title: Interference by carbamazepine and oxcarbazepine with serum- and urine-screening assays for tricyclic antidepressants.
abstract: OBJECTIVE
  The purpose of this work was to evaluate the potential cross-reactivity of 2 antiepileptic medications containing 3-ringed structures, namely, carbamazepine and oxcarbazepine, with screening assays for tricyclic antidepressants.
  
  
  METHODS
  A cross-sectional study of 52 patients between 3 and 19 years of age who had been prescribed either carbamazepine or oxcarbazepine was conducted. A serum fluorescence-polarized immunoassay and a urine enzyme-linked immunoassay were used. The serum carbamazepine or oxcarbazepine level was measured. Gas chromatography/mass spectrometry, a confirmatory test for tricyclic antidepressant detection, was subsequently performed on the serum specimen.
  
  
  RESULTS
  A linear dependency on medication level was observed with the serum fluorescence-polarized immunoassay assay. This relationship was stronger for carbamazepine (4.2 microg/L tricyclic antidepressant detected per microgram/liter of carbamazepine) than for oxcarbazepine (0.7 microg/L tricyclic antidepressant detected per milligram/liter). At higher carbamazepine levels (8.0-11.6 mg/L), 12 of 13 patients had a positive serum fluorescence-polarized immunoassay result; at lower levels (0.1-7.9 mg/L), only 1 of 20 had a positive result. None of the patients who were receiving oxcarbazepine showed significant tricyclic antidepressant activity on either assay.
  
  
  CONCLUSIONS
  Carbamazepine interferes at a statistically significant level with serum fluorescence-polarized immunoassay assay and in a dose-dependent fashion. Neither carbamazepine nor oxcarbazepine exhibit significant tricyclic antidepressant activity on urine enzyme-linked immunoassay assay.
authors.affiliation: Division of Emergency Medicine, Children's Hospital Boston, Boston, MA 02115, USA. mohsen.saidinejad@childrens.harvard.edu
authors.forename: Mohsen
authors.initials: M
authors.lastname: Saidinejad
authors.forename: Terence
authors.initials: T
authors.lastname: Law
authors.forename: Michele Burns
authors.initials: MB
authors.lastname: Ewald
mesh_terms: D000293:Adolescent; D000328:Adult; D000927:Anticonvulsants / Q000097:blood / Q000494:pharmacology*; D000929:Antidepressive Agents, Tricyclic / Q000097:blood* / Q000652:urine*; D002220:Carbamazepine / Q000031:analogs & derivatives* / Q000097:blood / Q000494:pharmacology*; D002648:Child; D002675:Child, Preschool; D003429:Cross Reactions; D003430:Cross-Sectional Studies; D004797:Enzyme-Linked Immunosorbent Assay; D016231:Fluorescence Polarization Immunoassay; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D016014:Linear Models; D000078330:Oxcarbazepine
chemical_list: D000927:Anticonvulsants; D000929:Antidepressive Agents, Tricyclic; D002220:Carbamazepine; D000078330:Oxcarbazepine