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Levothyroxine Sodium Capsules Name: Levothyroxine Sodium Capsules - Levothyroxine Sodium Capsules 100 mg - Levothyroxine Sodium Capsules tablet - Levothyroxine Sodium Capsules drug - Levothyroxine Sodium Capsules action - Levothyroxine Sodium Capsules effects of - Levothyroxine Sodium Capsules used to treat - Levothyroxine Sodium Capsules treats - Levothyroxine Sodium Capsules the effects of - Levothyroxine Sodium Capsules missed dose - Levothyroxine Sodium Capsules weight loss Description TIROSINT (levothyroxine sodium) is L-thyroxine. The orally administered gelatin capsules contain synthetic L-3,3',5,5'-tetraiodothyronine sodium salt [levothyroxine (T4) sodium]. Synthetic T4 is chemically identical to that produced in the human thyroid gland. Levothyroxine (T4) sodium has an empirical formula of C15H10I4NNaO4 • x H2O (where x = 5), molecular weight of 798.86 g/mol (anhydrous), and structural formula as shown: The inactive ingredients in TIROSINT are gelatin, glycerin and water. Clinical pharmacology Mechanism of Action Thyroid hormones exert their physiologic actions through control of DNA transcription and protein synthesis. Triiodothyronine (T3) and L-thyroxine (T4) diffuse into the cell nucleus and bind to thyroid receptor proteins attached to DNA. This hormone nuclear receptor complex activates gene transcription and synthesis of messenger RNA and cytoplasmic proteins. The physiological actions of thyroid hormones are produced predominantly by T3, the majority of which (approximately 80%) is derived from T4 by deiodination in peripheral tissues. Pharmacodynamics Thyroid hormone synthesis and secretion is regulated by the hypothalamic-pituitary-thyroid axis. Thyrotropin-releasing hormone (TRH) released from the hypothalamus stimulates secretion of thyrotropin-stimulating hormone (TSH), from the anterior pituitary. TSH, in turn, is the physiologic stimulus for the synthesis and secretion of thyroid hormones, T4 and T3, by the thyroid gland. Circulating serum T3 and T4 levels exert a feedback effect on both TRH and TSH secretion. When serum T3 and T4 levels increase, TRH and TSH secretion decrease. When thyroid hormone levels decrease, TRH and TSH secretion increase. TSH, along with T4 levels and other laboratory and clinical data, is primarily used for both the diagnosis of hypothyroidism and evaluation of levothyroxine therapy adequacy [Dosage and Administration (2.4)]. There are drugs known to affect thyroid hormones and TSH levels by various mechanisms. Some drugs may cause a transient decrease in TSH secretion without hypothyroidism: dopamine ( > 1 mcg per kg per min), glucocorticoids (hydrocortisone > 100 mg per day or equivalent) and octreotide ( > 100 mcg per day). Thyroid hormones regulate multiple metabolic processes and play an essential role in normal growth and development, and normal maturation of the central nervous system and bone. The metabolic actions of thyroid hormones include augmentation of cellular respiration and thermogenesis, as well as metabolism of proteins, carbohydrates, and lipids. The protein anabolic effects of thyroid hormones are essential to normal growth and development. PharmacokineticsAbsorption Absorption of orally administered T4 from the gastrointestinal (GI) tract ranges from 40% to 80%. The majority of the levothyroxine dose is absorbed from the jejunum and upper ileum. The relative bioavailability of TIROSINT capsules compared to another marketed levothyroxine sodium tablet, is approximately 103%. T4 absorption is increased by fasting, and decreased in malabsorption syndromes and by certain foods such as soybeans. Dietary fiber decreases the bioavailability of T4. Absorption may also decrease with age. In addition, many drugs and foods affect T4 absorption. [See DRUG INTERACTIONS]Distribution Circulating thyroid hormones are greater than 99% bound to plasma proteins, including thyroxine-binding globulin (TBG), thyroxine-binding prealbumin (TBPA), and thyroxine-binding albumin (TBA), whose capacities and affinities vary for each hormone. The higher affinity of both TBG and TBPA for T4 partially explains the 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 [See DRUG INTERACTIONS]. Thyroid hormones do not readily cross the placental barrier [See Use In Specific Populations]. Metabolism T4 is slowly eliminated. 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 the major site of degradation for both T4 and T3, with T4 deiodination also occurring at a number of additional sites, including the kidney and other tissues. Approximately 80% of the daily dose of T4 is deiodinated to yield equal amounts of T3 and reverse T3 (r T3). T3 and r T3 are further deiodinated to diiodothyronine. Thyroid hormones are also metabolized via conjugation with glucuronides and sulfates and excreted directly into the bile and gut where they undergo enterohepatic recirculation. Elimination Thyroid hormones are primarily eliminated by the kidneys. A portion of the conjugated hormone reaches the colon unchanged and is eliminated in the feces. Approximately 20% of T4 is eliminated in the stool. Urinary excretion of T4 decreases with age. Table 6: Pharmacokinetic Parameters of Thyroid Hormones in Euthyroid Patients Animal Toxicology and/or Pharmacology No animal toxicology studies have been conducted with Levothyroxine Sodium. What is levothyroxine (levothroid, levoxyl, synthroid, tirosint, unithroid)? Levothyroxine is a replacement for a hormone that is normally produced by your thyroid gland to regulate the body's energy and metabolism. Levothyroxine is given when the thyroid does not