What is the perioperative management of levothyroxine (Synthroid) therapy?

From the Guidelines

For perioperative management of levothyroxine (Synthroid) therapy, patients should continue taking their usual dose up until the day of surgery, with the goal of maintaining stable thyroid hormone levels to prevent hypothyroidism-related complications, as supported by the American Thyroid Association (ATA) and European Thyroid Association (ETA) guidelines 1. The management of levothyroxine therapy in the perioperative period is crucial to prevent potential complications.

• The drug of choice for thyroid hormone suppression therapy is levothyroxine (LT4), and the suppressive dose varies according to age and body mass index 1.
• TSH suppressive treatment with LT4 is beneficial in high-risk thyroid cancer patients, as it may decrease progression of metastatic disease, thus reducing cancer-related mortality 1.
• In patients with persistent or metastatic disease, an undetectable serum TSH (<0.1 mU/l) should be maintained during follow-up, while in patients free of disease, LT4 therapy may be shifted from suppressive to replacement 1.
• The rationale for continuing levothyroxine perioperatively is to maintain stable thyroid hormone levels, as hypothyroidism can lead to hemodynamic instability, impaired drug metabolism, and delayed recovery.
• For patients unable to take oral medications postoperatively, levothyroxine can be administered intravenously at approximately 80% of the oral dose.
• If a patient must miss doses for several days, this is generally not concerning as levothyroxine has a long half-life (7 days).
• For patients with severe hypothyroidism or cardiac disease, maintaining consistent thyroid hormone levels is more critical, and consultation with endocrinology is recommended for emergency surgeries in patients with uncontrolled hypothyroidism.

From the FDA Drug Label

Patients with coronary artery disease who are receiving levothyroxine therapy should be monitored closely during surgical procedures, since the possibility of precipitating cardiac arrhythmias may be greater in those treated with levothyroxine. Notify your physician or dentist that you are taking Levothyroxine Sodium Tablets, USP prior to any surgery.

The perioperative management of levothyroxine (Synthroid) therapy involves:

• Monitoring patients with coronary artery disease closely during surgical procedures due to the risk of precipitating cardiac arrhythmias
• Notifying the physician or dentist prior to any surgery that the patient is taking levothyroxine sodium tablets 2 Key points to consider:
• Cardiac risk: Patients with coronary artery disease may be at increased risk of cardiac arrhythmias during surgery
• Pre-surgical notification: Patients should inform their physician or dentist about their levothyroxine therapy before undergoing surgery 2

From the Research

Perioperative Management of Levothyroxine Therapy

The management of levothyroxine (LT4) therapy in the perioperative period is crucial to prevent hypo- or hyperthyroidism. Several studies have investigated the optimal dosing scheme for LT4 after thyroidectomy.

• A study published in 2019 3 developed a decision tree to estimate LT4 dose adjustments and reduce the time to euthyroidism. The decision tree used thyroid-stimulating hormone values at first dose adjustment and correctly predicted the dose adjustment within the smallest LT4 dose increment 75% of the time.
• Another study published in 2021 4 assessed the risk of perioperative thyroid storm in hyperthyroid patients and found that preoperative treatment is warranted to prevent this complication.
• A study published in 2006 5 investigated the adequacy of thyroid hormone replacement therapy after thyroid surgery and found that an optimal replacement therapy dose is necessary to avoid over- and undersubstitution.
• A comprehensive comparison and evaluation of levothyroxine dosing schemes was published in 2019 6, which found that a novel Poisson regression model was the most accurate in predicting euthyroid dose.
• A literature review published in 2020 7 explored the limits and drawbacks of LT4 replacement therapy in patients who had undergone thyroidectomy and found that approximately 75% of patients require a dose adjustment, suggesting that factors other than body weight play a role in determining the proper LT4 dose.

Factors Affecting LT4 Dose Adjustments

Several factors can affect LT4 dose adjustments, including:

• Lack of compliance 7
• Changes in LT4 formulation 7
• Dosage errors 7
• Increased serum levels of T4-binding globulin 7
• Body mass changes 7
• Dietary habits 7
• Concomitant ingestion of certain medications, such as calcium supplements, ferrous sulfate, proton-pump inhibitors, bile acid sequestrants, and sucralfate 7
• Gastrointestinal conditions and their treatments 7

LT4 Formulations

New formulations of LT4, such as soft gel capsules and oral solutions, have recently become available 7. The liquid formulation is supposed to overcome food and beverage interference with absorption of LT4 tablets.