Stability of drugs of abuse in oral fluid collection devices with purpose of external quality assessment schemes.

As the stability of drugs of abuse in oral fluid can affect drug testing results, we evaluated this parameter together with recovery for the principal drugs of abuse in two collection devices typically used to ship oral fluid samples to testing laboratories. Two different samples were prepared using Cozart Drug Detection System and Intercept oral fluid collection devices with 600 ng/mL of 6-monoacetylmorphine (6-MAM) and cocaine and 240 ng/mL of Delta-tetrahydrocannabinol (THC) and 11-nor-9-carboxy-Delta-tetrahydrocannabinol (THCCOOH). Samples were sent at ambient temperature by courier to the participating laboratories (n = 19) the same day of preparation. Samples were analyzed upon reception (about 48-72 hours after shipment). Percent coefficients of variation, calculated using robust mean and robust standard deviation, were around 30% for all analytes, except for THCCOOH in both samples (between 50% and 80%) and THC in 1 sample (50%). Percent coefficients of variation were also high (between 50% and 70%) for morphine and benzoylecgonine, formed after 6-MAM and cocaine spontaneous hydrolysis. On average, 9%-12% 6-MAM was converted to morphine and between 26% and 41% cocaine to benzoylecgonine. Good recoveries were observed for the acid metabolite of THC in both collection devices, whereas THC was always scarcely recovered. Depending on the collection device used, obtained results may confound the interpretation and estimation of blood drug concentration, given an oral fluid drug concentration and subsequent consideration of time elapsing from drug consumption.