Carol Eustice is a writer covering arthritis and chronic illness, who herself has been diagnosed with both rheumatoid arthritis and osteoarthritis.
Riteesha G. Reddy, MD, is a board-certified rheumatologist and internist at a private practice in Dallas, Texas.
Methotrexate is a common prescription medication for rheumatoid arthritis, other inflammatory types of arthritis and autoimmune disease, several types of cancer, and more. Methotrexate dosage is different from that of other medications in that you only take it once a week.
That can be confusing, especially if your healthcare provider or pharmacist haven't explained it. It's not uncommon for someone to overdose on methotrexate because they take it every day. Too much methotrexate can cause severe toxic effects, especially liver toxicity. Never take more than is prescribed or change the dosing schedule on your own.
This article goes through the uses of methotrexate and the doses for them, plus the side effects and warnings you need to be aware of with this drug.
Methotrexate is approved by the Food and Drug Administration (FDA) for some types of autoimmune arthritis and other autoimmune diseases. It's used off-label (without FDA approval) for several other diseases in this category.
In autoimmune diseases, your immune system mistakenly attacks healthy cells in your body as if they were a virus or bacterium. Methotrexate calms the immune system and lessens the attack.
Rheumatoid arthritis (RA) involves autoimmune activity against the lining of your joints (the synovium). It commonly strikes the hands, wrists, and knees but can target any joint.
Some people with RA develop systemic disease, meaning the immune system targets organs or systems throughout the body. Common targets are the eyes, heart, and lungs.
The oral (tablet) form of methotrexate is typically prescribed for RA. The injectable form may be used if you have trouble swallowing the pills.
The suggested weekly adult dose of methotrexate for rheumatoid arthritis is:
If the starting dose doesn't give you enough symptom relief, your healthcare provider may gradually increase it, usually to a weekly dosage of 20 mg.
Some studies have suggested that the optimal dosage is between 25 mg and 30 mg, but that increases the risk of bone marrow suppression and other serious side effects.
Psoriatic disease includes plaque psoriasis and psoriatic arthritis. Methotrexate is used for both of these conditions.
Plaque psoriasis, also called just psoriasis, is an autoimmune disease that speeds up the growth of new skin cells. New cells form before the old ones have sloughed off, so they "pile up" on the surface. The result is thick, scaly patches that may itch or be quite painful.
The once-a-week adult methotrexate dosage for psoriasis is:
Psoriasis on darker skin may be a dark brown or violet with gray scales. On light skin, it's usually red with white or silvery scales.
Psoriatic arthritis (PsA) involves both psoriasis and joint pain. Methotrexate is given off-label for PsA.
The weekly adult dose of pill or injectable methotrexate for PsA is:
Polyarticular juvenile idiopathic arthritis (PJIA) is a type of childhood arthritis involving five or more joints. ("Polyarticular" means "many joints.")
Healthcare providers calculate the pediatric methotrexate dosage based on the child's body weight. The formula for the weekly dose (pills or injections) is:
Higher doses haven't been shown to work better, so pediatric doses are usually kept in this range.
In systemic lupus erythematosus (SLE or lupus), the immune system not only attacks various tissues around the body, but the inflammatory response is also out of control. Common targets include:
Methotrexate is prescribed off-label for SLE. The weekly dosage depends on whether it's given as a pill or injection.
For pills, the dosage guidelines say:
For methotrexate injections, it's:
Most people with lupus respond well to injected dosages between 7.5 mg and 20 mg.
For children with lupus, the pill form may be given at weekly dosages of:
Few studies have tested methotrexate for childhood lupus so the maximum safe dosage hasn't been established. In one study, 80% of kids responded to the 5 mg or 10 mg dosage.
Methotrexate pills and injections are used off-label for treating Crohn's disease, which causes inflammation in your digestive tract. It's a condition that typically has flares (times of intense symptoms) and remissions (times of lesser or absent symptoms).
Crohn's disease most often causes pain and other symptoms in the small intestine and first portion of the large intestine. But it can affect any part of the digestive system.
