Clinical Chemistry, Vol 33, 2299-2300, Copyright © 1987 by American Association for Clinical Chemistry

Stability of 5-fluorouracil in whole blood and plasma [published erratum appears in Clin Chem 1988 Jul;34(7):1505]

RF Murphy, FM Balis and DG Poplack
Pediatric Branch, National Cancer Institute, Bethesda, MD 20892.

We studied the stability of 5-fluorouracil (5-FU) in plasma and whole blood kept at room temperature and on ice for 1 to 24 h. At room temperature, there was a steady loss of 94% of the parent drug over 24 h in whole blood and 52% in plasma. In the presence of an excess of uracil, 5-FU was stable for 24 h, suggesting that the loss of 5-FU is the result of enzymatic degradation. 5-FU is more stable in whole blood and plasma when samples are kept cold. For blood and plasma samples maintained on ice, the loss was only 30% and 10% of the parent drug in the respective samples over 24 h. Frozen plasma samples (-20 degrees C) were stable for five weeks. Blood specimens collected for quantifying 5- FU should be immediately placed on ice, and the plasma should be separated and frozen as promptly as possible.