Page 1352 - Problem-Based Feline Medicine

1344 PART 16 DRUGS

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Metronidazole Disorientation.
Ataxia.
Seizures.
Blindness.
Opioids: morphine Inconsistent sedation.
derivatives (excluding Increased risk of excitation.
meperidine [pethidine],
butorphanol and
buprenorphine)
Organophosphates Acute toxicity – hypersalivation, vomiting, diarrhea, muscle tremors.
Chronic or delayed toxicity – paresis or paralysis which may or may not be
reversible.
Potassium bromide Depression.
Severe coughing.
Tetracyclines Hepatic lipidosis.
Increased ALT activity.
Ptyalism.
Anorexia.
Thiacetarsamide Drug fever.
Respiratory distress.
Fulminant pulmonary edema.

Most differences between dogs and cats in drug dispo-
INTRODUCTION
sition relate to differences in Phase II metabolism,
although deficiencies in Phase I metabolism may be
SPECIAL CONSIDERATIONS RELATED involved in some drug toxicities in cats including chlo-
TO DRUG USE IN CATS ramphenicol toxicity.
During Phase II metabolism, parent drugs or Phase
Why are cats different?
I metabolites are bound (conjugated) to large molecules
There are some important differences in drug disposi- such as glucuronide, glutathione, sulfate and acetyl
tion between dogs and cats that can have a profound groups, and amino acids (e.g. glycine and taurine)
influence on dosing recommendations for cats. resulting in a water-soluble, inactive compound.
The majority of the difference in drug disposition
between cats and dogs relates to differences in drug FELINE DRUG METABOLISM
metabolism.
Cats are deficient in some glucuronyl transferases
which are important for glucuronidation.
DRUG METABOLISM – GENERAL ● Drugs that are excreted as glucuronide conjugates
in other species such as aspirin, benzoic acid, acet-
Water-soluble drugs can be excreted in urine without
aminophen (paracetamol) and hexachlorophene
being metabolized.
may have a prolonged half-life in cats.
Drugs that are lipid soluble must be converted to ● Increased half-life increases the risk of toxicity
water-soluble metabolites that can be excreted, usu- due to drug accumulation.
ally by the kidney.
Not all drugs that are glucuronidated are a problem in
Drug metabolism occurs in the liver in two phases (I cats. Cats are only deficient in certain families of
and II). glucuronyl transferases.