Usage
- Vitamin D is prescribed for preventing and treating vitamin D deficiency, which can manifest as rickets in children and osteomalacia in adults. It contributes to calcium absorption, supporting bone health, and plays a role in immune function and muscle strength. It is also prescribed to treat hypoparathyroidism and familial hypophosphatemia.
- Pharmacological Classification: Vitamin (Fat-soluble) and Hormone precursor.
Alternate Names
- Calciferol (Vitamin D3), Ergocalciferol (Vitamin D2), Cholecalciferol
- Brand names: Drisdol, Calciferol. Many vitamin D supplements are available over the counter.
How It Works
- Pharmacodynamics: Vitamin D promotes calcium absorption in the intestines and maintains serum calcium and phosphate concentrations necessary for bone mineralization and neuromuscular function. It also modulates cell growth, neuromuscular and immune function, and reduces inflammation.
- Pharmacokinetics:
- Absorption: Vitamin D3 (cholecalciferol) is produced endogenously in the skin upon exposure to sunlight and is also absorbed from the diet. Vitamin D2 (ergocalciferol) is obtained through diet. Both forms are absorbed from the small intestine.
- Metabolism: Vitamin D is hydroxylated in the liver to form 25-hydroxyvitamin D [25(OH)D], the major circulating form. This is further hydroxylated in the kidneys to its active form, 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol.
- Elimination: Vitamin D metabolites are primarily excreted in bile and feces.
- Mode of Action: The active form of vitamin D, calcitriol, binds to the vitamin D receptor (VDR), a nuclear receptor present in various tissues. This complex regulates gene transcription, influencing calcium and phosphate homeostasis, cell differentiation, and immune function.
Dosage
Standard Dosage
Adults:
- Prevention of Deficiency: 600-800 IU (15-20 mcg) daily. Some guidelines suggest higher doses (1500-2000 IU/day).
- Treatment of Deficiency: Dosage depends on severity and individual patient factors. Typically, higher doses (e.g., 50,000 IU weekly or daily doses of several thousand IUs) are used initially, followed by maintenance doses of 600-800 IU daily.
Children:
- Prevention of Deficiency: 400 IU (10 mcg) daily for infants up to 1 year, 600 IU (15 mcg) daily for children older than 1 year.
- Treatment of Deficiency: Dosages depend on the severity of deficiency and are typically determined by a pediatrician based on serum 25(OH)D levels.
Special Cases:
- Elderly Patients: May require higher doses due to reduced skin synthesis and intestinal absorption. 800 IU (20 mcg) daily is often recommended.
- Patients with Renal Impairment: Calcitriol, the active form of vitamin D, may be necessary as impaired kidney function can affect conversion. Dosage should be carefully monitored.
- Patients with Hepatic Dysfunction: Close monitoring and dose adjustment may be necessary due to the liver’s role in vitamin D metabolism.
- Patients with Comorbid Conditions: Conditions like malabsorption syndromes, hyperparathyroidism, sarcoidosis, and lymphoma require careful monitoring and dosage adjustments.
Clinical Use Cases
- Intubation, Surgical Procedures, Mechanical Ventilation, ICU Use, Emergency Situations: These situations don’t typically warrant specific Vitamin D dosing. However, pre-existing or developing deficiency during prolonged hospital stays may require assessment and supplementation as clinically indicated.
Dosage Adjustments
- Dose modifications are based on serum 25(OH)D levels, patient response, and the presence of underlying conditions. Close monitoring of serum calcium and phosphate levels is important, particularly during initial treatment.
Side Effects
Common Side Effects (with excessive intake):
- Nausea, vomiting, constipation, weakness, loss of appetite, metallic taste, dry mouth, dehydration.
Rare but Serious Side Effects:
- Hypercalcemia (elevated blood calcium), which can lead to kidney stones, kidney damage, confusion, heart rhythm abnormalities.
Long-Term Effects:
- Long-term excessive intake can cause calcium deposits in soft tissues and organs.
Adverse Drug Reactions (ADR):
- Severe hypercalcemia requires immediate medical attention.
Contraindications
- Hypercalcemia, hypervitaminosis D, hypersensitivity to vitamin D, malabsorption syndrome, granulomatous diseases (like sarcoidosis). Use cautiously in patients with kidney disease, hyperparathyroidism, and history of kidney stones.
