There are more than 5,000 approved prescription and over-the-counter medications with labeled indications for veterinary patients. And a number of those products pose a health hazard to humans.

Those hazards range from mild to life-threatening and include bronchospasm, central nervous system stimulation, induction of miscarriage, and sudden death, according to the 2009 paper "Human Health Hazards of Veterinary Medications: Information for Emergency Departments."

“[But] not all of those drugs will be found in every single v­­et practice,” lead author Elaine Blythe, PharmD, told NEWStat. Some are more common in a small animal practice, some are more common in production animal medicine, and some are exclusive to exotic and wildlife practices.

Blythe, an associate professor of veterinary pharmacology at the St. Matthews University School of Veterinary Medicine, Grand Cayman Island, BWI, and an adjunct professor at the University of Florida College of Pharmacy, wrote the paper to inform and support emergency room personnel, drug information centers, and poison control centers on veterinary medication hazards to humans, but she told NEWStat many people in the veterinary profession are unfamiliar with the human hazards those medications may pose—both to themselves and to others.

Carfentanil: The original “elephant tranquilizer”

“Carfentanil was the first drug from the veterinary side to really make a big splash in the [public consciousness,]” she said. But that was nearly two decades ago. “Now xylazine is at the top of the list.”

A synthetic opioid roughly 10,000 times more potent than morphine, carfentanil was used by wildlife veterinarians as a sedative agent for elephants and other large mammals. Although no longer manufactured due to human health concerns, carfentanil was still commercially available when Blythe wrote that paper.

It was taken off the market after the US Food and Drug Administration (FDA) discovered that drug cartels were putting it in heroin.

“They were calling it the elephant tranquilizer,” Blythe said. “It’s incredibly lethal.” She said carfentanil has no place in human medicine. “Never has, never will.”

“Even the [cartels] have backed off using it because it was killing off their customer base.”

When carfentanil became unavailable, Blythe said wildlife veterinarians turned to two primary alternatives: thiafentanil and etorphine. Both are anywhere from 3,000 to 5000 times more potent than morphine, and both pose a potential hazard to humans who work with them.

She said human ERs close to the areas where those drugs are being used by wildlife veterinarians—such as wildlife parks or zoos—should be apprised of the dangers.

“Ideally, the ER personnel there will at least have known of these drugs. [And] exotic wildlife practitioners would be the only subset of veterinarians who would use them,” she added. “If you need to take down a buffalo, giraffe, rhinoceros, or elephant, you’re going to use ultra-potent opioids.”

The risk to humans? “They’re very lipophilic, so if you get an accidental spray or you’re downwind of a dart that maybe popped out of an animal and you get that spray in your face, you can get enough absorbed across mucous membranes to cause respiratory depression or ev­en death.”

“Never work alone with these drugs and always have the antidote to hand,” Blythe warned. “Not just for the animal, but for any human who might get exposed; have that antidote drawn up and ready.”

Clenbuterol: an “urban myth” weight loss drug

Frequently used for horses who have reactive airway disease, clenbuterol has effects similar to anabolic steroids and is not approved for use in humans in the US, but some athletes and bodybuilders use clenbuterol to help them reach their fitness goals.

“It’s not so much performance enhancing as it’s been seen as a ‘weight loss bullet,’ which it is not,” Blythe said. “That’s an urban myth.”

“Athletes have figured out since clenbuterol is not prescription, they can buy them from catalog outlets or order them online,” she said.

Clenbuterol contains both testosterone and estrogen. And online tutorials will tell you how to separate out the estrogen component. But as Blythe points out, these are athletes, not pharmaceutical chemists: “They can’t fully separate out the testosterone component from the estrogen component, so they’re typically self-injecting a fair amount of estrogen.”

They can develop gynecomastia, an overdevelopment or enlargement of the breast tissue in men or boys. “It’s very unsafe. It’s very unhealthy.”

So what’s the attraction? Clenbuterol’s repartitioning effect, according to Blythe: Imagine you could eat all the coconut cream pie wanted and your body stored it as muscle instead of fat, said Blythe. “That’s why people abused it.”

And because it’s a beta agonist, it increases all functions of the heart. “It’ll go 150 miles an hour,” Blythe said. “These people presented to the ER as if they were having a heart attack.” 

Micotil: Accidental injection can mimic heart attack

An antimicrobial used in treatment of Bovine Respiratory Disease (BRD), Micotil is an injectable form of tilmicosin. “At the time I wrote that article there were about 28 reported deaths in the United States from that drug; about half were accidental . . . It’s quite cardiotoxic.”  

She said many vets won’t use Micotil anymore due to the extreme human health hazards, and they don’t have to because we have newer and safer drugs from that same category of antimicrobials.

Nevertheless, she knows a number of vets who still choose to use Micotil because it’s less expensive, but they will make the client sign an additional document that says something along the lines of, “I’ve told you this can be hazardous, don’t use it with automatic syringes.”

