Not a lot of people know that some veterinary drugs can be shed by your pet in their saliva, urine, through the skin onto their fur, and by careless handling of the product itself. Once absorbed by you, it could interfere with your physiology, and/or other in-contact pets. Potential effects include hormonal balance, neurological function, or immune response, especially in vulnerable people like children, pregnant women, or those with chronic illness or immune suppression.
In rare cases it can be fatal, although such drugs are often restricted to use by a veterinarian only.
One such dangerous drug, now rarely used by veterinarians when tranquilising large animals and wild animals, is called Immobilon. One drop contamination from a dart can cause respiratory and heart failure resulting in death unless the antidote is given immediately. The antidote was usually drawn up ready just in case, and someone else there was briefed on where it was and what to do in an emergency….
The Liverpool Cream for horse sarcoids is a mixture of strychnine and arsenic! Veterinarians only administer it wearing 2 pairs of gloves – to be sure, to be sure!! The treated sarcoid is covered by a dressing to prevent contact, but dressings can fall off or be pulled off too, so beware if this product is ever used on one of your horses.
It probably doesn’t even occur to most owners that certain commonly prescribed medications can have effects on human health. After all, it’s been prescribed for their dog/cat/horse and not a person.
Whatever is prescribed for your animals by a veterinarian, always ask if there are any handling precautions and/or potential dangers to family members – both humans and other animals. Veterinarians are just as capable as anybody else of being distracted and forgetting to tell you, or he/she thinks they have already when they haven’t. You can never go wrong by asking and clarifying what a risk might be and what to look out for if it happens. It might be only relevant to pregnant women, but you still should know because you don’t know who you might meet up with.
Here’s a brief rundown of what you need to know for the most commonly prescribed vet meds that might be encountered.
1. Hormone-Based Medications
These are often given to manipulate heat timing or if there has just been an unplanned mating. They can also be used to treat an open pyometra medically rather than surgically.
Sometimes post-spay, bitches can become urinary incontinent to varying degrees. Giving an oestrogen can sometimes help improve this.
They can be shed via saliva, urine, skin, and grooming behaviours. Clearly, the larger the breed of dog, the bigger the dose given and the more recently it’s been administered, the greater the risk, but there are potential consequences which include hormonal imbalances, early puberty in children, gynecomastia in men, menstrual disturbances and potential miscarriage in pregnancy.
⚠️ Case reports have linked transdermal oestrogen exposure to breast development in young boys and menstrual disruption in women (FDA, 2010).
Precautions: Don’t cuddle pets just treated with hormonal meds. Gloves are a must when handling urine or cleaning up accidents, at least in the immediate day or 2 post administration, but check to see the duration of action in case it should be for longer.
2. Chemotherapy Agents
I’m not a fan of treating a toxic condition by increasing toxicity but if used then drugs such as cyclophosphamide, chlorambucil, vincristine and doxorubicin can be shed through vomit, urine, faeces, and saliva for up to 72 hours after dosing.
The risk to humans is as for humans treated with these drugs but to a lesser dose-dependent degree, including bone marrow suppression, cancer, birth defects, skin irritation or ulceration on contact
According to the American Veterinary Medical Association, even trace contact from pet waste can expose owners to cytotoxic compounds.
Precautions: Use gloves for litter changes, walk clean-ups, or laundry for chemo-treated pets. Designate a “no snuggle zone” for at least 3 days after administration.
3. Antibiotics and Resistance Risk
We tend to think of antibiotics as life-saving and therefore safe, but there are some that require careful handling. These include cefovecin, a long-acting injectable antibiotic, enrofloxacin (Baytril) and clindamycin. Beware accidental injection or needle injuries!
They are shed through saliva, faeces, and skin and can cause allergic reactions, microbiome disruption, and more generally will accelerate the development of antimicrobial-resistant organisms (e.g. MRSA, MRSP) in the home. A 2019 study found that pets treated with long-acting antibiotics like cefovecin can carry and shed resistant bacteria for weeks, potentially colonising the human family they live with.
Precautions: Use narrow-spectrum antibiotics when possible. Wash hands after handling pet saliva or picking up poo. I don’t encourage it anyway, but avoid letting your pet lick you on the mouth especially of they are on meds!
