Euthyrox 0.100mg (100mcg) Tablets
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 medicine that replaces a hormone your body normally makes, called thyroid hormone. This hormone is essential for your body's energy, growth, and metabolism. People take it when their thyroid gland doesn't make enough of its own hormone (a condition called hypothyroidism).
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 the bathroom.
Protect it from heat and light.
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 the bathroom.
Protect it from heat and light.
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 on an empty stomach, typically 30-60 minutes before breakfast, with a full glass of water.
- Avoid taking with food, calcium, iron, antacids, or other medications within 4 hours (some sources recommend 1 hour, others 4 hours, or even 12 hours for specific drugs like bile acid sequestrants).
- Take at the same time each day for consistent absorption.
- Do not switch between different brands or generic formulations without consulting your doctor, as small differences in potency can affect TSH levels.
- Inform your doctor about all other medications, supplements, and dietary changes.
Available Forms & Alternatives
Available Strengths:
- Euthyrox 100mcg Tablets
- Euthyrox 0.125mg (125mcg) Tablets
- Euthyrox 88mcg Tablets
- Euthyrox 0.05mg (50mcg) Tablets
- Euthyrox 0.075mg (75mcg) Tablets
- Euthyrox 0.137mg (137mcg) Tab
- Euthyrox 0.175mg (175mcg) Tabs
- Euthyrox 0.150mg (150mcg) Tab
- Euthyrox 0.025mg (25mcg) Tab
- Euthyrox 0.112mg (112mcg) Tablets
- Euthyrox 0.2mg (200mcg) Tab
- Euthyrox 0.075mg (75mcg) Tablets
- Euthyrox 0.088mg (88mcg) Tablets
- Euthyrox 0.100mg (100mcg) Tablets
Dosing & Administration
Adult Dosing
Standard Dose:
Initial dose typically 1.6 mcg/kg/day (e.g., 100-125 mcg/day for a 70 kg adult) for primary hypothyroidism. Adjust dose by 12.5-25 mcg increments every 4-6 weeks until TSH is normalized.
Dose Range:
25 - 300 mg
Condition-Specific Dosing:
hypothyroidism_initial:
1.6 mcg/kg/day
hypothyroidism_elderly_cardiac:
Initial 12.5-25 mcg/day, titrate slowly
myxedema_coma:
300-500 mcg IV loading dose, then 50-100 mcg IV daily
Pediatric Dosing
Neonatal:
10-15 mcg/kg/day (0-3 months)
Infant:
6-8 mcg/kg/day (3-6 months); 5-6 mcg/kg/day (6-12 months)
Child:
4-5 mcg/kg/day (1-5 years); 3-4 mcg/kg/day (6-12 years)
Adolescent:
2-3 mcg/kg/day (12-17 years, during growth spurt); 1.6 mcg/kg/day (after growth spurt, adult dose)
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, but monitor TSH and clinical response.
Moderate:
No specific dose adjustment required, but monitor TSH and clinical response.
Severe:
No specific dose adjustment required, but monitor TSH and clinical response. May require lower doses due to decreased T4 to T3 conversion.
Pharmacology
Mechanism of Action
Levothyroxine (T4) is a synthetic form of the natural thyroid hormone, thyroxine. It is converted to its active metabolite, liothyronine (T3), in peripheral tissues. T3 then enters the cell nucleus and binds to thyroid hormone receptors, regulating gene expression and controlling numerous metabolic processes, including protein, carbohydrate, and lipid metabolism, and influencing growth and development.
Pharmacokinetics
Absorption:
Bioavailability:
48-80% (variable, depends on formulation and presence of food/other medications)
Tmax:
2-4 hours
FoodEffect:
Decreased and delayed absorption when taken with food, especially fiber, soy, and calcium/iron supplements. Should be taken on an empty stomach.
Distribution:
Vd:
0.11-0.13 L/kg
ProteinBinding:
>99% (primarily to thyroxine-binding globulin (TBG), transthyretin, and albumin)
CnssPenetration:
Limited
Elimination:
HalfLife:
6-7 days (euthyroid); 9-10 days (hypothyroid); 3-4 days (hyperthyroid)
Clearance:
Approximately 0.05 L/hr
ExcretionRoute:
Renal (approximately 80% as metabolites), Fecal (approximately 20% as unchanged drug and metabolites)
Unchanged:
<1% (primarily excreted as metabolites)
Pharmacodynamics
OnsetOfAction:
Gradual, clinical effects typically seen within 3-5 days, but full therapeutic effect may take 4-6 weeks.
PeakEffect:
4-6 weeks (time to achieve steady-state TSH levels)
DurationOfAction:
Long, due to long half-life.
