The drug to report
She has primary hyperparathyroidism with a serum calcium of 11.6 mg/dL (normal 8.6–10.2) and recurrent kidney stones. Thiazide diuretics such as hydrochlorothiazide reduce urinary calcium excretion and raise serum calcium, so they are avoided in hyperparathyroidism and reported for review. Hydrochlorothiazide is the medicine the nurse reports.
How thiazides raise calcium
Thiazides act on the distal convoluted tubule of the kidney, where they block sodium reabsorption. As a secondary effect, they increase calcium reabsorption in the same segment, so less calcium leaves in the urine and more stays in the blood. In a person with normal parathyroid function this effect is modest, but in hyperparathyroidism, where calcium is already high, a thiazide can push the level higher and worsen symptoms such as fatigue, constipation, confusion, and dysrhythmias. Loop diuretics, by contrast, increase urinary calcium excretion.
| Drug | Class | Effect on serum calcium |
|---|
| Amlodipine besylate | Calcium channel blocker | No rise |
| Hydrochlorothiazide | Thiazide diuretic | Raises it |
| Metoprolol tartrate | Beta blocker | No effect |
| Losartan potassium | Angiotensin receptor blocker | No rise |
Why the other drugs are not the concern
Amlodipine blocks calcium channels in vascular smooth muscle, but it does not change serum calcium; the word calcium in its class name is a common trap. Metoprolol slows the heart and lowers blood pressure without affecting calcium. Losartan lowers blood pressure through the renin-angiotensin system and does not raise serum calcium.
Nursing application
The nurse reports the hydrochlorothiazide so the provider can consider an alternative antihypertensive. The nurse also reviews other sources of calcium elevation, such as calcium supplements, vitamin D in high doses, and lithium, and encourages fluids and mobility while she awaits surgery.
Exam takeaway
Watch out Thiazides hold calcium in; loop diuretics push calcium out. In hypercalcemia or hyperparathyroidism, report any thiazide.