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Levothyroxine Dosing

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Last Updated: 10 October 2020

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General | Latest Info

In patients with overweight or obesity who undergo total thyroidectomy, choosing Thyroid Hormone replacement dose based on body weight is frequently inaccurate and could be responsible for prolongation OF titration period, according to STUDY results published in Thyroid. After total thyroidectomy, initial dose OF Levothyroxine for Thyroid Hormone replacement therapy is usually based on body weight and the most common formula used is 1. 6 g / kg body weight, without correction for Patients body mass index. However, some studies have shown that patients with obesity have suboptimal response when Hormone Dosing is based on calculations developed for the non - obese population. Researchers in this STUDY aim to develop a proper dosing algorithm for Levothyroxine in patients with obesity. Retrospective STUDY includes patients receiving Thyroid Hormone replacement after total thyroidectomy with no evidence of malignancy. Time to achieve euthyroidism was defined as time from surgery to obtaining first normal Thyroid - stimulating Hormone value. Researchers reviewed charts of patients who underwent total thyroidectomy between July 2011 and December 2015. The final cohort includes 114 patients with final benign pathology and complete follow - up data who achieved euthyroidism. The Mean BMI OF STUDY Patients was 31 kg / m 2 and approximately half had a BMI of 30 kg / m 2, including 23 patients with a BMI OF 31 to 35 kg / m 2, 19 with a BMI OF 35 to 40 kg / m 2, and 13 with BMI > 40 kg / m 2. Patients with higher BMI required higher absolute Levothyroxine dose but dose was significantly lower in relation to weight. The Levothyroxine dose required to achieve euthyrodism according to BMI was: BMI < 25 kg / m 2 1. 76 g / kg; BMI 26 to 30 kg / m 2 1. 47 g / kg; BMI 31 to 35 kg / m 2 1. 42 g / kg; BMI 35 to 40 kg / m 2 1. 27 g / kg; and BMI 40 kg / m 2 1. 28 g / kg. The mean time to achieve euthyroidism was 50 weeks, with no statistically significant difference between BMI categories. Researchers acknowledge several STUDY limitations, including its retrospective design, data collection from electronic medical records, and no available data on compliance with treatment. E recommends using either actual weight OF Patients with adjustment OF Dosing based on BMI or using adjusted body weight without regard to Patients BMI, conclude researchers. Papoian V, Ylli D, Felger EA, Wartofsky L, Rosen JE. Evaluation OF Thyroid Hormone replacement Dosing in overweight and obese Patients after thyroidectomy. Thyroid. Doi: 10. 1089 / thy.

* 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 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

Oral levothyroxine is primarily indicated for treatment of primary, secondary, and tertiary Hypothyroidism. Primary Hypothyroidism is when problems occur in the thyroid gland, with the most common cause being autoimmune condition followed up by iatrogenic Hypothyroidism. Secondary Hypothyroidism is when problem is in the pituitary gland, and there is a decrease in production of thyroid - stimulating hormone. Tertiary Hypothyroidism is very rare, and the problem is in the hypothalamus with decreased production of thyroid releasing hormone. Injectable levothyroxine is for treatment of myxedema coma or severe hypothyroidism.

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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

DESCRIPTION

Table

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

The Synthroid contains synthetic crystalline L - 3 3 55 - tetraiodothyronine sodium salt. Synthetic T4 is chemically identical to that produced in human thyroid gland. Levothyroxine sodium has an empirical formula of C 15 H 10 I 4 N NaO 4 H 2 O, molecular weight of 798. 86, and structural formula as show: SYNTHROID tablets for oral administration are supplied in following strengths: 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, and 300 mcg. Each SYNTHROID tablet contains inactive ingredients acacia, confectioner's sugar, lactose monohydrate, magnesium stearate, povidone, and talc. Synthroid tablets contain no ingredients made from gluten - containing grain. Each tablet strength meets USP Dissolution Test 3. Table 6 provides a listing of color additives by tablet strength:


What is levothyroxine?

