The effect of various postphlebotomy storage conditions on drug levels

Monitoring drug levels in patients is standard practice in presentday critical care medicine. Clinical laboratories, however, are often unable to assay drug levels immediately following phlebotomy. This may result in blood samples being kept under a variety of storage conditions for nonuniform periods of time. The current study evaluated the stability of eight frequently monitored medications and one of their metabolities, in whole blood and plasma, at 4 degrees C or 25 degrees C, for up to 72 hours. The drugs included antibiotics, a bronchodilator, antiarrhythmics, and an anticonvulsant. Significant changes in drug levels were not identified at the time points studied. Our data suggests that meticulous postphlebotomy handling of blood samples may not be essential to obtain accurate levels of the drugs studied.