Fostemsavir, sold under the brand name Rukobia, is an antiretroviral medication for adults living with HIV/AIDS who have tried multiple HIV medications and whose HIV infection cannot be successfully treated with other therapies because of resistance, intolerance or safety considerations. The most common adverse reaction is nausea. Severe adverse reactions included elevations in liver enzymes among participants also infected with hepatitis B or C virus, and changes in the immune system (immune reconstitution syndrome).