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Levothyroxine 500mg/5ml Inj, 5ml

Manufacturer FRESENIUS KABI USA Active Ingredient Levothyroxine Injection Solution(lee voe thye ROKS een) Pronunciation lee voe thye ROKS een
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.
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Drug Class
Thyroid hormone replacement
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Pharmacologic Class
Thyroid hormones
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Pregnancy Category
Category A
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FDA Approved
Jan 1955
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DEA Schedule
Not Controlled

Overview

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What is this medicine?

Levothyroxine is a man-made version of a hormone naturally produced by your thyroid gland. It's used to treat an underactive thyroid (hypothyroidism) or to replace thyroid hormone when your body doesn't make enough. The injectable form is typically used in emergencies like severe hypothyroidism (myxedema coma) or when you can't take medicine by mouth.
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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 be sure to follow all instructions provided. This drug is administered via intravenous injection.

If you need to store this medication at home, consult with your doctor, nurse, or pharmacist to determine the proper storage procedure.

In the event that you miss a dose, contact your doctor to receive guidance on the appropriate course of action.
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Lifestyle & Tips

  • For oral forms, take on an empty stomach, at least 30-60 minutes before breakfast, and separate from other medications and supplements (especially calcium, iron, antacids) by at least 4 hours.
  • Maintain a consistent schedule for administration.
  • Report any new or worsening symptoms to your doctor.
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Available Forms & Alternatives

Available Strengths:

Dosing & Administration

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Adult Dosing

Standard Dose: Initial IV dose for myxedema coma: 300-500 mcg (0.3-0.5 mg) as a single bolus. Maintenance IV dose: 75-100 mcg (0.075-0.1 mg) daily. For patients unable to take oral, IV dose is typically 50% of the oral dose.
Dose Range: 75 - 500 mg

Condition-Specific Dosing:

myxedemaComa: Initial: 300-500 mcg IV bolus. Maintenance: 75-100 mcg IV daily. Consider lower initial dose (100-300 mcg) for patients with known cardiovascular disease.
oralIntolerance: 50% of the patient's usual oral levothyroxine dose administered IV daily.
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Pediatric Dosing

Neonatal: Not established for IV use in myxedema coma. Oral is preferred for congenital hypothyroidism. If IV is necessary due to inability to take oral, consult specialist; dose is highly individualized and typically 50% of oral dose.
Infant: Not established for IV use in myxedema coma. Oral is preferred for congenital hypothyroidism. If IV is necessary due to inability to take oral, consult specialist; dose is highly individualized and typically 50% of oral dose.
Child: Not established for IV use in myxedema coma. Oral is preferred for hypothyroidism. If IV is necessary due to inability to take oral, consult specialist; dose is highly individualized and typically 50% of oral dose.
Adolescent: Not established for IV use in myxedema coma. Oral is preferred for hypothyroidism. If IV is necessary due to inability to take oral, consult specialist; dose is highly individualized and typically 50% of oral dose.
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Dose Adjustments

Renal Impairment:

Mild: No specific adjustment needed.
Moderate: No specific adjustment needed.
Severe: No specific adjustment needed.
Dialysis: No specific adjustment needed; not significantly dialyzable.

Hepatic Impairment:

Mild: Caution advised; monitor thyroid function closely.
Moderate: Caution advised; monitor thyroid function closely. May require lower doses.
Severe: Caution advised; monitor thyroid function closely. May require significantly lower doses due to impaired metabolism and protein binding.

Pharmacology

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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 cellular processes involved in metabolism, growth, and development.
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Pharmacokinetics

Absorption:

Bioavailability: 100% (IV administration)
Tmax: Not applicable for IV (immediate systemic availability)
FoodEffect: Not applicable for IV

Distribution:

Vd: Approximately 10-13 L (for T4)
ProteinBinding: Greater than 99% (primarily to thyroxine-binding globulin (TBG), transthyretin, and albumin)
CnssPenetration: Limited

Elimination:

HalfLife: Approximately 6-7 days (euthyroid individuals); 9-10 days (hypothyroid); 3-4 days (hyperthyroid)
Clearance: Approximately 1.1 L/day (euthyroid)
ExcretionRoute: Primarily renal (approximately 80% as metabolites), with some fecal excretion (approximately 20%)
Unchanged: Less than 1% (renal)
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Pharmacodynamics

