Asparaginases are cell cycle–specific and act during the G1phase. They include:
Asparaginase is administered parenterally. It’s considered 100% bioavailable when administered I.V. and about 50% bioavailable when administered I.M.
After administration, asparaginase remains inside the blood ves-sels, with minimal distribution elsewhere. The metabolism of as-paraginase is unknown; only trace amounts appear in urine.
Asparaginase and pegaspargase capitalize on the biochemical dif-ferences between normal cells and tumor cells.
Most normal cells can synthesize asparagine, but some tumor cells depend on other sources of asparagine for survival. Asparaginase and pegaspargase help to degrade asparagine to aspartic acid and ammonia. Deprived of their supply of asparagine, the tumor cells die.
Asparaginase is used primarily in combination with standard chemotherapy to induce remission in patients with acute lympho-cytic leukemia.
Pegaspargase is used to treat acute lymphocytic leukemia in pa-tients who are allergic to the native form of asparaginase.
Asparaginase drugs may interact with other drugs. Asparaginase and pegaspargase may reduce the effectiveness of methotrexate. Concurrent use of asparaginase with prednisone or vincristine in-creases the risk of toxicity. (See Adverse reactions to asparagi-nase drugs.)