Cats care

Drugs to Avoid in Cats : Human Medications That Are Dangerous to Cats

May 14, 2023

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Drugs to Avoid in Cats : Human Medications That Are Dangerous to Cats

It’s important to keep in mind that cats are not humans. Cats’ systems are exquisitely sensitive to a wide variety of medications, and they lack the enzymes necessary to effectively break down and eliminate many human drugs from their bodies. Cats are also not small dogs, and some medications that our canine companions can take safely are toxic to our feline friends.While veterinarians do use some human medications to treat animals, it’s important to remember that not all drugs meant to treat people are safe for cats, and even the ones that are may only be safe at extremely controlled doses. Their safety may also be affected by individual patient concerns such as age and concurrent illness.

Drugs are the modern world medicines for diseases that animals suffer from. While medicating cats, drugs are to be given only after being advised by veterinarians. As the cat is already suffering, care is to be taken to see that it further does not succumb to drug toxicity. As cats are lacking many drug conjugation pathways, they cannot metabolise certain drugs as other animals leading to slow metabolism and excretion of those drugs causing toxicities and other side effects. So, alternate therapeutic regimen or adjustment of dose of those drugs can be prescribed. The most accepted conjugation defect is reduced glucuronidation of phenolic drugs, such as acetaminophen and propofol. The drugs elimination mechanisms like conjugation, oxidation in cat vary from other animals like dogs and humans, and thus are excreted unchanged into the urine and/or bile. Drugs like aspirin, acetaminophen, propofol requiring metabolic conjugation, like glucuronidation, sulfation, glycination occur slower in cats. On the other hand piroxicam is eliminated more speedily in cats as it is metabolised by oxidation. This review aims to enlist all the drugs contraindicated in cats along with their side effects which can be of help to doctors, veterinarians as well as cat owners.

Mechanisms causing difference in metabolism in cats

Cats lack UDP-glucuronosyltransferase (UGT) enzymes like UGT1A6 and UGT1A9 responsible for glucuronidation of these drugs in other species. So, Slower carprofen clearance results from deficient glucuronidation and slower aspirin clearance occurs due to poor glycine conjugation. Cats are also deficient in N-acetyltransferase (NAT) enzymes specifically NAT2 which is responsible for N-acetylation conjugation pathways resulting in acetaminopheninduced methemoglobinemia. The deficiency of thiopurine methyltransferase (TPMT) responsible for S-methylation results in azathioprine toxicity. Drugs that are eliminated by oxidation have no changed effect in cats. Piroxicam is cleared more rapidly in cats than other animals and humans. The intensity of drug binding to plasma protein may also result in differences in highly bound drugs pharmacokinetic.

Molecular basis for difference of metabolism in cats

Since last few decades, this difference in metabolism and excretion of drugs in cats in comparison to other species has been studied. The deficiencies in 4 different types of drug elimination pathways are studied like § Glucuronidation (UGTS) § Acetylation (NATS) § Methylation (Thiopurine methyltransferase [TPMT]) § Active transport (ATP-binding cassette G2 [ABCG2])

UGT deficiency

Glucuronidation is the most important process of metabolism which transfers glucuronic acid to a variety of drugs, toxins, steroids and bilirubuin like endogenous compounds thus promoting better elimination of these compounds into urine and/or bile. The main sites of drug metabolism like liver, kidney, intestinal mucosa express UGT. The oldest broadly accepted idiosyncrasy of cat is deficient glucuronidation. Literatures as old as 60 years show inability of cat to glucuronidate drugs and toxins [18]. This deficiency in cat is not specific to all glucuronidated drugs but depends on structure of drug. It affects the simple planar phenolic structured drugs which are to be mainly metabolized by UGT1A1, essential for glucuronidation and clearance of bilirubin. UGT1A isoforms like UGT1A6 and UGT1A9 particularly found in liver. 10 different UGT1As are expressed in dogs liver, 9 different UGT1As are expressed in human liver but feline liver have only 2 isoforms (UGT1A1 and UGT1A2) and the UGT1A6 pseudogene. No UGT1A isoform related to UGT1A6 or UGT1A9 was expressed in cat liver. UGT1A6 gene identification by DNA sequencing proved multiple mutations suggesting a functional UGT1A6 gene present at one point in cats that had been permanently disabled in cat into a pseudogene [19]. Carnivore species(African lion, cheetah, leopard, tiger, leopard, margay, tigrina, lynx, golden cat, bobcat, puma, Florida panther, cat) showed UGT1A6 mutations which evolved them differently them from Carnivora species (wolves, bears, raccoon, ferret) between 11 and 35 million years ago. Drug like morphine is selectively glucuronidated in humans by UGT2B7 gene. Although Cats express feline orthologs of human UGT2B7 and UGT2B15, it shows reduced morphine glucuronidation which gets compensated by sulfation pathways clearance. Drug like lorazepam is selectively glucuronidated in humans by UGT2B15 gene but it is glucuronidated speedily in cats as feline ortholog of human UGT2B15 is expressed in cats [20] . Preservative like benzoic acid and Benzyl alcohol (is metabolized to benzoic acid) and excreted as the glucuronide or glycine conjugate in most species. Cats are unable to glucuronidate benzoic acid, but can glycinate it slowly. So, benzyl alcohol used in pharmaceutical preparations for cats are minimized.

