An old drug to combat a re-emerging intestinal parasite

A brief treatment with quinacrine is effective in treating intestinal Giardia infections that are refractory to the usual treatment, according to a study led by ISGlobal in collaboration with researchers from the University of Zaragoza, the Tropical Medicine Unit of Drassanes-PROSICS and the Sant Joan de Deu Hospital. The results, published in the Journal of Infectious Diseases, pave the way to exploring new ways to treat a frequent parasite in international travellers and that is re-emerging in industrialized countries.

Giardia duodenalis is one of the most common intestinal parasitic protozoa among humans and more than 1 billion people in the world are at risk of getting infected. Although typically associated with consumption of water contaminated with parasite cysts in poor areas of developing countries, the infection is re-emerging in industrialized countries. Giardiasis symptoms vary widely from asymptomatic to chronic diarrhea for reasons that could relate to age, previous exposure to the parasite, or parasite genotype (assemblage A or B). Some infections are refractory to the standard treatment with nitroimidazole but for the moment there is no validated second-line regimen.

The goal of this study was to determine the frequency of nitroimidazole refractory girardiasis among patients attending three tropical medicine units, attempt to identify risk factors associated with persisting infection, and evaluate the efficacy of quinacrine in the treatment of refractory cases. The results show that in 77 patients analyzed (8 had no travel history outside Spain), around 20% of the infections persisted despite nitroimidazole treatment. A short-course regimen (5-days) with quinacrine was 100% effective in eliminating the parasite in these patients, without any of the side effects associated with the drug when administered at higher dosis or longer periods of time. No significant association was found between giardiasis persistence and other risk factors such as the geographic area where the parasite was acquired. The study shows for the first time that parasites of assemblage A genotype are also associated with refractory giardiasis.

The authors conclude that quinacrine should be considered a second line-treatment when possible, but Ana Requena-Méndez, first author of the study, points out that further studies are needed on the efficacy and safety of the drug, initially used as an antimalarial medicine, before it is approved to treat persistent giardiasis.