False-positive amphetamine toxicology screen results in three pregnant women using labetalol.
BACKGROUND
Labetalol is commonly used for control of hypertension in pregnancy. A component of the workup for new-onset hypertension in pregnancy often includes a urine drug screen. A labetalol metabolite is structurally similar to amphetamine and methamphetamine, thus causing potential cross-reactivity in drug immunoassays.


METHODS
We present one case of cocaine-induced hypertensive crisis superimposed on chronic hypertension and two cases of severe preeclampsia for which patients required escalating doses of labetalol for hypertension, with subsequent false-positive amphetamine urine drug screen results.


CONCLUSIONS
In pregnant women requiring labetalol for treatment of hypertensive disease, a urine drug screen may be falsely positive for amphetamines and methamphetamines. Providers should be cognizant of this possibility when interpreting the results of urine drug screens.
From the Department of Obstetrics, Gynecology, and Reproductive Sciences, University of California, San Francisco, San Francisco, California.
Lynn M
LM
Yee
Danny
D
Wu
D000328:Adult; D000661:Amphetamine / Q000633:toxicity / Q000652:urine*; D000959:Antihypertensive Agents / Q000008:administration & dosage*; D002585:Cesarean Section; D002908:Chronic Disease; D003042:Cocaine / Q000633:toxicity; D003429:Cross Reactions; D005189:False Positive Reactions; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D006801:Humans; D046110:Hypertension, Pregnancy-Induced / Q000139:chemically induced / Q000188:drug therapy*; D007118:Immunoassay / Q000379:methods; D007231:Infant, Newborn; D007741:Labetalol / Q000008:administration & dosage*; D009543:Nifedipine / Q000627:therapeutic use; D011247:Pregnancy; D011256:Pregnancy Outcome; D011654:Pulmonary Edema / Q000188:drug therapy / Q000628:therapy; D050497:Stillbirth; D015813:Substance Abuse Detection
D000959:Antihypertensive Agents; D000661:Amphetamine; D003042:Cocaine; D009543:Nifedipine; D007741:Labetalol
Moeller KE, Lee KC, Kissack JC. Urine drug screening: practical guide for clinicians. Mayo Clin Proc 2008;83:66–76.
National Institute on Drug Abuse. Methamphetamine abuse and addiction. National Institute of Health Publication No. 06-4210. National Institute on Drug Abuse Research Report Series 2006:1–7.
Chan P, Chen JH, Lee MH, Deng JR. Fatal and nonfatal methamphetamine intoxication in the intensive care unit. J Toxicol Clin Toxicol 1994;32:147–55.
Erkinaro T, Kavasmaa T, Ylikauma L, Mäkikallio K, Haapsamo M, Acharya G, et al. Placental and fetal hemodynamics after labetalol or pindolol in a sheep model of increased placental vascular resistance and maternal hypertension. Reproductive Sciences 2009;16:749–57.
Vigil-De Gracia P, Lasso M, Ruiz E, Vega-Malek JC, de Mena FT, López JC, et al. Severe hypertension in pregnancy: hydralazine or labetalol. A randomized clinical trial. Eur J Obstet Gynecol Reprod Biol 2006;128:157–62.
Apple FS, Googins MK, Kastner S, Nevala K, Edmondson S, Kloss J. Labetalol: false-positive indices by EMIT-d.a.u. assay and Toxi-Lab A urine screen. Clin Chem 1985;31:1250–1.
Gilbert RB, Peng PI, Wong D. A labetalol metabolite with analytical characteristics resembling amphetamines. J Anal Toxicol 1995;19:84–6.