Levothyroxine 0.075mg (75mcg) Tabs
WARNING: Do not use this drug for weight loss. Severe and sometimes deadly side effects may happen with this drug if it is taken in large doses or with other drugs for weight loss. If you have questions, talk with the doctor. @ COMMON USES: It is used to add thyroid hormone to the body.It is used to manage thyroid cancer.It may be given to you for other reasons. Talk with the doctor.
Drug Class
Thyroid hormone replacement
Pharmacologic Class
Thyroid hormones
Pregnancy Category
Category A
FDA Approved
Jul 1949
DEA Schedule
Not Controlled
Overview
What is this medicine?
Levothyroxine is a synthetic hormone that replaces the natural thyroid hormone (thyroxine or T4) that your body normally makes. It is used to treat an underactive thyroid gland (hypothyroidism) or to suppress TSH in certain thyroid cancers. It helps regulate your body's metabolism, energy levels, and many other functions.
How to Use This Medicine
Taking Your Medication Correctly
To get the most benefit from your medication, follow your doctor's instructions carefully. Read all the information provided with your prescription and follow the instructions closely.
Take your medication on an empty stomach, at least 30 to 60 minutes before breakfast.
Some brands of this medication may be more likely to cause choking, gagging, or trouble swallowing. If this is the case, you must take it with a full glass of water. Check with your pharmacist to see if this applies to your specific product.
If you need to, you can crush the tablet and mix it with 1 or 2 teaspoons (5 or 10 mL) of water. Take the dose immediately after mixing, and do not store it for future use.
Important Interactions to Consider
Do not take iron products, antacids containing aluminum or magnesium, or calcium carbonate within 4 hours before or 4 hours after taking this medication.
If you take other medications, they may need to be taken at a different time than this medication. Consult with your doctor or pharmacist to determine the best schedule.
Certain foods, such as soybean flour (found in infant formula), may affect how this medication works in your body. Discuss this with your doctor.
If you regularly drink grapefruit juice or eat grapefruit, talk to your doctor about potential interactions.
Using the Correct Form of Your Medication
There are different brands and forms of this medication. Do not switch between them without consulting your doctor.
Continue taking your medication as directed by your doctor or healthcare provider, even if you feel well.
Storing and Disposing of Your Medication
Store your medication at room temperature in a dry place, away from heat and light. Do not store it in a bathroom.
If your medication comes in a blister pack, do not remove it until you are ready to take it. Do not store the removed medication for future use.
What to Do If You Miss a Dose
Take a missed dose as soon as you remember.
If it is close to the time for your next dose, skip the missed dose and return to your regular schedule.
Do not take two doses at the same time or take extra doses.
To get the most benefit from your medication, follow your doctor's instructions carefully. Read all the information provided with your prescription and follow the instructions closely.
Take your medication on an empty stomach, at least 30 to 60 minutes before breakfast.
Some brands of this medication may be more likely to cause choking, gagging, or trouble swallowing. If this is the case, you must take it with a full glass of water. Check with your pharmacist to see if this applies to your specific product.
If you need to, you can crush the tablet and mix it with 1 or 2 teaspoons (5 or 10 mL) of water. Take the dose immediately after mixing, and do not store it for future use.
Important Interactions to Consider
Do not take iron products, antacids containing aluminum or magnesium, or calcium carbonate within 4 hours before or 4 hours after taking this medication.
If you take other medications, they may need to be taken at a different time than this medication. Consult with your doctor or pharmacist to determine the best schedule.
Certain foods, such as soybean flour (found in infant formula), may affect how this medication works in your body. Discuss this with your doctor.
If you regularly drink grapefruit juice or eat grapefruit, talk to your doctor about potential interactions.
Using the Correct Form of Your Medication
There are different brands and forms of this medication. Do not switch between them without consulting your doctor.
Continue taking your medication as directed by your doctor or healthcare provider, even if you feel well.
