The Food and Drug Administration on May 23 alerted dog owners and veterinarians about the risk of accidental overdose of dogs treated with the drug Sileo, a prescription gel given by mouth to treat noise aversion.
Sileo is packaged in an oral dosing syringe with a ring-stop mechanism on the plunger that must be "dialed" and locked into place to administer the correct dose. Since Zoetis began marketing Sileo in May 2016, the FDA has received 28 reports involving overdoses in dogs resulting from the ring-stop mechanism not properly locking at the intended dose. As of early June, the agency had not determined whether the overdoses resulted from improper use of the ring-stop.
FDA spokeswoman Lindsay Dashefsky told JAVMA, "We took this action because the risk of medication error and overdosage described in these reports may be reduced by greater awareness on the part of veterinarians and dog owners, particularly pertaining to the proper use of the oral dosing syringe.
"We also wanted to increase user awareness prior to the summer months when this product is more likely to be used."
In some cases, the entire contents of the dosing syringe were administered. In 15 of the 28 reports, dogs experienced clinical signs of overdose, including lethargy, sedation, sleepiness, slow heart rate, loss of consciousness, shallow or slow breathing, trouble breathing, impaired balance or incoordination, low blood pressure, and muscle tremors.
Zoetis spokeswoman Colleen White said in a statement that in those rare cases of overdose, clinical effects were temporary.
Dr. Sharon Campbell, Zoetis' companion animal medical lead for analgesia, sedation, anesthesia, and behavior, said Zoetis has stressed all along that the syringe is a novel way to deliver drugs but that clients must be shown how to lock the ring-stop.
"From our perspective, it's an end-user issue, not a mechanical failure," she said. "We have received syringes from overdose cases. We put them through a quality assurance evaluation and found they worked properly." She said thousands of dogs have been treated safely for noise aversion with Sileo.
The FDA and Zoetis encourage veterinary staff members to educate dog owners on operation of the syringe. The Sileo package gives step-by-step dosing instructions, and instructional videos are posted on the product website.