The drug is available under the brand names Levothroid, Levoxyl, Levo-T, Synthroid, Tirosint, and Unithroid.
Thyroid hormones affect the metabolism of protein, fats, and carbohydrates. They also affect a person's growth and development.
If untreated, hypothyroidism can lead to poor growth, slow speech, loss of energy, weight gain, hair loss, dry skin, and increased sensitivity to cold temperatures.
Levothyroxine can help reverse these symptoms. The drug can also help treat the congenital form of hypothyroidism, as well as an enlarged thyroid gland (goiter) and thyroid cancer.
Levothyroxine has been available in the United States since the 1950s, but the Food and Drug Administration (FDA) didn't approve it until 2000.
Levothyroxine Warnings
Thyroid hormone is not a treatment for obesity, and people with normal thyroid function should not take levothyroxine.If you have a healthy thyroid and take levothyroxine, you could develop life-threatening side effects. This is particularly true if you take the drug with amphetamines.
Although levothyroxine treats an underactive thyroid, it's not a cure for the condition. You should also understand that it may take several weeks before you see an improvement in your symptoms.
Women on long-term levothyroxine therapy may be at greater risk for osteoporosis. Over time, the drug can lead to a decrease in bone mineral density.
A study published in 2014 in the Journal of Preventive Medicine & Public Health investigated the link between the risk for broken bones and levothyroxine use among older women with underactive thyroids.
The researchers concluded that doctors should be particularly concerned about the overuse of levothyroxine in older women with osteoporosis.
Before taking levothyroxine, tell your doctor if you've ever had:
- Diabetes
- Heart disease, such as atherosclerosis ("hardening of the arteries")
- High blood pressure
- Chest pain (angina)
- Irregular heartbeat
- Heart attack
- Kidney disease
- Hepatitis
- Underactive adrenal or pituitary gland
- Blood-clotting disorders
People with heart disease, or older people at greater risk for heart disease, may need a lower dose of levothyroxine.
Levothyroxine and Pregnancy
Tell your doctor if you are pregnant, may become pregnant, or are breastfeeding before taking levothyroxine.Research shows that it's safe to take levothyroxine during pregnancy, though it's likely your doctor will adjust your dose of levothyroxine during your pregnancy.
If you find out you have hypothyroidism during pregnancy, your doctor will probably treat the condition.
Also, women with underactive thyroid may need to take levothyroxine to ensure that they produce enough breast milk. Because of this, doctors may vary the dosage for women who are breastfeeding
It's generally considered safe for children to take levothyroxine.
Levothyroxine Side Effects
- Weight loss
- Tremor
- Headache
- Nausea
- Vomiting
- Diarrhea
- Stomach cramps
- Nervousness
- Irritability
- Insomnia
- Excessive sweating
- Increased appetite
- Fever
- Changes in menstrual cycle
- Sensitivity to heat
- Temporary hair loss, especially among children during the first month of treatment
- Chest pain
- Rapid or irregular heartbeat or pulse
Levothyroxine Interactions
Types of drugs that interact with levothyroxine include:
- Amphetamines
- Aspirin
- Blood thinners such as warfarin (Coumadin)
- Antidepressants or drugs used to treat anxiety
- Heart medications, such as metoprolol (Lopressor, Toprol), propranolol (Inderal), and digoxin (Lanoxin)
- Anti-seizure drugs such as phenytoin (Dilantin)
- Estrogens and oral contraceptives
- Diabetes medications, including insulin
Other Interactions
You should take levothyroxine on an empty stomach 30 to 60 minutes before breakfast.Talk with your doctor about how certain foods could affect the absorption of the drug and your dosage of the medication.
Levothyroxine Dosage
When giving levothyroxine to an infant or child, you can crush the tablet and mix it in 1 to 2 teaspoons of water. Don't mix the medication with food or soybean infant formula. Use this mixture right away.
Your dosage of levothyroxine depends on many variables, including:
- Your age
- Your weight
- The severity of your condition
- Other health problems you may have
- Other medications you are taking
If your dose is too strong, your thyroid levels will get too high, which can lead to heart problems and bone loss.
Your doctor will probably start you on a low dose of levothyroxine and gradually increase it until your thyroid level is within a normal range.
Once your doctor finds the right dose of medication for you, you won't need to go to the doctor as frequently.
Your dose will likely remain the same for years unless you become pregnant, develop heart disease, or begin hormone replacement therapy.
Levothyroxine Overdose
You shouldn't take more levothyroxine than your doctor prescribes.If you take too much of the drug, you may develop symptoms of overactive thyroid, including fatigue, sensitivity to heat, increased appetite, and sweating.
Symptoms of a levothyroxine overdose may also include:
- Confusion and disorientation
- Shock
- Coma
- Death
Missed Dose of Levothyroxine
It's important not to skip doses of levothyroxine. If you accidentally miss a dose, take the missed dose as soon as you remember it.If it's almost time for your next regular dose, however, skip the missed dose.
Don't take twice as much levothyroxine at one time to make up for a missed dose.
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