Absorption, distribution, and excretion of 5-azacytidine (NSC-102816) in man.

Patients with advanced cancer were given 5-azacytidine labeled at position 4 with radioactive carbon (14C) by either the intravenous (iv) or subcutaneous (sc) route. Absorption of the drug from the sc injection site was rapid and peak plasma levels were attained within one-half hour. Within 2 hours, the plasma level of radioactivity was approximately equal to that noted in the patients treated iv. The plasma half-life after iv injection was 3.5 hours; after sc administration, the plasma half-life was 4.2 hours. Patients receiving the drug sc excreted less drug in the urine than did those receiving the drug iv. No radioactivity was detected in the expired carbon dioxide when the drug was given by either route. Drug uptake into tumor tissue was always greater than uptake into surrounding normal tissue. The highest concentrations of radioactivity in the tissues were achieved when the drug had been given iv. Traces of radioactivity were still detectable in the tissues for as long as 6 days after administration of the drug. The incorporation of radioactivity into tumor RNA but not into DNA was demonstrated. The maximum level of radioactivity detected in the spinal fluid was equivalent to 0.2 microg of 5-azacytidine per milliliter of fluid.