Differentiating Medicinal from Illicit Use in Positive Methamphetamine Results in a Pain Population

Abstract

In addition to illicit methamphetamine, there are prescription and over-the-counter medications that, if ingested, may yield positive methamphetamine (MAMP) results on laboratory urine drug tests. The purpose of the study is to estimate the prevalence of medicinal and illicit MAMP in the pain population using chiral analysis to determine the relative amounts of the d and l-MAMP enantiomers. This retrospective analysis included the LC-MS/MS results and prescriber provided medication histories of 485,889 de-identified urine specimens from patients treated for pain. Two groups of 100 specimens each were subjected to chiral analysis. Group 1 contained specimens that were MAMP positive and amphetamine negative. Group 2 contained randomly selected MAMP positive specimens. The overall MAMP positivity rate of the 485,889 specimens tested was 1.6%. The prevalence of MAMP medications based on reported medications and detection of l-MAMP in Group 1 and Group 2 was 44% and 6%, respectively. These data indicate that the use of both illicit and medicinal MAMP is found in this patient population, and that medicinal use is underreported in clinical histories. Therefore, clinical laboratories should provide on request chiral analysis to aid in differentiating illicit and medicinal MAMP.

Review and Recommendations for Drug Testing in Substance Use Treatment Contexts

“…Metabolites: The main metabolites found in the urine of methamphetamine users are amphetamine and 4-hydroxymethamphetamine, with some unchanged methamphetamine as well, depending on the pH level of the urine being analyzed [28,87,88]. More acidic urine will yield higher concentrations of unchanged methamphetamine as opposed to urine with more alkaline levels of pH [87].…”

“…Methamphetamine is a chiral compound with two different enantiomers occurring in nature, the levorotary enantiomer (l-meth) or the dextrorotary enantiomer (d-meth). While these compounds, l-meth and d-meth, may not differ much in terms of chemistry, they have very distinct pharmacological effects and are hence used for different purposes [88].…”

“…The testing window for methamphetamine use is one (1) to four (4) days depending on duration of use, weight of the person being tested, metabolism, the route of administration, and body/fat composition [88]. Finally, the sensitivity, or "cut-off " concentration, of the test can affect the results as well [87].…”

“…Some over-the-counter medications such as Vick's Vapor Inhaler, used as a decongestant, contain l-meth and can cause false positives on laboratory tests conducted on urine using standard LC-MS/MS methods to screen for methamphetamine [88]. Other drugs metabolize into l-meth, such as selegiline, also cause false positives.…”

“…In order to distinguish between the two during a urine analysis, a chiral analysis must be conducted on the urine sample to determine the percent composition of each enantiomer present. This analysis has been determined to be the most accurate method of determining the proper source of the methamphetamine being detected [88]. Drug testing programs at Federal workplaces have determined that any percent composition of d-meth that is 20% or higher shows that either illicit methamphetamine, Desoxyn (d-methamphetamine HCL), or benzphetamine, which metabolizes into d-meth, is the source of the positive result.…”