Study Results Show ACTIVYL® by Merck Animal Health Outperforms FRONTLINE® Plus


February 26, 2014 9:46 am ET

Eliminates More Than 99 Percent of Fleas: More Flea-Free Pets and Fewer Fleas in the Home

Merck Animal Health today released the results of a head-to-head research study that showed ACTIVYL® (indoxacarb) was more effective than  FRONTLINE® Plus (fipronil [s]-methoprene) in controlling flea populations on pets.1 ACTIVYL eliminated more than

99 percent of fleas on pets after two monthly applications versus a 54.8 percent reduction achieved by FRONTLINE Plus (p≤ 0.0079).1 At the end of the two-month study, nearly five times more pets treated with ACTIVYL were flea free, and ACTIVYL users found significantly fewer fleas in their homes.1

“The pets in this study had the largest natural flea burdens the investigators had ever seen and were under continual reinfestation pressure. The data clearly show that ACTIVYL was still able to effectively control the flea infestations,” said Kathleen Heaney, D.V.M., director of technical services for Merck Animal Health. “Following monthly treatments, pets treated with ACTIVYL saw a reduction in fleas of 95 percent at one month and 99.1 percent at two months. In contrast, pets treated monthly with FRONTLINE Plus saw a reduction of 49.5 percent at one month and a reduction of 54.8 percent at two months.”1

Flea control is critical to maintaining good pet health, as fleas can cause anemia and allergic dermatitis, and can also transmit bacteria and other parasites to dogs and cats.2 The success or failure of products for flea control depend on a product’s ability to suppress flea reproduction for the duration of the treatment period.3,4 A single female flea can lay up to 50 eggs per day.5

“When used as directed, ACTIVYL has been shown to kill fleas before they lay eggs for a full month and beyond,2 which means the product more effectively controlled flea reproduction, and as a result, there were significantly fewer fleas in homes where pets were treated with ACTIVYL,” said

Dr. Heaney. “This also meant a reduction in emerging flea populations. We are excited about the findings from this study, and it reinforces our confidence in the performance of ACTIVYL.”

Thirty-two dogs and three cats with natural flea infestations living in 18 homes were treated topically with a 19.53% w/w spot-on formulation of indoxacarb.1 Another 30 dogs and two cats living in 19 different homes were treated topically with either fipronil (9.8% w/w)/(s)-methoprene (8.89% w/w) or fipronil (9.8% w/w)/(s)-methoprene (11.8% w/w), respectively.1 Homes were randomly assigned to treatment. All products were applied according to label directions by study investigators on day 0 and again between days 28 and 30.1 Flea populations on pets were assessed using visual area counts and premise flea infestations were assessed using intermittent-light flea traps on days 0, 7, 14, 21, 28–30, 40–45, and 54–60.1

The research study, which took place last summer in Tampa, Fla., was conducted by Michael Dryden, D.V.M., Ph.D., Kansas State University, to evaluate and compare two spot-on topical flea products to control flea infestations on naturally infested dogs and cats: ACTIVYL by Merck Animal Health and FRONTLINE Plus by Merial. Read Dr. Dryden’s full study at: For more information about ACTIVYL, please visit

ACTIVYL® is a registered trademark of Merck Animal Health. FRONTLINE® Plus is a registered trademark of Merial. 

About Merck Animal Health

Today’s Merck is a global healthcare leader working to help the world be well. Merck Animal Health, known as MSD Animal Health outside the United States and Canada, is the global animal health business unit of Merck. Merck Animal Health offers veterinarians, farmers, pet owners and governments one of the widest range of veterinary pharmaceuticals, vaccines and health management solutions and services. Merck Animal Health is dedicated to preserving and improving the health, well-being and performance of animals. It invests extensively in dynamic and comprehensive R&D resources and a modern, global supply chain. Merck Animal Health is present in more than 50 countries, while its products are available in some 150 markets. For more information, visit


Merck forward-Looking Statement

This news release includes “forward-looking statements” within the meaning of the safe harbor provisions of the United States Private Securities Litigation Reform Act of 1995. These statements are based upon the current beliefs and expectations of Merck’s management and are subject to significant risks and uncertainties. If underlying assumptions prove inaccurate or risks or uncertainties materialize, actual results may differ materially from those set forth in the forward-looking statements.

Risks and uncertainties include but are not limited to, general industry conditions and competition; general economic factors, including interest rate and currency exchange rate fluctuations; the impact of pharmaceutical industry regulation and health care legislation in the United States and internationally; global trends toward health care cost containment; technological advances, new products and patents attained by competitors; challenges inherent in new product development, including obtaining regulatory approval; Merck’s ability to accurately predict future market conditions; manufacturing difficulties or delays; financial instability of international economies and sovereign risk; dependence on the effectiveness of Merck’s patents and other protections for innovative products; and the exposure to litigation, including patent litigation, and/or regulatory actions.

Merck undertakes no obligation to publicly update any forward-looking statement, whether as a result of new information, future events or otherwise. Additional factors that could cause results to differ materially from those described in the forward-looking statements can be found in Merck’s 2012 Annual Report on Form 10-K and the company’s other filings with the Securities and Exchange Commission (SEC) available at the SEC’s Internet site (


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1 Dryden MW, et al: Evaluation of indoxacarb and fipronil (s)-methoprene topical spot-on formulations to control flea populations in naturally infested dogs and cats in private residences in Tampa, FL. USA. Parasites & Vectors 2013, 6:366.

2 Dryden et al. Efficacy of indoxacarb applied to cats against the adult cat flea, Ctenocephalides felis, flea eggs and adult flea emergence Parasites & Vectors 2013, 6:126.

3 Dryden M, Carithers D, McBride A, Riggs B, Smith L, Davenport J, Smith V, Payne P, Gross S: A comparison of flea control measurement methods for tracking flea populations in highly infested private residences in Tampa FL, following topical treatment of pets with FRONTLINE® Plus (fipronil/(S)-methoprene). Intern J Appl Res Vet Med 2011, 9(4):356-567.

4 Dryden MW, Payne PA, Smith V, Riggs B, Davenport J, Kobuszewski D: Efficacy of dinotefuran–pyriproxyfen, dinotefuran–pyriproxyfen–permethrin and fipronil–(S)-methoprene topical spot-on formulations to control flea populations in naturally infested pets and private residences in Tampa, FL. Vet Parasitol 2011, 182:281–286.

5 Dryden, MW., D.V.M., Ph.D., and Shawn Dryden. “Flea Fact Sheet.” Dr. Flea: Dr. Michael Dryden.



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