Stability of rapa in whole blood

Sirolimus (rapamycine) is a potent immunosuppressive agent with a molecular weight of 913.6 d and UV absorption at 278 nm. Sirolimus has been widely accepted to be used as an agent to prevent organ rejection after kidney transplantation in concentration controlled studies. Whole blood matrix is the choice of measurement as 95% of the drug is sequestered within erytrocytes. The aim of this study is to assess the stability of whole blood samples containing sirolimus after freezing and thawing following 8-12 h stay at room temperature. Group 1 whole blood samples were freezed and thawed. Where group 2 samples were left in room temperature 8-12 h before freezing and thawing procedures. Solid phase extraction was performed in both groups; before (group 1: freshly done; group 2: after 8-12 h) and after freezing. A High Performance Liquid Chromatography (HPLC) with UV detection was used to measure parent compound sirolimus in whole blood samples. Mean percent deviation in the 2nd group was 37.89 plus or minus 12.05. Whole blood immediately frozen and thawed did not show only significant differences where as leaving blood sample at room temperature before freezing and thawing rendered significant changes in sirolimus levels. We conclude that whole blood samples should immediately be frozen if analysis will be done later on.