Morphine and etorphine: XIV. Detection by ELISA in equine urine.

This research study discusses the development of simple, efficient tests for detecting the presence of the drugs morphine and etorphine in horse urine, improving the speed and efficacy of these tests for use in horse racing.

Methodology

• The researchers developed antibodies that specifically recognize the drugs morphine and etorphine. Antibodies are proteins that the immune system uses to identify and neutralize foreign objects like bacteria and viruses. In this study, they were used to identify and bind to the specific drugs in urine samples.
• Next, these antibodies were used to create two separate enzyme-linked immunosorbent assays (ELISAs). An ELISA is a common laboratory test that effectively measures the concentration of substances like drugs, hormones or antibodies in biological samples, like blood or urine. This method allowed the researchers to easily detect the presence of these drugs in equine urine.
• The design these tests followed is a single-step procedure that can be completed within 2 hours. The outcomes can be read visually, enhancing their simplicity and user-friendliness.

Test Effectiveness and Specificity

• For the morphine and etorphine tests, the amount of drug needed to achieve 50% inhibition (I50) in the ELISA was 1.5 ng/mL and 250 pg/mL, respectively. The I50 value is a key parameter in studies like this as it indicates the concentration of a drug required to produce half its maximum effect.
• The study also assessed how selective these antibodies were in picking up other similar substances. The antibody against morphine had cross-reactivity with other opioids such as levorphanol, hydromorphone, and oxycodone. This means the test may give a positive result if these substances are present. The anti-etorphine antibody, on the other hand, did not react with other opioids such as buprenorphine, diprenorphine, oxymorphone, morphine, or thebaine, ensuring its specificity for etorphine.

Real-World Application

• These tests were able to detect morphine or its metabolites in horse’s urine for up to 8 hours after administration. A certain dose of etorphine was also detectable for up to 48 hours after administration. This time-window is essential in horse racing where testing often occurs prior to or after the races.
• The study states that the ELISA tests have detected positives in post-race urine samples, reinforcing their usefulness in real-world situations. As such, these tests have the potential to greatly improve both pre-race and post-race testing for morphine and etorphine, thereby ensuring fair competition in horse racing.