Storing and Disposing of Your Medication
Store your medication at room temperature in a dry place, away from heat and light. Do not store it in a bathroom.
If your medication comes in a blister pack, do not remove it until you are ready to take it. Do not store the removed medication for future use.
What to Do If You Miss a Dose
Take a missed dose as soon as you remember.
If it is close to the time for your next dose, skip the missed dose and return to your regular schedule.
Do not take two doses at the same time or take extra doses.
Lifestyle & Tips
- Take your medication exactly as prescribed by your doctor, usually once daily on an empty stomach, 30-60 minutes before breakfast, with a full glass of water.
- Avoid taking other medications, vitamins, or supplements (especially iron, calcium, antacids) within 4 hours of taking levothyroxine, as they can interfere with absorption.
- Do not switch between different brands or generic versions of levothyroxine without consulting your doctor, as formulations can vary and affect absorption.
- Inform your doctor about all medications, supplements, and herbal products you are taking, as many can interact with levothyroxine.
- Continue taking levothyroxine even if you feel better; it is usually a lifelong therapy.
- Report any new or worsening symptoms to your doctor.
- Maintain a consistent diet; large changes in dietary fiber or soy intake can affect absorption.
Available Forms & Alternatives
Available Strengths:
- Levothyroxine 0.100mg(100mcg) Tab
- Levothyroxine 0.075mg (75mcg) Tabs
- Levothyroxine 0.125mg (125mcg) Tab
- Levothyroxine 0.05mg (50mcg) Tab
- Levothyroxine 0.025mg (25mcg) Tab
- Levothyroxine 0.112mg (112mcg) Tabs
- Levothyroxine 0.137mg (137mcg) Tab
- Levothyroxine 0.175mg (175mcg) Tabs
- Levothyroxine 500mcg Inj, 1 Vial
- Levothyroxine Sod 100mcg Inj, 1vial
- Levothyroxine 200mcg Inj, 1 Vial
- Levothyroxine 0.088mg (88mcg) Tab
- Levothyroxine 0.100mg (100mcg) Tab
- Levothyroxine 0.150mg (150mcg) Tab
- Levothyroxine 0.2mg (200mcg) Tab
- Levothyroxine 0.3mg (300mcg) Tab
- Levothyroxine 0.013mg (13mcg) Caps
- Levothyroxine 0.025mg (25mcg) Caps
- Levothyroxine 0.05mg (50mcg) Caps
- Levothyroxine 0.075mg (75mcg) Caps
- Levothyroxine 0.088mg (88mcg) Caps
- Levothyroxine 0.100mg (100mcg) Caps
- Levothyroxine 0.112mg (112mcg) Caps
- Levothyroxine 0.125mg (125mcg) Caps
- Levothyroxine 0.137mg (137mcg) Caps
- Levothyroxine 0.150mg (150mcg) Caps
- Levothyroxine 0.175mg (175mcg) Caps
- Levothyroxine 0.2mg (200mcg) Caps
- Levothyroxine 0.125mg (125mcg) Tabs
- Levothyroxine 100mcg/5ml Inj, 5ml
- Levothyroxine 100mcg/ml Inj, 1ml
- Levothyroxine 500mg/5ml Inj, 5ml
- Levothyroxine 200mcg/5ml Inj, 5ml
Dosing & Administration
Adult Dosing
Standard Dose:
Initial dose typically 1.6 mcg/kg/day orally once daily for primary hypothyroidism. 0.075mg (75mcg) is a common maintenance dose.
Dose Range:
25 - 300 mg
Condition-Specific Dosing:
primaryHypothyroidism:
Initial: 1.6 mcg/kg/day orally once daily. Adjust by 12.5-25 mcg increments every 4-6 weeks based on TSH. Maintenance: 100-125 mcg/day (average).
subclinicalHypothyroidism:
Initial: 12.5-25 mcg/day orally once daily. Adjust based on TSH.
thyroidStimulatingHormoneSuppression:
Higher doses (e.g., 2 mcg/kg/day or more) to achieve TSH suppression, typically <0.1 mIU/L for high-risk thyroid cancer.
myxedemaComa:
IV administration, typically 200-500 mcg loading dose, followed by daily maintenance.
