From the FDA Drug Label
Cholestyramine resin may interfere with the pharmacokinetics of drugs that undergo enterohepatic circulation Because cholestyramine binds bile acids, cholestyramine resin may interfere with normal fat digestion and absorption and thus may prevent absorption of fat soluble vitamins such as A, D, E and K. When cholestyramine resin is given for long periods of time, concomitant supplementation with water-miscible (or parenteral) forms of fat soluble vitamins should be considered Bleeding tendencies due to hypoprothrombinemia (Vitamin K deficiency) as well as Vitamin A (one case of night blindness reported) and D deficiencies
Medications that are contraindicated with vitamin D (Cholecalciferol) due to potential adverse interactions include:
- Cholestyramine, as it may prevent absorption of fat-soluble vitamins such as vitamin D 1 Key considerations:
- Concomitant supplementation with water-miscible (or parenteral) forms of fat-soluble vitamins should be considered when taking cholestyramine resin for long periods of time 1
- Patients taking cholestyramine resin may experience vitamin D deficiency, which can lead to bleeding tendencies and other adverse effects 1
From the Research
Medications such as thiazide diuretics, lithium, and certain anticonvulsants should be used with caution when taking vitamin D due to potential adverse interactions, including hypercalcemia, as noted in a 2021 study on drug-related hypercalcemia 2. When considering the use of vitamin D supplements, it is essential to be aware of potential interactions with other medications.
- Certain anticonvulsants, such as phenytoin, phenobarbital, and carbamazepine, can alter vitamin D metabolism in the liver, reducing its effectiveness.
- Corticosteroids, like prednisone and dexamethasone, can also impact vitamin D levels by affecting calcium absorption.
- Cholesterol-lowering statins, such as atorvastatin and simvastatin, may interact with vitamin D, although the exact mechanism is not fully understood.
- Diuretics, including thiazide and loop diuretics, can increase or decrease calcium levels, which can, in turn, affect vitamin D activity.
- Certain antibiotics, like rifampin, can increase vitamin D metabolism, reducing its effectiveness.
- Bile acid sequestrants, such as cholestyramine and colestipol, can decrease vitamin D absorption from the gut.
- Lithium, a medication used to treat bipolar disorder, can cause hypercalcemia, particularly when combined with vitamin D supplements, as noted in a study on drug-related hypercalcemia 2. These interactions can lead to adverse effects, such as hypercalcemia, or reduced efficacy of either the medication or vitamin D supplement. It is crucial to consult a healthcare provider before taking vitamin D supplements, especially if you are already taking any of these medications, to determine the best course of action and avoid potential adverse interactions, as suggested by a 2024 study on targeting calcitriol metabolism in acute vitamin D toxicity 3. A 2021 literature review on the potential impact of medication on vitamin D status also highlights the importance of considering these interactions to avoid vitamin D depletions, especially in elderly individuals taking multiple medications 4.