What is it about?

Hydroxychloroquine is a mainstay treatment for lupus, but blood levels vary widely between people taking the same dose, and it does not work equally well for everyone. In 102 Japanese patients we measured both the drug and the active substance the body converts it into (desethylhydroxychloroquine, DHCQ), in whole blood and plasma, and tested the genes controlling that conversion. Patients with more DHCQ — not more of the parent drug — were more likely to have well-controlled disease.

Featured Image

Why is it important?

Blood-level monitoring of hydroxychloroquine currently measures the parent drug. Our findings suggest that the active substance formed from it is more closely related to disease control, and that a common gene variant (CYP2D6*10) — frequent in East Asian populations but rare in Europe — largely explains why some patients form less of it. This points towards monitoring that reflects an individual’s own metabolism, although the separation between groups was modest and needs confirmation in other cohorts.

Perspectives

As a hospital pharmacist I have often seen patients on identical doses respond very differently, and genotype alone seldom explained it. Measuring the metabolite alongside the parent drug was our attempt to capture what each patient’s body actually does with the drug. The separation was modest and the cutoffs were derived and tested in the same cohort, so we offer them as hypotheses, not as a monitoring target. Confirmation in independent cohorts, ideally with dose adjustment, is what is needed next.

Keita Hirai
Wakayama Medical University

Read the Original

This page is a summary of: Desethylhydroxychloroquine and CYP2D6 polymorphisms are associated with low disease activity in patients with systemic lupus erythematosus, British Journal of Clinical Pharmacology, October 2026, Wiley,
DOI: 10.1002/bcp.70893.
You can read the full text:

Read

Resources

Contributors

The following have contributed to this page