What the lab can and cannot do: clinical interpretation of drug testing results

Abstract

Urine drug testing is one of the objective tools available to assess adherence. To monitor adherence, quantitative urinary results can assist in differentiating "new" drug use from "previous" (historical) drug use. "Spikes" in urinary concentration can assist in identifying patterns of drug use. Coupled chromatographic-mass spectrometric methods are capable of identifying very small amounts of analyte and can make clinical interpretation rather challenging, specifically for drugs that have a longer half-life. Polypharmacy is common in treatment and rehabilitation programs because of co-morbidities. Medications prescribed for comorbidities can cause drug-drug interaction and phenoconversion of genotypic extensive metabolizers into phenotypic poor metabolizers of the treatment drug. This can have significant impact on both pharmacokinetic (PK) and pharmacodynamic properties of the treatment drug. Therapeutic drug monitoring (TDM) coupled with PKs can assist in interpreting the effects of phenoconversion. TDM-PKs reflects the cumulative effects of pathophysiological changes in the patient as well as drug-drug interactions and should be considered for treatment medications/drugs used to manage pain and treat substance abuse. Since only a few enzyme immunoassays for TDM are available, this is a unique opportunity for clinical laboratory scientists to develop TDM-PK protocols that can have a significant impact on patient care and personalized medicine. Interpretation of drug screening results should be done with caution while considering pharmacological properties and the presence or absence of the parent drug and its metabolites. The objective of this manuscript is to review and address the variables that influence interpretation of different drugs analyzed from a rehabilitation and treatment programs perspective.

Evaluation of adherence monitoring in buprenorphine treatment: A pilot study using timed drug assays to determine accuracy of testing

“…Study limitations include a lack of measurement of urine creatinine (UCr) and specific gravity to control for dilution, adulteration and tampering. UCr has been shown to be a marker of dilution, with lower urinary creatinine a potential marker of sample tampering 9,40 . There is also a potential that in order to produce timed urines, patients ingested large volumes of water and inadvertently diluted urine samples below the detection threshold of testing.…”

“…Interpretation of drug screening (both plasma and urine) requires an understanding of the pharmacological properties, metabolism and other influencing factors such as drug–drug interactions. Phenoconversion as a result of drug–drug interaction has been shown to influence the plasma concentration and the amount of drug extracted in urine 9 . Further, detection rates are highly dependent on detection thresholds of the assay used.…”

Promising approaches and kinetic prospects of the microbial degradation of pharmaceutical contaminants

“…Table 1 lists the classification and characteristics of pharmaceutical pollutants. 22–45 Antiviral medications are used to treat viral infections such as influenza, hepatitis, polio, measles, and small pox by inhibiting the pathogen growth. Antiviral medicines are more active in nature during viral propagation.…”

Doping Prevalence among U.S. Elite Athletes Subject to Drug Testing under the World Anti-Doping Code

“…The primary problem appears to be that there is no gold standard method to estimate doping. For example, although drug and urine tests are critical for detecting and deterring doping, testing only captures a distinct moment in time [ 4 ]. Further, the World Anti-Doping Agency (WADA)’s Prohibited List contains hundreds of prohibited substances and methods, some for which there are no effective detection methods [ 5 , 6 ].…”