Metoject Pen (Methotrexate)

Methotrexate, an antimetabolite immunosuppressant, is indicated for several chronic inflammatory and autoimmune conditions.

• Rheumatoid arthritis: decreases joint inflammation, alleviates pain, and helps prevent joint damage.
• Psoriatic arthritis: controls joint swelling and skin lesions, improving functional ability.
• Severe psoriasis: suppresses rapid skin cell growth, leading to reduction of plaques and scaling.
• Juvenile idiopathic arthritis: used in pediatric patients to control joint inflammation when other therapies are insufficient.

• Methotrexate inhibits the enzyme dihydrofolate reductase, preventing conversion of dihydrofolate to tetrahydrofolate, a cofactor required for synthesis of purine nucleotides and thymidylate. This blockade reduces DNA synthesis and cell proliferation, particularly affecting rapidly dividing immune cells. The resulting immunosuppression diminishes cytokine production and inflammatory responses in target tissues. Additionally, methotrexate interferes with the adhesion of leukocytes to endothelium and modulates adenosine release, further contributing to its anti‑inflammatory effect.

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

Common Side Effects

• Nausea: mild to moderate stomach upset.
• Fatigue: feeling of tiredness or low energy.
• Mouth ulcers: painful sores in the oral cavity.
• Elevated liver enzymes: mild, reversible increase in hepatic enzymes.

Serious or Rare Side Effects

• Bone marrow suppression: decreased blood cell production leading to anemia, infection risk.
• Severe liver toxicity: hepatitis or fibrosis with prolonged use.
• Pulmonary toxicity: interstitial pneumonitis presenting with cough and shortness of breath.

When using Methotrexate, several precautions should be observed to minimize risks and ensure safe therapy.

• Baseline testing: obtain complete blood count, liver and renal function before starting.
• Monitoring: repeat laboratory tests regularly to detect toxicity early.
• Pregnancy: avoid use in pregnancy; effective contraception required for women of childbearing potential.
• Drug interactions: review concomitant medications for potential additive toxicity.
• Infection risk: monitor for signs of infection and postpone dosing if active infection present.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

Methotrexate can interact with several medicines, altering its efficacy or increasing toxicity.

Major Interactions (Avoid)

• Non‑steroidal anti‑inflammatory drugs (NSAIDs): may increase risk of gastrointestinal ulceration and renal toxicity.
• Proton pump inhibitors: can raise methotrexate plasma levels, especially at high doses.
• Trimethoprim‑sulfamethoxazole: may potentiate bone marrow suppression.

Moderate Interactions (Monitor Closely)

• Azathioprine or mycophenolate: combined immunosuppression may heighten infection risk.
• Live vaccines: reduced efficacy and potential for infection; avoid during therapy.
• Vitamin supplements containing folic acid: may diminish therapeutic effect; adjust under physician guidance.