エルゴカルシフェロール (ビタミンD2)
**エルゴカルシフェロール（ビタミンD2）**は脂溶性ビタミンおよび**ビタミンDアナログ**であり、主に獣医療において副甲状腺機能低下症に伴う低カルシウム血症の管理に使用されます。 * **費用対効果**：カルシトリオールやジヒドロタキステロール（DHT）の安価な代替薬として選択されることが多いです。 * **効果発現の遅延**：肝臓および腎臓での酵素的活性化が必要なため、活性代謝物と比較して血清カルシウムに対する最大効果を得るまでに時間がかかります（5〜21日）。 * **毒性の長期化**：脂溶性が高く脂肪に蓄積されます。高カルシウム血症が発症した場合、投与を中止しても毒性作用が最大18週間持続する可能性があります。 > **臨床上のポイント**：猫はコレカルシフェロール（ビタミンD3）と比較して、エルゴカルシフェロールを25-ヒドロキシ化形態に効率的に変換できません。したがって、猫の低カルシウム血症の管理には通常カルシトリオールが推奨されます。
作用機序: 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.
動物種別の用量
- 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.
用量は獣医療従事者向けの臨床リファレンスです。必ず最新の添付文書と個々の患者で確認してください。
投与経路
禁忌
- Hypercalcemia
- Vitamin D toxicity
- Malabsorption syndrome
- Abnormal sensitivity to the effects of vitamin D
有害事象
- Hypercalcemia
- Hyperphosphatemia
- Nephrocalcinosis
- Soft tissue mineralization
薬物相互作用
- 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.
モニタリング
- 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)
過量投与
### 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.
VetSheet の薬剤リファレンスは、獣医療従事者向けの臨床意思決定支援を目的としており、専門的判断やメーカーの最新添付文書に代わるものではありません。