|Illegal Drug||Legal Limit|
Cocaine is metabolised by our bodies very quickly. The rate of metabolism depends upon the concentration of the drug. There are three main routes by which cocaine gets ‘bio-transformed’ (broken-down);
The method that’s important to us is ‘De-methylation‘. This is the process whereby cocaine is metabolised into Benzoylecgonine (the primary active metabolite of cocaine). Around 40% of cocaine is metabolised into benzoylecgonine.
Cocaine is eliminated from your blood within 4 – 6 hours, whereas benzoylecgonine can be present for up to 6 days after administration.
Benzoylecgonine is detectable in your blood within 30 minutes of cocaine consumption. This amount will then rise gradually over the next 2 – 3 hours. So, if you were to ‘sniff’ a 35mg line of cocaine at 10:00pm, Benzoylecgonine would be detectable by 10:30pm. By 01:30am, this will have rose to 130 micrograms (the legal limit is 50 micrograms).
The prescribed limits for drug driving are 400,000 times lower than that for drink driving. This is because drugs exist within our bodies in minute quantities. This presents practical problems for laboratories when trying to produce accurate results. We do not intend to ‘spill our trade secrets’ on this page, but we’re quite happy to outline the four key aspects of a drug driving defence.
The most common method of analysis for Benzoylecgonine is Gas-Chromotography Mass-Spectometry (GC-MS). This is considered the ‘gold standard’ in commercial drug testing. GC-MS is a specialised analytical method that, until recently, wasn’t offered by many laboratories due to its complex (and expensive) ‘two-stage’ analytical process. It enables scientists to identify and quantify individual metabolites within a blood sample.
Despite this method being one of the most accurate ‘large scale’ analytical methods, the laboratory are still required to deduct 30% from the measured result to allow for ‘normal analytical variation’. If this method of analysis is as accurate as the experts say, there would be no requirement to reduce the result by one third. This indicates the potential for unreliable results. If the laboratory has failed to deduct this amount, you could be wrongly (and unfairly) charged with drug driving.
Laboratories wishing to undertake drug testing of this type are required to attain a specific accreditation by the United Kingdom Accreditation Service (UKAS). Part of this validation process requires laboratories to frequently measure their analytical performance in terms of accuracy and precision (due to the huge margin for error with drug analysis).
M.A.J. Law has recently received information that a leading UK laboratory has failed a number of quality control and assurance tests. It has been confirmed that a large amount of results were incorrectly calculated due to a ‘data anomaly’. The same laboratory has since had its accreditation withdrawn.
Laboratories are required to calibrate testing instruments at the beginning of each day. This process involves analysing a number of solutions (calibrants) each containing a different known drug concentration. The results of the calibration test are then plotted to produce a calibration graph. These results must fall within a validated range (the ‘standard deviation’) recommended by the United Kingdom Accreditation Service (UKAS).
No analytical method is 100% accurate. False positives do occur.
Benzoylecgonine is a ‘fingerprint metabolite’. This means that no other drug or prescription medicine produces exactly the same metabolite. However, some medicines produce metabolites that are similar in structure. Laboratories who don’t enforce a strict quality control procedure could mistakenly detect what thy believe to be benzoylecgonine, when in fact it’s nothing more than a prescription medicine.