Levothyroxine sodium tablets (Euthyrox) exert therapeutic effects by supplementing thyroid hormones. Their efficacy is closely related to drug interactions, and special attention should be paid to absorption interference and metabolic effects. The following explanation is provided from three aspects: mechanism of action, indications, and drug interactions, with a focus on analyzing common risks associated with combinations such as calcium agents and anticoagulants.

1. Effect

(1) Pharmacological mechanism

Levothyroxine sodium is converted into triiodothyronine (T3) in the body, which binds to thyroid hormone receptors (THR) to regulate cell metabolism, growth and development, as well as energy balance.

(2) Indications

For replacement therapy of primary/secondary hypothyroidism and postoperative TSH suppression therapy for differentiated thyroid cancer, the dosage needs to be adjusted based on TSH or FT4 levels.

2. Drug interactions

(1) Absorption interference type

Calcium/iron/antacids form insoluble complexes, reducing bioavailability, and should be taken with an interval of ≥4 hours.

Proton pump inhibitors increase gastric pH, reducing drug dissolution. It is recommended to monitor TSH and increase the dosage as appropriate.

(2) Metabolic effects

Hepatic enzyme inducers (such as rifampin) accelerate metabolism, necessitating an increase in the dosage of levothyroxine and regular re-examination of TSH.

Amiodarone inhibits the conversion of T4 to T3, which may lead to thyroid dysfunction. Therefore, it is necessary to monitor FT4 levels and clinical symptoms.

(3) Pharmacodynamic synergism/antagonism

The anticoagulant effect of warfarin is enhanced, and close monitoring of INR values is required to prevent bleeding.

The efficacy of hypoglycemic drugs may be diminished, and blood glucose monitoring should be intensified during the initial phase of treatment.

(4) Special precautions

When combined with a bile acid sequestrant (colestyramine), it is recommended to either space out the dosing by 12 hours or adjust the dosing regimen.

Pregnant women need to increase the dosage to 12.5-25μg/day, and resume the original dosage immediately after giving birth.