Methylene blue is commonly used in diagnostic procedures and is also used to treat a number of medical conditions (see Facts about methylene blue box). 

Uses

As a medication, it is mainly used to treat methemoglobinemia by converting the ferric iron in hemoglobin to ferrous iron.Specifically, it is used to treat methemoglobin levels that are greater than 30% or in which there are symptoms despite oxygen therapy.It has previously been used for cyanide poisoning and urinary tract infections, but this use is no longer recommended.

Precautions

Your doctor will check your progress closely while you are receiving this medicine. This will allow your doctor to see if the medicine is working properly. Blood tests may be needed to check for unwanted effects.

Using this medicine while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using this medicine, tell your doctor right away.

This medicine may cause serious allergic reactions, including anaphylaxis. Anaphylaxis requires immediate medical attention. The most serious signs of this reaction are very fast or irregular breathing, gasping for breath, or fainting. Other signs may include changes in color of the skin of the face, very fast but irregular heartbeat or pulse, hive-like swellings on the skin, and puffiness or swellings of the eyelids or around the eyes. If these side effects occur, get emergency help at once.

Make sure your doctor knows about all the other medicines you are using. This medicine may cause a serious condition called serotonin syndrome when taken with other medicines to treat depression (eg, amitriptyline, bupropion, citalopram, desipramine, duloxetine, escitalopram, fluoxetine, fluvoxamine, imipramine, nortriptyline, paroxetine, sertraline, venlafaxine, Aventyl?, Celexa?, Cymbalta?, Effexor?, Elavil?, Lexapro?, Luvox?, Norpramin?, Pamelor?, Paxil?, Prozac?, Tofranil?, Wellbutrin?, or Zoloft?), medicine to treat migraine headaches (eg, eletriptan, sumatriptan, zolmitriptan, Imitrex?, Relpax?, or Zomig?), ergot medicine (eg, ergotamine, Cafergot?, Ergomar?, or Wigraine?), or certain antibiotics (eg, linezolid, Zyvox?). Check with your doctor first before taking any other medicines. The symptoms of serotonin syndrome include mental changes (confusion, hyperactivity, memory problems), muscle twitching, excessive sweating, shivering or shaking, diarrhea, trouble with coordination, or fever.

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

This medicine may cause dizziness, confusion, or trouble in seeing clearly. Make sure you know how you react to this medicine before you drive, use machines, or do other jobs that require you to be alert or able to see well.

This medicine may make your skin more sensitive to sunlight. Use a sunscreen when you are outdoors. Avoid sunlamps and tanning beds.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

Side effects

Methylene blue is a monoamine oxidase inhibitor (MAOI),and if infused intravenously at doses exceeding 5 mg/kg, may precipitate serious serotonin toxicity, serotonin syndrome, if combined with any selective serotonin reuptake inhibitors (SSRIs) or other serotonin reuptake inhibitor (e.g., duloxetine, sibutramine, venlafaxine, clomipramine, imipramine).

Methylene blue is typically given by injection into a vein. Common side effects include headache, vomiting, confusion, shortness of breath, and high blood pressure.Other side effects include serotonin syndrome, red blood cell breakdown, and allergic reactions.Use often turns the urine, sweat, and stool blue to green in color.While use during pregnancy may harm the baby, not using it in methemoglobinemia is likely more dangerous.