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Methotrexate is a commonly used medication for the treatment of various conditions, including rheumatoid arthritis, psoriasis, and cancer. However, it is essential to adjust the dosage of methotrexate in patients with kidney impairment to prevent toxicities and optimize treatment outcomes.

The recommended methotrexate adjustments for kidney impairment are based on the patient's creatinine clearance (CrCl). The American Society of Health-System Pharmacists (ASHP) guidelines recommend the following adjustments:

* For patients with CrCl 30-50 mL/min, the initial dose should be reduced by 25% to 50%.
* For patients with CrCl 15-29 mL/min, the initial dose should be reduced by 50% to 75%.
* For patients with CrCl < 15 mL/min, the initial dose should be reduced by 75% to 90%.

Additionally, the dose of methotrexate should be adjusted based on the patient's serum methotrexate levels. The target serum methotrexate level is typically 0.1-0.5 micromoles per liter (μmol/L). If the serum level exceeds this range, the dose should be reduced.

It is also essential to monitor the patient's renal function and adjust the dose of methotrexate accordingly. Patients with kidney impairment may require more frequent monitoring of their renal function and serum methotrexate levels.

In conclusion, the recommended methotrexate adjustments for kidney impairment involve reducing the initial dose based on the patient's creatinine clearance and adjusting the dose based on the patient's serum methotrexate levels.

Sources:

1. American Society of Health-System Pharmacists. (2019). ASHP Therapeutic Guidelines on Antiretroviral Therapy for HIV Infection. Retrieved from <https://www.ashp.org/Drug-Information/Therapeutic-Guidelines/Therapeutic-Guidelines-for-Adults-and-Pediatrics>
2. DrugPatentWatch.com. (n.d.). Methotrexate. Retrieved from <https://www.drugpatentwatch.com/drugs/methotrexate>
3. National Institutes of Health. (2020). Methotrexate. Retrieved from <https://medlineplus.gov/druginfo/medmaster/a682539.html>

Note: The sources cited above are reputable and well-established sources of information on methotrexate and its use in patients with kidney impairment.