Pediatric Dosing
Neonatal:
Initial: 10-15 mcg/kg/day orally once daily (for congenital hypothyroidism). Adjust based on TSH and T4.
Infant:
Initial: 5-6 mcg/kg/day orally once daily (for acquired hypothyroidism). Adjust based on TSH and T4.
Child:
Initial: 4-5 mcg/kg/day orally once daily (for acquired hypothyroidism). Adjust based on TSH and T4.
Adolescent:
Initial: 2-3 mcg/kg/day orally once daily (for acquired hypothyroidism). Adjust based on TSH and T4. May transition to adult dosing (1.6 mcg/kg/day) as growth slows.
Dose Adjustments
Renal Impairment:
Mild:
No specific dose adjustment required.
Moderate:
No specific dose adjustment required.
Severe:
No specific dose adjustment required.
Dialysis:
No specific dose adjustment required. Levothyroxine is highly protein-bound and not significantly removed by dialysis.
Hepatic Impairment:
Mild:
No specific dose adjustment required.
Moderate:
No specific dose adjustment required.
Severe:
No specific dose adjustment required. Metabolism may be slightly altered, but clinical significance is usually minimal; monitor TSH and adjust as needed.
Pharmacology
Mechanism of Action
Levothyroxine sodium is a synthetic L-isomer of thyroxine (T4), a naturally occurring thyroid hormone. T4 is converted to its active metabolite, L-triiodothyronine (T3), in peripheral tissues. T3 and T4 then bind to thyroid hormone receptors in the cell nucleus, regulating gene expression and controlling numerous metabolic processes, including protein, carbohydrate, and lipid metabolism, and influencing growth and development.
Pharmacokinetics
Absorption:
Bioavailability:
48-80% (highly variable, influenced by food, other medications, and gastrointestinal conditions)
Tmax:
2-4 hours
FoodEffect:
Decreased absorption when taken with food, especially fiber, calcium, iron, and certain foods (e.g., soybean flour, cottonseed meal, walnuts). Should be taken on an empty stomach, preferably 30-60 minutes before breakfast.
Distribution:
Vd:
0.11-0.13 L/kg
ProteinBinding:
>99% (primarily to thyroxine-binding globulin (TBG), transthyretin (TTR), and albumin)
CnssPenetration:
Limited (T4 crosses BBB, but T3 is more active in CNS)
Elimination:
HalfLife:
6-7 days (euthyroid), 9-10 days (hypothyroid), 3-4 days (hyperthyroid)
Clearance:
Approximately 0.05 L/hr (euthyroid)
ExcretionRoute:
Primarily renal (conjugated metabolites), small amount in feces (unabsorbed drug and biliary excretion)
Unchanged:
<1% (renal excretion of unchanged drug)
Pharmacodynamics
OnsetOfAction:
Gradual, clinical effects may take several days to weeks
PeakEffect:
Peak therapeutic effect typically seen after 4-6 weeks of consistent dosing, once steady-state TSH levels are achieved.
DurationOfAction:
Long (due to long half-life), effects persist for several days after discontinuation.
