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PetDosageChart

Tapazole (Methimazole) Dosage for Cats

Antithyroid ⏱ Onset: 1-2 weeks for clinical effect ⏳ Duration: 12 hours per dose

This dosage information is for educational purposes only. Always consult your veterinarian before giving any medication to your pet. Dosages may vary based on your pet's health conditions, other medications, and individual factors.

Content reviewed by licensed veterinarians. This information is sourced from veterinary drug references including Plumb's Veterinary Drug Handbook and the Merck Veterinary Manual.

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Tapazole Dosage Chart for Cats by Weight

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Weight Low Dose Standard Dose Max Dose Frequency
3 lbs (1.4 kg) 0.5mg 1mg 1.5mg every 8-12 hours
4 lbs (1.8 kg) 1mg 1.5mg 2mg (2.5mg tablet) every 8-12 hours
5 lbs (2.3 kg) 1mg 1.5mg 2.5mg (2.5mg tablet) every 8-12 hours
6 lbs (2.7 kg) 1.5mg 2mg (2.5mg tablet) 2.5mg (2.5mg tablet) every 8-12 hours
7 lbs (3.2 kg) 1.5mg 2.5mg (2.5mg tablet) 3mg (2.5mg tablet) every 8-12 hours
8 lbs (3.6 kg) 2mg (2.5mg tablet) 2.5mg (2.5mg tablet) 3.5mg every 8-12 hours
9 lbs (4.1 kg) 2mg (2.5mg tablet) 3mg (2.5mg tablet) 4mg every 8-12 hours
10 lbs (4.5 kg) 2.5mg (2.5mg tablet) 3.5mg 4.5mg (2 × 2.5mg) every 8-12 hours
12 lbs (5.4 kg) 2.5mg (2.5mg tablet) 4mg 5.5mg (2 × 2.5mg) every 8-12 hours
14 lbs (6.3 kg) 3mg (2.5mg tablet) 4.5mg (2 × 2.5mg) 6.5mg every 8-12 hours
16 lbs (7.3 kg) 3.5mg 5.5mg (2 × 2.5mg) 7.5mg (3 × 2.5mg) every 8-12 hours
18 lbs (8.2 kg) 4mg 6mg 8mg (3 × 2.5mg) every 8-12 hours
20 lbs (9.1 kg) 4.5mg (2 × 2.5mg) 7mg (3 × 2.5mg) 9mg every 8-12 hours
25 lbs (11.3 kg) 5.5mg (2 × 2.5mg) 8.5mg 11.5mg every 8-12 hours

What is Tapazole (Methimazole) used for in cats?

hyperthyroidism thyroid hormone reduction pre-surgical thyroid stabilization

How to give Tapazole 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.

Available Forms

tablet, transdermal gel, liquid

Give with Food?

Yes — give with food

Side effects of Tapazole in cats

Common side effects

vomiting
loss of appetite
lethargy
facial itching and scratching

Serious side effects

  • liver toxicity (jaundice)
  • bone marrow suppression
  • bleeding disorders
  • severe skin lesions

When to call the vet

Call your vet immediately if your cat shows any of these signs:

  • Yellowing of the gums or skin (jaundice)
  • Persistent vomiting or refusal to eat for more than 24 hours
  • Unusual bleeding or bruising
  • Severe facial itching or scratching at the face and neck
  • Lethargy or collapse

Related Medications for Cats

Anticonvulsant / Analgesic

Neurontin

Gabapentin

For pain management

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Antihistamine

Benadryl

Diphenhydramine

For allergies

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NK1 receptor antagonist / Antiemetic

Cerenia

Maropitant

For vomiting

View dosage chart
H2 receptor antagonist

Pepcid

Famotidine

For stomach acid reduction

View dosage chart

Sources & References

The dosage information on this page is compiled from the following veterinary and pharmaceutical references:

  • Plumb's Veterinary Drug Handbook — the standard veterinary pharmacology reference used by veterinarians worldwide.
  • Merck Veterinary Manual — a trusted, peer-reviewed resource for veterinary professionals and pet owners.
  • DailyMed (FDA Drug Labels) — official FDA-approved drug labeling and prescribing information for Methimazole.

Frequently Asked Questions

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.

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