Sunday, 21st October 2018

Drug Testing

Opiate Drug Testing

Drug testing methods

Most blood and urine tests for the presence of heroin differ from alcohol test results as these measure a metabolite of heroin (morphine) which is itself active. Heroin is metabolised to 6-monoacetyl morphine and then to morphine in the blood. Alcohol produces clear dose-related impairment as measured by breath, blood or urine tests. The presence of morphine in urine merely signifies that the person had used or been exposed to opiates at some point prior to the test.
In the light of the serious consequences for the individual, and liabilities which can be incurred in the event of a positive or incorrect test result, Simpson et al discussed the need for established procedures covering storage, chain of custody, confirmation of results and appropriate legal standards for "library" matching of spectra from unknown substances (e.g. designer drugs) requiring identification.

Four British police forces tested sweat or saliva testing devices in early 1998, however in December 1998 the DETR stated that "the operating mechanisms in both deviced sometimes failed or proved unreliable, and the notation by police of positive or negative readings from the devices simply cannot be regarded as meaningful. We cannot therefore use the data in any way that could be construed as indicative of drug use among drivers and it would be irresponsible if we were to attempt to do so" and conceded that "the incidence of drugs in road accident casualties...does not give us any help with accident causation". Niedbala et al found "93.6% agreement between oral fluid and urine" when testing for opiates, and concluded "oral fluid may be a reliable matrix for opiate detection". Gjerde et al found that morphine levels in blood to have resulted from metabolism of codeine and/or ethylmorphine, stressing the importance of analysing body fluids for a spectrum of opiate drugs where these are suspected to have caused impairment.

Urine screening is the most common method of detecting use of cocaine and other drugs. Following collection, samples are subjected to a chemical or immunological screening test, involving a colour change on a dipstick, with positive samples confirmed by GCMS or similar analytical methods.

Hair testing studies have claimed that morphine can be detectable for over 6 months, but hair analysis if further complicated by the variability in growth rates and the tendency for the hair of afro-caribbean or other dark haired ethnic groups to bind more effectively to certain drugs, compared to caucasians. Piekoszewski et al, studying opiates in hair, saliva and blood serum, concluded: "From the clinical toxicology point of view, hair analysis is supplementary to urine, serum or saliva determination, but in drug testing at the workplace it can play a crucial role." Tagliaro et al concluded that "analytical and interpretative problems still remain and these limit the acceptance of this methodology, especially when the results from hair analysis".

Huestis et al reported sweat patches to provide positive results for morphine in addicted persons, but concluded "the percentage of false-negative results, at least in this treatment population, indicates that weekly sweat testing may be less sensitive than thrice weekly urine testing in detecting opiate use.".

Saliva testing is unlikely to become the preferred substrate for determining opiate intoxication or recent use, Samyn et al. reported "Recent heroin abuse (n = 5) could be demonstrated to some extent with Drugwipe on samples from the tongue but only the two subjects with the highest saliva concentrations of MAM (> 500 ng/ml) and morphine (> 500 ng/ml) were positive." Furthermore results can be influenced by the sampling methodology, Kato et al reported that stimulation of saliva (by sour candy) decreased the levels of cocaine and metabolites compared to unstimulated saliva, attributed to lower buccal pH in the stimulated condition.

Passive Exposure & False Positives

Passive inhalation of smoked cocaine and cannabis can produce positive test results, Although I am unaware of studies of passive exposure to smoked heroin, it is entirely possible that false-positives could also result from a person being in the same room or car as a heroin smoker.

Morphine can also be produced by other opiates, including those in prescribed and over the counter pain-relief preparations. Gjerde et al found that morphine levels in blood to have resulted from metabolism of codeine and/or ethylmorphine, stressing the importance of analysing body fluids for a spectrum of opiate drugs where these are suspected to have caused impairment. Monoacetylmorphine has been proposed as a urinary marker for recent heroin use.

Meneely found that ingestion of poppy-seeds (25g) in cakes generated opiate-positive urine tests (300 ng/ml cutoff levels), although "no subjects were found to exhibit symptoms of opiate impairment." In the USA, workplace testing cut-off levels for morphine were increased from 300ng/ml to 2000ng/ml in November 1998, to avoid false positives arising from medicinal codeine preparations and poppy-seed foodstuffs. By contrast, the legal limit of plasma morphine for driving under Belgian law is 20ng/ml, equivalent to 10ng/ml in blood, levels of 500ng/ml were found in saliva.
3 Opiate Pharmacokinetics

Pharmacokinetics is the study of the time course of how drugs are distributed in the body, how long the effects last and how such effects relate to drug tests.

Vandevenne et al, reviewing detection times, reported "Experimental data for total morphine using a cut-off of 300 ng/mL suggest a detection time of 1 to 1.5 days for relatively low doses of heroin (3-12 mg) administered via i.v., IN or i.m. route." Cone et al found heroin levels in the blood to peak at 5 minutes after nasal spray or intramuscular injection, identifying the need to monitor blood levels of "heroin, 6-acetylmorphine, and morphine"

Smith et al investigated the reliability of increased immunoassay cut-off levels in detecting known doses of morphine - 8 subject received intravenous doses of 3, 6, and 12 mg heroin HCl and four smoked 3.5-, 5.2-, 10.5-, or 13.9-mg doses of heroin (base) - and eliminating false positives, finding "Detection times for morphine using the 300-ng/mL cutoff assays was approximately 12 h for low dose and 24 to 48 h for higher doses of heroin. For the two 2000-ng/mL cutoff concentration assays detection time was about 12 h."

Dihydrocodeine can be detected in urine for up to 4 days. As codeine and other opiates require much larger doses than heroin for their effects, they are likely to remain detectable for longer periods.

Summary - Drug Testing

Urine tests can remain positive for 1-2 days following an individual dose of heroin, and up to 4-5 days following cessation among chronic heavy users, or where high doses are used. The dosages used in most laboratory experiments (up to 14mg smoked) are lower than would be obtained from smoking a £10 bag (100-200mg) of typical purity street heroin (20-70%) - i.e. theoretical available dosages of 20 to 140mg pure drug.

If a test to determine heroin intoxication is required (as in driving cases), rather than just to determine whether an individual has used at some time in the near to medium-term past (e.g. for employment and rehabilitation purposes), an assay of morphine, and other markers (e.g. 6-monoacetyl morphine) is required from blood or saliva samples.

Presence of morphine in urine may indicate use of heroin in the previous 1-4 days, however positive results can be produced by medicines and poppy-seed foodstuffs.

Presence of drugs in urine provides only evidence of past exposure, and cannot provide evidence of a person being under the influence of a drug at the time the sample was taken, or at any particular point in the past.