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Thursday, November 14, 2019

Levothyroxine Sodium: Uses, Indications, Dosages, Precautions, contraindications, Side Effects & Interactions

         



Levothyroxine Sodium





Levothyroxine Soduim
(lee-voh-thigh-ROX-een SO-dee-um)
T4, L-ThyroxineHormone (thyroid)


Eltroxin (CAN), Levo-T, Levothroid, Levoxyl, PMS-Levothyroxine Sodium (CAN), Synthroid, Unithroid


General Information


Levothyroxine is the main hormone produced by the thyroid gland. A deficiency in the natural hormone causes hypothyroidism, which is associated with symptoms such as weight gain and reduced bodily functions. A synthetic preparation is administered to replace the natural hormone when it is deficient. It is also sometimes given in association with Carbimazole or Propylthiouracil in the treatment of an overactive thyroid gland. Levothyroxine is also administered (in higher doses) to people who have had thyroid cancer. Levothyroxine doses are generally increased gradually to help prevent side effects and special attention is required in patients with heart problems such as angina


Action


Check protein synthesis; increases metabolism, cardiac output, renal blood flow, O2 consumption, body temperature, blood volume, growth, development at the cellular level through the action on the thyroid hormone receptors

Therapeutic result: correction of the lack of thyroid hormone


Availability (Rx)


• Capsules (Tirosint): 13 mcg, 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112mcg, 125 mcg, 137mcg or 150 mcg
• Injection, Powder for Reconstitution: 100mcg, 200 mcg, 500 mcg. Tablets: 25mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg,112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200mcg, 300 mcg


Uses


Hypothyroidism, myxedema coma, thyroid hormone replacement, thyrotoxicosis, congenital hypothyroidism, some types of thyroid cancer, suppression of pituitary TSH (usually administered orally)


Indications and Dosages

‣  Mild hypothyroidism

Tablets

Adults 

Initial: 50 mcg per day, increased from 25 to 50 mcg every 2-3 weeks until the desired response occurs or the therapeutic blood level is reached. Maintenance: from 75 to 125 mcg per day

Dose adjustment: for elderly patients and those with cardiovascular disease or chronic hypothyroidism, the starting dose is generally reduced from 12.5 to 25 mcg per day and then increased from 12.5 to 25 mcg every 3-4 weeks until response desired. For the elderly patients, the maintenance dose is limited to 75 mcg per day


Usual pediatric dose

Note: the dosage is highly personalized and based on body weight and age (see manufacturer's dosage). The following information represents common ranges observed at each age

Child ˃12 years: PO 2-3 mcg / kg / day administered in a single dose am

Usual: 150 to 200 mcg per day

6-12 year old boy: PO 4-5 mcg / kg / day administered as a single dose am

Usual: 100 to 150 mcg per day

Children from 1 to 5 years: PO from 5 to 6 mcg / kg / day administered in a single dose am

Usual: 75 to 100 mcg per day

Children 6-12 months: PO 6-8 mcg / kg / day administered in a single dose am

Usual: 50-75 mcg / day

Children ˂6 months: PO 8-10 mcg / kg / day administered in a single dose am

Normal: 25-50 mcg / day

Children 3 months and younger

Usual: 10-15 mcg / day


‣ Severe hypothyroidism


Adults ˂50 years

Initial: 12.5 to 25 mcg per day. Increased by 25 mcg every 2-3 weeks until the desired response occurs or the therapeutic blood level is reached. Maintenance: from 75 to 125 mcg per day. Maximum: 200 mcg per day

Adult 50 years

No heart disease or 50 year with heart disease: PO 25-50 mcg / day, head q6-8wk

Adult ˃50 years

With heart disease: PO 12.5-25 mcg / day, value at 12.5-25 mcg q6-8wk


Usual pediatric dose

Note: the dosage is highly personalized and based on body weight and age (see manufacturer's dosage). The following information represents common ranges observed at each age

Child ˃12 years

PO 2-3 mcg / kg / day administered in a single dose am

Usual: 150 to 200 mcg per day

6-12 year old boy

PO 4-5 mcg / kg / day administered as a single dose am

Usual: 100 to 150 mcg per day

Children from 1 to 5 years

PO from 5 to 6 mcg / kg / day administered in a single dose am

Usual: 75 to 100 mcg per day

Children 6-12 months

PO 6-8 mcg / kg / day administered in a single dose am

Usual: 50-75 mcg / day

Children ˂6 months

PO 8-10 mcg / kg / day administered in a single dose am

Usual: 25-50 mcg / day

Children 3 months and younger

usual: 10-15 mcg / day



I.V. or I.M.injection

Adults 

50 to 100 mcg per day until reaching the therapeutic level in the blood

Children 

75% P.O. dose daily until it reaches the therapeutic level in the blood


‣ Myxedema Coma


I.V. injection

Adults 

200 to 500 mcg per day 1. If there is no significant improvement, 100 to 300 mcg in day 2. The daily dose continued as prescribed until the therapeutic level of blood and P.O. Administration is tolerated

