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Calcitriol
Systematic (IUPAC) name
(1R,3S)- 5-[2-[(1R,3aR,7aS)-1- [(2R)-6-hydroxy-6-methyl-heptan-2-yl]- 7a-methyl-2,3,3a,5,6,7-hexahydro-1H- inden-4-ylidene]ethylidene]- 4-methylidene-cyclohexane-1,3-diol
Identifiers
CAS number	32222-06-3
ATC code	A11CC04 D05AX03
PubChem	134070
DrugBank	APRD00246
Chemical data
Formula	C27H44O3
Mol. mass	416.64 g/mol
Pharmacokinetic data
Bioavailability	?
Metabolism	Renal
Half life	5–8 hours
Excretion	Renal
Therapeutic considerations
Pregnancy cat.	B3 (Au), C (U.S.)
Legal status	S4 (Au), POM (UK)
Routes	Oral, IV, topical

Calcitriol (INN) (pronounced /ˌkælsɨˈtraɪɒl/, /ˌkælˈsɨtriːɒl/) or 1,25-dihydroxycholecalciferol (abbreviated 1,25-(OH)₂D₃) is the active form of vitamin D found in the body (vitamin D₃). It increases the absorption of calcium and phosphate from the gastrointestinal tract and kidneys and inhibits release of PTH.

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

Contents 1 Production and function 2 Metabolism 3 Indications 4 Adverse effects 5 See also 6 Additional images 7 References

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) 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 PTH.

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

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

Calcitriol is indicated for:^[1]

• 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.^[2] The vitamin D analogue calcipotriol is more commonly used for psoriasis.

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.^[1]

• Vitamin D#Synthesis mechanism .28form 3.29

Calcitriol synthesis

v • d • e Endocrine system: hormones/endocrine glands (Peptide hormones, Steroid hormones)
Hypothalamic-pituitary	Hypothalamus: TRH, CRH , GnRH, GHRH, somatostatin, dopamine - Posterior pituitary: vasopressin, oxytocin - Anterior pituitary: α (FSH, LH, TSH), GH, prolactin, POMC (ACTH, MSH, endorphins, lipotropin)
Adrenal axis	Adrenal medulla: epinephrine, norepinephrine - Adrenal cortex: aldosterone, cortisol, DHEA
Thyroid axis	Thyroid: thyroid hormone (T3 and T4) - calcitonin - Parathyroid: PTH
Gonadal axis	Testis: testosterone, AMH, inhibin - Ovary: estradiol, progesterone, inhibin/activin, relaxin (pregnancy)
Other end. glands	Pancreas: glucagon, insulin, somatostatin - Pineal gland: melatonin
Non-end. glands	Placenta: hCG, HPL, estrogen, progesterone - Kidney: renin, EPO, calcitriol, prostaglandin - Heart atrium: ANP - Stomach: gastrin, ghrelin - Duodenum: CCK, GIP, secretin, motilin, VIP - Ileum: enteroglucagon - Adipose tissue: leptin, adiponectin, resistin - Thymus: Thymosin - Thymopoietin - Skeleton: Osteocalcin - Liver/other: Insulin-like growth factor (IGF-1, IGF-2)
Target-derived	NGF, BDNF, NT-3

v • d • e Vitamins (A11)
fat soluble	A (Retinol, Beta-carotene) - D (Ergocalciferol, Cholecalciferol, Dihydrotachysterol, Calcitriol, Calcidiol) - E (Tocopherol) - K (Naphthoquinone)
water soluble: B vitamins	B1 (Thiamine, Sulbutiamine, Benfotiamine) - B2 (Riboflavin) - B3 (Niacin, Nicotinamide) - B5 (Pantothenic acid, Dexpanthenol, Pantethine) - B6 (Pyridoxine, Pyridoxal phosphate) - B7 (Biotin) - B9 (Folic acid) - B12 (Cyanocobalamin, Hydroxocobalamin, Mecobalamin)
water soluble: other	C (Ascorbic acid) - Choline

v • d • e Antipsoriatics (D05)
Topical: tars	Tar
Topical: antracens	Dithranol
Topical: psoralens	Trioxysalen - Methoxsalen
Topical: other	Fumaric acid - Calcipotriol - Calcitriol - Tacalcitol - Tazarotene
Systemic: psoralens	Trioxysalen - Methoxsalen - Bergapten
Systemic: retinoids	Etretinate - Acitretin