Hydroxyurea is already on the World Health Organization’s essential medicines list, is available in generic form for about 50 cents a pill and can be stored at room temperature, Dr. Ware said.

If this study raises interest in buying millions of additional doses for use in Africa, the drug could presumably be made far more cheaply, he added.

Even though the study was fairly large, it had some limitations.

It was intended to prove only that the drug was safe for children aged 1 to 10. It was not designed to test various dosages to find the ideal one, nor to determine how many lab tests are needed to monitor children taking the drug, nor to determine the long-term effects.

So further work will be needed, researchers said.

Also, the research was done without a placebo control — a group of similar children not getting the drug. Oversight boards in the four test countries felt it would be unethical to deny the drug to any child, since it was known to work elsewhere, said Dr. Leon Tshilolo, a pediatric hematologist at the Monkole Hospital Center in Kinshasa, Democratic Republic of Congo, and the study’s lead author.

To compensate for the lack of a placebo group, the researchers watched children for two months before starting them on hydroxyurea. That established the baseline rates at which the children normally suffered pain crises, needed blood transfusions and got malaria or other infections.

The results “mean survival will be better even in very low-resource settings,” Dr. Tshilolo said.

Image Dr. Leon Tshilolo, a pediatric hematologist at the Monkole Hospital Center in Kinshasa, Democratic Republic of Congo with a patient.

Hydroxyurea was originally developed to fight blood cancers like leukemia, and people taking it must be monitored to make sure that it does not dangerously lower their white blood cell and platelet counts.