Preventive efficacy of four or six monthly oral doses of 24 µg/kg moxidectin compared to six monthly doses of Heartgard® Plus or Interceptor® Plus against macrocyclic lactone-resistant heartworm (Dirofilaria immitis) strains in dogs

Table 3 Efficacy of oral moxidectin (24 µg/kg) compared to Heartgard® Plus or Interceptor® Plus (ZoeLA strain)

Treatment	Oral dosage	Days of treatment	No. of infected dogs^a	Adult D. immitis worm counts		Efficacy compared to negative control^c
Treatment	Oral dosage	Days of treatment	No. of infected dogs^a	Individual worm counts	Geometric mean^b	% Reduction
Negative control	na	0, 30, 60, 90, 120, 150	6 of 6	24, 36, 36, 39, 41, 41	35.6^f	na
Moxidectin	24 µg/kg	0, 30, 60, 90	5 of 6	0, 1, 1, 1, 2, 3	1.1^g	96.8
Moxidectin	24 µg/kg	0, 30, 60, 90, 120, 150	5 of 6	0, 1, 1, 2^*, 2, 4	1.4^g	96.1
Heartgard® Plus	Min. of 6 µg/kg^d	0, 30, 60, 90, 120, 150	6 of 6	25, 25, 27, 27, 36, 36	29.0^f	18.7
Interceptor® Plus	Min. of 500 µg/kg^e	0, 30, 60, 90, 120, 150	6 of 6	16, 26, 28, 33, 34, 37	28.1^f	21.2

^aEach dog was inoculated with 50 infective ZoeLA L₃ of D. immitis on Day -30, except for one dog (*) treated with six monthly doses of moxidectin which received 49 infective larvae
^bGeometric mean counts with the same superscript letters (f-g) are not significantly different (P ≥ 0.05)
^cAll dogs were necropsied for recovery of adult D. immitis on Day 243 (273 days post-inoculation)
^dHeartgard® Plus (ivermectin + pyrantel pamoate) administered according to commercial label directions which resulted in administration of 6.2–15.5 µg/kg of ivermectin
^eInterceptor® Plus (milbemycin oxime + praziquantel) administered according to commercial label directions which resulted in administration of 0.5–1.2 mg/kg milbemycin oxime

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