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  • Author or Editor: Kenneth S. Todd Jr. x
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Sixteen helminth-free pony foals were inoculated with a mean (±sd) 2,000 (±545.5) infective Parascaris equorum eggs (day 0). Foals were allocated to replicates of 4, and treatments within each replicate were assigned at random. Treatment administered on postinoculation day (pid) 28 included no treatment (control), 0.2 mg of ivermectin/kg of body weight, 10 mg of oxibendazole/kg, or 6.6 mg of pyrantel base (pamoate)/kg. Paste formulations of the anthelmintics were administered orally. The foals were euthanatized 14 days after treatment (pid 42) and examined for P equorum larvae in the small intestine. The mean ± sd (and range) numbers of fourth-stage P equorum larvae recovered from nontreated foals and those treated with ivermectin, pyrantel, or oxibendazole were 1,603.8 ± 1,026.8 (305 to 2,480), 29.3 ± 55.8 (0 to 113), 413.0 ± 568.1 (0 to 1,204), or 889.5 ± 1,123.1 (1 to 2,345), respectively. Compared with the value for control (nontreated) foals, treatment with ivermectin, pyrantel, and oxibendazole was 98.2, 74.2, and 44.5% effective, respectively, when administered 28 days after experimentally induced infection with P equorum. Adverse reactions attributable to treatment were not observed.

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in Journal of the American Veterinary Medical Association


One hundred four heartworm-free Beagles < 1 year old were studied to determine the efficacy of ivermectin chewable tablets and of 2 other ivermectin tablet formulations against heartworm larvae. At 30 days after sc inoculation of dogs with infective Dirofilaria immitis larvae, all ivermectin formulations were given orally at dosage of 6 μg/kg of body weight. The ivermectin chewable tablets also were given orally at dosage of 2 and 6 μg/kg at 30 and 45 days, respectively, after injection of larvae. Replicates of 6 or 8 dogs in each study were formed on the basis of gender and body weight and, within replicates, were randomly allocated to treatment groups. At 30 days after injection of larvae, the additional dogs (in replicates of 8) were assigned to the control group and to the group given ivermectin chewable tablets at dosage of 6 μg/kg. All dogs were housed individually. Necropsy was performed approximately 5 or 6 months after larvae were administered.

In both trials, all control dogs had heartworms at necropsy (Univerity of Illinois—geometric mean, 35.0; Florida—geometric mean, 26.1). In both trials, the ivermectin chewable tablet (6 μg/kg) and both tablet formulations (6 μg/kg) given at 30 days after larval injection, and the chewable formulation (6 μg/kg) given at 45 days after larval injection were 100% effective (P < 0.01) in preventing development of induced infection with D immitis. Of 8 dogs at the University of Illinois that were given ivermectin chewable tablets (2 μg/kg) at 30 days after larval injection, 6 had heartworms (geometric mean, 2.25; efficacy, 93.6%; P < 0.01) and 5 of 7 dogs treated similarly in Florida had heartworms (geometric mean, 4.4; efficacy, 83.3%; P < 0.05).

Drug-related adverse reactions were not observed in either trial.

Free access
in American Journal of Veterinary Research