27.3 Calcium Preparations, Vitamin D, Bisphosphonates, Calcimimetics, and Peptide Hormones

Calcium Preparations, Vitamin D, and Other Drugs for Hypoparathyroidism

Calcium and vitamin D are essential for maintaining healthy bones and normal cellular function. When the parathyroid glands can't regulate calcium on their own (as in hypoparathyroidism), medications step in to restore balance. Left untreated, low calcium can lead to tetany, seizures, and cardiac arrhythmias, so getting these drugs right matters.

This section covers five drug classes used to manage calcium and bone disorders: calcium preparations, vitamin D, bisphosphonates, calcimimetics, and peptide hormones. Each works through a different mechanism, and nurses need to understand how they differ to monitor patients safely and provide effective education.

Drug Class Characteristics

Calcium Preparations are oral supplements like calcium carbonate and calcium citrate that directly raise serum calcium levels. Calcium carbonate contains the most elemental calcium per tablet but requires stomach acid for absorption, so it should be taken with meals. Calcium citrate is absorbed without stomach acid, making it a better choice for patients on proton pump inhibitors or with achlorhydria.

• Common side effects: constipation, bloating, and hypercalcemia at high doses

Vitamin D is a fat-soluble vitamin that enhances calcium absorption from the gut. Two forms you'll see most often:

• Calcitriol (active form, 1,25-dihydroxyvitamin D): works quickly because it doesn't need renal activation. This is the preferred form in hypoparathyroidism since these patients lack PTH to stimulate renal conversion.
• Ergocalciferol (vitamin $D_2$): requires hepatic and renal activation, so onset is slower.
• Side effects: hypercalcemia and hypercalciuria, which can lead to kidney stones

Bisphosphonates such as alendronate and risedronate are antiresorptive agents. They inhibit osteoclast activity, slowing bone breakdown and reducing calcium loss from bone. These are primarily used for osteoporosis rather than hypoparathyroidism itself.

• Side effects: esophageal irritation (patients must stay upright 30 minutes after taking), and with long-term use, osteonecrosis of the jaw and atypical femur fractures

Calcimimetics like cinacalcet are allosteric activators of calcium-sensing receptors on the parathyroid gland. They "trick" the gland into sensing higher calcium levels, which suppresses PTH secretion. These are used in hyperparathyroidism (not hypoparathyroidism) to lower elevated PTH and calcium.

• Side effects: nausea, vomiting, and hypocalcemia

Peptide Hormones include teriparatide and recombinant PTH (1-84). These are synthetic forms of parathyroid hormone that stimulate osteoblast activity and bone formation. Teriparatide is given by daily subcutaneous injection and is used for severe osteoporosis. Recombinant PTH can also be used as replacement therapy in refractory hypoparathyroidism.

• Side effects: hypercalcemia, hypercalciuria, and a rare risk of osteosarcoma (carries a boxed warning; avoid use beyond 2 years)

Indications and Mechanisms of Action

Indications for these drug classes center on two goals:

• Treating hypocalcemia due to hypoparathyroidism and maintaining normal serum calcium and phosphate levels
• Preventing complications of calcium imbalance: tetany, seizures, cardiac arrhythmias, and long-term osteoporosis

How each class works:

Potential side effects across classes:

• Hypercalcemia (calcium preparations, vitamin D, peptide hormones): watch for confusion, fatigue, constipation, excessive thirst
• Hypocalcemia (calcimimetics): watch for paresthesias, muscle cramps, Chvostek's and Trousseau's signs
• GI disturbances: constipation (calcium), nausea/vomiting (calcimimetics)
• Renal complications: hypercalciuria and nephrolithiasis (vitamin D, peptide hormones)
• Bone-related issues: osteonecrosis of the jaw (bisphosphonates), osteosarcoma risk (peptide hormones)

Nursing Considerations

Monitoring parameters:

• Serum calcium, phosphate, and magnesium levels (check frequently during dose adjustments, then periodically once stable)
• Renal function: creatinine and BUN
• Bone mineral density (BMD) scans for patients on long-term therapy
• Signs and symptoms of hypercalcemia or hypocalcemia at every assessment

Key drug interactions to watch:

• Calcium preparations decrease absorption of bisphosphonates, tetracyclines, levothyroxine, and fluoroquinolones. Separate administration by at least 2 hours.
• Vitamin D toxicity risk increases with concurrent thiazide diuretics (thiazides reduce renal calcium excretion) and high-dose calcium supplements.
• Bisphosphonates have decreased absorption when taken with calcium, iron, or magnesium supplements. Must be taken on an empty stomach with plain water only.
• Calcimimetics combined with other calcium-lowering drugs (bisphosphonates, denosumab) increase the risk of severe hypocalcemia.

Administration tips:

1. Give calcium carbonate with meals for better absorption; calcium citrate can be taken with or without food.
2. Separate calcium from interacting drugs by at least 2 hours.
3. For bisphosphonates: patient takes the tablet first thing in the morning with a full glass of plain water, on an empty stomach, and remains upright for at least 30 minutes. No food, drink, or other medications during that window.
4. Encourage adequate hydration to reduce the risk of renal stones.
5. Assess for Chvostek's sign (facial twitching when tapping the facial nerve) and Trousseau's sign (carpopedal spasm with BP cuff inflation) in patients at risk for hypocalcemia.

Patient Education

Proper usage:

• Follow the prescribed dosage and schedule closely. Don't double up on missed doses.
• Take calcium carbonate with meals. If using bisphosphonates, follow the specific empty-stomach and upright-posture instructions exactly.
• Stay well hydrated throughout the day to protect kidney function.

Dietary considerations:

• Eat a balanced diet with calcium-rich foods (dairy, leafy greens, fortified foods) and adequate vitamin D.
• Limit high-phosphate foods like processed meats, colas, and packaged snacks, since elevated phosphate can further lower calcium.
• Limit alcohol, which interferes with bone metabolism and vitamin D activation.

Signs of complications to report immediately:

• Hypercalcemia: fatigue, confusion, constipation, abdominal pain, excessive thirst, frequent urination
• Hypocalcemia: tingling or numbness in fingers/toes/lips, muscle cramps, spasms, seizures
• Renal issues: flank pain, blood in urine, changes in urinary frequency
• Bone-related concerns: jaw pain, loose teeth, or delayed healing after dental work (especially on bisphosphonates)

Follow-up care:

• Attend regular appointments for serum calcium, phosphate, and magnesium monitoring.
• Get periodic BMD scans as ordered to assess bone health over time.
• Inform your dentist about bisphosphonate use before any dental procedures.
• Report any new or worsening symptoms to your healthcare provider promptly.