Laboratory evaluations of the immediate and sustained efficacy of lotilaner (Credelio™) against four common species of ticks affecting dogs in North America
Murphy et al. Parasites & Vectors
Laboratory evaluations of the immediate and sustained efficacy of lotilaner (Credelio™) against four common species of ticks affecting dogs in North America
Martin Murphy 2
Roberto Garcia 1
Daniela Karadzovska 0
Daniela Cavalleri 2
Dan Snyder 1
Wolfgang Seewald 2
Theresa Real 1
Jason Drake 1
Scott Wiseman 3
Steve Nanchen 2
0 Elanco Animal Health , Yarrandoo, NSW , Australia
1 Elanco Animal Health , 2500 Innovation Way, Greenfield, IN 46140 , USA
2 Elanco Animal Health , Mattenstrasse 24a, 4058 Basel , Switzerland
3 Elanco Animal Health , Southampton, Hants , UK
Background: Effective control of tick infestations on dogs is important to reduce the risk of transmission of bacterial, viral, and protozoal pathogens. Laboratory studies were initiated to determine the efficacy of lotilaner against common ticks infesting dogs in the United States. Methods: Eight studies investigated the efficacy of lotilaner against ticks. In two studies dogs were infested with both Dermacentor variabilis and Rhipicephalus sanguineus: one additional study was completed for each of these species. Two studies assessed infestations with Amblyomma americanum and two with Ixodes scapularis. In all studies, dogs were ranked and blocked by counts from pre-treatment infestations and randomly allocated, at least eight per group, to be treated orally with lotilaner (minimum dose rate 20 mg/kg), or to be untreated controls. Treatments were administered on Day 0, within 30 min after dogs were fed. In all studies, infestations were performed with 50 adult ticks on Days -2, 7, 14, 21 and 28, and also on Day 35 for R. sanguineus, D. variabilis and I. scapularis. Tick counts were completed 48 h after treatment or after each subsequent challenge. An adequate infestation was defined as at least 25% of the infestation dose recovered from each of at least six control animals at each evaluation. Efficacy calculations for the primary objective were based on geometric means. Results: In all studies, lotilaner was 100% effective against existing infestations. For post-treatment assessments, on only two occasions did efficacy fall below 99%: in one D. variabilis study efficacy was 98.0% on Day 35 and in one I. scapularis study efficacy on Day 16 was 98.4%. Only mild and transient adverse events were observed, and none were considered to be related to treatment. Conclusion: Lotilaner was completely effective against existing infestations with four common species of ticks, D. variabilis, R. sanguineus, A. americanum and I. scapularis, that affect dogs in North America, with at least 4 weeks efficacy of 98.0% or more against subsequent challenge infestations. These results show that lotilaner is a highly effective isoxazoline that offers sustained efficacy against ticks through and beyond the one-month end-of-dose treatment interval.
Lotilaner; Credelio; Ticks; Ixodes; Rhipicephalus; Amblyomma; Dermacentor; Dog
Effective control of tick infestations on dogs is important
to reduce the risk of transmission of a variety of bacterial,
viral, and protozoal pathogens. Ticks are also a source of
irritation at the site of their attachment, and when attached
to a host can be difficult to remove. Improper removal can
lead to longer term inflammatory consequences [
Yearround tick control is, therefore, important, and products
that are used should be effective against attached ticks and
provide post- treatment protection that will limit the risk of
prolonged attachment from new challenges, particularly
as acaracidal levels may decline toward the end of the
between-dose period (end-of-dose).
Four species of ticks that commonly infest dogs in
North America are Dermacentor variabilis, Rhipicephalus
sanguineus, Amblyomma americanum and Ixodes
scapularis. Until recently, control of these species has been
dependent on topically applied chemicals or on the use of
collars that release chemicals onto the treated animal’s
hair coat. Both measures carry some risk of owner
exposure to the pesticide, or of oral ingestion by the treated
or in-contact pets [
]. A limitation of externally applied
products is the potential for climatic factors and water
exposure to reduce ongoing efficacy [
to ensure effectiveness, topical products must be
carefully applied by the owner.
