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Introduction
Susan Sommers knew something was seriously wrong. Her lively two year
old Abyssinian cat, Pyewacket, was anything but lively. Although he ate
his breakfast in his normal fashion, he vomited soon afterward and had
become progressively more lethargic as the minutes passed. When the
normally fastidious feline became too lethargic to seek out his
litterbox and defecated where he was sitting, Ms. Sommers whisked him in
to my cat practice immediately.
I knew something was instantly amiss when the normally fidgety Pyewacket
was very subdued on the exam table. During the physical examination I
detected a very striking clinical sign: Pye’s mucous membranes – his
gums and tongue – were a purplish-brown color, rather than the usual
pink. His body temperature was low, and his face seemed puffy to me. I
drew some blood for some basic laboratory tests, and the appearance of
the blood spelled serious trouble. Rather than the typical purplish red
color, this blood was brown, resembling chocolate syrup. The brownish
hue is caused by high levels of methemoglobin, a type of hemoglobin that
forms when the iron component of the hemoglobin becomes oxidized,
rendering the hemoglobin incapable of carrying oxygen. A light bulb went
off in my head. Although I hadn’t seen a case like this since I was an
intern 15 years ago, I had to ask Ms. Sommers: could Pyewacket have
ingested Tylenol?
“Oh my goodness!” cried Ms. Sommers. “ Yes, he could have! My husband’s
been sick and there are lots of medications around the apartment,
including Tylenol!”
Companion animals are at risk for developing toxicosis to prescription
drugs as well as over-the-counter (OTC) medications, either by
deliberate administration of the medication by owners, or by accidental
consumption of improperly stored drugs. Dogs are more likely to chew on
pill vials or tubes of ointment, eating the pills or ointment when the
container finally breaks open. Cats, on the other hand, are generally
more discrete about what they put in their mouths and are less likely to
voluntarily ingest medications. With cats, toxicity tends to occur when
well-intentioned owners unknowingly administer a seemingly harmless OTC
medication, often with devastating results. Acetaminophen and aspirin
are perhaps the most notorious of the OTC drugs that are harmful to
cats, however, a variety of other medications have the potential to
cause serious illness in cats.
Antidiarrheal drugs can be found in nearly every household medicine
cabinet. Kaolin-pectin combinations (such as Kaopectate®) have been used
for decades to treat diarrhea in humans and small animals. The old
formulation contained only kaolin and pectin. Later forms contained
attapulgite. All three of these substances were very safe in animals
because they were not absorbed into the bloodstream after
administration; they exerted their effects locally, in the intestine. In
December 2002, however, Kaopectate® was reformulated to contain the drug
bismuth subsalicylate, a drug that can be toxic to cats.
Bismuth subsalicylate (which happens to also be the chief ingredient in
Pepto-Bismol®) is related to aspirin. Cats are very sensitive to
salicylate formulations. They cannot metabolize and excrete them
efficiently. A tablespoon of regular strength Kaopectate® contains the
equivalent of 130 milligrams of aspirin; the extra strength formulation
has the equivalent of 230 milligrams. One tablespoon of the extra
strength formula would probably cause toxicosis in a 5 lb. cat. For this
reason, Kaopectate® or Pepto-Bismol® are NOT recommended for feline
gastrointestinal problems.
Veterinarians use OTC analgesic drugs in companion animals to treat
musculoskeletal inflammation and pain, control fevers, and inhibit blood
clotting. Aspirin is a non-steroidal anti-inflammatory drug (NSAID)
that, for many years, had been used to control musculoskeletal pain and
inflammation in dogs, and sometimes cats. In recent years, a multitude
of safer and more effective oral pain relievers have been developed,
making aspirin an uncommon first choice for joint and skeletal disease
in companion animals. In cats, aspirin is mainly used to inhibit blood
clotting. Cats with certain heart diseases like hypertrophic
cardiomyopathy are at increased risk for developing dangerous blood
clots. Aspirin is frequently prescribed in an effort to inhibit blood
clot formation, however, the dose must be strictly adhered to. “Cats do
not metabolize NSAIDs the same way dogs do” warns Dr. Michael Stone, an
internal medicine specialist at Cummings School of Veterinary medicine
at Tufts University. “Pet owners should be very cautious when giving
aspirin”. Cats are typically prescribed 81 milligrams - a baby aspirin,
or ¼ of a regular (not extra-strength) adult aspirin – every 48 to 72
hours. The inability of felines to metabolize NSAIDs has made treating
musculoskeletal pain in cats a challenge. Fortunately, new NSAIDs have
become available that have been shown to be effective and reasonably
safe in cats, such as meloxicam (Metacam®). This is a veterinary drug
and should only be prescribed after thorough consultation with a
veterinarian. Other over-the-counter NSAIDs such as ibuprofen (Advil®,
Nuprin®, Motrin®) or naproxen (Aleve®) should never be given to cats.
