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Common Feline Toxicities

by Chelsea Sonius
Fall 2011


INTRODUCTION

A variety of household chemicals, human medications, plants, and even veterinary products marketed for dogs can be toxic to cats.  Further,cats are uniquely susceptible to a variety of toxins that other species are not.  The aim of this paper is to promote awareness of common toxins encountered by cats.  The first step in preventing intoxication is knowledge of the toxins that exist.  The author has chosen several toxins to elaborate on throughout this paper.  This is by all means not an all‐inclusive list.  If you would like further information regarding common feline toxicities, following this paper is a list of other commonly encountered feline poisons, along with links to the Animal Poison Control website. 

If you believe that your cat (or any other pet) has had exposure to a toxin, contact the Animal Poison Control immediately at (888) 426-4435 and seek immediate veterinary care.  For all of the toxins described, time is the most crucial factor in determining a successful outcome.

ACETAMINOPHEN

Toxicant Information: Acetaminophen is a commonly used human pain reliever and fever reducer.  It is the active ingredient of Tylenol and is also found in many other over the counter products targeedt for headache relief, menstrual aches, muscle aches, allergy relief, tooth pain, cold symptoms, sore throats, and as a general fever reducer.  There are MANY brands that contain this product, and all feline owners should be aware of what household medications may contain this drug.  A list of brands that carry acetaminophen can be found at this U.S. National Library of Medicine site.  Some of the more common American brands are provided below.  This list is by no means, all inclusive.  Many other drugs also contain acetaminophen.  For a list of medications containing this drug, please follow the link above.

The toxic dose of acetaminophen in cats has been reported to be 10 mg/kg (4.5 mg/lb).  The typical amount of acetaminophen in a Tylenol tablet is 352 mg.  This means that even a very small, partial amount of Tylenol ingestion (less than 1/10th of a tablet in some instances) can cause toxicity in the feline species.  Acetaminophen should NEVER be administered to cats and cats should never have access to drugs containing acetaminophen or bottles previously containing acetaminophen.

Mechanism of Toxicity:  Following administration or ingestion, acetaminophen is metabolized by the liver into a compound called N-acetyl-p-benzoquinone imine (NAPQI), a compound that can be toxic to cells in the body.  In humans with a normally functioning liver this compound then becomes conjugated/attached to a molecule called GSH to form a new compound called mercapturic acid.  This conjugation reaction neutralizes the toxic NAPQI.  In healthy humans, no more than 5% of acetaminophen is converted to this toxic compound. (1,2)

Cats, however, are very limited in their ability to produce GSH.  Therefore they have an extremely limited ability to convert this compound into a neutral substance.  Consequently, cats are extremely susceptible to the toxic effects of this drug as compared to humans. and other species. (3)  These toxic metabolites may cause illness by any of the following routes:

Clinical Signs:  Clinical signs of acetaminophen intoxication are variable.  Clinical Signs commonly present after 1 to 2 hours of exposure, but in some instances may not appear for a longer period of time.  Clinical signs in the cat are attributable to the toxic effects described above.  One study attempted to document the prevalence of clinical signs in cats presenting with acetaminophen toxicity. (5)

Diagnosis:  Diagnosis of acetaminophen toxicity is most commonly made by historical evidence and clinical signs.  Common laboratory abnormalities seen in cats with acetaminophen toxicity include Heinz body formation evident on a blood smear, a decreased PCV (decreased red blood cell numbers), and elevations in hepatic laboratory values. (6)  Plasma, serum, and urine can be tested for the presence of acetaminophen; however, the tests results often take several days and are not available at the time that treatment is needed. (7)

Treatment:  Treatment components for acetaminophen toxicosis include initial decontamination, antidotal therapy, antioxidant replenishment, supportive therapy, and potentially methemoglobinemia/anemia correction.

Prognosis and Outcome:  The most important survival factor is the amount of time that passes between initial toxicant exposure and treatment.  Cats that are treated sooner have a much better prognosis.  One study has shown that cats treated after more than 17 hours typically do not survive (5).

Prevention:  As the old adage says, an ounce of prevention is worth a pound of cure.  Owners should educate themselves about the ingredients in all medications throughout the house.  Medications should be stored in a secure location where pets have no access.  Further, old medication bottles should be disposed of immediately, and pets should not have access to empty bottles.

