Treatment of Hypothyroidism
The standard treatment for hypothyroidism is oral levothyroxine (T4) monotherapy, which should be continued lifelong in most patients. 1
Diagnosis and Classification
Before initiating treatment, proper diagnosis is essential:
- Primary hypothyroidism (most common): Elevated TSH with low or normal free T4
- Secondary/central hypothyroidism: Low/normal TSH with low free T4
- Subclinical hypothyroidism: Elevated TSH with normal free T4
Diagnosis requires:
- Initial measurement of serum TSH, followed by free T4 if necessary
- Serial TSH measurements (a single abnormal value is insufficient)
- Anti-TPO antibodies may help identify autoimmune etiology but aren't routinely required 1
Treatment Protocol
Initial Dosing
- Standard adult starting dose: 1.6 mcg/kg/day for overt hypothyroidism 1, 2
- Elderly patients: Start at lower doses (12.5-50 mcg/day) due to increased risk of cardiovascular complications 1, 2
- Pregnant patients:
- Pre-existing hypothyroidism: Increase pre-pregnancy dose by 12.5-25 mcg/day
- New onset (TSH ≥10 IU/L): 1.6 mcg/kg/day
- New onset (TSH <10 IU/L): 1.0 mcg/kg/day 2
- Pediatric patients: Start at one-fourth the recommended full replacement dose and increase weekly by one-fourth until full dose is reached to minimize hyperactivity risk 2
Monitoring and Dose Adjustments
- Monitor TSH and free T4 every 6-8 weeks during dose adjustments 1, 2
- Once stable, evaluate every 6-12 months in adults 2
- Pediatric monitoring: 2 and 4 weeks after initiation, 2 weeks after any dose change, then every 3-12 months 2
- Target TSH within normal range (age and trimester-specific for pregnant women) 1, 2
Special Considerations
Pregnancy
- Measure TSH and free T4 as soon as pregnancy is confirmed and at minimum during each trimester
- Maintain TSH in trimester-specific reference range
- Return to pre-pregnancy dose immediately after delivery 2
Elderly Patients
- Lower starting doses to prevent cardiac overload and arrhythmias
- Atrial fibrillation is the most common arrhythmia with overtreatment 2
Thyroid Cancer Patients
- Require higher doses (2.11 mcg/kg/day vs 1.63 mcg/kg/day for primary hypothyroidism) 1
- Dosage based on target level of TSH suppression for cancer stage and clinical status 2
Administration Considerations
- Take levothyroxine consistently, typically in the morning on an empty stomach
- Separate from food, calcium, iron supplements, and certain medications by at least 4 hours
- Poor absorption may necessitate alternative formulations (liquid) or administration routes in refractory cases 3
Potential Complications
- Undertreatment: Persistent hypothyroid symptoms, cardiovascular disease, increased mortality 1
- Overtreatment: Subclinical hyperthyroidism, atrial fibrillation, heart failure, osteoporosis, neuropsychiatric problems 1, 2
Alternative Treatments
While levothyroxine monotherapy remains the standard of care, some patients report persistent symptoms despite normalized TSH levels. Although combination therapy with levothyroxine plus liothyronine (T3) has been studied, there is insufficient evidence to recommend it routinely 4, 5.
Pitfalls to Avoid
- Relying on a single abnormal TSH measurement for diagnosis
- Failing to adjust dosage during pregnancy
- Starting with full doses in elderly or cardiac patients
- Premature dose adjustments before reaching steady state (6-8 weeks)
- Overlooking medication interactions that affect levothyroxine absorption
Remember that untreated hypothyroidism can lead to serious complications including cardiovascular disease, preeclampsia in pregnancy, and in severe cases, myxedema coma 1, 2.