Children

75% P.O. daily dose up to the therapeutic blood level and P.O. Administration is tolerated


‣ Suppression of thyroid stimulating hormone in thyroid cancer, nodules, euthyroid

PO

Adults, the elderly

2-6 mcg / kg / day for 7-10 days


‣ Usual IV maintenance dose  IV

Adults, elderly, children. Starting dose about half of the previously established oral dose


P.O. Route

Onset: 3-5 days, peak: 3-4 weeks Duration: 1-3 weeks

I.V. Route

Onset: 6–8 h, Peak: 24 h, Duration: unknown

I.M. Route

Onset: unknown, peak: unknown, duration: 1-3 weeks


Contraindications


Hypersensitivity to tablet components, such as tartrazine. Acute myocardial infarction, unopened or open subclinical thyrotoxicosis, incorrect adrenal insufficiency (can cause acute adrenal crisis); myocardial infarction and thyrotoxicosis without complications from hypothyroidism, treatment of obesity


Drug / Laboratory interactions

Individual Drugs


adrenocorticoids: possibly adjustments in the dose of adrenocorticoids as the thyroid status changes antacids containing aluminum and magnesium, bile acid sequestrants, calcium carbonate, cation exchange resins, cholestyramine, colestipol, ferrous sulphate, kayexalate, orlistat, sucralfate: possible reduced effects of levothyroxine amiodarone, iodine: possibly hyperthyroidism

beta-blockers: possibly impaired action of beta-blockers and reduction of the conversion of T4 to triiodothyronine (T3)

Drug Classifications


• Antidiabetic drugs: when thyroid replacement occurs, antidiabetic requirements may change; monitor 

• Cholestyramine, colestipol, enteral nutrition, antacids, calcium

• Iron supplements: may reduce the absorption of levothyroxine. Separate administration times

• Digoxin: can alter the required dose of digoxin as thyroid function is corrected due to the increase in the metabolic rate; monitor.

 Estrogen: decrease in the effects of the thyroid hormone. Selective serotonin reuptake inhibitors: reduction of the effects of levothyroxine

 Oral anticoagulants: can alter the effects of oral anticoagulants

 Sympathomimetics: may increase the risk of coronary insufficiency

 Antiepileptic medicines These medicines can reduce the effect of levothyroxine

 Sucralfate The absorption of levothyroxine can be reduced with sucralfate

 Antidepressants Levothyroxine can increase the effects of tricyclic antidepressants

 Oral contraceptives can increase the need for levothyroxine


Drug / Herb

Decrease: effect of thyroid hormone: soy


Drug / Laboratory tests


Increase: CPK, LDH, AST, blood sugar
Decrease: thyroid function test

Foods

Coffee, dairy products, soy flour (formula for infants), cotton seed flour, nuts and dietary fiber, nuts: possible reduction of the absorption of levothyroxine from the gastrointestinal tract


Precautions

Pregnancy A, breastfeeding, geriatric, angina, hypertension, ischemia, heart disease, other cardiovascular diseases, adrenal insufficiency, myxedema, diabetes mellitus and tasteless, swallowing disorders  

Make sure to tell your doctor if:
• You have high blood pressure
• You have heart problems
• Do you have diabetes
• You are taking other medications

Maternal / newborn:

Category A: can be used during pregnancy


  • Presumed safe during breastfeeding; Pay attention and watch the baby. The drug passes into breast milk, but adverse effects on the baby are unlikely, when normal doses. Talk to your doctor
  • Myxedema coma is a disease of the elderly. An approved oral dosage form


It should be used in pediatric patients to maintain an euthyroid state in simple hypothyroidism

Elderly


More sensitive to effects. Atrial fibrillation is a common side effect related with levothyroxine treatment in the elderly



Administration / Management

IV Route

Reconstitution

Administer IV after dilution with the diluent provided (0.9% NaCl), 500 mcg / 5 ml, 200 mcg / 2 ml; shake well; administer through a Y-tube or a 3-way tap; give 100 mcg or less for 1 minute; do not add to IV infusion; It is considered incompatible in the syringe with all other products

Rate of Administration


  • Use immediately; discard unused portions
  • Give each 100 mcg or less for 1 minute

