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CALCITONIN
Calcitonin is the hypocalcaemic hormone is a single chain polypeptide with 32 amino acid (MW 3600) produced
by parafollicular 'C' cells of thyroid gland
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Synthesis and secretion of calcitonin is regulated by plasma Ca2 concentration itself: rise in plasma Ca2+ increases, while fall
in plasma Ca2+ decreases calcitonin release
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Actions
The actions of calcitonin arc generally opposite to that of PTH
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The actions of calcitonin are mediated through a G-protein coupled calcitonin receptor (CTR) and increase in cAMP
formation, but its target cells are different from that of PTH
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because it is more potent and longer acting due to slower metabolism
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I IU = 4 μg of the standard preparation
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Bad taste, flu-like symptoms, allergic reactions and joint pain are
the other adverse effects
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Hypercalcaemic states Hyperparathyroidism, hypervitaminosis D
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Post menopausal osteoporosis
Paget’s disease

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VITAMIN D
Vitamin D is the collective name given to antirachitic substances synthesized in the body and found in foods activated by
UV radiation
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D2 : calciferol- prcscnt in irradiated food yeasts, fungi, bread, milk
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Actions
I
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As a result increase
synthesis of calcium channels and a carrier protein for Ca2+ called 'calcium binding protein' (Ca BP) or Calbindin
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Calcitriol enhances resorption of calcium and phosphate from bone by promoting recruitment and differentiation of
osteoclast precursors in the bone remodeling units,it mainly appears to help bone mineralization indirectly by
maintaining normal plasma calcium and phosphate concentration, as well as by inducing proteins like osteocalcin
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Other actions of calcitriol on immunological cells- lymphokine production, proliferation and differentiation of epidermal
cells and certain malignant cells, neuronal and skeletal muscle function have also been demonstrated
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As
a consequence PTH is secreted and calcium is mobilized from bone in order to restore plasma Ca2 +
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Hypervitaminosis D It may occur due to chronic ingestion of large doses (- 50,000 IU/day) or due to increased sensitivity of tissues to vit D
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These are: hypercalcaemia, weakness, fatigue, vomiting, diarrhoea,
sluggishness, polyuria
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low calcium diet, plenty of fluids and corticosteroids
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Pharmacokinetics
Vit D is well absorbed from the intestines in the presence of bile salts, mainly through lymphatics
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Malabsorption and steatorrhoea interfere with its absorption
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Unitage and preparations
I μg of cholecalciferol = 40 IU of vit D
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Calcifero/ (Ergocalclferol, vit D2) As solution in oil, filled in gelatin capsules 25,000 and 50,000 IU caps
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Cholecalciferol (vit D3) As granules for oral ingestion and oily solution for i
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injection
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Calcitriol 0
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Alfacalcidol
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Dihydrotachysterol A synthetic analogue of vit D2
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Use
1Prophylaxis ( 400 JU/day) and treatment (3000-4000 I U/day) of nutritional vit D deficiency
is g iven to prevent or treat rickets in children and osteomalacia in adults
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Metabolic rickets
(a) Vit D resistant rickets: X-linked disorders of calcium and phosphate metabolism
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(b) Vit D dependent rickets: Another genetic disorder -Administration of calcitriol or alfacalcidol is effective in normal
doses
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Senile or postmenopausal osteoporosis
Age-related decrease in calcium absorption from gut has been noted
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However, benefit in terms of improved bone mass or reduced fracture risk

is controversial or marginal
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Hypoparathyroidism )
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Fanconi syndrome Vit D can raise the lowered phosphate levels that occur in this condition
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A non hypercalcaemic analogue of vit D Calcipotrio/ is used locally in plaque type psoriasis,

BISPHOSPHONATES
Bisphosphonates (BP s) are analogues of pyrophosphate: carbon atom replacing oxygen in the P-0- P skeleton
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They are the most effective antiresorptive
drugs
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The second and third generation
compounds are more potent, have higher efficacy and additional mode of action
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Hypercalcaemia of malignancy
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Oral administration of BPNs All oral BPs are to be taken on empty stomach in the morning with a full glass of water
and the patient is instructed not to lie down or take food for at least 30 min
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These
measures are needed to prevent contact of the drug with esophageal mucosa which results in esophagitis, erosions
and ulcers

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