Drug Interactions between dihydrotachysterol and Wellesse Vitamin D3

GENERALLY AVOID: Due to a narrow therapeutic index, vitamin D analogs given in combination with each other or with pharmacologic doses of vitamin D may demonstrate additive effects resulting in toxicity manifested as hypercalcemia, hypercalciuria, and hyperphosphatemia. Progressive hypercalcemia due to overdosage of vitamin D and its metabolites can be dangerous and sufficiently severe as to require emergency attention. Acute hypercalcemia may exacerbate tendencies for cardiac arrhythmias and seizures and may potentiate the action of digitalis drugs. Chronic hypercalcemia can lead to generalized vascular calcification, nephrocalcinosis, and calcifications of the cornea or other soft tissues. Immobilized patients are particularly vulnerable to the risk of hypercalcemia.

MANAGEMENT: Vitamin D analogs should not be used in combination with each other or with pharmacologic doses of vitamin D. Serum calcium and phosphorus levels must be closely monitored during therapy with a vitamin D analog, especially early in treatment during dosage adjustment. The serum calcium X phosphorus product should be maintained at less than 55 in patients with chronic kidney disease and should not be allowed to exceed 70 in any patient. An estimate of daily dietary calcium intake should be made and the intake adjusted when indicated. Patients should be advised to avoid an abrupt increase in dietary calcium intake, as it may trigger hypercalcemia, and to contact their physician if they experience early symptoms of vitamin D intoxication associated with hypercalcemia such as weakness, fatigue, headache, somnolence, vertigo, tinnitus, anorexia, nausea, vomiting, constipation, dry mouth, metallic taste, muscle pain, bone pain, ataxia, and hypotonia. Late symptoms may include polyuria, polydipsia, weight loss, nocturia, conjunctivitis, photophobia, rhinorrhea, pruritus, hyperthermia, decreased libido, and cardiac arrhythmias. Radiographic evaluation of suspect anatomical regions may be useful in the early detection of hypercalcemia. If hypercalcemia develops, treatment with vitamin D and any calcium product should be stopped immediately.

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