For Crohn's, methotrexate is typically used in addition to other medications. For the pill form, the weekly dosage for Crohn's disease is:
For methotrexate injections, the weekly dosage varies depending on how active the disease is:
Injections are typically preferred for people whose Crohn's disease interferes with absorption in the small intestine.
Methotrexate was a cancer drug before it was approved for rheumatoid arthritis. It's also used to treat ectopic pregnancies. Both these uses stem from methotrexate's ability to stop certain cells from growing.
The dosage used for rheumatoid arthritis and other inflammatory diseases is small compared to that used for cancer and ectopic pregnancy. Pills that you manage at home are less likely for these uses than injections or infusions that are given by medical personnel.
Acute lymphocytic leukemia (ALL) is a blood cancer. It causes rapid overgrowth of immature white blood cells called lymphocytes. After starting in the bone marrow, it quickly invades the bloodstream and possibly other organs and systems.
For ALL, the methotrexate dosage is weight-based. It's part of a chemotherapy regimen involving several drugs. It may be given in intramuscular injections, or, especially for higher doses, intravenously (IV).
The dosage of intramuscular injections is the same for children and adults:
IV methotrexate for ALL is given by a healthcare provider at a medical facility. The schedule and dosage depend on the disease state and many other factors. It may be given more or less frequently than once a week.
IV dosage may range from:
Once cancer is in remission, methotrexate pills, injections, or IV infusions may be used as maintenance therapy to help prevent a recurrence.
The maintenance dosage may be adjusted based on lab test and other factors.
ALL is a type of non-Hodgkin lymphoma. Methotrexate is used to treat many cancers in this group plus some types of head and neck cancer, lung cancer, breast cancer, and bladder cancer. Each cancer type has its own dosage guidelines.
In an ectopic pregnancy, the fetus implants and develops outside of the uterus, usually in a fallopian tube. As the fetus grows, the fallopian tube generally ruptures. This can cause life-threatening internal bleeding and emergency surgery is required.
So far, doctors are unable to re-implant a fetus developing ectopically to a uterus or other location. The pregnancy is always lost.
Some ectopic pregnancies are removed surgically. Others are treated with methotrexate because it stops cells from growing. The body can then absorb the pregnancy over the next several weeks.
Methotrexate injections are used for ectopic pregnancies. Several dosing options are available:
While you're on methotrexate, you'll need to have periodic laboratory tests to monitor:
If your test results worsen, your healthcare provider may switch you to a different drug.
The most common side effects of methotrexate are:
To avoid nausea, you may be advised to divide the dose throughout the day (but all pills are still taken on the same day). Your doctor may also switch you to a subcutaneous (under the skin) injection.
Methotrexate comes with several important warnings. Paying attention to these can help you avoid problems or spot them early.
When you're taking methotrexate, you need to take a few safety precautions:
You need to be especially careful with methotrexate if you have a couple of health conditions.
Methotrexate is dangerous during pregnancy and breastfeeding. It's only used during pregnancy as a cancer treatment, and the risks and benefits must be carefully weighed.
If you're taking this drug, take steps to avoid getting pregnant for at least six months after you stop taking it.
Your healthcare provider should go over these risks with you before prescribing methotrexate. Be sure you also discuss birth control and follow safety measures:
During or after use, methotrexate may cause:
It's unknown whether methotrexate infertility is reversible.
The risk of methotrexate toxicity is higher if it's taken with certain other medications, such as:
These drug interactions can be deadly. Make sure your healthcare provider and pharmacist have a complete list of your medications, both prescription and over-the-counter.
If you have signs of an allergic reaction while taking methotrexate, get emergency medical attention. Signs to watch for include:
Stop taking methotrexate and call your healthcare provider if you develop:
Call your provider right away if you notice any of these symptoms. Don't wait to see if symptoms go away on their own.
Always follow the exact dosing directions for methotrexate and watch for potential problems and side effects. Taken properly, methotrexate can be a safe and effective medication for autoimmune disease, cancer, and ectopic pregnancy.
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