Methotrexate, a medication commonly used to treat conditions such as rheumatoid arthritis, psoriasis, and certain types of cancer, can have its effectiveness altered when co-administered with other drugs. This is because methotrexate interacts with other medications in various ways, which can impact its strength and efficacy.

When methotrexate is taken with certain drugs, it can either increase or decrease its concentration in the body. For instance, probenecid, a medication used to treat gout, can increase methotrexate levels in the body, potentially leading to toxicity [1]. On the other hand, medications such as folic acid, which is often prescribed alongside methotrexate to reduce its side effects, can decrease methotrexate levels, potentially reducing its effectiveness [2].

Moreover, methotrexate can affect the metabolism and elimination of other medications. For example, methotrexate can inhibit the metabolism of theophylline, a medication used to treat asthma, leading to increased theophylline levels in the body and an increased risk of adverse effects [3].

It is important to note that the impact of methotrexate co-administration on medication strength can vary depending on several factors, including the dose and frequency of administration, the route of administration, and the individual patient's health status. Therefore, it is crucial to consult with a healthcare provider before starting or stopping any medication, especially when taking methotrexate or other medications that may interact with it.

In summary, methotrexate co-administration can impact medication strength by altering the levels of methotrexate or other medications in the body. Healthcare providers must carefully consider the potential interactions when prescribing methotrexate and other medications.

Sources:

1. "Methotrexate and Probenecid Interaction" (n.d.) <https://www.drugs.com/drug-interactions/methotrexate-probenecid-interaction.html>
2. "Methotrexate and Folic Acid Interaction" (n.d.) <https://www.drugs.com/drug-interactions/methotrexate-folic-acid-interaction.html>
3. "Methotrexate and Theophylline Interaction" (n.d.) <https://www.drugs.com/drug-interactions/methotrexate-theophylline-interaction.html>
4. "Methotrexate" (2021) <https://www.drugpatentwatch.com/drugs/methotrexate>