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Antithyroid · For Cats

Tapazole dosage reference for cats (Methimazole)

This page's standard weight-based reference is 0.75 mg per kg (0.34 mg per lb), with every 8-12 hours recorded as the reference frequency. Use the calculator to see the arithmetic for your cat's weight, then confirm the indication, product, and actual dose with a veterinarian.

Onset
1-2 weeks for clinical effect
Duration
12 hours per dose
Class
Antithyroid

Weight-based calculator estimate from the references listed on this page. This page has not been independently DVM-reviewed — see our methodology .

This information is for educational purposes only. Always consult your veterinarian before giving medication to your pet. Do not use this calculator for emergencies, overdoses, pregnancy, very young animals, very old animals, pets with liver/kidney disease, or pets taking multiple medications.

Each medication page lists the references recorded for its data. The calculator math and editorial presentation are maintained by PetDosageChart; a page is independently DVM-reviewed only when a named reviewer byline appears. See our methodology and limitations.

Methimazole (often known by brand names such as Tapazole and Felimazole) is an antithyroid commonly used in veterinary medicine for hyperthyroidism, thyroid hormone reduction, and pre-surgical thyroid stabilization. Understanding the correct dosage, administration, and potential side effects of Methimazole is critical for your cat’s safety and well-being.

A typical Methimazole dose for cats is around 0.75 mg/kg every 8-12 hours, within a usual range of 0.5-1 mg/kg. Available forms include tablet, transdermal gel, and liquid.

Calculator Warning: Use this only as an educational estimate. Your veterinarian may prescribe a different dose based on your pet’s condition, age, weight, other medications, and medical history.

Methimazole Dosage Calculator for Cats

Enter your cat’s weight below to estimate the Methimazole dose from the 0.75 mg/kg guideline. Your veterinarian may adjust it for your cat’s age, condition, and other medications, so treat the result as an educational starting point, not a prescription.

Dosage Calculator · 01

Enter your cat's weight

Quick Dosage Chart

Typical Methimazole amounts for common cat weights, for quick reference:

Dosage Chart · 02

Tapazole weight-based reference chart for cats

Scroll sideways to see full table

Weight Lower Reference Standard Reference Upper Reference Frequency
3 lbs (1.4 kg) 0.70 mg 1.0 mg 1.4 mg every 8-12 hours
4 lbs (1.8 kg) 0.90 mg 1.4 mg 1.8 mg every 8-12 hours
5 lbs (2.3 kg) 1.1 mg 1.7 mg 2.3 mg (2.5mg tablet) every 8-12 hours
6 lbs (2.7 kg) 1.4 mg 2.0 mg (2.5mg tablet) 2.7 mg (2.5mg tablet) every 8-12 hours
7 lbs (3.2 kg) 1.6 mg 2.4 mg (2.5mg tablet) 3.2 mg every 8-12 hours
8 lbs (3.6 kg) 1.8 mg 2.7 mg (2.5mg tablet) 3.6 mg every 8-12 hours
9 lbs (4.1 kg) 2.0 mg (2.5mg tablet) 3.1 mg (2.5mg tablet) 4.1 mg every 8-12 hours
10 lbs (4.5 kg) 2.3 mg (2.5mg tablet) 3.4 mg 4.5 mg (2 × 2.5mg) every 8-12 hours
12 lbs (5.4 kg) 2.7 mg (2.5mg tablet) 4.1 mg 5.4 mg (2 × 2.5mg) every 8-12 hours
14 lbs (6.3 kg) 3.1 mg 4.7 mg (2 × 2.5mg) 6.3 mg every 8-12 hours
16 lbs (7.3 kg) 3.6 mg 5.5 mg (2 × 2.5mg) 7.3 mg (3 × 2.5mg) every 8-12 hours
18 lbs (8.2 kg) 4.1 mg 6.1 mg 8.2 mg every 8-12 hours
20 lbs (9.1 kg) 4.5 mg (2 × 2.5mg) 6.8 mg 9.1 mg every 8-12 hours
25 lbs (11.3 kg) 5.7 mg 8.5 mg 11.3 mg every 8-12 hours

Parenthetical tablet amounts are arithmetic comparisons only. They do not account for scoring, release type, concentration, product labeling, or whether this medication is appropriate for an individual animal.

By Weight

Tapazole reference by cat weight

Choose a common weight to open its optional reference page. Use the main medication calculator for a different exact weight.

Common-weight pages are convenience views of the same educational reference, not separate medical recommendations.

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How to Give Methimazole to Your Cat

Methimazole tablets can be given directly by mouth or crushed and mixed with a small amount of wet food. If your cat resists pilling, a transdermal gel applied to the inner ear flap (pinna) is an excellent alternative — rotate ears with each dose to avoid skin irritation. Wear gloves when handling the transdermal gel. Consistency in timing is important for thyroid control.

It is generally recommended to give Methimazole with food to help reduce stomach upset. It may interact with anticoagulants (warfarin), digoxin, phenobarbital, and other hepatotoxic drugs.

Side Effects and Safety

Common side effects include vomiting, loss of appetite, lethargy, and facial itching and scratching. More serious side effects can occur, such as liver toxicity (jaundice), bone marrow suppression, bleeding disorders, and severe skin lesions.

Cautions · 12

When Tapazole should be used with caution or avoided

Some cats should not take Tapazole, or need a different dose and closer monitoring. Tell your veterinarian about your pet's full health history and every other medication or supplement they take before giving Tapazole.

