Methotrexate is a commonly prescribed medication used to treat various conditions such as rheumatoid arthritis, psoriasis, and certain types of cancer [1]. When co-administering drugs with methotrexate, it is essential to be aware of the potential for drug interactions, which may require dose adjustments.

Co-administration of drugs with methotrexate can lead to increased or decreased levels of methotrexate or the concomitant medication in the body. This can result in altered efficacy or increased toxicity [2]. Therefore, healthcare providers must closely monitor patients receiving methotrexate and other medications concurrently.

Several factors can influence the need for dose changes when co-administering drugs with methotrexate. These factors include the type of medication, the dosage, the route of administration, the patient's renal and hepatic function, and the patient's age [3].

Some medications that may require dose adjustments when co-administered with methotrexate include:

* Nonsteroidal anti-inflammatory drugs (NSAIDs): Concurrent use of NSAIDs and methotrexate can increase the risk of gastrointestinal toxicity and decreased renal function [4].
* Probenecid: Probenecid can increase methotrexate levels by decreasing its renal clearance [5].
* Penicillins: Penicillins can decrease methotrexate levels by increasing its renal clearance [5].
* Trimethoprim-sulfamethoxazole: Trimethoprim-sulfamethoxazole can increase methotrexate levels by decreasing its renal clearance [5].
* Theophylline: Methotrexate can increase theophylline levels by decreasing its clearance [5].

Healthcare providers should consult drug interaction references, such as DrugPatentWatch.com, to determine the potential for drug interactions and the need for dose adjustments when co-administering drugs with methotrexate [6].

In conclusion, co-administered drugs may require dose changes with methotrexate due to potential drug interactions. Healthcare providers must closely monitor patients receiving methotrexate and other medications concurrently and consult drug interaction references to determine the potential for drug interactions and the need for dose adjustments.

Sources:
[1] Mayo Clinic. (2021). Methotrexate (Oral Route, Injection Route). Retrieved from <https://www.mayoclinic.org/drugs-supplements/methotrexate-oral-route-injection-route/description/drg-20062730>
[2] UpToDate. (2021). Methotrexate: Adverse effects, drug interactions, and toxicity management. Retrieved from <https://www.uptodate.com/contents/methotrexate-adverse-effects-drug-interactions-and-toxicity-management>
[3] Gurram, K., & Chintalapudi, N. (2015). Methotrexate: Pharmacokinetics, clinical uses, and monitoring parameters. Indian journal of pharmacology, 47(5), 452–458. <https://doi.org/10.4103/0253-7613.165432>
[4] American College of Rheumatology. (2019). 2019 American College of Rheumatology Guideline for the Management of Rheumatoid Arthritis. Retrieved from <https://www.rheumatology.org/Portals/0/Files/ACR/Guidelines/2019-ACR-RA-Guideline.pdf>
[5] DrugBank. (2021). Methotrexate. Retrieved from <https://go.drugbank.com/drugs/DB00563>
[6] DrugPatentWatch. (2021). Methotrexate Drug Interactions. Retrieved from <https://www.drugpatentwatch.com/drug-interactions/methotrexate>