Leucovorin

INDICATIONS AND USAGE Leucovorin calcium rescue is indicated after high dose methotrexate therapy in osteosarcoma. Leucovorin calcium is also indicated to diminish the toxicity and counteract the effects of impaired methotrexate elimination and of inadvertent over dosages of folic acid antagonists. Leucovorin calcium is indicated in the treatment of megaloblastic anemias due to folic acid deficiency when oral therapy is not feasible. Leucovorin is also indicated for use in combination with 5-fluorouracil to prolong survival in the palliative treatment of patients with advanced colorectal cancer. Leucovorin should not be mixed in the same infusion as 5-fluorouracil because a precipitate may form.

DOSAGE AND ADMINISTRATION Advanced Colorectal Cancer Either of the following two regimens is recommended: 1. Leucovorin is administered at 200 mg/m 2 by slow intravenous injection over a minimum of 3 minutes, followed by 5-fluorouracil at 370 mg/m 2 by intravenous injection. 2. Leucovorin is administered at 20 mg/m 2 by intravenous injection followed by 5-fluorouracil at 425 mg/m 2 by intravenous injection. 5-Fluorouracil and leucovorin should be administered separately to avoid the formation of a precipitate. Treatment is repeated daily for five days. This five-day treatment course may be repeated at 4 week (28-day) intervals, for 2 courses and then repeated at 4 to 5 week (28 to 35 day) intervals provided that the patient has completely recovered from the toxic effects of the prior treatment course. In subsequent treatment course, the dosage of 5-fluorouracil should be adjusted based on patient tolerance of the prior treatment course. The daily dosage of 5-fluorouracil should be reduced by 20% for patients who experienced moderate hematologic or gastrointestinal toxicity in the prior treatment course, and by 30% for patients who experienced severe toxicity (see PRECAUTIONS : Laboratory Tests ). For patients who experienced no toxicity in the prior treatment course, 5-fluorouracil dosage may be increased by 10%. Leucovorin dosages are not adjusted for toxicity. Leucovorin Rescue After High-Dose Methotrexate Therapy The recommendations for leucovorin rescue are based on a methotrexate dose of 12 to 15 grams/m 2 administered by intravenous infusion over 4 hours (see methotrexate package insert for full prescribing information). 4 Leucovorin rescue at a dose of 15 mg (approximately 10 mg/m 2 ) every 6 hours for 10 doses starts 24 hours after the beginning of the methotrexate infusion. In the presence of gastrointestinal toxicity, nausea or vomiting, leucovorin should be administered parenterally. Do not administer leucovorin intrathecally. Serum creatinine and methotrexate levels should be determined at least once daily. Leucovorin administration, hydration, and urinary alkalization (pH of 7.0 or greater) should be continued until the methotrexate level is below 5 x 10 -8 M (0.05 micromolar). The leucovorin dose should be adjusted or leucovorin rescue extended based on the following guidelines: GUIDELINES FOR LEUCOVORIN DOSAGE AND ADMINISTRATION DO NOT ADMINISTER LEUCOVORIN INTRATHECALLY Clinical Situation Laboratory Findings Leucovorin Dosage and Duration Normal Methotrexate Elimination Serum methotrexate level approximately 10 micromo-molar at 24 hours after administration, 1 micromolar at 48 hours, and less than 0.2 micromolar at 72 hours. 15 mg PO, IM, or IV q 6 hours for 60 hours (10 doses starting at 24 hours after start of methotrexate infusion). Delayed Late Methotrexate Elimination Serum methotrexate level remaining above 0.2 micrommolar at 72 hours, and more than 0.05 micromolar 96 hours after administration. Continue 15 mg PO, IM, or IV q 6 hours, until methotrexate level is less than 0.05 micromolar. Delayed Early Methotrexate Elimination and/or Evidence of Acute Renal Injury Serum methotrexate level of 50 micromolar or more at 24 hours, or 5 micromolar or more at 48 hours after administration, OR; a 100% or greater increase in serum creatinine level at 24 hours after methotrexate administration (e.g., an increase from 0.5 mg/dL to a level of 1 mg/dL or more). 150 mg IV q 3 hours, until methotrexate level is less than 1 micromolar; then 15 mg IV q 3 hours until methotrexate level is less than 0.05 micromolar. Patients who experience delayed early methotrexate elimination are likely to develop reversible renal failure. In addition to appropriate leucovorin therapy, these patients require continuing hydration and urinary alkalization, 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 abnormalities described in the table above. These abnormalities may or may not be associated with significant clinical toxicity. If significant clinical toxicity is observed, leucovorin 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. Impaired Methotrexate Elimination or Inadvertent Overdosage Leucovorin rescue should begin as soon as possible after an inadvertent overdosage and within 24 hours of methotrexate administration when there is a delayed excretion (see WARNINGS section). Leucovorin 1

ADVERSE REACTIONS Allergic sensitization, including anaphylactoid reactions and urticaria, has been reported following the administration of both oral and parenteral leucovorin. No other adverse reactions have been attributed to the use of leucovorin per se . The following table summarizes significant adverse events occurring in 316 patients treated with the leucovorin/5-fluorouracil combinations compared against 70 patients treated with 5-fluorouracil alone for advanced colorectal carcinoma. These data are taken from the Mayo/NCCTG large multicenter prospective trial evaluating the efficacy and safety of the combination regimen. PERCENTAGE OF PATIENTS TREATED WITH LEUCOVORIN/FLUOROURACIL FOR ADVANCED COLORECTAL CARCINOMA REPORTING ADVERSE EXPERIENCES OR HOSPITALIZED FOR TOXICITY (High LV*) /5-FU (Low LV † ) /5-FU 5-FU Alone (N=155) (N=161) (N=70) Any ‡ Grade 3 +§ Any ‡ Grade 3 +§ Any ‡ Grade 3 +§ (%) (%) (%) (%) (%) (%) Leukopenia 69 14 83 23 93 48 Thrombocytopenia 8 2 8 1 18 3 Infection 8 1 3 1 7 2 Nausea 74 10 80 9 60 6 Vomiting 46 8 44 9 40 7 Diarrhea 66 18 67 14 43 11 Stomatitis 75 27 84 29 59 16 Constipation 3 0 4 0 1 - Lethargy/Malaise/Fatigue 13 3 12 2 6 3 Alopecia 42 5 43 6 37 7 Dermatitis 21 2 25 1 13 - Anorexia 14 1 22 4 14 - Hospitalization for Toxicity 5% 15% 7% * High LV = Leucovorin 200 mg/m 2 † Low LV = Leucovorin 20 mg/m 2 ‡ Any = percentage of patients reporting toxicity of any severity § Grade 3+ = percentage of patients reporting toxicity of Grade 3 or higher

Drug Interactions Folic acid in large amounts may counteract the antiepileptic effect of phenobarbital, phenytoin and primidone, and increase the frequency of seizures in susceptible pediatric patients. Preliminary animal and human studies have shown that small quantities of systemically administered leucovorin enter the CSF primarily as 5-methyltetrahydrofolate and, in humans, remain 1 to 3 orders of magnitude lower than the usual methotrexate concentrations following intrathecal administration. However, high doses of leucovorin may reduce the efficacy of intrathecally administered methotrexate. Leucovorin may enhance the toxicity of 5-fluorouracil (see WARNINGS section).