Synthroid (Levothyroxine Sodium)

Synthroid is a human medication that may be prescribed off-label by a veterinarian to treat hypothyroidism in dogs. Hypothyroidism in dogs is a condition caused by the underproduction of thyroid hormones due to inflammation or degeneration of the thyroid glands. In dogs, this condition is most frequently seen in middle-aged, medium-to-large breeds. Additionally, Synthroid may be used off-label for cats, particularly when hyperthyroidism treatments result in acquired hypothyroidism.

The active ingredient in Synthroid is Levothyroxine sodium, a synthetic form of the naturally occurring thyroid hormone, thyroxine, which is vital for regulating metabolism and various physiological processes. In pets with hypothyroidism, the thyroid gland fails to produce sufficient thyroxine, leading to several health issues. Administering levothyroxine sodium helps replace the missing hormone and normalises the thyroid hormone levels in your pet's body.

The administration of Synthroid should be strictly as per the veterinarian's prescription. Preferably this medication should be given at the same time each day and is typically once a day. The dosage depends on the dog's weight and severity of their condition which will be determined by your veterinarian.

Overdose:

Overdoses can lead to serious symptoms such as agitation, seizures, and elevated heart rate. In such cases, immediately contact your veterinarian or the New Zealand National Poisons Centre at www.poisons.co.nz/animal-helpline/ or phone number 0800 869 738.

Known hypersensitivity to levothyroxine or any of the formulation components.

Untreated adrenal insufficiency (Addison’s disease): Starting levothyroxine without addressing low cortisol can worsen the condition.

Thyrotoxicosis: Dogs with uncontrolled hyperthyroidism (excess thyroid hormone production) should not be given Synthroid as it will exacerbate the condition.

Heart disease: Levothyroxine can be used under veterinary supervision in dogs with controlled heart disease.

While most pets tolerate Synthroid well, a minority may experience side effects such as:

• Loss of appetite
• Weight loss
• Skin irritation or itching
• Vomiting
• Lethargy
• Diarrhoea
• Increased thirst
• Increased respiratory rate

In rare cases, allergic reactions such as hives, rash, or facial swelling might occur. If any of the above symptoms occur it is important to contact your veterinarian.

Store Synthroid at a controlled room temperature, avoiding direct sunlight and moisture. Ensure the container is tightly closed and out of reach of children and other pets.

Regular monitoring of thyroid levels may be recommended by your veterinarian, especially when initiating or adjusting the dosage.

How long does it take for Synthroid to show results in pets?

• This can differ among individual pets, however typically, some pets can show improvement within the first 1-2 weeks. However, changes in weight, hair coat quality, and neurological signs may take 8-12 weeks for notable improvements.

Can Synthroid be used for both cats and dogs?

• While primarily used for dogs, in some cases, it may be prescribed for cats “off-label” by a veterinarian for certain thyroid conditions.

What should I do if I miss giving a dose to my pet?

• Consult your veterinarian for guidance. Generally, you should give the missed dose as soon as you remember, or skip it if it's nearly time for the next dose. Avoid double dosing.

Are there any special considerations while using Synthroid?

• Consistent timing for administering the medication and adherence to the prescribed dosage are important. Also, ensure other pets do not have access to the medicated pet's faeces.