Tafenoquine for Relapsing Babesiosis: A Case Series.

Background: Relapsing babesiosis often occurs in highly immunocompromised patients and has been attributed to the acquisition of resistance against drugs commonly used for treatment such as atovaquone, azithromycin, and clindamycin. Tafenoquine, which is approved for malaria prophylaxis and presumptive antirelapse treatment of Plasmodium vivax malaria, has shown activity against Babesia microti in several animal models of acute infection and in a single human case of relapsing babesiosis. Here, we report 5 cases of relapsing babesiosis treated with tafenoquine, including the previous case, and begin to define the conditions for optimal use of tafenoquine in relapsing babesiosis.
Methods: A definitive diagnosis of babesiosis was made by microscopic examination of Giemsa-stained thin blood smears or a real-time polymerase chain reaction (PCR) that targets the parasite 18S rRNA gene. Clearance of B. microti infection was ascertained by use of blood smear and real-time PCR.
Results: Tafenoquine was initiated with a loading dose of 600 mg. A weekly maintenance dose consisted of 200 mg or 300 mg; the lower dose was associated with a delayed clearance of B. microti. In 2 cases, all antimicrobial agents but tafenoquine were discontinued prior to clearance of infection. In 2 other cases, clearance was achieved while tafenoquine was administered along with other antimicrobial agents. In 3 of these 4 cases, tafenoquine was used in combination with atovaquone-proguanil. Other agents included atovaquone, azithromycin, and/or clindamycin. In 1 case, tafenoquine was administered alone and failed to prevent relapse.
Conclusions: Tafenoquine can be a useful adjunct for the treatment of highly immunocompromised patients experiencing relapsing babesiosis caused by B. microti.
Competing Interests: Potential conflicts of interest . P. J. K. reports payments to the Yale School of Public Health from Gold Standard Diagnostics; payments made to self from UpToDate, Inc, for a chapter that addresses the modalities available for treatment of human babesiosis and that mentions tafenoquine as a promising therapeutic approach; and serving on the American Lyme Disease Foundation Board of Directors (no monetary compensation). E. V. reports payments made to Tufts Medical Center from Gold Standard Diagnostics; payments made to self from UpToDate, Inc, for a chapter that addresses the modalities available for treatment of human babesiosis and that mentions tafenoquine as a promising therapeutic approach; and patent application PCT/US2020/062315, Compositions and Methods for the Prophylaxis and Treatment of Babesiosis (pending). All other authors report no potential conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.
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