Levothyroxine sodium

ATC code

H03AA01

Therapeutic class

Thyroid hormone preparation · Thyroid hormone

Forms

oral tablet

Brand names

Eutirox (ES) · Levothyrox (FR) · Synthroid (US) · Levoxyl (US)

Overall confidence

medium

Regulatory sources consulted

Approved indications

Replacement therapy for primary, secondary, or tertiary hypothyroidism.
TSH (thyroid-stimulating hormone) suppression as an adjunct in the management of differentiated thyroid carcinoma.
Treatment of benign euthyroid goiter and prophylaxis of recurrence after goiter surgery.

Contraindications

Absolute

Hypersensitivity, untreated adrenal insufficiency, untreated pituitary insufficiency, untreated thyrotoxicosis, acute myocardial infarction, acute myocarditis, and acute pancarditis.

Clinical warnings

Boxed warning · Thyroid hormones, including levothyroxine, should not be used for the treatment of obesity or for weight loss. Large doses can cause serious and potentially life-threatening cardiovascular adverse events, especially when used with sympathomimetic amines. — AEMPS SPC

Drug interactions

ModerateCalcium saltsA12AA
Mechanism: Chelation in the gastrointestinal tract, decreasing levothyroxine absorption.
Recommendation: Administer levothyroxine at least 4 hours before calcium salts.
AEMPS SPC
ModerateProton pump inhibitorsA02BC
Mechanism: Increased gastric pH reduces the dissolution and absorption of levothyroxine.
Recommendation: Monitor thyroid function (TSH) when starting or stopping the PPI. A levothyroxine dose adjustment may be necessary.
AEMPS SPC

Adverse events

Common (≥1%)

palpitations · insomnia · headache · nervousness · tachycardia · diarrhea · weight loss · tremor · heat intolerance

Rare but serious

atrial fibrillation · osteoporosis · myocardial infarction · heart failure · thyroid storm

Pregnancy and lactation

FDA category: A

Maintaining normal thyroid function during pregnancy is essential for maternal and fetal health. The levothyroxine dose often needs to be increased. It is compatible with breastfeeding.

Recent literature (PubMed)

[Bariatric surgery and drugs: Review of the literature and Adverse Drug Reactions analysis in French National Pharmacovigilance Database].
Nicol C, et al. · Therapie · 2024 · Relevance 3/5
Revisión sobre el manejo de fármacos post-cirugía bariátrica. Destaca la falta de guías oficiales y el impacto potencial en la absorción de medicamentos de ventana terapéutica estrecha como la levotiroxina. Un análisis de la base de datos de farmacovigilancia francesa no fue concluyente para establecer una relación causal clara entre la cirugía y los efectos adversos reportados.