interaction of some drugs and vitamin D supplementation

Last edited 05/2022

  • The effect of vitamin D can be decreased by concomitant treatment with phenytoin, barbiturates or corticosteroids because of changes in metabolic activation.
  • Effects of digoxin and other cardiac glycosides may be accentuated by oral administration of calcium plus vitamin D:
    • strict medical supervision is needed in patients on this combination and, if necessary, monitoring of ECG and calcium concentrations when using vitamin D supplementation in these situations
  • There is an increased risk of hypercalcemia when receiving thiazide diuretics, as they can reduce urinary calcium excretion.
  • Calcium salts may reduce absorption of levothyroxine, bisphosphonates, sodium fluoride, quinolone or tetracycline antibacterials or iron :
    • it is advisable to allow 2-4 hours before taking a calcium-containing vitamin D supplement when on such medication

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