Methotrexate Injection is a widely used antimetabolite and immunosuppressive drug that interferes with DNA synthesis, repair, and cellular replication. It is employed in the treatment of various cancers, autoimmune diseases, and inflammatory conditions.

Here are the key details:

1. Composition and Form

• Active ingredient: Methotrexate (sodium salt for injection).

• Supplied as a sterile solution or lyophilized powder for intravenous (IV), intramuscular (IM), or subcutaneous (SC) injection.

• Available in various strengths depending on indication.

2. Mechanism of Action

• Inhibits dihydrofolate reductase (DHFR), blocking the conversion of dihydrofolate to tetrahydrofolate.

• Reduces synthesis of purines and pyrimidines, impairing DNA, RNA, and protein synthesis.

• More effective in rapidly dividing cells, such as cancer cells or activated immune cells.

• Also has anti-inflammatory and immunosuppressive effects at lower doses.

3. Indications

Oncology:

• Acute lymphoblastic leukemia (ALL), lymphoma, breast cancer, osteosarcoma, and other malignancies.

• Used in high-dose protocols for cancers, often with leucovorin rescue to prevent toxicity.

Non-oncologic:

• Rheumatoid arthritis, psoriasis, and other autoimmune or inflammatory disorders (typically lower doses).

• Ectopic pregnancy (single-dose or multiple-dose protocol).

4. Administration

• IV infusion: over several minutes to hours depending on dose.

• IM or SC injection: for autoimmune diseases or when IV access is difficult.

• High-dose methotrexate requires careful monitoring and leucovorin rescue to reduce toxicity.

• Dose is highly variable depending on indication, body surface area, and patient condition.

5. Side Effects

Common:

• Nausea, vomiting, mouth ulcers, fatigue.

• Mild liver enzyme elevation with long-term use.

Serious:

• Myelosuppression: leukopenia, anemia, thrombocytopenia.

• Hepatotoxicity and fibrosis with chronic therapy.

• Pulmonary toxicity: interstitial pneumonitis, pulmonary fibrosis.

• Nephrotoxicity (especially with high-dose therapy).

• Gastrointestinal ulceration or bleeding.

• Teratogenicity (contraindicated in pregnancy).

6. Contraindications

• Hypersensitivity to methotrexate.

• Pregnancy or breastfeeding.

• Severe renal or hepatic impairment.

• Pre-existing bone marrow suppression or infections.

7. Precautions

• Monitor blood counts, liver and kidney function, and electrolytes during therapy.

• Ensure adequate hydration and urinary alkalinization for high-dose regimens to prevent renal toxicity.

• Avoid live vaccines during immunosuppressive therapy.

• Use contraception during and after therapy in men and women due to teratogenicity.

• Monitor for drug interactions (NSAIDs, antibiotics, and other nephrotoxic or hepatotoxic drugs).

8. Storage

• Store refrigerated or at room temperature depending on product labeling.

• Protect from light.

• Use aseptically; discard unused portions of single-use vials.