Levothyroxine 100mcg/ml Inj, 1ml
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
Pharmacologic Class
Thyroid hormone replacement
Pregnancy Category
Category A
FDA Approved
Aug 1982
DEA Schedule
Not Controlled
Overview
What is this medicine?
Levothyroxine is a man-made version of a hormone naturally produced by your thyroid gland. It's used to replace this hormone when your body doesn't make enough, which helps regulate your body's energy and metabolism. The injectable form is typically used when you can't take it by mouth, such as during severe illness or surgery.
How to Use This Medicine
To use this medication correctly, follow your doctor's instructions and carefully read all accompanying information. Take this medication exactly as directed, and adhere to all guidelines provided. This drug is administered via intravenous injection.
For storage and disposal, consult with your doctor, nurse, or pharmacist to determine the best approach if you need to keep this medication at home.
If you miss a dose, contact your doctor immediately to receive guidance on the appropriate course of action.
For storage and disposal, consult with your doctor, nurse, or pharmacist to determine the best approach if you need to keep this medication at home.
If you miss a dose, contact your doctor immediately to receive guidance on the appropriate course of action.
Lifestyle & Tips
- For long-term oral therapy, take on an empty stomach, at least 30-60 minutes before breakfast, and at least 4 hours apart from calcium, iron, antacids, or other medications that can interfere with absorption.
- Maintain a consistent diet; avoid sudden changes in fiber intake.
- Do not use for weight loss; it is ineffective and dangerous in individuals with normal thyroid function.
- Report any new or worsening symptoms to your doctor immediately.
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 varies by indication. For myxedema coma: 200-500 mcg IV as a single bolus, then 100-300 mcg IV daily. For patients unable to take oral therapy: 50% of the patient's usual oral levothyroxine dose administered IV daily.
Dose Range:
100 - 500 mg
Condition-Specific Dosing:
myxedemaComaInitial:
200-500 mcg IV bolus
myxedemaComaMaintenance:
100-300 mcg IV daily
oralIntolerance:
50% of usual oral dose IV daily
Pediatric Dosing
Neonatal:
Not established for IV myxedema coma; for oral intolerance, dose is typically 50-75% of oral dose, adjusted based on weight and thyroid function tests.
Infant:
Not established for IV myxedema coma; for oral intolerance, dose is typically 50-75% of oral dose, adjusted based on weight and thyroid function tests.
Child:
Not established for IV myxedema coma; for oral intolerance, dose is typically 50-75% of oral dose, adjusted based on weight and thyroid function tests.
Adolescent:
Not established for IV myxedema coma; for oral intolerance, dose is typically 50-75% of oral dose, adjusted based on weight and thyroid function tests.
Dose Adjustments
Renal Impairment:
Mild:
No specific adjustment needed.
Moderate:
No specific adjustment needed.
Severe:
No specific adjustment needed.
Dialysis:
No specific adjustment needed; levothyroxine is highly protein-bound and not significantly removed by dialysis.
Hepatic Impairment:
Mild:
No specific adjustment needed.
Moderate:
No specific adjustment needed.
Severe:
No specific adjustment needed; however, monitor thyroid function closely as hepatic metabolism may be altered in severe liver disease.
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, which regulate gene expression, influencing protein synthesis and metabolic processes. Thyroid hormones are essential for normal metabolism, growth, and development, and play a role in calorigenesis, protein, carbohydrate, and lipid metabolism.
Pharmacokinetics
Absorption:
Bioavailability:
100% (IV)
Tmax:
Not applicable (IV)
FoodEffect:
Not applicable (IV)
Distribution:
Vd:
10-13 L
ProteinBinding:
>99% (primarily to thyroxine-binding globulin [TBG], thyroxine-binding prealbumin [TBPA], and albumin)
CnssPenetration:
Limited
Elimination:
HalfLife:
6-7 days (euthyroid individuals); 9-10 days (hypothyroid); 3-4 days (hyperthyroid)
Clearance:
Approximately 0.05 L/hour
ExcretionRoute:
Renal (approximately 80% of metabolites), biliary/fecal (approximately 20% of metabolites and unabsorbed drug)
Unchanged:
<1% (renal)
Pharmacodynamics
OnsetOfAction:
Within hours (IV), but full therapeutic effect may take several days to weeks due to long half-life and conversion to T3.
