First-generation antihistamine · For Dogs

Chlor-Trimeton dosage reference for dogs (Chlorpheniramine)

This page's standard weight-based reference is 0.35 mg per kg (0.16 mg per lb), with Every 8-12 hours recorded as the reference frequency. Use the calculator to see the arithmetic for your dog'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 and Chlorphen) is a first-generation antihistamine commonly used in veterinary medicine for Allergies, Itching, Allergic reactions, Hives, and Insect bite reactions. Understanding the correct dosage, administration, and potential side effects of Chlorpheniramine is critical for your dog’s safety and well-being.

A typical Chlorpheniramine dose for dogs is around 0.35 mg/kg Every 8-12 hours, within a usual range of 0.2-0.5 mg/kg. Available forms include Tablet and Syrup.

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 Dogs

Enter your dog’s weight below to estimate the Chlorpheniramine dose from the 0.35 mg/kg guideline. Your veterinarian may adjust it for your dog’s age, condition, and other medications, so treat the result as an educational starting point, not a prescription.

Dosage Calculator · 01

Enter your dog's weight

Quick Dosage Chart

Typical Chlorpheniramine amounts for common dog weights, for quick reference:

Dosage Chart · 02

Chlor-Trimeton weight-based reference chart for dogs

Scroll sideways to see full table

Weight	Lower Reference	Standard Reference	Upper Reference	Frequency
5 lbs (2.3 kg)	0.46 mg	0.80 mg	1.1 mg	Every 8-12 hours
10 lbs (4.5 kg)	0.90 mg	1.6 mg	2.3 mg	Every 8-12 hours
15 lbs (6.8 kg)	1.4 mg	2.4 mg	3.4 mg (4mg tablet)	Every 8-12 hours
20 lbs (9.1 kg)	1.8 mg	3.2 mg (4mg tablet)	4.5 mg (4mg tablet)	Every 8-12 hours
25 lbs (11.3 kg)	2.3 mg	4.0 mg (4mg tablet)	5.7 mg	Every 8-12 hours
30 lbs (13.6 kg)	2.7 mg	4.8 mg (4mg tablet)	6.8 mg	Every 8-12 hours
40 lbs (18.1 kg)	3.6 mg (4mg tablet)	6.3 mg	9.1 mg	Every 8-12 hours
50 lbs (22.7 kg)	4.5 mg (4mg tablet)	7.9 mg (2 × 4mg)	11.3 mg (3 × 4mg)	Every 8-12 hours
60 lbs (27.2 kg)	5.4 mg	9.5 mg	13.6 mg	Every 8-12 hours
70 lbs (31.7 kg)	6.3 mg	11.1 mg (3 × 4mg)	15.8 mg (4 × 4mg)	Every 8-12 hours
80 lbs (36.3 kg)	7.3 mg (2 × 4mg)	12.7 mg (3 × 4mg)	18.1 mg	Every 8-12 hours
90 lbs (40.8 kg)	8.2 mg (2 × 4mg)	14.3 mg	20.4 mg (5 × 4mg)	Every 8-12 hours
100 lbs (45.4 kg)	9.1 mg	15.9 mg (4 × 4mg)	22.7 mg	Every 8-12 hours
120 lbs (54.4 kg)	10.9 mg	19.0 mg (5 × 4mg)	27.2 mg (7 × 4mg)	Every 8-12 hours
150 lbs (68 kg)	13.6 mg	23.8 mg (6 × 4mg)	34.0 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 dog 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 Dog

Give chlorpheniramine tablets by mouth with food to reduce stomach upset. The small 4 mg tablets can be given whole or hidden in a soft treat or pill pocket. If using syrup, measure the dose carefully with a syringe. Avoid any product containing decongestants (pseudoephedrine or phenylephrine). Maintain a consistent dosing schedule every 8-12 hours for best allergy control.

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

Side Effects and Safety

Common side effects include Drowsiness, Dry mouth, Sedation, and Decreased appetite. More serious side effects can occur, such as Urinary retention, Severe sedation, Rapid heart rate, and Seizures at high doses.

Cautions · 12

When Chlor-Trimeton should be used with caution or avoided

Some dogs 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.

Glaucoma
Urinary obstruction
Severe heart disease
Hypersensitivity to antihistamines

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 dog's medications and supplements.

CNS depressants

Anticholinergic drugs

MAO inhibitors

Barbiturates

Calculator Limits · 14

When not to use this calculator

This calculator gives a general educational estimate for a healthy adult dog 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 dogs
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 dog's current, accurate weight
For combination products that contain additional active ingredients

Overdose · 15

Suspected overdose: what to do

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

Excessive sedation or inability to wake your dog
Difficulty urinating or no urine output
Rapid or irregular heartbeat
Tremors or seizure activity
Allergic reaction to the medication (facial swelling, hives, difficulty breathing)

Frequently Asked Questions

Frequently Asked · 07

Questions about this medication

How does chlorpheniramine compare to diphenhydramine (Benadryl) for dogs?

Chlorpheniramine is generally less sedating than diphenhydramine while still providing effective antihistamine action. It can be a good alternative for dogs that become too drowsy on Benadryl, though individual responses vary between dogs.

Can I use the human version of chlorpheniramine for my dog?

Plain chlorpheniramine tablets (4 mg) can be used, but you must avoid any formulations containing decongestants like pseudoephedrine or phenylephrine, as these are dangerous for dogs. Always check the ingredient list and consult your vet.

How long can my dog take chlorpheniramine?

Chlorpheniramine can be used long-term for chronic allergies under veterinary supervision. Unlike steroids, antihistamines have fewer long-term side effects. However, some dogs may develop tolerance over time, requiring a switch to a different antihistamine.

Will chlorpheniramine make my dog sleepy?

Drowsiness is the most common side effect, especially during the first few days of use. Most dogs develop some tolerance to the sedation over time. If excessive drowsiness persists, consult your vet about adjusting the dose.

Can chlorpheniramine be combined with other allergy treatments?

Yes, chlorpheniramine is often used alongside other treatments such as omega-3 fatty acids, medicated shampoos, or even other allergy medications under veterinary guidance. Combining therapies can improve allergy control.

Use This Guide Safely · 08

What weight alone cannot tell you

The calculator performs one narrow job: it multiplies your dog'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 reactions, Hives, Insect bite reactions
Recorded forms: Tablet, Syrup
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

Glaucoma; Urinary obstruction; Severe heart disease; Hypersensitivity to antihistamines.

Recorded interactions

CNS depressants; Anticholinergic drugs; MAO inhibitors; Barbiturates.

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

Related · 08

Related medications for dogs

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 0.35 mg per kg (0.16 mg per lb) of body weight, given Every 8-12 hours. The calculator multiplies that basis by your dog'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 dogs 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