Adults

1-2 tablets daily, preferably with or after meals.

Elderly

Same as adults, but caution is advised in patients with renal impairment.

Renal_impairment

Use with caution. Dosage adjustment may be necessary based on serum calcium and phosphate levels. Avoid in severe renal impairment.

Onset

Gradual; clinical effects on bone density take several weeks to months to become apparent.

Excretion

Calcium is primarily excreted via feces, with a smaller amount excreted renally. Vitamin D3 metabolites are excreted mainly in bile and a small amount in urine.

Half life

Elemental calcium has a relatively short half-life in the bloodstream. Vitamin D3 (cholecalciferol) has a half-life of about 24 hours, but its active metabolite (calcifediol) has a half-life of 2-3 weeks.

Absorption

Calcium carbonate is absorbed in the small intestine, with absorption efficiency varying (typically 20-30%). Vitamin D3 is fat-soluble and well absorbed from the gastrointestinal tract, especially in the presence of bile salts.

Metabolism

Calcium is primarily regulated by parathyroid hormone and calcitonin. 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).

Bisphosphonates

Calcium can interfere with bisphosphonate absorption. Administer at least 30-60 minutes apart.

Thiazide diuretics

May increase the risk of hypercalcemia.

Cardiac glycosides (e.g., Digoxin)

Hypercalcemia may potentiate the effects of cardiac glycosides, increasing the risk of arrhythmias.

Tetracyclines and Fluoroquinolones

Calcium can reduce the absorption of these antibiotics. Administer at least 2-3 hours apart.