ジヒドロタキステロール
Dihydrotachysterol
別名: DHT · Hytakerol · AT 10 · Atiten · Dihydral · Dygratyl · Tachyrol · Tachystin · dichysterol · dihydrotachysterol2
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 |
|---|---|---|---|---|---|
| Hypocalcemia secondary to hypoparathyroidism | Initially give 0.03 mg/kg PO for several days or until effect is demonstrated, then give 0.02 mg/kg for 2 days, then 0.01 mg/kg per day. | PO | q24h | — | 🌎 NA |
- Hypocalcemia secondary to hypoparathyroidism: Pet should remain hospitalized until serum calcium concentration remains stable between 8-9.5 mg/dL. Recheck serum calcium on a weekly basis during early stages of treatment; recheck every 2-3 months long-term. Some dogs and cats that appear to be resistant to treatment on tablets or capsules may respond to the liquid form.
猫
| 適応 | 用量 | 経路 | 頻度 | 期間 | 地域 |
|---|---|---|---|---|---|
| Hypocalcemia secondary to hypoparathyroidism | Initially give 0.03 mg/kg PO for several days or until effect is demonstrated, then give 0.02 mg/kg for 2 days, then 0.01 mg/kg per day. | PO | q24h | — | 🌎 NA |
| Chronic hypocalcemia with oral calcium tx | Initially: 0.02-0.03 mg/kg/day PO. Maintenance: 0.01-0.02 mg/kg PO q24-48h. | PO | q24-48h | — | 🌎 NA |
- Hypocalcemia secondary to hypoparathyroidism: Pet should remain hospitalized until serum calcium concentration remains stable between 8-9.5 mg/dL. Recheck serum calcium on a weekly basis during early stages of treatment; recheck every 2-3 months long-term. Some dogs and cats that appear to be resistant to treatment on tablets or capsules may respond to the liquid form.
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
ジヒドロタキステロール (DHT) は、合成の脂溶性ビタミンDアナログであり、獣医学においては主に副甲状腺機能低下症または重度の腎疾患に続発する低カルシウム血症の管理に使用されます。
歴史的に重要な薬物ですが、商業的な入手可能性の問題や、カルシトリオールのより好ましい薬物動態プロファイル（発現が早く作用時間が短いため、偶発的な高カルシウム血症の管理が容易）により、現在では臨床使用の大部分がカルシトリオールに取って代わられています。
重要な臨床的ポイント：
- 作用発現：エルゴカルシフェロール（ビタミンD2）より早いが、カルシトリオールよりは遅い。
- 腎臓での活性化をバイパス：コレカルシフェロールとは異なり、DHTは活性化のために腎臓の1-α-ヒドロキシラーゼを必要としないため、重度の腎不全患者にも有効です。
- 毒性のリスク：その効果が消失するまでに1〜3週間かかることがあるため、医原性高カルシウム血症の重大なリスクがあり、厳密なモニタリングが必要です。
作用機序
Dihydrotachysterol acts as a synthetic analog of 1,25-dihydroxyvitamin D. Its mechanism of action involves several key steps:
- Hepatic Activation: DHT is absorbed from the GI tract and transported to the liver, where it undergoes hydroxylation by hepatic 25-hydroxylase → 25-hydroxydihydrotachysterol (the active metabolite).
- Receptor Binding: The active metabolite binds to Vitamin D Receptors (VDR) in target tissues (primarily intestine, bone, and kidneys).
- Calcium Homeostasis:
- Intestine: Stimulates the synthesis of calcium-binding proteins (e.g., calbindin) → significantly enhances dietary calcium and phosphorus absorption.
- Bone: Works synergistically with parathyroid hormone (PTH) to promote the accretion and resorption of minerals, mobilizing calcium into the extracellular fluid.
- Kidneys: Promotes the reabsorption of calcium by the renal tubules.
Clinical Pearl: Because the active form of DHT is structurally similar to 1,25-dihydroxyvitamin D, it effectively bypasses the need for renal 1-alpha-hydroxylase, an enzyme often deficient in chronic kidney disease.
安全性・警告
禁忌
- Pre-existing hypercalcemia
- Vitamin D toxicity
- Malabsorption syndromes
- Abnormal sensitivity to the effects of vitamin D
有害事象
- Hypercalcemia (manifesting as polydipsia, polyuria, anorexia, vomiting, lethargy)
- Nephrocalcinosis (soft tissue mineralization)
- Hyperphosphatemia
注意事項
Important Warnings
- Hyperphosphatemia: Use with extreme caution. Many clinicians consider hyperphosphatemia or a combined calcium/phosphorus product of >70 mg/dL to be an absolute contraindication due to the risk of metastatic soft tissue mineralization (nephrocalcinosis).
- Renal Dysfunction: Use with extreme caution when receiving the drug for non-renal indications.