Safety & Warnings
Side Effects
Serious Side Effects: Seek Medical Help Right Away
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor immediately or seek medical attention:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Signs of high blood pressure, including:
+ Severe headache or dizziness
+ Passing out
+ Changes in eyesight
Chest pain or pressure
Fast or abnormal heartbeat
Shortness of breath
Sudden weight gain or swelling in the arms or legs
Headache
Feeling tired or weak
Changes in appetite
Unintentional weight changes
Diarrhea, stomach cramps, or vomiting
Mood changes, such as feeling irritable, nervous, excitable, or anxious
Shakiness
Trouble sleeping
Sensitivity to heat
Excessive sweating
Fever
Muscle cramps
Muscle weakness
Flushing
Bone pain
Changes in menstrual periods
In children: hip or knee pain, or a limp
In infants: changes in the shape of the head and face
Other Possible Side Effects
Like all medications, this drug can cause side effects. While many people may not experience any side effects or only minor ones, it's essential to discuss any concerns with your doctor. If you experience any of the following side effects or any other unusual symptoms, contact your doctor for advice:
* Hair loss (usually temporary and resolves on its own within the first few months of treatment)
Reporting Side Effects
This list is not exhaustive, and you may experience other side effects not mentioned here. If you have questions or concerns about side effects, contact your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor immediately or seek medical attention:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Signs of high blood pressure, including:
+ Severe headache or dizziness
+ Passing out
+ Changes in eyesight
Chest pain or pressure
Fast or abnormal heartbeat
Shortness of breath
Sudden weight gain or swelling in the arms or legs
Headache
Feeling tired or weak
Changes in appetite
Unintentional weight changes
Diarrhea, stomach cramps, or vomiting
Mood changes, such as feeling irritable, nervous, excitable, or anxious
Shakiness
Trouble sleeping
Sensitivity to heat
Excessive sweating
Fever
Muscle cramps
Muscle weakness
Flushing
Bone pain
Changes in menstrual periods
In children: hip or knee pain, or a limp
In infants: changes in the shape of the head and face
Other Possible Side Effects
Like all medications, this drug can cause side effects. While many people may not experience any side effects or only minor ones, it's essential to discuss any concerns with your doctor. If you experience any of the following side effects or any other unusual symptoms, contact your doctor for advice:
* Hair loss (usually temporary and resolves on its own within the first few months of treatment)
Reporting Side Effects
This list is not exhaustive, and you may experience other side effects not mentioned here. If you have questions or concerns about side effects, contact your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Seek Immediate Medical Attention If You Experience:
- Symptoms of over-replacement (hyperthyroidism): Chest pain, rapid or irregular heartbeat (palpitations), excessive sweating, heat intolerance, nervousness, tremor, insomnia, unexplained weight loss, diarrhea.
- Symptoms of under-replacement (hypothyroidism): Persistent fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, depression, slow heart rate.
- Allergic reaction: Rash, itching/swelling (especially of face/tongue/throat), severe dizziness, trouble breathing.
Before Using This Medicine
Before Taking This Medication: Important Information to Share with Your Doctor
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the allergic reaction you experienced, including any symptoms that occurred.
Certain health conditions, including:
+ An overactive thyroid gland
+ A weak adrenal gland
+ Difficulty swallowing
This list is not exhaustive, and it is crucial to discuss all your health problems with your doctor.
Additionally, provide your doctor and pharmacist with a comprehensive list of:
All prescription and over-the-counter medications you are taking
Any natural products or vitamins you are using
Your overall health status
This information will help your doctor determine whether it is safe for you to take this medication, considering your unique health profile and other medications you are using. Never start, stop, or adjust the dose of any medication without first consulting your doctor to ensure your safety.
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the allergic reaction you experienced, including any symptoms that occurred.
Certain health conditions, including:
+ An overactive thyroid gland
+ A weak adrenal gland
+ Difficulty swallowing
This list is not exhaustive, and it is crucial to discuss all your health problems with your doctor.
Additionally, provide your doctor and pharmacist with a comprehensive list of:
All prescription and over-the-counter medications you are taking
Any natural products or vitamins you are using
Your overall health status
This information will help your doctor determine whether it is safe for you to take this medication, considering your unique health profile and other medications you are using. Never start, stop, or adjust the dose of any medication without first consulting your doctor to ensure your safety.
