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 2 Adult D. immitis antigen and microfilariae test results (ZoeLA strain)

Treatment group	Days of treatment	Individual	Day-35		Day 60		Day 180		Day 210		Day 236
Treatment group	Days of treatment	Individual	Ag	MF	Ag	MF	Ag	MF	Ag	MF	Ag	MF
Placebo	0, 30, 60, 90, 120, 150	1	−	−	−	−	+	+	+	+	+	+
		2	−	−	−	−	+	+	+	+	+	+
		3	−	−	−	−	+	+	+	+	+	+
		4	−	−	−	−	+	+	+	+	+	+
		5	−	−	−	−	+	+	+	+	+	+
		6	−	−	−	−	+	+	+	+	+	+
Simparica Trio^®^a	0, 30, 60, 90, 120, 150	1	−	−	−	−	−	−	−	−	[−]	−
		2‡	−	−	−	−	+	−	+	−	+	−
		3	−	−	−	−	−	−	−	−	−	−
		4‡	−	−	−	−	−	−	−	−	[−]	−
		5	−	−	−	−	−	−	−	−	[−]	−
		6	−	−	−	−	−	−	+	−	+	−
Heartgard^® Plus^b	0, 30, 60, 90, 120, 150	1	−	−	−	−	+	+	+	+	+	+
		2	−	−	−	−	+	+	+	+	+	+
		3	−	−	−	−	+	+	+	+	+	+
		4	−	−	−	−	+	+	+	+	+	+
		5	−	−	−	−	+	+	+	+	+	+
		6	−	−	−	−	+	+	+	+	+	−
Interceptor^® Plus^c	0, 30, 60, 90, 120, 150	1	−	−	−	−	+	+	+	+	+	+
		2	−	−	−	−	+	+	+	+	+	+
		3	−	−	−	−	+	+	+	+	+	+
		4	−	−	−	−	+	+	+	+	+	+
		5	−	−	−	−	+	+	+	+	+	+
		6	−	−	−	−	+	+	+	−	+	−

^aSimparica Trio (24 µg/kg moxidectin + 1.2 mg/kg sarolaner + 5 mg/kg pyrantel) was administered according to commercial label direction, which resulted in the administration of {23.1‡}25.0–44.9 µg/kg of moxidectin
^bHeartgard Plus (6 µg/kg ivermectin + 5 mg/kg pyrantel) administered according to commercial label directions, which resulted in administration of {5.62‡} 6.2–11.8 µg/kg of ivermectin
^cInterceptor Plus (500 µg/kg milbemycin oxime + 5 mg/kg praziquantel) administered according to commercial label directions, which resulted in administration of 0.5–1.0 mg/kg milbemycin oxime
‡ Designates individuals that were mis-dosed and altered dosing outside of commercial labeling that resulted
Brackets [] indicate samples heat-treated and adult heartworm antigen tests conducted again that were negative after heat treatment
Ag, adult D. immitis antigen test; MF, D. immitis microfilariae test; Min, minimum; − negative, + positive

ISSN: 1756-3305