Cell cycle-specific (S phase) antimetabolite that inhibits folic acid reductase by blocking the enzyme dihydrofolate reductase. Arrests DNA, RNA, and protein synthesis.

Trophoblastic neoplasms; acute leukemia; meningeal leukemia; breast carcinoma; head, neck, and lung neoplasms; Burkitt’s lymphoma; osteosarcoma; lymphosarcoma; mycosis fungoides.

Hepatic and intracellular metabolism; excreted primarily through the kidneys.

Methotrexate is given by numerous dosing schedules; consult literature and manufacturer’s guidelines for dosing.

♦ Trophoblastic neoplasms: three to five cycles of 15 to 30 mg/day IM or PO for 5 days.

♦ Leukemia induction: 3.3 mg/m² per day with pred-nisone 60 mg/m² per day.

♦ Leukemia maintenance: 2.5 mg/kg IV every 14 days or 15 mg/m² PO or IM twice a week.

♦ Lymphoma: Burkitt’s stage I or II: 10 to 25 mg/day PO for 4 to 8 days; stage III, concurrently with combination therapy.