High-dose methotrexate therapy is monitored at regular intervals following a methotrexate dose. Testing detects toxic concentrations of methotrexate at these time points. A drug called leucovorin (folinic acid) can be given as a "rescue" treatment to protect a person from the toxic effects of methotrexate. The methotrexate test series identifies the need for leucovorin and guides the timing and amount of its administration.
Low-dose methotrexate therapy is rarely monitored by a methotrexate test. It is usually monitored by assessing the function of the kidney, the liver, and bone marrow cell production. Testing may include a complete blood count (CBC) to measure red blood cell counts, white blood cell counts, and platelets; a blood urea nitrogen (BUN) and creatinine to evaluate kidney function; and a liver panel (or one or more of its component tests) to evaluate liver function.
A methotrexate test is typically ordered at regular intervals (e.g., at 24 hours, 48 hours, and at 72 hours as needed) after administration of high-dose methotrexate. Tests to monitor blood cell counts and kidney and liver function are also ordered at regular intervals during methotrexate therapy.
A methotrexate test may also be ordered whenever a person has symptoms or signs that suggest methotrexate toxicity. It is rarely ordered in conjunction with low-dose methotrexate therapy.
Common side effects associated with methotrexate use (that may be seen without toxic concentrations of methotrexate) include:
Sensitivity to sunlight
Low blood counts
More serious signs and symptoms seen with methotrexate toxicity include:
With therapeutic drug monitoring, there is typically a "therapeutic range," with a lower limit that is associated with effectiveness and an upper limit associated with unacceptable side effects and toxicity. With high-dose methotrexate, the primary focus is on an upper limit – toxicity, the drug's effect on the kidney, liver, and blood cell counts, and on unacceptable side effects.
Test results are used to guide the amount and timing of leucovorin (folinic acid) given as a "rescue" treatment.
Low-dose methotrexate is rarely monitored with a methotrexate test. The therapeutic concentration of the drug depends upon the condition and the timing of the blood collection.
Although the risks of side effects and organ damage increase with increasing levels of methotrexate, a person may experience side effects from methotrexate use without having high blood levels of the drug.
A variety of prescription and over-the-counter medications and supplements can interfere or interact with methotrexate, including aspirin, ibuprofen, and other nonsteroidal anti-inflammatory drugs (NSAIDs), phenytoin, retinol, theophylline, digoxin, sulfadiazine, warfarin, certain antibiotics, and vitamin E. These substances may need to be avoided, or the dosages of methotrexate and other medications may need to be adjusted.
Excessive alcohol use can increase the risk of methotrexate-associated liver damage.
Methotrexate may cause sterility.
Methotrexate must not be taken while a woman is pregnant or breast-feeding.
Tell your health practitioner if you have or have had any of these conditions, which may preclude use of the drug or warrant caution:
Sensitivity to methotrexate and associated side effects increase with age, while individuals' response to methotrexate therapy varies. Some of the variation in effectiveness and toxicity is thought to be due to genetic variations. Researchers are examining this idea and it may eventually lead to the clinical use of one or more genetic tests to help predict a person's response to methotrexate.
This article was last reviewed on January 14, 2014. | This article was last modified on January 14, 2014.
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