Curavivax randomised 419 patients with uncomplicated Plasmodium vivax malaria in Brazil to chloroquine or dihydroartemisinin-piperaquine, each with primaquine started on day 0 or delayed to day 42. The delayed-primaquine arms are the informative comparison, because they isolate what the blood-stage drug does without radical cure masking it.
With primaquine delayed, day-42 recurrence was 2.4% with dihydroartemisinin-piperaquine and 27.3% with chloroquine — a hazard ratio of 0.08 with an interval from 0.00 to 0.22, p below 0.0001. Where primaquine was given from day 0, the two partners were indistinguishable: 1.0% against 2.0%, with an interval so wide it carries no information. All treatments were well tolerated.
The practical reading is about what happens when radical cure is delayed or not given — which, given G6PD testing constraints, is a large share of real-world vivax care. In that situation the choice of schizontocide stops being neutral and becomes the difference between one recurrence in forty and one in four.
- Brazil, single centre — chloroquine resistance in vivax varies by region
- The benefit appears only where primaquine is delayed or absent
- With day-0 primaquine both regimens performed equally well
- Relevant wherever G6PD testing delays radical cure, which is much of routine practice
- Day 42 recurrence includes relapse and recrudescence, which this design cannot separate
The statistics, in plain English
Note the two intervals. The delayed-primaquine comparison gives a hazard ratio of 0.08 with an interval of 0.00 to 0.22 — large, precise, and clearly real. The day-0 comparison gives 0.48 with an interval running to 40,209, which is what happens when there are almost no events: the point estimate is meaningless and the honest reading is simply that no difference was detected.
Read the rest in the app
You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.
Scan to keep reading on your phone. No account needed to start.
Tomorrow morning, before your first patient
One edition a day for infectious diseases, written by the desk, every claim tied to its paper. Six minutes.
Get the app — free