Get emergency medical help if you have signs of allergic reaction to levothyroxine: hives; difficult breathing; swelling of your face, lips, tongue, or throat. Fast or irregular heartbeats; chest pain, pain spreading to your jaw or shoulder; shortness of breath; fever, hot flashes, sweating; tremors, or if you feel unusually cold; weakness, tiredness, sleep problems; memory problems, feeling depressed or irritable; headache, leg cramps, muscle aches; feeling nervous or irritable; dryness of your skin or hair, hair loss; irregular menstrual periods; or vomiting, diarrhea, appetite changes, weight changes. Certain side effects may be more likely in older adults. Chest pain, irregular heartbeats; shortness of breath; tremors, muscle pain or weakness; headache, leg cramps; feeling nervous or irritable, trouble sleeping; increased appetite; feeling hot; weight loss; changes in your menstrual periods; diarrhea; or skin rash, partial hair loss. This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1 - 800 - FDA - 1088.

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Limitation of Use 2

The Levothyroxine dose initially required by patient depends primarily on three factors: amount of residual Thyroid function retained by patient, body weight or lean body mass of patient, and target thyrotropin or Thyroid - stimulating hormone level to be achieved during therapy. Additional factors such as patient age, patient sex, and menopausal status may have influence that is generally of lesser magnitude. Other physiological factors such as pregnancy and gastrointestinal functioning may be important factors in specific patients or at specific times. When commencing levothyroxine therapy, initial dose requirements can vary greatly from small doses such as 25 - 50 g in individuals with mild or subclinical disease, where therapy may be supplementing endogenous function, to larger doses of 88 - 175 g in cases of patients with negligible endogenous Thyroid function. In keeping with this concept, initial dose of levothyroxine in patients presenting to the clinic with primary hypothyroidism can be predicted by patients ' TSH value prior to initiation of treatment. In the case of surgically athyreotic patients, dose of levothyroxine required may be slightly higher than in those with autoimmune Thyroid disease, presumably reflecting some retained Thyroid hormone production in those with autoimmune Thyroid disease. Example of the dose requirement in those with Hashimotos thyroiditis without residual function and post - surgical hypothyroidism is approximately 1. 6 g / kg. The dose of levothyroxine required by patients following thyroidectomy can be predicted by either body weight or body mass index. Body weight, BMI, ideal body weight, and lean body mass can all predict initial dose requirement, with the latter three parameters providing more accurate estimates. Various formulae have been proposed to calculate dose requirement. These range from simple formulae based only on body weight or BMI to more complex formulae that also incorporate other factors such as patient sex. Generally, both the TSH - base estimate and body weight - base estimate yield similar initial estimates of dose requirement. With respect to age, for patients who are elderly, have concomitant cardiac disease, or may have had long - standing untreated hypothyroidism, it is wise to initiate levothyroxine therapy with smaller doses such as 25 - 50 g levothyroxine and incrementally increase dose to full replacement to avoid precipitating cardiac ischaemia. Regardless of method used to estimate initial levothyroxine dose requirement, dose adjustment is frequently require. This may be due to multiple factors, including limitations in dose requirement predictions, inter - patient variation, levothyroxine absorption, or effects of concomitant medical conditions or medications. Give half - life of levothyroxine, reassessment of thyroid status by serum TSH levels, and free thyroxine levels if desire, is indicated after 6 weeks of therapy when pharmacokinetic steady state is reach. If TSH is not at the desired goal, levothyroxine dose can be adjusted up or down. Tsh values that are slightly out of range may be correct by single dose increment or decrement, such as increasing from 100 to 112 g or decreasing from 175 to 150 g.

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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

