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All about: Calcitriol

Big Image Pronouncation: (Kal-si-TRYE-ole)
Class: Fat-soluble vitamin

Trade Names:
Calcijex
- Injection 1 mcg/mL

Trade Names:
Rocaltrol
- Capsules 0.25 mcg
- Capsules 0.5 mcg
- Oral solution 1 mcg/mL

Trade Names:
Calcitriol Injection
- Injection 2 mcg/mL

Mechanism of Action

Pharmacology

Supply of vitamin D depends mainly on exposure to ultraviolet rays of the sun for conversion of 7-dehydrocholesterol in the skin to vitamin D 3 (cholecalciferol). Vitamin D 3 is activated in the liver and kidney before fully active as a regulator of calcium and phosphorus metabolism at target tissues.

Pharmacokinetics

Absorption

Oral

Rapidly absorbed from the intestine. T max is 3 to 6 h.

Distribution

Approximately 99.9% protein bound. Excreted in breast milk in low levels.

Metabolism

The first pathway involves 24-hydroxylase to produce calcitroic acid; the second pathway involves hydroxylation and cyclization. Calcitrol also undergoes enterohepatic recycling.

Elimination

The t ½ is about 5 to 8 h. About 27% is excreted in the feces and 7% in the urine within 24 h.

Special Populations

Renal Function Impairment

The t ½ is increased by at least 2-fold.

Children

The t ½ is prolonged.

Indications and Usage

Dialysis (Oral, IV)

Hypocalcemia and resultant metabolic bone disease in patients on chronic renal dialysis.

Predialysis (Oral)

Secondary hyperparathyroidism and resultant metabolic bone disease in patients with moderate to severe chronic renal failure (Ccr 15 to 55 mL/min) not yet on dialysis.

Hypoparathyroidism (Oral)

Hypocalcemia in patients with postsurgical hypoparathyroidism, idiopathic hypoparathyroidism, and pseudohypoparathyroidism.

Unlabeled Uses

Decreased severity of psoriatic lesions with an initial oral dose of 0.25 mcg twice daily and topically 0.1 to 0.5 mcg/g petrolatum.

Contraindications

Hypercalcemia or patients with vitamin D toxicity; hypersensitivity to any component of this product.

Dosage and Administration

Dialysis

PO 0.25 mcg/day. Unsatisfactory response, increase dose by 0.25 mcg/day at 4- to 8-wk intervals. Obtain serum calcium levels at least twice weekly during this titration. Normal or only slightly reduced calcium levels may respond to doses of 0.25 mcg every other day.

IV 0.02 mcg/kg (1 to 2 mcg) 3 times/wk, every other day. May increase 0.5 to 1 mcg, every 2 to 4 wk. During this titration, obtain serum calcium levels twice weekly.

Hypoparathyroidism

PO Initial dose is 0.25 mcg/day in the morning. Unsatisfactory response, increase dose at 2- to 4-wk intervals. During this titration, obtain serum calcium levels 2 times/wk.

Adults and children (6 yr of age and older)

PO 0.5 to 2 mcg daily.

Children (1 to 5 yr of age)

PO Have usually been given 0.25 to 0.75 mcg daily.

Discontinue if hypercalcemia or serum calcium times phosphate product (Ca × P) totals more than 70.

Predialysis

PO Initial dose is 0.25 mcg/day in adults and children older than 3 yr of age. Dosage may be increased up to 0.5 mcg/day. In patients younger than 3 yr of age, dosage is 10 to 15 ng/kg/day.

General Advice

  • Oral
  • Administer prescribed dose without regard to meals, but administer with food if GI upset occurs.
  • Administer dose in the morning to patient with hypoparathyroidism.
  • Administer prescribed dose of oral solution using disposable graduated oral dispensers supplied with medication.
  • Injection
  • For IV bolus injection only. Not for intradermal, subcutaneous, IM, or intra-arterial administration.
  • Do not administer if particulate matter, cloudiness, or discoloration noted.
  • Discard any unused solution. Do not save for future use.

Storage/Stability

Oral

Store capsules and oral solution at controlled room temperature (59° to 86°F). Protect from light.

