What oral medication should be initiated to manage symptoms of hypothyroidism in a 60-year-old female with hypertension (high blood pressure) and a history of non-ST-segment elevation myocardial infarction (NSTEMI), presenting with fatigue, malaise, constipation, and weight gain, and laboratory results showing elevated thyroid-stimulating hormone (TSH) and low free T4 levels?

Levothyroxine 12.5 mcg Daily Should Be Initiated

For this 60-year-old female with a history of NSTEMI and current overt hypothyroidism (TSH 12 mIU/L, free T4 0.2 ng/dL), levothyroxine 12.5 mcg daily is the appropriate initial dose due to her significant cardiac risk factors. 1, 2

Rationale for Low-Dose Initiation in Cardiac Patients

Patients over 60 years with known coronary artery disease require a conservative starting approach to avoid precipitating cardiac complications. 1, 2

• For patients >70 years or with cardiac disease/multiple comorbidities, start with a lower dose of 25-50 mcg/day and titrate gradually 1
• However, given this patient's recent NSTEMI, an even more cautious approach with 12.5 mcg daily is warranted 1, 2
• Elderly patients with underlying coronary disease are at increased risk of cardiac decompensation, angina, or arrhythmias even with therapeutic levothyroxine doses 1, 3
• Rapid normalization of thyroid hormone levels can unmask or worsen cardiac ischemia in patients with coronary artery disease 4, 1

Why Other Options Are Inappropriate

Levothyroxine 50 mcg or 100 mcg daily would be dangerously high initial doses for this patient:

• The full replacement dose of approximately 1.6 mcg/kg/day (approximately 100 mcg for her 66 kg weight) is only recommended for patients <70 years without cardiac disease or multiple comorbidities 1, 5
• Starting at 50 mcg in a patient with recent NSTEMI carries unacceptable risk of precipitating acute coronary syndrome, arrhythmias, or heart failure 4, 1
• Even 25 mcg may be too aggressive given her recent NSTEMI history 1, 2

Desiccated thyroid 60 mg daily is not recommended:

• Levothyroxine monotherapy is the standard of care and first-line treatment for hypothyroidism 1, 6, 3
• Desiccated thyroid contains both T4 and T3 in non-physiologic ratios and has unpredictable absorption 7, 5
• There is no evidence supporting combination therapy over levothyroxine monotherapy 3, 7

Titration Strategy and Monitoring

After initiating levothyroxine 12.5 mcg daily, careful dose escalation is essential:

• Recheck TSH and free T4 in 6-8 weeks after any dose adjustment 1, 6
• Increase by 12.5-25 mcg increments based on TSH response and cardiac tolerance 1
• For elderly patients with cardiac disease, use smaller increments (12.5 mcg) to avoid cardiac complications 1
• Target TSH should be within the reference range (0.5-4.5 mIU/L) with normal free T4 levels 1, 6

Critical Safety Considerations

Close monitoring for cardiac symptoms during titration is mandatory:

• Assess for new or worsening angina, palpitations, dyspnea, or arrhythmias at each follow-up 4, 1
• If cardiac symptoms develop, hold the dose and reassess before resuming at a lower dose 4, 2
• For patients with atrial fibrillation, cardiac disease, or serious medical conditions, consider more frequent monitoring within 2 weeks of dose adjustment 1
• The BP should be lowered slowly in patients with acute coronary syndrome, with caution advised in inducing falls of DBP below 60 mm Hg 4

Common Pitfalls to Avoid

• Never start at full replacement dose in elderly patients with cardiac disease - this can precipitate myocardial infarction, heart failure, or fatal arrhythmias 4, 1, 2
• Do not use desiccated thyroid preparations - they lack standardization and have no proven benefit over levothyroxine 3, 7
• Avoid adjusting doses too frequently - wait 6-8 weeks between adjustments to reach steady state 1, 6
• Do not undertreated out of excessive caution - untreated hypothyroidism itself worsens cardiovascular outcomes and increases mortality 6, 7, 5