There is provided a pharmaceutical or veterinary formulation comprising: (a) a plurality of particles having a weight-, number-, or volume-based mean diameter that is between amount 10 nm and about 700 μm, which particles comprise solid cores coated with zinc oxide; suspended in (b) an oleaginous carrier system comprising a pharmaceutically-acceptable or veterinarily-acceptable oil, which zinc oxide coated particles comprise: (1) solid cores comprising a biologically-active agent; (2) one or more discrete layers surrounding said cores, said one or more layers each comprising at least one separate zinc oxide coating. Said zinc oxide coated particles are preferably synthesized via a gas phase coating technique, such as atomic layer deposition. When the cores comprise biologically-active agent, and the particles are suspended in an oleaginous carrier system, the formulation may provide for the delayed or sustained release of said active agent without a burst effect.