An apparatus for injecting a dose of medication into a bottle includes a tank, an outlet or mouth, a doser, and a conduit connecting the tank, the outlet mouth and the doser to each other. The conduit includes a portion disposed between the doser and the outlet mouth. The apparatus additionally includes a valve and a cursor movable internally of the portion of the conduit between an occluding position and an enabling position. A first magnet is borne by the cursor, while a second magnet arranged externally of the conduit is movable beside the conduit and interacts magnetically with the first magnet so that the second magnet is able to draw the cursor between the occluding position and the enabling position.