has not been established; cumulative doses may lead to dyspnea, chest pain, tremor, cyanosis, and hemolytic anemia; because methylene blue absorbs light in the deoxyhemoglobin range, concurrent pulse oximetry may be unreliable
Ascorbic acid (Vita-C, Cecon, Cevalin)
Antioxidant and coenzyme for reduction. It may be helpful in the treatment of congenital methemoglobinemia if used daily and on a continual basis.
Adult
200-500 mg/d PO; some authors recommend using higher doses of up to 1000 mg/d
Pediatric
Administer as in adults
High doses (ie, >1 g/d) increase plasma levels of ethinyl estradiol, thus, women who use PO contraceptives may have breakthrough bleeding when the ascorbic acid is discontinued; decreases effects of warfarin and fluphenazine; increases aspirin levels
None known
Pregnancy
C - Safety for use during pregnancy has not been established.
Precautions
Has been shown to lead to nephrolithiasis; very large doses can lead to renal failure; may cause hyperoxaluria; may cause significant hemolysis with G6PD deficiency
More on Methemoglobinemia |
| Overview: Methemoglobinemia |
| Differential Diagnoses & Workup: Methemoglobinemia |
 Treatment & Medication: Methemoglobinemia |
| Follow-up: Methemoglobinemia |
| Multimedia: Methemoglobinemia |
| References |
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References
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Further Reading
Keywords
methemoglobinemia, methemoglobin, cyanosis, glucose-6-phosphate dehydrogenase deficiency, cytochrome b5 oxidase deficiency, acquired methemoglobinemia, congenital methemoglobinemia, encephalopathy, microcephaly, hypertonia, athetosis, opisthotonus, strabismus, mental retardation, growth retardation, diagnosis, treatment
