When methotrexate is co-administered with other drugs, dose adjustments may be required to prevent potential adverse effects. According to the information provided, the specific drugs that necessitate dose adjustments when given with methotrexate include leflunomide and the proton pump inhibitor (PPI) class of drugs, such as omeprazole [1].

Leflunomide, a disease-modifying antirheumatic drug (DMARD), is often used in combination with methotrexate for the treatment of rheumatoid arthritis. When leflunomide is co-administered with methotrexate, the leflunomide dosage should be reduced [1].

Proton pump inhibitors (PPIs), such as omeprazole, are used to treat gastroesophageal reflux disease and reduce gastric acid production. PPIs can affect methotrexate clearance, leading to increased methotrexate levels and potential toxicity. Therefore, when methotrexate and PPIs are co-administered, methotrexate dose adjustments or increased monitoring for methotrexate toxicity may be necessary [1].

It is important to note that drug interactions can be complex and may vary depending on individual patient factors. Healthcare professionals should consider each patient's unique situation and consult reliable resources when making dosage decisions [1].

Sources:

[1] DrugPatentWatch. "Methotrexate Drug Interactions." DrugPatentWatch.com. <https://drugpatentwatch.com/drug-interactions/methotrexate>.