Interference of ofloxacin with determination of urinary porphyrins

• Published in: Clinical chemistry (Baltimore, Md.) Vol. 40; no. 3; pp. 417 - 419
• Main Authors: Schoenfeld, N, Mamet, R
• Format: Journal Article
• Language: English
• Published: Washington, DC Am Assoc Clin Chem 01.03.1994; American Association for Clinical Chemistry
• Subjects: Analysis; Biological and medical sciences; Chromatography, High Pressure Liquid; Ciprofloxacin - urine; False Positive Reactions; General pharmacology; Humans; Medical sciences; Nalidixic Acid - urine; Norfloxacin - urine; Ofloxacin - urine; Pharmacology. Drug treatments; Porphyrins - urine; Spectrometry, Fluorescence; Porphyria; Quinolone derivative; Urine; Analysis method; Porphyrin; Interference
• ISSN: 0009-9147; 1530-8561
• DOI: 10.1093/clinchem/40.3.417

The second-generation quinolone ofloxacin interferes with the screening test of porphyrins. We observed a 20-fold increase in the porphyrin concentration measured in urine of an ofloxacin-treated patient, compared with drug-free normal urine. Two other fluorinated 4-quinolones tested, norfloxacin and ciprofloxacin, had a less marked effect (a twofold increase), whereas the first-generation quinolone, nalidixic acid, did not affect the measured porphyrin concentration at all. The interference is probably due to the overlap in the emission fluorescence spectra of ofloxacin and urinary porphyrins at approximately 600 nm. To avoid a false-positive diagnosis of porphyria, we suggest using HPLC to separate ofloxacin (10-min retention time) from urinary porphyrins (which only start to elute at 12 min). Nonetheless, given a threefold increase in urinary porphyrins observed in the urine of an ofloxacin-treated patient, we also discuss a possible interference of the drug with the metabolism of porphyrins.