Rob Armstrong

Parasites & Vectors

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The conclusion of a comparative efficacy study of fluralaner and sarolaner against the tick Amblyomma americanum on dogs is based on results obtained at study times that are outside the fluralaner label recommendations

LETTER TO THE EDITOR Open Access
The conclusion of a comparative efficacy
study of fluralaner and sarolaner against
the tick Amblyomma americanum on dogs
is based on results obtained at study times
that are outside the fluralaner label
recommendations
Rob Armstrong
Abstract
The only fluralaner-related conclusion presented in a study comparing the efficacy of fluralaner and sarolaner for
control of the tick Amblyomma americanum on dogs is based on study times that are outside the label administration
recommendations. Label recommendations for fluralaner treatment of A. americanum on dogs in the USA require
re-administration at 56 days. This 56 day re-administration was not conducted in the study; therefore, all assessed
time points following 56 days post-treatment in the study present comparisons that are not consistent with fluralaner
administration recommendations. The only comparative time point assessed prior to 56 days showing a difference
between treatments was at 42 days post-administration, a time point when methodological problems were identified
by the investigators. Therefore, the only comparative study conclusion that a difference was shown between fluralaner
and sarolaner beyond 6 weeks (42 days) after treatment is not based on recommended product use. Furthermore, if
the study does not show that there is a difference between the treatments at times when the products are used as
recommended, then there also can be no comparative discussion of the risk of tick-borne pathogen transmission risk
between treatments.
Keywords: Fluralaner, Sarolaner, Ambloymma americanum, Efficacy, Bravecto, Simparica
Letter to the Editor
A recent publication compares the efficacy of sarolaner
and fluralaner in a challenge study on dogs with the tick
Amblyomma americanum [1]. The study duration ex-
tends beyond 56 days; however, the investigators did not
re-treat study dogs with fluralaner at day 56, as recom-
mended for control of this tick on the product label in
the USA [2] - the only country where this tick is included
on the product label. Therefore, the investigators did not
administer fluralaner (Bravecto, MSD Animal Health,
Madison, NJ, USA) according to product label recommen-
dations. This failure to follow label recommendations is
noted in the discussion, but is not recorded in the
abstract. In contrast, the comparative product sarolaner
(Simparica, Zoetis, Florham Park, NJ, USA) was adminis-
tered every 30 days throughout the study in accordance
with its USA label recommendations [3].
The comparative results for the efficacy of the two
treatments should only be presented during the period
of the study when the products were used as recom-
mended. Therefore, any comparative results beyond day
42 in this study (the last assessment point before the
8 week mark) are not based on the recommended use.
Comparative results at 58 days post-administration were
assessed at 2 days beyond the recommended fluralaner
re-administration date, 48 hours after fluralaner shouldCorrespondence: robert.armstrong@merck.com
MSD Animal Health, 2 Giralda Farms, Madison, NJ 07940, USA
© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Armstrong Parasites & Vectors  (2017) 10:159 
DOI 10.1186/s13071-017-2100-1
have been re-administered if the label recommendations
were followed.
The results presented in the paper [1] show that all re-
ported efficacies between the treatments are not signifi-
cantly different until 42 days post-administration (except
for a marginal significance of P = 0.044 at 12 h on day 0).
At the 42 day time point both treatments had a low effi-
cacy, and the authors report in the discussion that that the
reason for this is unknown and may relate to a prolonged
time between tick infestation and onset of tick feeding [1].
Therefore, it is quite possible that the reported difference
at this time point is associated with a methodological
problem.
The only conclusion presented in the paper that follows
from the study objective of comparing the efficacy of
fluralaner and sarolaner is that a difference is apparent
from day 42 and later [1]. However, as shown above, the
results at day 42 are associated with a methodological
problem, and the comparisons beyond 42 days are
assessed at a time when fluralaner use would not be as
recommended on the product label. Therefore, the only
comparative conclusion reached in the paper is not based
on correct administration of fluralaner.
Furthermore, a number of one-sided statements are
presented in the paper regarding tick-borne pathogen
transmission, e.g. “the consistent efficacy of a single oral
dose of sarolaner shown in this study should help to re-
duce the risk of a treated dog on a monthly treatment
regime becoming infected with the pathogens transmit-
ted by A. americanum” [1]. These one-sided statements
are inappropriate because the results presented do not
show a difference between the products when used as
recommended.
Acknowledgments
The author acknowledges the support of colleagues in research, technical
services and legal counsel in reviewing the text of the letter.
Competing interests
Rob Armstrong is an employee of MSD Animal Health.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
Received: 26 August 2016 Accepted: 20 March 2017
References
1. Six RH, Young DR, Myers MR, Mahabir SP. Comparative speed of kill of
sarolaner (Simparica™ Chewables) and fluralaner (Bravecto®) against induced
infestations of Amblyomma americanum on dogs. Parasit Vectors. 2016;9:399.
2. FDA, FOI. NADA 141–426. BRAVECTO. http://www.fda.gov/downloads/
animalveterinary/products/approvedanimaldrugproducts/
foiadrugsummaries/ucm399075.pdf. Accessed 20 Aug 2016.
3. FDA, FOI. NADA 141–452. SIMPARICA. http://www.fda.gov/downloads/
AnimalVeterinary/Products/ApprovedAnimalDrugProducts/
FOIADrugSummaries/UCM488816.pdf. Accessed 23 Aug 2016.
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The conclusion of a comparative efficacy study of fluralaner and sarolaner against the tick Amblyomma americanum on dogs is based on results obtained at study times that are outside the fluralaner label recommendations

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