Methotrexate, a medication commonly used to treat conditions such as rheumatoid arthritis, psoriasis, and certain types of cancer, can impact the effectiveness of other medications. This is because methotrexate can interact with other drugs, affecting their absorption, metabolism, and elimination from the body.

One way methotrexate can impact other medications is by displacing them from plasma proteins, which are responsible for transporting drugs throughout the body. When methotrexate binds to these proteins, it can displace other drugs that are also bound to them, increasing the amount of free drug in the bloodstream. This can lead to an increased risk of toxicity and decreased effectiveness of the other medication.

Methotrexate can also affect the metabolism of other drugs by inhibiting certain enzymes. For example, methotrexate is a folic acid antagonist, which means it inhibits the enzyme dihydrofolate reductase. This enzyme is responsible for the metabolism of folic acid, a vitamin that is essential for the synthesis of DNA and RNA. By inhibiting this enzyme, methotrexate can affect the metabolism of other drugs that rely on this pathway for their activation or elimination.

Furthermore, methotrexate can affect the absorption of other medications by altering the pH of the gastrointestinal tract. Methotrexate is acidic and can lower the pH of the stomach, which can affect the absorption of other drugs that are sensitive to pH changes.

It is important to note that the impact of methotrexate on other medications can vary depending on several factors, including the dose and frequency of methotrexate administration, the route of administration, and the individual patient's renal and hepatic function.

In summary, methotrexate can impact the effectiveness of other medications by displacing them from plasma proteins, inhibiting certain enzymes, and altering the pH of the gastrointestinal tract. Healthcare providers should be aware of these potential interactions and monitor patients closely when prescribing methotrexate in combination with other medications.

Sources:

1. DrugPatentWatch.com. (n.d.). Methotrexate. Retrieved from <https://www.drugpatentwatch.com/drugs/methotrexate>
2. Mayo Clinic. (2021). Methotrexate (Oral Route, Injection route). Retrieved from <https://www.mayoclinic.org/drugs-supplements/methotrexate-oral-route-injection-route/side-effects/drg-20063030>
3. National Library of Medicine. (2021). Methotrexate. Retrieved from <https://medlineplus.gov/druginfo/meds/a682132.html>
4. UpToDate. (2022). Methotrexate: Mechanism of action, administration, adverse effects, and toxicity. Retrieved from <https://www.uptodate.com/contents/methotrexate-mechanism-of-action-administration-adverse-effects-and-toxicity>