calcitriol (systemic)

Absorption: IV administration results in complete bioavailability; Well absorbed following oral administration.

Distribution: Unknown.

Protein Binding: 99.9%.

Metabolism/Excretion: Undergoes enterohepatic recycling and is excreted mostly in bile.

Half-Life: Normal renal function: 5–8 hr; Chronic renal failure: 16–22 hr.

Time/Action Profile ⬆ ⬇

(effects on serum calcium)

ROUTE	ONSET	PEAK	DURATION
PO	2–6 hr	2–6 hr	3–5 days

Contraind./Precautions ⬆ ⬇

Contraindicated in:

Hypersensitivity;
Hypercalcemia;
Vitamin D toxicity;
Lactation: Lactation.

Use Cautiously in:

OB: Use during pregnancy only if potential maternal benefit justifies potential fetal risk.

Adv. Reactions/Side Effects ⬆ ⬇

Seen primarily as manifestations of toxicity (hypercalcemia)

CV: arrhythmias, hypertension

Derm: pruritus

EENT: conjunctivitis, photophobia, rhinorrhea

F and E: hypercalcemia, polydipsia

GI: ↑liver enzymes, abdominal pain, anorexia, constipation, dry mouth, nausea, PANCREATITIS, vomiting

GU: ↓libido, albuminuria, azotemia, nocturia, polyuria

Local: pain at injection site

Metab: hyperthermia, weight loss

MS: bone pain, metastatic calcification, muscle pain

Neuro: dysgeusia, headache, somnolence, weakness

Misc: hypersensitivity reactions

Interactions ⬆ ⬇

Drug-drug:

Cholestyramine, colestipol, or mineral oil may ↓ absorption.
Thiazide diuretics and calcium-containing drugsmay ↑ risk of hypercalcemia.
Corticosteroids may ↓ effectiveness.
Digoxin may ↑ risk of arrhythmias.
Magnesium-containing drugs may ↑ risk of hypermagnesemia; avoid concurrent use.
Vitamin D supplements↑ risk of hypercalcemia; avoid concurrent use.

Drug-Food:

Ingestion of foods high in calcium content (see Food Sources for Specific Nutrients) may ↑ risk of hypercalcemia.

Route/Dosage ⬆ ⬇

Hypocalcemia Associated with Hypoparathyroidism or Pseudohypoparathyroidism

PO (Adults and Children ≥6 yr): 0.25 mcg once daily initially; if needed, may ↑ dose by 0.25 mcg/day at 2–4 wk intervals (typical dosage = 0.5–2 mcg/day).
PO (Children 1–5 yr): 0.25–0.75 mcg once daily.
PO (Children <1 yr): 0.04–0.08 mcg/kg once daily.

Secondary Hyperparathyroidism in Chronic Kidney Disease

PO (Adults ): Patients on dialysis:0.25 mcg once daily; may ↑ by 0.25 mcg/day at 4-8-wk intervals, up to 0.5–1 mcg/day. Patients not on dialysis:0.25 mcg once daily; may ↑ to 0.5 mcg once daily, if needed
PO (Children >20 kg): Patients not on dialysis:0.25 mcg once daily; adjust dose based on intact parathyroid hormone (iPTH) concentrations.
PO (Children 10–20 kg): Patients not on dialysis:0.1–0.15 mcg once daily; adjust dose based on iPTH concentrations
PO (Children <10 kg): Patients not on dialysis:0.05 mcg every other day; adjust dose based on iPTH concentrations
IV (Adults ): Patients on dialysis:0.5 mcg 3 times weekly; may ↑ by 0.5–1 mcg at 2-4-wk intervals (range: 0.5–4 mcg 3 times weekly).
PO IV (Children and iPTH >1,000 pg/mL): Patients on dialysis:0.025 mcg/kg 3 times weekly; adjust dose based on iPTH concentrations.
PO IV (Children and iPTH 501–1,000 pg/mL): Patients on dialysis:0.015 mcg/kg 3 times weekly; adjust dose based on iPTH concentrations.
PO IV (Children and iPTH 300–500 pg/mL): Patients on dialysis:0.0075 mcg/kg 3 times weekly; adjust dose based on iPTH concentrations.

Rickets

PO (Adults and Children ): Vitamin D-dependent: 1 mcg once daily; Vitamin D-resistant: 0.015–0.02 mcg/kg once daily (range 0.03–0.06 mcg/kg/day; max = 2 mcg/day).

