Dihydrotachysterol
Also known as: DHT · Hytakerol · AT 10 · Atiten · Dihydral · Dygratyl · Tachyrol · Tachystin · dichysterol · dihydrotachysterol2
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| 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.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| 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.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Dihydrotachysterol (DHT) is a synthetic, fat-soluble vitamin D analog primarily utilized in veterinary medicine to manage hypocalcemia secondary to hypoparathyroidism or severe renal disease.
While historically significant, its clinical use has largely been supplanted by calcitriol due to commercial availability issues and calcitriol's more favorable pharmacokinetic profile (faster onset and shorter duration of action, which makes managing accidental hypercalcemia easier).
Key clinical points:
- Faster onset than ergocalciferol (Vitamin D2), but slower than calcitriol.
- Bypasses renal activation: Unlike cholecalciferol, DHT does not require the enzyme 1-alpha-hydroxylase in the kidneys to become active, making it effective in patients with severe renal failure.
- Toxicity risk: Because its effects can take 1 to 3 weeks to dissipate, iatrogenic hypercalcemia is a significant risk and requires diligent monitoring.
Mechanism of action
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.
Safety & warnings
Contraindications
- Pre-existing hypercalcemia
- Vitamin D toxicity
- Malabsorption syndromes
- Abnormal sensitivity to the effects of vitamin D
Adverse effects
- Hypercalcemia (manifesting as polydipsia, polyuria, anorexia, vomiting, lethargy)
- Nephrocalcinosis (soft tissue mineralization)
- Hyperphosphatemia
Precautions
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.
Drug interactions
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.
Monitoring
- 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)
Pharmacokinetics
Absorption
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.
Distribution
Widely distributed and highly protein-bound in plasma.
Metabolism
Hydroxylated in the liver to 25-hydroxy-dihydrotachysterol, the active form of the drug. Does not require parathormone activation in the kidneys.
Elimination
Excreted primarily via bile and feces. Offloads relatively rapidly compared to some other forms of vitamin D, with effects dissipating in 1-3 weeks.
Overdose
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.
Available products
Formulations
- Tablets (compounded)
- Capsules (compounded)
- Oral liquid/concentrate (compounded)
Veterinary
- None commercially available (must be compounded)
Human-labeled
- None commercially available (must be compounded)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
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.
Client information
Important Information for Pet Owners
Dihydrotachysterol (DHT) is a medication used to help your pet's body absorb and maintain normal levels of calcium, usually because their parathyroid glands or kidneys are not functioning properly.
- Strict Dosing: Give this medication exactly as prescribed. Never change the dose or give extra calcium supplements without explicit instructions from your veterinarian. Even small changes can cause dangerous shifts in blood calcium levels.
- Signs of High Calcium (Hypercalcemia): Watch closely for increased thirst (drinking more water), increased urination, loss of appetite, vomiting, or severe lethargy. Contact your vet immediately if you notice these signs.
- Signs of Low Calcium (Hypocalcemia): If the dose is too low, your pet may show signs of low calcium, including muscle tremors, facial twitching, stiffness, weakness, uncoordinated walking (ataxia), behavioral changes, or seizures.
- Frequent Blood Tests: Your pet will need frequent blood tests, especially when starting the medication, to ensure their calcium levels are safe. This is mandatory for their safety.
- Administration: If your pet is not responding well to pills, your vet may switch them to a liquid form, which is sometimes absorbed better.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.