Bilayer tablets based on poly (epsilon-caprolactone) and polymethylmethacrilates as controlled-release systems for ruminants.

Rumen-stable devices ensure a protection of active ingredients against chemical degradation and bacterial fermentation processes that occur in the rumen. These systems should also provide postruminal bioavailability and controlled release of the active ingredient. The objective of this study was the preparation of bilayer tablets as rumen-stable delivery systems, designed for the oral administration of active ingredients (folic acid) to ruminants. The tablets are composed of two layers: layer A ("high-density layer") constituted by poly (epsilon-caprolactone) mixed with iron powder and characterized by sufficient density to avoid rumination; layer B ("release layer"), containing folic acid (25 mg), poly (epsilon-caprolactone) or polymethylmethacrylates (Eudragit RS and RL) designed to be rumen-stable and to target a controlled release of folic acid in the intestinal tract. In vitro rumen-protection tests were performed in buffer systems at pH 5.5 and pH 2.0, simulating a ruminal and abomasal environment, to verify the stability of bilayer tablets at these conditions. In vitro release tests were carried out in phosphate buffer at pH 7.4, to study the release behavior of the dosage forms in the intestinal environment. A preliminary in vivo test was carried out with radiographic images made after administration of the tablets to sheep, to evaluate their capacity to be retained in the reticulum-rumen. The amount of iron powder used provides a density of about 2.3 g/cm3 to the whole tablet. The tablets having layer B constituted by poly (epsilon-caprolactone) or Eudragit RS do not disintegrate in buffer media at pH 5.5 and pH 2.0, and they are characterized by a sustained release at pH 7.4. Radiological preliminary tests show that these prepared bilayer tablets are able to be retained in the reticulum-rumen tract of the sheep.