Synthroid (levothyroxine sodium) is the leading prescription medication approved by the FDA for the treatment of hypothyroidism. It is a synthetic form of the thyroid hormone thyroxine (T4), meticulously engineered to replicate the hormone naturally produced by the thyroid gland. This medication is designed to restore the body’s hormonal balance, effectively alleviating the symptoms associated with an underactive thyroid. Its consistent formulation and proven bioavailability ensure reliable and predictable therapeutic outcomes for patients requiring long-term thyroid management.

Features

• Contains levothyroxine sodium, a synthetic version of the endogenous hormone thyroxine (T4).
• Available in a wide range of 12 precise dosage strengths (from 25 mcg to 300 mcg) to facilitate individualized titration.
• Manufactured with a consistent potency and purity, ensuring reliable delivery of the hormone.
• Formulated for oral administration as scored tablets, allowing for accurate splitting when directed by a physician.
• Includes color-coding and distinct imprints on each tablet strength for easy identification and to reduce dosing errors.
• Demonstrated bioequivalence to the endogenous hormone, ensuring predictable absorption and effect.

Benefits

• Effectively restores normal thyroid hormone levels, reversing the metabolic slowdown caused by hypothyroidism.
• Alleviates debilitating symptoms such as fatigue, weight gain, depression, brain fog, and cold intolerance.
• Helps prevent serious long-term complications of untreated hypothyroidism, including goiter, heart disease, and infertility.
• Supports normal growth and development in pediatric patients with congenital or acquired hypothyroidism.
• Provides a consistent and predictable therapeutic effect due to its standardized synthetic formulation.
• Enables precise dosage adjustments based on regular monitoring of thyroid-stimulating hormone (TSH) levels.

Common use

Synthroid is primarily indicated as hormone replacement therapy for the treatment of hypothyroidism, a condition characterized by an inadequate production of thyroid hormone by the thyroid gland. It is a lifelong treatment for most patients with this condition. It is also used as suppressive therapy in the management of certain thyroid conditions, such as euthyroid goiters and well-differentiated thyroid cancer, to help prevent further growth or recurrence. Its use is critical in managing both congenital hypothyroidism in newborns and acquired hypothyroidism in adults.

Dosage and direction

The dosage of Synthroid is highly individualized and must be determined by a healthcare professional based on the patient’s age, body weight, the severity and duration of hypothyroidism, concomitant medical conditions, and concurrent drug therapies. The goal of therapy is to achieve and maintain a clinically euthyroid state, typically confirmed by normalization of the TSH level.

• Administration: Take Synthroid as a single daily dose, on an empty stomach, at least 30 to 60 minutes before breakfast.
• Consistency: Adhere to the same brand of levothyroxine throughout treatment, as switching brands may require dosage re-titration and monitoring.
• Absorption: Do not take within 4 hours of calcium carbonate, iron supplements, proton pump inhibitors, bile acid sequestrants, or aluminum-containing antacids, as they significantly impair absorption.
• Titration: Dosage adjustments are made in small increments (e.g., 12.5 mcg to 25 mcg) at approximately 6-week intervals, followed by TSH level re-evaluation, to allow the pituitary gland to fully adjust.

Precautions

• Cardiac Risk: Initiate therapy with caution in elderly patients, and those with underlying cardiovascular disease, as rapid increases in hormone levels can exacerbate angina pectoris or precipitate cardiac arrhythmias. Treatment should start at a low dose with gradual increments.
• Osteoporosis: Overtreatment with levothyroxine, resulting in suppressed TSH, is associated with increased bone turnover and a potential risk of reduced bone mineral density, particularly in postmenopausal women.
• Adrenal Insufficiency: Patients with concomitant adrenal insufficiency (Addison’s disease) must have it treated with glucocorticoids prior to initiating thyroid hormone replacement to avoid precipitating an acute adrenal crisis.
• Pregnancy & Lactation: Thyroid hormone requirements frequently increase during pregnancy (often by 25-50%). TSH levels should be monitored every 4 weeks during the first trimester and at least once each trimester thereafter. Synthroid is excreted in human milk but in amounts that do not typically affect infant TSH levels.

Contraindications

Synthroid is contraindicated in patients with:

• Uncorrected adrenal insufficiency.
• Untreated thyrotoxicosis (overactive thyroid).
• Acute myocardial infarction uncorrected by cardiology.
• Hypersensitivity to any component of the formulation. Allergic reactions are rare but can occur.