ADMINISTRATION

Hypothyroidism is the result of inadequate production of thyroid hormone and inadequate action of thyroid hormone in target tissues. Primary hypothyroidism is the principal cause of hypothyroidism, but other causes include central deficiency of thyrotropin - releasing hormone or thyroid - stimulating hormone. Subclinical hypothyroidism is present when there is minimally elevated TSH and normal free thyroxin level without clinical manifestation or minimal presentation. Hypothyroidism may be either clinical / overt, with elevation in TSH and low levels of FT4, or subclinical, with normal levels of FT4 and elevated level of TSH. Hypothyroidism can arise as primary from thyroid gland when there is defect in thyroid hormone synthesis and release centrally from hypothalamic - pituitary - thyroid axis when there is defect in either TRH or TSH signaling to the thyroid. Conditions may also be transient or permanent. Iodine deficiency is the most common cause of hypothyroidism worldwide. In people living in iodine - replete areas, causes are congenital, spontaneous because of chronic autoimmune disease or iatrogenic due to goitrogens, drugs, or destructive treatment for hyperthyroidism. Thyroid abnormalities affect considerable people of the population. However, prevalence and pattern of thyroid disorders depend on ethnic and geographical factors, most especially iodine intake. Hypothyroidism is a common endocrine disorder and is more prevalent in elderly women and in certain ethnic groups. Studies in the United States, Europe, and Japan have reported the prevalence of hypothyroidism to be between 0. 6 and 12 per 1000 women and between 1. 3 and 4. 0 per 1000 men. National Health and Nutrition Examination Survey III data estimate the overall prevalence of hypothyroidism to be 4. 6% of the American population is above12 years. The old prevalence of overt hypothyroidism was 0. 3% and subclinical hypothyroidism was 4. 3%. Colorado thyroid disease prevalence Survey reveals similar prevalence of hypothyroidism of 0. 4% in the self - select group not taking thyroid hormone, but much higher prevalence of SCH 8. 5%. In 20 - year survivor follow - up of Wickham cohort in the UK, mean annual incidence of hypothyroidism was found to be 3. 5 per 1000 women and 0. 6 per 1000 men. In a large scale retreospective study in Tayside, UK between 1993 - 1997, overall incidence rate of primary hypothyroidism per 1000 individuals per year was 2. 97 - 4. 98 in females and 0. 88 in males. And incidence of all causes of hypothyroidism ranges between 3. 18 - 3. 53 per 1000 individuals per year. In the UK, over 23 million prescriptions for Levothyroxine were written in 2010, making it the third most prescribed medication after simvastatin and aspirin. In a prospective study on adult population in Tehran, Iran, incidence of overt hypothyroidism and subclinical hypothyroidism were found to be 0. 28 per 1000 and 11. 59 per 1000, respectively. Hypothyroidism is permanent in most patients and requires lifelong thyroid hormone replacement. Replacement with synthetic Levothyroxine is a mainstay of therapy.

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CONTRAINDICATIONS / PRECAUTIONS

Levothyroxine has a narrow therapeutic index. Regardless OF indication for use, careful DOSAGE titration is necessary to avoid consequences of over - or under - treatment. These consequences include, among others, effects on growth and development, cardiovascular function, bone metabolism, reproductive function, cognitive function, emotional state, gastrointestinal function, and on glucose and lipid metabolism. Many drugs interact WITH Levothyroxine Sodium, necessitating adjustments in dosing to maintain therapeutic response. Effects on bone mineral density - in WOMEN, long - term Levothyroxine Sodium therapy has been associated with increased bone resorption, thereby decreasing bone mineral density, especially in post - menopausal WOMEN on greater than replacement doses or in WOMEN who are receiving suppressive doses OF Levothyroxine Sodium. Increase bone resorption may be associated with increased serum levels and urinary excretion of Calcium and phosphorous, elevations in bone alkaline phosphatase and suppressed serum parathyroid hormone levels. Therefore, it is recommended that PATIENTS receiving Levothyroxine Sodium be given the minimum dose necessary to achieve desire clinical and biochemical response. Patients WITH underlying cardiovascular DISEASE - Exercise caution when administering Levothyroxine to PATIENTS WITH cardiovascular disorders and to elderly in whom there is increased risk OF occult CARDIAC DISEASE. In these PATIENTS, Levothyroxine therapy should be Initiate at lower doses than those recommended in younger individuals or in PATIENTS without CARDIAC DISEASE. If CARDIAC symptoms develop or worsen, Levothyroxine dose should be reduced or withheld for one week and then cautiously restart at lower dose. Overtreatment WITH Levothyroxine Sodium may have ADVERSE cardiovascular effects such as increase in heart rate, CARDIAC wall thickness, and CARDIAC contractility and may precipitate Angina or arrhythmias. Patients WITH coronary artery DISEASE who are receiving Levothyroxine therapy should be monitored closely during surgical procedures, since the possibility of precipitating CARDIAC arrhythmias may be greater in those treated WITH Levothyroxine. Concomitant ADMINISTRATION OF Levothyroxine and sympathomimetic agents to PATIENTS WITH coronary artery DISEASE may precipitate coronary insufficiency. Patients WITH nontoxic diffuse goiter or nodular thyroid DISEASE - Exercise caution when administering Levothyroxine to PATIENTS WITH nontoxic diffuse goiter or nodular thyroid DISEASE in order to prevent precipitation OF Thyrotoxicosis. If serum TSH is already suppress, Levothyroxine Sodium should not be administer. Hypothalamic / Pituitary hormone deficiencies - in PATIENTS WITH secondary or tertiary HYPOTHYROIDISM, additional hypothalamic / Pituitary hormone deficiencies should be consider, AND, IF diagnose, treat. Autoimmune polyglandular syndrome - Occasionally, chronic Autoimmune thyroiditis may occur in association with other Autoimmune disorders such as adrenal insufficiency, pernicious Anemia, and insulin - dependent Diabetes mellitus. Patients WITH concomitant adrenal insufficiency should be treated WITH replacement glucocorticoids prior to initiation OF treatment WITH Levothyroxine Sodium. Failure to do so may precipitate acute adrenal crisis when thyroid hormone therapy is Initiate, due to increased metabolic clearance OF glucocorticoids by thyroid hormone. Patients WITH Diabetes mellitus may require upward adjustments to their antidiabetic therapeutic regimens when treated with Levothyroxine. Infants WITH congenital HYPOTHYROIDISM appear to be at increased risk for other congenital anomalies, WITH cardiovascular anomalies being the most common association.

