Methemoglobin is a form of hemoglobin (HEEM o glo bin). Hemoglobin is a substance in blood that carries oxygen and distributes it to your tissues and organs. However, methemoglobin is not a type of hemoglobin that is useful in carrying oxygen.

Methemoglobin normally exists in small amounts in the blood. However, when methemoglobin levels increase, the blood is less efficient in circulating oxygen. The resulting lack of oxygen throughout the body can cause symptoms such as pale or blue-colored skin.

Methemoglobinemia is a condition in which methemoglobin is present in high levels in the blood. Methemoglobinemia can occur when a person is exposed to certain drugs or chemicals such as nitrites.

Methylene blue injection is used to treat methemoglobinemia. methylene blue works by converting methemoglobin to a more efficient type of hemoglobin to better carry oxygen throughout the body.

Methylene blue may also be used for purposes not listed in this medication guide.

You should not be treated with methylene blue if you have glucose-6-phosphate dehydrogenase (G6PD) deficiency.

Many drugs can interact with methylene blue. Tell your doctor about all your current medicines and any you recently stopped using, especially an antidepressant.

Methylene blue is injected into a vein through an IV. A healthcare provider will give you this injection. The IV infusion can take up to 30 minutes to complete.

Your breathing, blood pressure, oxygen levels, kidney function, and other vital signs will be watched closely while you are receiving methylene blue. Your blood will also need to be tested to help your doctor determine that the medicine is working.

You may only need to receive one dose of methylene blue. If you do need a second dose, it can be given 1 hour after your first dose.

Methylene blue will most likely cause your urine or stools to appear blue or green in color. This is a normal side effect of the medication and will not cause any harm. However, this effect may cause unusual results with certain urine tests.

You should not be treated with methylene blue if you are allergic to it, or if you have:

• a genetic enzyme deficiency called glucose-6-phosphate dehydrogenase (G6PD) deficiency.

Many drugs can interact with methylene blue. Tell your doctor about all your current medicines and any you recently stopped using, especially:

• alfentanil, fentanyl;

• buspirone;

• digoxin, digitalis;

• dihydroergotamine, ergotamine;

• phenytoin;

• pimozide;

• quinidine;

• warfarin (Coumadin, Jantoven);

• an MAO inhibitor--isocarboxazid, linezolid, phenelzine, rasagiline, selegiline, tranylcypromine, and others;

• an "SSRI" antidepressant--citalopram, escitalopram, fluoxetine, paroxetine, sertraline, Prozac, Paxil, Zoloft, and others;

• an "SNRI" antidepressant--desvenlafaxine, duloxetine, levomilnacipran, milnacipran, venlafaxine, Effexor, Cymbalta, Pristiq, and others;

• other antidepressants--bupropion, clomipramine, mirtazapine; or

• medicine to prevent organ transplant rejection--cyclosporine, sirolimus, tacrolimus.

To make sure methylene blue is safe for you, tell your doctor if you have:

• liver disease; or

• kidney disease.

Using methylene blue during pregnancy could harm the unborn baby. Tell your doctor if you are pregnant.

Do not breast-feed within 8 days after you received methylene blue. If you use a breast pump during this time, throw out any milk you collect. Do not feed it to your baby.

Because you will receive methylene blue in a clinical setting, you are not likely to miss a dose.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Overdose symptoms may include vomiting, stomach pain, chest pain or tightness, wheezing, trouble breathing, feeling like you might pass out, fast heart rate, anxiety, confusion, tremor, dilated pupils, blue-colored skin or lips, numbness, or tingling.

methylene blue may cause blurred vision and may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be alert and able to see clearly.

For at least 24 hours after treatment with methylene blue, avoid exposure to sunlight or tanning beds. This medicine can make you sunburn more easily. Wear protective clothing and use sunscreen (SPF 30 or higher) when you are outdoors.

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Tell your caregivers right away if you have:

• confusion or weakness;

• pale or yellowed skin;

• dark colored urine;

• fever; or

• high levels of serotonin in the body--agitation, hallucinations, fever, fast heart rate, overactive reflexes, nausea, vomiting, diarrhea, loss of coordination, fainting.

Common side effects of methylene blue may include:

• pain in your arms or legs;

• blue or green urine;

• altered sense of taste;

• headache, dizziness;

• sweating, skin discoloration;

• nausea; or

• feeling hot.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Many drugs can interact with methylene blue, and some drugs should not be used together. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide. Tell your doctor about all medicines you use, and those you have recently used before your treatment with methylene blue.