4. Topical Parasite Treatments
I have covered the dangers of the various spot-on parasite treatments in past articles, but they deserve a mention and inclusion as a reminder. These are probably the most likely medications that people inadvertently but routinely expose themselves to. The most common ones are listed below.
Advocate (imidacloprid + moxidectin)
Stronghold (selamectin)
Frontline (fipronil)
They are shed through skin and onto the fur for days after application. If you consider that the first spot-on products were originally licensed to be used every 3 months, but then shortened to monthly as fleas became more resistant to them, you can see how long these chemicals really continue to be secreted post application. They are distributed throughout the body so that everywhere is protected, although the highest concentration will be at the point of application soonest after administration.
They are primarily neurotoxins, so represent the greatest risk to infants and toddlers because of their smaller size and thinner skin. Symptoms include headaches, nausea, endocrine disruption (some ingredients mimic hormones) and even seizure risk in sensitive individuals, and or those already prone to seizures for whatever medical reason of their own.
A 2022 review in Toxics journal found that dermal exposure to fipronil has been linked to neurological effects and potential endocrine disruption in humans.
Precautions: Keep children especially away from recently treated pets. Apply spot-ons just before bedtime and wash hands after touching your pet’s fur for at least 48 hours post-treatment to minimise maximum exposure, although you must consider there will be some for at least 3 months post last application.
5. Biologics & Monoclonal Antibodies
I have discussed monoclonal antibodies recently for itchy dogs and a while back for arthritis, but are mentioned here for completeness.
Cytopoint (lokivetmab – anti-IL-31 antibody
Librela (bedinvetmab) - anti-NGF for osteoarthritis
The risk is potentially higher as they are biological products, although being injections the risk to owners is very low and possibly only theoretical. There is no firm data but are potentially shed via saliva or broken skin.
Theoretically, they could cause immune dysregulation, especially in those with autoimmune disease or on immunosuppressants, but there are no reports to date and have been relatively widely used and on the market for sufficiently long that there would be some evidence emerging.
Precautions: Caution is prudent by avoiding contact with open wounds or saliva for 24 hours post-injection, but risk remains minimal if at all at this point in time.
6. Thyroid Meds & Sedatives
There are various thyroid meds listed below as it’s a relatively common condition.
Methimazole (for hyperthyroid cats – transdermal or oral)
Levothyroxine (for dogs)
Buprenorphine (oral transmucosal pain relief in cats)
Phenobarbital, Diazepam
They are shed mostly via saliva and urine and directly from a cream if not handled properly. Symptoms include drowsiness or dizziness (if absorbed transdermally), thyroid hormone imbalance if prolonged exposure and potential drug interactions, especially in children or people on SSRIs or blood pressure meds.
In one reported case, an owner developed thyrotoxicosis after applying methimazole cream to a cat daily without gloves.
Precautions: Always wear gloves when handling and administering these drugs, especially transdermal ones!
7. Cushing’s Disease Medications
I’ve covered Cushing’s Disease in a recent article, but care needs to be taken when handling the following medications should you go down that route.
Trilostane (Vetoryl)
Trilostane is a 3β-hydroxysteroid dehydrogenase inhibitor that blocks adrenal cortisol production. It is usually administered orally in capsules once daily.
Shedding is primarily via urine and faeces, with possible saliva contamination. Be aware that powder from a broken capsules is especially dangerous and can cause
Reproductive toxicity – may interfere with hormone production.
Teratogenic potential for developing foetus, so pregnant women should absolutely avoid contact.
Endocrine disruption – adrenal suppression is what it’s designed to do on a dose dependent basis.
Skin irritation or allergic reactions possible.
⚠️ The Vetoryl datasheet clearly states:
“Women who are pregnant or intending to become pregnant should avoid handling the capsules.”
(Dechra Vetoryl SPC)
Precautions for owners:
Never open or crush capsules
Wash hands immediately after giving
Wear gloves when cleaning up urine or faeces
Dispose of pet waste carefully (especially in multi-pet or child-accessible homes)
Mitotane (Lysodren)
Mitotane is rarely used now but still prescribed in some severe cases or off-label. It is a cytotoxic drug that destroys the adrenal cortex (previously used in human cancer therapy).
