Thyroxin (also known as levothyroxine or T4) is a synthetic form of the thyroid hormone thyroxine. It is commonly used to treat hypothyroidism, a condition where the thyroid gland does not produce enough thyroid hormone. Here are some key points about thyroxin¹²³:

Uses:

1. Hypothyroidism Treatment: Primarily used to treat hypothyroidism by supplementing low thyroid hormone levels.
2. Goiter Reduction: Can help decrease the size of enlarged thyroid glands (goiter).
3. Thyroid Cancer Management: Used alongside surgery and radiotherapy to treat thyroid-dependent well-differentiated thyroid cancer.

Mechanism of Action:

Levothyroxine mimics the body's endogenous thyroxine (T4). Normally, T4 is produced by the thyroid gland and then converted into the active form, T3 (triiodothyronine), which regulates metabolism by increasing gluconeogenesis, protein synthesis, and mobilization of glycogen stores².

Pharmacokinetics:

1. Absorption: It is absorbed mainly from the jejunum and ileum. The absorption rate varies from 40% to 80% and can be influenced by factors such as fasting or food intake. Its bioavailability is approximately 93% when taken as a tablet compared to oral solutions.
2. Binding: Thyroid hormones are highly bound to plasma proteins, which affects their metabolic clearance and half-life.
3. Metabolism and Excretion: Metabolized mainly in the liver and excreted via the kidneys.

Interactions:

• Food and Supplements: Levothyroxine absorption can be significantly affected by food and dietary supplements. Coffee, soy products, fiber, calcium, and iron supplements can decrease its absorption³. Taking the medication at the same time every day, especially in the morning on an empty stomach, can help mitigate these interactions.
• Other Medications: Certain medications and physiological conditions can alter the binding and effectiveness of thyroid hormones.

Recommendations:

• Take the medication on an empty stomach, preferably 30 to 60 minutes before breakfast.
• Maintain a consistent time interval between taking levothyroxine and consuming coffee, calcium, or iron supplements to avoid interaction and ensure proper absorption.

If you have specific needs or conditions regarding thyroxin supplementation, consult your healthcare provider for personalized advice.

Footnotes

1. Mayo Clinic, "Levothyroxine (Oral Route) Description and Brand Names," source. ↩

2. Bibinaz Eghtedari, "Levothyroxine - StatPearls - NCBI Bookshelf," source. ↩ ↩²

3. Agnieszka Wiesner, "Levothyroxine Interactions with Food and Dietary Supplements–A Systematic Review," source. ↩ ↩²