Precautions & Cautions
Important Information for All Patients Taking This Medication
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication. To ensure continuous treatment, do not allow your supply of this medication to run out. You may not experience the full effects of this medication for several weeks.
Special Considerations
If you have diabetes (high blood sugar), consult your doctor, as this medication may affect your blood sugar control. Your doctor may need to adjust your diabetes medications. Monitor your blood sugar levels as directed by your doctor and undergo regular blood tests as recommended.
If you take biotin or any products containing biotin, stop taking it at least 2 days before having your thyroid levels checked to ensure accurate test results.
Potential Risks and Side Effects
High doses of this medication may increase the risk of developing weak bones (osteoporosis), particularly after menopause. Discuss your risk factors with your doctor, who can help determine if you are at higher risk.
This medication may also affect fertility, potentially leading to difficulty getting pregnant or fathering a child. If you plan to conceive, consult your doctor before starting treatment.
If you are 65 or older, use this medication with caution, as you may be more susceptible to side effects.
Pregnancy and Breastfeeding
If you are pregnant, plan to become pregnant, or are breastfeeding, inform your doctor to discuss the benefits and risks of this medication to you and your baby.
Pediatric Patients
If you are giving this medication to a child and their weight changes, consult your doctor, as the dosage may need to be adjusted. Never give your child more of this medication than prescribed, as this can increase the risk of severe side effects.
In some cases, this medication may affect growth in children and teenagers. Regular growth checks may be necessary. Consult your doctor to discuss any concerns.
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication. To ensure continuous treatment, do not allow your supply of this medication to run out. You may not experience the full effects of this medication for several weeks.
Special Considerations
If you have diabetes (high blood sugar), consult your doctor, as this medication may affect your blood sugar control. Your doctor may need to adjust your diabetes medications. Monitor your blood sugar levels as directed by your doctor and undergo regular blood tests as recommended.
If you take biotin or any products containing biotin, stop taking it at least 2 days before having your thyroid levels checked to ensure accurate test results.
Potential Risks and Side Effects
High doses of this medication may increase the risk of developing weak bones (osteoporosis), particularly after menopause. Discuss your risk factors with your doctor, who can help determine if you are at higher risk.
This medication may also affect fertility, potentially leading to difficulty getting pregnant or fathering a child. If you plan to conceive, consult your doctor before starting treatment.
If you are 65 or older, use this medication with caution, as you may be more susceptible to side effects.
Pregnancy and Breastfeeding
If you are pregnant, plan to become pregnant, or are breastfeeding, inform your doctor to discuss the benefits and risks of this medication to you and your baby.
Pediatric Patients
If you are giving this medication to a child and their weight changes, consult your doctor, as the dosage may need to be adjusted. Never give your child more of this medication than prescribed, as this can increase the risk of severe side effects.
In some cases, this medication may affect growth in children and teenagers. Regular growth checks may be necessary. Consult your doctor to discuss any concerns.
Overdose Information
Overdose Symptoms:
- Signs and symptoms of hyperthyroidism: Palpitations, tachycardia, arrhythmias, chest pain, angina, tremor, nervousness, insomnia, irritability, hyperkinesia, diaphoresis, flushing, fever, headache, diarrhea, vomiting, weight loss, menstrual irregularities, heat intolerance.
What to Do:
Seek immediate medical attention. Call 911 or Poison Control (1-800-222-1222). Treatment is symptomatic and supportive, including beta-blockers for cardiovascular effects, and measures to reduce absorption if recent ingestion.
