Correspondence
Misdiagnosis of a Mexiletine Overdose Because of a Nonspecific Result of Urinary Toxicologic Screening
N Engl J Med 2000; 343:1971December 28, 2000
- Article
To the Editor:
It has been suggested that toxicologic screening rarely leads to changes in medical management in the emergency department.1 We present a case of an overdose that was misdiagnosed because of the nonspecific nature of an immunoassay.
A 17-year-old boy was brought to the hospital in status epilepticus. His glucose and electrolyte levels were normal; he had a serum ethanol level of 14.2 mmol per liter. He was treated with repeated intravenous doses of diazepam and phenytoin. The seizures subsided after 1 hour, but he continued to experience agitation and hallucinations, which gradually subsided over the next 24 hours. Toxicologic screening of a urine specimen by fluorescence polarization immunoassay (AxSYM system, Abbott Laboratories) was positive for benzodiazepines and amphetamines. The boy denied taking amphetamines, and his parents were not aware of substance abuse on his part. The prolonged seizures were attributed to the use of amphetamines and ethanol.
Follow-up urinary drug screening by automated high-performance liquid chromatography on the REMEDi HS system (Bio-Rad Laboratories) was negative for amphetamines but positive for large amounts of mexiletine, an antiarrhythmic agent. This finding was confirmed by thin-layer chromatography. A serum sample analyzed for mexiletine by high-performance liquid chromatography showed a value in the toxic range (44.4 μmol per liter; therapeutic range, 4.2 to 11.2). Further inquiry revealed that the boy's mother was being treated with mexiletine and that the drug was available in their home. The patient, who had been sent home, was brought back to the hospital and reassessed by a psychiatrist. It was determined that he had made an attempt at suicide, and an affective disorder was diagnosed. He admitted that he had made previous suicide attempts, which his parents had not known about.
Immunoassays for urinary drug screening are the most commonly used tests for drug abuse, because they are rapid and inexpensive.2 However, cross-reactivity among drugs is a concern.3 The immunoassays for amphetamines are subject to cross-reactivity by many structurally related compounds,4 including mexiletine, ephedrine, phenylephrine, and labetalol. Our case illustrates the importance of confirming positive results of urinary drug screening with more specific tests.
4 ReferencesEran Kozer, M.D.
Zul Verjee, Ph.D.
Gideon Koren, M.D.
Hospital for Sick Children, Toronto, ON M5G 1X8, Canada1
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- Citing Articles (4)
Citing Articles
1
W. Y. Lin, M. L. Pan, H. Y. Wang, Y. O. Su, P. W. Huang. (2012) Analysis of carbamazepine serum by differential pulse voltammetry (DPV) and comparison with fluorescence polarization immunoassay (FPIA): an animal study. Medicinal Chemistry Research
CrossRef2
H. Y. Wang, M. L. Pan, Y. L. Oliver Su, S. C. Tsai, C. H. Kao, S. S. Sun, W. Y. Lin. (2011) Comparison of Differential Pulse Voltammetry (DPV)—a new method of carbamazepine analysis—with Fluorescence Polarization Immunoassay (FPIA). Journal of Analytical Chemistry 66:4, 415-420
CrossRef3
Loralie J. Langman, Bhushan M. Kapur. (2006) Toxicology: Then and now. Clinical Biochemistry 39:5, 498-510
CrossRef4
2006. Mexiletine. , 2329-2333.
CrossRef
