DIHYDROTACHYSTEROL

DIHYDROTACHYSTEROL (dye-hye-droe-tak-iss'ter-ole) DHT, DHT Intensol Classifications: vitamin d; serum calcium regulator; Therapeutic: vitamin d Pregnancy Category: C

Availability

0.125 mg, 0.2 mg, 0.4 mg tablets; 0.2 mg/mL oral solution

Action

Oil-soluble reduction product of ergocalciferol (vitamin D₂) with pharmacologic actions similar to those of both ergocalciferol and parathyroid hormone. In comparison with ergocalciferol, dihydrotachysterol promotes less intestinal absorption of calcium but almost equal phosphate diuresis.

Therapeutic Effect

Acts like parathyroid hormone in ability to raise serum calcium concentrations rapidly; also reported to increase intestinal absorption of sodium, potassium, and magnesium.

Uses

Hypocalcemia associated with hypoparathyroidism, both postoperative and idiopathic, and in pseudohypoparathyroidism. Also for prophylaxis of hypocalcemic tetany following thyroid surgery.

Unlabeled Uses

Vitamin D-resistant rickets (familial hypophosphatemia), osteoporosis, and renal osteodystrophy.

Contraindications

Sensitivity to vitamin D; hypercalcemia and hypocalcemia associated with renal insufficiency and hyperphosphatemia; renal stones, hypervitaminosis D; pregnancy (category C). Safe use in children in amounts exceeding RDA is not established.

Cautious Use

Cardiac disease, arteriosclerosis; hyperphosphatemia; renal disease; sarcoidosis; lactation.

Route & Dosage

Hypoparathyroidism, Pseudohypoparathyroidism Adult: PO 0.75–2.5 mg/d for several days, then 0.2–1 mg/d (may need 1.5 mg/d) Child: PO 1–5 mg/d for 4 d, then 0.5–1.5 mg/d Neonate: PO 0.05–0.1 mg/d Thyroidectomy-induced Hypocalcemia Adult: PO 0.25 mg/d Renal Osteodystrophy Adult: PO 0.1–0.6 mg/d Child: PO 0.1–0.5 mg/d

Administration

Oral

• Withhold drug if signs and symptoms of hypercalcemia appear (see Appendix F) and report to physician.
• Store in tightly closed, light-resistant containers at 15°–30° C (59°–86° F) unless otherwise directed.

Adverse Effects (≥1%)

CNS: Drowsiness, headache, weakness, vertigo, ataxia, atonia, mental depression. Endocrine: Hypercalcemia. GI: Anorexia, nausea, vomiting, metallic taste, dry mouth, thirst, diarrhea, constipation, abdominal pain. Urogenital: Nocturia, polyuria, renal calculi. Special Senses: Tinnitus.

Interactions

Drug: Not established.

Pharmacokinetics

Absorption: Readily from small intestines. Peak: 2 wk. Duration: 2 wk. Distribution: Distributed in breast milk. Metabolism: In liver to active metabolite. Elimination: Primarily in bile and feces.

Nursing Implications

Assessment & Drug Effects

• Lab tests: serum and urinary calcium levels at least weekly during first month of therapy until they are stabilized, then monthly thereafter.
• Supplement with 10–15 g of oral calcium lactate or gluconate daily; adequate calcium intake is necessary for clinical response to therapy.
• Restrict dietary phosphate or administer calcium carbonate supplements with meals, or both, to bind intestinal phosphates and improve calcium balance in patients with hyperphosphatemia.
• Monitor hypoparathyroid patients receiving thiazide diuretics closely; they are prone to develop hypercalcemia.

Patient & Family Education

• Learn S&S of hypercalcemia (see Appendix F).

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Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug