Metex Pen (Methotrexate)

Methotrexate is a folate antagonist used across several inflammatory and malignant disease pathways.

• Rheumatoid arthritis: reduces joint inflammation and slows structural damage.
• Psoriatic arthritis: alleviates skin and joint symptoms while limiting disease progression.
• Juvenile idiopathic arthritis: controls systemic inflammation and improves functional outcomes.
• Crohn's disease: induces remission of intestinal inflammation.
• Certain cancers (e.g., leukemia, lymphoma): interferes with rapid cell proliferation as part of chemotherapy protocols.

• Methotrexate inhibits dihydrofolate reductase, decreasing tetrahydrofolate production and thereby limiting purine and pyrimidine synthesis. This reduction in DNA, RNA, and protein synthesis leads to suppressed proliferation of immune cells and malignant cells, providing immunosuppressive and antineoplastic effects.

Methotrexate can cause a range of adverse reactions that vary in frequency and severity.

Common Side Effects

• Nausea or vomiting: gastrointestinal upset that may improve with food.
• Fatigue: persistent tiredness often reported during treatment.
• Oral mucositis: soreness or ulceration of the mouth lining.
• Elevated liver enzymes: mild, transient changes in hepatic function tests.
• Cytopenias: mild reductions in white blood cells or platelets.

Serious or Rare Side Effects

• Severe liver toxicity: potential for fibrosis or cirrhosis with prolonged use.
• Pulmonary fibrosis: interstitial lung disease presenting with cough and dyspnea.
• Bone marrow suppression: profound pancytopenia increasing infection risk.
• Renal impairment: acute kidney injury from precipitation of drug crystals.
• Life‑threatening infections: opportunistic infections due to immunosuppression.

Methotrexate requires careful monitoring and specific safety measures before and during therapy.

• Pregnancy: contraindicated (Category X); teratogenic risk mandates effective contraception.
• Renal function: assess baseline creatinine and adjust dose in impairment.
• Hepatic function: monitor liver enzymes regularly; avoid in pre‑existing severe liver disease.
• Hematologic status: perform complete blood counts to detect cytopenias early.
• Infection risk: defer treatment in active infections and avoid live vaccines.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Methotrexate interacts with several medicines that can alter its efficacy or toxicity.

Major Interactions (Avoid)

• Non‑steroidal anti‑inflammatory drugs (NSAIDs): increase methotrexate toxicity.
• Trimethoprim‑sulfamethoxazole: heightens risk of myelosuppression.
• Live vaccines: may cause severe infection due to immunosuppression.

Moderate Interactions (Monitor Closely)

• Azathioprine: additive bone‑marrow suppression requiring blood‑count surveillance.
• Proton pump inhibitors: may affect methotrexate absorption and clearance.
• Alcohol: potentiates hepatic toxicity; limit consumption.