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Levothyroxine Dosage Chart

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Last Updated: 10 October 2020

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General | Latest Info

Hypothyroidism is a common medical condition which causes deficiency or low level of thyroid hormone. Patients with Hypothyroidism are treated by taking thyroid hormone pills on a daily basis. The majority of patients with Hypothyroidism take a synthetic form of thyroid hormone called Levothyroxine. The Levothyroxine structure is identical to T 4, main hormone secreted into the blood by the thyroid gland. The dose of Levothyroxine for ANY individual patient is different;. The best dose should be able to keep the level of thyroid hormone tests within normal range and help to improve symptoms of hypothyroidism. However, many patients with Hypothyroidism DO not take the right dose and are either over - treated or undertreated. Over - treatment may cause irregular heart beats and bone loss in the elderly and under - treatment may cause symptoms like weight gain, fatigue as well as other serious health issues like higher cholesterol level, and, in severe cases, heart problems and even death. In this study, authors evaluated the effect of sex, age and body weight on blood level of thyroid hormone in patients taking Levothyroxine. Younis IR et al 2018 Stable isotope pharmacokinetic studies provide insight into the effects of age, sex, and weight on Levothyroxine metabolism. Thyroid 28: 41 - 49. Epub 2018 Jan 2.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Levothyroxine Dosage

Levothyroxine is contraindicate in any patient WITH known hypersensitivity to Levothyroxine or any OF its excipients; however, there is no well - documented evidence in literature OF true allergic or idiosyncratic reactions to thyroid hormone. Hypersensitivity reactions to inactive ingredients have occurred in PATIENTS treated with thyroid hormone products. Levothyroxine Injection and Tablets ARE synthetically derived and may be used in PATIENTS allergic to desiccated thyroid or thyroid extract derived from pork or beef. Levothyroxine is contraindicated for use in PATIENTS WITH diagnosed but untreated adrenal insufficiency. Initiation OF thyroid hormone therapy prior to initiating glucocorticoid therapy may precipitate acute adrenal crisis in PATIENTS WITH adrenal insufficiency due to an increase in the body's demand for adrenal hormones. Treat PATIENTS WITH adrenal insufficiency WITH replacement glucocorticoids prior to initiating treatment WITH Levothyroxine. Serum TSH is not a reliable Measure OF Levothyroxine DOSE adequacy in PATIENTS WITH Secondary HYPOTHYROIDISM or Tertiary HYPOTHYROIDISM and should not be used to Monitor therapy. Inappropriate TSH may be seen IF HYPOTHYROIDISM is caused by TSH deficiency, and TSH will not normalize WITH thyroid treatment. Use serum free - T4 level to monitor for adequacy OF therapy in this patient population. Many authorities recommend lower INITIAL dosages and slower titration of thyroid hormones in PATIENTS WITH CARDIAC DISEASE and coronary artery DISEASE. Thyroid hormones such as Levothyroxine should be used WITH great caution in PATIENTS where integrity of the cardiovascular system is suspect. All Levothyroxine dosage formulations ARE cardiostimulatory and should be used WITH great caution in PATIENTS WITH angina pectoris, uncontrolled hypertension, CARDIAC arrhythmias, CAD, previous history OF acute myocardial infarction, or current acute myocardial infarction. If adverse CARDIAC symptoms develop or worsen during treatment, reduce or withhold Levothyroxine and cautiously restart at lower DOSE. Over - treatment WITH thyroid hormones may cause CARDIAC stimulation and lead to increased heart rate, CARDIAC wall thickening, and increased CARDIAC contractility, which may precipitate angina or CARDIAC arrhythmias. Concomitant Administration OF Levothyroxine WITH vasopressors or sympathomimetic agents may precipitate coronary insufficiency and associate symptoms, particularly in myxedematous PATIENTS or those WITH CAD. Fluid therapy should be administered WITH great care to prevent CARDIAC decompensation. In PATIENTS WITH compromised CARDIAC function, use thyroid hormones in conjunction WITH careful CARDIAC monitoring. A Lower starting DOSE is recommended in adults and Pediatric PATIENTS at risk of heart failure or sensitive to thyroid stimulation. Careful monitoring is also recommended during surgery, as some anesthetic agents may induce changes in heart rate or blood pressure when administered WITH thyroid hormones. Levothyroxine therapy can worsen glycemic control in PATIENTS WITH diabetes mellitus, and result in increased antidiabetic agent or insulin requirements. Effects see ARE poorly understood and depend upon a variety OF factors such as DOSE and type OF thyroid preparations and endocrine status OF patient. Blood glucose should be monitored closely during concomitant therapy, particularly during initiation, DOSE adjustments, or discontinuation OF therapy. Levothyroxine should not be used for obesity treatment or weight loss.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

What is Synthroid?

