Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 19, 1998
Publication Date: N/A
Interpretive Summary: In order to provide for long-lasting control of livestock pests, ivermectin was formulated into bioabsorbable, injectable microspheres. The drug was incorporated into a copolymer formulation similar to bioabsorbable suture material used in surgery. In conducting trials, spherical beads which contained 30% ivermectin and were approximately twice the diameter of human nhair in size were injected subcutaneously into the goats and cattle. The study using goats determined which formulation might be most useful in cattle. When a 50:50 poly(lactide-co-gycolide) copolymer was injected into the cattle, two peaks of ivermectin were observed in the serum of treated cattle. The first peak occurred at about 1 wk posttreatment and the second peak occurred about 6 wk later. The treatment provide 100% control of lone star ticks feeding on the treated animals for 8 wk and declined to 44% control by the 12th wk posttreatment. In addition, the treatment provided greater than 98% control of larval horn flies in the manure of the treated cattle for 10 wk posttreatment. Therefore, a single injection of the microsphere formulation provided 8-10 wk control of both of these important livestock pests. The injectable microsphere formulation developed in these studies should be useful in a variety of other applications ranging from the control of cattle fever ticks in south Texas to heartworms in dogs.
Technical Abstract: A bioabsorbable, injectable microsphere formulation containing ivermectin in poly(lactide-co-glycolide) copolymer (PLA/PGA) was developed to provide delivery of the drug for control of livestock pests. A solvent evaporation technique was used to produce the spherical beads containing about 30% ivermectin and ranged in size from 25-250 microns. The pattern of delivery yof the drug into the blood stream of spanish goats was characterized for a 50:50 PLA/PGA and a 90:10 PLA/PGA copolymer formulation and a PLA monomer formulation. When the 50:50 PLA/PGA formulation was used in cattle at the rate of 2 mg AI/kg body wt, 2 peaks of 45-50 ppb ivermectin in serum were observed. The 1st peak was about 1 wk post-injection and the 2nd peak, which was broader than the first, occurred about 6-7 wk post-injection. Percentage inhibition of estimated larvae (EL) for lone star ticks, A. americanun, placed on treated cattle was 100% for the first 8 wk post- injection and was 75, 57, 46 and 44% for wk 9, 10, 11, and 12, respectively. The treatment provided 98-100% control of larval horn flies, H. irritans, in the manure of treated cattle for 10 wk. The bioassay results against lone star ticks and larval horn flies were in agreement with the serum concentration data. The injectable microsphere formulation of ivermectin should be useful in a variety other applications ranging from the control of Boophilus sp. ticks in south Texas to heartworms in pets.