  • liver disease
  • autoimmune disease
  • known hypersensitivity to methimazole
  • pregnancy

Interactions · 13

Tapazole drug interactions

Tapazole can interact with other drugs. This list is not complete — always give your veterinarian a full list of your cat's medications and supplements.

anticoagulants (warfarin)
digoxin
phenobarbital
other hepatotoxic drugs

Calculator Limits · 14

When not to use this calculator

This calculator gives a general educational estimate for a healthy adult cat at a known weight. Do not rely on it in these situations — talk to your veterinarian instead:

  • In an emergency, or after accidental ingestion or a suspected overdose
  • For pregnant or nursing pets
  • For very young or very old cats
  • For pets with liver disease, kidney disease, or another chronic illness
  • For pets taking several medications at once
  • When you are not sure of your cat's current, accurate weight
  • For combination products that contain additional active ingredients

Overdose · 15

Suspected overdose: what to do

If you think your cat had too much Tapazole, or swallowed any medication by accident, act right away. Do not wait for symptoms to appear.

  • Call your veterinarian or the nearest emergency animal hospital.
  • ASPCA Animal Poison Control Center: (888) 426-4435
  • Pet Poison Helpline: (855) 764-7661

A consultation fee may apply to the poison hotlines. Have the medication packaging ready, and note how much your pet may have taken and when. Do not try to make your pet vomit unless a veterinarian tells you to.

When to Call the Vet

If your cat experiences any of the following, contact your veterinarian or an emergency clinic immediately:

Frequently Asked Questions

Frequently Asked · 07

Questions about this medication

How long does a cat need to take methimazole?
Methimazole is typically a lifelong medication for cats with hyperthyroidism unless they undergo radioactive iodine therapy or surgical thyroidectomy. It does not cure the condition but effectively controls thyroid hormone levels when given consistently.
Can methimazole cause kidney problems in cats?
Methimazole does not directly damage the kidneys, but lowering thyroid levels can unmask underlying chronic kidney disease (CKD). Hyperthyroidism increases blood flow to the kidneys, which can hide declining kidney function. Your vet will monitor kidney values closely after starting treatment.
Is the transdermal methimazole gel as effective as tablets?
Yes, transdermal methimazole gel applied to the inner ear flap is effective for most cats, though absorption can be slightly less predictable than oral dosing. It is an excellent option for cats that are difficult to pill. Blood levels should still be monitored regularly.
How often should thyroid levels be checked on methimazole?
Thyroid levels (T4) should be rechecked 2-3 weeks after starting or adjusting the dose, then every 3-6 months once stable. Kidney values and a complete blood count should also be monitored at these visits.
What happens if I miss a dose of methimazole for my cat?
If you miss a dose, give it as soon as you remember unless it is close to the next scheduled dose. Do not double up. Missing occasional doses may cause a temporary rise in thyroid levels, but one missed dose is unlikely to cause a crisis. Consistent dosing is important for long-term control.

Use This Guide Safely · 08

What weight alone cannot tell you

The calculator performs one narrow job: it multiplies your cat's weight by the lower, standard, and upper mg/kg values recorded for Tapazole. It cannot decide whether this drug, indication, formulation, or schedule is appropriate for an individual animal.

Context in this medication record

Commonly listed uses
hyperthyroidism, thyroid hormone reduction, pre-surgical thyroid stabilization
Recorded forms
tablet, transdermal gel, liquid
Reference timing
every 8-12 hours; onset 1-2 weeks for clinical effect; duration 12 hours per dose

Individual checks a calculator cannot perform

  • Confirm the diagnosis and the reason this medication is being considered.
  • Match the exact product, concentration, route, and whether a tablet may be split.
  • Account for age, pregnancy, organ function, genetics, allergies, and prior reactions.
  • Review every prescription, over-the-counter product, and supplement your pet takes.

Recorded cautions

liver disease; autoimmune disease; known hypersensitivity to methimazole; pregnancy.

Recorded interactions

anticoagulants (warfarin); digoxin; phenobarbital; other hepatotoxic drugs.

These lists reproduce the structured record used by this page and may not be exhaustive. Show your veterinarian the product label and your cat's complete medication list before acting on a number.

Related · 08

Related medications for cats

Sources · 09

Sources & references

The structured medication record behind this page names the references below. The links open the publisher or official resource; they do not turn this page into a prescription for an individual animal.

Source names are shown at the record level; passage-level page and label citations are still being added. Read our methodology and limitations.

Transparency · 11

How this page was made

This page's structured medication record includes Plumb's Veterinary Drug Handbook among its source names. PetDosageChart applies the record's mg/kg values to the entered weight and presents the arithmetic result. A source record is not the same as an individualized prescription or an independent clinical review.

Sources cited
  • Plumb's Veterinary Drug Handbook
  • Merck Veterinary Manual
Calculator formula
Doses scale linearly from a standard basis of 0.75 mg per kg (0.34 mg per lb) of body weight, given every 8-12 hours. The calculator multiplies that basis by your cat's weight and shows an arithmetic comparison with recorded tablet sizes. That comparison does not determine whether a tablet is scored, splittable, or appropriate for your pet.
Editorial owner
Prepared and maintained by the PetDosageChart editorial team, a software-led publisher and not a veterinary practice.
DVM review status
Not independently DVM-reviewed. A named reviewer and review date appear here only after a confirmed review.

More on our methodology and editorial process — how we source, calculate, and review cats dosage data.

Safety · 10

More resources