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MISSION PHARM.
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00076011101

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Uses

Methemoglobinemia

Methylene blue is used for the treatment of drug-induced methemoglobinemia. Methylene blue has been used for methemoglobinemia associated with certain drugs (e.g., dapsone, benzocaine, lidocaine), occupational or other exposures to toxic chemicals (e.g., hydrazine, aniline and other amine-substituted benzenes, chloronitrobenzene and other nitro-substituted benzenes, nitrates, nitrites), or substance abuse (e.g., inhalation or ingestion of volatile nitrites).

Methylene blue will not reverse methemoglobinemia in patients with glucose-6-phosphate dehydrogenase (G-6-PD) deficiency, and may induce or exacerbate hemolysis in these patients.(See Cautions: Adverse Effects.)

Methylene blue has been used for the treatment of cyanosis in patients with congenital methemoglobinemia related to cytochrome b5 reductase deficiency, but is ineffective in patients with hemoglobin M (abnormal hemoglobin molecules).

Methylene blue is not effective for the treatment of sulfhemoglobinemia.

Ifosfamide-induced Encephalopathy

Methylene blue has been used in the management of ifosfamide-induced encephalopathy. Although methylene blue has resulted in rapid improvement in CNS function in some patients, beneficial effects have not been consistently reported and further clinical studies are needed to establish the role of the drug in the management of ifosfamide-induced encephalopathy. Methylene blue does not appear to be effective when used prophylactically in an attempt to prevent ifosfamide-associated encephalopathy.

Use as a Dye

Methylene blue is used as a bacteriologic stain, as an indicator dye, and for surgical and medical marking.

Methylene blue has been administered by local injection or instillation as a diagnostic (visualizing) dye in a variety of procedures, including sentinel lymph node biopsy in cancer patients (e.g., breast cancer patients), endoscopic evaluation of lesions in patients with gastroesophageal reflux disease (GERD) or Barrett's esophagus, urologic evaluation in patients with ureteral or renal pelvis injury, and thoroscopic procedures in patients with pulmonary nodules.

Photodynamic Therapy

Although further study is needed to evaluate safety and efficacy, methylene blue has been used topically as a photosensitizer for photodynamic therapy (PDT) in the topical treatment of dermatologic or mucocutaneous infections (e.g., herpes labialis, eczema herpeticum, oral candidiasis, cutaneous leishmaniasis, chromoblastomycosis) or chronic dermatologic or mucocutaneous conditions (e.g., plaque psoriasis, oral lichen planus).

Cyanide and Carbon Monoxide Poisoning

Although methylene blue was used in the past as an antidote for cyanide poisoning, it is no longer recommended for this use. Cyanide poisoning usually is treated with an antidote regimen consisting of amyl nitrite, sodium nitrite, and sodium thiosulfate or with hydroxocobalamin. When sodium nitrite is used for cyanide poisoning, methylene blue should not be used in an attempt to treat excessive methemoglobinemia induced by the antidote because reduced cyanide binding and increased toxicity occurs.

Methylene blue is of no value in the treatment of carbon monoxide poisoning.

Cystitis and Urethritis

Methylene blue was used in the past as a mild urinary antiseptic and stimulant to mucous surfaces in the treatment of cystitis and urethritis, but is no longer recommended for this use.

Urolithiasis

Methylene blue has been used alone and in combination with ascorbic acid for the management of chronic urolithiasis. Although methylene blue appears to have some inhibitory effect on the formation of calcium oxalate and calcium phosphate crystals in some patients, the drug is not currently recommended for this use and is ineffective in dissolving previously formed stones.

Dosage and Administration

Administration

Methylene blue is administered by slow IV injection over a period of several minutes. The drug has been given by IV infusion. Extravasation and high local concentrations of methylene blue should be avoided.(See Cautions: Adverse Effects.)

Methylene blue has been administered orally, but oral preparations are no longer commercially available in the US. It has been suggested that an oral solution can be prepared extemporaneously by diluting 5-10 mL of the commercially available 10-mg/mL solution for IV use in 100-200 mL of water.

When used as a diagnostic (visualizing) dye, methylene blue has been administered by local instillation or injection. In addition, methylene blue has been administered topically for photodynamic therapy (PDT).(See Cautions: Adverse Effects.)

Methylene blue should not be administered by subcutaneous, intrathecal, or intraspinal injection.(See Cautions: Precautions and Contraindications.)

