Methotrexate Rescue in Osteosarcoma

Rescue After High-dose Methotrexate Therapy
in Osteosarcoma¹

The safety and efficacy of FUSILEV rescue following high-dose methotrexate were evaluated in 16 patients age 6-21 who received 58 courses of therapy for osteogenic sarcoma. High-dose methotrexate was one component of several different combination chemotherapy regimens evaluated across several trials. Methotrexate 12 g/m² IV over 4 hours was administered to 13 patients, who received FUSILEV 7.5 mg every 6 hours for 60 hours or longer beginning 24 hours after completion of methotrexate. Three patients received methotrexate 12.5 g/m² IV over 6 hours, followed by FUSILEV 7.5 mg every 3 hours for 18 doses beginning 12 hours after completion of methotrexate. The mean number of FUSILEV doses per course was 18.2 and the mean total dose per course was 350 mg. The efficacy of FUSILEV rescue following high-dose methotrexate was based on the adverse reaction profile.

Adverse Reactions with High-dose
Methotrexate Therapy

The incidence of adverse reactions may be underestimated because not all patients were fully evaluable for toxicity for all cycles in the clinical trials. Leukopenia and thrombocytopenia were observed, but could not be attributed to high-dose methotrexate with FUSILEV rescue because patients were receiving other myelosuppressive chemotherapy.

Dosing and Administration

The recommendations for FUSILEV rescue are based on a methotrexate dose of 12 grams/m² administered by intravenous infusion over 4 hours (see methotrexate package insert for full prescribing information). FUSILEV rescue at a dose of 7.5 mg (approximately 5 mg/m²) every 6 hours for 10 doses starts 24 hours after the beginning of the methotrexate infusion.

Serum creatinine and methotrexate levels should be determined at least once daily. FUSILEV administration, hydration, and urinary alkalinization (pH of 7.0 or greater) should be continued until the methotrexate level is below 5 x 10^-8 M (0.05 micromolar). The FUSILEV dose should be adjusted or rescue extended based on the following guidelines.

Patients who experience delayed early methotrexate elimination are likely to develop reversible renal failure. In addition to appropriate FUSILEV therapy, these patients require continuing hydration and urinary alkalinization, and close monitoring of fluid and electrolyte status, until the serum methotrexate level has fallen to below 0.05 micromolar and the renal failure has resolved.

Some patients will have abnormalities in methotrexate elimination or renal function following methotrexate administration, which are significant but less severe than the abnormalities described in the table above. These abnormalities may or may not be associated with significant clinical toxicity. If significant clinical toxicity is observed, FUSILEV rescue should be extended for an additional 24 hours (total of 14 doses over 84 hours) in subsequent courses of therapy. The possibility that the patient is taking other medications which interact with methotrexate (e.g., medications which may interfere with methotrexate elimination or binding to serum albumin) should always be reconsidered when laboratory abnormalities or clinical toxicities are observed.

Delayed methotrexate excretion may be caused by accumulation in a third space fluid collection (i.e., ascites, pleural effusion), renal insufficiency, or inadequate hydration. Under such circumstances, higher doses of FUSILEV or prolonged administration may be indicated.

Although FUSILEV may ameliorate the hematologic toxicity associated with high-dose methotrexate, FUSILEV has no effect on other established toxicities of methotrexate such as the nephrotoxicity resulting from drug and/or metabolite precipitation in the kidney.

Reference:
1. Fusilev [prescribing information]. Irvine, CA: Spectrum Pharmaceuticals, Inc; 2011.