Ergocalciferol
Vitamins
Vitamins
Vitamin D2, made from plants and fungi. Activated like D3; prescribed for hypoparathyroidism and hard-to-treat rickets. Its safety margin is narrow.
Also called: vitamin D2
Quick facts
- Group
- Vitamins
- Target
- Vitamin D receptor (VDR), through its active metabolite
- Used for
- Hypoparathyroidism · Refractory
- Key effects
- Mostly signs of excess · Thirst
- Monitor
- Blood calcium · Kidney function and phosphate
- ATC
- A11CC01
No doses: the clinician sets them by the current guideline.
Mechanism of action
Ergocalciferol is converted in the liver to 25-hydroxyvitamin D and in the kidney to the 1,25-dihydroxy form. The active metabolite increases absorption of calcium and phosphate in the gut, mobilises them from bone and increases their reabsorption in the kidney tubule, a step regulated by parathyroid hormone.
- Liver: ergocalciferol → 25-hydroxyvitamin D
- Kidney: → 1,25-dihydroxyvitamin D (active)
- Gut, bone and kidney release more calcium and phosphate into blood
Indications
- Hypoparathyroidism Hypoparathyroidism (incl. post-thyroidectomy hypocalcaemia) →
- Refractory (vitamin D-resistant) rickets Rickets and osteomalacia →
- Familial hypophosphataemia
Adverse effects
Common
- Mostly signs of excess: loss of appetite, nausea, weakness, weight loss, vague aches, constipation
- Thirst, frequent urination and night-time urination
Contraindications
- Hypercalcaemia
- Malabsorption syndrome
- Hypervitaminosis D or abnormal sensitivity to vitamin D
Key interactions
- Mineral oil
- Reduces absorption of vitamin D
- Thiazide diuretics
- Can cause hypercalcaemia in hypoparathyroid patients taking ergocalciferol
- Other vitamin D or calcium supplements
- Add to the total intake and to the risk of toxicity
What is monitored
- Blood calcium, frequently when high doses are used
- Kidney function and phosphate
- In breastfed infants of treated mothers: the infant's calcium
Administration and safety
- Total vitamin D from fortified foods, supplements and other prescriptions is reviewed before starting.
- Calcium and phosphate intake are managed alongside it; a low-phosphate diet may be needed.
Pregnancy and breastfeeding
Amounts above the recommended intake are avoided unless clearly needed: excess vitamin D caused fetal abnormalities in animals. Its active metabolite passes into milk and can raise the infant's calcium.
Nursing care
- Teach the signs of hypercalcaemia: thirst, frequent urination, nausea, constipation, weakness, confusion.
- Remind that lab tests are done before and during treatment.
- Ask about kidney or liver disease and malabsorption.
Pharmacokinetics
- Absorption
- Fat-soluble; absorbed from the gut, possibly less in older adults; mineral oil reduces absorption
- Metabolism
- Activated by the liver and then the kidney
- Onset and duration
- Delayed by about 10–24 hours while active metabolites are made; toxicity can last two months or more after stopping
Test yourself
Think of the answer, then tap the question to see it.
What are the three label indications of prescription ergocalciferol?
Hypoparathyroidism, refractory rickets and familial hypophosphataemia.
Why can vitamin D toxicity last for weeks after stopping ergocalciferol?
It is fat-soluble and stored, so effects can persist for two months or more.
Which diuretic class can push a patient on vitamin D into hypercalcaemia?
Thiazide diuretics.
Connections
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - ERGOCALCIFEROL capsule (DailyMed (U.S. National Library of Medicine), 2026); Ergocalciferol: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.