There are some significant risks to humans as you might expect of a cancer drug, being carcinogenic and mutagenic. It is extremely hazardous if touched, inhaled, or accidentally ingested with adverse effects being linked to bone marrow suppression and liver damage.
It is shed in urine, faeces, and saliva for several days. There is a more direct risk from fine powder from tablets that can be inhaled or contaminate surfaces.
Precautions:
Use gloves, masks, and eye protection when handling.
Strict hygiene is required for anyone cleaning up after treated animals.
It is not recommended for use in households with young children or pregnant women, and in most cases, pets being administered it were often kept in a practice on an inpatient basis throughout the course of treatment.
8. mRNA
Thankfully, mRNA products have not (yet) been authorised for veterinary use in the UK, but as has been found with the COVID jabs in people, shedding of the mRNA itself, and protein it directs the body to produce must be considered highly probable, with all the risk this platform has been shown to have associated with it. I have covered this is a past article.
Large Animal Alert: Hidden Human Risk in Horse Drugs
It isn’t just pet owners who need to be careful about handling meds. Some equine medications pose serious health concerns for humans, particularly due to their potency and the forms in which they’re administered (powders, drenches, feed additives). A horse dose will naturally be a large amount, so drugs may be a more concentrated preparation than their dog/cat equivalent which makes an accidental contamination potentially more hazardous. There are some specific horse meds to be aware of.
Pergolide (Prascend) – for Equine Cushing’s (PPID)
Pergolide is a dopamine receptor agonist used to reduce ACTH secretion. Owners can be contaminated by a number of possible routes, depending on what they might have to do to the tablets to get their horse to take them. If you have to powder the tablets to hide them in the food, then there is a risk from inhalation of crushed tablets or powder. Washing out food bowls afterwards might be overlooked but will be contaminated by residues and saliva. Ditto water buckets. If you have to make up a solution to drench your horse, you might get more than you intended too if/when they move their head or spit it out at the wrong moment!
Symptoms to be aware of include dizziness, nausea, impulse control disorders (seen in Parkinson’s patients on dopamine agonists), hormonal disruption (due to prolactin suppression), and cardiac fibrosis (pergolide was withdrawn from human use because of this in 2007). Pergolide crosses the blood-brain barrier and may impact the neurological and/or endocrine systems, especially in sensitive individuals.
Precautions:
Always wear gloves.
Avoid inhaling powder when preparing feed.
Wash hands after contact.
Pregnant or breastfeeding women should avoid handling pergolide altogether.
Natural Treatments
There is often an assumption that natural products are automatically safe, and whilst in many cases this is true, it isn’t the full story. Remember Samuel Hahnemann developed homeopathy because of the toxic reactions he’d seen from herbal preparations. Herbs and essential oils are by definition the most concentrated active compounds and quality can vary between different preparations of supposedly the same product. The root and leaf of the same plant can have very different concentrations and properties, so best take advise ONLY from those who are qualified rather than some random person off Facebook, who I have no doubt has good intentions.
I won’t go into all the potential hazards from all the different essential oils such as Tea Tree, Peppermint, Eucalyptus etc. As with Pharma, children are potentially at the greatest risk because of the dose relative to their size and the fact that they’re growing. Essential Oils are chosen for their biological and physiological effect, but it must be the right one in the right circumstance. For example, tea tee oil and lavender can have endocrine disruption effects. Toxicity is more likely from accidental spillage or “play” than from contamination from pets, but owners should be aware of what they have and how accessible to small hands it might be.
Herbal tinctures are naturally concentrated preparations of potent herbs such as Valerian, Arnica, Comfrey, Goldenseal, etc. In the right dose they’re great, but bear in mind that these are similar classes of anti-nutrients in plants that we avoid consuming for carnivores because of their adverse effects. They don’t have to kill in an instant like yew or hemlock, but over time they can compromise function if included chronically or at the wrong dose rate.
Special Populations to Protect
Certain people are much more vulnerable to the risks associated with drug shedding:
Babies/children: simply because of their smaller body weight, the dosage for the same absolute amount shed will be higher compared with an adult. Where the risks are to DNA, the fact that growing individuals have more dividing cells makes shedding potentially more hazardous.
