Levothyroxine (a synthetic form of the hormone thyroxine) is given to people who don’t produce enough thyroid hormone – as is the case in congenital hypothyroidism or Hashimoto’s thyroiditis.

Levothyroxine reproduces the hormone that your body produces naturally. It currently comes in three different tablet strengths: 25mcg, 50mcg and 100 mcg.

The amount of levothyroxine your child is prescribed will depend on their size and weight and also on the results of their thyroid blood tests. The blood tests take place regularly to make sure that thyroid levels are within the reference range, and the amount of levothyroxine prescribed will be adjusted accordingly. As your child grows, they will usually need more levothyroxine.

Levothyroxine may also be given as part of the treatment for an over-active thyroid. This treatment is known as ‘block and replace’.

Levothyroxine is usually prescribed in tablet form. Giving levothyroxine to infants can be a challenge, but if the tablet is crushed it can be given in liquid (preferably water). You should not add the crushed tablet to your baby’s feeding bottle as it is important the baby gets the whole dose of levothyroxine and that none is left behind in any unfinished milk. Mix the crushed tablet with the liquid and give it on a spoon or with a medicine dispenser pipette. Do not give your baby a full feed immediately after giving the levothyroxine in case the baby is sick and loses some of the dose. Once your child is old enough to drink from a cup or beaker, you can give the tablets along with a drink of water. Although some pharmacists may offer to make up suspensions of levothyroxine to be helpful, you should never use these as the suspension does not deliver the right dose consistently.

Top tips

Different types of levothyroxine (particularly tablets versus solutions) could have slightly different amounts of levothyroxine and it has been suggested that taking the same type may help to improve the accuracy of your child’s blood tests. Ask your GP or endocrinologist to be consistent and use the same type or formulation each time.

Eltroxin® Oral Solution is a liquid form of levothyroxine that comes in three strengths: 25mcg, 50mcg and 100mcg. The same volume of liquid can have different amounts of thyroxine in it so make sure you know which one your child has been prescribed. It may be prescribed for babies or young children who have difficulty in swallowing tablets.

Only use levothyroxine in tablet form or liquid levothyroxine even if you pharmacist offers to make up suspensions of levothyroxine to be helpful. You should not use these as the suspension does not deliver the right dose consistently.

Make sure your child takes their tablets every day. Ideally, get them to take the tablets in the morning with water, at least half an hour before they have eaten or drunk anything else. Some food and drink, such as milk or grapefruit juice, can affect the absorption of the tablet.

Supplements, for example, calcium, iron, soy and multi-vitamin tablets can also affect the absorption of levothyroxine. If your child needs to take any of these supplements, make sure it is at least four hours after they have taken their levothyroxine.

Check with your chemist before giving your child over-the-counter drugs – even things that you might think are safe such as nose drops.

Other drugs can interact with levothyroxine. Make sure you tell your doctor that your child is taking levothyroxine if he or she prescribes any other drugs. Medication such as cholesterol-lowering drugs (eg cholestyramine, colestipol) can affect the absorption of levothyroxine.

Store levothyroxine at room temperature away from moisture and heat. Check the expiry dates as out-of-date tablets can lose their strength.

If you are travelling by sea or air, take your child’s levothyroxine in your hand luggage in the original container.

Side effects

If your child takes too much levothyroxine, they may get some of the symptoms of an over-active thyroid. This is why it is important to have regular blood tests to check the thyroid hormone levels.