Does Lidocaine Cause False Positive Results on Cocaine Urine Drug Screen?

BACKGROUND

Individuals who have tested positive for cocaine have claimed that lidocaine, or its primary metabolite, norlidocaine (monoethylglycinexylidide (MEGX)), have caused false positive results for the cocaine metabolite benzoylecgonine (BE) on urinary immunoassay testing.

OBJECTIVE

The goal of the study was to determine if lidocaine exposure from routine medical procedures can result in false positives on a commercially available cocaine immunoassay urine drug screen (UDS).

METHODS

We performed a cross-sectional observational study of patients receiving lidocaine as part of their regular care. Standard immunoassay drug screens and confirmatory liquid chromatography-mass spectrometry (LC-MS) were performed on all urine samples to assess for MEGX and BE.

RESULTS

In total, 168 subjects were enrolled; 121 samples positive for lidocaine were ultimately included for analysis. One hundred fourteen of the 121 were also positive for MEGX. None of the 121 were positive for cocaine/BE on the UDS (95% CI), 0-3.7% for the full sample and 0-3.9% for the 114 who tested positive for MEGX.

CONCLUSION

The present study found no evidence that lidocaine or norlidocaine are capable of producing false positive results on standard cocaine urine immunoassays.

A preliminary investigation of the toxic effects of Benzylpenicilloic acid

Benzylpenicilloic acid (BPNLA) is a major cleavage product of benzylpenicillin G (BP) generated after heating treatment. It is found in animal derived products from the unstable residual penicillin. Previous studies have only reported the allergic reaction caused by BPNLA, but not described its toxicity. In this study, the toxicity of BPNLA was evaluated to report the potential public health risk posed by animal derived products using in vivo and in vitro models, including the acute toxicity assays, cytotoxicity assays, apoptosis assays and cell cycle progression assay. The LD₅₀ value for BPNLA was 8.48 g/kg [bw] intraperitoneally. BPNLA showed cytotoxicity and inhibition of cell proliferation on SK-N-SH cells, MRC-5 cells and GC-1 cells. Further, Annexin-v/PI staining and Hoechst 33342 staining showed increased cell apoptosis and nucleus morphological changes with toxic levels of BPNLA. BPNLA arrested cells in G1 phase and reduced cells population in S phase in a dose-dependent manner. This work suggests that BPNLA might be a potential toxic agent and might have public health significance. However, the toxic concentrations of BPNLA are relatively high compared to levels that would result from the degradation of antibiotics residues in meat from animals that have received a therapeutic dose of benzylpenicillin.

Clinical Interpretation of Urine Drug Tests: What Clinicians Need to Know About Urine Drug Screens

Urine drug testing is frequently used in clinical, employment, educational, and legal settings and misinterpretation of test results can result in significant adverse consequences for the individual who is being tested. Advances in drug testing technology combined with a rise in the number of novel misused substances present challenges to clinicians to appropriately interpret urine drug test results. Authors searched PubMed and Google Scholar to identify published literature written in English between 1946 and 2016, using urine drug test, screen, false-positive, false-negative, abuse, and individual drugs of abuse as key words. Cited references were also used to identify the relevant literature. In this report, we review technical information related to detection methods of urine drug tests that are commonly used and provide an overview of false-positive/false-negative data for commonly misused substances in the following categories: cannabinoids, central nervous system (CNS) depressants, CNS stimulants, hallucinogens, designer drugs, and herbal drugs of abuse. We also present brief discussions of alcohol and tricyclic antidepressants as related to urine drug tests, for completeness. The goal of this review was to provide a useful tool for clinicians when interpreting urine drug test results and making appropriate clinical decisions on the basis of the information presented.

The clinical impact of a false-positive urine cocaine screening result on a patient's pain management

BACKGROUND

The urine of a patient admitted for chest and epigastric pain tested positive for cocaine using an immunoassay-based drug screening method (positive/negative cutoff concentration 150 ng/mL). Despite the patient's denial of recent cocaine use, this positive cocaine screening result in conjunction with a remote history of drug misuse impacted the patient's recommended pain therapy. Specifically, these factors prompted the clinical team to question the appropriateness of opioids and other potentially addictive therapeutics during the treatment of cancer pain from previously undetected advanced pancreatic carcinoma.

OBJECTIVE

After pain management and clinical pathology consultation, it was decided that the positive cocaine screening result should be confirmed by gas chromatography-mass spectrometry (GC-MS) testing.

RESULTS

This more sensitive and specific analytical technique revealed that both cocaine and its primary metabolite benzoylecgonine were undetectable (i.e., less than the assay detection limit of 50 ng/mL), thus indicating that the positive urine screening result was falsely positive. With this confirmation, the pain management service team was reassured in offering intrathecal pump (ITP) therapy for pain control. ITP implantation was well tolerated, and the patient eventually achieved excellent pain relief. However, ITP therapy most likely would not have been utilized without the GC-MS confirmation testing unless alternative options failed and extensive vigilant monitoring was initiated.

CONCLUSION

As exemplified in this case, confirmatory drug testing should be performed on specimens with unexpected immunoassay-based drug screening results. To our knowledge, this is the first report of a false-positive urine cocaine screening result and its impact on patient management.