Levothyroxine, a synthetic form of the thyroid hormone thyroxine, is commonly prescribed for the treatment of hypothyroidism. Its effectiveness can be influenced by various factors that affect its absorption in the gastrointestinal tract. Factors that can result in poor absorption of levothyroxine include:
- Intake Timing and Food Interactions: Levothyroxine is best absorbed on an empty stomach. The presence of food can significantly reduce its absorption. It is generally recommended to take levothyroxine at least 30 to 60 minutes before breakfast or at least three to four hours after dinner.
- Medication Interactions: Several medications can interfere with levothyroxine absorption, including calcium and iron supplements, aluminum-containing antacids, proton pump inhibitors, and certain cholesterol-lowering drugs (such as cholestyramine and colestipol).
- pH Changes in the Stomach: Variations in the acidity of the stomach, which can be influenced by age, certain medical conditions, or medications (like antacids, H2 blockers, and proton pump inhibitors), can affect levothyroxine absorption.
- Malabsorption Syndromes: Conditions that lead to general malabsorption such as coeliac and Crohn’s disease can impair the absorption of many medications, including levothyroxine.
- Surgery and Gastric Bypass: Patients who have undergone gastric bypass or other forms of gastrointestinal surgery may have altered absorption of levothyroxine.