ETHYLENE GLYCOL

Toxicant Information:  Ethylene Glycol is a very dangerous toxin to cats.  It is most commonly found in antifreeze (coolant) and windshield de-icing agents.  However, it can also be found in a variety of other substances, such as photographic color film processing chemicals, rust removers, brake fluid, motor oil, and in industrial solvents. (9,10)

Mechanism of Toxicity:  Unmetabolized ethylene glycol is not toxic; toxins are formed when ethylene glycol undergoes metabolism.  There are several steps in ethylene glycol metabolism.  Some of the most important metabolites that contribute to ethylene toxicicity are glycoaldehyde, glycolic acid, and oxalic acid.

Owners should be aware that even a drop or two of ethylene glycol lapped up or cleaned off a contaminated paw is enough to cause severe illness in cats.  If ethylene glycol intoxication is suspected, immediate veterinary care should be sought.

Clinical Signs:  The clinical signs of ethylene glycol intoxication are commonly described in stages.

Diagnosis: Diagnosis is typically made by a combination of historical evidence, clinical signs as described above, laboratory analysis, and potentially diagnostic imaging.  During the different stages of ethylene glycol intoxication, diagnostic testing will yield different results.

Treatment:  Treatment aims are similar to those described above for acetaminophen toxicity and include decontamination, antidotal therapy, and supportive care.

Prognosis and Outcome: The amount of ingested ethylene glycol and the time since exposure to ethylene glycol will determine the clinical outcome.  Treatment outcomes are best for cats that have therapy initiated within 3 hours of exposure. (11)  The prognosis becomes much poorer with delays in treatment.  Prognosis is grave if kidney damage is evident.

Prevention: All pet owners should take the handling of antifreeze very seriously.  Even a small drop on the garage floor can prove fatal to a cat.  Owners should read labels of the antifreeze, de‐icer photography film chemicals, etc.  Bottles should be stored in a secure location and should only be used in areas for which the pet has no access.  Empty bottles should be discarded in an area for which the pet will have no access.  Vehicles should be checked immediately when leaks are suspected; again, even a drop or two can prove fatal to a cat.

LILY INGESTION

Toxicant Information:  Liles are a very popular household and garden plant.  Unbeknownst to many pet owners, lilies are extremely toxic to cats and quickly induce acute renal failure.  Lily species that have been demonstrated to induce kidney failure in cats include the Lilium and Hemerocallis genera.  These plants are particularly common around Easter and times of celebration.  They are also commonly planted in outdoor gardens.  Common names for plants included in these genera include: (14)

All parts of the lily are toxic, and ingestion of even a small portion of a leaf or stem can induce illness, renal failure, and death in cats.

Mechanism of Toxicity:  The mechanism of toxicity has yet to be elucidated; however, what is established is that these plants ultimately lead to renal failure and death in cats if left untreated.  Initially, it is thought that lilies cause gastrointestinal upset in the first few hours after ingestion.  Over the next several hours this leads to polyuria (increased urination).  Without adequate fluid replenishment dehydration ensues, which is thought to promote the development of acute renal failure.  Cats are uniquely susceptible to the toxic effects of lily species, and recent research suggests that cats may have a unique metabolism that converts :therwise nontoxic lily substrate to toxic lily substrate. (14)

Clinical Signs:  Clinical signs seen in cats with lily toxicity are those of gastrointestinal upset and kidney disease.  Like ethylene glycol poisoning, clinical signs are often seen in two stages.

Diagnostics:  Again, diagnosis is typically made with a combination of historical evidence, clinical signs, and corroborating laboratory evidence.  Unfortunately, however, there are no specific laboratory tests hat are able to discriminate lily-induced renal failure from other forms of renal failure.

Treatment:  Unfortunately, no antidotal therapy is available for the treatment of lily toxicity.  The mainstays of treatment are decontamination therapy as described for acetaminophen toxicity and aggressive fluid therapy for the purposes of maintaining hydration status and diuresis.  It is imperative that these treatment strategies be undertaken before the development of anuria and renal failure, as the only effective etreatment strategy for renal failure s peritoneal dialysis or hemodialysis. (15)

Prognosis:  Cats treated with decontamination and fluid therapy in the initial stage of lily intoxication (i.e. before polyuria develops) have been shown to have an excellent prognosis. (14)  However, cats that develop uncorrected dehydration, anuria, and renal failure carry a very grave prognosis.  The only means for which a cat with renal failure can be treated is with peritoneal dialysis or hemodialysis.  It is therefore, imperative that cats be treated as soon as possible following known lily ingestion.

