Pharmacology: Pharmacodynamics: Tonacal is a vitamin-mineral combination.
Vitamin D supplementation corrects an insufficient vitamin D intake and increases the intestinal absorption of calcium. The optimal vitamin D dose in elderly subjects is 500-1000 IU/day. Calcium supplementation balances a dietary calcium deficiency. The usual calcium requirement of the elderly is 1500 mg/day. Vitamin D and calcium supplementation correct secondary senile hyperparathyroidism.
An 18 months, double-blind, placebo-controlled study carried out in 3270 women living in institutions, aged 84±6 years and receiving a vitamin D3 supplement (800 IU/day) and calcium phosphate (corresponding to 1200 mg/day of elemental calcium) showed a significant decrease in PTH secretion. After 18 months, following an "intention to treat" (ITT) analysis 80 hip fractures were observed in the calcium vitamin D3 group and 110 hip fractures in the placebo group (p=0.004). In a follow-up study after 36 months, 137 women with at least 1 fracture of the hip were observed in the calcium vitamin D3 group (n=1176) versus 178 in the placebo group (n=1127) (p≤0.02).
Pharmacokinetics: Calcium: Absorption: In the stomach, Calcium Carbonate (Tonacal) releases calcium ions depending upon pH. The amount of calcium absorbed by the gastrointestinal tract is in the order of 30% of the ingested dose.
Distribution and Metabolism: 99% of calcium is stored in the hard matter of bones and teeth. The remaining one percent is found in intra- and extracellular liquids. Approximately 50% of total blood calcium is found in the physiologically active ionised form, of which approximately 10% in complexes with citrate, phosphate or other anions with 40% remaining bound to proteins, mainly albumin.
Elimination: Calcium is eliminated in the urine, faeces and in the sweat. Kidney excretion depends on glomerular filtration and calcium reabsorption by the tubules.
Vitamin D: Absorption: Vitamin D is easily absorbed by the small intestine.
Distribution and Metabolism: Cholecalciferol and its metabolites circulate in the blood, linked to a specific alpha globulin. Cholecalciferol is metabolised in the liver by hydroxylation to its active form, 25-hydroxycholecalciferol. It is then metabolised in the kidneys to 1,25-dihydroxycholecalciferol. 1,25-dihydroxycholecalciferol is the metabolite responsible for the increase in calcium absorption. The vitamin D3 that is not metabolised is stored in adipose and muscle tissue.
Elimination: Vitamin D3 is excreted via the faeces and urine. The plasma half-life is in the order of several days.
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Information checked by Dr. Sachin Kumar, MD Pharmacology