OnsetOfAction: Within hours (IV administration, though full clinical effect may take days due to long half-life and cellular processes)
PeakEffect: Several days to weeks (due to long half-life and accumulation)
DurationOfAction: Days to weeks (due to long half-life)

Safety & Warnings

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BLACK BOX WARNING

Thyroid hormones, including levothyroxine, 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.
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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 or seek immediate 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. Many people may not experience any side effects or may only have mild ones. If you are bothered by any of the following side effects or if they do not go away, contact your doctor:

* Hair loss (usually temporary and resolves on its own within the first few months of treatment)

This is not a complete list of possible side effects. If you have questions or concerns about side effects, talk to your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
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Seek Immediate Medical Attention If You Experience:

  • Symptoms of too much thyroid hormone (hyperthyroidism): rapid heart rate, palpitations, chest pain, sweating, nervousness, tremors, unexplained weight loss, diarrhea, insomnia.
  • Symptoms of too little thyroid hormone (hypothyroidism, if dose is too low): extreme tiredness, weight gain, constipation, feeling cold, dry skin, hair loss, depression, slow heart rate.
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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, 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

Before starting, stopping, or changing the dose of any medication, including this one, consult with your doctor to confirm it is safe for you to do so.
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Precautions & Cautions

Important Information for 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.

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 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.

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 higher risk of developing osteoporosis.

This medication may affect fertility, potentially making it difficult to become pregnant or father a child. If you plan to conceive, consult your doctor before starting treatment.

If you are 65 years or older, use this medication with caution, as you may be more susceptible to side effects.

Pregnancy and Breastfeeding

Inform your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. Your doctor will discuss the benefits and risks of this medication for you and your baby.

Special Considerations for Children

If your child is taking this medication and experiences a change in weight, 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.
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Overdose Information

Overdose Symptoms:

  • Palpitations
  • Tachycardia
  • Arrhythmias (e.g., atrial fibrillation)
  • Chest pain (angina)
  • Tremors
  • Nervousness
  • Insomnia
  • Diarrhea
  • Weight loss
  • Heat intolerance
  • Fever
  • Seizures (rare)
  • Coma (rare)

What to Do:

Seek immediate medical attention. Call 911 or Poison Control at 1-800-222-1222. Treatment is supportive and may include beta-blockers for cardiac symptoms, corticosteroids, and measures to reduce absorption if oral overdose. IV fluids and electrolyte correction may be needed.

Drug Interactions

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Major Interactions

  • Amiodarone (alters thyroid hormone metabolism)
  • Warfarin (enhances anticoagulant effect)
  • Antidiabetic agents (may increase blood glucose, requiring dose adjustment)
  • Sympathomimetics (increased risk of cardiac adverse effects)
  • Tyrosine kinase inhibitors (e.g., imatinib, sunitinib - may decrease levothyroxine efficacy)
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Moderate Interactions

  • Antacids (aluminum, magnesium, calcium - decrease absorption if given orally, but less relevant for IV)
  • Iron supplements (decrease absorption if given orally, but less relevant for IV)
  • Cholestyramine, colestipol, sevelamer (decrease absorption if given orally, but less relevant for IV)
  • Proton pump inhibitors (may decrease absorption if given orally, but less relevant for IV)
  • Estrogens (increase TBG, may require higher levothyroxine dose)
  • Androgens (decrease TBG, may require lower levothyroxine dose)
  • Beta-blockers (may inhibit T4 to T3 conversion)
  • Corticosteroids (may inhibit T4 to T3 conversion)
  • Phenytoin, carbamazepine, rifampin (increase thyroid hormone metabolism, may require higher levothyroxine dose)

Monitoring

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Baseline Monitoring

Thyroid Stimulating Hormone (TSH)

Rationale: Primary indicator of thyroid function and adequacy of replacement.

Timing: Prior to initiation of therapy.

Free Thyroxine (Free T4)

Rationale: Direct measure of unbound, active thyroid hormone.

Timing: Prior to initiation of therapy.

Cardiac status (ECG, vital signs)

Rationale: To assess for underlying cardiovascular disease, especially important before high-dose IV therapy for myxedema coma.

Timing: Prior to initiation of therapy.

Adrenal function (e.g., cortisol levels)

Rationale: To rule out co-existing adrenal insufficiency, which must be treated before or concurrently with thyroid hormone replacement.

Timing: Prior to initiation of therapy, especially in myxedema coma.

