Dogs that are bitten by ticks risk being infected by Borrelia burgdorferi, a bacterium that can cause Lyme Disease. The prevalence of Borrelia burgdorferi varies depending on the geographic region. Areas such as the northeastern United States can experience up to a 13.3% infection rate, compared to 1.4% in the American west.1
Ticks attach to a host and feast on its blood. The tick can then transmit the infection through its salivary glands 24 to 48 hours after its initial feeding. Most infected dogs will remain clinically stable. However, some may present with symptoms such as fever, anorexia, depression, lethargy, enlarged lymph nodes, and shifting leg lameness.1
On May 18, 2021, the FDA approved a label extension for the ectoparasiticide veterinary drug sarolaner (Simparica; Zoetis) to include the prevention of Borrelia burgdorferi. Sarolaner was already approved to treat and prevent flea infestations (Ctenocephalides felis) and for the treatment and control of tick infestations (Amblyomma americanum [lone star tick], Amblyomma maculatum [Gulf Coast tick], Dermacentor variabilis [American dog tick], Ixodes scapularis [black-legged tick], and Rhipicephalus sanguineus [brown dog tick]).2
Sarolaner’s new indications added prevention of Borrelia burgdorferi infections because of its ability to kill Ixodes scapularis vector ticks. These new indications are for dogs aged 6 months or older and weighing 2.8 pounds or more.2
The active ingredient in sarolaner is an acaricide and insecticide, meaning it is poisonous to mice, ticks, and insects. Sarolaner inhibits the GABA neurotransmitter receptor’s function and glutamate’s function. GABA blocking results in uncontrolled neuromuscular activity in acarines and insects, which ultimately causes their death. This medication is selectively toxic to fleas and ticks since their GABA receptors are more sensitive to sarolaner than mammalian GABA receptors are, making this drug safe for dogs.2
Sarolaner is given by mouth once a month.2 The recommended minimum dosage is 0.91mg/lb (2mg/kg).3
Sarolaner—a chewable tablet—can be given by hand or in food and it should be noted that the dog must consume the entire dose. After administration, owners should ensure the dog consumed the entire dose. If a dose is missed, owners should administer a dose and resume monthly dosing.
Sarolaner is not for use in humans or cats. It must be kept in a safe location away from animals and children to prevent accidental ingestion.3
Adverse effects observed in a well-controlled United States field study include vomiting, diarrhea, lethargy, tremors, decreased conscious proprioception, ataxia, decreased or absent menace, and/or seizures. Post-approval adverse drug events, listed in decreasing order of frequency include vomiting, tremors, lethargy, seizure, diarrhea (with and without blood), anorexia, ataxia, pruritus, hypersalivation, and hyperactivity.3
Two laboratory studies demonstrated that sarolaner can prevent Borrelia burgdorferi by killing the infected ticks before they can transmit the bacteria. This placebo-controlled study used 20 beagles. The researchers experimentally infested the dogs were with adult Ixodes scapularis ticks with 60% of them carrying Borrelia burgdorferi. Skin biopsies and blood samples were taken from the dogs to test if there were Borrelia burgdorferi antibodies present.2
At the end of the studies, sarolaner was found to be more than 96% effective at killing the infected ticks for 33 days. This medication was also 100% effective at preventing Borrelia burgdorferi infections by killing the ticks before they were able to transmit the infection to the dogs. The treated dogs tested negative for Borrelia burgdorferi in blood samples and PCR testing of the skin biopsies, compared to the untreated dogs who tested positive for both.2
Isabella L. Bean and Ryan Moriarty are 2022 PharmD candidates at the University of Connecticut in Storrs.
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