Drugs for hyperthyroidism
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Drugs for Hyperthyroidism: A Comprehensive Overview
Antithyroid Drugs: Methimazole and Propylthiouracil
Methimazole (MMI) and Propylthiouracil (PTU) Usage
Methimazole (MMI) and Propylthiouracil (PTU) are the primary antithyroid drugs used to manage hyperthyroidism. These drugs inhibit thyroid hormone synthesis and are used as the main treatment or as preparation before radioiodine therapy or thyroidectomy. MMI is preferred due to its longer half-life and fewer severe side effects compared to PTU, which can cause fatal liver damage. PTU is mainly reserved for pregnant women and thyroid crises due to its safety profile in these specific conditions.
Efficacy and Adverse Effects
Studies have shown that the titration regimen (low dose) of antithyroid drugs is effective for 12 to 18 months, with fewer adverse effects compared to the block-replace regimen (high dose) . The block-replace regimen has higher incidences of rashes and withdrawal due to side effects . Continued thyroxine treatment following initial antithyroid therapy does not significantly reduce relapse rates .
Nonthionamide Antithyroid Drugs (NTADs)
Alternative Treatments
For patients who cannot tolerate thionamide drugs due to severe side effects like agranulocytosis and hepatotoxicity, nonthionamide antithyroid drugs (NTADs) are an important alternative. NTADs include iodine-containing compounds, lithium carbonate, perchlorate, glucocorticoids, and cholestyramine. These drugs are particularly useful in situations requiring rapid reduction of thyroid hormone levels, such as thyroid storm or preoperative preparation.
Future Developments
Emerging treatments include rituximab, small-molecule ligands (SMLs), and monoclonal antibodies targeting the thyroid-stimulating hormone receptor (TSHR). These novel therapies are under development and hold promise for more targeted and effective management of hyperthyroidism.
Chinese Herbal Medicines
Combined Therapy Benefits
In some countries, Chinese herbal medicines are used alone or in combination with antithyroid drugs to treat hyperthyroidism. Studies suggest that combining Chinese herbal medicines with antithyroid drugs may lower relapse rates, reduce adverse effects, and improve thyroid function and antibody status. However, due to methodological limitations, strong evidence supporting the clinical use of specific herbal formulations is lacking.
Radioactive Iodine Therapy
High-Dose Protocols
Radioactive iodine (131I) therapy is widely used in the United States for treating Graves' disease. A high-dose protocol designed to deliver 8 mCi to the thyroid gland 24 hours after administration has been effective for most patients. However, younger patients with larger thyroid glands, higher serum T4 concentrations, and those pretreated with antithyroid medication for more than four months are at higher risk for treatment failure and may require higher doses.
Conclusion
The management of hyperthyroidism involves a variety of drug therapies, each with its own benefits and limitations. Methimazole and Propylthiouracil remain the cornerstone treatments, with Methimazole being preferred due to its safety profile. Nonthionamide drugs offer alternatives for patients who cannot tolerate thionamides, and emerging therapies promise future advancements. Chinese herbal medicines may provide additional benefits when combined with conventional treatments, though more robust evidence is needed. Radioactive iodine therapy remains a highly effective option, particularly with high-dose protocols tailored to patient-specific factors.
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