Controlled release parasitic formulations and method

DETAILED DESCRIPTION OF THE INVENTION This invention provides a controlled release formulation which can be administered therapeutically or prophylactically to an animal suffering from endoparasitic infestation or being prone to development of such parasitic infestation.
Such formulation provides effective treatment and control of endoparasitic infestations for a prolonged period of time following a single administration.
Periodic administration of the formulation thus provides indefinite protection to animals.
Typically, a single administration of a controlled release formulation of this invention provides effective control of parasitic infestation for a period of about ten to about sixty days.
The formulations provided by this invention require a copolymeric material which is uniquely and ideally suited to the controlled release of an effective amount of a pharmaceutical agent to an animal such that the animal can be effectively treated with a minimum of administrations.
Such copolymeric material is prepared by a process which permits the substantially complete removal of polymerization catalyst, thereby permitting the total degradation of the copolymeric matrix in a biological system without the concomitant accumulation of toxic residues in animal tissues.
This aspect of the invention is of particular significance in the treatment of animals utilized in the production of meat and other animal products intended for human consumption.
The new copolymer is described in detail by Nevin in Ser.
No.
75,296 filed Sept.
12, 1979.
The copolymers required for the formulations of this invention are prepared by condensation of lactic acid and glycolic acid in the presence of a readily removable polymerization catalyst.
Such catalysts include strong acid ion-exchange resins in the form of beads or similarly hard structures which are easily removed by filtration or similar techniques.
Particularly preferred polymerization catalysts include commercially available strong acid ion-exchange resins such as Amberlite IR-118(H), Dowex HCR-W (formerly Dowex 50W), Duolite C-20, Amberlyst 15, Dowex MSC-1, Duolite C-25D, Duolite ES-26 and related strong acid ion-exchange resins