Adults

Typically 1-2 tablets daily, or as directed by a physician. It is best taken with meals.

Elderly

Same as adult dosage, but caution should be exercised in patients with impaired renal function.

Renal_impairment

Use with caution and monitor serum calcium and phosphate levels. Dosage adjustment may be necessary. Contraindicated in severe renal impairment.

Onset

Gradual, as it involves replenishment of body stores and bone mineralization.

Excretion

Unabsorbed calcium is excreted in feces. Absorbed calcium is primarily excreted by the kidneys. Vitamin D metabolites are primarily excreted via bile and feces, with a smaller amount via urine.

Half life

Vitamin D3 has a long half-life, ranging from days to weeks, depending on body stores and fat solubility. Calcium's systemic half-life is shorter, but its incorporation into bone is prolonged.

Absorption

Calcium carbonate is absorbed in the small intestine, primarily through active transport and passive diffusion. Vitamin D3 is absorbed in the small intestine (jejunum and ileum), requiring bile salts, and is then transported to the liver and kidneys for activation.

Metabolism

Vitamin D3 is hydroxylated in the liver to 25-hydroxyvitamin D (calcifediol) and then in the kidneys to the active form, 1,25-dihydroxyvitamin D (calcitriol). Calcium is not metabolized in the traditional sense but is constantly regulated.

Corticosteroids

May reduce calcium absorption.

Thiazide diuretics

May increase the risk of hypercalcemia by reducing calcium excretion.

Digitalis glycosides

Increased risk of cardiac arrhythmias if hypercalcemia develops.

Bisphosphonates and Levothyroxine

Calcium can interfere with the absorption of these drugs. Separate administration by several hours.

Tetracyclines and Quinolone antibiotics

Calcium can chelate these antibiotics, reducing their absorption. Administer at least 2 hours before or 4-6 hours after calcium.