CONTROLLED RELEASE COMPOSITIONS FOR ADMINISTRATION OF THERAPEUTIC AGENTS TO RUMINANTS

Une composition a liberation controlee pour administrer un agent therapeutique a un ruminant, utilisant un dispositif intraruminal, consiste en une pilule comprimee ou bol comprenant l'agent therapeutique, un materiau de support et facultativement un agent liant et/ou de glissement. Le materiau de support est constitue d'un materiau tensioactif ou d'un agent emulsifiant pouvant former une pilule ou bol coherent dans un moule sous pression lorsqu'il est melange a l'agent therapeutique et pouvant absorber de l'eau a l'interface pilule/eau, lorsqu'il est comprime en pilule ou bol, pour produire le gonflement du materiau et un coloide d'eau resultant; l'effort d'affaissement critique de ce coloide est sensiblement plus faible que celui du materiau sec et il n'est pas diminue de maniere significative par l'eau absorbee ulterieurement, le coloide etant a meme de reduire sensiblement la vitesse de penetration ulterieure de l'eau dans le corps du materiau recouvert de coloide. Le dispositif intraruminal decrit fait partie de l'invention. A controlled release composition for administering a therapeutic agent to a ruminant, using an intraruminal device, consists of a compressed tablet or bolus which comprises the therapeutic and a carrier material is formed from a non-tacky free flowing powder in which 90% of the particles are less than 100 mu m (200 mesh sieve) and which can be mixed with the therapeutic agent to give a uniform, intimate and reproducible mixture such that when the tablet or bolus contacts an aqueous medium a fluid from the aqueous medium is absorbed at the tablet/aqueous medium interface into the body of the tablet to a predetermined depth of penetration so as to produce a gelled volume contiguous with the interface corresponding to the depth of penetration of the fluid, said gel hindering further penetration of the fluid into the tablet beyond the prearranged depth in order to maintain the rate of fluid penetration constant and the integrity of the tablet beyond the prearranged depth of penetration of the fluid to prevent release of therapeutic agent therefrom and said gel having a yield stress which is substantially less than the yield stress of the corresponding volume of the tablet before gelling and which sharply declines with increasing water content up to a preselected critical water content thereby permitting controlled release of therapeutic agent from the gel in use.