Drontal Plus is a fast-acting dewormer that starts working quickly after administration. According to the manufacturer, Bayer Animal Health, the active ingredients in Drontal Plus (praziquantel, pyrantel pamoate, and febantel) work to kill intestinal parasites within 24 hours of treatment. The exact time it takes for Drontal Plus to start working may vary based on individual circumstances, such as the type and severity of the parasitic infection, and the overall health of the dog.