Storage

Store the vials at room temperature

PO Route



  • In am if possible as single dose to decrease sleeplessness; at same time each day to maintain product level; take on empty stomach
  • Administer before breakfast to prevent insomnia
  • Only for hormonal imbalances; it should not be used for obesity, male infertility, menstrual conditions, lethargy
  • Lower dose that relieves symptoms; lower dose for geriatric patients and for those with heart disease
  • Crush and mix with water; non-dairy formula or breast milk for babies, children
  • Take 4 hours minimum between antacids, iron, calcium supplements

! Do not interchangeably use different brands of levothyroxine, although the bioequivalence problems between manufacturers are minimized with the current manufacturing process. It is better for patients to use the same product during treatment or to be carefully monitored during product changes. Start small dose therapy and gradually increase the dose as prescribed


Pharmacokinetics



  • Absorption: irregular (PO); complete (IV)
  • Distribution: widely distributed
  • Metabolism: liver; enterohepatic recirculation
  • Excretion: stool through bile; breast milk (small quantities)
  • Half-life: 6-7 days


Side Effects


• CNS: fatigue, headache, dizziness, involuntary movements, confusion, tremor, drowsiness, euphoria, convulsions, tremors

• CV: hypotension, heart block, CV collapse, bradycardia, arrest 

•  EENT: tinnitus, blurred vision

• GI: nausea, vomiting, anorexia

• HEMA: methemoglobinemia

• INTEG: skin rash, urticaria, edema, swelling, petechiae, itching

• MISC: febrile response, phlebitis at inj site

• RESP: dyspnea, respiratory depression



Nursing considerations

Baseline Assessment

Obtain baseline TSH, T3, T4, weight, vital signs. Signs / symptoms of diabetes, diabetes insipidus, adrenal insufficiency, hypopituitarism may intensify. Dealing with adrenocortical steroids prior to thyroid therapy in coexisting hypothyroidism and hypoadrenalism

Intervention / Evaluation

 Determine whether the patient is taking anticoagulants, antidiabetic agents; document in the table. Take B / P, pulse before each dose; Monitor the I&O report and weight every day with the same clothes, using the same scale, at the same time of day

T3, T4, FTI, which have decreased; TSH radioimmunoassay, which increases; radioabsorption, which increases if the patient receives too low a dose of medication

 Monitor pro-time (may require an anticoagulant reduction); bleeding control, bruising  Evaluate the increase in nervousness, excitability, irritability, which may indicate a too high dose of drugs, usually after 1-3 weeks of treatment

 Evaluate cardiac status: angina, palpitations, chest pain, VS change; the geriatric patient heart problems may be undetected and baseline ECG should be completed before treatment

Children

(Undertreatment): May decrease intellectual development, linear growth
(Overtreatment): adversely affects brain maturation, accelerates bone age


Monitor Thyroid Function Tests


Therapeutic response: absence of depression; increased weight loss, urine production, pulse, appetite; absence of constipation, peripheral edema, intolerance to cold; pale, cold, dry skin; brittle nails, alopecia, thick hair, menorrhagia, night blindness, paraesthesia, syncope, amazement, coma, rosy cheeks


Patient / Family education


 Teach the patient that the product is not a cure but controls the symptoms and that the treatment is long term

 Instruct the patient to report excitability, irritability, anxiety, sweating, heat intolerance, chest pain, palpitations, which indicate an overdose

 Follow-up visits to the office, thyroid function tests are essential

 Take your medications at the same time every day, preferably in the morning

 Advise the patient not to change brands unless approved by the prescriber; bioavailability can differ from; do not take with food; Absorption will decrease

• Teach the patient that the product can be suspended after childbirth; will be the thyroid panel evaluated after 1-2 months

 Monitor pulse for rate, rhythm; reports irregular rhythm or pulse greater than 100 beats / min

 Promptly report chest pain, weight loss, anxiety, tremors, insomnia

• Tell patient to notify prescriber if rash or hives develop during drug use

• Inform the patient that temporary hair loss may occur during the first few months of levothyroxine therapy

• Inform the woman of childbearing  age to notify the doctor immediately if she is pregnant as the dose of levothyroxine may need to be increased

• Teach the patient that the product should not be taken to reduce weight

• Advise the patient to avoid iodine over the counter preparations; read the labels; to separate antacids, iron, calcium based products for 4 hours

• Advise the patient To avoid iodine-rich foods, iodized salt, soy, tofu, turnips, iodine-rich seafood, bread

• Children may present reversible hair loss, increased aggression during the first one few months of therapy

• The complete therapeutic effect can take 1 to 3 weeks


Antidote


Inform the doctor of any side effects. A reduction in dosage generally reduces symptoms. Supportive treatment should be started according to the patient's medical condition


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