Ibuprofen has a narrow margin of safety in dogs, and cats, with their
inability to metabolize these drugs, are thought to be twice as
sensitive as dogs to ibuprofen’s toxic effects. “Ibuprofen and naproxen
are especially dangerous, and may be fatal”, says Dr. Stone.
Acetominophen is often grouped with the NSAIDs, although technically it
is somewhat different. Although most readily recognized by the trade
name Tylenol, acetaminophen is the major ingredient of most aspirin-free
pain relievers and cold remedies, including Excedrin®, Panadol®,
Anacin®, Midol®, Pamprin®, BromoSeltzer®, and Percogesic®. Many
decongestant products and “cold” or “flu” formulas contain
acetaminophen. For example, a single adult dose of Nyquil® syrup
contains 1000 milligrams of acetaminophen, the equivalent of more than
three Tylenol tablets. This is a frighteningly large dose, considering
that ingestion of one 325-mg tablet by a cat results in severe toxicosis,
and two tablets ingested within 24 hours is fatal. “Acetaminophen
toxicity is one of the more common toxicity cases that pass through our
Intensive Care Unit” says Dr. Stone. In 95% of cases, acetaminophen
toxicosis in cats results from administration by the owner for relief of
pain, fever, and non-specific ailments. Pyewacket Sommers was unusual in
that respect – he was not given the drug intentionally. Being a curious
Abyssinian that was into everything, he presumably stumbled upon Tylenol
that was improperly stored. .
At toxic doses, acetaminophen often causes hepatic necrosis – death of
liver cells – especially in dogs. Cats, however, are more likely to
develop methemoglobinemia, a condition of excess methemoglobin in the
bloodstream. Methemoglobin is an abnormal form of hemoglobin that is
incapable of transporting oxygen. As methemoglobin levels start to rise,
clinical signs develop, such as chocolate-brown mucous membranes, fast
heart rate, labored breathing, depression, vomiting, edema (swelling) of
the face, neck and limbs, hypothermia, ataxia (incoordination) and coma.
Cats may become jaundiced as liver failure develops. Time is of the
essence in treating acetaminophen toxicity. Although Pyewacket was
brought in immediately after his clinical signs became apparent, the
presence of facial swelling and hypothermia suggests that he had
ingested the Tylenol 12 to 24 hours prior to presentation.
Treatment for acetaminophen toxicity involves providing supplemental
oxygen, administering intravenous fluids, and giving several drugs
intravenously, including vitamin C, cimetidine (Tagamet), and N-acetylcysteine,
a drug that provides the body with excessive amounts of the amino acid
cysteine. This amino acid is necessary for the liver to repair itself
and counteract acetaminophen’s toxic effects. Treatment tends to be less
efficacious when initiated more than 8 hours after ingestion, and sadly,
therapy was ineffective in little Pyewacket. Despite aggressive
treatment, Pyewacket succumbed to his intoxication.
Conclusion
Ultimately, any oral medication can potentially cause toxicosis in
companion animals, especially cats, with their small body size and
unique metabolic pathways. It behooves us to remember the words of the
15th century Austrian physician-alchemist Paracelsus, who wrote “What is
there that is not a poison? All things are poison. The dose determines
that a thing is not a poison.” Cat owners should be certain to keep all
medications safely stored, and have the phone number of their
veterinarian and national poison control center readily accessible in
case of a toxin-related emergency. “No product, over-the-counter or
otherwise, should be given to a cat without the advice of a
veterinarian” says Dr. Stone.
Updated 2/9/06 |
