Methotrexate is classed as an antineoplastic, or cancer fighting; an antimetabolite; and an immunosuppressant. Methotrexate is primarily used to treat cancer. Unlabeled uses are psoriatic arthritis and systemic lupus erythematosus. Methotrexate interferes with cell division, affecting both malignant and healthy cells. Its greatest effect is on rapidly dividing cells such as cells of the bone marrow, skin and gastrointestinal tract. Because of this action, methotrexate increases patient risk for developing adverse effects across multiple body systems.
Toxicity
Methotrexate is metabolized in the liver and excreted in the urine. Patients with impaired kidney and liver functions are at great risk for toxicity because these conditions slow down clearance of the drug. Billie Ann Wilson, Ph.D., Margaret Shannon, Ph.D., and Kelly Shields, Pharm.D., authors of "Pearson Nurse's Drug Guide 2010," report that methotrexate is readily absorbed in the skin, kidneys, liver, spleen and gallbladder. Because of this characteristic, methotrexate causes skin, liver and gastrointestinal toxicity. The National Institutes of Health report that severe and fatal skin reactions occurred within days of methotrexate administration.
Patients need to be observed for ulcerative stomatitis, which is inflammation of the oral mucosa with ulcer formation accompanied by redness and swelling of the tongue and gums, which are early symptoms of toxicity. Alcohol use is not recommended and simultaneous nonsteroidal anti-inflammatories use should be avoided because of the increased risk of toxicity. Patients obtain regular lab work to monitor liver enzymes to screen for toxicity.
Bone Marrow Suppression
Methotrexate causes bone marrow suppression with potential for the development of severe and life-threatening blood disorders, such as aplastic anemia. Anemia is an insufficient number of circulating red blood cells. Aplastic anemia is essentially a loss of red blood cell production. Early symptoms are fatigue, pallor, rapid heart rate and shortness of breath.
Opportunistic Infection
Methotrexate affects white blood cell production, causing low numbers of infection-fighting leukocytes and clot-forming platelets. People taking methotrexate are at risk for opportunistic infections and bleeding. Opportunistic infections are uncommon severe infections that occur when a person is immunocompromised. Pneumocystis carinii pneumonia is one such infection that is often fatal. An early symptom to look for and that warrants medical evaluation is dry cough.
Tumor Lysis Syndrome
Tumor lysis syndrome occurs after large numbers of cells are destroyed during cancer therapy. When cells are destroyed they release waste products and create toxins in the body called endotoxins. Tumor lysis syndrome causes high levels of potassium, uremic acid and phosphate and low levels of calcium in the body. Symptoms are heart arrhythmias, seizures and sudden death. Blood electrolyte levels are checked frequently to monitor for this complication.
References
- National Institutes of Health: Methotrexate
- "Pearson Nurse's Drug Guide 2010"; B.A. Wilson, T.M. Shannon and K.M. Shields; 2010
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