Q: Are angiotensin-converting enzyme inhibitors (ACEIs) indicated for the treatment of CRF? What about calcium channel antagonists
A: Loss of nephrons in CRF results in afferent glomerular arteriole vasodilatation, which causes intraglomerular pressure to
increase. This "hyperfiltration" can lead to progressive loss of nephrons. Treatment with ACEIs result in efferent arteriolar
vasodilatation, which reduces intraglomerular hypertension. In a study of dogs with surgically-induced CRF, enalapril was
associated with a reduction of glomerular and systemic hypertension and proteinuria, prompting investigators to conclude that
ACEIs might be effective in modulating progressive renal injury in dogs with CRF. Similarly, in cats with the remnant kidney
model of CRF, treatment with benazepril sustained single nephron GFR and was associated with a significant reduction in systemic
hypertension and an increase in whole kidney GFR. The conclusion of this study was that ACEIs might slow the rate of disease
progression in cats with CRF.
Amlodipine had an antihypertensive effect in cats with coexistent systemic hypertension and remnant kidney-induced renal insufficiency.
Therefore, treatment with CCAs can improve the prognosis for cats with hypertension by decreasing the risk of ocular and/or
neurologic injury. In many feline cases, CCAs are more effective in reducing systemic hypertension than ACEIs. Inasmuch as
ACEIs normalize intraglomerular pressures to a greater extent than CCAs, combination treatment may be indicated in cats when
ACEIs alone fail to control systemic hypertension.
Q: When should I treat anemia in CRF patients?
A: After initiation of the previously discussed treatments, the anemia of CRF should be treated if it appears to be contributing
to the patient's poor quality of life. Studies assessing the effects of recombinant human erythropoietin (r-HuEPO) treatment
on anemia in dogs and cats with CRF have generally shown it to be successful. The cost of treatment for medium-sized and large-breed
dogs is high, however. Recombinant erythropoietin treatment also often results in heightened appetite, weight gain, increased
strength and an improved sense of well-being. It's important to keep in mind that there is a potential for antibodies to form
in up to 30-40 percent of dogs and cats treated with r-HuEPO. If antibodies are produced against r-HuEPO, then they also can
react with endogenous erythropoietin, making the animal transfusion-dependent. Because of the potential for antibody formation,
many clinicians reserve the use of r-HuEPO for patients whose anemia is moderate to severe and contributing to poor quality
of life. Commercially available canine and feline recombinant erythropoietin would improve our ability to treat the anemia
of CRF significantly.
Q: How do I stimulate appetite in a CRF patient?
A: The most important aspect of stimulating appetite is control of metabolic deficits and excesses associated with CRF (e.g.,
dehydration, acidosis, anemia, hypertension). Second, gastrointestinal tract dysfunction (e.g., motility, acidity, constipation,
oral disease) should be addressed. Third, feeding management problems (force feeding, sudden dietary change, not recognizing
social and antisocial eaters, and giving pills and injections associated with feeding) should be addressed. In general, tricks
designed to increase diet palatability and use of appetite stimulants are less effective. Vomiting can be treated with metoclopramide,
which blocks the chemoreceptor trigger zone and increases gastric motility and emptying without increasing gastric acid secretion.
H2-receptor blockers (e.g., ranitidine) and proton pump blockers (e.g., omeprazole) have been shown to effectively decrease
gastric acid secretion, which can attenuate vomiting in dogs and cats with CRF.
Q: Are feedings tubes helpful?
A: If vomiting can be controlled, but the animal still will not eat enough to meet its daily caloric requirements, then a feeding
tube might be indicated. Cats tend to tolerate gastrostomy tubes especially well, and they can remain in place for months.
Esophagostomy and gastrostomy tubes not only facilitate provision of potentially unpalatable, and appropriate, calories but
also provide a relatively stress-free route for fluid therapy and medications.
Q: When should I initiate subcutaneous fluid therapy?
A: Daily maintenance fluid requirements in animals with CRF are higher than those of normal animals because of polyuria. If
the patient with CRF is not able to drink enough to keep up with its urine output, then daily subcutaneous fluids might be
indicated. In some cases, owners are able to perform this treatment at home. If in doubt, a trial of subcutaneous fluid therapy
may be indicated. If the patient seems energized by the fluids and BUN and creatinine concentrations are decreased, then continued
therapy is warranted.