Cross-Reactivity of Chloroquine and Hydroxychloroquine With DRI Amphetamine Immunoassay.

BACKGROUND: Chloroquine and hydroxychloroquine are medical drugs used to treat the chemoprophylaxis of malaria and a second-line anti-inflammatory drug. METHODS: We performed a study of cross-reactivity of chloroquine and hydroxychloroquine in the DRI Amphetamine Assay inspired by a case report of a self-ingestion of chloroquine after a family dispute, that involved the following: (1) an in vitro study with control samples of healthy subjects, (2) an in vivo study with samples of patients with rheumatoid arthritis, and (3) an evaluation of the cross-reactivity of chloroquine and hydroxychloroquine in 3 additional immunoassays. RESULTS: In the case report, the Amphetamine DRI assay resulted positive both at 1000 ng/mL cutoff (1507 and 1137 ng/mL) and at 500 ng/mL cutoff (1178 and 642 ng/mL). Chloroquine urine levels were 103,900 and 100,900 ng/mL at 5 and 9 hours after ingestion. The results with control samples showed a positive cross-reactivity of chloroquine in the DRI Amphetamine Assay (approximately 0.74% and 0.89% at cutoff of 1000 and 500 ng/mL, respectively). Hydroxychloroquine did not cross-react with the DRI Amphetamine Assay up to 1,000,000 ng/mL. In patients treated with chloroquine or hydroxychloroquine, DRI Amphetamine did not produce false-positive results. The comparative assay study showed a positive cross-reactivity of chloroquine in the Emit II Plus Amphetamines Assay with control samples. CONCLUSIONS: Chloroquine can cause false-positive results in the DRI Amphetamine Assay when it is present at high concentrations. Hydroxychloroquine did not produce false-positive results neither in the DRI Amphetamine Assay nor in the others immunoassays evaluated.

Fenofibric Acid Can Cause False-Positive Urine Methylenedioxymethamphetamine Immunoassay Results.

We present a false-positive result of ecstasy (3,4-methylenedioxy-NN-methylamphetamine) screening due to the therapeutic use of fenofibrate, an antihyperlipidemic drug. Our hypothesis was that the main metabolite of fenofibrate, fenofibric acid, was responsible for this cross-reactivity on a DRI(®) Ecstasy Assay, using a cut-off of 500 ng/mL. We estimated that the addition of 225 µg/mL pure fenofibric acid to blank urine would be sufficient to result in a positive DRI(®) Ecstasy Assay. The results obtained on the urine samples analyses of the patient show that the DRI(®) Ecstasy Assay resulted negative 2 days after discontinuing fenofibrate treatment, when the urine fenofibric acid concentration corrected by creatinine and determinated by gas chromatography-mass spectrometry was 20.3 µg/mg creatinine. The cross-reactivity data for fenofibric acid would seem to indicate that there was insufficient concentration of measured compound to account for the positive immunochemical results for ecstasy. This apparent discrepancy can be explained in several ways, one of them is that the ß-glucuronidase-resistent fenofibric acid isomers are responsible. This process could explain the low recovery of free fenofibric acid when we use the developed method for its quantification in urine samples. Positive results on immunoassay screening must be considered presumptive until confirmation with another method based on a different principle, preferably gas chromatography-mass spectrometry or liquid chromatography-mass spectrometry.