Injexate (Methotrexate)

• Methotrexate is used in the management of autoimmune disorders and malignancies by targeting rapidly dividing cells.
• Rheumatoid arthritis: reduces joint inflammation and slows disease progression.
• Psoriasis: diminishes skin lesions and plaque formation.
• Acute lymphoblastic leukemia: interferes with leukemic cell proliferation.
• Non-Hodgkin lymphoma: impedes growth of malignant lymphocytes.
• Gestational trophoblastic disease: promotes resolution of abnormal trophoblastic tissue.

• Methotrexate inhibits dihydrofolate reductase, preventing the conversion of dihydrofolate to tetrahydrofolate. This blockade disrupts folate-dependent synthesis of purines and thymidylate, leading to impaired DNA, RNA, and protein synthesis in rapidly dividing cells, which underlies its immunosuppressive and antineoplastic effects.

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

Common Side Effects

• Nausea and vomiting: gastrointestinal upset occurring shortly after administration.
• Fatigue: persistent tiredness not relieved by rest.
• Elevated liver enzymes: mild hepatic enzyme changes detected in blood tests.
• Mouth sores: ulceration of oral mucosa.
• Low blood counts: mild reductions in white cells or platelets.

Serious or Rare Side Effects

• Pulmonary toxicity: interstitial pneumonitis presenting with cough and dyspnea.
• Severe hepatotoxicity: significant liver injury requiring monitoring.
• Bone marrow suppression: profound pancytopenia increasing infection risk.
• Renal impairment: decreased kidney function affecting drug clearance.
• Severe cutaneous reactions: Stevens‑Johnson syndrome or toxic epidermal necrolysis.

• Methotrexate requires careful monitoring and specific safety measures.
• Renal function assessment: evaluate creatinine clearance before and during therapy.
• Liver monitoring: perform baseline and periodic liver function tests.
• Hematologic surveillance: conduct regular complete blood counts.
• Avoid pregnancy: contraindicated in women of childbearing potential; use effective contraception.
• Store at 2-8°C: keep refrigerated, protect from light, do not freeze or shake.

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

Major Interactions (Avoid)

• Non‑steroidal anti‑inflammatory drugs (NSAIDs): increase methotrexate serum levels and risk of toxicity.
• Proton pump inhibitors: may reduce renal clearance, enhancing toxicity.
• Trimethoprim‑sulfamethoxazole: additive bone marrow suppression.

Moderate Interactions (Monitor Closely)

• Penicillins and cephalosporins: may modestly raise methotrexate concentrations.
• Azathioprine: combined immunosuppression may heighten infection risk.
• Live vaccines: reduced efficacy and potential for infection.