What oral medication should be initiated to manage a 60-year-old female patient's symptoms of fatigue, malaise, constipation, and weight gain, with a history of hypertension and non-ST-segment elevation myocardial infarction (NSTEMI), elevated thyroid-stimulating hormone (TSH) and low free T4 levels?

Management of Hypothyroidism in a 60-Year-Old Female with Cardiovascular History

Levothyroxine 50 mcg daily should be initiated to manage this patient's symptoms of hypothyroidism, given her age and cardiovascular history. 1

Patient Assessment

This 60-year-old female presents with:

• Classic hypothyroid symptoms: fatigue, malaise, constipation, and weight gain
• Laboratory confirmation: TSH 12 mIU/L (elevated) and free T4 0.2 ng/dL (low)
• Significant cardiovascular history: hypertension and NSTEMI

Treatment Rationale

Medication Selection

• Levothyroxine is the standard treatment for hypothyroidism, not desiccated thyroid
• Desiccated thyroid extract contains both T4 and T3 in a fixed ratio (approximately 4:1) and lacks consistency in T4 and T3 content 2
• The variable T3 content in desiccated thyroid can cause transient episodes of hyperthyroidism, which would be particularly dangerous in a patient with cardiovascular disease

Dosing Considerations

• For patients older than 60 years or with known/suspected ischemic heart disease, a lower starting dose of levothyroxine (12.5 to 50 mcg per day) is recommended 3
• The patient's weight of 66 kg would typically suggest a full replacement dose of approximately 100 mcg (1.5-1.8 mcg/kg/day) 3
• However, her age (60) and history of NSTEMI necessitate a more cautious approach with a lower starting dose of 50 mcg daily
• Starting with 100 mcg would be too aggressive given her cardiac history
• Starting with 12.5 mcg would be too conservative and may delay symptom improvement

Monitoring and Follow-up

• Check TSH and free T4 levels 6-8 weeks after initiating therapy 4
• Target a TSH level within the normal reference range (0.4-4.0 mIU/L) 4
• Dose adjustments should be made in small increments (12.5-25 mcg) based on TSH results
• More frequent monitoring may be necessary in patients with cardiovascular disease

Special Considerations for Cardiac Patients

• Levothyroxine increases myocardial oxygen demand, which can exacerbate ischemic heart disease
• Thyroid hormone replacement can increase the response to oral anticoagulants, requiring dose adjustment of anticoagulants 5
• Levothyroxine may reduce the therapeutic effects of digitalis glycosides 5
• Careful monitoring for signs of cardiac decompensation is essential during the initial treatment phase

Medication Administration

• Levothyroxine should be taken on an empty stomach, 30-60 minutes before breakfast with a full glass of water 4
• Many medications can interfere with levothyroxine absorption, including:
  • Calcium supplements
  • Iron supplements
  • Proton pump inhibitors
  • Antacids
• These should be taken at least 4 hours apart from levothyroxine 5

Common Pitfalls to Avoid

1. Overtreatment: Starting with too high a dose in patients with cardiac disease can precipitate angina, arrhythmias, or heart failure
2. Undertreatment: Persistent hypothyroid symptoms can continue to affect quality of life
3. Medication interactions: Failure to account for medications that affect levothyroxine absorption or metabolism
4. Inadequate monitoring: Not checking thyroid function tests at appropriate intervals
5. Ignoring persistent symptoms: Some patients may require dose adjustments despite normalized TSH

By starting with levothyroxine 50 mcg daily, closely monitoring thyroid function, and making gradual dose adjustments as needed, this patient's hypothyroid symptoms can be safely and effectively managed while minimizing cardiovascular risk.