In the U.S.—

Other commonly used names are aniline violet; methylthionine chloride; tetramethylthionine chloride.

• Antimethemoglobinemic
• Diagnostic aid, tissue dye

Methylene ( METH-i-leen) blue is used to treat a condition called methemoglobinemia. This condition occurs when the blood cannot deliver oxygen where it is needed in the body. Methylene blue is also used as a dye to stain certain parts of the body before or during surgery.

Oral
• Tablets (U.S.)

Parenteral
• Injection (U.S. and Canada)

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For methylene blue, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to methylene blue. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Studies on effects in pregnancy have not been done in either humans or animals.

Breast-feeding—It is not known whether methylene blue passes into breast milk. Although most medicines pass into breast milk in small amounts, many of them may be used safely while breast-feeding. Mothers who are taking this medicine and who wish to breast-feed should discuss this with their doctor.

Children—Babies are especially sensitive to the effects of methylene blue. This may increase the chance of side effects during treatment.

Older adults—Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults. Although there is no specific information comparing the use of methylene blue in the elderly with use in other age groups, this medicine is not expected to cause different side effects or problems in older people than it does in younger adults.

Other medicines—Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. Tell your health care professional if you are taking any other prescription or nonprescription (over-the-counter [OTC]) medicine.

• Glucose-6-phosphate dehydrogenase (G6PD) deficiency—Methylene blue may cause anemia or make methemoglobinemia worse

• Kidney disease—In patients with kidney disease methylene blue may accumulate in the body; smaller doses of this medicine may be needed

• Methemoglobinemia to treat cyanide toxicity—Methylene blue may make cyanide toxicity worse by increasing the amount of cyanide in the blood

For patients taking the tablet form of this medicine:

• Take tablets after meals with a full glass (8 ounces) of water.

Take this medicine only as directed. Do not take more of it and do not take it more often than recommended on the label unless directed by your doctor. To do so may increase the chance of side effects.

Dosing—

The dose of methylene blue will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of methylene blue. If your dose is different, do not change it unless your doctor tells you to do so.

• For oral dosage form (tablets):
  • For methemoglobinemia:
    • Adults and children—100 to 300 milligrams (mg) a day.
• For injection dosage form:
  • For methemoglobinemia:
    • Adults and children—Dose is based on body weight or size and must be determined by your doctor. The dose is usually 1 to 2 mg per kilogram (kg) (0.45 to 0.9 mg per pound) of body weight, or 25 to 50 mg per square meter of body surface area, injected into a vein over a period of five minutes. A second dose may be given after one hour, if needed.

Missed dose—

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage—

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Keep the medicine from freezing. Do not refrigerate.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

Before you have any medical tests, tell the doctor in charge that you are taking this medicine. The results of some tests may be affected by this medicine.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

• Symptoms of overdose
  • Anxiety;  back pain;  bluish fingernails, lips, or skin;  chest pain;  chills;  confusion;  difficulty in breathing;  dizziness;  headache;  leg pain;  nausea and vomiting;  severe sweating;  stomach pain;  trembling;  unusual tiredness or weakness 
  
  

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

• More common
  • Greenish blue to blue discoloration of urine and stools 
  
  

• Less common
  • Diarrhea;  nausea and vomiting;  painful urination or increased need to urinate (with tablet form)  
  
  

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.