Comparison of the effects of daily and intermittent-dose calcitriol on serum parathyroid hormone and ionized calcium concentrations in normal cats and cats with chronic renal failure.
BACKGROUND
Chronic renal failure is complicated by secondary hyperparathyroidism, which traditionally has been controlled by dietary restriction of phosphorus and administration of phosphorus binders. Early treatment of patients with chronic renal failure with calcitriol may be indicated because once established, parathyroid gland hyperplasia does not readily resolve with therapy.


OBJECTIVE
Daily and intermittent dosing of calcitriol will decrease plasma parathyroid hormone concentration in normal cats and cats with chronic renal failure without causing ionized hypercalcemia.


METHODS
Ten normal cats; 10 cats with chronic renal failure.


METHODS
Phase 1 was daily calcitriol administration (2.5 ng/kg PO q24h) for 14 days. Phase 2 was intermittent calcitriol administration (8.75 ng/kg PO q84h) for 14 days. A 7-day washout period separated phases 1 and 2. Before each phase, calcitriol, parathyroid hormone, and ionized calcium concentrations were measured. On days 1, 2, and 3 of both phases, serum ionized calcium concentrations were measured. On the last day of both phases, calcitriol, parathyroid hormone, and ionized calcium concentrations were measured 0, 2, 4, and 6 hours after calcitriol administration.


RESULTS
Overall, serum parathyroid hormone concentrations were significantly higher in cats with chronic renal failure than in normal cats (P = .022), but serum parathyroid hormone concentrations for both normal cats and cats with chronic renal failure were not significantly different before and after 14 days of treatment with calcitriol, regardless of whether calcitriol was administered daily or intermittently. Adverse effects of calcitriol administration (specifically ionized hypercalcemia) were not seen in either feline group during either phase of the study over the 3-day evaluation after calcitriol administration was initiated.


CONCLUSIONS
At the dosages used, calcitriol treatment did not result in significant differences in serum parathyroid hormone concentrations before and after treatment in both normal cats and cats with chronic renal failure. With these dosages, adverse affects of calcitriol administration were not seen. Potential reasons for lack of apparent effect include small sample size, insufficient duration of study, insufficient dosage of calcitriol, problems with formulation or administration of calcitriol, and variable gastrointestinal absorption of calcitriol.
Hostutler
Roger A
RA
Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Ohio State University, Columbus, OH 43210, USA.
DiBartola
Stephen P
SP
Chew
Dennis J
DJ
Nagode
Larry A
LA
Schenck
Patricia A
PA
Rajala-Schultz
Päivi J
PJ
Drost
W Tod
WT
D000284:Administration, Oral; D000818:Animals; D002117:Calcitriol / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D002118:Calcium / Q000097:blood*; D002120:Calcium Channel Agonists / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D002371:Cat Diseases / Q000097:blood* / Q000188:drug therapy; D002415:Cats; D018592:Cross-Over Studies; D004334:Drug Administration Schedule; D005260:Female; D006934:Hypercalcemia / Q000097:blood / Q000188:drug therapy / Q000662:veterinary*; D006962:Hyperparathyroidism, Secondary / Q000097:blood / Q000209:etiology / Q000517:prevention & control / Q000662:veterinary; D007676:Kidney Failure, Chronic / Q000097:blood / Q000150:complications / Q000188:drug therapy / Q000662:veterinary*; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood*; D016896:Treatment Outcome
D002120:Calcium Channel Agonists; D010281:Parathyroid Hormone; D002117:Calcitriol; D002118:Calcium