马来酸氯苯那敏-Chlorpheniramine Maleate

Chlorpheniramine Maleate (Overview)

Chlorpheniramine maleate is a propylamine (alkylamine) class antihistamine, appearing as a white, crystalline, tasteless powder.

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Storage

Chlorpheniramine tablets and extended-release tablets should be stored in tight containers.

Extended-release capsules should be kept in sealed containers.

Oral solutions should be protected from light and prevented from freezing.

All chlorpheniramine products should be stored at room temperature (15–30 °C).

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Pharmacology / Indications / Pharmacokinetics

Chlorpheniramine is an H₁-receptor antagonist that competitively inhibits histamine at H₁ receptor sites.

It does not neutralize or prevent histamine release, but blocks its effects on cells.

In addition to antihistaminic effects, these drugs may exhibit anticholinergic and central nervous system (CNS) depressant activity (sedation).

Some antihistamines also have antiemetic (e.g., diphenhydramine) or antiserotonergic (e.g., cyproheptadine, azatadine) effects.

In veterinary medicine, antihistamines are mainly used to reduce or prevent histamine-mediated adverse reactions.

Chlorpheniramine is commonly used in cats for pruritus (itching) and may also act as a mild sedative in small animals due to its CNS-depressant properties.

Pharmacokinetic data in domestic animals are lacking.

In humans, chlorpheniramine is well absorbed orally, but undergoes significant first-pass metabolism in the gastrointestinal mucosa and liver, resulting in only 25–60% bioavailability in systemic circulation.

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Safety

Contraindications:

Do not use in animals allergic to chlorpheniramine or other antihistamines.

Because of its anticholinergic properties, it should be used with caution in patients with:

•Narrow-angle glaucoma

•Prostatic hypertrophy

•Pyloroduodenal obstruction or bladder neck obstruction

•Chronic obstructive pulmonary disease (with abnormal mucus secretion)

•Hyperthyroidism, cardiovascular disease, or hypertension

Adverse Effects:

•CNS depression: drowsiness, sedation, lethargy

•Gastrointestinal upset: diarrhea, vomiting, anorexia

•Anticholinergic reactions: dry mouth, urinary retention

Sedation may diminish with prolonged use.

Cats may exhibit paradoxical excitement rather than sedation. Palatability issues are also common.

Overdose can cause CNS excitation (from restlessness to seizures) or depression (from somnolence to coma), along with anticholinergic effects, respiratory depression, and potentially death.

Treatment of overdose:

•Standard gastrointestinal decontamination (emesis or lavage if oral ingestion)

•Administer calcium salts and/or activated charcoal after vomiting/lavage

•Provide symptomatic and supportive care

•Phenytoin (IV) is recommended for antihistamine-induced seizures in humans

•Avoid barbiturates or diazepam in such cases

Drug Interactions:

•Co-administration with other CNS depressants enhances sedation

•Antihistamines may partially antagonize the anticoagulant effects of heparin and warfarin

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Dosage

Note: Contents of extended-release capsules may be mixed with food but should not be dissolved before administration.

Dogs:

•4–8 mg (maximum 0.5 mg/kg) orally every 8–12 hours

•Commonly used as an adjunctive therapy for mast cell tumors

•4–12 mg total dose, orally 2–3 times daily

•For hereditary allergic pruritus: 0.4–0.8 mg/kg, 2–3 times daily

•As a mild sedative: 0.22 mg/kg orally every 8 hours

•Alternatively, 4–20 mg total daily dose, divided every 8–12 hours

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Source: Veterinary Drug Manual

Compiled and Published by: Mao Pipi Veterinary Care