Prevention:  While both indoor and outdoor cats are commonly exposed to a variety of toxic lily species, strictly indoor cats more commonly present for lily intoxication.  One explanation for this is that most owners are not aware that lilies are toxic to cats, and further, many owners are also not aware of all of the species of plants that they bring into their home.  Additionally, it has been speculated that indoor only cats commonly chew on houseplants from boredom.

Before bringing a plant into the home, owners should check the ASPCA plant website. "A Guide to Plant Poisoning of Animals in North America" written by Anthony Knight is another great reference for owners.  Lily species should be considered toxic until proven otherwise by an exhaustive research effort.  Cats should never be trusted with access to lilies, toxic lilies should not be brought into the home, and toxic lily species should not be planted outside, as roaming cats will have access.

PERMETHRIN

Toxicant Information:  Permethrin is a synthetic chemical that is as a topical insecticide.  It is commonly found in over the counter flea and tick control products labeled for dogs, but is a neurotoxin in cats.  Because many owners are unaware of the toxic potential of these products, they are often applied topically to cats for purposes of insecticide control.  The cat then absorbs the chemical through its skin and the toxic effects of this product become apparent several hours later.  Products containing permethrins should never be used in cats.  Some common canine flea and tick control products containing permethrin include the following:

A brief internet search will reveal to you the vast number of products containing permethrin, and the list above is by all means, non‐inclusive.  Additionally, many environmental insect control products contain permethrin.  Owners should evaluate the chemicals found in all insect control products, insect repellants, and human ectoparasite control products (i.e. scabies and lice control products).

Additional information on flea control in cats and products containing permethrin can be found on the FabCats and ASPCA Animal Poison Control Website.

Mechanism of Toxicity:  Permethrin acts to alter transmission of neuronal impulses and causes neuronal toxicity eventually leading to death in insects.  Most mammals are not susceptible to the toxic effects of permethrin, however, cats are known to be exquisitely sensitive to the toxic effects of permethrin and suffer neurologic symptoms and toxicity following permethrin exposure.  Unlike the toxins discussed thus far, permethrins cause toxicity by absorption through the skin.  Once absorbed into the skin it is metabolized by the liver.  As discussed earlier, cats are deficient in their hepatic glucoronidation capabilities, and it has been postulated that this is one mechanism that makes cat susceptible to the toxic effects of permethrin. (16)

Clinical Signs:  The primary clinical signs seen in cats with permethrin toxicity are neuromuscular in nature and be apparent from the initial time of exposure up to a few days following exposure.  A recent study documented the distribution of clinical signs seen in cats presenting for permethrin toxicity. (17)  The following clinical signs, in order of most to least common, may be observed:

Diagnosis:  Diagnosis is made by history of exposure to permethrin containing products and presenting clinical signs.  Unfortunately, there are no diagnostic tests that are useful in identifying/diagnosing permethrin toxicity.  For this reason, it is imperative that owners provide a thorough history of any recently utilized canine flea/tick control, insect control products, or insect repellants.

Treatment:  Decontamination and supportive therapy are the only treatment strategies available for cats suffering permethrin toxicity; there is no antidotal therapy available.

Prognosis:  Prognosis is generally quite good if appropriate decontamination and supportive care procedures are initiated in a timely fashion.  Many studies have attempted to describe the survival rates of cats suffering permethrin toxicity; ranges from 63% to 95% have been reported. (16,20)

Prevention: Owners should be aware of the ingredients found in all insect/pesticide control products that they intend to use, including veterinary products. Cats should NEVER receive any products containing permethrin.  They should not have intimate contact with dogs that have recently had permethrin products applied, nor should they be exposed to an environment in which permethrin products have just utilized.  Before purchasing products, owners should do a thorough investigation of all ingredients.  If in doubt of the ingredients contained in a product, do not use the product.  A veterinarian should be consulted with questions regarding flea, tick, and other insect control products for cats and dogs.

