Colecalciferol (Vitamin D3)

Colecalciferol, also known as vitamin D3 and cholecalciferol, is a type of vitamin D that is normally produced by the skin when exposed to sunlight; it is also found in some foods and can be taken as a dietary supplement. It is used to treat and prevent vitamin D deficiency and related diseases, including rickets (primarily children). It is also used for familial hypophosphatemia, hypoparathyroidism, which causes low blood calcium levels, and Fanconi syndrome. Vitamin D supplements may not be effective in people with severe kidney disease. It is usually taken by mouth in the form of drops. Vitamin D3 is available as an OTC ("over the counter") product without a prescription.

Pharmacodynamics

Colecalciferol alone is inactive and must first be activated in the liver. All of its metabolites are bound to vitamin D-binding protein in the blood. The action of calcitriol is mediated by the vitamin D receptor, a nuclear receptor that regulates the synthesis of hundreds of proteins and is present in virtually every cell in the body.

Pharmacokinetics

Colecalciferol is readily absorbed from the small intestine in the presence of fat absorption defects. Protein binding for colecalciferol is 50 to 80%. Specifically, vitamin D3 (from food or skin) is bound in plasma to vitamin D-binding protein (DBP) formed in the liver. In the liver, colecalciferol is hydroxylated to calcidiol (25-hydroxycholecalciferol) by the enzyme vitamin D 25-hydroxylase. In the kidney, calcidiol then serves as a substrate for 1-alpha-hydroxylase, resulting in calcitriol (1,25-dihydroxycholecalciferol), the biologically active form of vitamin D3. Degradation occurs via the enzyme 24-hydroxylase and excretion occurs entirely through the intestine.

Interactions

Since it is a naturally occurring vitamin, no interactions are to be expected.

Side effects

Side effects are not expected with normal use. In case of very strong overdose ostheoporosis may occur. Furthermore, calcium deposits in kidneys and other organs may occur, which may irreversibly impair their function.