What Factors Affect a Sufficient Methotrexate Dose?

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  • Written By: Lee Johnson
  • Edited By: John Allen
  • Last Modified Date: 10 November 2019
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A sufficient methotrexate dose is affected by many factors, such as the specific condition the drug is being used to treat, the age of the patient, and the size of the patient. For example, an adult taking the drug to treat rheumatoid arthritis requires a 7.5 milligram (mg) dosage of the drug per week. A child taking the drug for the same condition should be given between 5 and 15 mg of the treatment per meter squared (m2) in body size. A sufficient methotrexate dose for an adult taking the drug for lymphoma, specifically a Burkitt’s tumor in stages one or two, is 10 to 25 mg per day for four to eight days.

The most obvious factor which affects a sufficient methotrexate dose is the condition that the drug is treating. For example, if an adult patient is taking the drug for psoriasis, he or she should be given between a 10 and 25 mg dose per week until he or she responds to the treatment. An adult patient taking the treatment for rheumatoid arthritis only requires 7.5 mg per week. The maximum dosage that can be taken in a week is also determined by the condition. For example, patients suffering from psoriasis can take up to 30 mg per week, and patients suffering from rheumatoid arthritis can take up to 20mg per week.


Older patients can generally handle a larger methotrexate dose than younger patients, so age is an important factor in determining a sufficient dose. An adult taking the drug for neoplastic diseases can be prescribed anything from 30 mg per m2 in body size to 40 mg per m2 weekly. This can increase dramatically, up to 12,000 mg per m2 if the drug is taken with leucovorin. Children can only be prescribed between 7.5 and 30 mg per m2, and the treatment can only be administered once every two weeks.

Methotrexate is a drug which can have numerous side effects, and some of these are possibly fatal. The drug can, for example, cause death or defects in unborn babies, so it should never be taken by pregnant women. Other possibly fatal side effects include bone marrow suppression and lung infections. As a result of these serious possible reactions, the methotrexate dose should only be increased by a medical professional, according to the patient’s response to the treatment.

These potential dangers associated with the treatment mean that the methotrexate dose may need to be altered depending upon the patient’s body size. This is indicated by dosages with a “per m2” indication on them. The simple reason for this is that larger patients can handle larger doses of the treatment, and dosages that are too large could have negative effects on smaller patients.


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