Dosage

Drug-Induced Methemoglobinemia

For the treatment of methemoglobinemia in adults or children, the usual dosage of methylene blue is 1-2 mg/kg given by slow IV injection over a few minutes (usually 3-10 minutes). Symptomatic improvement usually occurs within 30 minutes. The IV dose may be repeated after 30-60 minutes, if required.

The manufacturer recommends a maximum IV dosage of 2 mg/kg of methylene blue. Some experts recommend a maximum total dose of 5-7 mg/kg during the first few hours of treatment.

Ifosfamide-induced Encephalopathy

For the management of ifosfamide-induced encephalopathy, 50 mg of methylene blue has been given by slow IV injection over at least 5 minutes; 1-6 doses have been given daily until symptoms resolved.

Cautions

Adverse Effects

Large IV doses of methylene blue may produce nausea, vomiting, abdominal pain, precordial pain, dizziness, headache, profuse sweating, dyspnea, hypertension, and mental confusion. Urinary tract irritation may occur.

High IV dosage or high local concentrations of methylene blue may cause formation of methemoglobin and cyanosis.

Hemolysis and hemolytic anemia may occur, especially in young infants and patients with glucose-6-phosphate dehydrogenase (G-6-PD) deficiency.

Hypersensitivity, manifested as wheal and flare reactions at the injection site, has been reported. Severe hypersensitivity reactions, including anaphylaxis, generalized urticaria, and hypotension, tachycardia, and bronchospasm, have been reported following local instillation or injection of methylene blue.

Methylene blue imparts a blue-green color to saliva, urine, feces, and skin. Bluish skin discoloration from excessive methylene blue dosage can be mistaken for methemoglobinemia.

Methylene blue is a potent inhibitor of monoamine oxidase (MAO), and may cause potentially fatal serotonin toxicity (serotonin syndrome) if used concomitantly with serotonergic drugs. Signs and symptoms of serotonin syndrome include mental changes (confusion, hyperactivity, memory problems), muscle twitching, excessive sweating, shivering, shaking, diarrhea, loss of coordination, and/or fever.(See Drug Interactions: Serotonergic Drugs.)

IV administration of methylene blue has caused adverse local effects, including pain, burning sensation, rash, necrosis, abscess, ulceration, and thrombophlebitis; extravasation has caused tissue necrosis.

Oral administration of methylene blue has caused adverse GI effects and dysuria.

Topical application of methylene blue may stain the skin; skin stains may be removed by hypochlorite solution.

Subcutaneous or intradermal injection of methylene blue has caused adverse skin and tissue reactions (e.g., erythematous macular lesions, superficial ulcers, abscess formation, skin and fat necrosis) at the injection site.(See Cautions: Precautions and Contraindications.)

Intrathecal injection of the drug has caused neural damage.(See Cautions: Precautions and Contraindications.)

Precautions and Contraindications

Methylene blue is contraindicated in patients with known hypersensitivity to the drug. Epinephrine and other appropriate agents and equipment should be available for immediate use in case an anaphylactic reaction occurs.

Methylene blue is contraindicated in women who are or may become pregnant.(See Cautions: Pregnancy.)

Subcutaneous, intrathecal, and intraspinal injection of methylene blue are contraindicated.(See Cautions: Adverse Effects.)

To prevent local high concentrations of methylene blue and production of additional methemoglobin, IV injections must be made slowly and recommended dosage should not be exceeded.(See Cautions: Adverse Effects.)

Long-term administration of methylene blue may result in marked anemia due to accelerated destruction of erythrocytes; hemoglobin concentrations should be checked frequently.

Because of the risk of paradoxical methemoglobinemia and hemolysis, methylene blue should be avoided in patients with known or suspected G-6-PD deficiency.

Methylene blue should be used with caution in patients with severe renal impairment. Some clinicians suggest that initial dosage may not need to be reduced when methylene blue is used for the treatment of methemoglobinemia in patients with renal impairment, but creatinine clearance should be considered if the drug is given by continuous IV infusion.

Because of the risk of serotonin syndrome, methylene blue generally should not be used in patients receiving serotonergic drugs.(See Drug Interactions: Serotonergic Drugs.)

Pediatric Precautions

Use of methylene blue in neonates and young infants has caused hemolysis, hemolytic anemia, hyperbilirubinemia, and phototoxicity. Fatalities have been reported.

Pregnancy

Methylene blue is contraindicated in women who are or may become pregnant. There is epidemiologic evidence that methylene blue is a teratogen, and the drug can cause fetal harm if administered during pregnancy. Use of methylene blue in amniocentesis has been associated with atresia of the ileum and jejunum, ileal occlusion, and other adverse effects in neonates.