Safety & Warnings
Side Effects
Urgent Side Effects: Seek Medical Help Right Away
While rare, some people may experience severe and potentially life-threatening side effects when taking this medication. If you notice any of the following symptoms, contact your doctor or seek medical attention immediately:
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 irritability, nervousness, excitement, anxiety, or other emotional shifts
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. Many people experience no side effects or only mild ones. If you notice 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 is not an exhaustive list of possible side effects. If you have questions or concerns about side effects, consult your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
While rare, some people may experience severe and potentially life-threatening side effects when taking this medication. If you notice any of the following symptoms, contact your doctor or seek medical attention immediately:
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 irritability, nervousness, excitement, anxiety, or other emotional shifts
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. Many people experience no side effects or only mild ones. If you notice 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 is not an exhaustive list of possible side effects. If you have questions or concerns about side effects, consult 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 too much thyroid hormone (hyperthyroidism): rapid heart rate, palpitations, nervousness, tremor, excessive sweating, heat intolerance, weight loss, diarrhea, insomnia.
- Symptoms of too little thyroid hormone (hypothyroidism) despite medication: persistent fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, depression.
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, to ensure safe treatment, tell your doctor and pharmacist about:
All prescription and over-the-counter (OTC) medications you are taking
Any natural products or vitamins you are using
All your health problems
It is vital to verify that it is safe to take this medication with all your other medications and health conditions. Never start, stop, or change the dose of any medication without first consulting 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, to ensure safe treatment, tell your doctor and pharmacist about:
All prescription and over-the-counter (OTC) medications you are taking
Any natural products or vitamins you are using
All your health problems
It is vital to verify that it is safe to take this medication with all your other medications and health conditions. Never start, stop, or change the dose of any medication without first consulting your doctor.
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 uninterrupted 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 with your doctor, as this medication may affect your blood sugar control. Your doctor may need to adjust your diabetes medications. Be sure to monitor your blood sugar levels as directed by your doctor and undergo regular blood tests as recommended.
If you are taking biotin or a product 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 osteoporosis (weak bones), particularly after menopause. Discuss your individual risk factors with your doctor. Additionally, this medication may affect fertility, making it more difficult to become pregnant or father a child. If you plan to conceive, consult with your doctor before starting this medication.
If you are 65 years 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 potential benefits and risks to you and your baby.
Pediatric Patients
If you are giving this medication to a child, monitor their weight changes and consult with your doctor, as the dosage may need to be adjusted. Never give your child more of this medication than prescribed, as this may increase the risk of severe side effects. In some cases, this medication may affect growth in children and teenagers, so regular growth checks may be necessary. Consult with 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 uninterrupted 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 with your doctor, as this medication may affect your blood sugar control. Your doctor may need to adjust your diabetes medications. Be sure to monitor your blood sugar levels as directed by your doctor and undergo regular blood tests as recommended.
If you are taking biotin or a product 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 osteoporosis (weak bones), particularly after menopause. Discuss your individual risk factors with your doctor. Additionally, this medication may affect fertility, making it more difficult to become pregnant or father a child. If you plan to conceive, consult with your doctor before starting this medication.
If you are 65 years 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 potential benefits and risks to you and your baby.
Pediatric Patients
If you are giving this medication to a child, monitor their weight changes and consult with your doctor, as the dosage may need to be adjusted. Never give your child more of this medication than prescribed, as this may increase the risk of severe side effects. In some cases, this medication may affect growth in children and teenagers, so regular growth checks may be necessary. Consult with your doctor to discuss any concerns.
Overdose Information
Overdose Symptoms:
- Palpitations
- Tachycardia (rapid heart rate)
- Arrhythmias (irregular heartbeats)
- Chest pain (angina)
- Tremor
- Nervousness
- Irritability
- Insomnia
- Excessive sweating
- Heat intolerance
- Weight loss
- Diarrhea
- Vomiting
- Fever
- Seizures (rare)
- Coma (rare)
What to Do:
Seek immediate medical attention. Call 911 or your local emergency number. For poison control, call 1-800-222-1222. Management is supportive and symptomatic, often involving beta-blockers for cardiac symptoms.
Drug Interactions
Major Interactions
- Amiodarone (alters thyroid hormone metabolism)
- Oral anticoagulants (e.g., Warfarin - increased anticoagulant effect)
- Sympathomimetics (e.g., decongestants - increased risk of cardiac effects)
- Tyrosine kinase inhibitors (e.g., Sunitinib, Imatinib - may increase levothyroxine requirements)
Moderate Interactions
- Calcium carbonate/supplements (decreased levothyroxine absorption)
- Iron supplements (decreased levothyroxine absorption)
- Antacids (aluminum, magnesium hydroxide - decreased levothyroxine absorption)
- Proton pump inhibitors (e.g., Omeprazole - decreased levothyroxine absorption due to altered gastric pH)
- Sucralfate (decreased levothyroxine absorption)
- Cholestyramine, Colestipol (decreased levothyroxine absorption)
- Soy products/formula (decreased levothyroxine absorption)
- Fiber supplements (decreased levothyroxine absorption)
- Sertraline (may increase levothyroxine requirements)
- Rifampin, Carbamazepine, Phenytoin, Phenobarbital (CYP inducers, may increase levothyroxine metabolism)
- Estrogens (oral contraceptives, HRT - increase TBG, may increase levothyroxine requirements)
- Androgens (decrease TBG, may decrease levothyroxine requirements)
- Beta-blockers (may decrease T4 to T3 conversion)
- Corticosteroids (may decrease T4 to T3 conversion and TBG)
Minor Interactions
- Grapefruit juice (minor effect on absorption)
Monitoring
Baseline Monitoring
Thyroid Stimulating Hormone (TSH)
Rationale: Primary indicator of thyroid function and adequacy of thyroid hormone replacement.