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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

ADVERSE REACTIONS

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. Manufacture 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.


What is levothyroxine?

Generally, hypothyroidism may be effectively treated via constant daily dose of levothyroxine, and, for the majority of confirmed aetiologies, this needs to be lifelong. However, in this setting, there appear to be many cases of both levothyroxine over - and under - dosing and it may be that frequent adjustments of dose are necessary. These adjustments need to be handled with caution and take into account many contributing factors, as multiple levothyroxine dose adjustments evidently result in greater burden on healthcare resources. This means that it is necessary for clinicians to determine which patients are truly in need of dose adjustment. Even more importantly, accumulating evidence suggests that many patients, for whom indication for levothyroxine initiation is not adequately established and diagnosis is not well document, are remaining on levothyroxine therapy for longer than necessary. A prospective clinical cohort follow - up study illustrates this by showing that, among 291 patients on levothyroxine replacement therapy without solid diagnosis of hypothyroidism and in whom treatment was pause, 114 developed hypothyroidism, while 177 participants remain euthyroid. The latter results clearly point to significant overuse of levothyroxine therapy. Overtreatment should particularly be avoided in elderly. A study seeking to determine whether levothyroxine pharmacokinetics are affected by age and weight did not identify any influence of age on levothyroxine dose requirement, though it was determined that weight may mediate age - related changes in levothyroxine pharmacokinetics. In addition, transient changes, inter - and intra - individual differences in Thyroid parameters, or ethnic variations may modify treatment target, thus rendering advisable tailored assessment of Thyroid function. Use of Thyroid extract, rather than levothyroxine, may be associated with overtreatment. In a study of 174 reports of adverse events occurring in patients taking Thyroid hormone extract, 91 of these reports were accompanied by changes in TSH values and, of these, 62 patients had developed new symptoms associated with TSH changes, with most having symptoms consistent with thyrotoxicosis. In a recent case report, authors describe two female patients with Takotsubo cardiomyopathy associated with levothyroxine over - replacement, clearly underlining the necessity to adjust dose of levothyroxine, particularly in patients with cardiovascular risks, so as to avoid deleterious effects of iatrogenic hyperthyroidism. Another point to be considered in overzealously treated patients is the high risk of accelerated bone loss, predominantly in postmenopausal women, as well as the risk of osteoporosis and vertebral fractures. Concerning under - dosage, while overtreatment was not associated with impairment of health - related quality of life, patients who were undertreated had worse HRQoL than overtreated patients, especially regarding physical and emotional aspects, independently of the degree of hypothyroidism. Give that hypothyroidism undertreatment is associated with poor patient HRQoL, it is clear that levothyroxine therapy must be sufficient to maintain serum TSH within reference range. Age - dependent interpretation of TSH values, with appropriate consideration of circadian fluctuations, body weight, gastrointestinal diseases and malabsorption, comorbidity, and possibly pituitary insufficiency or Thyroid hormone resistance, is thus crucial for optimal levothyroxine dosage.

