Dermatologists are being urged to consider warning patients about the toxic effects of topical minoxidil in pets in the wake of a study that has found a high hospital rate among cats and dogs exposed to the hair loss treatment.

Canadian researchers reviewed 94 cases of minoxidil exposure among cats (n = 68) and dogs (n = 26) reported in peer-review studies, finding that 97.8% of these cases resulted in hospitalisation and 14.7% of cats died.

Dogs were mostly exposed to the treatment through exploratory behaviours such as rummaging through rubbish, while cats were more likely to be exposed from human contact such as licking human skin or contaminated bedding.

Routes of minoxidil exposure included:

• Oral ingestion (70.2%)
• Dermal application (9.6%)
• Both oral ingestion and dermal application (20.2%)

Pets presented with symptoms such as hypothermia, hypotension, and tachypnea and were typically examined by a vet within hours of exposure.

The authors attributed cats’ increased vulnerability to toxicity to “lower body weight and deficient glucuronidation pathways to metabolise toxins”.

“Our findings highlight the importance of warning patients about the toxic effects of minoxidil in their pets, as even minimal exposure can be life-threatening,” they wrote in the Journal of the American Academy of Dermatology [link here].

“There is an urgent need for medical, veterinary and regulatory communities to reevaluate how pet-specific warning information about minoxidil is disseminated to the public.”

In a letter to the editor [link here], doctors from the dermatology department of Princess Alexandra Hospital in Brisbane said the report highlighted the under-recognised risk of topical minoxidil toxicosis in animals and was an important consideration for clinicians recommending the products.

However, they questioned the suggestion of oral minoxidil representing a safer alternative, noting that oral minoxidil was a significantly more potent agent.

They also pointed out that topical minoxidil formulations often contained additional ingredients such as propylene glycol, ethylene glycol and ethanol – that were independently toxic to cats and dogs, while off-label formulations might also include additional toxicity from tea tree oil, sodium hydroxide, or ethanolamines.

“The high rate of adverse events associated with inadvertent topical minoxidil in pets represents a call to action for researchers to further investigate the mechanism underlying minoxidil toxicosis and the factors that influence risk,” they said.