PeakEffect:
Peak TSH suppression or normalization typically occurs within 4-6 weeks of stable dosing.
DurationOfAction:
Long, due to long half-life (effects persist for several days after discontinuation).
Confidence:
Medium
Safety & Warnings
BLACK BOX WARNING
Thyroid hormones, including levothyroxine, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss. In euthyroid patients, doses within the range of daily hormonal requirements are ineffective for weight reduction. Larger doses may produce serious or even life-threatening manifestations of toxicity, particularly when given in association with sympathomimetic amines such as those used for their anorectic effects.
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 feeling irritable, nervous, excitable, anxious, or restless
Shakiness
Trouble sleeping
Sensitivity to heat
Excessive sweating
Fever
Muscle cramps
Muscle weakness
Flushing
Bone pain
Changes in menstrual periods
Additional Side Effects in Children:
Hip or knee pain
Limping
Additional Side Effects in Infants:
Changes in the shape of the head and face
Other Possible Side Effects
Most people do not experience severe side effects, and some may have only minor side effects. However, 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, 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.
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 feeling irritable, nervous, excitable, anxious, or restless
Shakiness
Trouble sleeping
Sensitivity to heat
Excessive sweating
Fever
Muscle cramps
Muscle weakness
Flushing
Bone pain
Changes in menstrual periods
Additional Side Effects in Children:
Hip or knee pain
Limping
Additional Side Effects in Infants:
Changes in the shape of the head and face
Other Possible Side Effects
Most people do not experience severe side effects, and some may have only minor side effects. However, 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, 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:
- Chest pain, shortness of breath, rapid or irregular heartbeat (palpitations)
- Excessive sweating, heat intolerance
- Nervousness, anxiety, tremors
- Unexplained weight loss or gain
- Severe fatigue, cold intolerance, constipation (signs of under-treatment)
- Swelling in hands, feet, or face
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
This list is not exhaustive, and it is crucial to discuss all your health problems and medications with your doctor.
To ensure your safety, please inform 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
Before making any changes to your medication regimen, including starting, stopping, or adjusting the dose of any medication, consult with your doctor to confirm it is safe to do so.
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
This list is not exhaustive, and it is crucial to discuss all your health problems and medications with your doctor.
To ensure your safety, please inform 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
Before making any changes to your medication regimen, including starting, stopping, or adjusting the dose of any medication, consult with your doctor to confirm it is safe to do so.
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.
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 advised.
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 osteoporosis (weak bones), particularly after menopause. Discuss your risk factors with your doctor, who can help determine if you are at a higher risk of developing osteoporosis.
This medication may also affect fertility, potentially leading to difficulties in getting pregnant or fathering a child. If you plan to conceive, consult your doctor before starting this medication.
Special Considerations
If you are 65 or older, use this medication with caution, as you may be more susceptible to side effects.
If you are pregnant, planning to become pregnant, or breastfeeding, inform your doctor to discuss the benefits and risks of this medication to you and your baby.
Pediatric Patients
If your child is taking this medication and experiences any changes in weight, consult your doctor, as their dose 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, so consult your doctor to determine the best course of action.
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.
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 advised.
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 osteoporosis (weak bones), particularly after menopause. Discuss your risk factors with your doctor, who can help determine if you are at a higher risk of developing osteoporosis.
This medication may also affect fertility, potentially leading to difficulties in getting pregnant or fathering a child. If you plan to conceive, consult your doctor before starting this medication.
Special Considerations
If you are 65 or older, use this medication with caution, as you may be more susceptible to side effects.
