It has a good safety profile when used in healthy dogs.
Note: Even though chlorpheniramine is available over-the-counter, it could be unsafe for dogs with certain medical conditions or who are taking certain medication. Always consult with a vet before use.
The typical dosage of chlorpheniramine for treating dogs is 4 – 8 mg every 8 to 12 hours, with a maximum dose of 1.1 mg/lb. Some vets recommend dosing by the dog’s weight at 0.9 – 1.7 mg/lb every 8 to 12 hours, but many agree on the upper limit of 1.1 mg/lb. Slightly lower amounts of around 0.5 mg/lb (up to 7 mg every 8 hours) could be used for sedation.
Always follow the dosage recommended by your vet.
Branded formulations include Chlor-Trimeton and Piriton. If you’re using a branded medicine check the packaging to make sure it contains no active ingredients other than chlorpheniramine.
If you have sustained-release chlorpheniramine capsules you can pop them open and pour the contents onto your dog’s food, but make sure he eats it before the medicine dissolves. Avoid letting him chew on them and avoid crushing the capsules.
Is It Safe?
Chlorpheniramine is considered quite safe for healthy dogs, unless an overdose is given. Be careful when treating a dog with medical conditions, because it might not be suitable for dogs with:
- Angle-closure glaucoma
- Bladder neck obstruction
- Chronic obstructive pulmonary disease (COPD)
- Enlarged prostate
- Gastric outflow obstruction
- Heart disease
- Kidney or liver impairment
The drug is metabolized by the liver and excreted by the kidneys, so it’s wise to remain cautious when treating dogs with impaired liver or kidney function. The drug’s half-life may also be longer in these cases.
Overdoses can cause severe and dangerous side effects, seek immediate veterinary help if an overdose has been given. If overdose-induced seizures occur do not administer diazepam (Valium) or barbiturates.
Pregnancy/Nursing: Avoid use in pregnant or nursing animals.
Following these guidelines will help you to use this medicine in the safest way possible:
- Only use under the guidance of a vet
- Tell the vet about any medical conditions your dog has and any medicines/supplements you are giving him
- Practice caution when using with anticoagulant drugs (e.g. warfarin) or MAOI drugs (e.g. amitraz)
- Practice caution when treating dogs with liver disease, as the drug is metabolized by the liver
What Is It Used For?
Chlorpheniramine is used to treat the following conditions:
- Mast cell tumors
It is not a treatment for the actual mast cell tumors themselves, but is sometimes used for adjunctive therapy to control the increased amounts of histamine in the body.
It is also occasionally used as a sedative.
Chlorpheniramine can cause the following side effects:
- Changes in appetite
- Urine retention
- Dry mouth
An overdose could cause seizures (do not treat these with barbiturates or Valium), coma, difficulty breathing, and even death in the most severe cases. If you suspect an overdose, immediately call your vet or the ASPCA poison control hotline on (888) 426-4435. If the medicine was given by mouth, you will usually be asked to make your dog vomit if he is alert and stable, and following this, activated charcoal is sometimes given. If seizures occur, Phenytoin is usually given intravenously.
DO NOT act before you have spoken to a veterinary professional or ASPCA poison control specialist.
Dr. R. Rosychuk
Dr. M. Papich
Plumb’s Veterinary Drug Handbook (sixth edition)