Cetirizine is a chemical compound, an antihistamine, selective peripheral antagonist of the histamine H1 receptor, a metabolite of hydroxyzine.

It is used as a symptomatic treatment for urticaria, seasonal and permanent allergic rhinitis.

It is considered a second-generation antihistamine.

Both cetirizine and levocetirizine showed significant improvement in nasal peak expiratory flow rate compared with the placebo group, and ceterizine appeared to be more effective than levocetirizine, (1)  R-enantiomer of cetirizine.

This preliminary study showed that a 4-week cetirizine treatment was able to improve quality of life significantly. Cetirizine treatment also significantly reduced symptom severity in Italian children with Seasonal allergic rhinitis and was safe (2).

Early treatment of symptomatic COVID-19 patients with antihistamines and azithromycin, and administration of antihistamines in asymptomatic and high risk patients, close contacts and relatives, had excellent outcomes in population reducing fatality rate, hospital admissions and ICU admissions in this elderly population, regardless of patient's age and risk factors (3).

Some of my observations. 

The active ingredient Cetirizine is marketed in tablet or drop form and, as we have seen from reading the scientific studies, it is effective and not a cause for concern at dose bases.

Unfortunately, in the drop packages, as excipients, in all of the products I examined,

two parabens are present:

E218 - Methylparaben 

E216 Propylparaben

and, in most of the tablet packages there is, in the coating film the

Titanium Dioxide E171

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Molecular Formula:  C₂₁H₂₅ClN₂O₃

Molecular Weight: 388.9 g/mol

CAS: 83881-51-0

UNII  YO7261ME24

EC Number: 620-533-8

DSSTox Substance ID: DTXSID4022787

Synonyms: 

• 2-(2-{4-[(4-chlorophenyl)(phenyl)methyl]piperazin-1-yl}ethoxy)acetic acid
• Cetirizin
• CETIRIZINE HYDROCHLORIDE
• 2-(2-(4-((4-Chlorophenyl)(phenyl)methyl)piperazin-1-yl)ethoxy)acetic acid

Acetic acid, (2-(4-((4-chlorophenyl)phenylmethyl)-1-piperazinyl)ethoxy)-

2-[2-[4-[(R)-(4-chlorophenyl)-phenylmethyl]piperazin-1-yl]ethoxy]acetic acid

References_______________________________________________________________________

(1) Lee CF, Sun HL, Lu KH, Ku MS, Lue KH. The comparison of cetirizine, levocetirizine and placebo for the treatment of childhood perennial allergic rhinitis. Pediatr Allergy Immunol. 2009 Aug;20(5):493-9. doi: 10.1111/j.1399-3038.2008.00816.x.

(2) Benazzo M, Leonardi S, Corsico A, Licari A, Miraglia Del Giudice M, Peroni D, Salpietro C, Marseglia GL, Ciprandi G. Cetirizine modifies quality of life and symptoms in children with seasonal allergic rhinitis: a pilot study. Acta Biomed. 2020 Jun 17;92(1):e2021003. doi: 10.23750/abm.v92i1.9948.

(3) Morán Blanco JI, Alvarenga Bonilla JA, Homma S, Suzuki K, Fremont-Smith P, Villar Gómez de Las Heras K. Antihistamines and azithromycin as a treatment for COVID-19 on primary health care - A retrospective observational study in elderly patients. Pulm Pharmacol Ther. 2021 Apr;67:101989. doi: 10.1016/j.pupt.2021.101989. 

Other relevant studies

Neuhaus W, Mandikova J, Pawlowitsch R, Linz B, Bennani-Baiti B, Lauer R, Lachmann B, Noe CR. Blood-brain barrier in vitro models as tools in drug discovery: assessment of the transport ranking of antihistaminic drugs. Pharmazie. 2012 May;67(5):432-9.

Sperl G, Gattner J, Deschner J, Wolf M, Proff P, Schröder A, Kirschneck C. Effects of Histamine Receptor Antagonist Cetirizine on Orthodontic Tooth Movement. Biomedicines. 2020 Dec 8;8(12):583. doi: 10.3390/biomedicines8120583.

Bielory L. Allergic inflammation of the anterior surface of the eye. Allergy Asthma Proc. 2020 Nov 1;41(6):449-453. doi: 10.2500/aap.2020.41.200068.

Iriarte Sotés P, Armisén M, Usero-Bárcena T, Rodriguez Fernández A, Otero Rivas M, Gonzalez MT, Meijide Calderón A, Veleiro B; Urtigal, the Galician Group of Interest in Urticaria. Up-Dosing Antihistamines in Chronic Spontaneous Urticaria: Efficacy and Safety. A Systematic Review of the Literature. J Investig Allergol Clin Immunol. 2020 Oct 8:0. doi: 10.18176/jiaci.0649.