Today I received an email from Zoetis (formerly Pfizer), promoting the company’s newly approved flea/tick preventive called Simparica. This medication contains the chemical sarolaner, which is closely related to the drugs afoxolaner (Nexgard) and fluralaner (Bravecto). I’ve spent countless hours on my blog responding to comments about Nexgard and Bravecto after I posted about them in November 2014. It is no surprise to me that Zoetis has jumped on this bandwagon. Here’s the lowdown on Simparica, based on the company-provided product insert.
Which Dogs Can Take It?
Dogs must be at least 6 months of age, weighing at least 2.8 pounds. Zoetis has NOT evaluated the use of Simparica in breeding, pregnant, or lactating dogs.
How Do I Give It?
Simparica is given by mouth once a month, with or without food. Chewables are flavored and available in six dosages based on body weight.
What Does It Work Against?
Fleas (Ctenocephalides felis), and
Ticks: American Dog tick (Dermacentor variabilis); Lone Star tick (Amblyomma americanum); Brown Dog tick (Rhipicephalus sanguineus); and Gulf Coast tick (Amblyomma maculatum)
Simparica does NOT repel fleas and ticks. In order for them to be exposed to the chemical, they must bite your dog. According to the email I received today, Simparica starts killing ticks in 8 hours and is >96.9% effective for 35 days against weekly reinfestations of the above named ticks. Simparica starts killing fleas within 3 hours and reduced the number of live fleas by >96.2% within 8 hours after flea infestation through Day 35. Note that these numbers are based on well-controlled laboratory studies.
How Does It Work?
Sarolaner is a chemical in the isoxazoline group, which inhibits the function of the neurotransmitter gamma aminobutyric acid (GABA) receptor and glutamate receptor in insects (fleas) and acarines (ticks). This leads to uncontrolled neuromuscular activity leading to death.
Is It Safe?
Precaution statement: “Simparica may cause abnormal neurologic signs such as tremors, decreased conscious proprioception, ataxia, decreased or absent menace, and/or seizures.”
The US field study included 479 dogs (315 dogs received Simparica and 164 dogs received an active control once monthly for three months). The top adverse reactions were vomiting (0.95%), diarrhea (0.63%), and lethargy (0.32%). One female dog age 8 years was lethargic, ataxic while trying to urinate, had elevated third eyelids, and had loss of appetite one day after taking both Simparica and a heartworm preventative containing ivermectin and pyrantel pamoate.
The margin of safety study included 8-week old Beagle puppies, who received doses of 0, 1x, 3x, and 5x the recommended maximum dose at 28-day intervals for 10 doses (8 dogs per group). The “0” dose group received a placebo. No neurologic signs were seen in the 1x group. Three pups exhibited tremors in the 3x group. In the 5x group, one pup had a seizure on Day 61; one pup had tremors on Day 0 and head incoordination on Day 140; and one pup had seizures after Doses 2 and 4 and tremors after Dose 2 and 3.
FURTHER INVESTIGATION NEEDED!!
I am astounded to read the final paragraph under Animal Safety on the product insert. I’ve included it word-for-word below. For me, these are simply the most intriguing four sentences I have read ALL YEAR.
Because I believe whatever happened in this dog is the VERY process that is occurring in all of the dogs who’ve experienced side effects with Bravecto and Nexgard. Some of these dogs have died. We must determine what is happening here!
“In a separate exploratory pharmacokinetic study, one female dog dosed at 12 mg/kg (3X the maximum recommended dose) exhibited lethargy, anorexia, and multiple neurological signs including ataxia, tremors, disorientation, hypersalivation, diminished proprioception, and absent menace, approximately 2 days after a third monthly dose. The dog was not treated, and was ultimately euthanized. The first two doses resulted in plasma concentrations that were consistent with those of the other dogs in the treatment group. Starting at 7 hours after the third dose, there was a rapid 2.5 fold increase in plasma concentrations within 41 hours, resulting in a Cmax more than 7-fold higher than the mean Cmax at the maximum recommended use dose. No cause for the sudden increase in sarolaner plasma concentrations was identified.“