Prescribing for Cats with Chronic Kidney Disease
Chronic kidney disease (CKD) is one of the most common presentations in older cats. Once the diagnosis is made, what often determines how long the patient lives is not the kidney itself, but how the other drugs that patient receives are managed.
This article is not about treating CKD as a whole. It is about what changes when you prescribe for a cat with reduced renal function.
Start with the stage: which patient are we talking about?
"Kidney patient" is not a single category. The internationally accepted IRIS staging system divides patients into four stages based on creatinine (and where available SDMA) measured in a stable patient, then substages them by proteinuria and blood pressure.
This staging is not an academic detail but a practical tool: the same drug may be used comfortably in an early stage yet require a longer dosing interval, or complete avoidance, in an advanced one.
Two rules matter:
- Staging is done in a stable patient. Creatinine measured in a dehydrated, vomiting or acutely ill cat does not reflect true renal reserve.
- It is confirmed by repeated measurements, not a single value.
What changes for renally excreted drugs?
If a drug is cleared predominantly by the kidney, it accumulates when filtration falls. There are two ways to manage this:
- Extend the dosing interval — the same dose given less often
- Reduce the dose — less drug at the same interval
Which one you choose depends on what the drug's efficacy is driven by. For drugs whose effect depends on peak concentration, extending the interval makes sense; for those whose effect depends on time spent above a threshold concentration, reducing the dose does.
In practice, the third and safest route is often this: if an alternative that is not renally cleared exists, choose it.