Chloroquine and hydroxychloroquine are medical drugs used to treat the chemoprophylaxis of malaria and a second-line anti-inflammatory drug.
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.
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.
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.