SAT-347 - Thinking under the Tongue: Sublingual Levothyroxine as A Practical Solution to Uncontrolled Hypothyroidism

Introduction

Severe hypothyroidism during pregnancy carries significant maternal and fetal risks. Oral levothyroxine remains the standard therapy, but management can be complicated by impaired absorption or socioeconomic barriers limiting access to care. We describe a case of refractory hypothyroidism in pregnancy successfully managed with sublingual levothyroxine as a practical and cost-effective alternative.

Case Presentation

A 29-year-old gravida 2 para 1 woman at 22 weeks’ gestation presented with vaginal bleeding and was found to have profound hypothyroidism. She had longstanding hypothyroidism diagnosed in childhood with positive thyroid peroxidase antibodies consistent with Hashimoto’s thyroiditis. Due to limited insurance coverage and financial constraints, she had not undergone regular thyroid function monitoring or dose adjustment for several years, including during the current pregnancy.

Initial laboratory evaluation revealed a thyroid-stimulating hormone (TSH) level of 424 µIU/mL (normal 0.4-4.0) and a free thyroxine (T4) level of 0.48 ng/dL (normal 0.8-2.0). She reported taking levothyroxine 175 µg daily on an empty stomach, with occasional missed doses. Physical examination was unremarkable without features of myxedema coma. High-dose oral levothyroxine (300 µg daily) was initiated.

To evaluate for impaired absorption, a levothyroxine absorption test was performed. Two hours after administration of 300 µg oral levothyroxine, free T4 0.53 ng/dL and free T3 0.78 pg/mL (normal 2.3-4.2) remained low, with TSH persistently elevated at 369 µIU/mL, indicating inadequate absorption.

Liquid levothyroxine was considered but was not feasible due to cost. As a pragmatic alternative, sublingual levothyroxine therapy was initiated. By 35 weeks’ gestation, thyroid function testing demonstrated normalization of TSH and free T4 levels. At three months postpartum, the patient remained clinically euthyroid on levothyroxine 200 µg sublingually daily (TSH 0.83 µIU/mL), and her infant was healthy at follow-up.

Discussion

Distinguishing true malabsorption from nonadherence or medication interference is essential in managing refractory hypothyroidism. Gastrointestinal malabsorption affects up to 15% of patients and may limit the efficacy of oral levothyroxine. Although liquid and soft-gel formulations enhance bioavailability, financial barriers frequently restrict their use. This case demonstrates that sublingual levothyroxine can achieve biochemical and clinical euthyroidism during pregnancy and postpartum, indicating adequate bioavailability via this route. This low-cost, accessible alternative may be particularly useful for resource-limited patients and can help reduce disparities in thyroid disease management.

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