CALCITRIOL- calcitriol solution
Calcitriol Injection is synthetically manufactured calcitriol and is available as a sterile, isotonic, clear, colorless to yellow, aqueous solution for intravenous injection. Calcitriol Injection is available in 1 mL ampuls. Each 1 mL contains calcitriol, 1 mcg; Polysorbate 20, 4 mg; sodium chloride 1.5 mg; sodium ascorbate 10 mg added; dibasic sodium phosphate, anhydrous 7.6 mg; monobasic sodium phosphate, dihydrate 2.0 mg; edetate disodium, dihydrate 1.1 mg added. pH 7.2 (6.5 to 8.0).
Calcitriol is a 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)2 D3 , 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)2 D3 (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)3 D3 and to calcitroic acid.
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 should not be given to patients with hypercalcemia or evidence of vitamin D toxicity.
Since calcitriol is the most potent metabolite of vitamin D available, vitamin D and its derivatives should be withheld during treatment.
A non-aluminum phosphate-binding compound should be used to control serum phosphorus 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. Radiographic evaluation of suspect anatomical regions may be useful in the early detection of this condition.
Excessive dosage of Calcitriol Injection induces hypercalcemia and in some instances hypercalciuria; therefore, early in treatment during dosage adjustment, serum calcium and phosphorus should be determined at least twice weekly. Should hypercalcemia develop, the drug should be discontinued immediately.
Calcitriol Injection should be given cautiously to patients on digitalis, because hypercalcemia in such patients may precipitate cardiac arrhythmias.
The patient and his or her parents should be informed about adherence to instructions about diet and calcium supplementation and avoidance of the use of unapproved non-prescription drugs, including magnesium-containing antacids. Patients should also be carefully informed about the symptoms of hypercalcemia (see ADVERSE REACTIONS).
Serum calcium, phosphorus, magnesium and alkaline phosphatase and 24-hour urinary calcium and phosphorus should be determined periodically. During the initial phase of the medication, serum calcium and phosphorus should be determined more frequently (twice weekly).
Adynamic bone disease may develop if PTH levels are suppressed to abnormal levels. If biopsy is not being done for other (diagnostic) reasons, PTH levels may be used to indicate the rate of bone turnover. If PTH levels fall below recommended target range (1.5 to 3 times the upper limit of normal), in patients treated with Calcitriol Injection, the Calcitriol Injection dose should be reduced or therapy discontinued. Discontinuation of Calcitriol Injection therapy may result in rebound effect, therefore, appropriate titration downward to a maintenance dose is recommended.
Magnesium-containing antacid and Calcitriol Injection should not be used concomitantly, because such use may lead to the development of hypermagnesemia.
Long-term studies in animals have not been conducted to evaluate the carcinogenic potential of Calcitriol Injection. Calcitriol was not mutagenic in vitro in the Ames Test nor was oral calcitriol genotoxic in vivo in the Mouse Micronucleus Test. No significant effects on fertility and/or general reproductive performances were observed in a Segment I study in rats using oral calcitriol at doses of up to 0.3 mcg/kg.
Calcitriol has been found to be teratogenic in rabbits when given orally at doses of 0.08 and 0.3 mcg/kg. All 15 fetuses in 3 litters at these doses showed external and skeletal abnormalities. However, none of the other 23 litters (156 fetuses) showed external and skeletal abnormalities compared with controls. Teratogenicity studies in rats at doses up to 0.45 mcg/kg orally showed no evidence of teratogenic potential. There are no adequate and well-controlled studies in pregnant women. Calcitriol Injection should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
Nonteratogenic Effects: In the rabbit, oral dosages of 0.3 mcg/kg/day administered on days 7 to 18 of gestation resulted in 19% maternal mortality, a decrease in mean fetal body weight and a reduced number of newborns surviving to 24 hours. A study of the effects on orally administered calcitriol on peri- and postnatal development in rats resulted in hypercalcemia in the offspring of dams given calcitriol at doses of 0.08 or 0.3 mcg/kg/day, hypercalcemia and hypophosphatemia in dams given calcitriol at a dose of 0.08 or 0.3 mcg/kg/day and increased serum urea nitrogen in dams given calcitriol at a dose of 0.3 mcg/kg/day. In another study in rats, maternal weight gain was slightly reduced at an oral dose of 0.3 mcg/kg/day administered on days 7 to 15 of gestation.
The offspring of a woman administered oral calcitriol at 17 to 36 mcg/day during pregnancy manifested mild hypercalcemia in the first 2 days of life which returned to normal at day 3.
It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk and because of the potential for serious adverse reactions in nursing infants from calcitriol, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.
Pediatric use information is approved for Abbott Laboratories’ calcitriol injection. However, due to Abbott Laboratories’ marketing exclusivity rights, this drug product is not labeled for pediatric use.
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