Calcitriol (systematic): Drug information
- Vitamin D Analog
Secondary Hyperparathyroidism in Chronic Kidney disease:
For Patients on Dialysis: Oral: Initial dose: 0.25 mcg once a day (manufacturer’s labeling)
Some experts advocate more conservative initial doses (e.g. 0.25 mcg thrice a week). Further, the dosage may be increased by 0.25mcg every other day.
IV: Start off carefully: 0.5mcg three times a week is the lowest recommended dose in the manufacturer’s labeling. Some experts approve more conservative initial doses (e.g. 0.25 mcg three times a week). They advocate adjusting the dose by 0.5 to 1 mcg at 2 to 4-week intervals.
Dosage range: 0.5 to 4 mcg 3 times a week. When there is a rise in the PTH level in response to therapy, the gradual dose reduction and discontinuation of the therapy may be necessary.
Patients with acute, chronic kidney disease not yet on dialysis:
Note: The magnitude of the PTH response is highly fluctuating. KDIGO regulation recommends starting with low doses independent of initial PTH concentration and then adjusting based on PTH response while avoiding hypercalcemia.
Oral: Initial dose is recommended to 0.25 mcg once a day (manufacturer’s labeling). Some experts recommend more conservative initial doses (e.g. 0.25 mcg 3 to 4 times weekly), and if the need arises, the dosage is increased to 0.5 mcg per day.
Discontinuation of therapy for hypercalcemia: It is advocated to discontinue the therapy if hypercalcemia occurs. It is recommended to monitor calcium and phosphorous levels daily until levels normalize. Upon normalization, treatment with calcitriol can be regained at a regular dose than that previously used. Examine your dietary calcium intake and adjust as specified.
IV: This may be allowed as bolus dose IV through the catheter at the end of hemodialysis.
Oral: May be administered without considering food. However, it is advisable to help with meals to reduce GI issues.
The following drug reactions and appearances are derived from product labeling unless otherwise mentioned.
>10%: Endocrine & metabolic: Hypercalcemia
Ø Hypersentivity to calcitriol,
Ø Other Vitamin D analogues,
Ø Any component of the formulation hypercalcemia,
Ø Vitamin D toxicity.
Dosage may be taken without considering meals. However, it is advisable to administer the dose with meals to reduce GI concerns. It is essential to maintain sufficient calcium intake during the therapy. There might be a need to limit the consumption of dietary phosphorus.
Mechanism of action:
- Calcitriol, the active form of Vitamin D (1,25 hydroxyvitamin D3), binds to activates Vitamin D receptors in the kidney, parathyroid gland, intestine, and the bone invigorating the intestinal calcium transport and absorption.
- It minimizes the parathyroid hormone (PTH) levels and improves calcium and phosphate homeostasis by restoring the bone resorption of calcium and elevating renal tubular reabsorption of calcium.
- Decreasing the renal conversion of vitamin D to its primary active metabolite (1,25 hydroxyvitamin D) in chronic renal failures leads to reduced activation of vitamin D receptor, which eventually withdraws restrictive repression of parathyroid hormone (PTH) release.
- Increased serum PTH (secondary hyperparathyroidism) minimizes calcium excretion and intensifies bone resorption.
Pharmacodynamics and Pharmacokinetics
At the start of action: Oral: 2 hours, maximum effect: 10 hours
Duration: Oral, IV: 3 to 5 days
Absorption: Oral: Rapid
Protein binding: 99.9%
Metabolism: Predominantly to calcitroic acid and a lactone metabolite
Renal function impairment: The half-life is increased by at least two-fold