A 48-year-old man participating in a residential treatment program was treated with
gatifloxacin for a
urinary tract infection. While taking the
antibiotic, two urine screens were positive for
opiates; results of previous urine
opiate screens had been negative. Confirmatory tests using a different assay method, however, gave negative results for
opiates. Two weeks after completing
gatifloxacin therapy, the patient's urine screen was negative for
opiates. Application of the Naranjo
adverse drug reaction probability scale indicated that
gatifloxacin probably was associated with this patient's positive urine
opiate screen.
Fluoroquinolones as a class are among several compounds that have demonstrated a propensity to cross-react with
enzyme immunoassay urine
drug screens for
opiates. Occurrence of cross-reactivity appears to vary among individual assays. The mechanism by which
fluoroquinolones cross-react with the immunoassay is unknown. Falsepositive results could have negative effects on patient care, and ramifications of a positive
drug screen include possible dismissal from a
substance abuse treatment program. Confirmatory analysis using a different assay method is therefore necessary to verify the presence of the target
drug.