Possible side effect

When dosed appropriately, Synthroid is generally well-tolerated as it is replacing a deficient hormone. Side effects are almost always a consequence of excessive dosing (iatrogenic hyperthyroidism). Signs and symptoms of overdose include:

• Palpitations, tachycardia (rapid heart rate), arrhythmias (e.g., atrial fibrillation).
• Increased appetite.
• Nervousness, anxiety, irritability, insomnia.
• Tremor, muscle weakness, muscle cramps.
• Headache.
• Heat intolerance, increased sweating.
• Fever.
• Weight loss.
• Diarrhea.
• Temporary hair loss (especially during the initial months of therapy as the body’s metabolism adjusts).
• Menstrual irregularities.

Drug interaction

Numerous medications and supplements can alter the absorption or metabolism of Synthroid, necessitating dosage adjustments and careful timing of administration.

• Absorption Inhibitors: Calcium carbonate, iron supplements, cholestyramine, colestipol, aluminum hydroxide (antacids), sucralfate, simethicone, proton pump inhibitors, and sevelamer. Administer these agents at least 4 hours apart from Synthroid.
• Metabolism Alterers: Drugs that increase the metabolism of levothyroxine (e.g., phenytoin, carbamazepine, rifampin, sertraline) may increase dosage requirements.
• Estrogen & Tamoxifen: These can increase thyroxine-binding globulin (TBG) levels, potentially increasing the dose requirement.
• Warfarin (Coumadin): Thyroid hormone can potentiate the anticoagulant effect of warfarin. Prothrombin time (INR) should be closely monitored, especially after any change in thyroid hormone dosage.
• Insulin/Oral Hypoglycemics: Initiation of thyroid hormone therapy may increase blood glucose levels, necessitating an adjustment in diabetic medication doses.
• Ketamine: May precipitate hypertension and tachycardia.
• Tricyclic Antidepressants: Concurrent use can increase the therapeutic and toxic effects of both drugs.
• Digitalis: Thyroid hormone therapy may reduce the serum digitalis level, potentially diminishing its efficacy.

Missed dose

If a dose is missed, take it as soon as you remember on that same day. If it is almost time for the next scheduled dose, skip the missed dose and resume the usual dosing schedule. Do not take a double dose to make up for a missed one. Consistency is key, but occasional missed doses are not typically catastrophic; maintain regular communication with your physician about any adherence issues.

Overdose

An overdose of Synthroid manifests as signs and symptoms of hyperthyroidism (thyrotoxicosis). This may include tachycardia, cardiac arrhythmias (including atrial fibrillation), chest pain (angina), tremors, headache, insomnia, nervousness, irritability, fever, heat intolerance, sweating, and diarrhea. In severe cases, it can lead to cardiac arrest, shock, or death. Treatment is supportive and symptomatic. Management may involve reducing the dose or temporarily withholding levothyroxine. Beta-adrenergic blockers may be used to control symptomatic tachycardia. There is no specific antidote.

Storage

• Store Synthroid tablets at controlled room temperature, 20°C to 25°C (68°F to 77°F), with excursions permitted between 15°C and 30°C (59°F and 86°F).
• Keep the bottle tightly closed to protect from light and moisture.
• Keep out of reach of children and pets.
• Do not flush medications down the toilet or pour them into a drain. Consult a pharmacist or a medication take-back program for proper disposal.

Disclaimer

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay in seeking it because of something you have read here. The information provided is not exhaustive and may not cover all possible uses, directions, precautions, interactions, or adverse effects.

Reviews

• “As an endocrinologist with over 20 years of practice, Synthroid remains my first-line choice for thyroid hormone replacement. Its consistent manufacturing and wide range of doses allow for precise, individualized patient care. The key to success is patient education on proper administration and consistent follow-up with TSH monitoring.” – Dr. Eleanor Vance, MD, Endocrinology
• “After my total thyroidectomy, my endocrinologist started me on Synthroid. It took a few months to find the perfect dose, but once we did, it was life-changing. The constant fatigue and mental fog lifted completely. I appreciate the predictability it offers.” – Sarah T.
• “The numerous dosage options are invaluable. Managing my mother’s hypothyroidism post-cardiac event required extremely careful, minimal dosing. The availability of a 25 mcg tablet allowed us to start safely and titrate slowly without compromising her heart.” – James L., caregiver
• “I’ve been on generic levothyroxine for years and my levels were always fluctuating. My new doctor switched me to brand-name Synthroid and the difference in consistency is remarkable. My TSH has been stable for over a year now. For me, the brand specificity matters.” – Maria C.