Three topical dermatologic medications and two classes of topical drugs used in humans are especially hazardous to pets exposed to these drugs, a scoping review found. Cats and dogs died in nearly a quarter of reported exposure cases.

The implicated drugs in 152 cases of pet poisonings (87 dogs and 65 cats) were vitamin D analogues in 37% of cases, 5-fluorouracil (5-FU) in 25.9%, minoxidil in 18.5%, estrogen in 14.8%, and corticosteroids in 3.7%, reported Nicole C. Pace, MD, assistant professor of dermatology at Geisel School of Medicine at Dartmouth, Hanover, New Hampshire, and colleagues in the Journal of the American Academy of Dermatology.

“Ultimately, all topical medications should be presumed to have the potential to be toxic to pets, and safety measures should be taken to avoid exposures,” they wrote.

Common symptoms in the pets after exposure included vomiting (44.1%), lethargy (36.2%), cardiac arrhythmias (28.9%), anorexia (17.7%), and seizures (17.1%). Pulmonary edema or pleural effusion was reported in 13.8%. Overall, 37 (24.3%) fatalities were reported, with especially high mortality rates linked to vitamin D analogues (56.3% of exposed dogs died), 5-FU (62.5% of exposed dogs died), and minoxidil (12.3% of exposed cats died).

“We were surprised that nearly a quarter of reported exposures resulted in death," co-author Natalie M. Fragoso, MD, assistant professor of dermatology at Geisel School of Medicine at Dartmouth, told Medscape Dermatology. “This may be due to a publication bias, but highlights the importance of this topic.”

The authors launched their review after hearing from two patients whose pets were exposed to a topical medication. Discussion of risk to pets “is not a routine part of counseling performed by dermatologists and providers when prescribing certain topical medications for patients,” Pace said in an interview. “We wanted to identify which medications had been reported to cause harm and how to help educate dermatologists, veterinarians, and other healthcare providers about the risks of potential exposures to pets.”

The review of 27 articles found that unintentional oral ingestion was the most common route of exposure in 50.7% of cases, followed by unintentional transdermal contact in 45.4%. “Exploratory behavior” in dogs — including rummaging through and chewing on medication containers — was a frequent cause of exposure. Cats were more likely to indirectly come into contact with medications by licking treated skin or via contaminated bedding.

In rarer cases, medications can be spilled onto pet fur or skin or onto surfaces that pets contact or are accidentally spilled onto pet fur or skin. Or the owner may apply the human topical medication directly onto the pet, often misguidedly.

The authors highlighted the following topical medications and formulations associated with the poisonings:

• 5-FU (5% cream). “Because 5-FU is cytotoxic to rapidly dividing cells, ingestion can damage gastrointestinal mucosa, bone marrow, liver, and the central nervous system,” Pace said.

• Vitamin D analogues (calcipotriene 0.005% cream, calcipotriene 0.005% ointment, maxacalcitol 0.0025% ointment, and tacalcitol 0.0004% ointment). “Because of their potent effects on calcium homeostasis, exposures may lead to hypercalcemia, renal injury, and cardiac effects,” Pace said.

• Minoxidil (5% solution and 5% foam). Because of its vasodilatory and cardiovascular effects (such as hypotension, tachycardia, arrhythmias, and pulmonary edema), “this can stress a small animal,” Pace said. In addition, “cats have a deficiency in the glucuronidation metabolic pathways through which minoxidil is metabolized, which likely leads to increased toxicity in cats compared to dogs,” Fragoso noted. “Dogs and cats have slower clearance and lower body weight, so doses that seem low in humans may be fatal in pets.”

• Estrogen (estradiol gel, cream, and spray). Ingesting estrogen at a concentration of 1 mg/kg or greater “can lead to bone marrow suppression and aplastic anemia,” Pace said. 

Earlier this year, a report presented at the annual meeting of the Society for Investigative Dermatology noted an increase in topical minoxidil poisoning reports to the American Society for the Prevention of Cruelty to Animals Animal Poison Control Center from 20 cases in 2013 to 213 cases in 2024.

Shari Lipner, MD, PhD, associate professor of clinical dermatology at Weill Cornell Medicine in New York City and a co-author of the minoxidil report, said the scoping review confirms “what veterinarians have been observing for many years.” She wasn’t involved in the current research.

In an interview, she noted that “cats and small dogs are particularly at risk because even trace amounts can be toxic.”

Lipner emphasized the severity of potential outcomes. “Depending on the drug and amount ingested, pets can suffer serious harm or death,” she said. “Pets can suffer vomiting, seizures, cardiac problems, or renal failure, sometimes within hours.”

As for treatment of exposures, Pace said that successful outcomes “will likely depend on how early the veterinarian is involved and how aggressive the care is. Many reported cases survived with intensive management, but fatalities still occurred.”

She added that “the rare use of advanced modalities — such as dialysis — suggests that for severe cases, conventional therapy may be insufficient. Many cases present late or with limited information, so treatments may be partly empirical.”

The study authors recommended that dermatologists talk to patients about the risks topical medications pose to pets.

Lipner agreed. “Asking if the patient has a pet should be a standard question on the new-patient intake form,” she said.

Lipner provides specific recommendations to patients. “I advise them to wash their hands after application, let treated areas dry or keep them covered, store products securely, and contact a veterinarian immediately if a pet licks or chews medication,” she said. “I also find putting this information on patient handouts helpful.”

Patients can also protect pets by applying products away from pet sleeping areas, avoiding pet contact with treated skin during absorption time, and ensuring proper disposal of applicators and containers, the authors of the review wrote. “If a patient reports a pet exposure or unexplained pet illness, encourage them to take the pet to a veterinarian immediately and bring the product bottle or label,” Fragoso said.

She cautioned that the “true incidence of such exposures is unknown. Many exposures likely go unreported because pet owners may not connect the signs and symptoms their pets are experiencing to a topical medication used by humans.”

Moving forward, she said, “Research is needed to better define safe thresholds, pharmacokinetics of topical agents in companion animals, species-specific sensitivity, and optimal treatments.”

No funding was reported. Fragoso disclosed having relationships with UCB, AbbVie, Amgen, Acelyrin, Boehringer Ingelheim, Insmed, Takeda Pharmaceuticals, and Target Derm. The other authors and Lipner reported having no disclosures.