Many more Americans may be getting opioids for their pets, and veterinarians appear to be prescribing increasingly potent versions of these drugs to animals, a small study suggests.

The researchers examined data on opioid tablets and patches dispensed or prescribed by 134 veterinarians at an academic small-animal hospital in Philadelphia from 2007 to 2017. Over the decade, the amount of opioids used for creatures like rabbits, birds and reptiles surged 41 percent even though visits to the hospital increased by only 13 percent.

"We have no way of knowing if any of these prescriptions were obtained by pet owners for themselves, and most were likely not," said senior study author Dr. Jeanmarie Perrone, a toxicologist with the emergency medicine department at the Perelman School of Medicine at the University of Pennsylvania in Philadelphia.

"However, the risk to humans is that leftover opioid prescriptions to animals end up in the same medicine cabinets as leftover opioids for people, leading to opportunities for misuse by teenagers or unintentional exposures in children that can be lethal," Perrone said by email.

The study included 366,468 pet visits to the animal hospital. During these visits, veterinarians prescribed a total of 105.2 million tablets of tramadol, more than 97,000 tablets of hydrocodone, almost 39,000 tablets of codeine and 3,153 fentanyl patches.

Most were for dogs

Dogs got the most drugs, accounting for 73 percent of these prescriptions, followed by cats at 22.5 percent and exotic animals at 4.5 percent.

A major factor contributing to the growing opioid crisis in the U.S. is the increasing availability of these drugs, which addicts often get from friends or relatives when they aren't able to obtain a prescription, researchers note in JAMA Network Open.

Although medical and dental health providers are the biggest source of these opioids, the current study suggests that veterinary prescriptions may also be part of the problem, they write.

Veterinarians and animal hospitals can be registered with the U.S. Drug Enforcement Administration, and in many states vets can prescribe, stock and dispense opioids without the same reporting requirements that are in place at many retail outlets.

Only 20 states require veterinarians to report opioid prescribing as medical doctors do to a registry designed to limit misuse, the study authors note.

Pennsylvania is one of many states without reporting requirements, and results from the study may reflect what happens in other states that lack registries to help curb abuse, Perrone said.

It's not clear if the increase in prescriptions in Pennsylvania might be due to an increased push to better manage pain for animals and pets, said Dr. Lee Newman, a researcher at the Colorado School of Public Health in Aurora, or if it is due to the growing number of people with substance abuse problems trying to get medications from veterinarians, or both.

Switch surmised

"It's speculation on my part, but it could be that when a human patient stops getting opioid prescriptions from their doctor that they next turn to the veterinarian to try to get drugs," Newman, who wasn't involved in the study, said by email.

While the study suggests that opioid prescribing from veterinarians represents only a small fraction of the overall opioid prescribing in the country, it also suggests that veterinary practices may be an overlooked part of the problem, said Kirk Evoy, an assistant professor in both the College of Pharmacy at the University of Texas at Austin, and at the School of Medicine at the University of Texas Health Science Center at San Antonio.

"This study brings to light that this is yet another potential source of access to opioids that many clinicians and policymakers may not be thinking about in their efforts to curtail the country's opioid abuse epidemic," Evoy, who wasn't

involved in the study, said by email.

"Furthermore, while human opioid prescribing has begun to level off in recent years in response to the opioid epidemic, this data seems to indicate that, at least in the specific hospital being studied, prescribing of opioids for animals has continued to climb," Evoy said.