Chlorpheniramine Maleate

Chlorpheniramine maleate is a first-generation H1 antihistamine used for symptomatic management of selected allergic conditions in dogs and cats. It has a long history of empirical veterinary use, particularly for pruritic skin disease in cats. The response depends on how much histamine contributes to the individual patient’s clinical signs.

Group

First-generation H1 antihistamine

Mechanism of Action

Chlorpheniramine inhibits signaling at histamine H1 receptors on blood vessels, sensory nerves and other effector tissues. This reduces histamine-mediated capillary leakage, swelling and stimulation of itch pathways. It acts on the tissue response to histamine rather than preventing histamine release. Central H1-receptor activity and additional antimuscarinic effects contribute to its broader pharmacologic profile.

Dose Rates

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Allergic signs	Reference only	PO		4–8 mg per dog orally every 12 hours, but no more than 0.5 mg/kg per dose. Both constraints must be applied; the schema cannot encode a per-kg cap against a fixed amount.
Allergic signs with fixed-dose ceiling	Reference only	PO		Additional alternatives: 4–8 mg orally every 8–12 hours or 2–8 mg every 12 hours, each subject to a maximum of 0.5 mg/kg per dose. The two constraints require a dedicated capped fixed-dose calculation.
Alternative allergic-sign treatment	4–12 mg/animal	PO	Every 8–12 h	Separate historical alternative; do not combine with capped fixed-dose instructions from another regimen.
Atopic pruritus trial	Reference only	PO		Historical trial alternatives are 0.4–0.8 mg/kg or 0.2–0.8 mg/kg two to three times daily; those bullets do not explicitly assign a route. They differ from the lower fixed-dose capped regimens.
Mild sedation	0.22 mg/kg	PO	Every 8 h

Cats

Use / stage	Dose	Route	Schedule	Instructions
Allergic signs	2 mg/animal	PO	Every 12 h
Allergic signs	2–4 mg/animal	PO	Every 12–24 h
Allergic signs	2 mg/animal	PO	Every 8–12 h
Pruritus	2–4 mg/animal	PO	Every 12 h	Some cats can be maintained once daily after control.
Mild sedation	1–2 mg/animal	PO	Every 12–24 h
Higher-dose mild sedation	2–4 mg/animal	PO	Every 12–24 h

Ferrets

Use / stage	Dose	Route	Schedule	Instructions
Allergic signs	1–2 mg/kg	PO	Every 8–12 h

Birds

Use / stage	Dose	Route	Schedule	Instructions
Drinking-water medication	Reference only	PO		One 4 mg tablet in 240 mL drinking water, changed daily. Delivered mg/kg depends on water consumption and cannot be calculated as a fixed bird dose.

Indications

Adjunctive symptomatic relief of allergic pruritus in dogs and cats, with variable and often limited clinical response.
Symptomatic treatment of histamine-associated urticaria and other cutaneous allergic reactions in dogs and cats.

Contraindications

Glaucoma, ileus or cardiac arrhythmias where antimuscarinic activity is undesirable.
Urinary outflow or pyloroduodenal obstruction, prostatic enlargement and secretion-sensitive lower-airway disease require caution.
Use cautiously with hyperthyroidism, cardiovascular disease or hypertension.

Interactions

No veterinary interactions are identified in the supplied material.

Adverse effects

Sedation
Dry mouth and reduced gastrointestinal secretion

Preparations

Preparation	Form	Strength	Route
Chlorpheniramine Maleate 2 mg tablet	Tablet	2 mg / tablet	PO
Chlorpheniramine Maleate 4 mg tablet	Tablet	4 mg / tablet	PO
Chlorpheniramine Maleate 8 mg tablet	Tablet	8 mg / tablet	PO
Chlorpheniramine maleate syrup 2 mg/5 mL	Oral Liquid	2 mg / 5 mL	PO

Monitoring and Administration

Avoid substituting combination cold or cough remedies that contain other active ingredients.

The dog fixed dose is limited by a simultaneous weight-based ceiling: do not exceed 0.5 mg/kg per dose. The current schema cannot encode this cap against a fixed-dose regimen.

Protect oral liquid from freezing.

The source’s feline 0.5–2 mg example does not agree with its stated quarter-to-half of a 4 mg tablet (1–2 mg); this inconsistent example is not used for calculation.

Sustained-release beads must remain intact; placing intact beads in food does not justify crushing or dissolving them.