Discovery of the novel family of compounds, the
isoxazolines, has allowed the development of orally administered
products with the potential to provide knockdown of
infesting fleas and ticks and activity against post-treatment
]. Lotilaner is a newly developed isoxazoline that
has been shown to have rapid absorption and a long
halflife following oral administration of a flavoured chewable
tablet to dogs [
]. This rapid absorption of lotilaner has
been shown to translate into a rapid onset of activity against
fleas with high efficacy sustained through 35 days after a
single treatment [
]. To determine if lotilaner would
provide equivalent sustained efficacy against ticks, eight studies
were undertaken in which treated dogs were challenged
with one or more of each of four common species of ticks
that infest dogs in North America.
The objective of each study was to determine the efficacy
and safety of lotilaner flavoured chewable tablets when
dosed orally to dogs at a minimum dose rate of 20 mg/kg
against infestations of ticks present at the time treatment
was administered, or against new infestations at 28 to
35 days post-treatment. In two studies dogs were infested
with both D. variabilis and R. sanguineus (Studies 1 and 2)
and there was one additional study for each of those species
(Studies 3 and 4, respectively). Two studies were conducted
for each of A. americanum (Studies 5 and 6) and I.
scapularis (Studies 7 and 8). In the A. americanum studies, too
few ticks were available to allow meaningful challenges
beyond Day 28. All studies were single-center, investigator/
assessor-blinded, and randomised with eight or ten healthy
dogs per study group.
Studies were completed at laboratories in the United States
(Arkansas, Georgia, and Texas), Ireland and Switzerland.
Protocols were prepared in consideration of the
recommendations set forth by the World Association for the
Advancement of Veterinary Parasitology guidelines for
evaluation of the efficacy of parasiticides for the
treatment, prevention and control of flea and tick
infestations of dogs and cats [
]. Studies were conducted
according to the principles of Good Clinical Practices
and Good Laboratory Practices (GLP) for Non-Clinical
Laboratory Studies [
Animals and housing
Seven of the eight studies enrolled 16 Beagle dogs; 20
dogs were enrolled in Study 6. Dogs were at least
6 months old, and weighing from 6.7 to 20.0 kg. Before
enrollment, all dogs had been acclimated to the study
facility. To qualify for inclusion each dog was required
to be healthy and to demonstrate susceptibility to tick
infestation based on retention of at least 25% of a tick
challenge conducted, depending on the study, from
Day -14 to Day -7. Dogs were excluded if pregnant or
lactating, or if they had been exposed to ectoparasiticide
treatments for 8 weeks to 6 months before study
enrollment, depending on the duration of activity of the product
used. All dogs were individually housed during tick
challenge periods, had access to water ad libitum and were
fed a commercially available high quality complete canine
diet according to each facility’s standard procedure.
Tick infestations and counts
Tick infestations were completed by gentle application
to a dog’s dorsal or lateral rump or abdomen, with either
sedation with medemotidine, or manual restraint
without sedation for up to a minute to allow ticks to crawl
into the dog’s hair. For each study, infestations were
completed by applying approximately 50 ticks of the
relevant species (approximately male:female ratio, 1:1)
on Day -2, and post-treatment on Days 7, 14, 21, and 28,
and also on Day 35 for R. sanguineus, D. variabilis and I.
Ticks of each species tested were obtained from
laboratory-maintained colonies. All colonies were
initiated with field isolates and had been refreshed at yearly
or two-yearly intervals with additional field-caught ticks
from different areas. In one I. scapularis study, ticks
were field-collected by flagging vegetation in South
Carolina. Captured ticks were maintained in glass vials
with moist filter paper and placed in a chamber which
provided a relative humidity and temperature of
approximately 98.5% and 11.1 °C, respectively.
Tick removals from dogs and counts of live ticks were
completed at approximately 48 h post-treatment and
approximately 48 h after each subsequent infestation. Study
tick count procedure consisted of a thorough examination
of all body areas by palpation with the finger tips (thumb
counting) first to locate and count the attached/free ticks
followed by combing the animal’s coat to remove all ticks.
