Patient Counseling Services: Methimazole Transdermal Gel (Veterinary)

Veterinary Use Only

What is this medication?

The preparation dispensed for your cat is a transdermal gel containing the drug Methimazole.  The concentration of Methimazole will vary depending on what your Veterinarian has ordered.  Commonly prescribed doses are 1mg, 2.5mg, 3.5mg, and 5.0mg.  In an attempt to keep the amount of gel for each dosing application, as small as possible, the mg amounts mentioned above are usually contained in volumes no larger than 0.1ml.  The transdermal gel allows the drug to be transported across the skin barrier, to gain access to the micro-circulation of the animal’s blood stream.  This allows the drug to reach the thyroid gland, which is the target organ for this drug.  The transdermal gel use may be one of several varieties including pluronic lecithin organogel (PLO) or Lipoderm® gel/cream.

What is this medication used for?

Methimazole is used to treat hyperthyroidism.   The drug can be used orally or in a transdermal form, in animals as well as humans.  Where the thyroid gland is hyperactive, resulting in the condition known as hyperthyroidism.  Methimazole is used to reduce thyroid gland activity and therefore reducing circulating blood levels of thyroid hormone.

How is the medication to be used?

Most commonly the gel is dispensed in 1ml topical syringes.  This dispensing system allows for easy and accurate dosing.  Dispense the proper amount of medication prescribed by your physician onto a gloved finger and apply to the inside of your cat’s ear.  Rub in well, rotate the site of application daily and alternate the ear used with each application.  This ensures consistent drug absorption, prevents drug accumulation and prevents sensitization to the components of the transdermal gel.

How should this medication be stored?

Keep the medication at room temperature, but do not expose to any extremes in heat or cold.  The preparation has an expiry date which indicates the date beyond which time you should not continue to use the gel and/or when the gel should be replaced with a new batch.  If there is any discoloration or separation of the product within the time defined by the beyond use date, discontinue use and contact our pharmacist.

Are there any special precautions or side effects to watch for?

Take great care when applying the product and use disposable latex or vinyl gloves. Wash your hands after applying the medication to prevent any absorption into your skin.  The gel has temperature dependent viscosity properties; therefore as it is rubbed into the skin it will warm up and become more viscous and harder to rub.

Since Methimazole is used to treat hyperthyroidism, an excess can cause hypothyroidism.  Symptoms to watch for are cold intolerance, weight gain despite decreased appetite, constipation, decreased energy, changes in the animal’s fur and an increase in sleep requirements.

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