Table

HormoneRatio in ThyroglobulinBiologic Potencyt 1/2 (days)Protein Binding (%) a
Levothyroxine (T4)10 - 2016-7 b99.96
Liothyronine (T3)14299.5

Thyroid hormones exert their physiologic actions through control of DNA transcription and protein synthesis. Triiodothyronine and L - thyroxine diffuse into the cell nucleus and bind to thyroid receptor proteins that attach to DNA. This hormone nuclear receptor complex activates gene transcription and synthesis of messenger RNA and cytoplasmic proteins. Physiological actions of thyroid hormones are produced predominantly by T3, majority of which is derived from T4 by deiodination in peripheral tissues. Absorption of orally administered T4 from gastrointestinal tract ranges from 40% to 80%. The majority of SYNTHROID dose is absorbed from the jejunum and upper ileum. The relative bioavailability of SYNTHROID tablets, compared to equal nominal dose of oral levothyroxine sodium solution, is approximately 93%. T4 absorption is increased by fasting, and decrease in malabsorption syndromes and by certain foods such as soybeans. Dietary fiber decreases bioavailability of T4. Absorption may also decrease with age. In addition, many drugs and foods affect T4 absorption. Circulating thyroid hormones are greater than 99% bound to plasma proteins, including thyroxine - binding globulin, thyroxine - binding prealbumin, and albumin, whose capacities and affinities vary for each hormone. The higher affinity of both TBG and TBPA for T4 partially explains higher serum levels, slower metabolic clearance, and longer half - life of T4 compared to T3. Protein - bound thyroid hormones exist in reverse equilibrium with small amounts of free hormone. Only unbound hormone is metabolically active. Many drugs and physiologic conditions affect the binding of thyroid hormones to serum proteins. Thyroid hormones do not readily cross the placental barrier. T4 is slowly eliminate. The major pathway of thyroid hormone metabolism is through sequential deiodination. Approximately 80% of circulating T3 is derived from peripheral T4 by monodeiodination. The liver is a major site of degradation for both T4 and T3, with T4 deiodination also occurring at a number of additional sites, including kidney and other tissues. Approximately 80% of the daily dose of T4 is deiodinated to yield equal amounts of T3 and reverse T3. T3 and rT3 are further deiodinated to diiodothyronine. Thyroid hormones are also metabolized via conjugation with glucuronides and sulfates and excreted directly into bile and gut where they undergo enterohepatic recirculation. Thyroid hormones are primarily eliminated by the kidneys. Portion of conjugate hormone reach colon unchanged and is eliminated in feces. Approximately 20% of T4 is eliminated in stool. Urinary excretion of T4 decreases with age.

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Table 1. SYNTHROID Dosing Guidelines for Pediatric Hypothyroidism

AGEDaily Dose Per Kg Body Weight a
0-3 months10-15 mcg/kg/day
3-6 months8-10 mcg/kg/day
6-12 months6-8 mcg/kg/day
1-5 years5-6 mcg/kg/day
6-12 years4-5 mcg/kg/day
Greater than 12 years but growth and puberty incomplete2-3 mcg/kg/day
Growth and puberty complete1.6 mcg/kg/day

Table2

Strength (mcg)Color additive(s)
25FDC Yellow No. 6 Aluminum Lake a
50None
75FDC Red No. 40 Aluminum Lake, FDC Blue No. 2 Aluminum Lake
88FDC Blue No. 1 Aluminum Lake, FDC Yellow No. 6 Aluminum Lake a , DC Yellow No. 10 Aluminum Lake
100DC Yellow No. 10 Aluminum Lake, FDC Yellow No. 6 Aluminum Lake a
112DC Red No. 27 30 Aluminum Lake
125FDC Yellow No. 6 Aluminum Lake a , FDC Red No. 40 Aluminum Lake, FDC Blue No. 1 Aluminum Lake
137FDC Blue No. 1 Aluminum Lake
150FDC Blue No. 2 Aluminum Lake
175FDC Blue No. 1 Aluminum Lake, DC Red No. 27 30 Aluminum Lake
200FDC Red No. 40 Aluminum Lake
300DC Yellow No. 10 Aluminum Lake, FDC Yellow No. 6 Aluminum Lake a , FDC Blue No. 1 Aluminum Lake
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Conclusion