Ticks were considered alive if legs reacted to a tactile or
stimulus or to exhaled air (carbon dioxide) and were
considered dead if they did not.
Randomization and treatment
Between one and 2 weeks before administration of study
treatment, a pre-treatment infestation was performed and
ticks removed and counted 48 h later. Counts of living,
attached ticks were used for ranking, blocking and
randomising each dog to one of the two treatment groups.
In each study, dogs in one group received lotilaner
chewable flavoured tablets, administered orally as close as
possible to the minimum recommended dose rate of
20 mg/kg, without underdosing. Based on the available
tablet sizes of 56.25 mg, 112.5 mg and 225 mg dogs were
dosed with the best tablet combination to reach this target
dose rate, according to their body weight. Dogs in the
other group were untreated or sham-treated negative
controls to facilitate blinding of study staff. All dogs had
consumed at least one-third of the daily ration within
30 min before dosing. On Day 0, treatments were
administered directly into each dog’s mouth to ensure the
targeted dose was delivered.
Clinical observations were made before dosing and at
approximately one, six and 8 h (± 15 min) post-dose to
observe for adverse events. Post-dose observations of
each dog’s health were performed at least once daily
through to the end of the study.
The individual dog was the experimental unit. The efficacy
of lotilaner was calculated separately for each tick species
by comparing geometric, and arithmetic mean counts in
the lotilaner group with those of the untreated control
group. Abbott’s formula was used to calculate efficacy.
Percent efficacy ¼ 100
where Mc is the mean number of live ticks (per species
on animals) in the untreated control group, and Mt. is the
mean number of live ticks on animals in the treated group.
There were separate calculations for each tick species at
each counting time point. Since the calculation of the
geometric mean involved taking the logarithm of the tick
count of each animal, for any tick counts that were equal
to zero a one (1) was added to the count for every animal
in every group. If a one (1) was added to the tick count,
this constant (1) was subtracted from the resultant
calculated geometric mean before calculating percent efficacy.
Lotilaner was considered effective at a given time point if
the following criteria were met for the treatment group and
tick species at that time point: (i) An adequate infestation
was achieved in control group dogs. An adequate infestation
was defined as at least 25% of the infestation dose (i.e. ≥ 12
ticks) were recovered from each of at least 6 control animals
at each evaluation; (ii) There was a statistically significant
difference (two-sided level, P < 0.05) in geometric mean tick
counts between the treated group and the untreated control
group, with a significantly lower number of live (attached
and unattached) ticks in the treated group compared to the
negative control; (iii) The treated group had a calculated
efficacy of at least 90%.
Spanish translation of the article is available in Additional
An adequate infestation (at least six untreated control
dogs with an attachment rate greater than 25% for the
tested tick species, and an average control group
infestation rate greater than 25%, or 12 ticks) was demonstrated
in all but three studies. The exceptions were in
controlgroup infestation rates in a D. variabilis study (Study 2, on
Day 9), a R. sanguineus study (Study 3, Day 2), and in the
study with field-collected I. scapularis (Study 8, Day 16).
At each of these assessments, there were no live ticks on
In all eight studies against the four species tested,
on Day 2 (48 h post-treatment), no live ticks were
found on any lotilaner-treated dog (Tables 1, 2, 3, 4;
Figs. 1, 2, 3, 4). The high efficacy against ticks was
sustained in all studies throughout the post-treatment
assessment periods, and on only two occasions did
geometric mean live tick count efficacy fall below
99%: in a D. variabilis study this was due to the
presence on Day 35 of three live unengorged ticks on a
single dog, and in an I. scapularis study on Day 16 a
single dog had three live attached, engorged ticks and
one dog had one live attached, engorged tick.
