エルゴカルシフェロール (ビタミンD2)
Ergocalciferol
Vitamin D2, Calciferol, activated ergosterol
別名: Drisdol · Calciferol Drops · Vitamin D2 · Viosterol · Activated ergosterol · Irradiated ergosterol
VetSheet 獣医チームが監修更新日 2026年4月5日エビデンスに基づく獣医学リファレンス
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
動物種別用量
🌎 NA — North America🌍 EU — Europe
犬
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| 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 | 🌎 NA |
- Maintenance therapy of parathyroid failure after using parenteral calcium to control hypocalcemic tetany: 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.
猫
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| 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 | 🌎 NA |
- Maintenance therapy of parathyroid failure after using parenteral calcium to control hypocalcemic tetany: 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.
用量は獣医専門家向けの臨床参考資料です。必ず最新の医薬品情報および個別症例に基づいて確認してください。
概要
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:
- Ergocalciferol → hepatic 25-hydroxylase → 25-hydroxyvitamin D2 (calcidiol, partially active).
- 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.
安全性・警告
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
注意事項
Important Warnings
- Renal Impairment: Patients with kidney dysfunction may not convert ergocalciferol into the primary active metabolite. Calcitriol or DHT is preferred as they bypass renal activation.
- Hyperphosphatemia: Use with extreme caution. Elevated calcium and phosphorus simultaneously can lead to severe metastatic soft tissue mineralization (monitor calcium x phosphorus product).
- Monitoring Commitment: Chronic therapy should not be initiated unless owners are willing to commit to ongoing, rigorous patient monitoring.
- Pregnancy: Hypervitaminosis D has been implicated in causing teratogenic effects. Weigh potential benefits against risks.
- Nursing: Large doses of vitamin D are excreted into milk. Consider using milk replacer for offspring of dams receiving therapeutic dosages.
医薬品相互作用
Can reduce the effects of vitamin D analogs by decreasing calcium absorption and increasing renal excretion.
Patients are highly sensitive to the arrhythmogenic effects of hypercalcemia; intensified monitoring is required.
Patients are sensitive to the effects of hypercalcemia; intensified monitoring is required.
May reduce the amount of orally administered ergocalciferol absorbed from the GI tract.
May cause hypercalcemia when given in conjunction with Vitamin D analogs due to decreased renal calcium excretion.
監視
- 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)
薬物動態
吸収
Absorbed from the small intestine in the presence of bile salts.
分布
Stored extensively in the liver and fat. Several days of therapy may be required until distribution steady state is achieved.
代謝
Hydroxylated in the liver to 25-hydroxyvitamin D, then activated in the kidneys to 1,25-dihydroxyvitamin D. Cats do not appear to convert ergocalciferol to its 25-hydroxylate form as well as cholecalciferol.
消失
Effects may persist for up to 18 weeks once treatment is discontinued due to slow release from fat stores.
過剰投与
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.
製品
製剤
- Oral Liquid (Drops)
- Oral Capsules
ヒト用医薬品
- Ergocalciferol Oral Liquid (Drops): 8,000 Units/mL (200 micrograms/mL) in 60 mL
- Ergocalciferol Oral Capsules: 50,000 Units (1.25 mg)
規制ステータス
規制データなし: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
保管・安定性
Ergosterol is sensitive to light, heat, and air. Store capsules or liquid at room temperature (15-30°C) and protect from light.
飼主向け情報
- 費用と効果：エルゴカルシフェロールは他のビタミンD薬（カルシトリオールなど）より安価ですが、効果が現れるまでに時間がかかり、体内に長く留まるため、通常は第一選択とはなりません。
- 生涯にわたる治療：副甲状腺の問題に対するビタミンD製剤の使用には、通常、生涯にわたる治療と定期的な血液検査のための通院が必要です。
- 高カルシウム血症のリスク：この薬は低カルシウム血症を治療しますが、過剰摂取すると血中カルシウム濃度が危険なレベルまで上昇する可能性があります。薬は体脂肪に蓄積されるため、この毒性作用は薬を中止した後も何週間も続くことがあります。
- 症状に注意：ペットに多飲、多尿、嘔吐、極度の疲労などの高カルシウム血症の兆候が見られた場合は、すぐに獣医師に連絡してください。
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