A client brings a 13-year-old M/N Siamese cat into the clinic for an examination. The client states that the cat has been drinking more water and urinating more frequently in the litterbox. Because this is an older cat, the veterinarian collects blood to assess this cat's liver and kidney enzymes. A urine sample is also collected to assess whether the increased drinking and urinating are due to

Question

an infection or systemic disease. The blood results indicate that the cat has elevated liver and kidney enzymes. The urinalysis indicates that the cat also has a bacterial urinary tract infection. In addition to medication to treat liver and kidney disease, the client is given antibiotics to treat her cat's urinary tract infection. The client feels that because this cat has multiple health problems, it would be better to give a larger dose of antibiotics so that the infection can be cleared more quickly. Why is this not a good idea?

What will be an ideal response?

Answer 1

There are two major concerns with this cat regarding drug use: metabolism and excretion of the drug. The kidneys and the liver both play a significant role in drug metabolism and excretion. Since this cat has elevated kidney

and liver enzymes, metabolism and excretion of the antibiotic will be altered. Most drug metabolism takes place in the liver by the reaction of liver enzymes with the drug. These drug-metabolizing enzymes, often referred to as microsomal enzymes, of which cytochrome P450 is a part, typically convert the parent drug to a more water-soluble metabolite. This water-soluble metabolite

is more readily excreted by the kidneys. If the liver is diseased, the production of metabolizing enzymes is reduced, and drug metabolism may be impaired. If drug metabolism is impaired, the drug may

accumulate in the body and produce toxicity. Giving a higher dose of drug in this case will result in more toxic side effects from altered metabolism.

Drugs are usually eliminated from the body via the kidneys. The efficiency with which drugs are excreted by the kidneys diminishes in animals with kidney disease. This may necessitate a reduction in the dose or fewer drug administrations to prevent the accumulation of toxic concentrations of drug. Giving a higher dose of drug in this case will result in more toxic side effects due to altered excretion.