Ergocalciferol
**Ergocalciferol (Vitamin D2)** is a fat-soluble vitamin and **Vitamin D analog** used primarily in veterinary medicine to manage hypocalcemia associated with hypoparathyroidism. * **Cost-effective**: Often chosen as a less expensive alternative to calcitriol or dihydrotachysterol (DHT). * **Delayed onset**: Because it requires both hepatic and renal enzymatic activation, it takes longer (5-21 days) to achieve maximal effects on serum calcium compared to active metabolites. * **Prolonged toxicity**: It is highly lipophilic and stored in fat. If hypercalcemia develops, toxic effects can persist for up to 18 weeks even after discontinuation. > **Clinical Pearl**: Cats do not efficiently convert ergocalciferol to its 25-hydroxylated form compared to cholecalciferol (Vitamin D3). Therefore, calcitriol is generally preferred in feline patients for managing hypocalcemia.
Mecanismo: Ergocalciferol is an inactive prodrug that requires a two-step enzymatic activation process to regulate calcium homeostasis: 1. Ergocalciferol → **hepatic 25-hydroxylase** → 25-hydroxyvitamin D2 (calcidiol, partially active). 2. 25-hydroxyvitamin D2 → **renal 1-alpha-hydroxylase** → 1,25-dihydroxyvitamin D2 (fully active calcitriol equivalent). The active metabolite binds to intracellular **Vitamin D Receptors (VDR)**, acting as a hormone alongside parathyroid hormone (PTH) and calcitonin to: * Enhance intestinal absorption of calcium and phosphate. * Promote renal tubular reabsorption of calcium. * Increase the rate of accretion and osteoclastic resorption of minerals in bone, mobilizing calcium into the extracellular fluid.
Dosificación por especie
- Maintenance therapy of parathyroid failure after using parenteral calcium to control hypocalcemic tetany · Initially 4000-6000 Units/kg PO once daily. Maintenance doses usually range from 1000-2000 Units/kg PO once daily to once weekly. · PO · once daily to once weekly · Lifelong · Patient should be hospitalized initially. Adjust dosage to maintain serum calcium concentrations between 8-9.5 mg/dL. Goal is to prevent hypocalcemic tetany, but not induce hypercalcemia.
- Maintenance therapy of parathyroid failure after using parenteral calcium to control hypocalcemic tetany · Initially 4000-6000 Units/kg PO once daily. Maintenance doses usually range from 1000-2000 Units/kg PO once daily to once weekly. · PO · once daily to once weekly · Lifelong · Patient should be hospitalized initially. Adjust dosage to maintain serum calcium concentrations between 8-9.5 mg/dL. Goal is to prevent hypocalcemic tetany, but not induce hypercalcemia.
Las dosis son una referencia clínica para veterinarios colegiados. Confirme siempre con la ficha técnica vigente y el paciente individual.
Vías de administración
Contraindicaciones
- Hypercalcemia
- Vitamin D toxicity
- Malabsorption syndrome
- Abnormal sensitivity to the effects of vitamin D
Efectos adversos
- Hypercalcemia
- Hyperphosphatemia
- Nephrocalcinosis
- Soft tissue mineralization
Interacciones farmacológicas
- Corticosteroids · Can reduce the effects of vitamin D analogs by decreasing calcium absorption and increasing renal excretion.
- Digoxin · Patients are highly sensitive to the arrhythmogenic effects of hypercalcemia; intensified monitoring is required.
- Verapamil · Patients are sensitive to the effects of hypercalcemia; intensified monitoring is required.
- Mineral Oil · May reduce the amount of orally administered ergocalciferol absorbed from the GI tract.
- Thiazide Diuretics · May cause hypercalcemia when given in conjunction with Vitamin D analogs due to decreased renal calcium excretion.
Monitorización
- Serum calcium concentrations (weekly initially, then monthly for 6 months, then every 2-3 months)
- Serum phosphorus concentrations
- Renal function parameters (BUN, Creatinine)
- Clinical signs of hypercalcemia (PU/PD, lethargy, anorexia, vomiting)
Sobredosis
### Acute Toxicity * The toxic acute oral dose of ergocalciferol in dogs is reported as **4 mg/kg (160,000 Units/kg)**. * **Decontamination**: Acute ingestions should be managed using established protocols for removal or prevention of GI absorption. Orally administered **mineral oil** may reduce absorption and enhance fecal elimination. ### Chronic Overdosage (Hypercalcemia) * **Immediate Action**: Temporarily discontinue ergocalciferol and any exogenous calcium therapy. * **Medical Management**: If hypercalcemia is severe, administer **0.9% normal saline** (calcium-free IV fluids), **furosemide** (to promote calciuresis), and **corticosteroids** (to decrease GI absorption and increase renal excretion of calcium). Urine acidification may also be employed. * **Prolonged Effect**: Because of the long duration of action (potentially up to 18 weeks), hypercalcemia may persist for weeks to months. Restart therapy at a reduced dosage only when calcium serum levels return to the normal range.
La referencia de fármacos de VetSheet está destinada a veterinarios colegiados como apoyo a la decisión clínica, no sustituye el juicio profesional ni la ficha técnica vigente del fabricante.