Please be cautious: Concomitant intake of thiazide diuretics with vitamin D or calcium supplements can lead to hypercalcemia especially in patients having certain risk factors!!
Q1- Who are patients at risk of hypercalcemia due to concomitant vitamin D / thiazide intake?
Intake of thiazide diuretics in combination with calcium and vitamin D supplements may cause hypercalcemia in:
1- elderly
2- compromised renal function
3- using high dose calcium supplements
4- uncontrolled entry of calcium into the extracellular fluid (e.g. hyperparathyroidism or sarcoidosis)
5- those being treated for osteoporosis, and those receiving high dosages of vitamin D for hypoparathyroidism
Q2- What is mechanism of hypercalcemia by concomitant vitamin D / thiazide intake?
1-thiazide diuretics decrease urinary calcium excretion while vitamin D supplementation enhances intestinal calcium absorption .
2- Thiazides may also enhance responsiveness of bone and renal tubule to parathyroid hormone,
Q3- What are the recommendations for patients taking thiazides and vitamin D concomitantly?
1-Serum calcium should be monitored if thiazide diuretics are coadministered with high dosages of calcium and/or vitamin D.
2-Patients should be advised to seek medical attention if they experience signs and symptoms of hypercalcemia such as dizziness, weakness, lethargy, headache, myalgia, anorexia, nausea, vomiting, and seizures.
3- If vitamin D is taken in a high dose then Decrease of vitamin D dose by 50% is recommended .