Drug Interactions
- Aluminum-containing antacids: Reduced vitamin D absorption.
- Anticonvulsants (phenobarbital, phenytoin): Increased vitamin D metabolism, decreased calcium absorption.
- Atorvastatin: Reduced vitamin D absorption.
- Calcipotriene: Increased effects and side effects of calcipotriene.
- Cholestyramine: Reduced vitamin D absorption.
- Digoxin: Increased risk of digoxin toxicity with hypercalcemia.
- Diltiazem, Verapamil: Reduced effectiveness of these drugs with hypercalcemia.
- Thiazide diuretics: Increased risk of hypercalcemia.
- Steroids: Reduced calcium absorption and vitamin D metabolism.
- Stimulant laxatives: Reduced vitamin D and calcium absorption.
- Orlistat: Reduced vitamin D absorption.
- CYP3A4 substrates: Potential for altered metabolism of both vitamin D and the substrate drug.
Pregnancy and Breastfeeding
- Vitamin D supplementation is generally recommended during pregnancy and breastfeeding (400-600 IU/day). Higher doses may be necessary to correct deficiencies, but should be monitored. Excessive intake can lead to fetal or neonatal hypercalcemia.
Drug Profile Summary
- Mechanism of Action: Binds to the vitamin D receptor (VDR) and regulates gene transcription, influencing calcium and phosphate homeostasis.
- Side Effects: Nausea, vomiting, constipation, weakness (with excessive intake); hypercalcemia (serious).
- Contraindications: Hypercalcemia, hypervitaminosis D, hypersensitivity.
- Drug Interactions: Numerous interactions, including aluminum antacids, anticonvulsants, statins, thiazides.
- Pregnancy & Breastfeeding: Supplementation generally recommended; avoid excessive doses.
- Dosage: Variable depending on age, condition, and response; monitoring required.
- Monitoring Parameters: Serum 25(OH)D, calcium, and phosphate levels.
Popular Combinations
- Vitamin D is often combined with Calcium in supplements for bone health.
Precautions
- Monitor serum calcium and phosphate. Consider underlying conditions affecting vitamin D metabolism and drug interactions. Excessive sun exposure does not cause vitamin D toxicity, but supplementation should not exceed safe upper limits.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Vitamin D?
A: The recommended dosage varies with age and clinical context. 600-800 IU/day is generally recommended for adults for preventing deficiency. Higher doses are used for treating deficiency. Infants and children have different dosage requirements.
Q2: How is vitamin D deficiency diagnosed?
A: Measurement of serum 25-hydroxyvitamin D [25(OH)D] is the most reliable indicator.
Q3: What are the signs and symptoms of vitamin D toxicity?
A: Nausea, vomiting, weakness, confusion, loss of appetite, and potentially more severe symptoms like kidney problems and heart rhythm abnormalities.
Q4: Can I get enough vitamin D from sunlight?
A: Sun exposure can contribute significantly to vitamin D levels, but factors like time of day, season, latitude, skin pigmentation, and sunscreen use influence production. Supplementation may be needed, especially during winter months.
Q5: What foods are rich in vitamin D?
A: Oily fish (salmon, mackerel, sardines), egg yolks, fortified foods (milk, cereals).
A: Yes, Vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Vitamin D3 is the form produced in the skin and is generally considered more effective at raising serum 25(OH)D levels.
Q7: How long does it take to correct vitamin D deficiency?
A: This varies depending on the severity of the deficiency, individual factors, and the dosage used. Monitoring of 25(OH)D levels helps guide treatment duration.
Q8: What is the role of Vitamin D in bone health?
A: It facilitates calcium absorption and maintains appropriate calcium and phosphate levels, crucial for bone mineralization.
Q9: Can Vitamin D interact with other medications I’m taking?
A: Yes, Vitamin D has several potential drug interactions. It’s essential to inform your physician about all medications and supplements you are taking.
Q10: Should pregnant and breastfeeding women take vitamin D supplements?
A: Supplementation is generally recommended to ensure adequate vitamin D levels for both mother and child. Dosage should be discussed with a healthcare professional.
