CALCITRIOL
Clinical safety rating: safe
Animal studies have demonstrated safety
Calcitriol, the active form of vitamin D, binds to vitamin D receptors (VDR) in target tissues, modulating gene transcription. It increases intestinal calcium and phosphate absorption, enhances renal tubular reabsorption of calcium, and promotes bone mineralization by stimulating osteoblast activity.
| Metabolism | Primarily metabolized in the kidney and intestine via 24-hydroxylase (CYP24A1) to inactive metabolites (e.g., calcitroic acid). No major hepatic cytochrome P450 involvement. |
| Excretion | Renal (fecal after biliary excretion of metabolites): ~10% unchanged in urine; ~70% as metabolites in feces via bile. |
| Half-life | 5–8 hours (terminal) in normal renal function; prolonged up to 18–24 hours in chronic kidney disease (CKD) due to reduced clearance. |
| Protein binding | ~99% bound to vitamin D-binding protein (DBP) and albumin. |
| Volume of Distribution | 0.5–1.0 L/kg (indicates extensive tissue distribution, primarily to kidney, intestine, bone). |
| Bioavailability | Oral: ~70% (rapidly absorbed from small intestine). Intravenous: 100%. |
| Onset of Action | Oral: 2–6 hours (rise in serum calcium). Intravenous: within 1–2 hours. |
| Duration of Action | Oral: 3–5 days (calcemic effect persists after discontinuation). Intravenous: 2–3 days. |
0.25-0.5 mcg orally once daily, may increase by 0.25 mcg/day at 4-8 week intervals; maximum 2 mcg/day.
| Dosage form | CAPSULE |
| Renal impairment | GFR 15-59 mL/min: initial dose 0.25 mcg orally once daily; GFR <15 mL/min: avoid use or use with caution, dose adjustment not established. |
| Liver impairment | No specific guidelines for Child-Pugh; use with caution in severe hepatic impairment as calcitriol metabolism may be altered. |
| Pediatric use | Neonates and children: initial 0.25 mcg orally once daily; may increase by 0.25 mcg at 2-4 week intervals as needed; maximum 2 mcg/day. |
| Geriatric use | Start at low end of dosing range (0.25 mcg once daily) due to possible decreased renal function; monitor serum calcium and phosphorus closely. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Cholestyramine may impair absorption Magnesium-containing antacids may cause hypermagnesemia Can cause hypercalcemia monitor serum calcium levels.
| Breastfeeding | Calcitriol is present in breast milk in low concentrations. The M/P ratio is approximately 0.3–0.4. At maternal therapeutic doses, risk to the infant is minimal. Monitor infant serum calcium if maternal high doses are used. |
| Teratogenic Risk | Calcitriol is the active form of vitamin D. At therapeutic doses, no increased risk of major malformations has been consistently demonstrated. However, excessive doses (hypercalcemia) during pregnancy can lead to fetal hypercalcemia, aortic stenosis, retinopathy, and intellectual disability. First trimester: No clear teratogenicity at normal doses. Second and third trimesters: Maternal hypercalcemia from overdosage may cause fetal hypercalcemia and adverse effects. Avoid doses causing maternal serum calcium >11 mg/dL. |
■ FDA Black Box Warning
None officially designated by FDA. However, excessive administration may lead to hypercalcemia, hypercalciuria, and hyperphosphatemia, with risk of soft tissue calcification and renal toxicity.
| Common Effects | Hypercalcemia |
| Serious Effects |
["Hypercalcemia or evidence of vitamin D toxicity","Hypersensitivity to calcitriol or any component of the formulation","Hyperphosphatemia (unless adequately managed)"]
| Precautions | ["Hypercalcemia risk: avoid excessive dosing; monitor serum calcium, phosphate, and alkaline phosphatase regularly","Hypercalciuria: may cause nephrolithiasis; maintain adequate hydration","Digitalis toxicity: hypercalcemia increases risk; monitor cardiac status","Adynamic bone disease: excessive suppression of PTH in dialysis patients may lead to low bone turnover","Aluminum intoxication: concurrent use of aluminum-containing phosphate binders may increase toxicity"] |
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| Fetal Monitoring | Monitor maternal serum calcium, phosphate, and 1,25-dihydroxyvitamin D levels periodically. Assess renal function and urinary calcium excretion. Fetal monitoring: ultrasound for growth and amniotic fluid volume if maternal hypercalcemia or prolonged use. Neonatal monitoring: serum calcium and phosphate levels after birth. |
| Fertility Effects | No evidence of adverse effects on fertility in humans. Vitamin D receptors are expressed in reproductive tissues, and adequate vitamin D levels may support fertility, but calcitriol at therapeutic doses is not associated with impaired fertility. |
| Food/Dietary |
| High dietary calcium intake may increase risk of hypercalcemia; advise consistent calcium intake per healthcare provider. No specific restrictions with other foods. |
| Clinical Pearls | Monitor serum calcium and phosphate levels regularly; hypercalcemia risk especially with thiazide diuretics or high calcium intake. Calcitriol has a rapid onset (hours) and short half-life, making it ideal for acute management of hypocalcemia. Avoid concurrent use of magnesium-containing antacids due to risk of hypermagnesemia. |
| Patient Advice | Take exactly as prescribed, usually once daily with or without food. · Do not take additional calcium or vitamin D supplements without consulting your doctor. · Report symptoms of hypercalcemia: nausea, vomiting, constipation, muscle weakness, confusion, or irregular heartbeat. · Avoid excessive intake of calcium-rich foods (e.g., dairy products) unless advised. · Store at room temperature away from light and moisture. |