Controlled release bolus device

Claim 1

An improved controlled release bolus comprising a semipermeable membrane defining a compartment, the compartment being divided into first and second portions by a moveable interface, the first compartment portion containing a swellable agent, the second compartment portion containing a medicament to be dispensed, a densifier within the second compartment adjacent said membrane and a passageway through the membrane and densifier connecting said second compartment portion with the exterior of the bolus, having a central axis and a diameter such that when the bolus is in contact with water, the semipermeable membrane allow water to pass therethrough which is imbibed by the swellable agent which forces the interface to move the medicament to be dispensed through the passageway, wherein the improvement comprises an insert of rigid film having a central axis which is placed coaxially within the passageway, said inset comprising from 2 to 6 arm members connected together at and extending radially form said central axis of said insert a distance of approximately one-half of the diameter of the passageway.