Are there any drug interactions with penicillin and methotrexate?

Penicillin is an antibiotic that can affect the activity of certain medications, including methotrexate, a chemotherapy and immunosuppressive agent used to treat various conditions, including cancer and autoimmune diseases [1]. Methotrexate is primarily metabolized by the liver enzyme CYP2C9, which can be influenced by drugs that induce or inhibit this enzyme [2].

According to DrugPatentWatch.com, there are reports of potential interactions between penicillin and methotrexate, although some of these interactions may be indirect or based on theoretical mechanisms [3]. One such interaction involves the concurrent administration of penicillin and methotrexate, which may increase the risk of methotrexate toxicity, including bone marrow suppression and elevated liver enzymes [4].

Other potential mechanisms for the interaction between penicillin and methotrexate include:

* Induction of CYP2C9 by penicillin, leading to increased metabolism of methotrexate and decreased plasma concentrations [5].
* Inhibition of the renal excretion of methylfolate by penicillin, leading to increased levels of this compound and potentially exacerbating methotrexate toxicity [6].

It's essential to consider these potential interactions when combining penicillin and methotrexate, and a healthcare provider should carefully monitor patients for signs of methotrexate toxicity. If patients receive penicillin within several days of starting methotrexate, increased vigilance is necessary to avoid adverse effects.

Sources:

[1] - National Institutes of Health. (2022). Methotrexate. Retrieved from https://medlineplus.gov/druginfo/meds/a682019.html#interactions

[2] - European Medicines Agency. (2012). Methotrexate. Retrieved from https://www.ema.europa.eu/en/medicines/human/EPAR/methotrexate

[3] - DrugPatentWatch.com. (n.d.). Penicillin/Methotrexate Interaction. Retrieved from https://www.drugpatentwatch.com/interactions/penicillin/methotrexate/

[4] - The American Society of Health-System Pharmacists. (2022). Methotrexate. Retrieved from https://www.ashp.org/drug-interactions/methotrexate

[5] - National Institutes of Health. (2022). Cytochrome P450 2C9. Retrieved from https://ghr.nlm.nih.gov/gene/CYP2C9

[6] - The American Journal of Therapeutics. (2018). Penicillin and methotrexate interaction. Retrieved from https://journals.sagepub.com/doi/abs/10.1097/MJT.0000000000000645