What is the recommended dosing and counseling for levothyroxine (thyroid hormone replacement therapy)?

Levothyroxine Dosing and Counseling Guidelines

For patients with primary hypothyroidism, levothyroxine should be initiated at 1.6 mcg/kg/day for patients under 70 years without cardiac disease, while older patients or those with cardiac disease should start at lower doses of 25-50 mcg/day with gradual titration. 1, 2

Initial Dosing

Standard Dosing Approach

• For patients without risk factors (under 70 years old, not frail, without cardiac disease or multiple comorbidities), full replacement can be estimated using ideal body weight at approximately 1.6 mcg/kg/day 1, 3
• For patients older than 70 years and/or frail patients with multiple comorbidities (including cardiac disease), start with a lower dose of 25-50 mcg and titrate up gradually 1, 4
• Women who become pregnant while on levothyroxine should increase their weekly dosage by 30% (take one extra dose twice weekly), followed by monthly evaluation 5

Dose Adjustment for Elevated TSH

• For patients with elevated TSH levels, increase levothyroxine dose by 12.5-25 mcg daily to normalize TSH within the reference range 2
• Persistent TSH elevation >10 mIU/L warrants more urgent treatment 2
• Monitor TSH and free T4 after 6-8 weeks of dose adjustment, with further adjustments as needed until TSH normalizes 1, 2

Administration Guidelines

• Instruct patients to take levothyroxine as a single dose on an empty stomach, 30-60 minutes before breakfast with a full glass of water to avoid choking or gagging 6
• Inform patients that agents such as iron supplements, calcium supplements, and antacids can decrease levothyroxine absorption; these should not be taken within 4 hours of levothyroxine 6
• Advise patients that levothyroxine is typically a lifelong replacement therapy 6
• Store levothyroxine at 20°C to 25°C (68°F to 77°F) and protect from light and moisture 6

Monitoring Protocol

• Check TSH every 6-8 weeks while titrating hormone replacement to goal of TSH within the reference range 1, 2
• Free T4 can be used to help interpret ongoing abnormal TSH levels on therapy, as TSH may take longer to normalize 1
• Once adequately treated, repeat testing every 6-12 months or as indicated for a change in symptoms 1, 2
• Development of a low TSH on therapy suggests overtreatment or recovery of thyroid function; dose should be reduced or discontinued with close follow-up 1

Special Populations

Thyroid Cancer Patients

• For patients with thyroid carcinoma, TSH suppression may be indicated 1
• Patients with known residual carcinoma or at high risk for recurrence should have TSH levels maintained below 0.1 mU/L 1
• Disease-free patients at low risk for recurrence should have TSH levels maintained either slightly below or slightly above the lower limit of the reference range 1
• Patients who remain disease-free for several years can probably have their TSH levels maintained within the reference range 1

Elderly Patients

• Older patients require lower doses of levothyroxine compared to younger patients 4
• Some patients over age 60 may need as little as 50 mcg/day or less 4
• It may be reasonable to reassess the dose of levothyroxine after several years in older patients 4

Patient Counseling

• Inform patients that it may take several weeks before they notice an improvement in symptoms 6
• Instruct patients to notify their healthcare provider if they are pregnant or breastfeeding 6
• Advise patients that levothyroxine should not be used as a primary or adjunctive therapy in a weight control program 6
• Instruct patients to notify their physician of any other medical conditions they may have, particularly heart disease, diabetes, clotting disorders, and adrenal or pituitary gland problems 6
• Advise patients to report symptoms such as rapid or irregular heartbeat, chest pain, shortness of breath, leg cramps, headache, nervousness, irritability, sleeplessness, tremors, changes in appetite, weight changes, vomiting, diarrhea, excessive sweating, heat intolerance, fever, or changes in menstrual periods 6
• Inform patients that partial hair loss may occur rarely during the first few months of therapy but is usually temporary 6
• Patients whose TSH levels are chronically suppressed should be counseled to ensure adequate daily intake of calcium (1200 mg/day) and vitamin D (1000 units/day) 1

Potential Complications and Management

• For severe hypothyroidism with myxedema (bradycardia, hypothermia, and altered mental status), hospital admission is required 1
• Myxedema coma is a life-threatening emergency requiring admission and a high level of care 1
• If there is uncertainty about whether primary or central hypothyroidism is present, hydrocortisone should be given before thyroid hormone is initiated 1