Methotrexate is a medication used to treat cancer, autoimmune diseases, and other conditions. The appropriate dosage for elderly patients using methotrexate depends on various factors, including the patient's age, weight, overall health, and the condition being treated.

According to Drug Patent Watch [1], methotrexate is available in various forms, including tablets, injections, and oral solutions. The dosage of methotrexate should be individualized based on the patient's age, weight, and condition being treated. The drug should be used with caution in elderly patients due to age-related changes in liver and kidney function.

According to UpToDate [2], methotrexate can be toxic at high doses, and the risk of toxicity increases in elderly patients. To minimize the risk of toxicity, the dosage of methotrexate should be adjusted based on the patient's age, weight, and kidney function. In elderly patients, the dosage should be reduced and monitored carefully to avoid toxicity.

A study published in the Journal of Geriatric Oncology [3] examined the use of methotrexate in elderly patients with cancer. The study found that methotrexate was effective in treating cancer in elderly patients, but the dosage needed to be adjusted based on the patient's age, weight, and overall health. The study also found that careful monitoring of kidney function was necessary to avoid toxicity.

In conclusion, the appropriate dosage of methotrexate for elderly patients depends on various factors, including the patient's age, weight, and condition being treated. The dosage should be individualized and adjusted carefully to avoid toxicity. Close monitoring of kidney function is also necessary to ensure the safe use of methotrexate in elderly patients.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/METHOTREXATE
[2] https://www.uptodate.com/contents/therapeutic-use-and-toxicity-of-high-dose-methotrexate
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5153332/