Pharmacology Of Decitabine

Indication	For treatment of patients with myelodysplastic syndromes (MDS) including previously treated and untreated, de novo and secondary MDS of all French-American-British subtypes (refractory anemia, refractory anemia with ringed sideroblasts, refractory anemia with excess blasts, refractory anemia with excess blasts in transformation, and chronic myelomonocytic leukemia) and intermediate-1, intermediate-2, and high-risk International Prognostic Scoring System groups (scores ≥0.5).
Pharmacodynamics	Decitabine is an analogue of the natural nucleoside 2’-deoxycytidine. It functions in the same way as 5-Azacytidine. The antineoplastic activity of this drug is dependent on its intracellular conversion to its 5'-triphosphate metabolite.
Mechanism of action	Decitabine is believed to exert its antineoplastic effects following its conversion to decitabine triphosphate, where the drug directly incorporates into DNA and inhibits DNA methyltransferase, the enzyme that is responsible for methylating newly synthesized DNA in mammalian cells. This results in hypomethylation of DNA and cellular differentiation or apoptosis. Decitabine inhibits DNA methylation in vitro, which is achieved at concentrations that do not cause major suppression of DNA synthesis. Decitabine-induced hypomethylation in neoplastic cells may restore normal function to genes that are critical for the control of cellular differentiation and proliferation. In rapidly dividing cells, the cytotoxicity of decitabine may also be attributed to the formation of covalent adducts between DNA methyltransferase and decitabine that has been incorporated into DNA. Non-proliferating cells are relatively insensitive to decitabine. Decitabine is cell cycle specific and acts peripherally in the S phase of the cell cycle. It does not inhibit the progression of cells from the G1 to S phase.
Absorption	Not Available
Volume of distribution	Not Available
Protein binding	Plasma protein binding of decitabine is negligible (<1%).
Metabolism	The exact route of elimination and metabolic fate of decitabine is not known in humans. One of the pathways of elimination of decitabine appears to be deamination by cytidine deaminase found principally in the liver but also in granulocytes, intestinal epithelium and whole blood.
Route of elimination	Not Available
Half life	The terminal phase elimination half-life is 0.51 ± 0.31 hours.
Clearance	125 L/h/m2 [Patients receiving 15 mg/m2 3-hr infusion every 8 hours for 3 days] 210 L/h/m2 [20 mg/m2 1-hr infusion daily for 5 days]
Toxicity	There is no known antidote for overdosage with decitabine. Higher doses are associated with increased myelosuppression including prolonged neutropenia and thrombocytopenia.