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Oral Modified-release Delivery Systems |  |
| Several modified-release delivery systems have been developed that take advantage of the unique anatomy of the ruminant forestomach. These systems generally comprise intraruminal boluses with a controlled rate of release and are administered using a balling gun. Release of the active ingredient generally relies on erosion, diffusion from a reservoir, dissolution of a dispersed matrix, or an osmotic “driver.” Regurgitation during rumination is prevented by the bolus having a density
of ~3 g/cm3 or a variable geometry. |
| Several sustained-release boluses containing sulfonamides are available for treating cattle. These provide for the delivery of the active ingredient over a period of ~72 hr. Sustained-release boluses, which contain methoprene or diflubenzuron, are approved for the control of manure-breeding flies in cattle. |
| The intraruminal devices for supplementing cattle and sheep with copper, cobalt, or selenium are erodible systems that include intraruminal pellets (also known as bullets) and soluble glass boluses. Limitations of these systems include loss via regurgitation during rumination and the formation of calcium phosphate coatings on the surface of the pellets. Copper oxide needles encapsulated in gelatin are also available for supplementing sheep and cattle with copper. The gelatin
capsule dissolves in the rumen; however, they are not strictly intraruminal devices because the particles progress into the abomasum where some are trapped in the mucosal folds and release copper. Boluses of soluble glass containing copper, cobalt, and selenium are designed to dissolve in ruminal fluids, thereby releasing the incorporated elements. The composition of the glass determines the solubility of the bolus, with an increase in the ratio of monovalent to divalent cations
resulting in an increase in solubility. The glass boluses are retained in the rumen for up to 9 mo. |
| Most commercially available intraruminal boluses are continuous-release devices. A number of these depend on erosion for release of the active ingredient. |