produce enough of this hormone on its own. Levothyroxine treats hypothyroidism (low thyroid hormone). Levothyroxine is also used to treat or prevent goiter (enlarged thyroid gland), which can be caused by hormone imbalances, radiation treatment, surgery, or cancer. Levothyroxine should not be used to treat obesity or weight problems. Levothyroxine may also be used for purposes not listed in this medication guide. What is the most important information i should know about levothyroxine (levothroid, levoxyl, synthroid, tirosint, unithroid)? Since thyroid hormone occurs naturally in the body, almost anyone can take levothyroxine. You should not use this medication if you have had a heart attack, a thyroid disorder called thyrotoxicosis, or an adrenal gland problem that is not controlled by treatment. Before you take levothyroxine, tell your doctor if you have a serious thyroid disorder (thyrotoxicosis), heart disease, coronary artery disease, diabetes, anemia, problems with your pituitary or adrenal glands, a history of blood clots, if you have recently had a heart attack, or if you are having any symptoms of a heart attack (chest pain or heavy feeling, pain spreading to the arm or shoulder, nausea, sweating, general ill feeling). If you use insulin or take diabetes medicine by mouth, ask your doctor if your dose needs to be changed when you start using levothyroxine. Different brands of levothyroxine may not work the same. If you get a prescription refill and your new pills look different, talk with your pharmacist or doctor. It may take several weeks before your body starts to respond to this medication. Do not stop taking the medicine suddenly, even if you feel well. Many other medicines can be affected by your thyroid hormone levels. Other medicine may also increase or decrease the effects of levothyroxine. Tell your doctor about all medications you use, start using, or stop using during your treatment with levothyroxine. This includes prescription, over-the-counter, vitamin, and herbal products. Keep a list of all your medicines and show it to any healthcare provider who treats you. What happens if i miss a dose (levothroid, levoxyl, synthroid, tirosint, unithroid)? Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose. Side effects Common adverse reactions with levothyroxine therapy are primarily those of hyperthyroidism due to therapeutic overdosage [See OVERDOSAGE]. They include the following: - General: fatigue, increased appetite, weight loss, heat intolerance, fever, excessive sweating - Central nervous system: headache, hyperactivity, nervousness, anxiety, irritability, emotional lability, insomnia - Musculoskeletal: tremors, muscle weakness - Cardiovascular: palpitations, tachycardia, arrhythmias, increased pulse and blood pressure, heart failure, angina, myocardial infarction, cardiac arrest - Respiratory: dyspnea - Gastrointestinal (GI): diarrhea, vomiting, abdominal cramps, elevations in liver function tests - Dermatologic: hair loss, flushing - Endocrine: decreased bone mineral density - Reproductive: menstrual irregularities, impaired fertility Pseudotumor cerebri and slipped capital femoral epiphysis have been reported in children receiving levothyroxine therapy. Overtreatment may result in craniosynostosis in infants and premature closure of the epiphyses in children with resultant compromised adult height. Seizures have been reported rarely with the institution of levothyroxine therapy. Hypersensitivity Reactions Hypersensitivity reactions to inactive ingredients (in this product or other levothyroxine products) have occurred in patients treated with thyroid hormone products. These include urticaria, pruritus, skin rash, flushing, angioedema, various GI symptoms (abdominal pain, nausea, vomiting and diarrhea), fever, arthralgia, serum sickness and wheezing. Hypersensitivity to levothyroxine itself is not known to occur. Read the entire FDA prescribing information for Tirosint (Levothyroxine Sodium Capsules)Read More »
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Hipotireoza – nadomjesno liječenje levotiroksinom (Euthyrox™, Thyraq™, Letrox™) Hipotireoza je stanje kojeg karakterizira snižena razina hormona štitnjače do kojeg dolazi zbog nedostatne sinteze i lučenja istih od strane štitnjače. Bez obzira na uzroke hipotireoze, liječenje se uvijek provodi oralnim nadomjestkom hormona štitnjače – levotiroksinom. Levotiroksin, koji se na našem tržištu može nabaviti pod imenima Euthyrox™, Thyraq™ i Letrox™, je sintetska forma hormona terajodotironina (T4) i kao takav se nimalo ne razlikuje od hormona koji proizvodi sama štitnjača. Isto kao i T4, prirodnim putem se metabolizira se u T3, čime se nadomješta i manjak ovoga hormona. Nadomjesno liječenje levotiroksinom je idealan način za kompenziranje hipotireoze jer levotiroksin ima dosta dugo vrijeme poluživota u krvi – oko 7 dana, što podrazumijeva da se idealna razina hormona štitnjače može postići uzimanjem samo jedne doze dnevno. Uzimanje kombinacije levotiroskina i trijodotironina (T3) jednostavno ne bi dalo isti rezultat jer je vrijeme poluživota T3 puno kraće (manje od jednog dana) što bi zahtijevalo uzimanje nekoliko doza hormona tijekom dana. Također, ne preporuča se uzimanje tzv. prirodnih preparata hormona štitnjače. Dolazi u obliku tablete koju bi trebalo uzimati ujutro “na tašte” barem pola sata prije obroka, prvenstveno iz razloga što se značajno slabije apsorbira ukoliko se uzima zajedno s obrokom. Levotiroksin, obzirom da je kemijski identičan endogenom T4, nema gotovo nikakvih nuspojava osim onih vezanih uz davanje prevelike doze, a potpuno je siguran za uzimanje tijekom trudnoće.