Uncertainty in the “detection times” for drugs in horses

There are three major sources of uncertainty in the times for which drugs can be detected in a horse's blood or urine. First, horses are treated with drugs at one million-fold different doses, and they eliminate these doses at rates that vary about 300-fold. Second, the sensitivity of the tests that the analyst uses to detect these drugs can vary up to 100-fold or more. Third, horses treated with exactly the same doses of drugs can “spread out” or distribute the plasma levels of these drugs about50-fold in a skewed or irregular manner. In this distribution, a large proportion of horses show lowerblood levels of drugs, but a small proportion of horses show relatively much higher blood levels of drugs. Beyond this, the different pH (acidity) values of urine samples can cause urinary levels of drugs to vary by at least 200-fold. These factors cause large uncertainties concerning the blood or urinary levels of drugswhich are found even after the same doses of the same drug. These uncertainties result in considerable technical difficulties for the regulatory process of medication control.