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Should levothyroxine dose be individualized on the basis of clinical response and biochemical tests? What if a woman gets pregnant? What if you encounter heart problems or have to take medications for other medical conditions?

Levothyroxine is an artificial hormone made by chemical synthesis to resemble the natural thyroid hormone. It's a medication commonly used by people with underactive thyroid gland – a disease known as hypothyroidism. The medication has three ways of application:

  • Levothyroxine tablets
  • Levothyroxine capsules
  • Levothyroxine injection solution

Levothyroxine tablets are a common therapy for an underactive thyroid. They are sometimes prescribed to ease the symptoms of goiter, as well as a treatment for thyroid cancer. 

The medication is available under several brand names such as Synthroid, Unithroid, and Levoxyl, but it usually comes under its generic name – levothyroxine sodium.

Even though dosage tips of levothyroxine tablets may sound easy, beginning your treatment isn't that simple because the initial dose differs among patients. For many people, a lower amount of levothyroxine may be mild and inefficient, and high doses may be aggressive and cause heart issues and decreased bone density. 

This is why the dose of levothyroxine is determined after the examination of several factors such as: 

  • The age of a person
  • The person's body weight
  • The intensity of the disease
  • Other drugs and forms of therapy
  • Other possible health complications

When recommending levothyroxine for the first time, your physician will probably prescribe a low dose of the medication and slowly elevate it while the time passes and the body starts regulating the levels of your thyroid hormone.

As soon as you and your physician establish the perfect dosage for your specific case, you probably won't have to see each other that much. Once the dose is established, it will probably stay the same for years.

If you don't get pregnant, acquire some cardiac disease, or start with some form of hormone therapy, big chances are that once established dose of levothyroxine won't change for the rest of your life.

Levothyroxine dosage in adults 

The average full replacement dosage of levothyroxine for adults is 1.7 micrograms per kilogram of body weight (which would be around 100 micrograms for a person that weighs 70 kg). Total replacement therapy is conducted in otherwise healthy people younger than 50 years, and those older than 50 with no previous problems with thyroid health. 

It is advised to be careful when first recommending levothyroxine to older people, especially those with heart conditions or a life-long battle with an underactive thyroid. This is where doctors advise the low amounts of the medication to be applied first and suggest to elevate the dosage slightly over time, entirely under their supervision.

Elderly people with hypothyroidism may need smaller doses of levothyroxine because of their decreasing bone density. Research has found a correlation between levothyroxine and broken bones in an elderly population, so it is recommended to give these patients no more than 1 microgram of their body weight per day. 

When it comes to patients with heart conditions, the oral dosage of levothyroxine should be somewhere between 25 and 50 micrograms of their body weight. It is recommended to gradually elevate the amount of levothyroxine only after six to eight weeks, and only if absolutely necessary.

The starting amount of levothyroxine for people with a severely underactive thyroid gland is 12.5 to 50 micrograms a day, a dose that can be elevated gradually once or twice per month if necessary until the levels of thyroid-stimulating hormone are back on track.

Levothyroxine and children

If you decide to put your child on levothyroxine therapy, you should grind the tablet and blend it with some water (two teaspoons are often enough). You shouldn't put the drug into a child's formula or any type of food. It is recommended to give the solution to a child as soon as it's ready.

The established amounts of levothyroxine for pediatric inherited cases of the underactive thyroid gland are:

  • From birth to three months: 10 to 15 micrograms for one kilogram of a child's body weight daily
  • Three to six months: eight to 10 micrograms per kilogram
  • Six months to one year of age: six to eight micrograms per kilogram
  • From 12 months until the fifth birthday: five to six micrograms per kilogram
  • Six to 12 years: four to five micrograms per kilogram
  • For children older than 12 years: two to three micrograms per kilogram
  • After adolescence: 1.7 micrograms per kilo of body weight taken daily

Children with the possibility of some cardiac condition should be given low doses of levothyroxine.
Children with acute and long-existing hypothyroidism should have 25 micrograms of the medication per body weight once a day, and the dose should be elevated gradually once or twice a month until the thyroid-stimulating hormone levels are normalized.

Levothyroxine and heart conditions

Both underactive thyroid and heart conditions can benefit from therapy with levothyroxine, you just have to be careful and start your therapy with small amounts of the medication. It's advised to first undergo some screenings for heart problems such as an angiogram or cardiac stress test, and patients with coronary artery disease should undergo vascular surgical operation prior to the levothyroxine treatment. Also, it's good to closely observe those under levothyroxine therapy, as thyroid issues can disturb the heart as well. All things considered, most endocrinologists agree on one thing: the benefits of levothyroxine treatment in people with hypothyroid heart exceed the possible side effects.

Levothyroxine and pregnancy

Treating hypothyroidism in pregnancy should be a priority for expecting mothers because underactive thyroid can be dangerous for both mother and child. Without the proper treatment, a woman can even lose her baby. Pregnancy requires quite high levels of thyroid-stimulating hormone. Even in completely healthy women with a normally functioning thyroid gland, the thyroid works overtime to fulfill this sudden requirement. For patients with an underactive thyroid, Levothyroxine dosage should be much higher than it was before getting pregnant.

Most experts recommend that pregnant patients increase their Levothyroxine dosage as soon as they find out about their new condition. It's also recommended to keep track of your thyroid-stimulating hormone during the whole pregnancy.

What if I accidentally skip a dose?

For the best effect, it's recommended to take levothyroxine every day around the same time. If you – for some reason – skipped a dose, you shouldn't worry too much, just make sure that this happens rarely. Take your skipped dosage as soon as you remember, and never ingest more levothyroxine at once to compensate for the amount that you forgot.

Overdosing with levothyroxine

Ingesting more drug than recommended by your physician is officially considered an overdose. Ingesting levothyroxine in doses higher than recommended may lead to symptoms similar to those in hyperthyroidism such as:

  • Tiredness
  • Temperature intolerance
  • Increased perspiration
  • Food cravings
  • Feeling lost and confused
  • Severe consequences like coma and even death.

Levothyroxine and other drugs

Taking levothyroxine too close to other medications may cause certain adverse reactions. Some of these medications include:

  • Drugs commonly used to treat depression because they can cause arrhythmia
  • Albuterol and pseudoephedrine, commonly used to treat breathing problems, because they may cause various cardiac issues.
  • Ketamin – because it can increase your heart rate and cause hypertension.
  • Warfarin and other anticoagulants because they may cause bleeding.

There are medications that can cause malabsorption of levothyroxine such as anticonvulsants (used to treat seizures), medications that relieve stomach acidity and contain aluminum and magnesium hydroxide, as well as a few medications used in the treatment of cancer.
On the other hand, levothyroxine can make some drugs non-effective, especially drugs commonly used by diabetics such as metformin or insulin.

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