levothyroxine-Treatment of hypothyroidism in 2020

Hypothyroidism is a condition where in your thyroid gland becomes underactive and makes less amount or no thyroid hormone at all.

As the thyroid hormone is very much important for normal functioning of the body it is very important to treat it.

The best treatment is providing the body with synthetic or readymade thyroid hormone in the form of levothyroxine.

ALL YOU NEED TO KNOW ABOUT LEVOTHYROXINE as treatment of hypothyroidism.

Mechanism of action:

Levothyroxine is synthetic form of the T4 (thyroxine).

In the body the active form of thyroid hormone is T3 (triiodothyronin).

Levothyroxine in the body will get converted to its active form L-triiodothyronin.

Thyroid hormone brings about its metabolic effects by binding to the thyroid receptors present in the nucleus of the cell.

Pharmacokinetics of thyroxine

[Pharmacokinetics refer  to  what happens to the drug in the body which includes absorption of the drug, distribution of drug, binding or localization or storage of drug, its bio transformation or the chemical alteration of the drug in the body, and finally excretion of the drug out of the body.]

Absorption of levothyroxine

When given orally 40-80% of the drug is absorbed through the intestines, especially from jejunum and upper part of ileum.

The absorption of levothyroxine can be affected by various factors.

Levothyroxine absorption is decreased by:

  • increasing age
  • certain types of food like dietary fibers, grapefruit juice, walnuts, soy, soyabean flour, cotton seed meal,cows milk etc
  • malabsorption syndrome
  • certain drugs like iron, calcium, sucralfate, proton pump inhibitors etc

levothyroxine absorption is increased when given on empty stomach.

Therefore the doctor will always tell you to take you tablet in the morning 1hour before your breakfast.

Distribution of L-thyroxine

In the blood the 99% of the thyroid hormone is present in a metabolically inactive form, this is because they are bound to plasma proteins which make them inactive.

The remaining free form of thyroid hormone is the one which is metabolically active.

The thyroid hormone binds to  thyroxine binding globulin, transthyretin and albumin.


Breakdown of thyroid hormone occurs in the liver and also kidney.

Thyroid hormone is broken down by a process called sequential deiodination.CYP3A4 inducer drugs such as phenytoin, rifampin, carbamazepine will accelerate the metabolism of levothyroxine.


Thyroid hormone is excreted in urine by the kidneys and some amount goes in the bile which gets excreted in the stools.

Drug interaction

Drugs which makes the levothyroxine less effective:

  • – Ferrous sulphate and iron suppliments.
  • – Calcium carbonate
  • – Cholestyramine, colestipol.
  • – Rifampicin
  • – Carbamazepine and Phenobarbital.
  • – Sucralfate
  • – Proton pump inhibitor drugs like omeprazle, esomeprazole, rabeprazole etc
  • – Aluminun and magnesium containing antacids like milk of magnesia.
  • – matinib (anticancer drug)

NOTE :in this cases the dose of levothyroxine has to be increased.

Drugs which interects with levothyroxine during treatment of hypothyroidism are:

  • – When given along with ketamine it causes hypertension (high blood pressure )and tachycardia (increased heart rate).
  • – Toxicity is seen when given along with tricyclic and tetracyclic antidepressants.
  • – Levothyroxine is inhibited by lithium.
  • – Warfarin, digoxin if given along with levothyroxine will increase risk  of bleeding.

Uses of L-thyroxine

1.The main use of levothyroxine is in the treatment of hypothyroidism.

  • Patient is often started on a low dose 25mg -50mg  of levothyroxine  daily and then gradually increasing the dose to 100mg – 200mg  over 2-3week.
  • The dose adjustment is done by monitoring the clinical response and the serum TSH levels.
  • It takes more 4-6 wks to achieve a steady state concentration in the blood.
  • check the TSH levels in 6weeks and follow up with your health care provider.

2.Myxedema coma

  • It is a medical emergency.
  • This condition occurs due to acute hypothyroidism.
  • It can cause progressive mental deterioration and even death.
  • It is treated by giving rapid replacement of thyroid hormone by giving levothyroxine.
  • Dose: 200-500 mg injection intravenously followed by 100mg injection intravenously once daily till oral drug can be given OR 500mg of levothyroxine orally as loading dose followed by 100-300mg  orally once a day can be given.
  • As the time taken for absorption of oral levothyroxine is more than that of the intravenous dose , injections of levothyroxine is preferred in treatment of severe hypothyroidism .