Drug Interactions
Major Interactions
- Amiodarone (can cause hypo- or hyperthyroidism, requires close monitoring)
- Certain antacids (aluminum hydroxide, calcium carbonate, sucralfate - significantly decrease absorption)
- Iron supplements (ferrous sulfate - significantly decrease absorption)
- Calcium supplements (calcium carbonate, calcium citrate - significantly decrease absorption)
- Bile acid sequestrants (cholestyramine, colestipol, colesevelam - decrease absorption)
- Proton pump inhibitors (PPIs) and H2 blockers (may increase gastric pH, reducing absorption)
- Orlistat (may decrease absorption)
- Sodium polystyrene sulfonate (Kayexalate - decreases absorption)
- Tyrosine kinase inhibitors (e.g., imatinib, sunitinib, sorafenib - can alter thyroid function, requiring dose adjustment)
- Estrogens (oral - increase TBG, requiring higher levothyroxine dose)
- Androgens/Anabolic steroids (decrease TBG, potentially requiring lower levothyroxine dose)
- Warfarin (levothyroxine may enhance anticoagulant effect, increasing bleeding risk)
- Antidiabetic agents (levothyroxine may increase blood glucose, requiring adjustment of antidiabetic dose)
- Digoxin (levothyroxine may decrease digoxin levels, requiring dose adjustment)
Moderate Interactions
- Soy products (can decrease absorption)
- Dietary fiber (can decrease absorption)
- Grapefruit juice (inconsistent evidence, but some studies suggest reduced absorption)
- Rifampin (induces hepatic metabolism, may require higher levothyroxine dose)
- Phenytoin (induces hepatic metabolism, displaces from protein binding, may require higher levothyroxine dose)
- Carbamazepine (induces hepatic metabolism, may require higher levothyroxine dose)
- Sertraline (may increase levothyroxine requirements)
- Beta-blockers (may reduce conversion of T4 to T3)
- Corticosteroids (may inhibit T4 to T3 conversion)
- Salicylates (high doses can displace thyroid hormones from protein binding)
Minor Interactions
- Coffee (may slightly reduce absorption if taken concurrently)
Monitoring
Baseline Monitoring
Thyroid Stimulating Hormone (TSH)
Rationale: Primary diagnostic and monitoring tool for thyroid function. Elevated in primary hypothyroidism.
Timing: Before initiating therapy.
Free Thyroxine (Free T4)
Rationale: Measures unbound, active T4. Useful in conjunction with TSH, especially in central hypothyroidism or when TSH is unreliable.
Timing: Before initiating therapy.
Clinical Symptoms of Hypothyroidism
Rationale: Assess baseline symptoms (fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, bradycardia) to track improvement.
Timing: Before initiating therapy and periodically.
Cardiac Status (ECG, history of cardiovascular disease)
Rationale: Thyroid hormones affect cardiac function; caution needed in patients with pre-existing heart conditions, especially elderly.
Timing: Before initiating therapy, especially in elderly or those with cardiac risk factors.
Routine Monitoring
Thyroid Stimulating Hormone (TSH)
Frequency: Every 4-6 weeks after initiation or dose change, then every 6-12 months once stable.
Target: 0.4-4.0 mIU/L (for primary hypothyroidism, individualized for TSH suppression in cancer).
Action Threshold: Adjust dose if TSH is outside target range; higher TSH indicates under-replacement, lower TSH indicates over-replacement.
Free Thyroxine (Free T4)
Frequency: May be checked with TSH, especially if TSH is suppressed or in central hypothyroidism.
Target: 0.8-1.8 ng/dL (or laboratory-specific reference range).
Action Threshold: Adjust dose if Free T4 is consistently outside target range, particularly if TSH is also abnormal.
Clinical Symptoms
Frequency: At each follow-up visit.
Target: Resolution or significant improvement of hypothyroid symptoms.
Action Threshold: Persistent or worsening symptoms despite normal TSH may indicate need for further investigation or dose adjustment.
Bone Mineral Density (BMD)
Frequency: Periodically, especially in postmenopausal women or elderly patients on long-term suppressive therapy.
Target: Maintain normal BMD.
Action Threshold: Consider dose reduction if TSH is consistently suppressed below target in patients without thyroid cancer, to minimize risk of osteoporosis.
