From the Research
No, you should not order intravenous (IV) levothyroxine if the patient can take it orally (PO). According to the most recent and highest quality study, oral levothyroxine is the preferred route of administration in patients who can take medications by mouth 1. The indications for intravenous use of thyroid hormones are limited to situations where oral administration is not possible, such as insufficient resorption of oral medications, partial or total loss of consciousness, sedation in the intensive care unit, or shock.
Key Points to Consider
- Oral levothyroxine has a bioavailability of approximately 70-80%, which is sufficient for therapeutic effect.
- IV levothyroxine should be reserved for patients who cannot take oral medications, such as those who are NPO, have severe malabsorption disorders, are intubated, or are experiencing myxedema coma.
- IV administration is more expensive, requires more resources to administer, and carries risks associated with intravenous access.
- Oral levothyroxine is easier to administer, more convenient for the patient, and allows for more consistent hormone levels due to daily dosing.
Relevant Evidence
The study published in 2024 in the journal Hormone and metabolic research = Hormon- und Stoffwechselforschung = Hormones et metabolisme 1 provides the most recent and highest quality evidence on the indications for intravenous use of thyroid hormones. This study suggests that oral levothyroxine is the preferred route of administration in patients who can take medications by mouth, and that IV levothyroxine should be reserved for specific situations where oral administration is not possible.
Clinical Implications
In clinical practice, oral levothyroxine should be the first-line treatment for patients who can take medications by mouth. IV levothyroxine should only be considered in situations where oral administration is not possible, and the benefits of IV administration outweigh the risks. By prioritizing oral levothyroxine, clinicians can provide more convenient, cost-effective, and safe treatment for patients with hypothyroidism.