Swollen Matrix

Fig. 6. Winged device of Laby.7 The wings are held in place by a piece of tape during administration and passage down the esophagus.

of the life of the animal or during the processing of the animal in rendering plants. Lowe and McArthur41'42 developed improvements to the sealing mechanisms to insure that ruminai fluids do not enter the device through the end of the device containing the piston. This helps to ensure more consistent delivery of the payload.

This 'winged-cylinder' design of Laby and others has been commercialized as the Extender 100 for the delivery of albendazole37 to sheep. The device contains 3.85 g of drug that is released at a constant rate of 32.5 mg/day over 100 days. The devices are designed for sheep that weigh in the range of 35-65 kg. The performance of this system was detailed in a series of abstracts that appear in a publication entitled Australian Advances in Veterinary Science, published by the Australian Veterinary Association in 1988. In particular, one study compared the performance of treated ewes and lambs with either untreated controls or 'district' lambs that received a conventional regimen of a series of immediate release bolus doses. The treated animals had low worm burdens throughout the trial for those species that are sensitive to the albendazole. At the end of the trial period of about 1 year, the liveweights of the treated ewes were about 11 % greater than controls and 4% greater than the district animals. The treated lambs were 24% heavier than controls and 16% heavier than district lambs. This study clearly demonstrated that continuous administration of drug was superior to conventional treatments where animals were exposed to drug on an intermittent basis.

This 'winged-cylinder' design has also been utilized by Elanco for a device termed the Rumensin ABC for the delivery of monensin sodium to cattle for the treatment of bloat and for the enhanced rate of growth that arises from the continuous administration of this poly ether antibiotic.43 The Rumensin ABC bolus is composed of a typical winged-cylinder design wherein the cylinder is about 16 cm long with a diameter of about 3 cm. The core is composed of monensin sodium dispersed in hexaglycerol distearate. The drug is delivered at the rate of about 300 mg/day for 100 days. The clinical effects of the administration of this system can be seen in Table 3 where the liveweight gains, and Table 4 where the bloat scores, for treated and control animals are summarized. It can be seen that the treated animals gained an average of 8.5 kg more than the untreated animals. Of greater importance is the significant increase in the number of treated animals that survive through the grazing season. These results highlight the important life saving benefits that can be gained through the use of these

Table 3

Summary of liveweight gain data for the Rumensin ABC

Table 3

Summary of liveweight gain data for the Rumensin ABC

Treatment

Liveweight (kg)

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