If OTHERWISE HEALTHY: May initiate a full replacement dosage of roughly 1. 6 mcg / kg / Day PO. Adjust dose by 12. 5 mcg to 25 mcg increments every 4 to 6 weeks until the desired response. Geriatric PATIENTS or IF CARDIAC DISEASE PRESENT: Initiate WITH 12. 5 to 25 mcg PO once daily WITH gradual increments at 6 to 8 - week intervals as needed Elderly PATIENTS or those WITH subclinical HYPOTHYROIDISM target dose may be less than 1 mcg / kg / Day PO. Patients WITH SEVERE LONGSTANDING HYPOTHYROIDISM: Initially, 12. 5 to 25 mcg / Day PO WITH an increase of 12. 5 to 25 mcg / day every 2 to 4 weeks until at effective target dose. Pregnant WOMEN WITH NEW - ONSET HYPOTHYROIDISM: For moderate to SEVERE signs and symptoms, Initiate at full replacement dosage of roughly 1. 6 mcg / kg / Day PO. For mild HYPOTHYROIDISM, Initiate at 1 mcg / kg / Day PO. Max: Greater than 200 mcg / Day PO is rarely require. Rare PATIENTS may require up to 300 mcg / Day PO. Inadequate response to more than 300 mcg / Day may indicate poor compliance, malabsorption, drug interactions, or a combination of these factors. 1. 6 mcg / kg / Day PO once daily. Adjust by increments of 12. 5 to 25 mcg / day every 4 to 6 weeks until the patient has proper Clinical and TSH response. Hyperactivity can be minimized IF initiated at a dose that is 25% of recommended replacement dose, WITH weekly titration of approximately 25% of full recommended replacement dose to attain clinical goals. In SEVERE LONGSTANDING HYPOTHYROIDISM, Initiate WITH 12. 5 mcg to 25 mcg / day, and increase by 12. 5 mcg to 25 mcg every 2 to 4 weeks until the patient is clinically euthyroid and serum TSH level is normalize. Max: Greater than 200 mcg / Day PO is rarely require. Rare PATIENTS may require up to 300 mcg / Day PO. Inadequate response to more than 300 mcg / Day may indicate poor compliance, malabsorption, drug interactions, or a combination of these factors. If OTHERWISE HEALTHY: May initiate a full replacement dosage of roughly 1. 6 mcg / kg / Day PO. Adjust dose by 12. 5 mcg to 25 mcg increments every 4 to 6 weeks until the desired response. Geriatric PATIENTS or IF CARDIAC DISEASE PRESENT: Initiate WITH 12. 5 to 25 mcg PO once daily WITH gradual increments at 6 to 8 - week intervals as needed Elderly PATIENTS or those WITH subclinical HYPOTHYROIDISM may respond to less than 1 mcg / kg / Day PO. Patients WITH SEVERE LONGSTANDING HYPOTHYROIDISM: Initially, 12. 5 to 25 mcg / Day PO WITH an increase of 12. 5 to 25 mcg / day every 2 to 4 weeks until at effective target dose. Pregnant WOMEN WITH NEW - ONSET HYPOTHYROIDISM: For moderate to SEVERE signs and symptoms, Initiate at full replacement dosage of roughly 1. 6 mcg / kg / Day PO. For mild HYPOTHYROIDISM, Initiate at 1 mcg / kg / Day PO. Max: Greater than 200 mcg / Day PO is rarely require. Rare PATIENTS may require up to 300 mcg / Day PO. Inadequate response to more than 300 mcg / Day may indicate poor compliance, malabsorption, drug interactions, or a combination of these factors. 1. 6 mcg / kg / Day PO once daily. Hyperactivity can be minimized IF therapy is Initiate at a dose that is 25% of the recommended replacement dose.

