MDose · Veterinary drug reference
TIER2 TOPIC: FIRST-GENERATION ANTIHISTAMINES (CHLORPHENIRAMINE / HYDROXYZINE)
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Pending clinical review (PROPOSED)Rule-based (RULE_BASED)— applies to the facts and dose entries in this species selection; individual source records retain their own status.
Indications2
Pruritus/allergy adjunct (atopy trial, flea-allergy dermatitis); hydroxyzine = anxiolytic-antihistamine hybrid; chlorpheniramine = mast-cell-tumor mediator control adjunct (4–8 mg/dog)
DogCatExtra-label (EXTRA_LABEL)2 source records · View provenance
- Dog · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Indications table · Not applicable · Extra-label (EXTRA_LABEL) · Pending clinical review (PROPOSED) · Rule-based
Original excerpt: Pruritus/allergy adjunct (atopy trial, flea-allergy dermatitis); hydroxyzine = anxiolytic-antihistamine hybrid; chlorpheniramine = mast-cell-tumor mediator control adjunct (4–8 mg/dog) — Extra-label (OTC/human)
- Cat · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Indications table · Not applicable · Extra-label (EXTRA_LABEL) · Pending clinical review (PROPOSED) · Rule-based
Original excerpt: Pruritus/allergy adjunct (atopy trial, flea-allergy dermatitis); hydroxyzine = anxiolytic-antihistamine hybrid; chlorpheniramine = mast-cell-tumor mediator control adjunct (4–8 mg/dog) — Extra-label (OTC/human)
- Dog · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Indications table · Not applicable · Extra-label (EXTRA_LABEL) · Pending clinical review (PROPOSED) · Rule-based
Dose regimens0
No dose regimens recorded for this species selection.
Adverse effects4
Sedation/lethargy — Main effect (sometimes desired)
Other speciesNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Other species · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Side Effects / Adverse Effects table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Anticholinergic: dry mouth, urine retention, GI — Class
Other speciesNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Other species · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Side Effects / Adverse Effects table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Paradoxical excitement — Cats
CatNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Cat · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Side Effects / Adverse Effects table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Overdose: ataxia→seizures→coma — Narrow-ish margin in small dogs
DogNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Dog · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Side Effects / Adverse Effects table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Monitoring1
Pruritus scores, sedation level, response trial 1–2 weeks before judging
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Monitoring Parameters · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Precautions4
Glaucoma, prostatic hypertrophy, urinary retention, cardiac disease (anticholinergic); MAOI co-use
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Contraindications & Warnings table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Hydroxyzine is cetirizine's parent with a sedation engine — when the sedative antihistamine effect is wanted (anxious itchy dog at night), hydroxyzine; when not, use the metabolite (cetirizine — see cetirizine.md).
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Clinical pearl · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Chlorpheniramine's second job: MCT mediator-masking adjunct (H1 + partial mast-cell stabilization) — the historical protocol partner of the H2 blocker.
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Clinical pearl · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Cat + antihistamine = excitement lottery: warn the owner before the first dose.
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Clinical pearl · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Interactions3
Other anticholinergics/CNS depressants — Additive
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Drug Interactions table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Apomorphine note — Antihistamines can blunt emetic effects (class)
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Drug Interactions table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Ketoconazole (human, terfenadine-era) — QT class-history — modern H1s safer
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Drug Interactions table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Pharmacokinetics3
Mechanism — H1 blockade; hydroxyzine → active metabolite cetirizine (the Zyrtec lineage); sedating (crosses BBB)
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Pharmacokinetics table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Efficacy honesty — Mild benefit at best in canine atopy (diphenhydramine weaker still; cetirizine studied separately) — adjunct tier, not control
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Pharmacokinetics table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Anticholinergic load — Class drying/sedation
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Pharmacokinetics table · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Pregnancy / lactation considerations1
Avoid at high doses (class teratogenicity cautions).
Species not recordedNot applicable (NOT_APPLICABLE)1 source record · View provenance
- Species not recorded · Plumb's Veterinary Drug Handbook, 7th ed., p. 259–261 (chlorpheniramine), p. 629–631 (hydroxyzine) — Pregnancy & Lactation · Not applicable · Not applicable (NOT_APPLICABLE) · Pending clinical review (PROPOSED) · Rule-based
Sources: Plumb DC. Plumb's Veterinary Drug Handbook. 7th ed. PharmaVet Inc; 2011.