Preventive efficacy of six monthly oral doses of Simparica Trio®, Heartgard® Plus, and Interceptor® Plus against a macrocyclic lactone-resistant strain (ZoeLA) of heartworm (Dirofilaria immitis) in dogs

Table 3 Efficacy of oral Simparica Trio^® compared to Heartgard^® Plus or Interceptor^® Plus (ZoeLA strain)

Treatment	Oral ML dosage	Days of treatment	No. of infected dogs^a	Adult D. immitis worm counts		Efficacy compared to negative control^c
Treatment	Oral ML 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	23, 34, 36, 37, 40, 48	35.5 ^d	na
Simparica Trio^f	Min. 24 µg/kg moxidectin	0, 30, 60, 90, 120, 150	5 of 6	0, 1, 1, 1, 1‡, 3‡	1.0^e	97.2
Heartgard plus^g	Min. of 6 µg/kg ivermectin	0, 30, 60, 90, 120, 150	6 of 6	22, 33, 33, 34, 38, 3‡‡, 8	32.5^d	8.5
Interceptor plus	Min. of 500 µg/kg milbemycin oxime	0, 30, 60, 90, 120, 150	6 of 6	10, 12, 32, 32, 32, 34	22.8^d	35.9

^aEach dog was inoculated with 50 infective ZoeLA L3 of D. immitis on day −30
^bGeometric mean counts with the same superscript letters (d–e) are not significantly different (P > 0.05)
^cAll dogs were necropsied for recovery of adult D. immitis on day 241 (271 days post-inoculation)
^fAnalysis excluding underdosed dogs removed two dogs from this group with individual worm counts designated (‡); three of the four dogs remaining were infected with a geometric mean of 0.8 worms and reduction of 98.1%
^gAnalysis excluding underdosed dogs removed one dog from this group with an individual worm count designated (‡‡); five of the five dogs remaining were infected with a geometric mean of 31.5 worms and reduction of 11.3%

ISSN: 1756-3305