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PetDosageChart

First-generation antihistamine · For Cats

How much Chlor-Trimeton (Chlorpheniramine) can I give my cat?

Standard Chlor-Trimeton dose for cats is 0.5 mg per kg (0.23 mg per lb), given every 8-12 hours. Use the calculator below for your cat's exact weight, or jump to the weight-by-weight chart.

Onset
30-60 minutes
Duration
8-12 hours
Class
First-generation antihistamine

Calculator estimate from Plumb’s Veterinary Drug Handbook. Not yet vet-reviewed — see our methodology .

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. Sourced from Plumb's Veterinary Drug Handbook and the Merck Veterinary Manual.

Dosage Calculator · 01

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By Weight

Chlor-Trimeton dose by cat weight

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Dosage Chart · 02

Chlor-Trimeton dosage for cats by weight

Scroll sideways to see full table

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

Common Uses · 03

What is Chlor-Trimeton (Chlorpheniramine) used for in cats?

allergies itching allergic skin disease feline eosinophilic granuloma complex

Administration · 04

How to give Chlor-Trimeton to your cat

Typical cat dose is 1-2 mg per cat (one-quarter to one-half of a 4 mg tablet) given 2-3 times daily. The small tablet pieces can be hidden in a pill pocket, soft treat, or small amount of wet food. Chlorpheniramine is one of the better-tolerated antihistamines for cats compared to diphenhydramine (Benadryl), which is difficult to dose and poorly accepted by most cats. Use plain chlorpheniramine without added decongestants.

Available Forms

tablet

Give with Food?

Yes — give with food

Side Effects · 05

Side effects of Chlor-Trimeton in cats

Common side effects

drowsiness
dry mouth
decreased appetite
mild GI upset

Serious side effects — call your vet

  • urinary retention
  • severe sedation
  • paradoxical excitation
  • seizures (overdose)

Emergency · 06

When to call the vet

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

  • Difficulty urinating or no urine output (urinary retention)
  • Extreme sedation or inability to rouse
  • Agitation or hyperactivity (paradoxical reaction)
  • Seizures or tremors
  • No improvement in allergy symptoms after 2 weeks

For Dogs

Looking for Chlor-Trimeton dosage for dogs?

View the Chlor-Trimeton dosage chart and calculator for dogs.

Related · 08

Related medications for cats

Sources · 09

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 Chlorpheniramine.

Read more about our methodology and how we calculate dosages.

Transparency · 11

How this page was made

Sourced from Plumb's Veterinary Drug Handbook, the reference used in US vet schools. Every dose, frequency, and tablet count on this page is generated from that data, then checked against the published references below.

Sources cited
  • Plumb's Veterinary Drug Handbook
  • Merck Veterinary Manual
Calculator formula
Doses scale linearly from a standard basis of 0.5 mg per kg (0.23 mg per lb) of body weight, given every 8-12 hours. The calculator multiplies that basis by your cat's weight and rounds to the closest available tablet size.
Last-reviewed status
Automated from Plumb’s, not yet vet-reviewed.

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

Frequently Asked · 07

Questions about this medication

Is chlorpheniramine better than Benadryl for cats?
Many veterinarians prefer chlorpheniramine over diphenhydramine (Benadryl) for cats because it is better tolerated, easier to dose (smaller tablet), and has fewer side effects in felines. Benadryl has a very bitter taste that causes drooling and foaming in cats, making administration difficult. Chlorpheniramine is generally considered one of the best antihistamine choices for cats.
How much chlorpheniramine can I give my cat?
The typical dose is 1-2 mg per cat (not per kilogram), which is one-quarter to one-half of a 4 mg tablet, given every 8-12 hours. This is a flat dose rather than weight-based because the therapeutic range is narrow and most cats fall within a similar size range. Always consult your vet before starting.
Do antihistamines really work for cat allergies?
Antihistamines work for approximately 40-70% of cats with mild to moderate allergies. They are most effective when started early in an allergy flare. For cats that do not respond to antihistamines alone, they can be combined with other treatments like omega-3 fatty acids, steroids, or immunotherapy for better results.
Can I use the extended-release form of chlorpheniramine for my cat?
No, do not use extended-release or sustained-release formulations for cats. These are designed for humans and can release the drug too unpredictably in a cat's smaller GI tract. Use only the immediate-release 4 mg tablets, which can be safely split.
How long can a cat take chlorpheniramine?
Chlorpheniramine is safe for long-term use in cats for ongoing allergy management. Many cats take it seasonally or year-round with minimal side effects. Drowsiness usually diminishes after the first few days of use as the cat develops tolerance.

Safety · 10

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