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* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Introduction

Thyroxine was isolated on Christmas Day 1914 by Kendall. Its chemical structure was determined in 1926 by Harington, and it was synthesise in 1927 by Harington and Barger. Acidity of thyroxine molecule, which causes diminished absorption resulting in low bioavailability, was an unresolved problem for more than 20 years following its discovery. In 1949, commercial product containing synthesised sodium thyroxine was launched in the USA and some years later in Europe, signalling a new era in treatment of hypothyroidism, which had advanced from partially purified extracts of bovine Thyroid gland and desiccated thyroid extracts from sheep and pigs to fully synthesised thyroxine. The production of sodium thyroxine thus results in major pharmacological achievement in endocrinology, giving a more stable and effective thyroid hormone compound that, over the last few decades, has considerably improved the lives of millions of patients with various forms of hypothyroidism. The objective of this review is to provide an overview of when administration of levothyroxine is necessary, initial dosing and subsequent adjustment of levothyroxine, importance of avoiding under - and over - treatment with levothyroxine, need for levothyroxine dose adjustment through various phases of life, medical conditions and medications necessitating levothyroxine dose adjustments, as well as controversies about treatment with products other than levothyroxine. Diligent monitoring of patients taking levothyroxine and regular dose adjustment to achieve optimise treatment and avoidance of adverse events are particularly emphasise.


ADMINISTRATION

Administer on an empty stomach, at least 30 to 60 minutes before breakfast. Administer at least 4 hours apart from medications or food known to decrease absorption, and 4 hours apart from enteral feedings; evaluate need for dose adjustments when patient is regularly administering their dose within 1 hour of certain foods that may affect absorption. Soybean flour, cotton seed meal, walnuts, and dietary fiber decrease Levothyroxine absorption. Bioavailability is best when administered in a fasting state. May be administered intravenously or by intramuscular injection. Intravenous routes are prefer. Visually inspect parenteral products for particulate matter and discoloration before administration whenever solution and container permit. Reconstitution: Reconstitute by aseptically adding 5 mL of preservative - free 0. 9% Sodium Chloride Injection, USP to vial of lyophilized Levothyroxine Sodium for Injection. Do not use other solutions to Reconstitute. Shake well to dissolve completely. The resultant solution will have final concentration as follow: approximately 20 mcg / mL for 100 mcg vial. Approximately 40 mcg / mL for 200 mcg vial. Approximately 100 mcg / mL for 500 mcg vial. The Reconstitute Injection is preservative free and is stable for 4 hours; unused portions should be discard. Levothyroxine oral solution may be administered in water or directly into the mouth. To administer water, squeeze the contents of 1 single unit - dose ampule into a glass or cup containing water and stir. Do not dilute with any liquid other than water. Preparation should be administered immediately and consumed in its entirety to ensure all of the dose is receive. Rinse glass or cup with additional water and drink contents to ensure the entire dose is take. To administer directly, either squeeze it into your mouth or onto a spoon and immediately consume. Storage: Store unopened oral solution ampules in original container at 77 degrees F; excursions are permitted to 59 to 86 degrees F. Discard any unused ampules 15 days after opening pouch. Extemporaneous preparation of 25 mcg / mL Levothyroxine oral suspension: NOTE: Levothyroxine is not available as an FDA - approved oral suspension. With mortar and pestle, grind twenty - five 0. 1 mg Levothyroxine tablets into fine powder. In a separate container, measure 40 mL of glycerol. Add a small amount of glycerol to fine powder and mix into a uniform paste. Add geometric amounts of glycerol until the suspension is pourable. Transfer suspension to calibrated 100 mL amber bottle. In approximately 10 mL portions, rinse the mortar with remaining glycerol and transfer washings into amber bottle, trying to leave no Levothyroxine in the mortar. Add water to amber bottle to bring total volume to 100 mL. Label bottle appropriately, including'shake well before each use and refrigerate. Suspension is stable for 8 days when stored at approximately 4 degrees C.

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* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Discussion

