Amorphous ivermectin is provided, suitably in isolated solid form, and is suitably free of any additives or a support matrix, such as a solid dispersion. Also provided is a pharmaceutical formulation, for animal including human or veterinary use, comprising the amorphous ivermectin of the invention, and a pharmaceutically-​acceptable carrier therefor. Also provided is a medical device incorporating amorphous ivermectin according to the invention, or a medical device incorporating a pharmaceutical formulation according to the invention described herein. A method of prepg. amorphous ivermectin comprises the steps of prepg. a soln. of ivermectin in at least one solvent; removing the solvent by feeding the soln. to a spray dryer and collecting particles of ivermectin. Amorphous ivermectin as disclosed herein may be used as a medicament, in particular to treat conditions such as a medical condition caused by internal nematode infections including but not limited to onchocerciasis (river blindness)​, filariasis (elephantiasis)​, strongyloidiasis or demodicosis.