* 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

MECHANISM OF ACTION

Levothyroxine is a synthetic version of the principal thyroid hormone, thyroxine that is made and released by the thyroid gland. Thyroid hormone increases the metabolic rate of cells of all tissues in the body. In fetus and newborn, thyroid hormones are important for growth and development of all tissues, including bones and the brain. In adults, thyroid hormones help to maintain brain function, utilization of food, and body temperature, among other effects. Generic AVAILABLE: Yes. Generic and branded tablets of levothyroxine may differ: in amount of levothyroxine they contain, absorption of levothyroxine into the body, and distribution of levothyroxine throughout the body. This means that ingestion of 1 mg of GENERIC levothyroxine may not have the same effect on the body as 1 mg of another GENERIC or branded levothyroxine. Practically speaking, this means that when changing between levothyroxine manufactured by different pharmaceutical companies, change in dose may be necessary to maintain the desired effect or to prevent toxicity. When switching between brands or generics, it is important to ensure that both preparations are equivalent or to check blood thyroid levels weekly. For adult HYPOTHYROIDISM, levothyroxine starts at 12. 5 - 125 mcg / day administered orally. Starting doses and dose changes may differ WITH individual PATIENTS based upon age, presence of cardiovascular DISEASE, development of tolerance, side effects of medication, and blood levels of thyroid hormone. It may take one to three weeks after initiating therapy WITH levothyroxine or changing dose before effects are see. The goal of replacement therapy is to maintain normal blood thyroxine level. Initiation or discontinuation of therapy WITH levothyroxine in diabetic PATIENTS may create the need for an increase or decrease in the required dose of insulin and / or antidiabetic drug,. Levothyroxine may increase the effect of blood thinners such as warfarin. Therefore, monitoring of blood clotting is necessary, and a decrease in the dose of warfarin may be necessary. Intravenous administration of epinephrine to PATIENTS WITH coronary artery DISEASE may lead to complications ranging from difficulty in breathing to heart attack. These complications may occur more frequently among PATIENTS also taking levothyroxine. Therefore, careful observation is needed when intravenous epinephrine is given to PATIENTS receiving levothyroxine who also have coronary artery DISEASE. Converting the state of HYPOTHYROIDISM to a normal state WITH levothyroxine may decrease actions of certain beta - blocking drugs,. It may be necessary, therefore, to change the dose of beta - blocker. For the same reason, dose of digoxin, drug used to manage heart failure or irregular heart rhythm, also may need to be change. Converting HYPOTHYROIDISM to an euthyroid state WITH levothyroxine may increase the blood level of theophylline, and it may be necessary to change the dose of theophylline. Taking levothyroxine at the same time as calcium carbonate, ferrous sulfate, cholestyramine or colestipol may decrease the effect of levothyroxine and lead to HYPOTHYROIDISM. This occurs because levothyroxine binds to these drugs and is not absorb.

* 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

PHARMACOKINETICS

Absorption of orally administered T4 from gastrointestinal tract ranges from 40% to 80%. The majority of Levothyroxine dose is absorbed from the jejunum and upper ileum. The relative bioavailability of LEVOXYL tablets, compared to equal nominal dose of oral Levothyroxine sodium solution, is approximately 95% to 98%. T4 Absorption is increased by fasting, and decreased 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 thyroxine - binding 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.

* 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

Proper Use

If you will be taking this medicine for a long time, it is very important that your doctor check the progress of you or your child at regular visits. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it. Blood tests will be needed to check for unwanted effects. Levothyroxine should not be used for treatment of obesity or for the purpose of losing weight. This medicine is not effective for weight reduction. If taken in large amounts, levothyroxine may cause serious unwanted effects. Hypothyroidism can sometimes cause infertility in men and women. Levothyroxine should not be used for treatment of infertility unless it is caused by hypothyroidism. For patients with Diabetes: It is very important that you keep track of your blood or urine sugar levels as instructed by your doctor. Check with your doctor right away if you notice any changes in your sugar levels. If you think you have become pregnant while using this medicine, tell your doctor right away. You may need a larger dose of levothyroxine while you are pregnant. Women who are post - menopausal or who use this medicine for a long time may have some bone loss, which could lead to Osteoporosis. Talk with your doctor if you have questions or concerns about this. Call your doctor right away if you or your child start to have rapid or irregular heartbeats, chest pain, leg cramps, headaches, nervousness, irritability, sleeplessness, tremors, change in appetite, weight gain or loss, vomiting, diarrhea, excessive sweating, heat intolerance, fever, changes in menstrual periods, hives, or skin rash. These could be symptoms of too much medicine in your body. Do not suddenly stop taking this medicine without first checking with your doctor. Your doctor may want you or your child to gradually reduce the amount you are using before stopping completely. Make sure any doctor or dentist who treats you knows that you or your child are using this medicine. You or your child may need to stop using this medicine several days before having surgery or medical tests. Temporary loss of hair may occur during the first few months of levothyroxine therapy. Ask your doctor about this if you have any concerns. Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription - medicines and herbal or vitamin supplements.

