Action And Clinical Pharmacology: Dihydrotachysterol is hydroxylated in the liver to 25-hydroxydihydrotachysterol, which is the major circulating active form of the drug. It does not undergo further hydroxylation by the kidney and therefore is the analogue of 1,25-dihydroxyvitamin D. Dihydrotachysterol is effective in the elevation of serum calcium by stimulating intestinal calcium absorption and mobilizing bone calcium in the absence of parathyroid hormone and of functioning renal tissue. It also increases renal phosphate excretion. In contrast to parathyroid extract, dihydrotachysterol is active when taken orally, exerts a slow but persistent effect, and may be used for long periods without increasing the dosage or causing tolerance. Dihydrotachysterol is faster-acting than pharmacologic doses of vitamin D and is less persistent after cessation of treatment, thus decreasing the risk of accumulation and of hypercalcemia.
Indications And Clinical Uses: Acute, chronic and latent forms of postoperative tetany, idiopathic tetany and hypoparathyroidism.
Contra-Indications: In patients with hypercalcemia, hypersensitivity to the effects of dihydrotachysterol, and hypervitaminosis D.
Precautions: To prevent hypercalcemia, treatment should always be controlled by regular determinations of blood and urine calcium levels, mainly during the beginning of treatment and until the required maintenance dose has been established.
Serum calcium levels should be kept between 9 and 10 mg/mL (2.25 to 2.5 mmol/L).
The monitoring of calciuria is a convenient supplement to serum calcium determinations, but it should not be regarded as a substitute, because in hypoparathyroid patients treated with dihydrotachysterol, hypercalciuria can occur in the presence of hypocalcemia. Serum phosphate and magnesium and alkaline phosphatases may be periodically measured to monitor progress in particular situations.
In patients with renal osteodystrophy accompanied by hyperphosphatemia, maintenance of a normal serum phosphorus level by dietary phosphate restriction and/or administration of aluminum gels as intestinal phosphate binders is essential to prevent metastatic calcification.
Dihydrotachysterol should be administered with caution in patients with hypercalciuria or with a history of calcium lithiasis.
If nausea and vomiting are present, serum calcium level should be checked.
It is advisable to be very careful in using dihydrotachysterol in patients suffering from sarcoidosis, as these individuals are very sensitive to the effect of vitamin D.
Drug Interactions: Interactions with Other Medicaments and Other Forms of Interaction: Drugs with enzymatic induction effects such as phenobarbital, rifampicin and isoniazid, and anti-epileptics including phenytoin may impair the efficacy of treatment and require higher doses of dihydrotachysterol.
Concomitant therapy with thiazide diuretics and dihydrotachysterol in hypoparathyroidism may result in excessive hypercalcemia. Lowered doses of dihydrotachysterol and close monitoring of serum calcium levels are recommended.
Thyroid replacement therapy may increase clearance of dihydrotachysterol.
Cholestyramine may impair the absorption of dihydrotachysterol.
Hypercalcemia induced by excessive dosage of dihydrotachysterol may enhance the toxic effects of cardiac glycosides.
Pregnancy: As safe use in pregnancy has not been established, the use of dihydrotachysterol during pregnancy should be avoided unless, in the judgment of the physician, the potential benefits outweigh the possible hazards. Animal reproduction studies in several species have shown that hypervitaminosis D is associated with fetal abnormalities. These abnormalities were similar to the supravalvular aortic stenosis syndrome described by Black, which included infants exhibiting supravalvular aortic stenosis, elfin facies, and mental retardation.
Lactation: Dihydrotachysterol is excreted in breast milk and may cause hypercalcemia in the suckling infant. Dihydrotachysterol should not be given to women who are breast-feeding.
Adverse Reactions: Adverse effects are most likely to be due to overdosage and are manifested by symptoms of hypercalcemia.
First Signs Are: loss of appetite, nausea.
More Severe Manifestations Include: vomiting, urgency of micturition, polyuria, dehydration, thirst, vertigo, stupor, headache, abdominal cramps and paralysis. The calcium and phosphorus serum concentrations are increased.
Chronic Overdosage: With chronic overdosage, calcium may be deposited in many tissues, including arteries and kidneys, leading to hypertension and renal failure.
Symptoms And Treatment Of Overdose: Symptoms: Dihydrotachysterol may be toxic in doses as low as 25 mg/day, and is manifested by symptoms of hypercalcemia. The effects of dihydrotachysterol can persist for up to 1 month after cessation of treatment.
Treatment: Chronic Overdosage: the symptoms of hypercalcemia will usually respond to withdrawal of medication, bed rest, liberal fluid intake, and use of laxatives.
Acute Overdosage: emesis or gastric lavage should be performed if ingestion of dihydrotachysterol is recent. Serum calcium estimations should be helpful in determining management.
Massive Overdosage: corticosteroids (reduced intestinal absorption of calcium) should be administered. Resistant cases may also require the administration of neutral phosphate. Several months’ management may be required in such cases.
Dosage And Administration: For oral administration only. Treatment depends on the nature and the seriousness of the disorder and must be individualized. Serum calcium levels should be kept within the normal range (9 to 10 mg/mL).
The dosage can be reduced with supplementation by oral calcium lactate or gluconate (10 to 15 mg daily).
Adults and Geriatrics: Acute Cases: Initial Dose: In acute cases, 6 to 10 capsules (0.75 to 1.25 mg) may be given daily for 3 days. Serum and urinary calcium estimations should be determined 2 or 3 days following the initial treatment period. Maintenance Dose: Usually in the range of 2 to 14 capsules (0.25 to 1.75 mg) each week, administered in divided doses. The precise dosage depends on the results of serum and urinary calcium determinations.
Chronic Cases: In chronic cases, an initial dose of 4 capsules (0.5 mg) daily or on alternate days, may be sufficient to maintain normocalcemia.
The dose usually has to be increased during menstruation and periods of unusual activity.
Children: No specific dosage recommendation.
Availability And Storage: Each dark brown, soft capsule, imprinted with an open W contains: the equivalent of 0.125 mg of crystalline dihydrotachysterol. Nonmedicinal ingredients: caramel, cinnamyl alcohol, gelatin, glycerin, methylparaben, propylparaben, purified water, sesame oil and titanium dioxide. Energy: 1.51 kJ (0.36 kcal). Gluten-, lactose-, sucrose- and tartrazine-free. Bottles of 50.
HYTAKEROL® Sanofi Dihydrotachysterol Antitetany Steroid
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