Ergocalciferol

Ergocalciferol is vitamin D2, a fat-soluble vitamin used to replace vitamin D deficiency and support calcium regulation. Veterinary applications include selected deficiency states and management of hypocalcemia associated with hypoparathyroidism. It is a precursor requiring metabolic activation, which distinguishes it from active vitamin D preparations such as calcitriol.

Group

Vitamin D2

Mechanism of Action

Ergocalciferol is hydroxylated in the liver and subsequently in the kidney to active vitamin D metabolites. Binding of active metabolites to intracellular vitamin D receptors changes transcription of proteins involved in calcium and phosphate transport. Increased intestinal mineral absorption and effects on bone and renal handling raise calcium availability and support mineral homeostasis. The response depends on metabolic activation and the underlying disorder.

Dose Rates

Dog

Use / stage	Dose	Route	Schedule	Instructions
Hypoparathyroid hypocalcemia	500–2000 IU/kg	PO	Every 24 h	Do not use in: Hypercalcemia; Source small-animal regimen; titrate to measured calcium, not body weight alone.
Hypoparathyroidism — Initial	4000–6000 IU/kg	PO	Every 24 h	Hospitalized induction after control of hypocalcemic tetany with parenteral calcium; calcium monitoring determines transition.
Hypoparathyroidism maintenance adjustment	Reference only	PO		Once calcium remains 8–10 mg/dL without parenteral support, reduce the induction schedule to alternate days and titrate. Reported maintenance spans 1,000–2,000 IU/kg from daily to weekly; use serial calcium results rather than selecting an arbitrary interval.

Cat

Use / stage	Dose	Route	Schedule	Instructions
Hypoparathyroid hypocalcemia	500–2000 IU/kg	PO	Every 24 h	Do not use in: Hypercalcemia; Source small-animal regimen; titrate to measured calcium, not body weight alone.
Hypoparathyroidism — Initial	4000–6000 IU/kg	PO	Every 24 h	Hospitalized induction after control of hypocalcemic tetany with parenteral calcium; calcium monitoring determines transition.
Hypoparathyroidism maintenance adjustment	Reference only	PO		Once calcium remains 8–10 mg/dL without parenteral support, reduce the induction schedule to alternate days and titrate. Reported maintenance spans 1,000–2,000 IU/kg from daily to weekly; use serial calcium results rather than selecting an arbitrary interval.

Indications

Treatment of vitamin D deficiency and associated impaired mineralization, including nutritional rickets or osteomalacia in susceptible veterinary species.
Treatment of selected hypocalcemic patients with hypoparathyroidism, usually alongside calcium supplementation; clinical use depends on species and the available vitamin D preparation.

Contraindications

Pregnancy
Hypercalcemia
Not appropriate when renal activation to active vitamin D is impaired.

Interactions

High calcium intake increases hypercalcemia risk.

Adverse effects

Hypercalcemia and tissue mineralization

Toxicity

Overdose may produce prolonged hypercalcemia and renal injury.

Preparations

Preparation	Form	Strength	Route
Ergocalciferol 50000 IU capsule	Capsule	50000 IU / capsule	PO

Monitoring and Administration

Adjust treatment to serum calcium and renal parameters. One IU equals 0.025 mcg.