Details About Overdose or Poisoning Generic Salt :: Methylene Blue
Methylene Blue
Drug Pharmacology ::
I. Pharmacology.
A. Methyleneblue is a thiazine dye that increases the conversion of methemoglobinto hemoglobin. Methylene blue is reduced via methemoglobin reductaseand nicotinamide adenosine dinucleotide phosphate (NADPH) toleukomethylene blue, which in turn reduces methemoglobin.Glucose-6-phospate dehydrogenase is essential for generation of NADPHand is thus essential for the function of methylene blue as anantidote. Therapeutic effect is seen within 30 minutes. Methemoglobinis excreted in bile and urine, which may turn blue or green.
B. Methyleneblue has been used to treat ifosfamide-induced encephalopathy, but theexact pathophysiologic mechanisms responsible are not known. Methyleneblue may reverse the neurotoxic effects of the ifosfamide metabolites.
Drug Indications ::
Indications.
A. Methyleneblue is used to treat methemoglobinemia (see Methemoglobinemia), inwhich the patient has symptoms or signs of hypoxemia (eg, dyspnea,confusion, or chest pain) or has a methemoglobin level greater than30%. Note: Methylene blue is not effective for sulfhemoglobinemia.
B. Methylene blue has been used to reverse and prevent ifosfamide-related encephalopathy.
Drug Contra-Indications ::
III. Contraindications./b>
G6PD deficiency. Treatment with methylene blue is ineffective and may cause hemolysis.
Severe renal failure.
Known hypersensitivity to methylene blue.
Methemoglobin reductase deficiency.
E. Reversal of nitrite-induced methemoglobinemia for treatment of cyanide poisoning.
Drug Adverse Effects ::
IV. Adverse effects
Gastrointestinal upset, headache, and dizziness may occur.
Excessive doses of methylene blue (
7mg/kg) can actually cause methemoglobinemia by directly oxidizinghemoglobin. Doses greater than 15 mg/kg are associated with hemolysis,particularly in neonates. May also dye secretions and mucous membranesand interfere with clinical findings of cyanosis.
Long-term administration may result in marked anemia.
Extravasation may result in local tissue necrosis.
E. Use in pregnancy. FDAcategory C (indeterminate). This does not preclude its acute,short-term use for a seriously symptomatic patient (see Table III–1).
Drug Lab Interactions ::
Drug or laboratory interactions.
No known drug interactions, but the intravenous preparation should not be mixed with other drugs.
Transientfalse-positive methemoglobin levels of about 15% are produced bydosages of 2 mg/kg of methylene blue. It may also alter pulse oximeterreadings.
Drug Dose Management ::
Dosage and method of administration (adults and children)
A. Methemoglobinemia
1. Administer 1–2 mg/kg (0.1–0.2 mL/kg of 1% solution) IV slowly over 5 minutes. May be repeated in 30–60 minutes.
2. Simultaneous administration of dextrose may be warranted to provide adequate NAD and NADPH co-factors.
3. If no response after two doses, do not repeat dosing; consider G6PD deficiency or methemoglobin reductase deficiency.
4. Patientswith continued production of methemoglobin from a long-acting oxidantstress (eg, dapsone) may require repeated dosing every 6–8 hours for2–3 days.
5. Flush IV line with 15–30 mL of normal saline to reduce incidence of local pain.
B. Ifosfamide encephalopathy
1. Prophylaxis: Administer 50 mg PO or IV (slowly over 5 minutes) every 6 to 8 hours while receiving ifosfamide.
2. Treatment: Administer 50 mg IV (slowly over 5 minutes) every 4–6 hours until symptoms resolve.
Drug Chemical Formulations ::
Formulations
A. Parenteral. Methylene blue injection 1% (10 mg/mL).
The suggested minimum stocking level to treat a 70-kg adult for the first 24 hours is five ampules (10 mg/mL, 10 mL each).
