CALCITRIOL USE IN CRF DOGS OR CATS
Drs. Nagode & Chew
STEP 1: Determine that serum creatinine is consistently elevated above 2
mg/dl and USG is compatible with CRF as cause of azotemia. Patients are
best treated early in CRF as low calcitriol doses are useful in preventing
STEP 2: Establish a plasma phosphorous concentration at or below 6
mg/dl through use of phosphorus restricted diets, intestinal phosphorous
binders (use those containing aluminum rather than calcium), and, if
necessary, fluid diuresis.
In patients with serum creatinine of 2-3 mg/dl and serum phosphorus <
6 mg/dl: Start calcitriol at 2.5-3.5 ng/kg/day. In these patients the
PTH levels are often normal and the calcitriol is used to prevent PTH
increase to slow progression of the CRF and prevent symptoms related to PTH
In patients with a serum creatinine of > 3 mg/dl and serum
phosphorous < 6 mg/dl: A baseline PTH in these is useful since the
levels are commonly elevated and may require higher doses of calcitriol
(submit a serum sample to Michigan State Univ. (frozen, on ice, overnight)
Start calcitriol at 3.5 ng/kg/day. If clients refuse PTH assays, start
The calcitriol in any desired dose can now be made by a compounding
pharmacy and when doses >5 ng/kg are needed is best given at bedtime on
an empty stomach to prevent hypercalcemia.
STEP 4: Patient Monitoring:
a. When used as a "preventative": Assess serum calcium concentration
on day 10 after initiation of calcitriol therapy and every 6 months
thereafter. If hypercalcemia is detected, a week of discontinued calcitriol
will allow determination of whether or not the medication is the cause. Sometimes,
hypercalcemia is due to not enough calcitriol rather than too much. This
relates to the control calcitriol exerts on the "set point" for
PTH secretion aberrant in “tertiary hyperparathyroidism”. Serum creatinine
should be monitored q 1-3 mos. depending on the stability of the patient.
b. In patients with initial elevation of PTH: Along with those
measures recommended in step 4 (a), PTH levels should be reassessed 4-6
weeks following initiation of calcitriol. If still elevated, then increase
the dose by 1-2 ng/kg depending on prior response (do not exceed 6.6
ng/kg/day unless ionized calcium is measured). When higher doses seem
needed (5-7 ng/kg/day), a "pulse dosing" strategy is an
alternative (VCNA, Nov. 1996 pg.1319).
STEP 5: Determine clinical benefit by improved appetite,
attitude and mobility, as well as slowed progression of the CRF.