Immutrex (Methotrexate)

Methotrexate is employed across several disease categories, primarily targeting immune‑mediated conditions and certain malignancies.

• Rheumatoid arthritis: reduces joint inflammation and slows structural damage.
• Psoriasis: decreases skin lesions and plaque formation.
• Acute lymphoblastic leukemia: interferes with malignant cell proliferation.
• Non‑Hodgkin lymphoma: contributes to tumor regression in combination regimens.
• Ectopic pregnancy: terminates trophoblastic tissue to avoid surgical intervention.

• Methotrexate inhibits the enzyme dihydrofolate reductase, preventing the conversion of dihydrofolate to tetrahydrofolate, a cofactor required for synthesis of purine nucleotides and thymidylate. This blockade reduces DNA, RNA and protein synthesis, leading to suppressed proliferation of rapidly dividing cells, including activated lymphocytes and malignant clones, and induces immunosuppression. The drug also promotes accumulation of polyglutamated metabolites that further inhibit enzymes in the folate pathway, enhancing its cytotoxic and anti‑inflammatory effects.

Methotrexate may cause a range of adverse reactions, varying from mild to severe.

Common Side Effects

• Nausea or vomiting: transient gastrointestinal upset that may require anti‑emetic therapy.
• Fatigue: persistent tiredness affecting daily activities.
• Mouth sores: painful oral ulcerations that can impair nutrition.
• Elevated liver enzymes: mild hepatic irritation detected on routine labs.

Serious or Rare Side Effects

• Bone marrow suppression: decreased production of blood cells leading to anemia, leukopenia, or thrombocytopenia.
• Pulmonary toxicity: interstitial pneumonitis or fibrosis presenting with cough and shortness of breath.
• Severe hepatotoxicity: significant liver injury that may progress to fibrosis or cirrhosis.

When using Methotrexate, careful monitoring and specific precautions are essential to minimize risks.

• Renal function: assess baseline creatinine and adjust dosing in impairment.
• Hepatic monitoring: perform regular liver function tests during therapy.
• Hematologic surveillance: conduct complete blood counts to detect marrow suppression.
• Contraindications: avoid use in pregnancy due to teratogenicity and in patients with severe liver disease.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Methotrexate interacts with several medicines; some combinations require avoidance while others need close monitoring.

Major Interactions (Avoid)

• Non‑steroidal anti‑inflammatory drugs (NSAIDs): concomitant use can impair renal elimination of methotrexate, raising systemic exposure and risk of severe toxicity.
• Proton pump inhibitors (PPIs): these agents may decrease methotrexate clearance, leading to elevated plasma concentrations and potential adverse effects.

Moderate Interactions (Monitor Closely)

• Trimethoprim‑sulfamethoxazole: combined therapy can potentiate myelosuppression, requiring frequent blood count monitoring.
• Azathioprine or other immunosuppressants: additive effects on bone‑marrow suppression may occur, necessitating dose adjustments.
• Live vaccines: immunosuppression from methotrexate can allow uncontrolled replication of live attenuated organisms, so vaccination timing must be managed.