Use of methylene blue during pregnancy has resulted in hemolytic anemia, hyperbilirubinemia, methemoglobinemia, respiratory distress, skin staining, and phototoxicity in neonates.

If methylene blue is used during pregnancy or if the patient becomes pregnant, the patient should be apprised of potential fetal hazard.

Drug Interactions

Formal drug interactions have not been conducted to date.

Antimalarial Agents

Although the clinical importance is unclear, in vitro studies indicate that the antimalarial effects of methylene blue and artemisinin, artemether, or artesunate are synergistic and the antimalarial effects of methylene blue and mefloquine or quinine are additive against Plasmodium falciparum. Antagonism occurred when methylene blue was used with chloroquine or pyrimethamine in vitro.

Serotonergic Drugs

Concomitant use of methylene blue and serotonergic drugs may result in serotonin syndrome.

There have been case reports of serotonin syndrome in patients who received methylene blue while receiving serotonergic drugs, including selective serotonin-reuptake inhibitors (SSRIs) (e.g., citalopram, escitalopram, fluoxetine, fluvoxamine, paroxetine, sertraline), selective serotonin- and norepinephrine-reuptake inhibitors (SNRIs) (e.g., desvenlafaxine, duloxetine, venlafaxine), and clomipramine. Most of these cases occurred when methylene blue was used as a diagnostic (visualizing) dye (1-8 mg/kg IV) during parathyroid surgery; it is unclear whether there is a risk of serotonin syndrome when methylene blue is administered by other routes or in lower IV doses in patients receiving serotonergic drugs. While the US Food and Drug Administration (FDA) has not received reports of serotonin syndrome with concomitant use of methylene blue and vilazodone, the risk is considered comparable to that with SSRIs. The FDA has not concluded whether concomitant use of methylene blue and other drugs with lesser degrees of serotonergic activity, including tricyclic antidepressants (amitriptyline, desipramine, doxepin, imipramine, nortriptyline, protriptyline, trimipramine), monoamine oxidase (MAO) inhibitors (isocarboxazid, phenelzine, transdermal selegiline, tranylcypromine), amoxapine, bupropion, buspirone, maprotiline, mirtazapine, nefazodone, or trazodone, is associated with a risk of serotonin syndrome comparable to that reported when methylene blue is used concomitantly with SSRIs or SNRIs.

Because of the risk of serotonin syndrome, methylene blue generally should not be used in patients receiving serotonergic drugs. The FDA states that certain emergency situations (e.g., methemoglobinemia, ifosfamide-induced encephalopathy) may necessitate immediate use of methylene blue in a patient receiving a serotonergic drug. In such emergency situations, the availability of alternative interventions should be considered and the benefits of methylene blue should be weighed against the risk of serotonin syndrome. If methylene blue is indicated in such emergency situations, the serotonergic drug must be immediately discontinued and the patient monitored for symptoms of CNS toxicity (e.g., mental changes, muscle twitching, excessive sweating, shivering/shaking, diarrhea, loss of coordination, fever) for 2 weeks (5 weeks if the patient was receiving fluoxetine) or until 24 hours after the last methylene blue dose, whichever come first. Treatment with the serotonergic drug may be resumed 24 hours after the last methylene blue dose.

If nonemergency use of methylene blue is being planned for a patient receiving a serotonergic drug, the serotonergic drug should be withheld for at least 2 weeks (5 weeks if the patient was receiving fluoxetine) prior to initiating methylene blue.

Treatment with serotonergic drugs should not be initiated in a patient receiving methylene blue; when necessary, the serotonergic drug may be started 24 hours after the last methylene blue dose.

Pharmacokinetics

Methylene blue is well absorbed from the GI tract, and peak plasma concentrations occur approximately 1-2 hours after an oral dose. Oral absorption may be too slow and inconsistent for the treatment of severe methemoglobinemia; IV administration is necessary.

Following distribution into tissues, methylene blue is rapidly reduced to leukomethylene blue (leucomethylthioninium chloride). Metabolism to leucomethylene blue may be less efficient in neonates than in older individuals.

Methylene blue is excreted in urine and bile. About 75% of an oral dose of methylene blue is excreted in urine, mostly as stabilized colorless leukomethylene blue. On exposure to air, the urine turns green or blue, due to the presence of the oxidation product methylene azure (methylene blue sulfone). Some unchanged drug is also excreted in urine.

Following IV administration, the estimated half-life of methylene blue is 5-6.5 hours.

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