Clinical relevancy of the levothyroxine-continuous enteral nutrition interaction

The objective of this study was to determine if patients requiring levothyroxine therapy develop hypothyroidism during concurrent continuous enteral nutrition (EN).

Adult patients with a history of hypothyroidism, given levothyroxine via the feeding tube at the same dose given prior to hospital admission and who were referred to the nutrition support service for EN were evaluated. Thyroid function tests (TFTs) were performed prior to administration of levothyroxine-continuous EN, then approximately weekly thereafter. Patients who received less than 14 days of concurrent EN-levothyroxine therapy were excluded from the analysis.

Thirteen patients who received 20 ± 5 days of concurrent EN and levothyroxine were evaluated. Two patients developed subclinical hypothyroidism (thyrotropin [TSH] >6 and <10 mcIU/mL + normal fT(4)), and 6 developed overt hypothyroidism (TSH >10 mcIU/mL + low fT(4)) within 2 to 3 weeks of concurrent EN-levothyroxine therapy. Five patients remained euthyrotic. Differences between those who developed subclinical or overt hypothyroidism versus those who remained euthyrotic could not be explained by age, weight, levothyroxine dose, type of EN formula, or amount of EN received.

More than half of the patients receiving concurrent levothyroxine-continuous EN developed subclinical or overt hypothyroidism requiring therapeutic intervention. Routine weekly monitoring of TFTs for patients receiving concurrent levothyroxine-continuous EN is recommended.