Stability of trihexyphenidyl in stored blood and urine specimens

Trihexyphenidyl (THP) is an anticholinergic agent with forensic toxicological interest. The stability of THP was studied in postmortem blood and urine samples at a concentration of 0.25 microgram/ml under different storage temperatures. After solid phase extraction (SFE), THP was measured by gas chromatography. On day zero and at intervals over a 6 months period, there was no significant loss of THP at the storage temperatures -20 degrees C and 4 degrees C in the spiked and authentic samples. Blood and urine samples stored at 25 degrees C showed a maximum recovery loss (about 14%) of THP after 3 months of storage. This loss was considered a significant change and corresponded to a P value < 0.046. The study demonstrates that the analysis of blood and urine samples containing THP would produce consistent results when they are stored for 6 months at -20 or 4 degrees C and for 3 months at 25 degrees C.