Injection

Store injection at controlled room temperature (59° to 86°F).

Drug Interactions

Calcium supplements

Avoid uncontrolled intake of additional calcium-containing preparations.

Cholestyramine

May reduce intestinal absorption of fat soluble vitamins.

Ketoconazole

May reduce endogenous calcitriol concentrations.

Magnesium

Magnesium-containing products may cause hypermagnesemia and should be avoided during calcitriol administration to patients on chronic renal dialysis.

Phenytoin/Phenobarbital

Inhibits endogenous synthesis of calcitriol, therefore may require higher doses if given simultaneously.

Phosphate-binding agents

Because phosphate transport in the intestine, kidneys, and bones may be affected, the dosage of phosphate-binding agents must be adjusted based on serum phosphate concentration.

Thiazides

Known to induce hypercalcemia by the reduction of calcium excretion.

Vitamin D

To avoid possible additive effects and hypercalcemia, withhold pharmacologic doses of vitamin D and its derivatives.

Laboratory Test Interactions

None well documented.

Adverse Reactions

See overdosage section.

Precautions

Monitor

Calcium intake

Ensure that patient is receiving an adequate daily intake of calcium. Consider adding a calcium supplement if dietary calcium intake is less than 600 mg/day.

Dialysis patients

Ensure that serum calcium, phosphorous, magnesium, and alkaline phosphatase are determined periodically in patient on dialysis.

Hypercalcemia symptoms

Frequently assess patient for signs and symptoms of hypercalcemia (eg, weakness, headache, drowsiness, nausea, vomiting, bone pain, metallic taste, appetite loss, weight loss, polyuria, polydipsia, nocturia, photophobia, mental status change). Immediately inform health care provider if noted.

Hypercalcemic patients

Ensure that serum calcium and phosphorous are evaluated daily during periods of hypercalcemia.

Hypoparathyroid patients

Ensure that serum calcium, phosphorous, and 24-h urinary calcium are determined periodically in hypoparathyroid patient.

Predialysis patients

Ensure that serum calcium, phosphorous, alkaline phosphatase, creatinine, and intact parathyroid hormone (iPTH) are determined before starting therapy in predialysis patient. Thereafter, serum calcium, phosphorous, alkaline phosphatase, and creatinine should be determined monthly for 6 mo and then periodically thereafter. The iPTH should be determined every 3 to 4 mo.

Serum calcium levels

Ensure that serum calcium is evaluated before starting therapy, twice weekly during dosage adjustment, and then periodically thereafter, and that blood samples are taken without a tourniquet. If hypercalcemia is noted or if the serum calcium times phosphate product (Ca × P) is greater than 70, immediately discontinue therapy and notify health care provider.


Pregnancy

Category C .

Lactation

May be excreted in breast milk.

Children

Safety and efficacy not established in dialysis patients.

Elderly

Dose selection should be cautious, starting at the low end of the dosage range.

Overdosage

Symptoms

Adverse reactions are associated with excessive intake. The early stage of toxicity includes the following: weakness, headache, somnolence, nausea, vomiting, dry mouth, constipation, muscle pain, bone pain, metallic taste. The late stage symptoms of toxicity include the following: cardiac arrhythmias, hypertension, pruritus, conjunctivitis (calcific), anorexia, weight loss, pancreatitis, polyuria, polydipsia, nocturia, elevated BUN, nephrocalcinosis, hypercholesterolemia, elevated AST/ALT, albuminia, decreased libido, hyperthermia, photophobia, rhinorrhea, ectopic calcification, overt psychosis, dystrophy, sensory disturbances, dehydration, apathy, arrested growth, UTI.

Patient Information

  • Instruct patient to carefully follow the diet and calcium supplementation instructions supplied by health care provider.
  • Advise patient to take prescribed dose without regard to meals but to take with food if GI upset occurs.
  • Advise patient or caregiver using oral solution to use disposable graduated oral dispensers supplied with medication.
  • Instruct dialysis patient to avoid using any magnesium-containing products (eg, antacids).
  • Educate patient regarding signs and symptoms of hypercalcemia. Instruct patient to immediately inform health care provider if they occur.

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