Ergocalciferol

BRAND NAMES

Ergocalciferol (vitamin D2) is available under several brand names, including Drisdol, Calcidol, and Calciferol. It is available in both prescription and over-the-counter (OTC) forms, with generic versions also available. 

Here are some common brand and other names for ergocalciferol:

• Drisdol

• Calcidol

• Calciferol

• Deltalin (brand by Eli Lilly and Company, may not be currently marketed)

• D-Forte (Canada

MECHANISM OF ACTION

Ergocalciferol acts by being converted in the liver to 25-hydroxyvitamin D₂, and then in the kidneys to 1,25-dihydroxyvitamin D₂, its active hormonal form. This active metabolite binds to vitamin D receptors in the intestines, bones, and kidneys to regulate calcium and phosphate balance. It enhances intestinal calcium absorption, promotes bone mineralization, and suppresses elevated parathyroid hormone levels. Its actions resemble those of endogenous vitamin D, supporting skeletal and metabolic functions. Through these mechanisms, ergocalciferol maintains mineral homeostasis in the body.

PHARMACOKINETICS:

Absorption

Ergocalciferol, or vitamin D2, is well absorbed in the small intestine through a process involving both passive diffusion and carrier-mediated transport, with its absorption enhanced by the presence of dietary fat and bile salts.

Distribution

Ergocalciferol, a fat-soluble form of vitamin D, is widely distributed throughout the body after being absorbed, with significant concentrations found in adipose (fat) tissue, muscles, and the liver

Metabolism

Ergocalciferol (vitamin D2) is a biologically inactive precursor that undergoes a two-step metabolic process, primarily in the liver and kidneys, to become the active hormone 1,25-dihydroxyergocalciferol (ercalcitriol).

Excretion

The primary route of excretion is in the feces via the bile, with only small amounts eliminated in the urine. 

PHARMACODYNAMICS

The pharmacodynamics of ergocalciferol (vitamin D2) involve a two-step metabolic activation to its active form, which then acts as a hormone to regulate calcium and phosphate homeostasis in the body.

ADMINISTRATION

Ergocalciferol (vitamin D2) is mainly given orally in the form of capsules, tablets, or liquid solutions. In certain situations, a healthcare provider may deliver it through an intramuscular (IM) injection, although this injectable form is not currently available commercially in the U.S.

DOSAGE AND STRENGTH

Ergocalciferol (vitamin D2) is available in various strengths and dosages, which are determined by the specific medical condition being treated and must be individualized under close medical supervision. A common prescription strength is 1.25 mg (50,000 International Units or IU) in a capsule or oral solution form.

Ergocalciferol (vitamin D2) is available in various oral forms, including capsules, tablets, and liquid solutions. The strength of these preparations typically ranges from 400 IU to 50,000 IU per dose, allowing flexibility depending on the patient’s needs and the condition being treated.

For adults with vitamin D deficiency, a common regimen is 50,000 IU once weekly for 6–8 weeks, followed by a maintenance dose of 1,000–2,000 IU daily. For conditions like rickets or osteomalacia, daily doses of 1,000–2,000 IU are generally used, though higher doses may be prescribed under medical supervision.

Ergocalciferol is usually administered orally and is best absorbed when taken with food. The exact dose and duration should always be tailored by a healthcare provider based on age, medical condition, and blood vitamin D levels.

DRUG INTERACTIONS

Certain medications, like orlistat and cholestyramine, can reduce ergocalciferol absorption by interfering with fat uptake. Anticonvulsants and corticosteroids may increase vitamin D metabolism, lowering its effectiveness. Thiazide diuretics combined with ergocalciferol can raise the risk of hypercalcemia. Mineral supplements, particularly calcium, may enhance adverse effects when taken concurrently. Careful monitoring is required when interacting drugs are used.

FOOD INTERACTIONS

Taking ergocalciferol with high-fat meals significantly enhances absorption. Excessive dietary calcium may increase the risk of hypercalcemia when using high-dose vitamin D₂. Alcohol can impair liver function and potentially alter vitamin D metabolism. Patients with poor dietary fat intake may absorb less of the medication. Consistent eating patterns support stable vitamin D levels.

CONTRAINDICATIONS

Ergocalciferol is contraindicated in individuals with hypercalcemia or existing vitamin D toxicity. People with hypersensitivity to vitamin D products should avoid its use. Conditions causing increased vitamin D sensitivity, such as sarcoidosis, require caution. Severe renal impairment may alter metabolism and increase risk. Medical evaluation is essential before initiating high-dose therapy.

SIDE EFFECTS

• Nausea and vomiting

• Loss of appetite and weight loss

• Increased thirst and frequent or increased urination

• Unusual tiredness, weakness, muscle pain, or stiffness

• Constipation

• Dry mouth or a metallic taste

• Headache or drowsiness

OVER DOSE

Overdose typically results in severe hypercalcemia due to excessive vitamin D levels. Symptoms may include nausea, dehydration, weakness, and confusion. Prolonged overdose can cause kidney stones or renal failure. Treatment involves stopping the drug and lowering calcium levels with medical management. Quick intervention reduces the risk of long-term complications.

TOXICITY

Toxicity results from chronic excessive intake rather than a single high dose. Persistently high calcium levels may lead to calcification of soft tissues and organs. Toxicity can cause cardiac arrhythmias, kidney damage, and neurological symptoms. Because ergocalciferol is fat-soluble, it accumulates in tissues over time. Regular monitoring helps prevent toxic buildup during supplementation.