What It Is:

Calcitriol is the active form of vitamin D3, a fat-soluble vitamin essential for maintaining calcium and phosphorus balance in the body. It plays a crucial role in bone health by promoting the absorption of calcium and phosphate from the gastrointestinal tract. Calcitriol is synthesized in the kidneys from its precursor, calcidiol, which is formed in the liver from vitamin D3.

Dosage Forms and Strengths:

Calcitriol is available in various dosage forms, including:

1. Oral Capsules: Common strengths are 0.25 mcg and 0.5 mcg.
2. Oral Solution: Typically available in 1 mcg/mL concentration.
3. Topical Ointment: Used primarily for skin conditions, usually available in a 3 mcg/g concentration.

Brand and Generic Names:

Calcitriol is marketed under several brand names, including:

• Rocaltrol (brand name)
• Calcijex (brand name, often used in dialysis patients)

Generic versions are simply known as calcitriol, with various formulations available under different labels.

Indications for Use:

Calcitriol is prescribed for a variety of conditions, including:

1. Chronic Kidney Disease (CKD): To manage secondary hyperparathyroidism and improve calcium levels in patients undergoing dialysis.
2. Osteoporosis: As part of treatment regimens to improve bone density and strength.
3. Hypoparathyroidism: To manage low levels of parathyroid hormone (PTH) and maintain normal calcium levels.
4. Psoriasis: Topical calcitriol is used to manage psoriasis, a chronic skin condition characterized by scaling and inflammation.

Mechanism of Action:

Calcitriol exerts its effects by binding to vitamin D receptors in the intestines, bones, and kidneys. This interaction leads to increased intestinal absorption of calcium and phosphate, enhanced bone mineralization, and regulation of parathyroid hormone levels. By increasing serum calcium levels, calcitriol helps maintain proper bone health and support overall metabolic functions.

Administration and Dosage:

The dosage of calcitriol varies depending on the condition being treated:

1. For Chronic Kidney Disease: Typically, the oral dosage starts at 0.25 mcg once daily or every other day, adjusted based on serum calcium and phosphorus levels.
2. For Osteoporosis: The dosage usually ranges from 0.25 mcg to 1 mcg daily, tailored to the individual's needs and response.
3. For Hypoparathyroidism: Dosage is often initiated at 0.25 mcg to 1 mcg daily, with adjustments based on calcium levels.
4. For Psoriasis: Topical application of 3 mcg/g ointment is applied once or twice daily to affected areas.

Side Effects and Precautions:

Common side effects of calcitriol include:

• Hypercalcemia: Elevated calcium levels can cause symptoms such as nausea, vomiting, constipation, and confusion.
• Hyperphosphatemia: Increased phosphate levels can lead to itching and joint pain.
• Renal Issues: Potential for kidney stones or calcification, especially with prolonged use or high doses.

Precautions include:

• Regular Monitoring: Serum calcium and phosphate levels should be regularly monitored to prevent imbalances.
• Kidney Function: Patients with pre-existing kidney conditions need careful dosing and monitoring.
• Interactions: Calcitriol can interact with other medications, including corticosteroids and certain antacids, affecting its efficacy and safety.

Conclusion:

Calcitriol plays a vital role in managing calcium and phosphate balance in the body, supporting bone health, and treating specific conditions such as chronic kidney disease and osteoporosis. Its effectiveness relies on proper dosing and monitoring to mitigate potential side effects and complications. By understanding its mechanisms and adhering to prescribed guidelines, patients can effectively benefit from this crucial vitamin D derivative.