TY - JOUR T1 - Stability Studies of 5-Fluorocytosine in Aqueous Solutions JF - PDA Journal of Pharmaceutical Science and Technology JO - PDA J Pharm Sci Technol SP - 200 LP - 204 VL - 39 IS - 5 AU - L. Biondi AU - J. G. Nairn Y1 - 1985/09/01 UR - http://journal.pda.org/content/39/5/200.abstract N2 - The hydrolysis kinetics of 5-fluorocytosine was studied at pH 1-12, at 80°, 100°, and 121°C. The hydrolysis takes place by water attack on the protonated, neutral, and anionic forms of the drug, furthermore it is subject to catalytic hydrolysis by buffers in solution. The hydrolysis rates follow first-order kinetics. The pH profile indicates that 5-fluorocytosine has maximum stability near pH 6. In acid solution the drug deaminates to 5-fluorouracil, the final product. In neutral and basic solutions deamination takes place and nonchromophoric products are formed. The Arrhenius activation energy was found to be 25.4 Kcal/mol at pH 6.4 and the time required for 10% loss (t0.9) was estimated from the Arrhenius parameter (33 years at 25 °C). ER -