Timing: Before initiating therapy.
Free Thyroxine (FT4)
Rationale: Assesses circulating unbound T4 levels.
Timing: Before initiating therapy.
Clinical symptoms of hypothyroidism
Rationale: To establish baseline and track improvement.
Timing: Before initiating therapy.
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 (individualized based on patient age, comorbidities, and specific condition, e.g., post-thyroidectomy for cancer may target lower TSH).
Action Threshold: TSH outside target range indicates need for dose adjustment.
Free Thyroxine (FT4)
Frequency: May be monitored with TSH, especially if TSH is suppressed or in central hypothyroidism.
Target: 0.8-1.8 ng/dL (or laboratory specific range).
Action Threshold: FT4 outside target range, especially if TSH is also abnormal.
Clinical symptoms (e.g., fatigue, weight changes, cold intolerance, heart rate)
Frequency: At each visit.
Target: Resolution or improvement of hypothyroid symptoms, absence of hyperthyroid symptoms.
Action Threshold: Persistence of hypothyroid symptoms or emergence of hyperthyroid symptoms.
Symptom Monitoring
- Fatigue
- Weight gain or loss
- Cold or heat intolerance
- Constipation or diarrhea
- Dry skin or hair loss
- Bradycardia or tachycardia
- Muscle aches or weakness
- Depression or anxiety
- Irritability
- Nervousness
- Tremor
- Palpitations
- Insomnia
Special Patient Groups
Pregnancy
Thyroid hormone requirements often increase during pregnancy. It is crucial to continue levothyroxine therapy and monitor TSH levels frequently (e.g., every 4-6 weeks) to ensure adequate dosing. Untreated maternal hypothyroidism can lead to adverse fetal outcomes.
Trimester-Specific Risks:
First Trimester:
Increased levothyroxine dose may be needed early in pregnancy. Untreated hypothyroidism in the first trimester is associated with increased risk of miscarriage, preterm birth, and impaired neurocognitive development in the offspring.
Second Trimester:
Continued monitoring and dose adjustment as needed.
Third Trimester:
Continued monitoring and dose adjustment as needed. Dose typically peaks in the third trimester.
Lactation
Levothyroxine is compatible with breastfeeding. Only small amounts are excreted into breast milk, and it is not expected to cause adverse effects in breastfed infants. Maternal thyroid hormone requirements typically return to pre-pregnancy levels postpartum.
Infant Risk:
L1 (Safest)
Pediatric Use
Essential for normal growth and development. Dosing is weight-based and higher per kg than in adults, especially in infants. Close monitoring of TSH and FT4 is critical to prevent developmental delays (e.g., cretinism) due to undertreatment or adverse effects from overtreatment.
Geriatric Use
Older adults, especially those with underlying cardiovascular disease, should be started on lower initial doses (e.g., 12.5-25 mcg/day) and titrated slowly to avoid precipitating cardiac events. Monitor for signs of hyperthyroidism.
Clinical Information
Clinical Pearls
- Always take levothyroxine on an empty stomach, preferably 30-60 minutes before breakfast, to maximize absorption.
- Consistency is key: take it at the same time every day.
- Avoid taking levothyroxine with calcium, iron, antacids, or other interacting medications within 4 hours (or as advised by your pharmacist/doctor).
- TSH is the primary lab test for monitoring, but clinical symptoms are also important.
- Dose adjustments are typically made in 12.5-25 mcg increments every 4-6 weeks until TSH is stable.
- Patients with cardiac disease or elderly patients should start on lower doses and be titrated very slowly.
- Pregnancy significantly increases levothyroxine requirements; monitor TSH frequently.
- Do not switch between different brands or generic formulations without consulting your healthcare provider due to potential differences in bioavailability.
Alternative Therapies
- No direct therapeutic alternatives for thyroid hormone replacement; levothyroxine is the standard of care for hypothyroidism.
Cost & Coverage
Average Cost:
Varies widely, typically $10-$50 per 30 tablets
Generic Available:
Yes
Insurance Coverage:
Tier 1 (Generic) or Tier 2 (Brand)
General Drug Facts
If your symptoms or health issues persist or worsen, it is essential to contact your doctor promptly. To ensure safe and effective treatment, 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 for more information. If you have any questions or concerns about your medication, don't hesitate to reach out to 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 details about the medication taken, the amount, and the time it happened.