When hypothyroidism is detected in an infant or a child it is called cretinism.

Cretinism can be divided into two types on the basis of its causative factor:

  • Sporadic cretinism -is due to the result of failure of development of thyroid gland or due to any defect in the thyroid hormone synthesis.
  • Endemic cretinism – is due to extreme iodine deficiency in the mother. (this type of cretinism is preventable by ensuring intake of 150-200mg of iodine daily by the pregnant women. This is done by iodising the salt by adding iodate to it )

As thyroid hormone plays a crucial role in growth the development , these children must be started on levothyroxine therapy  as soon as possible.

Dose: 8-12mg/kg body weight given daily.

If treatment started early in life  it will help restore the growth and development of the child and to some extent can also reverse the mental retardation.

4.Hypothyroidism during pregnancy

Levothyroixine is category A drug in pregnancy therefore it is safe to be taken during pregnancy and lactation.

The requirement of thyroid hormone during  pregnancy is increases. Therefore your doctor might increase your dose of levothyroxine to meet the needs of the body.


6.Thyroid nodule

7.Papillary carcinoma of thyroid

Side effects of levothyroxine

1.Due to allergy to levothyroxine

  • Swelling of the face, eyes, lips.
  • Swelling of the larynx (part of wind pipe) this will cause difficulty in breathing.
  • Swelling of tongue this will also contribute to breathlessness.
  • Skin itching,rash or redness of skin.
  • Chest discomfort, or chest pain.
  • Difficulty in swallowing.
  • Thightness in chest
  • Irregular breathing.
  • Decreased urine output
  • Nausea, vomiting
  • Joint pain


2.Due to high dose of levothyroxine

  • Overtreatment of hypothyroidism with levothyroxine can lead to hyperthyroidism.
  • All the symptoms of hyperthyroidism are present such as: increased heart rate, anxiety, irritability, weight loss, lack of sleep, increased appetite, confusion etc
  • Extreme tiredness and fatigue
  • Nausea
  • Fast or slow irregular heart beats

3.Due to overdose of levothyroxine

  • Fever
  • Headache
  • Loss of coordination
  • Slurring of speech
  • Skin becomes cold and clammy
  • confusion
  • Decreased blood sugar levels
  • Heart failure
  • Coma

Other side effects of treatment of hypothyroidism include:

  • Pain and discomfort in the muscles, joints, back etc.
  • Tremors
  • Blurry vision
  • Seizures severe headache

Less common side effects of treatment of hypothyroidism are:

  • Headache
  • Muscle aches
  • Muscle weakness
  • Rapid mood changes
  • Restlessness
  • Diarrhea
  • Stomach cramps
  • Vomiting
  • Excessive tiredness and weakness

Side effects caused by overdose and high dose can be prevented by doing TSH

Reports evry 6months and adjusting the thyroid dose accordingly after taking advice from your doctor

Contraindications of L-thyroxine

  • Allergy to levothyroxine
  • Hyperthyroidism
  • Heart conditions like history of heart attack
  • People with diabetes
  • People with osteoporosis
  • People who have adrenal or pituitary problem
  • People with caugulation disorders

Symptomatic treatment of hypothyroidism

Treatment can be given to the patient to relieve the symptoms caused by the lack of thyroid hormone.


  • Sedentary lifestyle will also contribute to the increasing weight.
  • Some amount of exercise may help in trying to lose weight.
  • Daily walking or jogging or doing other exercises will keep you healthy and prevent obesity.
  • Eat healthy food and avoid oily food, junk food etc


  • Eat healthy diet and drink lots of water.
  • If the constipation remains  for long  u can try taking laxative or an enema, try to avoid sucralfate.


  • Keep the skin moist by applying moisturizing cream or lactocalamine lotion.
  • Drink sufficient amount of water to stay hydrated.


  • Apply pain relieving ointment
  • Hot compresses or application of ice pack might also help


  • Apply pain relieving ointment.
  • For stiffness physiotherapy may help.


  • Patient with depression should seek help from a physician.
  • If the depression is very severe then the patient might have to be started on anti-depression medications.

GOITER (diffuse enlargement of thyroid gland)

  • If goiter is large enough to cause pressure symptoms it should be removed by doing thyroidectomy surgery.

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