Glycine deficiency

Drugs like aspirin have slow clearance in cats due to poor glycine conjugation.

NAT2 Deficiency

Drugs like isoniazid, many of the sulfonamide antibiotics like sulfamethazine, sulfanilamide, sulfadimethoxine, dapsone, hydralazine, procainamide, acetaminophen need to be acetylated for metabolism. N-Acetylation is catalyzed by the N-acetyltransferase enzymes NAT1 and NAT2. Cats liver lack NAT2, but express NAT1, thus show lower enzyme activity than other species [21]. So, these drugs are acetylated more slowly in cats showing toxicities in cats.

TPMT deficiency Drugs like 6-mercaptopurine for cancer and azathioprine for immunosuppression require S-Methylation by TPMT for metabolism and excretion. Less TPMT activity in cat erythrocytes involving gene sequence differences affect enzyme level and affinity for substrate and activity.
ABCG2 deficiency Drugs like Fluoroquinolone antibiotic use ABCG2 transporter for efflux. Due to inefficient efflux by ABCG2 transporter from the feline eye, temporary and subsequently permanent blindness develop in cats.

Further molecular level studies are needed to understand the differences in cats in drug metabolism and disposition. It will help in more rational prescribing of prevailing medications, and effective and safer drugs discovery and development for cats. Pet owners of cats should be made aware to avoid these medications either intentionally or accidentally.

Top 10 OTC & Prescription Medications Toxic to Cats

As an emergency critical care veterinary specialist and toxicologist, the top 10 OTC and prescription medications that I commonly see poisoning cats in the veterinary ER are:

Antidepressants (e.g., Effexor™)
Amphetamines (e.g., ADD/ADHD medications like Adderall™)
Ibuprofen (e.g., Advil™, Motrin™)
Naproxen (e.g., Aleve™)
Aspirin
Acetaminophen (e.g., Tylenol™)
Triple antibiotic ointment (e.g., Neosporin™)
Topical creams (e.g., estrogen creams, diaper rash creams, etc.)
Bismuth subsalicylate (e.g., Pepto-Bismol™)
Chewable veterinary NSAIDs (e.g., Rimadyl™, Deramaxx™)

How Can You Protect Your Cat?

Being aware that human medications can have potentially devastating effects when eaten by a cat is the first step in protecting your feline friend. Next, follow these guidelines to provide further safety:

Always keep all medications in a secure area that your cat can’t access.
Don’t keep your medications in secondary containers that are easily tampered with such as plastic baggies.
When you are taking your medication, use extreme care to ensure that you don’t drop any pills or capsules on the floor. Consider making a habit of always opening your bottles while leaning over a sink or counter so it is more obvious to you when you have dropped one.
When you have visitors, make sure they understand how toxic human medications are to cats. Ask them to keep any medications they have secured at all times.
Keep your pet’s prescribed medications in a different spot from your prescribed and over-the-counter medicines, so it will be less likely for you to mix them up when giving your cat her meds.
Never, ever give a human medication to your cat without checking with your veterinarian first. Do not rely on the internet or friends or family members who may have used a particular medication in their cat before. Your cat’s veterinarian is best suited to determine the risks of a particular medicine to your individual cat.