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Antimicrobial Therapy in Dogs and Cats
Katrina R. Viviano, DVM, PhD, DACVIM (SAIM), DACVCP

School of Veterinary Medicine, University of Wisconsin, Madision, WI, USA

To optimize antimicrobial therapy, clinicians should dysfunction, dehydration, concurrent use with other
have a working knowledge of available antimicrobials nephrotoxic drugs or diuretics, and young or old age.
and their spectrum of activity. Of equal importance is an The active tubular reabsorption of AGs is a saturable
understanding of clinically important side‐effects, drug– process with an increase in nephrotoxicity when lower,
drug interactions, and knowledge of circumstances in more frequent dosing protocols are used. Despite AGs
which certain antimicrobials should be avoided, or dos- having a short elimination half‐life, they demonstrate a
age adjustments should be considered to minimize post-antibiotic effect and concentration‐dependent bac-
potential adverse effects. This chapter will summarize terial killing. Nephrotoxicity correlates with drug trough
these important considerations for commonly used anti- concentrations and is not observed following a high sin-
microbials in small animal medicine. The common gle dose; but is cumulative and occurs in association with
classes of antimicrobials used and the clinically impor- multidose protocols, within 5–7 days after initiating
tant antimicrobial side‐effects/drug–drug interactions therapy. Once‐daily dosing is recommended to minimize
in dogs and cats are summarized in Tables 114.1 and nephrotoxicity while maintaining efficacy.
114.2, respectively. Aminoglycoside nephrotoxicity is reversible if recog-
nized early so close monitoring is recommended. AGs
should be avoided in patients with underlying kidney
Common Classes of Antimicrobials disease. If an alternative antimicrobial with an appropri-
ate spectrum of activity is not available, dose reduction is
recommended in azotemic patients. To help prevent
Aminoglycosides (AG)
nephrotoxicity, all patients should be well hydrated
The AG spectrum of activity is primarily limited to gram‐ before and during the course of therapy. As mentioned
negative aerobes, including Pseudomonas aeruginosa. In above, once‐daily dosing is recommended, and when
vivo, AGs are considered synergistic with beta‐lactams. possible the duration of therapy should be limited to
AGs penetrate the bacterial cell envelope in part through 5–7 days. To detect proximal renal tubular damage, urine
an oxygen‐dependent active transport mechanism as well should be examined prior to and daily during therapy for
as passive diffusion. By co‐administering AGs with peni- the presence of granular casts, proteinuria, and glucosu-
cillins, the penicillins interfere with bacterial cell wall ria. Serum BUN and creatinine levels should also be
synthesis, enhancing the penetration of AGs into the monitored. Therapy should be discontinued if markers
bacterial cell envelope. of nephrotoxicity develop.
The dose‐dependent nephrotoxicity of the AGs limits Aminoglycosides also accumulate in the inner ear, lead-
their clinical use. AGs bind the brush border of the proxi- ing to dose‐dependent ototoxicity. Auditory toxicity is
mal renal tubular cells and accumulate in lysosomes more common with amikacin, while vestibular toxicity is
through active reabsorption. Through the inhibition of more common with gentamicin, especially in cats. Also,
lysosomal phospholipase, phospholipid metabolism is the use of AG is contraindicated in patients with disease
inhibited, resulting in renal tubular cell death. Risk factors of the neuromuscular junction (e.g., myasthenia gravis)
for nephrotoxicity include high dosages, multi-dose due to inhibition of acetylcholine release and decreased
protocols, long duration of treatment, pre-existing renal receptor sensitivity leading to neuromuscular blockade.

Clinical Small Animal Internal Medicine Volume II, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical