Leucovorin is a form of folic acid (a type of vitamin B). Folic acid helps your body produce and maintain new cells, and also helps prevent changes in DNA that may lead to cancer. A lack of folic acid in the body can cause anemia, a decrease in red blood cells that carry oxygen through your blood to your tissues and organs.

Leucovorin is used to treat anemia (low red blood cells) caused by a lack of natural folic acid in the body.

Leucovorin is also used to prevent serious side effects caused by large doses or accidental overdose of medications that can reduce the effects of folic acid in the body. This includes methotrexate, pyrimethamine, and others.

Leucovorin is sometimes used in a chemotherapy combination to lengthen survival time in people with advanced colorectal cancer. Leucovorin does not treat the cancer itself.

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

You should not be treated with leucovorin if you have pernicious anemia or other types of anemia caused by a lack of vitamin B12.

Leucovorin is injected into a muscle, or into a vein through an IV. A healthcare provider will give you this injection.

When treating an accidental overdose, leucovorin should be started as soon as possible for the best effect.

Leucovorin is usually given every 6 hours when used to treat accidental overdose or to prevent side effects from high-dose methotrexate or similar medicines.

When used in chemotherapy, leucovorin is usually given for 5 days in a row, every 4 to 5 weeks.

Follow your doctor's dosing instructions very carefully.

You will need frequent medical tests to help your doctor determine how long to treat you with leucovorin.

Leucovorin is usually given with other medications to help your kidneys remove methotrexate from your body if needed. You may also be treated with IV fluids to keep you from getting dehydrated.

You should not be treated with leucovorin if you have pernicious anemia or other types of anemia caused by a lack of vitamin B12.

If possible before you receive leucovorin, tell your doctor if you have:

• liver disease;

• kidney disease; or

• if you are dehydrated.

Also tell your doctor about all other medications you currently use. There are many other drugs that can interact with methotrexate and slow down your body's ability to process and eliminate the drug. This can affect how quickly methotrexate is able to leave your body, even with the help of leucovorin.

It is not known whether leucovorin will harm an unborn baby. Tell your doctor if you are pregnant.

It is not known whether leucovorin passes into breast milk or if it could harm a nursing baby. Tell your doctor if you are breast-feeding a baby.

In an emergency situation it may not be possible to tell your caregivers if you are pregnant or breast-feeding. Make sure any doctor caring for your pregnancy or your baby knows you have received this medicine.

Call your doctor for instructions if you miss an appointment for your leucovorin injection.

Since leucovorin is given by a healthcare professional in a medical setting, an overdose is unlikely to occur.

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

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

When used alone, leucovorin may cause few if any side effects. Some side effects can occur when leucovorin is used with fluorouracil.

Tell your caregivers or call your doctor right away if you have:

• nausea, vomiting, diarrhea;

• sores or redness in your mouth, pain when eating or swallowing;

• a seizure; or

• a light-headed feeling, like you might pass out.

Your cancer treatments may be delayed or permanently discontinued if you have certain side effects.

Serious side effects may be more likely in older adults and those who are overweight, malnourished, or debilitated.

Common side effects in people treated with leucovorin and fluorouracil may include:

• diarrhea; or

• mouth sores.

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.

Tell your doctor about all your current medicines and any you start or stop using, especially:

• fluorouracil;

• sulfamethoxazole and trimethoprim (such as Bactrim, Septra, SMZ-TMP or SMX-TMP); or

• seizure medicine--phenobarbital, phenytoin, primidone.

This list is not complete. Other drugs may interact with leucovorin, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide.