Calcitriol

[kal-si-tree-awl, -ol]

Calcitriol (INN) or 1,25-dihydroxycholecalciferol (abbreviated 1,25-(OH)₂D₃) (also known as calitrol) is the active form of vitamin D found in the body (1,25(OH)2D3). It increases the absorption of calcium and phosphate from the gastrointestinal tract and kidneys and inhibits release of calcitonin.

Calcitriol is marketed under various trade names including Rocaltrol (Roche), Calcijex (Abbott) and Decostriol (Mibe, Jesalis).

Production and function

It is produced in the kidneys via 25-Hydroxyvitamin D3 1-alpha-Hydroxylase by conversion from 25-hydroxycholecalciferol (calcidiol).

This is stimulated by a decrease in serum calcium and/or phosphate (PO₄³⁻), and an increase in parathyroid hormone (PTH) and/or prolactin levels. It increases blood calcium levels by increasing the absorption of calcium and phosphate from the gastrointestinal tract, increasing calcium and phosphate reabsorption in the kidneys, and inhibiting the release of calcitonin. Calcitriol acts in concert with parathyroid hormone (PTH).

Calcitriol is also commonly used as a medication in the treatment of hypocalcemia and osteoporosis.

Metabolism

Calcitriol becomes calcitroic acid through the action of 24-hydroxylase. Calcitroic acid is excreted in the urine.

Indications

Calcitriol is indicated for:

Treatment of hypocalcaemia – hypoparathyroidism, osteomalacia (adults), rickets (infants, children), renal osteodystrophy, chronic renal dialysis
Treatment of osteoporosis
Prevention of corticosteroid-induced osteoporosis

Calcitriol is also sometimes used topically in the treatment of psoriasis, however the evidence to support its efficacy is inconclusive. The vitamin D analogue calcipotriol is more commonly used for psoriasis.

Adverse effects

The main adverse drug reaction associated with calcitriol therapy is hypercalcaemia – early symptoms include: nausea, vomiting, constipation, anorexia, apathy, headache, thirst, sweating, and/or polyuria). Compared to other vitamin D compounds in clinical use (cholecalciferol, ergocalciferol), calcitriol has a higher risk of inducing hypercalcaemia. However, such episodes may be shorter and easier to treat due to its relatively short half-life.