Adults

For severe deficiency: 40000 IU once weekly for 6-8 weeks, followed by a maintenance dose as determined by a physician. For maintenance: 20000 IU every two weeks or 40000 IU once a month, depending on patient needs and serum levels.

Elderly

Similar to adult dosage; however, renal function and calcium levels should be monitored closely.

Renal_impairment

Use with caution. Dosage adjustment may be necessary based on serum calcium and phosphate levels. Active vitamin D metabolites may be preferred in severe renal failure.

Onset

Effects on serum calcium and phosphate levels typically observed within days to weeks of initiating therapy.

Excretion

Primarily excreted in bile and feces; a small amount is excreted in urine.

Half life

The elimination half-life of 25(OH)D (calcidiol) is approximately 15-30 days.

Absorption

Well absorbed from the small intestine, primarily in the presence of bile salts and dietary fat.

Metabolism

Metabolized in the liver to 25-hydroxycholecalciferol (calcidiol) and further in the kidneys to 1,25-dihydroxycholecalciferol (calcitriol).

Corticosteroids

May reduce Vitamin D action.

Cardiac glycosides

Increased risk of arrhythmia if hypercalcemia develops.

Thiazide diuretics

May increase the risk of hypercalcemia.

Orlistat, Cholestyramine, Mineral oil

May reduce absorption of Vitamin D and other fat-soluble vitamins.

Anticonvulsants (e.g., phenytoin, barbiturates)

May increase Vitamin D metabolism, reducing its effectiveness.