Calcitriol

Calcitriol injection is indicated in the management of hypocalcemia in patients undergoing chronic renal dialysis. It has been shown to significantly reduce elevated parathyroid hormone levels. Reduction of PTH has been shown to result in an improvement in renal osteodystrophy.

Calcitriol injection is for intravenous injection only.

The optimal dose of calcitriol injection must be carefully determined for each patient.

The effectiveness of calcitriol injection therapy is predicated on the assumption that each patient is receiving an adequate and appropriate daily intake of calcium. The RDA for calcium in adults is 800 mg. To ensure that each patient receives an adequate daily intake of calcium, the physician should either prescribe a calcium supplement or instruct the patient in proper dietary measures.

The recommended initial dose of Calcitriol Injection, depending on the severity of the hypocalcemia and/or secondary hyperparathyroidism, is 1 mcg (0.02 mcg/kg) to 2 mcg administered intravenously three times weekly, approximately every other day. Doses as small as 0.5 mcg and as large as 4 mcg three times weekly have been used as an initial dose. If a satisfactory response is not observed, the dose may be increased by 0.5 to 1 mcg at two to four week intervals. During this titration period, serum calcium and phosphorus levels should be obtained at least twice weekly. If hypercalcemia or a serum calcium times phosphate product greater than 70 is noted, the drug should be immediately discontinued until these parameters are appropriate. Then, the calcitriol injection dose should be reinitiated at a lower dose. Doses may need to be reduced as the PTH levels decrease in response to the therapy. Thus, incremental dosing must be individualized and commensurate with PTH, serum calcium and phosphorus levels. The following is a suggested approach in dose titration:

Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit.

Discard unused portion.

Adverse effects of calcitriol injection are, in general, similar to those encountered with excessive vitamin D intake. The early and late signs and symptoms of vitamin D intoxication associated with hypercalcemia include:

Drug Interactions

Concomitant use of magnesium-containing preparations should be used with caution or avoided since such use may lead to the development of hypermagnesemia.

Corticosteroids with glucocorticoid activity may counteract the bone and mineral metabolism effects of vitamin D analogues.

Cytochrome P450 enzyme-inducing anticonvulsants such as carbamazepine, phenobarbital and phenytoin may reduce the effects of vitamin D because they increase vitamin D catabolism.

Calcitriol Injection is synthetically manufactured calcitriol and is available as a sterile, isotonic, clear, colorless to yellow, aqueous solution for intravenous injection. Calcitriol Injection, USP is available in 1 mL ampules. Each 1 mL contains: Active: Calcitriol, 1 mcg. Inactives: Dibasic Sodium Phosphate, Anhydrous 7.6 mg; Edetate Disodium, Dihydrate 1.1 mg; Monobasic Sodium Phosphate, Monohydrate 1.8 mg; Polysorbate 20, 4 mg; Sodium Ascorbate 10 mg; Sodium Chloride 1.5 mg; pH Range is from 6.5 to 8.0 and Water for Injection.

Calcitriol is a colorless, crystalline compound which occurs naturally in humans. It is soluble in organic solvents but relatively insoluble in water. Calcitriol is chemically designated (5Z, 7E)-9,10 secocholesta 5,7,10(19)-triene-1α, 3β, 25-triol and has the following structural formula:

The other names frequently used for calcitriol are 1α,25-dihydroxycholecalciferol,1α, 25-dihydroxyvitamin D3,1,25-DHCC,1,25(OH)2D3 and 1,25-diOHC.

Calcitriol is the active form of vitamin D3 (cholecalciferol). The natural or endogenous supply of vitamin D in man mainly depends on ultraviolet light for conversion of 7-dehydrocholesterol to vitamin D3 in the skin. Vitamin D3 must be metabolically activated in the liver and the kidney before it is fully active on its target tissues. The initial transformation is catalyzed by a vitamin D3-25- hydroxylase enzyme present in the liver, and the product of this reaction is 25-(OH)D3 (calcifediol). The latter undergoes hydroxylation in the mitochondria of kidney tissue, and this reaction is activated by the renal 25-hydroxyvitamin D3-1 α-hydroxylase to produce 1,25-(OH)2D3 (calcitriol), the active form of vitamin D3.

The known sites of action of calcitriol are intestine, bone, kidney and parathyroid gland. Calcitriol is the most active known form of vitamin D3 in stimulating intestinal calcium transport. In acutely uremic rats, calcitriol has been shown to stimulate intestinal calcium absorption. In bone, calcitriol, in conjunction with parathyroid hormone, stimulates resorption of calcium; and in the kidney, calcitriol increases the tubular reabsorption of calcium. In vitro and in vivo studies have shown that calcitriol directly suppresses secretion and synthesis of PTH. A vitamin D-resistant state may exist in uremic patients because of the failure of the kidney to adequately convert precursors to the active compound, calcitriol.

Calcitriol when administered by bolus injection is rapidly available in the blood stream. Vitamin D metabolites are known to be transported in blood, bound to specific plasma proteins. The pharmacologic activity of an administered dose of calcitriol is about 3 to 5 days. Two metabolic pathways for calcitriol have been identified, conversion to 1,24,25-(OH)3D3 and to calcitroic acid.

Calcitriol Injection, USP is supplied in 1 mL ampules containing 1 mcg.

 

1 mcg/mL NDC 17478-831-01

Since calcitriol is the most potent metabolite of vitamin D available, prescription-based doses of vitamin D and its derivatives should be withheld or used with caution during treatment to avoid the risk of hypercalcemia.

A non-aluminum phosphate-binding compound should be used to control serum phosphorous levels in patients undergoing dialysis.

Overdosage of any form of vitamin D is dangerous (see also OVERDOSAGE). Progressive hypercalcemia due to overdosage of vitamin D and its metabolites may be so severe as to require emergency attention. Chronic hypercalcemia can lead to generalized vascular calcification, nephrocalcinosis and other soft tissue calcification. The serum calcium times phosphate (Ca x P) product should not be allowed to exceed 70 mg2/dL2. Radiographic evaluation of suspect anatomical regions may be useful in the early detection of this condition.