- Pregnancy: FDA Category C. Hypervitaminosis D has caused fetal abnormalities in various species. Weigh risks vs. benefits.
- Nursing: Vitamin D is excreted in breast milk in limited amounts; use with caution.
- Laboratory Interference: Serum cholesterol levels may be falsely elevated by vitamin D analogs when using the Zlatkis-Zak reaction.
医薬品相互作用
Use with vitamin D analogs may induce severe hypercalcemia.
Can nullify the calcium-elevating effects of vitamin D analogs.
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 DHT absorbed from the GI tract.
May reduce the amount of DHT absorbed from the GI tract.
May reduce the amount of DHT absorbed from the GI tract.
May induce hepatic enzyme systems and increase the metabolism of Vitamin D analogs, thus decreasing their activity.
May induce hepatic enzyme systems and increase the metabolism of Vitamin D analogs, thus decreasing their activity.
May induce hepatic enzyme systems and increase the metabolism of Vitamin D analogs, thus decreasing their activity.
May cause hypercalcemia when given in conjunction with Vitamin D analogs.
監視
- Serum calcium levels (closely/twice daily during initial treatment; at least 2-4 times yearly during maintenance)
- Serum phosphorus levels (particularly in renal failure patients)
- Calcium-phosphorus product (Ca x P)
薬物動態
吸収
Readily absorbed from the small intestine if fat absorption is normal. Bile is required for adequate absorption; patients with steatorrhea, liver, or biliary disease will have diminished absorption. Liquid dosage forms may have better bioavailability than tablets/capsules in some animals.
分布
Widely distributed and highly protein-bound in plasma.
代謝
Hydroxylated in the liver to 25-hydroxy-dihydrotachysterol, the active form of the drug. Does not require parathormone activation in the kidneys.
消失
Excreted primarily via bile and feces. Offloads relatively rapidly compared to some other forms of vitamin D, with effects dissipating in 1-3 weeks.
過剰投与
Acute Toxicity
Acute ingestions should be managed using established protocols for GI decontamination. Orally administered mineral oil may reduce absorption and enhance fecal elimination.
Chronic Toxicity (Hypercalcemia)
Hypercalcemia secondary to chronic dosing is a serious complication.
- Discontinue Therapy: Immediately stop DHT and any exogenous calcium supplementation.
- Severe Hypercalcemia Management: Administer furosemide, calcium-free IV fluids (e.g., 0.9% normal saline) to promote diuresis, urine acidification, and corticosteroids (which decrease intestinal calcium absorption and increase renal excretion).
- Monitoring: Because of the long duration of action of DHT (usually one week and potentially up to 3 weeks), hypercalcemia may persist for an extended period.
- Re-initiation: Restart DHT/calcium therapy at a reduced dosage with diligent monitoring only when serum calcium levels return to the normal range.
製品
製剤
- Tablets (compounded)
- Capsules (compounded)
- Oral liquid/concentrate (compounded)
動物用医薬品
- None commercially available (must be compounded)
ヒト用医薬品
- None commercially available (must be compounded)
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
Store at room temperature (15-30°C). Capsules or tablets should be stored in well-closed, light-resistant containers. Oral concentrate should be stored in tight, light-resistant containers.
飼主向け情報
飼い主の皆様へ
ジヒドロタキステロール (DHT) は、通常、副甲状腺や腎臓が正常に機能していないために、ペットの体がカルシウムを吸収し、正常なレベルを維持するのを助けるために使用される薬です。
- 厳密な投薬：処方された通りに正確にこの薬を与えてください。獣医師からの明確な指示なしに、用量を変更したり、追加のカルシウムサプリメントを与えたりすることは絶対に避けてください。わずかな変更でも、血中カルシウム濃度に危険な変動を引き起こす可能性があります。
- 高カルシウム血症の兆候：喉の渇きの増加（水を多く飲む）、尿量の増加、食欲不振、嘔吐、または重度の無気力に注意してください。これらの兆候に気づいた場合は、すぐに獣医師に連絡してください。
- 低カルシウム血症の兆候：用量が低すぎる場合、ペットは筋肉の震え、顔のけいれん、こわばり、脱力感、歩行のふらつき（運動失調）、行動の変化、または発作などの低カルシウムの兆候を示すことがあります。
- 頻繁な血液検査：ペットのカルシウムレベルが安全であることを確認するために、特に投薬の開始時には頻繁な血液検査が必要になります。これはペットの安全のために必須です。
- 投与方法：ペットが錠剤にうまく反応しない場合、獣医師は液体形式に変更することがあります。液体の方が吸収が良い場合があります。
VetSheet医薬品リファレンスは獣医専門家の臨床意思決定支援を目的としており、専門的判断または製造業者の最新医薬品情報の代替にはなりません。