ADDITIONAL TOXINS

The above four toxins were chosen at the author's discretion, and are by all means not an inclusive list of toxins to cats.  Below is a list of the most commonly encountered feline toxins.  The best way to prevent a toxin exposure is to become educated on potential toxins!  If you suspect that your cat (or any other animal) has ingested a potentially poisonous/toxic substance, the Animal Poison Control should be contacted immediately.  Further information about the Animal Poison Control can be found at the following links:
www.aspca.org/Pet-care/poison-control.aspx
www.aspca.org/pet-care/poison-control/what-to-do-if-your-pet-is-poisoned.aspx

The telephone number for nimal Poison Control is (888) 426-4435.  There is a $65 consultation fee for this service.

Commonly Encountered Human Drugs:

Insecticides, Herbicides, Rodenticides, and other Pesticides: Additional Toxins of Importance:

BIBLIOGRAPHY

1. Sturgill MG, Lambert GH. Xenobiotic-induced hepatotoxicity: mechanisms of liver injury and methods of monitoring hepatic function. Clin Chem 1997;43:1512-1526.

2. Maddrey WC. Drug-Induced Hepatotoxicity: 2005. Journal of Clinical Gastroenterology 2005;39:S83-S89.

3. Court MH, Greenblatt DJ. Molecular basis for deficient acetaminophen glucuronidation in cats : An interspecies comparison of enzyme kinetics in liver microsomes. Biochemical Pharmacology 1997;53:1041-1047.

4. Bischoff K. Toxicity of over-the-counter drugs In: C.Gupta, ed. Veterinary Toxicology: Basic and Clinical Principles. New York, NY: Elsevier, 2007.

5. Aronson LR, Drobatz K. Acetaminophen Toxicosis In 17 Cats. Journal of Veterinary Emergency and Critical Care 1996;6:65-69.

6. Osweiller GD. Over The Counter Drugs and Illicit Drugs of Abuse. The National Veterinary Medical Series: Toxicology. Philidelphia: Lippincot, Williams, and Wilkins, 1996.

7. Poppenga R. Toxicological Emergencies In: Drobatz KJaC, Merilee F, ed. Feline Emergency and Critical Care Medicine. Aimes, Iowa: Blackwell Publishing, Ltd, 2010.

8. Rumbeiha WLY, Oeheme FW. Comparison of N-acetylcisteine and methylene blue, alone or in combination, for treatemnt of acetaminophen toxicosis in cats. Am J Vet Res 1995;56:1529-1533.

9. Osweiller GD. Common Household Products In: Osweiller GD, ed. The National Veterinary Medical Series: Toxicology. Philadelphia: Lippincot Williams and Wilkins, 1996.

10. Thrall MaH, DW. Alcohols and Glycols In: Gupta R, ed. Veterinary Toxicology: Basic and Clinical Principles. New York, NY: Elseviere, 2007.

11. Dial SM TM, Hamar DW. Comparison of ethanol and 4-methylpyrazole as therapies for ethylene glycol intoxication in the cat. Am J Vet Res 1994;55:1771-1782.

12. Connally HE, Hamar DW, Thrall MA. Inhibition of canine and feline alcohol dehydrogenase activity by fomepizole. American Journal of Veterinary Research 2000;61:450-455.

13. Connally HE, Thrall MA, Hamar DW. Safety and efficacy of high-dose fomepizole compared with ethanol as therapy for ethylene glycol intoxication in cats. Journal of Veterinary Emergency and Critical Care 2010;20:191-206.

14. Fitzgerald KT. Lily Toxicity in the Cat. Topics in Companion Animal Medicine 2010;25:213-217.

15. Hall J. Lily Nephrotoxicity In: August JR, ed. Consultations in Feline Internal Medicine. Philadelphia: WB Saunders Company, 2001;308-310.

16. Richardson JA. Permethrin Spot‐On Toxicoses in Cats. Journal of Veterinary Emergency and Critical Care 2000;10:103-106.

17. Boland LA, Angles JM. Feline permethrin toxicity: retrospective study of 42 cases. Journal of Feline Medicine and Surgery 2010;12:61-71.

18. Sutton NM, Bates N, Campbell A. Clinical effects and outcome of feline permethrin spoton poisonings reported to the Veterinary Poisons Information Service (VPIS), London. Journal of Feline Medicine and Surgery 2007;9:335-339.

19. Dymond NL, Swift IM. Permethrin toxicity in cats: a retrospective study of 20 cases. Australian Veterinary Journal 2008;86:219-223.

20. Linnett PJ. Permethrin toxicosis in cats. Australian Veterinary Journal 2008;86:32-35.


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