calcitriol
Calcijex, Rocaltrol

Available forms
Available by prescription only
Capsules: 0.25 mcg, 0.5 mcg
Injection: 1 mcg/ml, 2 mcg/ml
Oral solution: 1 mcg/ml

Indications and dosages
 Management of hypocalcemia in patients undergoing long-term dialysis.  
Oral. Adults: Initially, 0.25 mcg P.O. daily. Dosage may be increased by 0.25 mcg daily at 4- to 8-week intervals. Maintenance dosage is 0.25 mcg every other day up to 0.5 to 1 mcg P.O. daily.
Parenteral. Adults: 1 to 2 mcg I.V. three times weekly, about every other day. Dosage may be increased by 0.25 to 0.5 mcg at 2- to 4-week intervals. Maintenance dosage is 0.5 to 4 mcg I.V. three times weekly.
 Management of hypoparathyroidism and pseudohypoparathyroidism. Adults and children age 6 and older: Initially, 0.25 mcg P.O. daily in the morning. Dosage may be increased at 2- to 4-week intervals. Maintenance dosage is 0.5 to 2 mcg daily.
Children ages 1 to 5 (hypoparathyroidism only): Initially, 0.25 mcg P.O. daily. Dosage may be increased at 2- to 4-week intervals. Maintenance dosage is 0.25 to 0.75 mcg P.O. daily.
 Prevention or management of secondary hyperparathyroidism and resultant metabolic bone disease in predialysis patients (moderate to severe chronic renal failure with creatinine clearance of 15 to 55 ml/minute). Adults and children age 3 and older: Initially, 0.25 mcg P.O. daily. Dose may be increased to 0.5 mcg daily, if needed.
Children younger than age 3: 0.01 to 0.015 mcg/ kg P.O. daily.
 Psoriasis vulgaris ◇. Adults: 0.25 mcg P.O. b.i.d. for 6 months and topically (0.1 to 0.5 mcg/g petroleum) daily for 8 weeks.

Pharmacodynamics
Antihypocalcemic action: Calcitriol is a vitamin D analogue (1,25-dihydroxycholecalciferol) or activated cholecalciferol. It promotes absorption of calcium from the intestine by forming a calcium-binding protein. It reverses the signs of rickets and osteomalacia in patients who can’t activate or use ergocalciferol or cholecalciferol. In patients with renal failure, it reduces bone pain, muscle weakness, and parathyroid serum levels.

Pharmacokinetics
Absorption: Absorbed readily after oral administration.
Distribution: Distributed widely and is protein-bound.
Metabolism: Metabolized in the liver and kidneys, with a half-life of 3 to 8 hours. No activation step is required.
Excretion: Excreted primarily in feces.

Contraindications and precautions
Contraindicated in patients with hypercalcemia or vitamin D toxicity. Withhold all preparations containing vitamin D.

Interactions
Drug-drug. Antacids containing magnesium: May induce hypermagnesemia, especially in patients with chronic renal failure. Avoid use together.
Cardiac glycosides: Increases risk of arrhythmias. Avoid use together.
Cholestyramine, colestipol, mineral oil: May alter calcitriol absorption. Avoid use together.
Corticosteroids: May counteract effects of vitamin D analogues. Don’t use together.
Orlistat: Decreases absorption of vitamin D. Give at least 2 hours apart.

Adverse reactions
CNS: headache, somnolence, weakness, irritability.
CV: hypertension, arrhythmias.
EENT: conjunctivitis, photophobia, rhinorrhea.
GI: nausea, vomiting, constipation, polydipsia, pancreatitis, metallic taste, dry mouth, anorexia.
GU: nephrocalcinosis, polyuria, nocturia.
Metabolic: weight loss.
Musculoskeletal: bone and muscle pain.
Skin: pruritus.
Other: hyperthermia, decreased libido.

Effects on lab test results
None reported.

Overdose and treatment
Treatment of hypercalcemia (a sign of overdose) requires discontinuation of drug, a low-calcium diet, increased fluid intake, and supportive measures. Calcitonin administration may help reverse hypercalcemia. In severe cases, death has followed CV and renal failure.

Special considerations
• Drug may alter serum alkaline phosphatase levels and may alter electrolytes, such as magnesium, phosphate, and calcium in serum and urine.
• Vitamin D intoxication is linked to hypercalcemia.
• Protect drug from heat and light.
• Calcitriol therapy may falsely elevate cholesterol determinations made using the Zlatkis-Zak reaction.
• Monitor serum calcium levels several times weekly after starting therapy.
• Monitoring urine calcium and urine creatinine may be very helpful in screening for hypercalciuria. The ratio of urine calcium to urine creatinine should be less than or equal to 0.18. A value of more than 0.2 suggests hypercalciuria, and the dose should be decreased regardless of serum calcium level. The product of serum calcium times phosphate shouldn’t exceed 70.
Breast-feeding patients
• Very little drug appears in breast milk; but the effect of vitamin D levels exceeding the recommended daily allowance in infants isn’t known. Large doses shouldn’t be administered to breast-feeding women.
Pediatric patients
• Some infants may be hyperreactive to drug. Long-term treatment has been well tolerated except for occasional episodes of electrolyte imbalance, which resolve with alteration of therapy.

Patient education
• Instruct patient on the importance of a calcium-rich diet.
• Tell patient that drug must not be taken by anyone for whom it wasn’t prescribed. It’s the most potent form of vitamin D.
• Advise patient to report adverse reactions immediately.
• Tell patient to avoid antacids containing magnesium and other drugs without medical approval.

Reactions may be common, uncommon, life-threatening, or COMMON AND LIFE THREATENING.
◆ Canada only
◇ Unlabeled clinical use