Doses - DIHYDROTACHYSTEROL, DHT
Vitamin D therapy for hypocalcemic conditions is often used with exogenously administeredcalcium products. Refer to the calcium monograph or the references cited below for further information.Dogs:
For hypocalcemia secondary to hypoparathyroidism:
a) Once life-threatening signs of hypocalcemia have been controlled with intravenouscalcium, give DHT initially at 0.03 - 0.06 mg/kg/day PO for 2-3 days, then 0.02 - 0.03mg/kg/day for 2-3 days, and finally 0.01 mg/kg/day until further dosage adjustments arerequired. Stable serum calcium levels (8.5-9.5 mg/dl) are usually achieved in a week.
Determine serum calcium levels twice daily during initial treatment period until levelshave stabilized in the low-normal range. (Peterson 1986)
b) 0.007 - 0.010 mg/kg PO once daily (maintenance dose); may require 1-2 weeks to restore normocalcemia. (Mulnix 1985)
c) For secondary hypoparathyroidism: During initial loading period with calcium and DHT, monitor serum calcium 1-2 times daily for 5-10 days. Give loading dose of DHTat 0.02 - 0.05 mg/kg PO once daily for 2-3 days, then 0.01 - 0.03 mg/kg PO once dailyfor 1 week. After a low normal serum calcium is achieved, give 0.01 mg/kg PO onceevery other day and then every third day etc., until it can be finally stopped. Dose shouldbe individualized for each animal. During loading period, calcium should be given at 25- 50 mg (elemental calcium)/kg/day divided 2-4 times a day. After 1 week, decrease doseto 15 - 25 mg (elemental calcium)/kg/day divided and gradually reduce. The goal is tokeep serum calcium levels in the low-normal range (7.5 - 9.5 mg/dl) so that theremaining parathyroid tissue will respond via feedback mechanisms.
For primary hypoparathyroidism (animals will require therapy for life): Loadingregimen is the same as for secondary hypoparathyroidism. Then DHT may be given at0.01 mg/kg PO once daily and eventually every other day if serum calcium levelspermit. Reduce oral calcium supplementation to as low a dose as possible; may considerreplacing pharmaceuticals with a high calcium diet. Monitoring of calcium levels may bereduced to 1-2 times per month after loading regimen is completed and animal isrelatively stable. Dosage adjustments of either DHT or calcium should be made inincrements of about 25%. Eventually, animal may only need to be monitored (serumcalcium) only several times a year. (Meuten and Armstrong 1989)
For hypocalcemia secondary to severe renal failure:
a) After hyperphosphatemia is controlled (do not use calcium and vitamin D if calcium/phosphate product is in excess of 70 mg/dl), use oral calcium carbonate therapy. If calcium alone does not resolve hypocalcemia add DHT at 0.125 mg per dog PO 3 times per week. Adjust dose based on serial calcium determinations. Maximum effect may require 2-4 weeks and duration may persist up to 1 week after treatment is discontinued. (Allen 1989)
b) In combination with calcium therapy, give DHT initially at 0.03 mg/kg/day for 2 days, then 0.02 mg/kg/day for 2 days, then 0.01 mg/kg/day maintenance dose. (Kay and Richter 1988)Cats:
For hypocalcemia secondary to hypoparathyroidism:
a) For secondary hypoparathyroidism: As per dogs in "c" above. Dosage is empirical.
Cats with hypoparathyroidism secondary to thyroidectomy may require treatment forseveral months. (Meuten and Armstrong 1989)
b) In combination with calcium therapy (initially at 50 - 100 mg/kg/day divided 3-4 timesdaily of elemental calcium), give DHT initially at 0.125 - 0.25 mg PO per day for 2-3days, then 0.08 - 0.125 mg per day for 2-3 days and finally 0.05 mg PO per day untilfurther dosage adjustments are necessary. Stable serum calcium levels (8.5-9.5 mg/dl)are usually achieved in about a week. Continue to monitor and adjust dosages of DHTand calcium to lowest levels to maintain normocalcemia. (Peterson and Randolph 1989)(Note: refer to the calcium monograph for further information.)
Monitoring Parameters -1) Serum calcium levels should be monitored closely (some clinicians recommend twicedaily) during the initial treatment period. When the animal is stabilized frequency may bereduced, but never discontinued. All animals receiving DHT therapy should have calciumlevels determined at least 2-4 times yearly. 2) Serum phosphorous (particularly in renal failure patients)
Client Information - Clients should be briefed on the symptoms of hypercalcemia (polydipsia, polyuria, anorexia) and hypocalcemia (muscle tremors, twitching, tetany, weakness, stiff gait, ataxia, behavioral changes, and seizures) and instructed to report these symptoms to the veterinarian.
