A comprehensive study of the stability of cocaine and its metabolites.

The stability of cocaine (COC) in blood bank blood, postmortem human whole blood, and buffers was evaluated with consideration for the presence of the degradation products, benzoylecgonine (BE) and ecgonine methyl ester (EME). At COC concentrations commonly seen, the rate of COC hydrolysis was independent of concentration. COC was stable in blood for at least 150 days if the blood was adjusted to pH 5 and preserved with 2% NaF or organophosphates and maintained at 4 degrees C or lower. Without preservation, most COC hydrolyzed to EME. The addition of a pseudocholinesterase (PChE) inhibitor without a reduction of pH caused COC to hydrolyze to BE. COC also hydrolyzed to BE in phosphate buffer. The rate of COC hydrolysis in all studies increased with increasing pH and temperature. COC was more stable in unpreserved postmortem blood than blood bank blood due to the lower pH of the former. The incubation of COC in enzyme solutions provided further evidence of the generally accepted hypothesis that COC is hydrolyzed to EME by PChE and to BE by chemical hydrolysis. In unpreserved blood, BE was more stable than EME at room temperature. There was little loss of BE or EME at refrigerated temperature over a period of 35 days and no evidence that EME or BE could be hydrolyzed enzymatically.