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One case of analytical interference between cannabis and niflumic acid resulting in a false-positive screening in a 3-year-old girl is described. The child was hospitalized because of behavioral disturbances of unknown origin. The only noteworthy finding in her medical history was a drug treatment including suppositories of niflumic acid, started 5 days before. The initial urinary toxicological screening was positive for cannabinoids, but the child's parents strongly denied the exposure. Another analysis was performed by the same laboratory on the same urine sample using chromatography and confirmed the absence of any cannabinoids, while clearly identifying the presence of niflumic acid. Immunoanalysis for toxicological analysis has various limitations that must be known. False-positive results of the urinary screening for cannabis in patients treated with niflumic acid are well recognized although seldom reported. All usual screening tests are not concerned by this ill-explained interference with niflumic acid and all formulations can be involved except transcutaneous formulations. Because of the wide use of this nonsteroidal anti-inflammatory drug, particularly in pediatric patients, it is important to know that this type of interference can occur with various screening tests for cannabis so that misleading conclusions can be avoided.


A Boucher, P Vilette, N Crassard, N Bernard, J Descotes. Urinary toxicological screening: analytical interference between niflumic acid and cannabis]. Archives de pédiatrie : organe officiel de la Sociéte française de pédiatrie. 2009 Nov;16(11):1457-60

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PMID: 19716686

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