Detection of abnormalities related to the structure and function of the kidneys, along with the absence of abnormalities related
to the lower urinary tract, suggested that the infection primarily involved the kidneys. Localization of infection within
the urinary tract should be considered because it might influence:
- the prognosis,
- the type, dosage and dose interval of antimicrobial agent selected,
- the duration of therapy.
What is your prognosis?
The answer to this question is linked to localization of the azotemia. Did this cat have pre-renal, primary renal or post-renal
azotemia? Our interpretation of this case was that the underlying causes of azotemia were multifactorial. In this patient,
clinical signs of dehydration were reliable evidence that a component of the azotemia was pre-renal in origin. The prognosis
for correction of the pre-renal component of the azotemia was good because it could be corrected rapidly by restoring vascular
volume and intrarenal blood pressure with replacement fluids.
This cat also clearly had chronic primary (or intrarenal) azotemia. Although the initiating cause of the CRF had not been
identified at the time of initial evaluation (day 1), structural and functional kidney changes in patients with CRF are typically
progressive and irreversible. Did this indicate that the decline in the intrarenal component of the azotemia was irreversible?
The answer is, not necessarily. In this cat, acute decompensation of CRF associated with the uremic crisis was likely related,
at least in part, to a recent onset of secondary bacterial UTI (so-called "acute-on-chronic" renal failure). Eradication of
the bacterial UTI by appropriate antimicrobic therapy selected on the basis of antimicrobial susceptibility tests had the
potential to result in reduction in the intrarenal component of the azotemia, recompensation of the CRF and substantial improvement
in the cat's quality of life. Although the uremic crisis could also have been related to outflow obstruction of urine caused
by the nephroliths, this was considered to be unlikely based on evaluation of the upper urinary tract by ultrasonography.
How would you manage the renal failure?
An appropriate quantity of lactated Ringer's solution was given intravenously to correct the dehydration and to restore renal
perfusion. Because the owners did not want to hospitalize the patient, they were taught how to continue fluid therapy with
lactated Ringer's solution given subcutaneously at home.
What drug would you select to manage the UTI?
Pending results of urine culture and susceptibility tests, initial therapy of the bacterial UTI consisted of parenterally
administered ampicillin, followed by oral amoxicillin. Subsequently, results of aerobic bacterial culture of an aliquot of
urine collected by cystocentesis revealed significant in vitro growth of Escherichia coli (Table 2) that was sensitive to several antimicrobics including amoxicillin, enrofloxacin, trimethoprim-sulfonamide, chloramphenicol
What dose of antimicrobial agent would you recommend?
In general, dosages of antimicrobics and intervals between maintenance dosages should conform to the recommendations of the
manufacturer. Whereas emphasis is placed on selecting drugs that attain high urine concentrations for treatment of lower UTI,
selection of drugs likely to attain high serum concentrations is recommended for treatment of bacterial infections of the
renal parenchyma. Why? Because concentrations of antimicrobics in the renal interstitial tissue are more likely to correspond
to serum concentrations of antimicrobics than urine concentrations.
What effect could reduced renal function have on drug metabolism?