Page 1353 - Problem-Based Feline Medicine

67 – SPECIAL CONSIDERATIONS RELATED TO DRUG USE IN CATS 1345

● The drug may have a wide safety margin and drugs DRUGS NOT RECOMMENDED FOR USE
may be metabolized by a different route in cats
IN CATS
(although this can result in toxicity for some drugs).
● For example, sulfation is well developed in cats
ACETAMINOPHEN (PARACETAMOL)
compared to dogs and acetylation, which is defi-
cient in dogs, appears to be well developed in cats.
Clinical action
Non-steroidal analgesic.
FELINE HEMOGLOBIN AND DRUGS

Feline hemoglobin is more susceptible to oxidation, Why shouldn’t it be used in cats?
and therefore methemoglobinemia formation, than in Glucuronidation is the major pathway for metabolism of
dogs. This increases the risk of adverse drug reactions. acetominophen in most species, but cats have a low
concentration of glucuronyl transferase.
There are a number of possible mechanisms including
the different structure of feline hemoglobin, lower Sulfation is the major metabolic pathway in the cat, but
concentrations or activities of intracellular repair its capacity is limited.
enzyme and differences in intracellular concentrations
As the dose is increased, a greater percentage of the
of glutathione-conjugating enzymes.
drug is oxidized, which results in toxic metabolites.
The metabolites are normally conjugated with glu-
OTHER PHYSIOLOGIC FACTORS THAT
INFLUENCE DRUG DISPOSITION tathione, but when hepatic glutathione is depleted,
the metabolite binds covalently to amino acid residues
Other physiologic factors that may influence drug dis- of protein in the liver resulting in centrilobular
position are similar in dogs and cats. hepatic necrosis.
Age-related differences should always be considered. Glutathione is easily depleted in cats as the reserves are
Pediatric and geriatric animals are potentially more limited.
susceptible to adverse drug effects due to:
● Alterations in drug distribution.
APOMORPHINE
– Greater volume of distribution in pediatric animals.
– Reduced lean body mass and total body water in
Clinical action
geriatric animals.
Anti-emetic.
– Lower plasma protein in young and old animals.
● Drug metabolism.
– Reduced hepatic metabolism in neonates. Why shouldn’t it be used in cats?
– Reduced hepatic blood flow and reduced hepato- Higher doses are required for anti-emetic action than in
cyte mass and function in geriatric animals. dogs.
● Drug elimination.
Significant CNS depression is associated with its use.
– Glomerular and tubular function are reduced in
neonates and old animals.
AZATHIOPRINE
Drug interactions and disease factors that influence
drug disposition such as hepatic, cardiac and renal
Clinical action
pathology have a similar importance in cats and dogs.
Cytotoxic.
The effect of inappetence in diseased cats is impor-
tant as dietary protein is an important source of sulfate
Why shouldn’t it be used in cats?
and other compounds used in Phase II drug metabolism
in cats. Taurine may also be important. Anorexic cats Although azathoprine has been used successfully to
therefore may be more susceptible to adverse drug treat immune-mediated disease in cats, serious bone
reactions because of reduced drug metabolism. marrow suppression has been reported in cats treated