Levothyroxine for Dogs - Uses, Dosage and Side Effects

To understand the effects of levothyroxine for dogs, we will need to understand hypothyroidism in dogs. Canine hypothyroidism is the most impactful thyroid-related disease in dogs. It is also one of the most prevalent in veterinary endocrinology.

The thyroid gland has very important functions such in terms of regulating metabolism, growth, development, nervous system processes and tissue recovery. In the case of hypothyroidism, the thyroid gland produces thyroid hormones below the normal level, altering these functions in the process.

Certain symptoms are common in dogs that experience hypothyroidism. As it can be a condition which is chronic over time, these symptoms can develop gradually, depending on the individual's experience. Common clinical signs include lethargy, obesity, exercise intolerance, poor coat quality, skin hyperpigmentation, neurological disorders, ocular problems and many others. Diagnosis can be carried out using blood tests and specific hormone tests.

Levothyroxine sodium is a synthetic molecule designed to replace the function of thyroxine (T4) in animals with primary hypothyroidism, i.e. when it is caused by alteration of the thyroid gland. In this case, modified hormones are used, since natural thyroxine is unreliable compared to synthetic products. The latter are more predictable and their action lasts longer in the body.

The main use of levothyroxine for dogs is the treatment of hypothyroidism. It is used to return thyroxine to a healthy level in the body, reversing the symptoms of the disease in the process. Synthetic T4 is capable of reversing the symptoms and pathophysiological processes associated with canine hypothyroidism, unless permanent damage has occurred.

The first symptoms that disappear are those related to the level of consciousness and the nervous system. If a notable improvement in this aspect is observed during the first week, it will be a marker of good prognosis. Dermatological symptoms are those that take the longest to recover, taking months of time in most cases.

Levothyroxine for dogs is administered orally either via tablet or oral solution. The latter is usually chosen for dogs that have problems ingesting tablets for whatever reason. The initial dose of levothyroxine for dogs ranges between 0.01 and 0.04 mg/kg of body weight.

One of the key factors for veterinarians determining the correct levothyroxine dose for dogs is the route of administration. The oral route is based on the absorption capacity of the small intestine of this drug, which can vary between 10 to 50%. To achieve basal levels of T4 in the blood, a higher concentration is needed if the drug is used in pills rather than in syrup.

Although we have talked about the oral route, the medication can also be administered intravenously. This format is reserved for extreme situations in which T4 levels in the blood have fallen drastically and is used in a clinical situation by a qualified veterinarian.

Take a look at the video below which explains how to give a dog a shot under the skin:

Levothyroxine poisoning can occur if the dog takes an overdose of the drug. Unlike other animal species, dogs are quite resistant to the toxic effect of this hormone, making an overdose difficult. In some cases, a multiplication of the initial dose of the drug by 20 will be required to observe signs of overdose. Thyrotoxicosis may also appear in dogs which have an exclusively meat diet or with other organic problems (kidney failure or liver impairment). If this happens, it is best to go to your veterinarian as soon as possible.

Some of the most common clinical signs of levothyroxine overdose in dogs are:

• Increased water intake
• Increased volume and frequency of urination
• Increased appetite
• Weight loss
• Hyperactivity
• Tachycardia
• Increased body temperature
• Gasp

Most signs disappear within 1 to 3 days after stopping the medication. If the overdose is sufficient that the dog goes into toxic shock, it will be considered a veterinary emergency and the dog will need to be clinically stabilized.

The dosage of levothyroxine sodium varies depending on the characteristics and needs of the individual animal. The maximum concentration of the drug is reached after 3 or 5 hours, prolonging its effect up to 15 hours in some cases. Taking the above into account, the usual frequency of administration is 1 or 2 times a day. The variability will depend on how the dog responds to the treatment.

It is very important to note that levothyroxine for dogs should not be given with food. This is because doing so reduces the bioavailability of the drug (i.e. the proportion of the drug that actually reaches the desired tissue). For this reason, it is very important in these cases to monitor the patient and see how they respond to the medication.

As mentioned in previous sections, levothyroxine overdose can lead to an undesirable situation for the dog. However, there are more common side effects associated with the consumption of levothyroxine sodium in dogs. Of ten these are related to the dog's skin.

In some cases, increased skin peeling may occur, which may be particularly serious in patients which already have skin problems as a result of their hypothyroidism. Additionally, the administration of levothyroxine may be associated with itching. In this case, the veterinarian must establish the plan to follow and withdraw the medication when necessary.

Other side effects to take into account are:

• Diarrhea
• Weight loss
• Vomiting
• Hyperarousal
• Tachycardia
• The same as associated with thyrotoxicosis

Finally, this drug is totally contraindicated in dehydrated patients, as well as dogs with kidney problems, liver problems or an allergy to levothyroxine sodium. It is vitally important to inform the veterinarian of any strange event that occurs during the administration of the medication so that appropriate measures can be taken.

To learn more about how irregular levels of thyroxine can affect canines, take a look at our article on whether hypothyroidism affects a dog's life expectancy.

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

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