What is the recommended treatment for a patient with hypothyroidism?

Treatment of Hypothyroidism

Levothyroxine monotherapy is the first-line treatment for hypothyroidism, with dosing tailored to age, cardiac status, and severity of disease. 1, 2, 3

Initial Treatment Selection

• Levothyroxine (T4) is the standard of care and should be used as first-line therapy for all patients with hypothyroidism. 1, 2, 4
• Levothyroxine monotherapy remains superior to combination therapy with T3, as the thyroid gland's secretion of both hormones is adequately replicated through peripheral conversion of T4 to T3. 5
• Treatment should be initiated immediately upon diagnosis to prevent serious complications including heart failure, myxedema coma, and in pregnant women, adverse pregnancy outcomes. 2, 3

Dosing Strategy

Full Replacement Dose (Younger, Healthy Patients)

• For patients <70 years without cardiac disease or multiple comorbidities, start with the full replacement dose of approximately 1.6 mcg/kg/day. 1
• This approach allows for rapid normalization of thyroid function and prevents complications from prolonged hypothyroidism. 1

Low-Dose Initiation (Elderly and High-Risk Patients)

• For patients >70 years or with cardiac disease/multiple comorbidities, start with a lower dose of 25-50 mcg/day and titrate gradually. 1, 6
• Elderly patients with coronary disease are at increased risk of cardiac decompensation, angina, or arrhythmias even with therapeutic levothyroxine doses. 1
• Rapid normalization of thyroid hormone levels can unmask or worsen cardiac ischemia in patients with coronary artery disease. 1

Monitoring and Dose Adjustment

• Monitor TSH every 6-8 weeks while titrating hormone replacement to achieve a target TSH of 0.5-4.5 mIU/L. 1, 3
• Adjust levothyroxine dose in increments of 12.5-25 mcg based on the patient's current dose and clinical characteristics. 1
• Use smaller increments (12.5 mcg) for elderly patients or those with cardiac disease to avoid cardiac complications. 1
• Once adequately treated, repeat TSH testing every 6-12 months or if symptoms change. 1, 3

Special Populations

Pregnancy

• Levothyroxine should not be discontinued during pregnancy, and hypothyroidism diagnosed during pregnancy should be promptly treated. 6
• TSH should be monitored and levothyroxine dosage adjusted during pregnancy, as requirements typically increase by 25-50%. 1, 6
• Untreated maternal hypothyroidism is associated with spontaneous abortion, gestational hypertension, pre-eclampsia, stillbirth, premature delivery, and adverse effects on fetal neurocognitive development. 6
• Target TSH <2.5 mIU/L in the first trimester. 1

Subclinical Hypothyroidism

• Initiate levothyroxine therapy for patients with TSH >10 mIU/L, regardless of symptoms. 1, 4
• This threshold carries approximately 5% annual risk of progression to overt hypothyroidism. 1
• For TSH 4.5-10 mIU/L, consider treatment in symptomatic patients, pregnant women or those planning pregnancy, patients with infertility, goiter, or positive anti-TPO antibodies. 1, 4

Critical Safety Considerations

• Before initiating levothyroxine, rule out concurrent adrenal insufficiency, as starting thyroid hormone before corticosteroids can precipitate adrenal crisis. 1
• In patients with suspected central hypothyroidism or hypophysitis, always start corticosteroids at least 1 week prior to thyroid hormone replacement. 1
• Approximately 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH, increasing risks for atrial fibrillation, osteoporosis, fractures, and cardiac complications. 1

Administration Guidelines

• Levothyroxine should be taken on an empty stomach, one-half to one hour before breakfast. 1
• Take at least 4 hours apart from iron, calcium supplements, or antacids to ensure optimal absorption. 1

Alternative Routes of Administration

• For patients with malabsorption or refractory hypothyroidism despite adequate oral dosing, consider liquid oral formulations, intravenous, intramuscular, or rectal administration. 7
• Intravenous levothyroxine ensures consistent delivery in critically ill patients where enteral absorption is unreliable. 1

Common Pitfalls to Avoid

• Never treat based on a single elevated TSH value, as 30-60% normalize on repeat testing. 1
• Avoid excessive dose increases that could lead to iatrogenic hyperthyroidism, which increases risk for osteoporosis, fractures, abnormal cardiac output, and ventricular hypertrophy. 1
• Do not adjust doses too frequently before reaching steady state—wait 6-8 weeks between adjustments. 1
• Overtreatment with levothyroxine (TSH <0.1 mIU/L) significantly increases the risk of atrial fibrillation, particularly in elderly patients. 1, 6