Browse the corpus

Oral levothyroxine is primarily indicated for treating primary, secondary, and tertiary hypothyroidism. Primary hypothyroidism is when the problem occurs in the thyroid gland. Secondary hypothyroidism is when the problem is in the pituitary gland, and there is a decrease in the production of thyroid-stimulating hormone (TSH). Tertiary hypothyroidism is sporadic. Additionally, levothyroxine has FDA approval for pituitary thyrotropin suppression as an adjunct to surgery and radioiodine therapy to manage thyrotropin-dependent well-differentiated thyroid cancer. This activity covers important information about prescribing levothyroxine, including mechanism of action, pharmacology, adverse event profiles, eligible patient populations, and monitoring, and highlights the interprofessional team's role in managing various forms of hypothyroidism with levothyroxine. Objectives: Explain the mechanism of action of levothyroxine. Describe the pathophysiology of the three primary forms of hypothyroidism. Outline the contraindications to initiating therapy with levothyroxine. Summarize interprofessional team strategies for improving care coordination and communication to advance levothyroxine and improve outcomes. Access free multiple choice questions on this topic.

Levothyroxine toxicity is rare; however, it is most likely to occur in the setting of accidental ingestion by children or older adults. Thyroxine (T4) and triiodothyronine (T3) levels rise within 1 to 2 hours of ingestion. In the initial stage of overdose (6 to 12 hours post-ingestion), the common signs of toxicity would be tremulousness, tachycardia, hypertension, anxiety, and diarrhea. Rarely convulsions, thyroid storms, acute psychosis, arrhythmias, and acute myocardial infarction may occur. Laboratory workup usually reveals elevated serum total T4 and T3, suppressed serum TSH, and elevated Free T4 and Free T3. Employ the following treatment approach in acute levothyroxine overdose. Administer activated charcoal to prevent the absorption of levothyroxine. Cholestyramine binds thyroxine and enhances its elimination. The dose used is 4 grams orally every 8 hours.[30] Beta-blockers are beneficial to alleviate the metabolic effects of thyroid hormone, mainly on the cardiac system (controlling tachycardia, preventing arrhythmias). Propranolol also blocks the peripheral conversion of T4 to T3. Glucocorticoids such as (Dexamethasone 4 mg orally) can reduce the conversion of LT4 to T3, the active hormone. Propylthiouracil can be used to prevent the conversion of T4 to T3. Hemodialysis is utilized in severe cases, but it is of limited benefit since T3 and T4 are primarily protein-bound. Hemoperfusion utilizing activated charcoal is a complex but efficient procedure for reducing thyroxine levels. Therefore, reserve it for adult patients with severe intoxication.[31] The severe cases of intoxication leading to a thyroid storm require treatment in a MICU.[32] In summary, it is essential to note that there is no antidote to treat levothyroxine overdose. Treatment options include gastric lavage, activated charcoal, cholestyramine, glucocorticoids, beta-blockers, propylthiouracil, and supportive measures.[33]

Upon first prescribing levothyroxine, medication adjustment should occur every 6 to 8 weeks until the patient reaches a steady state. Clinicians should also evaluate the response to levothyroxine by using a validated questionnaire, such as thyroid-related quality of life (ThyPRO) and the underactive thyroid treatment satisfaction questionnaire (ThySRQ).[34][35] If the patient has symptoms of hyperthyroidism, advise the patient to contact the clinician to determine if these are side effects of the medication. A clinician should then order TSH and free T4 levels immediately. If the free T4 comes back elevated, the clinician should decrease the dose of levothyroxine to prevent cardiac complications and other symptoms of hyperthyroidism. Finally, clinicians should refer the patient to an endocrinologist if hypothyroidism is due to central causes. In all the scenarios mentioned above, pharmacists should ensure proper dosing and report to the clinician if there is any potential drug-drug interaction or if supplies may dictate a change to a different formulation. In an acute overdose of levothyroxine, emergency department physician and triage nurses stabilize the patient, focusing on maintaining a patent airway, breathing, and circulation. Critical care physicians play an essential role in managing thyroid storms. In the case of extreme overdose where hemoperfusion or hemodialysis is planned, a nephrologist referral is required.[31] In such cases, nursing will play a crucial role in monitoring the patient, administering medication, and reporting any patient status changes to the clinician. As described above, multiple healthcare professionals take care of the patient prescribed levothyroxine for various indications. An interprofessional team-based approach involving clinicians (MDs, DOs, NPs, PAs), specialists, nurses, pharmacists, and other healthcare providers achieves maximum efficacy. It minimizes the adverse drug reactions associated with levothyroxine therapy which translates to improved patient outcomes. [Level 5]