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Routine Monitoring

Thyroid Stimulating Hormone (TSH)

Frequency: Every 4-6 weeks until stable, then every 6-12 months once stable.

Target: 0.4-4.0 mIU/L (individualized based on patient age, comorbidities, and specific condition being treated).

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 in central hypothyroidism.

Target: 0.8-1.8 ng/dL (individualized).

Action Threshold: Adjust dose if Free T4 is outside target range, particularly if TSH is also abnormal.

Clinical symptoms of hypo/hyperthyroidism

Frequency: Continuously

Target: Resolution of hypothyroid symptoms, absence of hyperthyroid symptoms.

Action Threshold: Adjust dose based on clinical response and laboratory values.

Cardiac monitoring (ECG, vital signs)

Frequency: Daily or as clinically indicated, especially during initial IV therapy for myxedema coma.

Target: Stable cardiac rhythm and vital signs.

Action Threshold: Address any signs of cardiac instability immediately.

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Symptom Monitoring

  • Symptoms of hypothyroidism (fatigue, weight gain, constipation, cold intolerance, dry skin, hair loss, bradycardia, depression, cognitive impairment)
  • Symptoms of hyperthyroidism (palpitations, tachycardia, anxiety, tremors, weight loss, heat intolerance, diarrhea, insomnia, sweating, chest pain)

Special Patient Groups

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Pregnancy

Category A. Levothyroxine is essential for normal fetal development. Hypothyroidism during pregnancy can lead to adverse maternal and fetal outcomes. Thyroid hormone requirements often increase during pregnancy, requiring dose adjustments.

Trimester-Specific Risks:

First Trimester: Untreated maternal 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 are crucial to maintain euthyroid state.
Third Trimester: Dose requirements may continue to increase. Monitor TSH every 4-6 weeks.
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Lactation

L1 - Safest. Levothyroxine is excreted in breast milk in minimal amounts that are not clinically significant and do not affect infant thyroid function. It is considered compatible with breastfeeding.

Infant Risk: Minimal to none.
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Pediatric Use

Crucial for normal growth and development. Untreated congenital hypothyroidism leads to irreversible intellectual disability and growth retardation. Dosing is weight-based and adjusted frequently based on TSH and Free T4 levels. IV formulation is rarely used in pediatrics except in severe, life-threatening situations where oral administration is not possible.

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Geriatric Use

Older patients, especially those with underlying cardiovascular disease, should be started on lower doses and titrated slowly to avoid precipitating cardiac events. Monitor for signs of cardiac toxicity. TSH target ranges may be slightly higher in very elderly individuals.

Clinical Information

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Clinical Pearls

  • IV levothyroxine is typically reserved for myxedema coma or situations where oral administration is not feasible (e.g., NPO status, severe malabsorption).
  • The IV dose is generally 50% of the patient's usual oral dose due to 100% bioavailability.
  • For myxedema coma, a large initial loading dose (300-500 mcg) is often given, followed by daily maintenance doses.
  • Always rule out adrenal insufficiency before initiating thyroid hormone replacement, especially in myxedema coma, as thyroid hormone can precipitate an adrenal crisis.
  • Administer IV levothyroxine slowly over 1-3 minutes.
  • Monitor cardiac status closely, especially in elderly patients or those with pre-existing heart disease, as rapid thyroid hormone replacement can exacerbate cardiac conditions.
  • Thyroid function tests (TSH, Free T4) should be monitored regularly to guide dose adjustments.
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Alternative Therapies

  • Liothyronine (T3, synthetic)
  • Desiccated thyroid extract (natural, contains T4 and T3)
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Cost & Coverage

Average Cost: Varies widely, typically $50 - $500+ per 500mcg/5ml vial
Generic Available: Yes
Insurance Coverage: Tier 1 or 2 (generic), Tier 3 (brand)
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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, and do not take medication prescribed for someone else. 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. Unless instructed to do so by a healthcare professional, avoid flushing medications down the toilet or pouring them down the drain. If you are unsure about the correct disposal method, consult your pharmacist for advice. Many communities have drug take-back programs, which your pharmacist can help you locate. Some medications may come with an additional patient information leaflet; check with your pharmacist to see if this applies to your prescription. 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 emergency medical attention. Be prepared to provide information about the medication taken, the amount, and the time it was taken, as this will aid in providing appropriate care.