First-generation antihistamine · For Cats

Chlor-Trimeton dosage reference for cats (Chlorpheniramine)

This page's standard weight-based reference is 0.5 mg per kg (0.23 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: 30-60 minutes
Duration: 8-12 hours
Class: First-generation antihistamine

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.

Chlorpheniramine (often known by brand names such as Chlor-Trimeton) is a first-generation antihistamine commonly used in veterinary medicine for allergies, itching, allergic skin disease, and feline eosinophilic granuloma complex. Understanding the correct dosage, administration, and potential side effects of Chlorpheniramine is critical for your cat’s safety and well-being.

A typical Chlorpheniramine dose for cats is around 0.5 mg/kg every 8-12 hours, within a usual range of 0.25-0.5 mg/kg. Available forms include tablet.

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.

Chlorpheniramine Dosage Calculator for Cats

Enter your cat’s weight below to estimate the Chlorpheniramine dose from the 0.5 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 Chlorpheniramine amounts for common cat weights, for quick reference:

Dosage Chart · 02

Chlor-Trimeton 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)	0.35 mg	0.70 mg	0.70 mg	every 8-12 hours
4 lbs (1.8 kg)	0.45 mg	0.90 mg	0.90 mg	every 8-12 hours
5 lbs (2.3 kg)	0.57 mg	1.1 mg	1.1 mg	every 8-12 hours
6 lbs (2.7 kg)	0.68 mg	1.4 mg	1.4 mg	every 8-12 hours
7 lbs (3.2 kg)	0.80 mg	1.6 mg	1.6 mg	every 8-12 hours
8 lbs (3.6 kg)	0.90 mg	1.8 mg	1.8 mg	every 8-12 hours
9 lbs (4.1 kg)	1.0 mg	2.0 mg	2.0 mg	every 8-12 hours
10 lbs (4.5 kg)	1.1 mg	2.3 mg	2.3 mg	every 8-12 hours
12 lbs (5.4 kg)	1.4 mg	2.7 mg	2.7 mg	every 8-12 hours
14 lbs (6.3 kg)	1.6 mg	3.1 mg (4mg tablet)	3.1 mg (4mg tablet)	every 8-12 hours
16 lbs (7.3 kg)	1.8 mg	3.6 mg (4mg tablet)	3.6 mg (4mg tablet)	every 8-12 hours
18 lbs (8.2 kg)	2.0 mg	4.1 mg (4mg tablet)	4.1 mg (4mg tablet)	every 8-12 hours
20 lbs (9.1 kg)	2.3 mg	4.5 mg (4mg tablet)	4.5 mg (4mg tablet)	every 8-12 hours
25 lbs (11.3 kg)	2.8 mg	5.7 mg	5.7 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

Chlor-Trimeton 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 Chlorpheniramine 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.

It is generally recommended to give Chlorpheniramine with food to help reduce stomach upset. It may interact with CNS depressants, anticholinergic drugs, and MAO inhibitors.

Side Effects and Safety

Common side effects include drowsiness, dry mouth, decreased appetite, and mild GI upset. More serious side effects can occur, such as urinary retention, severe sedation, paradoxical excitation, and seizures (overdose).

Cautions · 12

When Chlor-Trimeton should be used with caution or avoided

Some cats should not take Chlor-Trimeton, 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 Chlor-Trimeton.

urinary obstruction
glaucoma
severe cardiac disease
pregnancy

Interactions · 13

Chlor-Trimeton drug interactions

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

CNS depressants

anticholinergic drugs

MAO inhibitors

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 Chlor-Trimeton, 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:

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

Frequently Asked Questions

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.

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 Chlor-Trimeton. It cannot decide whether this drug, indication, formulation, or schedule is appropriate for an individual animal.

Context in this medication record

Commonly listed uses: allergies, itching, allergic skin disease, feline eosinophilic granuloma complex
Recorded forms: tablet
Reference timing: every 8-12 hours; onset 30-60 minutes; duration 8-12 hours

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

urinary obstruction; glaucoma; severe cardiac disease; pregnancy.

Recorded interactions

CNS depressants; anticholinergic drugs; MAO inhibitors.

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.

Plumb's Veterinary Drug Handbook — listed in this medication's source record.
Merck Veterinary Manual — listed in this medication's source record.
DailyMed label search for Chlorpheniramine — check current product and formulation labels; some veterinary uses may be off-label.

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 0.5 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 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

Pet Medication Safety Hub — What's safe, what's dangerous, and emergency signs
How we calculate dosages — Our sources, math, and review process
Printable emergency checklist — One-page reference for your fridge or first aid kit