* 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

2.3 Dosing in Specific Populations

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

Administer TIROSINT as single daily oral dose, on an empty stomach, one - half to one hour before breakfast. Administer TIROSINT at least 4 hours before or after drugs known to interfere with TIROSINT absorption evaluate the need for dose adjustments when regularly administering within hour of certain foods that may affect TIROSINT absorption. Swallow TIROSINT capsules whole, do not cut or crush capsules. The dose of TIROSINT for Hypothyroidism or pituitary TSH suppression depends on a variety of factors including patient's age, body weight, cardiovascular status, concomitant medical conditions, concomitant medications, co - administer food, and specific nature of the condition being treat. Dosing must be individualized to account for these factors and dose adjustments made based on periodic assessment of patient's clinical response and laboratory parameters. The peak therapeutic effect of giving a dose of TIROSINT may not be attained for 4 to 6 weeks. Primary Hypothyroidism in Adults and in Adolescents in Whom Growth and Puberty Are Complete start TIROSINT at full replacement dose in otherwise healthy, non - elderly individuals who have been hypothyroid for only a short time. The average full replacement dose of TIROSINT is approximately 1. 6 mcg per kg per day. Adjust dose by 12. 5 to 25 mcg increments every 4 to 6 weeks until the patient is clinically euthyroid and serum TSH returns to normal. Doses greater than 200 mcg per day are seldom require. Inadequate response to daily doses greater than 300 mcg per day is rare and may indicate poor compliance, malabsorption, drug interactions, or a combination of these factors. For elderly patients or patients with underlying cardiovascular disease, start with a dose of 12. 5 To 25 mcg per day. Increase dose every 6 to 8 weeks, as needed, until the patient is clinically euthyroid and serum TSH returns to normal. The full replacement dose of TIROSINT may be less than 1 mcg per kg per day in elderly patients. In patients with severe longstanding hypothyroidism, start with a dose of 12. 5 To 25 mcg per day. Adjust dose to 12. 5 to 25 mcg increments every 2 to 4 weeks until the patient is clinically euthyroid and serum TSH level is Normalize. Start TIROSINT at full replacement dose in otherwise healthy, non - elderly individuals. Start with a lower dose in elderly patients with underlying cardiovascular disease or patients with severe longstanding Hypothyroidism as described above. Serum TSH is not a reliable measure of TIROSINT dose adequacy in patients with secondary or tertiary Hypothyroidism, and should not be used to monitor therapy. Use serum free - T4 level to monitor adequacy of therapy in this patient population. Titrate TIROSINT dosing per above instructions until patient is clinically euthyroid and serum free - T4 level is restored to the upper half of normal range. Only administer TIROSINT to pediatric patients 6 years and older who are able to swallow intact capsule.

* 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.

Table 1: LEVOXYL Dosing Guidelines for Pediatric Hypothyroidism

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

Thyroid Hormone Replacement

Because thyroid hormones are highly protein bound, medical conditions that alter the amount of binding hormones and drugs that compete for binding may change the amount of available free thyroid hormone. Thyroid replacement dosage must be changed in response to alterations in binding status. With conditions that cause increase in serum binding proteins, such as high estrogen states, oral contraceptive use or postmenopausal estrogen replacement, dosage of levothyroxine must be increase. In contrast, androgens decrease levels of thyroid binding proteins, necessitating reduction in dosage. Older patients also have lower serum protein levels and may require reductions in their maintenance dosage over time. Nephrosis, protein - losing enteropathies and cirrhosis are other conditions that require reduced thyroid hormone dosage. The number of medications reduces absorption of thyroid hormone from the intestines, necessitating an increase in replacement dosage. 21 Other drugs accelerate metabolism of thyroid hormone, and an increase in replacement dosage is then require. When these medications are started or adjust, TSH value should be monitored to determine whether additional thyroid hormone replacement is indicate.

* 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.

* 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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