The invention provides a stable ectoparasiticidal aqueous suspension formulation
of a spinosyn, comprising the spinosyn, or a physiologically acceptable derivative
or salt thereof, milled to an average particle size of 1 to 15 microns, a surfactant
in an amount effective to facilitate wetting the milled particles; a dispersant
in an amount that forms a spinosyn;dispersant weight ration of from 3:1 to 1:5;
and water. It also provides a method of controlling an ectoparasite infestation
on a small ruminant or companion animal comprising administering an effective amount
of such an aqueous suspension formulation.