If you are pregnant, planning to become pregnant, or breastfeeding, inform your doctor to discuss the benefits and risks of this medication to you and your baby.
Pediatric Patients
If your child is taking this medication and experiences any changes in weight, consult your doctor, as their dose 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, so consult your doctor to determine the best course of action.
Overdose Information
Overdose Symptoms:
- Palpitations
- Tachycardia
- Arrhythmias
- Chest pain
- Tremor
- Nervousness
- Insomnia
- Diaphoresis
- Heat intolerance
- Weight loss
- Diarrhea
- Fever
- Seizures (rare)
- Cardiac arrest (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, including beta-blockers for cardiac effects, and measures to reduce absorption if oral overdose. IV overdose requires close cardiac monitoring.
Drug Interactions
Major Interactions
- Warfarin (potentiates anticoagulant effect, requiring reduced warfarin dose)
- Catecholamines (e.g., epinephrine, norepinephrine; increased risk of cardiac arrhythmias and coronary artery disease)
- Amiodarone (can cause hypo- or hyperthyroidism, alters T4 to T3 conversion)
- Certain anticonvulsants (e.g., carbamazepine, phenytoin, phenobarbital; may increase levothyroxine metabolism)
- Rifampin (increases levothyroxine metabolism)
- Sertraline (may increase levothyroxine requirements)
- Tyrosine kinase inhibitors (e.g., imatinib, sunitinib; may increase levothyroxine requirements)
Moderate Interactions
- Beta-blockers (may reduce conversion of T4 to T3)
- Tricyclic antidepressants (increased sensitivity to TCAs)
- Oral contraceptives/Estrogens (increase TBG, potentially increasing levothyroxine requirements)
- Androgens/Anabolic steroids (decrease TBG, potentially decreasing levothyroxine requirements)
- Corticosteroids (may decrease TSH secretion and T4 to T3 conversion)
- Insulin/Oral hypoglycemics (levothyroxine may increase blood glucose, requiring adjustment of antidiabetic agents)
Confidence Interactions
Monitoring
Baseline Monitoring
Thyroid Stimulating Hormone (TSH)
Rationale: Primary indicator of thyroid function and adequacy of thyroid hormone replacement.
Timing: Prior to initiation of therapy.
Free Thyroxine (Free T4)
Rationale: Measures unbound, biologically active T4, useful in assessing thyroid status, especially in central hypothyroidism or when TSH is unreliable.
Timing: Prior to initiation of therapy.
Cardiac status (ECG, vital signs)
Rationale: To assess for underlying cardiovascular disease, especially in elderly or those with myxedema, as thyroid hormone replacement can exacerbate cardiac conditions.
Timing: Prior to initiation, particularly in myxedema coma.
Adrenal function (if myxedema coma suspected)
Rationale: To rule out co-existing adrenal insufficiency, which must be treated prior to or concurrently with thyroid hormone replacement.
Timing: Prior to initiation in suspected myxedema coma.
Routine Monitoring
Thyroid Stimulating Hormone (TSH)
Frequency: Every 4-6 weeks until stable, then every 6-12 months.
Target: 0.4-4.0 mIU/L (euthyroid range), or individualized based on patient's condition (e.g., post-thyroidectomy for cancer suppression).
Action Threshold: Adjust dose if TSH is outside target range.
Free Thyroxine (Free T4)
Frequency: Often monitored concurrently with TSH, especially during initial titration or if TSH is suppressed/elevated.
Target: 0.8-1.8 ng/dL (euthyroid range), or individualized.
Action Threshold: Adjust dose if Free T4 is outside target range or inconsistent with TSH.
Clinical symptoms and signs of hypo/hyperthyroidism
Frequency: At every clinical visit.
Target: Resolution of hypothyroid symptoms, absence of hyperthyroid symptoms.
Action Threshold: Evaluate thyroid function tests and adjust dose if symptoms persist or new symptoms develop.