Symptom Monitoring
- Fatigue
- Weight changes (gain or loss)
- Cold intolerance
- Constipation
- Dry skin
- Hair loss
- Bradycardia or tachycardia
- Palpitations
- Nervousness or anxiety
- Tremor
- Insomnia
- Chest pain or angina (especially in patients with underlying cardiac disease)
- Muscle weakness or cramps
- Changes in menstrual cycle
Special Patient Groups
Pregnancy
Levothyroxine is Category A and is essential for pregnant women with hypothyroidism. Thyroid hormone requirements often increase during pregnancy (by 25-50% or more) due to increased TBG and placental deiodinase activity. Close monitoring of TSH (every 4-6 weeks) and dose adjustment are crucial to ensure adequate fetal thyroid hormone supply, which is vital for neurological development.
Trimester-Specific Risks:
First Trimester:
Crucial for fetal brain development. Inadequate maternal thyroid hormone can lead to impaired neurocognitive development in the child.
Second Trimester:
Continued need for adequate maternal thyroid hormone. Fetal thyroid gland begins to function, but still relies on maternal supply.
Third Trimester:
Continued need for adequate maternal thyroid hormone. Dose adjustments may still be necessary.
Lactation
Levothyroxine is considered safe during breastfeeding (L1). Minimal amounts are excreted into breast milk, and it does not adversely affect the nursing infant. It is essential for the mother's health and does not require discontinuation.
Infant Risk:
Very low risk. No adverse effects reported in breastfed infants.
Pediatric Use
Dosing is weight-based and higher per kg than in adults, especially in neonates and infants, due to rapid growth and development. Close monitoring of TSH and Free T4 is essential to ensure proper growth and neurocognitive development. Tablets can be crushed and suspended in a small amount of water or breast milk/formula and administered by spoon or dropper; do not mix with soy formula or iron-fortified formula as it can impair absorption.
Geriatric Use
Lower initial doses (e.g., 12.5-25 mcg/day) are often recommended, especially in patients with underlying cardiovascular disease, due to increased sensitivity to thyroid hormones and potential for cardiac adverse effects. Dose adjustments should be made in smaller increments and at longer intervals. Close monitoring for cardiac symptoms is important.
Clinical Information
Clinical Pearls
- Always take levothyroxine on an empty stomach, 30-60 minutes before breakfast, with water, and at least 4 hours apart from calcium, iron, antacids, and other interacting medications.
- Consistency is key: take it at the same time each day.
- Do not switch between different brands or generic manufacturers without consulting your physician, as bioequivalence can vary and may require re-monitoring of TSH.
- TSH is the primary lab test for monitoring, but Free T4 may be useful in specific situations (e.g., central hypothyroidism, TSH suppression therapy).
- Full therapeutic effect and TSH stabilization may take 4-6 weeks after a dose change.
- Patients with pre-existing cardiac disease should start with lower doses and titrate slowly to avoid exacerbating cardiac symptoms.
- Educate patients on symptoms of both under- and over-replacement.
- Levothyroxine is not for weight loss in euthyroid individuals and can cause serious adverse effects if misused for this purpose.
Alternative Therapies
- Liothyronine (synthetic T3) - used in specific cases, such as myxedema coma (IV) or for short-term TSH suppression before radioactive iodine therapy, but generally not for long-term monotherapy due to shorter half-life and fluctuating levels.
Cost & Coverage
Average Cost:
$10 - $50 per 30 tablets
Generic Available:
Yes
Insurance Coverage:
Tier 1 (Generic) or Tier 2/3 (Brand)
General Drug Facts
If your symptoms or health issues persist or worsen, it is essential to contact your doctor for further guidance. To ensure your safety, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so it's a good idea to check with your pharmacist. If you have any questions or concerns about this medication, don't hesitate to discuss them with your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately call your local poison control center or seek emergency medical attention. When seeking help, be prepared to provide information about the medication taken, the amount, and the time it happened.