Levothyroxine

What is levothyroxine?

Your child needs to take levothyroxine because their body is not making enough thyroid hormone. The body needs thyroid hormone to work properly. It 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 or an injection.

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 doctor or pharmacist 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 doctor or pharmacist tells you to. Do not change the amount you give your child without talking to your doctor.
• Do not stop giving your child levothyroxine unless your child's doctor 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, 1 hour before, or 2 hours after a meal. If this medication upsets your child's stomach, it can be given with food or milk.
• 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 soybean, fibre, or iron should not be used.

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

• Give the missed dose as soon as you remember.
• 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 2 doses to make up for 1 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 doctor 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 doctor 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 doctor 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 heart beat
• 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 doctor may order blood tests to check thyroid hormone levels. The doctor may then change the amount of levothyroxine your child takes depending on what the levels are.

Check with your child's doctor or pharmacist before you give your child any other medicines (prescription, non-prescription, herbal, or natural products). Levothyroxine does not work well with some medicines, such as cough and cold medicines.

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 doctor about this.

Do not give levothyroxine at the same time as foods containing soy (soy-based formulas), fibre, or iron. These foods can decrease the amount of levothyroxine that gets into the body.

If your child takes an antacid, iron supplements, cholestyramine (Questran), Kayexalate, Resonium or any medicine with calcium including multivitamins, give it 1 hour after or 2 hours before the levothyroxine.

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 doctor 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.

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.