Symptom Monitoring
- Fatigue
- Weight changes (gain or loss)
- Cold or heat intolerance
- Constipation or diarrhea
- Dry skin
- Hair loss
- Bradycardia or tachycardia
- Palpitations
- Nervousness or irritability
- Tremor
- Sleep disturbances
- Muscle weakness or cramps
- Changes in menstrual cycle
Special Patient Groups
Pregnancy
Levothyroxine is essential for normal fetal development and is a Category A drug. Thyroid hormone requirements often increase during pregnancy. It is crucial to continue levothyroxine therapy and adjust the dose as needed to maintain euthyroidism.
Trimester-Specific Risks:
First Trimester:
Untreated maternal hypothyroidism during the first trimester is associated with increased risk of miscarriage, preterm birth, and impaired neurocognitive development in the child.
Second Trimester:
Continued need for dose adjustment to maintain euthyroidism. Fetal thyroid gland begins to function in the second trimester.
Third Trimester:
Dose may need further adjustment. Close monitoring of TSH is essential throughout pregnancy and postpartum.
Lactation
Levothyroxine is considered safe during breastfeeding (L1). Minimal amounts are excreted into breast milk, and it does not adversely affect the nursing infant.
Infant Risk:
Low risk to infant.
Pediatric Use
Dosing is weight-based and critical for normal growth and neurocognitive development. Close monitoring of TSH and Free T4 is essential. IV formulation is typically reserved for acute situations like myxedema coma or when oral administration is not possible.
Geriatric Use
Lower initial doses are often recommended due to increased sensitivity to thyroid hormones and a higher prevalence of underlying cardiovascular disease. Close cardiac monitoring is advised during initiation and dose titration.
Clinical Information
Clinical Pearls
- The IV dose of levothyroxine is typically 50% of the patient's usual oral dose due to 100% bioavailability compared to variable oral absorption.
- For myxedema coma, a large IV loading dose is often given, followed by daily maintenance doses.
- Levothyroxine injection should be reconstituted immediately before use and administered as a single IV bolus or slow infusion over several minutes.
- Do NOT use levothyroxine for weight reduction in euthyroid patients; it is ineffective and potentially dangerous.
- Patients on chronic levothyroxine therapy who become NPO (nothing by mouth) should have their dose converted to IV to prevent hypothyroidism, especially if NPO for extended periods.
- Monitor for signs of adrenal insufficiency in patients with myxedema coma, and treat with corticosteroids before or concurrently with levothyroxine to prevent adrenal crisis.
Alternative Therapies
- Liothyronine (T3) injection (for rapid onset, e.g., severe myxedema coma, but shorter half-life requires more frequent dosing)
- Desiccated thyroid extract (contains T4 and T3, not available in injectable form)
Cost & Coverage
Average Cost:
Highly variable, typically several hundred to over a thousand USD per 100mcg/ml vial depending on supplier and quantity. per 1ml vial
Generic Available:
Yes
Insurance Coverage:
Tier 1 or 2 for generic, Tier 3 or higher for brand (oral). Injectable form coverage varies by indication and setting (inpatient vs. outpatient).
General Drug Facts
If your symptoms or health problems persist or worsen, it is essential to contact your doctor for further guidance. To ensure safe use, never share your medication with others or take someone else's medication. Store all medications in a secure location, out of reach of children and pets, to prevent accidental ingestion. Dispose of unused or expired medications properly; do not flush them down the toilet or pour them down the drain unless instructed to do so by your pharmacist or healthcare provider. For guidance on proper disposal, consult your pharmacist, who can also inform you about potential drug take-back programs in your area. Some medications may come with an additional patient information leaflet, which your pharmacist can provide. If you have any questions or concerns about your medication, discuss them with your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately contact your local poison control center or seek medical attention. Be prepared to provide information about the medication taken, the amount, and the time of ingestion to ensure prompt and effective treatment.