Alfacalcidol
2 medicines
Alfacalcidol is a ready-activated form of vitamin D that raises calcium levels and strengthens bone, and because it works without needing the kidneys, blood calcium must be checked regularly to avoid dangerous overdose.
Key facts
- Alfacalcidol is a synthetic, already-active form of vitamin D. It increases calcium absorption from food and helps the body hold on to calcium, supporting bone strength.
- It's taken once daily as a capsule or drops; effects on blood calcium can take several days to settle after any dose change.
- Because it's already active, alfacalcidol can push blood calcium up quickly. Regular blood calcium tests are required throughout treatment to catch this before it becomes dangerous.
- Seek urgent care for persistent vomiting, extreme thirst, confusion or severe abdominal pain, which can signal dangerously high calcium.
What Alfacalcidol treats
Alfacalcidol treats hypocalcaemia (low blood calcium) and renal osteodystrophy, the bone disease that develops when failing kidneys can no longer activate vitamin D on their own. It's also used for osteomalacia and some cases of hypoparathyroidism, where the parathyroid glands don't produce enough hormone to keep calcium balanced.
How Alfacalcidol works
Normally the kidneys convert vitamin D into its active form, calcitriol, in a tightly controlled step. Alfacalcidol skips that step: the liver converts it directly into calcitriol, so it keeps working even when the kidneys have failed. Calcitriol then increases calcium absorption from the gut and helps regulate how bone stores and releases calcium.
Before you take it
- Do not take alfacalcidol if you already have high blood calcium or signs of vitamin D toxicity.
- Tell your prescriber about kidney stones, sarcoidosis or other conditions that raise calcium sensitivity, and about any calcium or vitamin D supplements you take, since combining them increases the risk of overdose.
- Thiazide diuretics raise the risk of high calcium when combined with alfacalcidol. Magnesium- or aluminium-containing antacids can reduce its absorption.
- Pregnancy and breastfeeding need medical supervision, since calcium balance affects the baby.
Side effects
Early effects can include nausea, headache, dry mouth and mild stomach upset.
Stop and seek urgent medical care for:
- Persistent vomiting, severe thirst or confusion, which suggest high calcium.
- Unusual tiredness, bone pain or muscle weakness that worsens over time.
- Reduced urine output or blood in the urine.
Safety essentials
- Blood calcium, and often kidney function, must be checked regularly, especially when starting treatment or changing the dose, because alfacalcidol raises calcium directly and overdose is its main danger.
- Do not take extra calcium or vitamin D supplements without medical advice while on alfacalcidol.
- If blood tests show high calcium, treatment is usually paused or the dose lowered until levels return to normal.
This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.