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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 less than or equal to 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
greater than 3 mg/dl and serum phosphorous less than or equal to 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.
Doses greater than 5 ng/kg are best given at
bedtime on an empty stomach to prevent hypercalcemia. Low doses can be given
with 1st meal of day for convenience of owners.
Step 4: Patient Monitoring:
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When used as a "preventative": Asses serum
calcium concentration on days 7 and 14 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. Often times, 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. Serum creatinine should be
monitored on a regular basis (q 1-3 mos. depending on the stability of the
patient).
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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 dosed 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.
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