Applied Evidence

Refining your approach to hypothyroidism treatment

J Fam Pract. 2020 March;69(2):84-89

References

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For adults with cardiac disease, the risk of over-replacement limits initial dosing to 25 to 50 mcg/d for patients < 50 years (12.5-25 mcg/d; ≥ 50 years).³ For adults with subclinical hypothyroidism, it is reasonable to begin therapy at a lower daily dose (eg, 25-75 mcg/d) depending on baseline TSH level, symptoms (the patient may be asymptomatic), and the presence of cardiac disease (TABLE 2^3,4). Consider treatment in patients with subclinical hypothyroidism particularly when patients have a goiter or dyslipidemia and in women contemplating pregnancy in the near future. Elderly patients may require a dose 20% to 25% lower than younger adults because of decreased body mass.³

Levothyroxine is considered first-line therapy for hypothyroidism because of its low cost, dose consistency, low risk of allergic reactions, and potential to cause fewer cardiac adverse effects than triiodothyronine (T3) products such as desiccated thyroid extract.⁵ Although data have not shown an absolute increase in cardiovascular adverse effects, T3 products have a higher T3 vs T4 ratio, giving them a theoretically increased risk.^5,6 Desiccated thyroid extract also has been associated with allergic reactions.⁵

Consider treatment in adults with subclinical hypothyroidism when they have a goiter or dyslipidemia and in women contemplating pregnancy in the near future.

Use of liothyronine alone or in combination with levothyroxine lacks evidence and guideline support.⁴ Furthermore, it is dosed twice daily, which makes it less convenient, and concerns still exist that there may be an increase in cardiovascular adverse effects.^4,6 See TABLE 3⁷ for a summary of available products and their equivalent doses.

Maintaining patients on therapy

The maintenance phase begins once hypothyroidism is diagnosed and treatment is initiated. This phase includes regular monitoring with laboratory studies, office visits, and as-needed adjustments in hormone replacement dosing. The frequency at which all of these occur is variable and based on a number of factors including the patient’s other medical conditions, use of other medications including over-the-counter agents, the patient’s age, weight changes, and pregnancy status.^3,4,8 In general, dosage adjustments of 12.5 to 25 mcg can be made at 6- to 8-week intervals based on repeat TSH measurements, patient symptoms, and comorbidities.³

Instruct patients to take levothyroxine either in the morning at least 30 to 60 minutes before eating or 3 to 4 hours after the last meal of the day.

Once a patient is symptomatically stable and laboratory values have normalized, the recommended frequency of laboratory evaluation and office visits is every 12 months, barring significant changes in any of the factors mentioned above. At each visit, physicians should perform medication (including supplements) reconciliation and discuss any health condition updates. Changes to the therapy plan, including frequency or timing of laboratory tests, may be necessary if patients begin taking medications that alter the absorption or function of levothyroxine (eg, steroids).

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