CDN Pharmacology & Drug-Nutrient Interactions 2 — Questions and Answers
Question 1: Absorption of levothyroxine is significantly decreased when the medication is taken concurrently with which mineral supplement?
- Potassium
- Sodium
- Calcium (Correct answer)
- Phosphorus
Correct answer: Calcium
Calcium (as carbonate or citrate) binds levothyroxine in the gastrointestinal tract, reducing its bioavailability by up to 40%.
Question 2: Long-term corticosteroid therapy increases the risk of deficiency in which combination of nutrients, contributing to osteoporosis risk?
- Vitamins A and E
- Calcium and Vitamin D (Correct answer)
- Iron and Folate
- Zinc and Copper
Correct answer: Calcium and Vitamin D
Corticosteroids decrease intestinal calcium absorption, increase renal calcium excretion, and impair vitamin D metabolism, necessitating supplementation.
Question 3: High-dose niacin supplementation used to raise HDL cholesterol requires monitoring for which serious adverse effect?
- Hypoglycemia
- Hepatotoxicity (Correct answer)
- Renal failure
- Aplastic anemia
Correct answer: Hepatotoxicity
Sustained-release or high-dose niacin can cause dose-dependent hepatotoxicity, requiring periodic monitoring of liver function tests.
Question 4: Chronic use of the anticonvulsant phenytoin (Dilantin) is associated with decreased levels of which nutrient due to impaired absorption and accelerated catabolism?
- Vitamin K
- Vitamin B12
- Folate (Correct answer)
- Vitamin C
Correct answer: Folate
Phenytoin impairs intestinal folate absorption and induces hepatic enzymes that accelerate folate catabolism, increasing the risk of megaloblastic anemia.
Question 5: Which herbal supplement is known to induce CYP450 enzymes, potentially reducing the effectiveness of oral contraceptives and other medications?
- Echinacea
- St. John's Wort (Correct answer)
- Valerian
- Ginkgo biloba
Correct answer: St. John's Wort
St. John's Wort (Hypericum perforatum) strongly induces CYP3A4 and P-glycoprotein, leading to reduced plasma levels of many drugs including hormonal contraceptives.
Question 6: Bile acid sequestrants such as cholestyramine can impair absorption of fat-soluble vitamins. Which of the following is a water-soluble vitamin NOT affected by this mechanism?
- Vitamin A
- Vitamin D
- Vitamin B12 (Correct answer)
- Vitamin K
Correct answer: Vitamin B12
Vitamin B12 is water-soluble and absorbed via a different mechanism (intrinsic factor in the ileum), unlike fat-soluble vitamins A, D, E, and K which require bile for micellar absorption.
Question 7: Loop diuretics (e.g., furosemide) and thiazide diuretics frequently cause depletion of which electrolyte, potentially leading to cardiac arrhythmias?
- Sodium
- Potassium (Correct answer)
- Chloride
- Bicarbonate
Correct answer: Potassium
Both loop and thiazide diuretics increase renal potassium excretion, causing hypokalemia which can precipitate life-threatening cardiac arrhythmias.
CDN Pharmacology & Drug-Nutrient Interactions 2
Absorption of levothyroxine is significantly decreased when the medication is taken concurrently with which mineral supplement?