serum phosphorus increases. The level of calcium is regulated by the parathy-
roid hormone (PTH), calcitonin, and vitamin D.
Low serum calcium causes an increase in the production of PTH. PTH moves
calcium out of bone and into the serum. It increases the absorption of calcium
from the GI tract. PTH also increases reabsorption of calcium in the kidneys.
Calcitonin is produced by the thyroid gland. Production is increased when
there is a high serum calcium level. Calcitonin reverses the action of PTH by
increasing the absorption of calcium by bone, decreases calcium absorption in
the GI tract, and causes an increase in urine to excrete calcium.(^172) CHAPTER 10 Fluid and Electrolyte Therapy
Decreases Serum Calcium Increases Serum Calcium
Magnesium sulfate Calcium salts
Propylthiouracil (propacil) Vitamin D
Colchicines IV lipids
Pliamythin Kayexalate androgens
Neomycin Diuretics (Thiazides,
Acetazolamide
Chlorthalidone, Hygroten)
Aspirin
Anticonvulsants
Glutethimide
Estrogens
Aminoglycosides (gentamicin,
amikacin, tobramycin)
Phosphate preparations:
oral, enema, and IV (sodium
phosphate, potassium phosphate)
Corticosteroids (cortisone, prednisone)
Loop diuretics (furosemide [Lasix])
Table 10-2. Medications that increase and decrease serum calcium.