Levothyroxine

What is levothyroxine?

Your child needs to take levothyroxine because their body is not making enough thyroid hormone. The thyroid is a small, butterfly-shaped gland in the front of the neck. It produces hormones that affect all aspects of your child's health, including heart rate, energy metabolism (how effectively the body uses calories), growth and development.

Levothyroxine is also used to treat an enlarged thyroid gland, called a "goiter".

You may hear levothyroxine called by its brand names, Synthroid or Eltroxin. Levothyroxine comes as a tablet.

Before giving levothyroxine to your child

Your child should not take levothyroxine if they:

• has a condition called thyrotoxicosis (too much thyroid hormone in the body)
• has had any unusual or allergic reaction to levothyroxine or anything in the levothyroxine tablets
• recently had a heart attack
• has certain adrenal or pituitary gland problems

Talk with your child's health-care provider if your child has any of the following conditions. Precautions may need to be taken with this medicine if your child has:

• liver or kidney problems
• heart problems like hardening of the arteries, high blood pressure or chest pain (angina)
• diabetes

How should you give your child levothyroxine?

Follow these instructions when giving your child levothyroxine:

• Give this medicine exactly as your child's health-care provider tells you to. Do not change the amount you give your child without talking to your health-care provider.
• Do not stop giving your child levothyroxine unless your child's health-care provider tells you to.
• Give your child this medicine at the same time each day to avoid missing doses. Levothyroxine is usually given once a day.
• Levothyroxine works best if given when your child has an empty stomach, one hour before or two hours after a meal. If this medication upsets your child's stomach, it can be given with food, but check with your child's health-care provider before doing so. Certain foods, especially those containing calcium and iron, may reduce the absorption of the medicine and make it less effective.
• If your child cannot swallow the tablets, the tablets can be crushed and mixed with a small amount of water or soft foods like applesauce. Give this mixture right away. Foods or formula containing soy, fibre or iron should not be used.

How to give levothyroxine tablets to babies

Supplies

You will need the following supplies:

• pill splitter
• pill crusher
• a drop of water

Directions

Follow these instructions to give your baby levothyroxine tablets:

1. Wash your hands thoroughly using soap and water.
2. Split the tablet, if needed (your health-care provider will tell you if you need to do this).
3. Crush the tablet into a powder using the pill crusher.
4. Wet your finger with water and dip it into the powder.
5. Finger feed it to your baby, putting your finger into the side of the cheek, and let your baby suck it off your finger.
6. You may need to do this three or four times to get all the medication into your baby.
7. Ideally, give the medication a half hour or more before a feed. It tastes good, so babies like it!

Important points

• If your child vomits the entire feed within 30 minutes of receiving levothyroxine, please give the full dose to your child again.
• If your child vomits the entire feed more than 30 minutes from the time of levothyroxine administration, or if your child has spit ups, you do not need to repeat the dose.
• Give levothyroxine at about the same time every day so you get into a routine. You do not need to wake up your baby to give the medication; 30 to 60 minutes late is safe.
• The tablets should not be made into a suspension (a liquid containing the medication), even if the pharmacist suggests this. The tablet should be given as directed above.

What should you do if your child misses a dose of levothyroxine?

• Give the missed dose as soon as you remember. If you do not remember until the next day, give only one dose.
• If it is almost time for the next dose, skip the missed dose. Give the next dose at the regular time.
• Do not give your child two doses to make up for one missed dose.

How long does levothyroxine take to work?

It may take a few weeks before you notice that levothyroxine is working.

What are the possible side effects of levothyroxine?

Your child may have some of these side effects while they take levothyroxine. Check with your child's health-care provider if your child continues to have any of these side effects and they do not go away, or they bother your child:

• stomach cramps, vomiting (throwing up) or diarrhea (loose, watery bowel movements)
• trouble falling asleep
• hair loss (usually goes away)
• increase in appetite
• weight loss
• muscle cramps

Call your child's health-care provider during office hours if your child has any of these side effects:

• fever
• unusually heavy menstrual periods
• inability to cope with heat or excessive sweating
• tremors (trembling)
• changes in vision
• nervousness or irritability

Most of the following side effects are not common, but they may be a sign of a serious problem. Call your child's health-care provider right away or take your child to the Emergency Department if your child has any of these side effects:

• skin rashes, or hives (red, raised rash)
• chest pain
• fast or irregular heartbeat
• trouble breathing or shortness of breath
• seizures

What safety measures should you take when your child is using levothyroxine?

While your child is on this medicine, their health-care provider may order blood tests to check thyroid hormone levels. The health-care provider may then change the amount of levothyroxine your child takes depending on what the levels are.

There are some medicines that should not be taken together with levothyroxine, or, in some cases, the dose of levothyroxine or the other medicine may need to be adjusted. It is important to tell your health-care provider if your child takes any other medicines (prescription, over the counter or herbal). Some medicines include:

• blood thinner (warfarin)
• the antibiotic ciprofloxacin
• antacids
• cholestyramine
• iron-, magnesium- or calcium-containing supplements, including multivitamins
• potassium binders (including sodium polystyrene sulfonate (Kayexalate or Resonium))
• phosphate binders (sevelamer)
• certain diabetes medications
• certain seizure medications (carbamazepine, phenytoin)

Several of the above medications, including supplements and potassium or phosphate binders, can interfere with the absorption of levothyroxine if given at the same time. Please talk to your child’s health-care provider about how to space out these medications. Usually, levothyroxine should be given at least several hours before or after you give your child these other interacting medications.

If your child is on a blood thinning medication taken by mouth, such as warfarin (Coumadin), they may need less of the blood thinner when they start taking levothyroxine. Speak to your health-care provider about this.

Children with diabetes may need more of their diabetes medication when they are taking levothyroxine. If your child has diabetes, monitor their glucose level more often. Speak to your health-care provider about this.

Tell the doctor or dentist that your child is taking levothyroxine before your child has any operation or procedure, even on the teeth, or an emergency treatment.

What other important information should you know about levothyroxine?

• Keep all medicines out of your child’s sight and reach.
• Make sure you have enough medicine on hand to last through weekends, holidays or vacations.
• Keep a list of all medicines your child is taking and show the list to the health-care provider when needed.
• Do not share your child’s medicine with others. Do not give anyone else’s medicine to your child.
• Store levothyroxine tablets in a safe, dry place at room temperature. Do not store in a bathroom.
• Do not keep any medicines that are past the expiry date labelled on the bottle. Check with your pharmacist about the best way to throw away outdated or leftover medicines.

Keep levothyroxine out of your child’s sight and reach and locked up in a safe place. If your child takes too much levothyroxine, call your local Poison Information Centre at one of these numbers. These calls are free. 

• Call 1-844 POISON-X, or 1-844-764-7669, from anywhere in Canada except Quebec.
• Call 1-800-463-5060 if you live in Quebec.