False-positive EMIT II opiates from ofloxacin

Ther Drug Monit. 1997 Feb;19(1):98-9. doi: 10.1097/00007691-199702000-00019.


The cross-reactivities of four quinolone antibiotics--ofloxacin, norfloxacin, ciprofloxacin, and nalidixic acid--toward the EMIT II Opiates enzyme immunoassay were examined. Drug-free urine was spiked with the individual drugs up to 5,000 mg/L. Only ofloxacin showed potential for causing a false-positive opiates immunoassay screening result (apparent morphine > 300 micrograms/L). The method produced a positive opiate result at an ofloxacin concentration of 200 mg/L, a 0.16% cross-reactivity. Three hospitalized patients taking therapeutic doses of ofloxacin all gave false-positive EMIT II Opiates urine screening results. Three patients taking norfloxacin and three patients taking ciprofloxacin gave true-negative urine screening results. False-positive results were also obtained from the urines of two volunteers who each consumed a single 400-mg ofloxacin pill.

MeSH terms

  • Anti-Infective Agents / urine*
  • Antibodies / immunology
  • Ciprofloxacin / urine
  • Cross Reactions
  • Enzyme Multiplied Immunoassay Technique
  • False Positive Reactions*
  • Humans
  • Morphine / urine*
  • Nalidixic Acid / urine
  • Norfloxacin / urine
  • Ofloxacin / urine*


  • Anti-Infective Agents
  • Antibodies
  • Nalidixic Acid
  • Ciprofloxacin
  • Morphine
  • Ofloxacin
  • Norfloxacin