How do Levothyroxine and Carbidopa (C)-Levodopa (L) interact with food intake?

From the Guidelines

Levothyroxine should be taken on an empty stomach, ideally 30-60 minutes before breakfast, while carbidopa-levodopa's interaction with food depends on your specific symptoms, with a recommendation to take it at least 30 min before meals to maximize levodopa absorption and efficacy. For levothyroxine, food can reduce absorption by up to 40%, particularly high-fiber foods, coffee, and calcium-rich products, which can bind to the medication and decrease its effectiveness. Taking it consistently in relation to meals is crucial for maintaining stable thyroid hormone levels. Carbidopa-levodopa presents a more complex situation - taking it with food, especially protein-rich meals, can decrease its absorption and effectiveness, but food may also help reduce nausea, a common side effect. As stated in the espen guideline clinical nutrition in neurology 1, for Parkinson's patients experiencing motor fluctuations, taking carbidopa-levodopa on an empty stomach may provide faster symptom relief, while those with gastrointestinal side effects might benefit from taking it with a small, low-protein snack. Some key points to consider are:

• Taking levodopa-containing medications at least 30 min before meals to avoid interactions 1
• Compliance with a protein-redistribution dietary regimen to maximize levodopa absorption and efficacy 1
• Redistribution of protein intake throughout the day, with a low-protein breakfast and lunch, and consumption of a second course with no quantitative restrictions in terms of protein only at dinner 1
• The use of low-protein foods designed for patients with chronic renal failure to achieve protein redistribution 1
• Active monitoring to avoid potential complications, including weight loss, micronutrient deficits, hunger before dinner, and dyskinesias 1
• Adjusting the timing of protein intake throughout the day for optimal symptom control, as dietary protein competes with levodopa for absorption in the intestine and transport across the blood-brain barrier 1.

From the FDA Drug Label

Since levodopa competes with certain amino acids for transport across the gut wall, the absorption of levodopa may be impaired in some patients on a high protein diet. Administer levothyroxine sodium tablets at least 4 hours apart from these agents. Gastric acidity is an essential requirement for adequate absorption of levothyroxine. Sucralfate, antacids and proton pump inhibitors may cause hypochlorhydria, affect intragastric pH, and reduce levothyroxine absorption.

The interaction between Levothyroxine and Carbidopa-Levodopa with Food intake is as follows:

• Levothyroxine: Food intake may affect its absorption, particularly with certain foods or medications that alter gastric acidity, such as sucralfate, antacids, and proton pump inhibitors.
• Carbidopa-Levodopa: A high protein diet may impair the absorption of Levodopa due to competition with amino acids for transport across the gut wall. It is recommended to administer Levothyroxine at least 4 hours apart from certain agents that may affect its absorption 2. For Carbidopa-Levodopa, patients should be aware that a high protein diet may impact the efficacy of the medication 3.

From the Research

Interaction with Food Intake

• Levothyroxine absorption can be affected by food intake, with certain foods such as soybeans and coffee reducing absorption, while vitamin C may increase it 4
• Protein-rich food can delay and reduce levodopa absorption, therefore it is recommended to administer levodopa in a relatively empty stomach 5
• There is no significant difference in thyroid hormone levels in patients taking carbidopa-levodopa (Sinemet) after food intake 6

Specific Food Interactions

• Soybeans and coffee have the greatest impact on reducing levothyroxine absorption 4
• Vitamin C can increase levothyroxine absorption 4
• Protein-rich food can delay and reduce levodopa absorption 5

Clinical Significance

• The interactions between levothyroxine and food intake are clinically significant, and patients should be monitored for serum thyroid-stimulating hormone and free T4 values to reduce the risk of developing iatrogenic hyperthyroidism 4
• The timing and administration of levodopa with food can affect its efficacy and tolerability in patients with Parkinson's disease 5