Calcitriol vs Alfacalcidol

	Calcitriol	Alfacalcidol
Indications	·         Established postmenopausal osteoporosis ·         Renal osteodystrophy in patients on haemodialysis ·         Hypoparathyroidism and rickets ·         Secondary hyperparathyroidism in renal failure	·         Rena osteodystrophy in patients on haemodialysis ·         Hypoparathyroidism and pseudohypoparathyroidism ·         Adjunct to the management of tertiary hyperparathyroidism ·         Rickets and osteomalacia ·         Osteoporosis
Dosage	·         0.25 mcg BD daily ·         Initial dose 0.25 mcg. In patient with normal or only slightly reduced serum calcium levels, doses of 0.25 mcg EOD is sufficient ·         0.25 mcg/day given in the morning ·         Adult and child ≥3yo: initially 0.25 mcg/ml. child <3yo: 10-15 ng/kg/day	Initial dose adult and child above 20kg BW: 1 mcg daily; child under 20kg BW: 0.05 mcg/kg/day. Maintenance dose: 0.25-2 mcg daily
Pharmacodynamic	·         Immediate binding to small intestine receptors after oral intake absorption ·         Presence of plasma peaks, which increases risk of hypercalcemia and hypercalciuria	·         Undergo activation in liver first by 25-hydroxylation (prodrug) after oral intake absorption ·         Balanced plasma curve of calcitriol lowers the risk of hypercalcemia and hypercalciuria ·         Additional activation in bone tissue
Pharmacokinetic	·         Rapidly absorbed from intestine and reach peak serum concentrations within 3 to 6 hours ·         99.9% bound by alpha-globulin vitamin D binding protein in blood ·         Two pathways of metabolism: 24-hydroxylase in kidney to calcitroic acid and stepwise hydroxylation of carbon-26 and carbon-23 to lactone metabolite ·         Excreted primarily via faeces. Enterohepatic recycling and biliiary excretion also occurs.	·         Onset of action: 6 hours. Peak serum concentrations reach within 12 hours for PO, 4 hours for IV. ·         Bind extensively to vitamin D binding protein ·         Undergoes rapid hepatic conversion to 1, 25-dihydroxyvitamin D, the vitamin D metabolite which acts as a regulator of calcium and phosphate metabolism ·         Excreted mainly in bile and faeces, small amounts in urine

References:

1. MyBlueBook App.
2. Leo Pharma. Ask Your Question Osteoporosis. http://www.leo-sarath.com/Home/Ask-a-question/Osteoporosis.aspx#2
3. Roxane Laboratories. Calcitriol Capsules. http://bidocs.boehringer-ingelheim.com/BIWebAccess/ViewServlet.ser?docBase=renetnt&folderPath=/Prescribing+Information/PIs/Roxane/Calcitriol+Capsules/CalcitriolCapsules.pdf
4. EMC. Alfacalcidol 0.25microgram Capsules. https://www.medicines.org.uk/emc/medicine/26565