Primary hypothyroidism is common, occurring in 3 to 10 percent of women, frequently with its onset during childbearing years. 1 2 estimate 1 to 2 percent of all pregnant women receive levothyroxine therapy for hypothyroidism. Epidemiologic studies indicate that 0. 4 percent of pregnant women have serum thyrotropin concentrations above 10 U per milliliter at 15 to 18 weeks of gestation. 3 4 Thus, in the United States alone, minimum of 12 000 to 16 000 infants are born each year to women with either inadequately treated or undiscovered primary hypothyroidism. 5 6 During pregnancy, women's thyroid physiology undergoes well - defined changes, including an approximate doubling in thyroxine - binding globulin concentrations due to increases in estradiol concentrations, as well as a 30 to 40 percent increase in plasma volume. 7 - 11 these changes result in a significant increase in total thyroxine pool, primarily during the first trimester. This increment may be provided largely by thyroid stimulation induced by human chorionic gonadotropin, 7 810 since slight increase in free thyroxine and reduction in thyrotropin occur at 9 to 12 weeks of gestation. 8 12 in general, however, thyrotropin concentration stays within normal range for the remainder of pregnancy, despite an estimated 30 to 50 percent increase in levothyroxine requirement. 9 10 13 - 15 although this process is now recognized by endocrinologists and some hypothyroid patients are alert to the need for such an increase, many pregnant women are found to have high serum thyrotropin concentration at time of their initial obstetrical examination, at 8 to 12 weeks of gestation. 3 410 13 16 - 22 Thus, current practice permits transient period of Maternal hypothyroxinemia in the first trimester, which is time when free thyroxine concentration is typically slightly increase. It is known that a pregnant woman is the sole source of fetal supply of thyroid hormones from conception to approximately 13 weeks of gestation when fetal thyroid function has develop. Give possible association between gestational hypothyroidism and impaired intellectual and cognitive development in offspring, as well as increased rate of fetal death in women with elevated thyrotropin concentration, 3 20 23 24, current approach is suboptimal. In this prospective study, we seek to delineate precise timing and pattern of increased thyroid hormone requirement during pregnancy in order to determine appropriate recommendations for preventing first - trimester hypothyroidism. We use a strategy involving frequent monitoring of serum thyrotropin concentrations with concomitant adjustments in dose of levothyroxine to maintain thyrotropin at preconception concentrations. Women with primary hypothyroidism who desired pregnancy were recruited from endocrine outpatient clinics at Brigham and Women's Hospital, Boston. Maternal thyroid function, estradiol, and human chorionic gonadotropin were measured before and during pregnancy. Our goal was to assess biochemical thyroid status after first miss menstrual cycle, every two weeks throughout first trimester, and monthly thereafter until completion of pregnancy. This aim was achieved in most, but not all, subjects. At each visit, two aliquots of serum were obtain. First was frozen and saved for batch analysis at completion of study.

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* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

#3. Monitor Your Symptoms

Symptoms of hypothyroidism depend on the health of the thyroid and efficient production of thyroid hormone, but can include: increased cholesterol levels, depression, fatigue, hair loss, memory loss, dry, rough skin, and constipation. Levothyroxine sodium is also used to treat other types of thyroid hormone and thyroid disorders and conditions. Levothyroxine sodium should not be used to treat infertility unless it is caused by low thyroid hormone levels. Levothyroxine sodium is available under the following different brand names: Synthroid, Levoxyl, L Thyroxine, Levo T, Levothroid, Levothyroxine T4, Levoxine, Tirosint, and Unithroid.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Dosing Considerations

Avoid under - treatment or over - treatment with this drug. This may result in adverse effects. Initiate lower dose of medicine in the elderly, those with angina pectoris, cardiovascular disease, or in those with severe hypothyroidism. Long - term therapy decreases bone mineral density; use lowest dose in postmenopausal women and women using suppressive doses. Lower dose of Tirosint capsules may be required compared with standard T4 tablets for hypothyroidism in patients with impaired gastric acid secretion to reach their target TSH levels; Tirosint has shown improved absorption compared with conventional T4 tablets. Check for bioequivalence if switching brands / generics, or every week after switching from one levothyroxine sodium preparation to another.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Administration

Thyroxine is secreted by thyrocytes and is the main thyroid hormone in circulation. Thyroxine is actively transported to various organs where it is converted to triiodothyronine by activity of deiodinases. Triiodothyronine, active form of thyroid hormone, is secreted in small amounts by thyroid but is mainly generated via extrathyroidal conversion of prohormone thyroxine. Hypothyroidism is a common endocrine disease that requires timely and lifelong treatment since, if left untreated, it can contribute to hypertension, dyslipidaemia, and heart failure and induce reversible dementia and infertility, as well as neurosensory, musculoskeletal, and gastrointestinal symptoms. There is currently no other treatment for hypothyroidism, other than providing thyroid hormone replacement. Due to its long half - life of about 7 days, in patients in clinically euthyroid state, levothyroxine is the preferred first - line treatment for primary hypothyroidism and has been the most commonly prescribed treatment since the 1980s.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Sources

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

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