Alfacalcidol
Alfacalcidol is a member of the class of D3 vitamins that is calciol in which the hydrogen at the 1alpha position is replaced by a hydroxy group. It is an active metabolite of cholecalciferol, which performs important functions in regulation of the calcium balance and the bone metabolism. It has a role as a bone density conservation agent. It is a member of D3 vitamins, a seco-cholestane, a hydroxycalciol and a diol. It derives from a calciol.
Mechanism of effect
The active form of vitamin D3 (calcitriol) binds to intracellular receptors that then function as transcription factors to modulate gene expression. Like the receptors for other steroid hormones and thyroid hormones, the vitamin D receptor has hormone-binding and DNA-binding domains. The vitamin D receptor forms a complex with another intracellular receptor, the retinoid-X receptor, and that heterodimer is what binds to DNA. In most cases studied, the effect is to activate transcription, but situations are also known in which vitamin D suppresses transcription. Calcitriol increases the serum calcium concentrations by: increasing GI absorption of phosphorus and calcium, increasing osteoclastic resorption, and increasing distal renal tubular reabsorption of calcium. Calcitriol appears to promote intestinal absorption of calcium through binding to the vitamin D receptor in the mucosal cytoplasm of the intestine. Subsequently, calcium is absorbed through formation of a calcium-binding protein.
Pharmacodynamic
Alfacalcidol is Vitamin D-hormone analog which is activated by the enzyme 25-hydroxylase in the liver for systemic and in osteoblasts for local D-hormone actions.
Pharmacokinetics
Readily absorbed from small intestine (proximal or distal)
Bound to specific alpha globulins for transport.
metabolism:
activated in the liver.
Plasma half-life:
3 hours
Onset of action:
6 hours
Time to peak serum concentration:
Approximately 12 hours after a single dose.
Duration of action:
Up to 48 hours.
Elimination:
Biliary/renal.
3 hours
Onset of action:
6 hours
Time to peak serum concentration:
Approximately 12 hours after a single dose.
Duration of action:
Up to 48 hours.
Elimination:
Biliary/renal.
Drug indications
Indicated for the management of hypocalcemia, secondary hyperparathyroidism, and osteodystrophy in patients with chronic renal failure.
Dosage
Adults and children over 20 kg bodyweight:
1 microgram/day
Elderly:
0.5 microgram/day
Neonates and premature infants:
0.05 - 0.1 microgram/kg/day
Children under 20 kg bodyweight:
0.05 microgram/kg/day
1 microgram/day
Elderly:
0.5 microgram/day
Neonates and premature infants:
0.05 - 0.1 microgram/kg/day
Children under 20 kg bodyweight:
0.05 microgram/kg/day
Side effects
Skin rash and itchiness
Feeling dizzy
| Loss of appetite, loss of weight, feeling tired, feeling sick (nausea), feeling thirsty, sweating, a metallic taste in your mouth, a need to pass urine more often |
Points of recommendation
- Before you start the treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about alfacalcidol and will provide you with a full list of the side-effects which you may experience from taking it.
- Take alfacalcidol exactly as your doctor tells you to. It is usually taken as one dose a day. Try to take your doses at the same time of day each day, as this will help you to remember to take it regularly.
- There are three strengths of capsule and one strength of oral drop available - your doctor will tell you what dose to take each day. Your dose could change from time to time depending upon the results of your routine blood tests.
- If you forget to take a dose, take it as soon as you remember. If you do not remember until the following day, skip the missed dose. Do not take two doses together to make up for a forgotten dose.
Some medicines are not suitable for people with certain conditions, and sometimes a medicine may only be used if extra care is taken. For these reasons, before you start taking alfacalcidol it is important that your doctor knows:
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If you are pregnant or breastfeeding.
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If you have ever had kidney stones or you have other problems with your kidneys.
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If you know you have too much calcium in your blood or urine. This can happen with some cancers.
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If you have any heart problems.If you have an allergy to sesame oil (used
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.in One-Alpha® capsules).
Pregnancy level
Problems in humans have not been documented with intake of normal daily recommended amounts. There are insufficient data on acute and chronic vitamin D toxicity in pregnant women.
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