False-Positive Results in Urine Drug Screening in Healthy Volunteers Participating in Phase 1 Studies With Efavirenz and Rifampin

Radboud University Nijmegen, Nymegen, Gelderland, Netherlands
Therapeutic Drug Monitoring (Impact Factor: 2.38). 05/2006; 28(2):286. DOI: 10.1097/01.ftd.0000199359.87636.5d
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Available from: David Burger, Jan 20, 2014
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    ABSTRACT: Drug testing, commonly used in health care, workplace, and criminal settings, has become widespread during the past decade. Urine drug screens have been the most common method for analysis because of ease of sampling. The simplicity of use and access to rapid results have increased demand for and use of immunoassays; however, these assays are not perfect. False-positive results of immunoassays can lead to serious medical or social consequences if results are not confirmed by secondary analysis, such as gas chromatography-mass spectrometry. The Department of Health and Human Services' guidelines for the workplace require testing for the following 5 substances: amphetamines, cannabinoids, cocaine, opiates, and phencyclidine. This article discusses potential false-positive results and false-negative results that occur with immunoassays of these substances and with alcohol, benzodiazepines, and tricyclic antidepressants. Other pitfalls, such as adulteration, substitution, and dilution of urine samples, are discussed. Pragmatic concepts summarized in this article should minimize the potential risks of misinterpreting urine drug screens.
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    ABSTRACT: The rate of HIV-positive patients that fails to reach or to maintain a durable virological suppression under anti-retroviral (ARV) therapy might be as high as 50%, therefore new tools to improve ARV drug efficacy are urgently needed. Among others, therapeutic drug monitoring (TDM) is a strategy by which the dosing regimen for a patient is guided by measurement of plasma drug levels, enabling physicians to optimize ARV drug efficacy and to avoid drug-related toxicity. The most used analytical methods to determine plasma levels of ARV drugs are HPLC-UV and HPLC-MS(/MS), recently MALDI-based methods and enzyme immunoassay (EIA) technologies have been also employed. The wide inter-patient variability in ARV drug pharmacokinetic supports the application of TDM to the clinical management of HIV-infected patients. Drug-drug and drug-food interactions, drug binding to plasma proteins, drug sequestering by erythrocytes, hepatic impairment, sex, age, pregnancy, and host genetic factors are sources of inter-patient variability affecting ARV drug pharmacokinetics. Combining the information of TDM and resistance tests in genotypic inhibitory quotient (GIQ) is likely to be of great clinical utility. Indeed, only two clinical trials on GIQ, both conducted using ARV drugs not more commonly in use, have shown clinical benefits. The design of new trials with long follow-up and sample size representative of the current HIV prevalence is urgently needed to give indications for GIQ as an early predictor of virological response. Here, the basic principles and the available methods for TDM in the management of HIV-infected patients are reviewed.
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