Long term effects of levothyroxine
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Long-Term Effects of Levothyroxine: A Comprehensive Overview
Cardiovascular Effects of Long-Term Levothyroxine Therapy
Cardiovascular Abnormalities in Congenital Hypothyroidism Patients
Long-term levothyroxine therapy in young adults with congenital hypothyroidism (CH) has been associated with several cardiovascular abnormalities. Studies have shown that these patients exhibit left ventricular diastolic dysfunction, impaired exercise capacity, and increased intima-media thickness compared to controls. These cardiovascular issues are influenced by the number of episodes of abnormal TSH levels and mean TSH plasma levels during puberty.
Cardiac Effects in Thyroid Cancer and Goiter Patients
Patients undergoing long-term thyrotropin-suppressive therapy with levothyroxine, particularly those who are athyreotic post-thyroid cancer surgery or have diffuse/nodular goiter, show significant cardiac changes. These include increased heart rate, higher prevalence of atrial premature beats, and increased left ventricular mass index. Enhanced left ventricular systolic function has also been observed, indicating that suppressive doses of levothyroxine markedly affect cardiac function .
Cardiovascular Tolerability in Mood Disorder Patients
In patients with treatment-refractory mood disorders receiving supraphysiologic doses of levothyroxine, long-term cardiovascular assessments have shown no significant changes in heart measures over time. This suggests that high doses of levothyroxine do not increase the risk of cardiovascular disorders in these patients.
Impact on Thyroid Nodules and Goiter
Nodular Goiter Management
Levothyroxine suppressive therapy has been effective in reducing the volume of thyroid nodules and preventing the appearance of new nodules in patients with benign cold thyroid nodules. However, this effect is more pronounced in patients with complete TSH suppression. Despite these benefits, the therapy should be reserved for small nodules in younger patients due to potential side effects.
Effects on Sleep and Hypersomnia
Improvement in Idiopathic Hypersomnia
Levothyroxine has shown promising results in improving prolonged nocturnal sleep time and excessive daytime somnolence (EDS) in patients with idiopathic hypersomnia. After four weeks of treatment, significant reductions in total sleep time and ESS scores were observed, indicating improved sleep quality and reduced daytime sleepiness.
Effects on Serum Thyroid Hormone Concentrations and General Health
Study in Healthy Adult Horses
In a study involving healthy adult horses, long-term oral administration of levothyroxine significantly increased serum thyroxine concentrations without adversely affecting overall health. Some cardiac measurements changed over time, but values remained within normal ranges, suggesting that levothyroxine is well-tolerated in terms of general health and cardiac function.
Risk of Myocardial Infarction and Mortality
Subclinical Hypothyroidism Patients
Levothyroxine treatment in patients with subclinical hypothyroidism does not appear to reduce the risk of myocardial infarction, cardiovascular death, or all-cause mortality. However, a potential benefit was observed in patients under the age of 65, indicating that age may play a role in the effectiveness of levothyroxine therapy in reducing mortality risk.
Conclusion
Long-term levothyroxine therapy has diverse effects depending on the patient population and dosage. While it can lead to cardiovascular abnormalities in congenital hypothyroidism patients and those on suppressive therapy for thyroid cancer or goiter, it does not significantly increase cardiovascular risk in patients with mood disorders. Additionally, it shows benefits in managing thyroid nodules and improving sleep disorders. However, its impact on reducing mortality in subclinical hypothyroidism remains inconclusive, highlighting the need for careful patient selection and monitoring during therapy.
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