Tetramethylthionine Chloride Trihydrate
Methemoglobinemia – Diagnostic Aid
Action And Clinical Pharmacology: Methylene Blue activates a normally dormant reductase enzyme system which reduces the methylene blue to leucomethylene blue, which in turn is able to reduce methemoglobin to hemoglobin. Methylene Blue is absorbed from the gastrointestinal tract. It is believed to be reduced in the tissues to the leuco form which is slowly excreted, mainly in the urine together with some unchanged drug. Methylene Blue imparts a blue color to urine and faeces. In large doses Methylene Blue can produce methemoglobinemia.
Indications And Clinical Uses: Used in the treatment of methemoglobinemia. Also used as a bacteriological stain, as a dye in diagnostic procedures such as fistula detection, and for the delineation of certain body tissues during surgery.
Contra-Indications: In patients with severe renal impairment or a known hypersensitivity to the drug.
Precautions: Methemoglobin concentration should be closely monitored during treatment as Methylene Blue can produce methemoglobinemia in large doses.
Methylene Blue should be used with caution in the treatment of toxic methemoglobinemia; high doses can cause hemolytic anemias and patients with glucose-6-phosphate dehydrogenase (G6PD) deficiencies are particularly susceptible.
A rapid disappearance of cyanosis in response to Methylene Blue would be expected within one hour but might not occur if the patient has erythrocyte G6PD or NADPH-diaphorase deficiency or if methemoglobinemia is due to the ingestion of compounds such as aniline or dapsone. A second dose has been recommended if cyanosis does not disappear within 1 hour of Methylene Blue administration but results of a study in animals and of a patient with aniline poisoning indicated that an increased dosage of Methylene Blue might be of no additional benefit and could be potentially dangerous in that it could enhance Heinz body formation.
Methylene Blue should not be injected s.c. as it may cause necrotic abscesses. It should not be given by intrathecal injection as neural damage has occurred. Methylene Blue should be used with caution in patients with glucose-6-phosphate dehydrogenase deficiency.
Pregnancy and Lactation: Although intra-amniotic injection of Methylene Blue has been used to diagnose premature rupture of fetal membranes or to identify separate amniotic sacs in twin pregnancies, there have been several reports of hemolytic anemia (Heinz-body anemia) and hyperbilirubinemia in neonates exposed to Methylene Blue in the amniotic cavity. In most cases, exchange transfusions and/or phototherapy are required to control the jaundice.
Adverse Reactions: After i.v. administration Methylene Blue may cause nausea, vomiting, abdominal and chest pain, headache, dizziness, mental confusion, profuse sweating, and hypertension; with very high doses methemoglobinemia and hemolysis may occur.
Dosage: For the treatment of drug-induced methemoglobinemia as in nitrite poisoning, Methylene Blue is administered i.v. as a 1% solution in doses of 1 to 2 mg/kg body weight injected over a period of several minutes. A repeat dose may be given after 1 hour if required.
Availability And Storage: Each mL of sterile solution contains: tetramethylthionine chloride trihydrate 10 mg in water for injection. Nonmedicinal ingredients: sodium hydroxide and hydrochloric acid to adjust pH. Ampuls of 1 and 5 mL, boxes of 10. Store at room temperature (15 to 30°C).
METHYLENE BLUE Bioniche Tetramethylthionine Chloride Trihydrate Methemoglobinemia – Diagnostic Aid