Compositions for controlled availability of medically useful organophosphorus compounds

Claim 1

A composition adapted to administration of an organophosphorus drug to a warm-blooded animal to attain one or more of the following effects: (a) to kill parasites in the gastro-intestinal tract of an infested animal; (b) to increase the vitality of the fetus and new-born young of a pregnant mammal; and (c) to kill fly larvae feeding upon the excreted feces of the animal, said composition comprising small solid particles of an intimate physical combination of the essential ingredients: (a) an organophosphorus drug, (b) small solid porous particles of a polyvinylic resin and (c) at least one copolymer of styrene and maleic anhydride, said organophosphorus drug being one having the formula: ##STR6## wherein each R is alkyl of from 1 to 10 carbon atoms, X is oxygen or sulfur, Y is hydrogen or middle halogen and "hal" is middle halogen, said polyvinylic resin particles having a pore volume of from about 0.15 to about 0.70 cubic centimeters per gram and being from about 30- to about 100-mesh in size, and said styrene/maleic anhydride copolymer having a weight average molecular weight of from about 2,000 to about 200,000, a styrene-to-maleic anhydride residue ratio of from about 1:1 to about 4:1 and optionally having a material part of the maleic anhydride residues converted to maleic acid residues, the amount of said copolymer being from about 25 to about 120% of the pore volume of said polyvinylic resin, and the weight ratio of said drug to said copolymer being from about 0.5 to about 0.8, the amount of said drug being sufficient to attain the intended effect.