Protocol for Calcitriol Use in CRF Dogs or Cats

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 disease progression.

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.

Step 3: 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 toxicity. 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 calcitriol anyway.

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.

1. 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.

2. 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.