CALCITRIOL

(kal-si-trye'ole)
Calcijex, Rocaltrol
Classifications: hormones and synthetic substitutes; vitamin d analog
Pregnancy Category: C

Availability

0.25 mcg, 0.5 mcg tablets; 1 mcg/mL oral solution; 1 mcg/mL, 2 mcg/mL injection

Actions

Synthetic form of an active metabolite of ergocalciferol (vitamin D₂). In the liver, cholecalciferol (vitamin D₃) and ergocalciferol (vitamin D₂) are enzymatically metabolized to calcifediol, an activated form of vitamin D₃. Calcifediol is biodegraded in the kidney to calcitriol, the most potent form of vitamin D₃. Patients with nonfunctioning kidneys are unable to synthesize sufficient calcitriol and therefore must receive it pharmacologically.

Therapeutic Effects

By promoting intestinal absorption and renal retention of calcium, calcitriol elevates serum calcium levels, decreases elevated blood levels of phosphate and parathyroid hormone, and decreases subperiosteal bone resorption and mineralization defects in some patients.

Uses

Management of hypocalcemia in patients undergoing chronic renal dialysis and in patients with hypoparathyroidism or pseudohypoparathyroidism.

Unlabeled Uses

Selected patients with vitamin D–dependent rickets, familial hypophosphatemia (vitamin D–resistant rickets); management of hypocalcemia in premature infants.

Contraindications

Hypercalcemia or vitamin D toxicity; pregnancy (category C), lactation. Safe use in children not established.

Cautious Use

Hyperphosphatemia, patients receiving digitalis glycosides.

Route & Dosage

Hypocalcemia
Adult: PO 0.25 mcg/d, may be increased by 0.25 mcg/d q4–8wk for dialysis patients or q2–4wk for hypoparathyroid patients if necessary IV 0.5 mcg 3 times/wk at the end of dialysis, may need up to 3 mcg 3 times/wk
Child: PO On hemodialysis: 0.25–2 mcg/d. IV 0.01–0.05 mcg/kg 3 times/wk Renal failure without dialysis: PO 0.014–0.041 mcg/kg/d

Administration

Oral

Oral dose can be taken either with food or milk or on an empty stomach. Discuss with physician.
When given for hypoparathyroidism, the dose is given in the morning.
Capsules should be protected from heat, light, and moisture. Store in tightly closed container.

Intravenous

PREPARE: Direct: Give undiluted.

ADMINISTER: Direct: Give IV push over 30–60 s.

Adverse Effects (1%)

Body as a Whole: Muscle or bone pain. CV: Palpitation. GI: Anorexia, nausea, vomiting, dry mouth, thirst, constipation, abdominal cramps, metallic taste. Metabolic: Vitamin D intoxication, hypercalcemia, hypercalciuria, hyperphosphatemia. CNS: Headache, weakness. Special Senses: Blurred vision, photophobia. Urogenital: Increased urination.

Interactions

Drug: thiazide diuretics may cause hypercalcemia; calcifediol-induced hypercalcemia may precipitate digitalis arrhythmias in patients receiving digitalis glycosides.

Pharmacokinetics

Absorption: Readily absorbed from GI tract. Onset: 2–6 h. Peak: 10–12 h. Duration: 3–5 d. Metabolism: Metabolized in liver. Elimination: Excreted mainly in feces. Half-Life: 3–6 h.

Nursing Implications

Assessment & Drug Effects

Lab tests: Determine baseline and periodic levels of serum calcium, phosphorus, magnesium, alkaline phosphatase, creatinine; measure urinary calcium and phosphorus levels q24h.
Effectiveness of therapy depends on an adequate daily intake of calcium and phosphate. The physician may prescribe a calcium supplement on an as-needed basis.
Monitor for hypercalcemia (see Signs & Symptoms, Appendix F). During dosage adjustment period, monitor serum calcium levels particularly twice weekly to avoid hypercalcemia.
If hypercalcemia develops, withhold calcitriol and calcium supplements and notify physician. Drugs may be reinitiated when serum calcium returns to normal.

Patient & Family Education

Discontinue the drug if experiencing any symptoms of hypercalcemia (see Appendix F) and contact physician.
Do not use any other source of vitamin D during therapy, since calcitriol is the most potent form of vitamin D₃. This will avoid the possibility of hypercalcemia.
Consult physician before taking an OTC medication. (Many products contain calcium, vitamin D, phosphates, or magnesium, which can increase adverse effects of calcitriol.)
Maintain an adequate daily fluid intake unless you have kidney problems, in which case consult your physician about fluids.
Do not breast feed while taking this drug.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug