Levothyroxine
| Evidence Level: L3 | Predicted Indications: 10 |
Table of Contents
Levothyroxine: From Hypothyroidism to Endemic Goiter
One-Sentence Summary
Levothyroxine is a synthetic thyroid hormone, originally used to treat hypothyroidism and other thyroid-related conditions. The TxGNN model predicts it may be effective for endemic goiter, with no registered clinical trials but 20 publications (mostly 1988-1998 clinical studies and reviews) currently supporting this direction.
Note: among the ten predictions, the best-supported candidate is nodular goiter, which has 2 completed randomized trials. It is discussed in the conclusion.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | Hypothyroidism (the Singapore licence records contain no approved indication text; this is taken from the original indication list of the knowledge graph) |
| Predicted New Indication | Endemic goiter |
| TxGNN Prediction Score | 99.81% |
| Evidence Level | L3 |
| Singapore Market Status | ✓ Marketed |
| Number of Registrations | 15 |
| Recommended Decision | Proceed with Guardrails |
Why is This Prediction Reasonable?
Detailed mechanism of action data is not available. Based on known information, levothyroxine is a synthetic form of thyroxine (T4), the main hormone secreted by the thyroid gland. Its efficacy in hypothyroidism and other thyroid diseases is well established.
Endemic goiter is mainly caused by iodine deficiency. Low iodine leads to higher TSH, and TSH drives thyroid growth. Levothyroxine suppresses TSH and can therefore reduce goiter volume. This is a direct and well-understood mechanism that fits the drug's original thyroid-related indications.
Studies from 1988 to 1998 compared levothyroxine, iodide and the combination, and support efficacy. However, no registered clinical trials are available and the literature is dated. Iodine supplementation remains the preferred prevention and first-line approach. Levothyroxine alone does not correct the intrathyroidal iodine deficiency, and goiter may relapse after it is stopped.
Clinical Trial Evidence
Currently no related clinical trials registered for endemic goiter.
Literature Evidence
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 2515973 | 1989 | Multicentre randomized trial | Eur J Clin Invest | 166 patients randomized to levothyroxine, iodine, or a combination for 12 months |
| 3278876 | 1988 | Multicenter clinical study | Dtsch Med Wochenschr | 74 patients: levothyroxine alone vs levothyroxine plus iodide for 6 months, goiter reduction followed |
| 7900936 | 1993 | Comparative clinical study | Clin Endocrinol | Effect of levothyroxine vs iodine on thyroid size and growth-stimulating immunoglobulins |
| 9011485 | 1996 | Clinical study | Dtsch Med Wochenschr | Iodide (300 µg) vs levothyroxine (1.5 µg/kg) in middle-aged and elderly patients |
| 8676600 | 1996 | Clinical study | Klin Padiatr | 106 adolescents: iodine vs iodine plus levothyroxine, with lipid parameters |
| 11256036 | 2001 | Clinical study | Dtsch Med Wochenschr | Two dosages of levothyroxine-iodide combinations in euthyroid diffuse goiter |
| 1789063 | 1991 | Double-blind clinical study | Acta Endocrinol | Thyroid iodine concentration with iodine alone vs iodine plus levothyroxine |
| 24393641 | 1998 | Supplementation study | Asia Pac J Clin Nutr | Longitudinal study of 100 µg/day levothyroxine in an iodine-deficient Aboriginal community |
| 8147031 | 1993 | Review | Z Gesamte Inn Med | Iodine should be part of therapy; levothyroxine alone leaves intrathyroidal iodine deficiency unchanged |
| 15035314 | 2004 | Review | MMW Fortschr Med | Diagnosis and treatment of benign goiter, favouring combination therapy |
Singapore Market Information
| Authorization Number | Product Name | Dosage Form | Approved Indication |
|---|---|---|---|
| SIN09741P | EUTHYROX TABLET 100 mcg | Tablet | Not recorded |
| SIN13251P | Eltroxin Tablet 100mcg | Tablet | Not recorded |
| SIN16629P | ROVEXINE-25 TABLETS 25MCG | Tablet | Not recorded |
| SIN16695P | THYROCORD 75 TABLET 75 MCG | Tablet | Not recorded |
| SIN09760P | LEVOTHYROXINE SODIUM FOR INJECTION 500 mcg/vial | Powder for solution for injection | Not recorded |
There are 15 valid single-ingredient licences in total, all in oral tablet form except the injectable product.
Safety Considerations
- Contraindications suggested by the knowledge graph (not label text): hypertension, hypopituitarism and other pituitary hormone deficiencies, osteoporosis, diabetes mellitus and diabetic ketoacidosis, coronary artery disease, and myocardial infarction.
- Drug Interactions: 100 interactions were recorded. The ones listed are mostly moderate:
- Antidiabetic drugs (metformin, pioglitazone, acarbose, alogliptin, canagliflozin, dapagliflozin, empagliflozin, dulaglutide, albiglutide, chlorpropamide)
- Acid-suppressing drugs (omeprazole, rabeprazole, dexlansoprazole; cimetidine is minor)
- Calcium and magnesium products (calcium phosphate, calcium acetate, magnesium oxide)
- Sympathomimetics (epinephrine, isometheptene, diethylpropion)
- Monitoring points from the literature: long-term TSH suppression is associated with bone loss and atrial fibrillation, so over-suppression should be avoided.
Please refer to the package insert for full warnings and contraindications.
Conclusion and Next Steps
Decision: Proceed with Guardrails
Rationale: The mechanism for endemic goiter is clear and several multicenter clinical studies support efficacy. However, there are no registered trials, the literature is old, and iodine supplementation is the preferred first-line approach, so evidence is limited to L3.
Other predictions for reference:
- Nodular goiter is the strongest candidate (score 99.64%). It has two completed randomized trials: NCT00277589 (Phase 4, n=1,024, placebo-controlled) and NCT00941551 (n=150, post-lobectomy, phase N/A). Neither is Phase 3, so the L1 grade is tentative and L2 is defensible. Efficacy is modest and inconsistent. Decision: Proceed with Guardrails.
- Nontoxic goiter has one randomized trial against radioiodine (PMID 11238476). Radioiodine and surgery are generally preferred. Decision: Proceed with Guardrails, with L1 tentative.
- Substernal goiter, lingual goiter: only surgical case series, reviews or case reports. Decision: Hold.
- Dyshormonogenic goiter: only a preclinical study. It is a research question, not a repurposing candidate.
- Renal hypodysplasia/aplasia, bilateral renal agenesis, Potter sequence, Carney complex: no mechanistic rationale, trials or literature; likely knowledge-graph artifacts. Decision: Hold.
To proceed, the following is needed:
- Package insert warnings and contraindications from HSA (currently missing, and blocking safety screening)
- Detailed mechanism of action data
- Recent controlled evidence comparing levothyroxine with iodine in endemic goiter
- A monitoring plan for TSH, bone density and cardiac status
- Confirmation of the phase of the randomized trials for nodular and nontoxic goiter
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.