Calcium Metabolism Flashcards
What interaction promotes osteoclast differentiation?
RANKL binding to RANK on an osteoclast precursor
What is the function of calcitriol?
Increases calcium absorption
What is the function of endogenous parathyroid hormone on Ca2+?
Promotes bone resorption
What is the effect of exogenous parathyroid hormone on Ca2+?
Promotes bone deposition
What are the effects of PTH?
↑ renal Ca2+ resorption
↑ renal phosphate excretion
↑ renal synthesis of calcitrol
What regulates PTH?
Calcium Sensing Receptor - Ca2+ levels
What are the functions of vitamin D?
‐ augments absorption of Ca2+ and phosphate from the small intestine
‐ decreases renal excretion of both calcium and phosphate
‐ Inhibits production of PTH
What are the functions of calcitonin?
‐ secreted by the parafollicular cells of the parathyroid gland
‐ activity generally opposes the action of PTH
- secreted when Ca2+ levels are high
What is the most common cause of hypercalcemia?
Primary Hyperparathyroidism
What are common causes of hypocalcemia?
Hypoparathyroidism (PTH deficiency) and Vitamin D deficiency
What are common causes of hyperphosphatemia?
Chronic kidney disease and secondary hyperparathyroidism
What are the types of vitamin D used for supplementation?
- Ergocholecalciferol (vitamin D2)
- Cholecalciferol (vitamin D3)
What vitamin D has a rapidly acting effect within 24‐48hrs?
Calcitriol - 1,25 (OH)2 Vitamin D3
What vitamin D requires only hepatic hydroxylation to be active?
Doxercalciferol 1‐OH Vitamin D2
Vitamin D MOA
Agonists of VDR
- ↑Ca2+/PO4 intestinal absorption
- ↑Ca2+/PO4 renal absorption
- ↓PTH expression
Vitamin D SE
Hypercalcemia
Vitamin D Indications
- Nutritional Supplements
- Rickets & Osteomalacia
- Prevention of Osteoporosis
- Hypoparathyroidism
- Secondary Hyperparathyroidism
Vitamin D Contraindications
Hyperphosphatemia
What are these drugs: Alendronate, Pamidronate, Risendronate and Zoledronate?
Bisphosphonates
Bisphosphonate MOA
Inhibit Farensyl Pyrophosphate Synthase
↓ Protein farnesylation
↓ Osteoclast activity
↓ Bone resorption
What are bisphosphonates all analogs of?
All bisphosphonates are analogs of pyrophosphate
What is protein farnesylation?
Protein farnesylation is important for the function of many signaling proteins especially small GTPases e.g. Rac/Rho/cdc42 that are involved in the regulation of the cytoskeleton and other signaling pathways
Bisphosphonate Indications
- Osteoporosis
- Hypercalcemia
- Paget’s Disease
Bisphosphonate SE
- Severe GI effects
- Esophageal Irritation
- Ocular side effects
- Osteonecrosis of the Jaw
- Renal impairment
Bisphosphate Contraindications
- Esophageal disease
- Chronic kidney disease
Denosumab MOA
Anti‐RANKL mAb
RANKL antagonist
↓ Osteoclast bone resorption
Denosumab Indications
- Osteoporosis
- Hypercalcemia
- Giant Cell tumor of the bone
Denosumab SE
- Hypocalcemia
- Osteonecrosis of the Jaw
Denosumab Contraindications
Hypocalcemia
Teriparitide Indications
Osteoporosis
Teriparitide MOA
- PTH receptor agonist with intermittent activity as it is exogenous
- Stimulates osteoblasts
- Promotes bone growth
↑ Renal 1a‐hydroxylase activity
↑ Renal calcium reabsorption
Teriparitide SE
- Transient Hypercalcemia
- Hyperuricemia
- ↑ Risk of osteosarcoma
Teriparitide Contraindications
- History of gout
- Risk of osteosarcoma
- Active malignancy of the bone
- Radiation therapy of the bone
Raloxifene Indications
Osteoporosis (post menopausal women)
- This is a SERM drug
Raloxifene MOA
SERM - ER agonist in bone Anti‐estrogen in breast & uterus
↓ Genes involved in osteoclast activation
↓ Osteoclast activity
Raloxifene SE
↑ Risk venous thromboembolism
Calcitonin Indications
- Severe hypercalcemia
- Paget’s Disease
- Osteoporosis
Calcitonin MOA
Calcitonin receptor agonist - opposes PTH actions
Calcitonin SE
- Nausea
- Hand swelling
- Intestinal cramping
Cinacalcet Indications
- CKD/secondary hyperparathyroidism
- Hypercalcemia
- Primary hyperparathyroidism
Cinacalcet MOA
Calcimimetic - Allosterically enhances affinity of CaSR for Ca2+ so lower concentrations of calcium are sensed and PTH is more suppressed
Cinacalcet SE
- Hypocalcemia
- Seizure risk
Cinacalcet Contraindications
Contraindicated with serum Ca2+ is below 8.4 mg/dL