Dosage Forms/Preparations/FDA Approval Status/Withholding Times - Veterinary-Approved Products: None
Dihydrotachysterol Oral Concentrate Solution 0.2 mg/ml in 30 ml bottles, and 0.25 mg/ml (inoil) in 15 ml bottles; DHT® Intensol (Roxane), Hytakerol® (Winthrop); (Rx)
Dogs: 
For hypocalcemia secondary to hypoparathyroidism: a) Once life-threatening signs of hypocalcemia have been controlled with intravenouscalcium, give DHT initially at 0.03 - 0.06 mg/kg/day PO for 2-3 days, then 0.02 - 0.03mg/kg/day for 2-3 days, and finally 0.01 mg/kg/day until further dosage adjustments arerequired. Stable serum calcium levels (8.5-9.5 mg/dl) are usually achieved in a week.
Determine serum calcium levels twice daily during initial treatment period until levelshave stabilized in the low-normal range. (Peterson 1986)
b) 0.007 - 0.010 mg/kg PO once daily (maintenance dose); may require 1-2 weeks to restore normocalcemia. (Mulnix 1985)
c) For secondary hypoparathyroidism: During initial loading period with calcium and DHT, monitor serum calcium 1-2 times daily for 5-10 days. Give loading dose of DHTat 0.02 - 0.05 mg/kg PO once daily for 2-3 days, then 0.01 - 0.03 mg/kg PO once dailyfor 1 week. After a low normal serum calcium is achieved, give 0.01 mg/kg PO onceevery other day and then every third day etc., until it can be finally stopped. Dose shouldbe individualized for each animal. During loading period, calcium should be given at 25- 50 mg (elemental calcium)/kg/day divided 2-4 times a day. After 1 week, decrease doseto 15 - 25 mg (elemental calcium)/kg/day divided and gradually reduce. The goal is tokeep serum calcium levels in the low-normal range (7.5 - 9.5 mg/dl) so that theremaining parathyroid tissue will respond via feedback mechanisms.
For primary hypoparathyroidism (animals will require therapy for life): Loadingregimen is the same as for secondary hypoparathyroidism. Then DHT may be given at0.01 mg/kg PO once daily and eventually every other day if serum calcium levelspermit. Reduce oral calcium supplementation to as low a dose as possible; may considerreplacing pharmaceuticals with a high calcium diet. Monitoring of calcium levels may bereduced to 1-2 times per month after loading regimen is completed and animal isrelatively stable. Dosage adjustments of either DHT or calcium should be made inincrements of about 25%. Eventually, animal may only need to be monitored (serumcalcium) only several times a year. (Meuten and Armstrong 1989)
For hypocalcemia secondary to severe renal failure:
a) After hyperphosphatemia is controlled (do not use calcium and vitamin D if calcium/phosphate product is in excess of 70 mg/dl), use oral calcium carbonate therapy. If calcium alone does not resolve hypocalcemia add DHT at 0.125 mg per dog PO 3 times per week. Adjust dose based on serial calcium determinations. Maximum effect may require 2-4 weeks and duration may persist up to 1 week after treatment is discontinued. (Allen 1989)
b) In combination with calcium therapy, give DHT initially at 0.03 mg/kg/day for 2 days, then 0.02 mg/kg/day for 2 days, then 0.01 mg/kg/day maintenance dose. (Kay and Richter 1988)
Cats: 
For hypocalcemia secondary to hypoparathyroidism: a) For secondary hypoparathyroidism: As per dogs in "c" above. Dosage is empirical.
Cats with hypoparathyroidism secondary to thyroidectomy may require treatment forseveral months. (Meuten and Armstrong 1989)
b) In combination with calcium therapy (initially at 50 - 100 mg/kg/day divided 3-4 timesdaily of elemental calcium), give DHT initially at 0.125 - 0.25 mg PO per day for 2-3days, then 0.08 - 0.125 mg per day for 2-3 days and finally 0.05 mg PO per day untilfurther dosage adjustments are necessary. Stable serum calcium levels (8.5-9.5 mg/dl)are usually achieved in about a week. Continue to monitor and adjust dosages of DHTand calcium to lowest levels to maintain normocalcemia. (Peterson and Randolph 1989)(Note: refer to the calcium monograph for further information.)
Monitoring Parameters -
Client Information - Clients should be briefed on the symptoms of hypercalcemia (polydipsia, polyuria, anorexia) and hypocalcemia (muscle tremors, twitching, tetany, weakness, stiff gait, ataxia, behavioral changes, and seizures) and instructed to report these symptoms to the veterinarian.
Dosage Forms/Preparations/FDA Approval Status/Withholding Times - Veterinary-Approved Products: None
Human-Approved Products:
Dihydrotachysterol Oral Tablets 0.125 mg, 0.2 mg, 0.4 mg; DHT® Tablets (Roxane); (Rx)Dihydrotachysterol Oral Capsules 0.125 mg; Hytakerol® (Winthrop)Dihydrotachysterol Oral Concentrate Solution 0.2 mg/ml in 30 ml bottles, and 0.25 mg/ml (inoil) in 15 ml bottles; DHT® Intensol (Roxane), Hytakerol® (Winthrop); (Rx)