Availability ⬆ ⬇

(Generic available)

Capsules: 0.25 mcg; 0.5 mcg
Oral solution: 1 mcg/mL
Solution for injection: 1 mcg/mL

Assessment ⬆ ⬇

Assess for signs/symptoms of vitamin D deficiency (bone pain, muscle weakness, osteoporosis, fractures, hair loss) before and periodically during therapy.
Observe patient carefully for evidence of hypocalcemia (paresthesia, muscle twitching, laryngospasm, colic, cardiac arrhythmias, and Chvostek’s or Trousseau’s sign). Protect symptomatic patient by raising and padding side rails; keep bed in low position.
Children: Monitor height and weight; growth arrest may occur in prolonged high-dose therapy.

Lab Test Considerations:

Evaluate serum calcium and phosphorus concentrations twice weekly during initial therapy. Monitor serum calcium, phosphorus, magnesium, alkaline phosphatase, and intact PTH concentrations at least monthly thereafter. A ↓ in serum alkaline phosphatase levels may be an indication of impending hypercalcemia.
- The serum calcium times phosphate product (Ca * P) should not exceed 70 (patients may be at ↑ risk of calcification).
- May cause false ↑ cholesterol levels.

Toxicity and Overdose:

Toxicity is manifested as hypercalcemia, hypercalciuria, and hyperphosphatemia. Assess patient for appearance of nausea, vomiting, anorexia, weakness, constipation, headache, bone pain, and metallic taste. Later symptoms include polyuria, polydipsia, photophobia, rhinorrhea, pruritus, and cardiac arrhythmias. Notify health care provider immediately if these signs/symptoms of hypervitaminosis D occur. Treatment usually consists of discontinuation of calcitriol, a low-calcium diet, use of low-calcium dialysate in peritoneal dialysis patients, or administration of a laxative. IV hydration and loop diuretics may be ordered to ↑ urinary excretion of calcium. Hemodialysis may also be used. If patient has hyperphosphatemia, treatment with an oral phosphate-binding agent (calcium acetate, sevelamer, lanthanum carbonate) may be needed.

Implementation ⬆ ⬇

PO: Administer without regard to meals. Measure solution accurately with calibrated dropper. May be mixed with juice, cereal, or food, or dropped directly into mouth. Capsules and solution should be protected from light.

IV Administration:

IV Push: Administer as a bolus dose through the catheter at the end of hemodialysis.Store vials at room temperature and protect from light. Inspect for discoloration or particulate matter prior to use. Stable in tuberculin syringes and exposed to ambient room light for 8 hr. Discard unused portion.
Dosage Adjustments Based on iPTHIf iPTH is the same, ↑, or ↓ by <30%:↑ calcitriol dose. If iPTH is 1.5–3 times upper limit of normal or ↓ by 30%-59%:maintain calcitriol dose. If iPTH is ↑ by ≥60%:↓ calcitriol dose.
Y-Site Incompatibility: Do not administer other drugs through same IV line.

Patient/Family Teaching ⬆ ⬇

Explain the purpose and side effects of calcitriol. Advise patient to take as directed. Take missed doses as soon as remembered that day, unless almost time for next dose; do not double up on doses. Advise patient to read Medication Guide before starting and periodically during therapy in case of changes.
Emphasize the importance of follow-up exams to evaluate progress.
Review diet modifications with patient. See Food Sources for Specific Nutrients for foods high in calcium and vitamin D. Patients with chronic kidney disease must still consider renal failure diet in food selection. Health care professional may order concurrent calcium supplement. Explain that the best source of vitamins is a well-balanced diet with foods from the four basic food groups, as well as the importance of sunlight exposure.
Patients self-medicating with vitamin supplements should be cautioned not to exceed RDA. The effectiveness of megadoses for treatment of various medical conditions is unproved and may cause side effects.
Advise patient to notify health care professional of all Rx or OTC medications, vitamins, or herbal products being taken and to consult with health care professional before taking other medications.
Advise patient to avoid concurrent use of antacids containing magnesium.
Review symptoms of overdose and instruct patient to report these promptly to health care professional.
Rep: Advise women of reproductive potential to notify health care professional if pregnancy is planned or suspected or if breastfeeding. Advise the patient to follow the RDA for pregnant and lactating women. Very high or excessive doses or vitamin D are contraindicated during pregnancy and nursing because they cause hypercalcemia in both the mother and the newborn. Serum calcium levels of infants of mothers on oral calcitriol should be monitored if nursing cannot be avoided.

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Pronunciation ⬇

Classifications ⬆ ⬇

Indications ⬆ ⬇

Action ⬆ ⬇

Pharmacokinetics ⬆ ⬇