“If you accidentally inject yourself,” Blythe said, “you need to get yourself to an emergency department immediately and tell the physician what you have been exposed to, because most ER docs will not recognize Micotil and won’t know what it’s for.”

Which means they won’t recognize the hazard. “More importantly, if you just present to an ER saying, ‘I think I’m having a heart attack,’ the physician might go ahead and treat it like it’s a myocardial infarction, and that will actually make it worse.” 

Chloramphenicol: Gloves and a respirator required

Chloramphenicol works by killing bacteria or preventing their growth. Blythe called it an old antibiotic that has seen a resurgence.

“We kicked it to the curb back in the 1970s because of a human health hazard,” Blythe said. “Some people who ate chloramphenicol-tainted liver from cattle got aplastic anemia. It happened more often in Europe because they eat more organ meat than we do here in the US.”

But the FDA took note and decided the risk to humans was too great, so they completely pulled the injectable cattle formulations off the market. And while the oral formulations were still available, Blythe said the FDA’s actions made most large animal veterinarians leery of using them.

Blythe said that chloramphenicol has seen a resurgence because it’s pretty good for certain types of infections like MRSA and pyoderma: “Vets might use it to treat salmonella infections in reptiles—that is also another very common use of this drug.”

Blythe tells her students to glove-up and wear a respirator when handling chloramphenicol.

“Don’t breathe in any of those particles from the tablet. And if you send it home with a pet owner, you better educate them that this is a human health hazard. Give them gloves; give them a respirator,” she said.

Other veterinary drugs with potential human health hazards

• Ketamine  is a short-acting anesthetic developed to help people and pets during surgery, but it commonly turns up on the street for recreational use.

"There are vet formulations of ketamine, there are human formulations of ketamine,” Blythe said. “The veterinary formulations are 10 times stronger than the human formulations. And, of course, if you’ve got a vet drug formulated for a 1,200-pound horse, and you’re using it in a 100-pound woman, the risk for toxicity is pretty severe.”

• Xylazine  is a nonopioid veterinary sedative not approved for human use that has been linked to an increasing number of overdose deaths nationwide. Studies show people exposed to xylazine often knowingly or unknowingly used it in combination with other drugs, particularly fentanyl.

“It has pretty good sedative effects,” Blythe said. “Just in past year or two, we’re seeing veterinary xylazine being incorporated into virtually all illicit drugs.”

• Fentanyl  is an opiate narcotic medication that is used by veterinarians in general anesthesia and to treat animal patients suffering from moderate to severe pain. It also can be used as a sedative in some animal patients. Blythe said that fentanyl, like xylazine, is being incorporated into virtually every street drug.

“Whether you mix it with marijuana, heroin, crack, or methamphetamines, it’s going to increase some of the depressant effects of whatever it’s mixed with.”  She said that both xylazine and fentanyl are in “everything these days. Everything.”  

One difference between the two? Fentanyl is a scheduled (controlled) drug. Xylazine, although a prescription drug, is not—but this may change. Ohio’s governor just signed an emergency bill making xylazine a Schedule III controlled substance, effective immediately. Blythe said the DEA is aware that vet-label xylazine is being mixed into street drugs, but they’re refraining at this point in time from elevating it to a scheduled drug because most of the xylazine used by dealers is not the vet-label xylazine; it’s black market xylazine being shipped from overseas or manufactured by the cartels themselves.

“FDA-labeled xylazine still has legitimate uses, so we’re not going to restrict it, but we are aware that illicit forms are being mixed into all street drugs these days.” But it’s still a drug of abuse, Blythe warns, “So watch your inventory.” 

• Misoprostol  is used in equine reproduction. In human medicine, it’s used to prevent stomach ulcers while taking NSAIDS such as aspirin, ibuprofen, and naproxen, especially if you’re at risk for developing ulcers or have a history of ulcers. Vets will use the same drug for the same reasons in dogs.  

The human hazard? “It’s an abortifacient,” Blythe said, meaning it’s a drug used in combination with another drug called mifepristone to terminate a pregnancy in humans. Misoprostol can cause birth defects, premature birth, uterine rupture, miscarriage, or incomplete miscarriage and dangerous uterine bleeding. 

Blythe said veterinary staff must be very vigilant when dealing with misoprostol: “If you are pregnant, or trying to become pregnant, don’t touch it, don’t dispense it, do not clean up after a dog for whom that has been administered.”  

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The bottom line, said Blythe, is that veterinary staff need to be aware of the potential hazards of veterinary drugs to humans. Our job is to care for our animal patients, but at the same time, “You’ve got to protect human health.” 

Tony McReynolds is a temporarily petless freelance writer who lives near a dog park in Lafayette, Colorado. He dreams of one day owning a Newfie who isn't afraid of water (which the last one was, and seriously, how is that even possible?).           

Photo credit: ©  Elena Brovko   E+ via Getty Images Plus   

Disclaimer: The views expressed, and topics discussed, in any NEWStat column or article are intended to inform, educate, or entertain, and do not represent an official position by the American Animal Hospital Association (AAHA) or its Board of Directors.