FALSE-POSITIVE EMIT-II OPIATES FROM OFLOXACIN

The cross-reactivities of four quinolone antibiotics - ofloxacin, norf loxacin, ciprofloxacin, and nalidixic acid - toward the EMIT II Opiate s enzyme immunoassay were examined. Drug-free urine was spiked with th e individual drugs up to 5,000 mg/L. Only ofloxacin showed potential f or causing a false-positive opiates immunoassay screening result (appa rent morphine > 300 mu g/L). The method produced a positive opiate res ult at an ofloxacin concentration of 200 mg/L, a 0.16% crossreactivity . Three hospitalized patients taking therapeutic doses of ofloxacin al l gave false-positive EMIT II Opiates urine screening results. Three p atients taking norfloxacin and three patients taking ciprofloxacin gav e true-negative urine screening results. False-positive results were a lso obtained from the urines of two volunteers who each consumed a sin gle 400-mg ofloxacin pill.