the invention provides a pharmaceutical or veterinary implant , which when parenterally administered releases a pulse of at least one biologically active material at a controllable time interval after implantation . the implant comprises the biologically active material ; an excipient comprising at least one water soluble material and at least one water insoluble material ; and a polymer film coating adapted to rupture at a predetermined period of time after implantation , and wherein the excipients and polymers are biocompatible . the biologically active material is selected from the group consisting of antigens , antibodies , hormones , growth promotants , antibiotics , nutrients , minerals and vitamins . preferably the excipient comprises a combination of two or more water - soluble and water - insoluble materials .