Thyronorm for Cats



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What is Thyronorm?

Thyronorm is a brand name of a drug called thiamazole, marketed by Norbrook. Thyronorm reduces the levels of thyroid hormone in the blood, so it’s used to treat cats with hyperthyroidism.

What does Thyronorm for cats do?

Thyronorm contains thiamazole, which prevents the body from making thyroid hormone. The thiamazole stops iodide binding to the enzyme thyroid peroxidase, therefore preventing the thyroid hormones T3 and T4.

Because the body is making less thyroid hormone, the hormone quantities normalise and your cat’s hyperthyroid symptoms reduce. The medication is not permanent – as soon as you stop the Thyronorm, your cat will start over-producing thyroid hormone again.

What is Thyronorm for cats used for?

Thyronorm is prescribed for cats with hyperthyroidism (an overactive thyroid gland).

It can be used long-term to manage hyperthyroidism, or it can be used to regulate thyroid levels before more permanent treatment, like thyroid surgery.

What are the side effects of Thyronorm for cats?

Although Thyronorm is generally considered safe, like all drugs it does have side effects. These are uncommon. The side effects you might see with Thyronorm are:

  • Vomiting and appetite loss
  • Lethargy
  • Itching, especially of the head and neck
  • Blood cell changes
  • Lymph node problems

Generally, these side effects happen in less than 1% of treated cats, making them uncommon. If they do happen, they usually resolve once thiamazole is stopped. Since hyperthyroidism can become fatal if left untreated, most cats will benefit from treatment despite the small risk of problems.

Which cats can’t have Thyronorm?

Thyronorm needs to be prescribed by a vet. Generally, vets won’t prescribe Thyronorm to cats that are:

  • Suffering from diabetes or liver disease
  • Pregnant or lactating
  • Allergic to thiamazole or the other ingredients in the medication
  • Suffering from autoimmune disease
  • Suffering from diseases of the blood such as low red blood cells, low platelets, or low white blood cells

Having said this, your vet may still make the decision to prescribe Thyronorm to your cat on a risk-benefit analysis. In other words, if the likely benefits outweigh the likely risks.

How to give Thyronorm safely

  1. Follow vet instructions: Always use Thyronorm exactly as your vet has prescribed. This includes the right dose and frequency. Never adjust the dose on your own, even if your cat seems to be feeling better or worse. If you aren’t sure of the dose prescribed, please call your vet to confirm.
  2. Shake the bottle: Thyronorm is a suspension, and the drug may settle over time and become uneven in the bottle. Make sure you shake it before drawing up the dose.
  3. Check with your vet if giving anything else: Your vet should be aware of other drugs your pet is on, but it’s always worth double-checking in case there’s been a miscommunication somewhere. If your dog is on supplements or non-prescription treatments you should also tell your vet when they prescribe Thyronorm, as they may not be suitable to be given together.
  4. Use the correct syringe: The Thyronorm syringe has graduations for mg (eg dose) not ml (eg volume). Therefore, you can’t substitute a normal syringe. If you lose the syringe that comes with your Thyronorm, talk to your vet.
  5. Storage and Handling: Store Thyronorm according to the instructions on the label, usually in a cool and dry place. Make sure it’s out of reach of children and other pets.
  6. Report any accidental overdose to your vet immediately: If you have mistakenly given too much Thyronorm, report it to your vet as soon as you realise the error. They may recommend monitoring or symptomatic treatment, depending on the severity of the overdose.

What monitoring do cats on Thyronorm need?

The dose of Thyronorm your cat needs will vary depending on how they take it (with or without food) and how high their thyroid levels are. For this reason, your vet will start your cat on a standard ‘starting dose’, then take a blood sample again a couple of weeks later. They’ll then increase or decrease the dose, and check again.

Once the levels of thyroid hormone in the blood are in the normal range, and your cat appears to be stable, your vet will reduce the frequency of blood tests. Your cat will still need monitoring, as they may need to increase their dose as their hyperthyroidism worsens again.

Thyronorm FAQs

Is Thyronorm the same as thyroxine?

No – Thyronorm for cats is a brand name of a drug called thiamazole, which is used to decrease the amount of thyroid hormone in cats with hyperthyroidism. Thyroxine does the opposite – it treats hypothyroidism (too little thyroid hormone) by increasing the amount of thyroid hormone in the blood.

However, in the US there is a thyroxine tablet branded as Thyronorm.

What type of thyroid is Thyronorm for cats for?

Thyronorm for cats treats hyperthyroidism by reducing the levels of thyroid hormone.

How long do cats have to be on thyroid medication?

Hyperthyroidism cannot be treated with medication, but it can be managed. Therefore, cats with hyperthyroidism have to be on thyroid medication for the rest of their lives. Alternatively, thyroid medication like Thyronorm can be used to stabilise cats before a more permanent treatment like thyroid surgery or radiation therapy.

Can you give Thyronorm to cats on an empty stomach?

When giving Thyronorm, it doesn’t matter whether your cat’s stomach is empty or full, as long as you are consistent eg if it’s easiest to give just before food, then do this every day.

Can Thyronorm be given with food?

Thyronorm should ideally be given into your cat’s mouth, not on food, as this helps the medicine absorb. However, if your cat doesn’t tolerate this, you might be able to put it on a very small amount of food.

The most important thing is that the amount of food you give Thyronorm with, and the timing of their meal in relation to this, is consistent. Your vet will need to monitor your cat’s thyroid levels while they take Thyronorm, and they will adjust the Thyronorm dose off the back of the results.

So you’ll need to be consistent with their routine so they absorb the same amount of thiamazole each day, and then your vet can increase or decrease the prescribed dose to get your cat’s blood results perfect.

Thyronorm Datasheet

All drugs have a manufacturer’s datasheet, which gives information about the drug’s use and possible side effects. There is usually one in your Thyronorm box, but if you have lost it you can click on the button below to be taken on an online version.

Courses related to Thyronorm

Our ‘Hyperthyroidism in Cats’ course is currently being written. If you’d like to be notified when it goes live, sign up for our mailing list or follow us on Facebook or Instagram.

Please note that the information contained herein is provided for informational purposes only. Although it has been written by a vet, we cannot consider the individual nature of your pet’s problems so it does not constitute veterinary advice. If you have questions about your pet’s medication or their health you should contact a vet, who will be able to help.