Pregnant women: foetal sensitivity to hormones and toxins, especially in the first trimester.
Elderly or immunocompromised: less detoxification ability
People on other meds: higher risk of drug interactions or immune effects
Summary
Although I’ve highlighted certain better known risks, it is safer to assume that all foreign products administered to your pet have the potential to impact you and/or your family and those in-contact with your pet. It is better to be safe than sorry, and whilst I’m not advocating you dress up in a Hazmat suit when giving any meds to your pet, it makes sense to check out what you’re giving and determine any risks before handling the products and/or giving them to your pet, especially when the risks can be protracted as happens with the spot-on anti-parasitic drugs that are designed to be shed for months.
If having identified a hazard you need to take precautions, they are likely to be relatively simple. The more dangerous situations are usually covered by your veterinarian so as not to put the public at risk. So, we don’t need to avoid treatment, but we do need to handle meds wisely, which goes for human meds too. Understand the risks, and educate all in-contacts, especially children who might not think about what a cuddle after chemo or a head rub post-spot-on could really mean.
References: Pharmaceutical Drug Risks
1. FDA. (2010). Public Health Advisory: Information for Patients and Providers on Estrogen and Testosterone Gels. U.S. Food and Drug Administration.
https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/public-health-advisory-information-estrogen-and-testosterone-gels
2. Dechra Veterinary Products. (2023). Vetoryl 10–120 mg Capsules – SPC Summary. Veterinary Medicines Directorate (UK).
https://www.vmd.defra.gov.uk/productinformationdatabase/
3. AVMA. (2020). Chemotherapy Drugs at Home: Guidance for Pet Owners. American Veterinary Medical Association.
https://www.avma.org/resources-tools/animal-health-and-welfare/chemotherapy-home
4. Gómez-Poveda, B., & Vigo, E. (2019). Antibiotic resistance genes in pet animals: implications for human health. Frontiers in Microbiology, 10, 548.
https://www.frontiersin.org/articles/10.3389/fmicb.2019.00548/full
5. Giorgini, E., et al. (2022). Neurotoxic and endocrine effects of fipronil and imidacloprid in mammals: A review. Toxics, 10(4), 188.
https://www.mdpi.com/2305-6304/10/4/188
6. Dale, E., & Jarvis, S. (2007). Hyperthyroidism in a veterinary caregiver applying methimazole to a cat. Journal of Veterinary Internal Medicine.
https://pubmed.ncbi.nlm.nih.gov/17685659/
7. FDA. (2007). FDA Announces Market Withdrawal of Pergolide Products Used to Treat Parkinson’s Disease. U.S. Food and Drug Administration.
https://www.fda.gov/news-events/press-announcements/fda-announces-market-withdrawal-pergolide-products
References: Natural Remedies & Essential Oils
8. Beaumont, S. E., et al. (2013). Essential oil exposures in children: cause for concern. Clinical Toxicology, 51(9), 833–838.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3612440/
9. Henley, D. V., Lipson, N., Korach, K. S., & Bloch, C. A. (2007). Prepubertal gynecomastia linked to lavender and tea tree oils. New England Journal of Medicine, 356(5), 479–485.
https://www.nejm.org/doi/full/10.1056/NEJMoa064725
10. Health Canada. (2004). Health Canada advisory on comfrey-containing products. Government of Canada – Natural Health Products.
Archived link: https://www.canada.ca/en/health-canada/services/drugs-health-products/natural-non-prescription.html
11. Wynn, S. G., & Fougere, B. J. (2007). Veterinary Herbal Medicine. Mosby Elsevier.
(Referenced for valerian, skullcap, goldenseal, and other herbal safety profiles)
12. Upton, R. (2001). Goldenseal Root: Hydrastis canadensis – Herbal Review. American Herbal Pharmacopoeia.
(Summarises risks of berberine, neurotoxicity, and contraindications in pregnancy)
Thanks for this useful article, Roger. Crikey, all the more reason to keep my pup away from the vet if at all possible! Thankfully, so far she's a happy, healthy soul.