Levothyroxine (Synthroid) PDF

**Prototype: levothyroxine (Synthroid) ** - **Category**: Synthetic Thyroid Hormone Replacement  - **Primary Function**: The primary function of levothyroxine is to provide synthetic thyroxine (T4), which is converted into triiodothyronine (T3), the active form of thyroid hormone, with...

**Prototype: levothyroxine (Synthroid) ** - **Category**: Synthetic Thyroid Hormone Replacement  - **Primary Function**: The primary function of levothyroxine is to provide synthetic thyroxine (T4), which is converted into triiodothyronine (T3), the active form of thyroid hormone, within the body for clients with hypothyroidism.  - **Unique Features**: Levothyroxine has a high protein-binding capacity, resulting in a long half-life, which allows for once-daily dosing. Mechanism of Action - Levothyroxine supplements the deficiency of endogenous thyroid hormone in hypothyroidism by providing synthetic T4, which is subsequently converted into T3, thereby normalizing metabolic processes and energy utilization. When enough endogenous or synthetic thyroid hormone (T4 and subsequently converted T3) is present in the bloodstream, it signals the hypothalamus and pituitary gland to reduce the release of thyroid-releasing hormone (TRH) and thyroid-stimulating hormone (TSH), respectively. This regulatory mechanism uses a negative feedback loop to ensure thyroid hormone production remains within a normal range. By replacing or supplementing the deficient thyroid hormone with levothyroxine, the medication helps to restore this balance, effectively managing the symptoms of hypothyroidism while maintaining homeostasis.  Indications and Therapeutic Uses - **Hypothyroidism**: Levothyroxine is primarily indicated for the treatment of hypothyroidism, regardless of cause (congenital hypothyroidism, myxedema coma, simple goiter, and primary hypothyroidism in children and adults). Hypothyroidism is a condition where the thyroid gland is underactive and cannot produce sufficient amounts of thyroid hormones. - **Thyroid Hormone Regulation**: Levothyroxine can also be used to regulate thyroid hormone levels in clients who have had thyroid surgery, irradiation, or drug treatment for hyperthyroidism.  Side Effects and Adverse Reactions **Side Effect** **Description** --------------------- ------------------------------------------------------------------------------------------------------------------------------------------ Thyrotoxicosis In acute levothyroxine overdose, clients may experience symptoms that include increased heart rate, weight loss, and excessive sweating. Osteoporosis Long-term use at inappropriate doses can lead to accelerated bone turnover and an increased risk of this. Atrial Fibrillation Chronic overdose is associated with this heart rhythm in older adult populations. Precautions and Contraindications **Precautions** - Levothyroxine should be used cautiously in clients with certain cardiovascular disorders due to its potential to increase heart rate and blood pressure.  **Contraindications** - Levothyroxine is contraindicated in individuals with uncorrected adrenal insufficiency, as thyroid hormone replacement can exacerbate this condition.  Drug Interactions - The absorption of levothyroxine is decreased by concurrent intake of food, **\[calcium, magnesium, and iron\]** supplements, and other medications like **\[antacids and proton pump inhibitors\]**. To reduce the possibility of decreased absorption, levothyroxine should be administered on an empty stomach and separate administration of these drugs by 4 hours.  - Levothyroxine can interact with **\[warfarin\]** by increasing the degradation of vitamin K-dependent clotting factors, increasing its anticoagulant effects and bleeding risk.   - Levothyroxine can cause increased dosing requirements for medications like **\[insulin and digoxin\]**.  - Levothyroxine elevates the heart\'s sensitivity to **\[catecholamines\]**, heightening the possibility of arrhythmias.   Dosing, Administration, & Client Teaching **Dosing** - Dosing varies based on the condition, severity, and client response.  - Check drug dosing guidelines for individualized dosing.  - Oral administration with IV administration in acute settings (e.g., myxedema coma).  - Ensure levothyroxine is taken on an empty stomach, ideally 30 to 60 minutes before breakfast, to enhance absorption.  - Space medications that decrease absorption by 4 hours.  - Monitor TSH levels 6 to 8 weeks after starting treatment to determine if euthyroid state has been achieved with medication therapy (TSH should decrease to normal levels).  - Levothyroxine has a narrow therapeutic range, so providers should be cautious switching between different generic and brand name formulations.  **Administration** - Oral administration with IV administration in acute settings (e.g., myxedema coma).  - Oral levothyroxine should be taken on an empty stomach, ideally 30 to 60 minutes before breakfast, to enhance absorption.  **Client Teaching** - Teach the client that levothyroxine should be taken on an empty stomach, ideally 30 to 60 minutes before breakfast, to enhance absorption.  - Advise clients to maintain consistency in the timing of their dose to ensure stable thyroid hormone levels.  - Teach the client to avoid taking supplements that decrease absorption within 4 hours of levothyroxine.  - Advise clients that treatment is lifelong.  Labs to Monitor **Thyroid Function Labs ** - Monitor TSH levels 6 to 8 weeks after starting treatment to determine if euthyroid state has been achieved with medication therapy (TSH should decrease to normal levels with a goal range of 0.5-2 microunits/mL). T4 may also be used to evaluate therapy in clients where TSH remains high with a goal of normal to high T4 levels.