Yes, concurrent methotrexate use can impact medication dosages. Methotrexate is a disease-modifying antirheumatic drug (DMARD) commonly used to treat conditions such as rheumatoid arthritis, psoriasis, and certain types of cancer [1]. When prescribing other medications for patients on methotrexate, healthcare providers must consider potential drug-drug interactions, as methotrexate can influence the metabolism and clearance of various drugs [2].

Methotrexate is primarily metabolized by the liver enzyme dihydrofolate reductase, and it can inhibit the activity of this enzyme [1]. As a result, medications that also rely on dihydrofolate reductase for metabolism may have increased concentrations in the body when used concurrently with methotrexate [2]. This can lead to toxicity and adverse effects if medication dosages are not appropriately adjusted [1].

In some cases, methotrexate can increase the metabolism of other drugs by inducing cytochrome P450 enzymes [2]. This can lead to decreased concentrations of these drugs in the body, potentially reducing their effectiveness [1].

Healthcare providers must be aware of these interactions and carefully monitor patients on methotrexate who are starting or stopping other medications [2]. Regular laboratory tests, such as complete blood counts and liver function tests, can help identify potential issues early and allow for timely adjustments to medication dosages [1].

In summary, concurrent methotrexate use can impact medication dosages due to its effects on liver enzymes and cytochrome P450 enzymes. Healthcare providers must consider these interactions when prescribing medications for patients on methotrexate to ensure safe and effective treatment.

Sources:
[1] Methotrexate. (2021). In Mayo Clinic Diseases and Conditions. <https://www.mayoclinic.org/drugs-supplements/methotrexate-oral-route/side-effects/drg-20063830?p=1>
[2] Vocadlo, D. J., & Dann, C. E. (2012). Methotrexate: mechanisms of action and resistance. Nature Reviews. Rheumatology, 8(11), 655–666. <https://doi.org/10.1038/nrrheum.2012.151>
[3] Drug Patent Watch. (n.d.). Methotrexate. <https://www.drugpatentwatch.com/drugs/methotrexate>