Controlled sustained delivery of monensin in cattle: The monensin R.D.D.®

Abstract

A delivery device (Monensin R.D.D.) providing continuous dosing of cattle with the growthpromoting agent monensin sodium was developed for use in range cattle. The device is capable of delivering approximately 100 mg monensin per day for up to 150 days. The device consists of a core composed of crystalline monensin sodium (40%) dispersed in a matrix of 80 20 ( w w ) poly(lactic acid) / poly (glycolic acid) (PLA/PGA) copolymer. The copolymer matrix has a relatively low number-average molecular weight (M̄ n ) and is subject to degradation by means of hydrolysis and hydrolytic cleavage thus liberating the dispersed monensin. The monensin/copolymer core has a cylindrical shape. The core is assembled into a metal cylinder and secured by means of an adhesive filling the annular space between the matrix core and the interior wall of the cylinder. Either plastic snap-on end-caps with perforations or a plastic shell with perforated ends were applied to the metal cylinder to provide protection to the exposed flat faces of the cylindrical core matrix. By limiting the copolymer hydrolytic cleavage and subsequent dissolution to the two exposed faces a constant surface area for dissolution was obtained leading to a controlled daily dosage. Dissolution proceeded linearly from each face along the axis of the cylinder. Duration was determined by core length after the core matrix formulation was established. Extensive evaluation of release rates in rumen-fistulated cattle showed the copolymer M̄ n value to be the best predictor of device performance in vivo. The delivery system has the capability of controlling delivery of other rumen-active compounds such as anthelmintics, parasiticides, vitamins, minerals, etc. By proper selection of the copolymer different release rates and durations of activity can be obtained.