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Indications and Dosage
Oral
Hypocalcaemia caused by hypoparathyroidism Adult: Up to 5 mg (200 000 units) daily. May also be given via IM inj. Oral Deficiency due to malabsorption states or liver diseases Adult: Up to 1 mg (40 000 units) daily. May also be given via IM inj. Oral Nutritional deficiency Adult: 10 mcg (400 units) daily. May also be given via IM inj.
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Administration
May be taken with or without food.
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Contraindications
Hypercalcaemia. Evidence of vitamin D toxicity.
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Special Precautions
Excessive intake may lead to development of hyperphosphataemia or hypercalcaemia. Infants, renal impairment or calculi, heart disease. Monitor plasma phosphate & calcium level. Pregnancy, lactation.
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Adverse Reactions
Hyperphosphataemia or hypercalcaemia (in excessive intake). Associated effects of hypercalcaemia include hypercalciuria, ectopic calcification, & renal & CV damage.
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Drug Interactions
Increased risk of hypercalcaemia if given with thiazide diuretics, calcium or phosphate. Antiepileptics (e.g. carbamazepine, phenobarbitone, phenytoin & primidone) may increase vitamin D requirements. Rifampicin & isoniazid may reduce efficacy of vitamin D. Corticosteroids may counteract the effect of vitamin D. Digoxin or any cardiac glycoside. Reduced absorption when taken with cholestyramine, colestipol, mineral oil, orlistat. Ketoconazole.
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Food Interaction
Olestra (fat substitute).
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Lab Interference
Interfere with Zlatkis-Zak reaction causing a falsely increased serum cholesterol determination.
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Action
Description: Vit D may have anti-osteoporotic, immunomodulatory, anticarcinogenic, antipsoriatic, antioxidant & mood-modulatory activities. Along with parathyroid hormone & calcitonin, regulate serum calcium conc.
Onset: Slow. Duration: Relatively prolonged duration of action. Pharmacokinetics: Absorption: Well absorbed from the GI tract. Presence of bile is essential for adequate intestinal absorption. Hence absorption may be decreased in patients with decreased fat absorption. Distribution: Bound to a specific α-globulin. Can be stored in adipose & muscle tissue for long periods of time. Slowly released from storage sites & skin where it is formed in the presence of sunlight or uv light. May distribute into breast milk. Metabolism: Hydroxylated in the liver by the enzyme vitamin D 25-hydroxylase to form 25-hydroxycholecalciferol (calcifediol). Further hydroxylated in the kidneys by the enzyme vitamin D1-hydroxylase to form the active metabolites 1,25-dihydroxycholecalciferol (calcitriol). Further metabolism also occurs in the kidneys, including the formation of the 1,24,25-trihydroxy derivatives. Excretion: Mainly in the bile & faeces with only small amounts appearing in urine. |
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MIMS Class
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