There were no serious adverse events in
lotilanertreated dogs, and the observations of transient
nonserious events were consistent with those expected to
occur in laboratory dogs, particularly those exposed
to ticks, irrespective of treatment. These events,
which occurred in treated and control groups,
included mild skin disorder of crusts and focal alopecia
observed at sites of tick attachment, with lower
frequency in the lotilaner-treated dogs. There were
isolated incidents of loose stool, and one
lotilanertreated dog vomited following sedation with
medetomidine. None of the adverse events was regarded as
being related to administration of lotilaner, and none
In each study, lotilaner had eliminated all infesting ticks
by 48 h post-treatment. Against new infestation challenges
post-treatment, a single dose of lotilaner provided
consistent and sustained activity. At the Day 30 counts, lotilaner
was 100% effective against A. americanum, and efficacy of
at least 98.0% was maintained against D. variabilis, R.
sanguineus and I scapularis. For these three species,
efficacy against a Day 35 challenge was 98% to 100%, showing
that lotilaner sustains its efficacy through the end of the
1 month period and that there is no end-of-dose decline
The results reported herein compare favourably with
earlier isoxazoline reports that assessed the use of
isoxazolines against ticks. For instance, lotilaner efficacy was
100% against R. sanguineus and I. scapularis in at least
50% of post-treatment challenges. Another isoxazoline,
sarolaner achieved similar results against these tick species,
based on 48-h counts, through at least 1 month after
]. In contrast, afoxolaner, also an isoxazoline, did
not achieve 100% efficacy 48 h after any post-treatment
challenge in two studies with R. sanguineus [
with I. scapularis, according to the product’s Freedom of
Information summary, two studies of afoxolaner-treated
dogs indicated that efficacy did not reach 100% against
post-treatment challenges, although a published report of
one of these studies described 100% efficacy against the
challenge at Day 7 [
The effectiveness of lotilaner demonstrated in these
eight studies indicates its strong potential for use in the
treatment and control of canine tick infestations. This
Abbreviation: na not applicable because of insufficient infestations in control dogs
may be particularly important in geographies where there
needs to be heightened confidence in the sustained
endof-dose effectiveness of a tick control product. Results of
other studies have indicated that lotilaner has a rapid
onset (within 4 h) of activity in dogs after treatment both
against fleas and against the tick Ixodes ricinus [
8, 9, 17
Thus with a rapid onset of activity and sustained action
through the month following treatment, lotilaner can be a
valuable safe and effective addition to a veterinarian and a
pet owner’s armamentarium for the control of fleas and
ticks. The high efficacy maintained at Day 37 against D.
variabilis, R. sanguineus and I. scapularis and the almost
100% efficacy from Day 0 to Day 30 against A.
americanum also provide comfort to veterinarians and owners
that there will be minimal risk of infestations if a
scheduled monthly dosing is delayed by a few days.
Lotilaner provided excellent efficacy against existing
infestations with the common species of ticks that affect dogs
in North America, with a sustained efficacy of at least 98%
for at least 4 weeks against subsequent challenge
infestations. These results provide assurance that lotilaner is a
highly effective isoxazoline that offers sustained efficacy
against ticks through and beyond the one-month
end-ofdose treatment interval.
Additional file 1: Spanish translation of the article. (PDF 147 kb)
GLP: Good laboratory practice; Mc: Mean number of live ticks (per species on
animals) in the untreated control group; Mt: Mean number of live ticks on
animals in the treated group; Na: Not applicable because of insufficient
infestations in control dogs
The authors would like to thank Dr Bill Ryan of Ryan Mitchell Associates LLC
for assistance with the manuscript.
All studies were funded by Elanco.
Availability of data and materials
Due to commercial confidentiality of the research, data not included in the
manuscript can only be made available to bona fide researchers subject to a
All authors participated in the design and completion of the studies and
were involved in the drafting of the manuscript. All authors read and
approved the final manuscript.
All studies were approved by the Novartis Animal Health Global Animal
Consent for publication
MM, RG, DK, DC, DS, WS, TR, JD, SW and SN are employees of Elanco.
Springer Nature remains neutral with regard to jurisdictional claims in
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