Hydroxyzine

Evidence Level: L5

Predicted Indications: 1

Hydroxyzine

Pharmacist Assessment Report

Hydroxyzine: Rosacea conjunctivitis

One-Sentence Summary

Hydroxyzine is a first-generation H1-antihistamine, originally used for allergic and itch-related conditions such as atopic eczema, allergic rhinitis, conjunctivitis, urticaria and angioedema. The TxGNN model predicts it may be effective for rosacea conjunctivitis, but no registered clinical trials and only indirect literature (mostly reviews of other antihistamines) currently support this prediction.

Quick Overview

Item	Content
Original Indication	Not recorded in the local data
Predicted New Indication	Rosacea conjunctivitis
TxGNN Prediction Score	0.9970
Evidence Level	L5
Canada Market Status	Marketed (marketed DINs: 5 of 5)
Number of DINs	5 (marketed: 5)
Recommended Decision	Hold

Why is This Prediction Reasonable?

Currently, detailed mechanism of action data is not available in the data compiled for this report. Based on known pharmacology, hydroxyzine is a first-generation H1-receptor inverse agonist. Histamine released from mast cells drives the wheal-and-flare reaction in allergic urticaria, so blocking H1 receptors is a direct mechanistic fit.

Current guidance, including a Canadian position statement, favours newer-generation antihistamines as first-line therapy for urticaria and allergic rhinitis because of the sedation, cognitive impairment and other side effects of first-generation drugs such as hydroxyzine.

Clinical Trial Evidence

Currently no related clinical trials registered.

Literature Evidence

PMID	Year	Type	Journal	Key Findings
31582993	2019	Review (position statement)	Allergy Asthma Clin Immunol	Canadian society statement: newer-generation H1-antihistamines are safer and should be first-line for allergic rhinitis and urticaria. First-generation agents such as hydroxyzine carry sedation, cognitive impairment and other risks.
28913986	2017	Review	Allergy Asthma Immunol Res	Chronic spontaneous urticaria treatment starts with antihistamines, typically at doses above those for allergic rhinitis. Hydroxyzine was used similarly in the past.
16278258	2005	Review	Ann Pharmacother	Efficacy and safety of first- and newer-generation antihistamines in allergic rhinitis and chronic idiopathic urticaria.
12113226	2002	Review	Clin Allergy Immunol	H1-antagonists in children are effective for allergic rhinoconjunctivitis.
32127782	2020	Review	Clin Mol Allergy	Update on cetirizine, a hydroxyzine-derived second-generation antihistamine, in childhood allergic rhinitis and chronic spontaneous urticaria.
14680442	2004	Review	Expert Opin Pharmacother	Review of cetirizine, a hydroxyzine metabolite, in allergic disorders.
10582734	1999	Review	Ann Allergy Asthma Immunol	Use of cetirizine in dermatologic disorders, with efficacy and safety concerns.
7510611	1993	Review	Drugs	Cetirizine is effective and well tolerated in allergic rhinitis and chronic idiopathic urticaria.
7528133	1994	Review	Drugs	Loratadine was as effective as several antihistamines, including hydroxyzine, in controlled comparative studies.
11034010	2000	Case report	J Clin Gastroenterol	Case of cetirizine-induced cholestasis (a hydroxyzine metabolite); a safety signal rather than efficacy evidence.

Canada Market Information

DIN	Product Name	Dosage Form	Approved Indication
00646024	HYDROXYZINE	Not specified	Not specified
00646016	HYDROXYZINE	Not specified	Not specified
00646059	HYDROXYZINE	Not specified	Not specified
00742813	HYDROXYZINE HYDROCHLORIDE INJECTION USP	Injection	Not specified
00024694	ATARAX	Not specified	Not specified

Safety Considerations

Contraindication-related conditions (from the knowledge graph, not label text): The knowledge graph links hydroxyzine to a number of conditions, including:
- Cardiovascular: hypertension, coronary artery disease, myocardial infarction, heart conduction disease, sudden cardiac arrest
- Neurological and psychiatric: epilepsy, psychotic and schizoaffective disorders, substance abuse or dependence
- Eye: open-angle and angle-closure glaucoma
- Endocrine: hypothyroidism, hyperthyroidism, diabetes mellitus, diabetic ketoacidosis
- Other: liver disease, gallbladder disease, peptic ulcer disease, benign prostatic hyperplasia, hemoglobinopathy
These should be confirmed against the official product monograph.
Drug Interactions: 100 interactions were recorded. Examples among those listed:
- Major: morphine, potassium citrate, dolasetron
- Moderate: famotidine, hyoscyamine, loperamide, atropine, clarithromycin, levofloxacin, dicyclomine, dronabinol, palonosetron, trospium, and others
- Minor: cimetidine
Class-level concerns from the literature: First-generation antihistamines are associated with sedation, cognitive impairment, dry mouth, dizziness, orthostatic hypotension and, in some reports, sudden cardiac death.

Please refer to the package insert for official warnings and contraindications.

Conclusion and Next Steps

Decision: Hold

Rationale: The mechanism fits well and urticaria is already an original indication, but there are no registered trials and no hydroxyzine-specific efficacy evidence for allergic urticaria. Guidance also prefers second-generation antihistamines. Official safety information for the Canadian products could not be obtained, so safety screening cannot proceed yet.

To proceed, the following is needed:

Health Canada package insert warnings and contraindications (a blocking gap)
Approved indication text and dosage forms for the Canadian DINs
Detailed mechanism of action data (MOA)
Hydroxyzine-specific clinical evidence in urticaria, ideally compared with second-generation antihistamines

Other Predicted Indications (for reference)

Rank	Predicted Indication	TxGNN Score	Evidence Level	Comment
2	Rosacea conjunctivitis	0.9970	L5	No trials or literature. Antihistamines are not standard therapy, so the link is speculative. Hold.

Disclaimer

This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.