Cetirizine

Cetirizine is a second-generation antihistamine taken by mouth for allergic rhinitis and urticaria, and it is sometimes suggested for infectious conjunctivitis. There is no proof of benefit for this use: infectious conjunctivitis comes from a virus or bacteria, and blocking histamine does nothing about the cause of the inflammation. Bacterial cases respond to topical antibiotics prescribed by a doctor, while viral cases usually clear on their own with eye hygiene and supportive care. The substance is harmless in this role, but do not use it in place of treatment with proven benefit, since that risks missing the care you actually need.

Cetirizine is not effective for the common cold. The 2015 Cochrane review «Antihistamines for the common cold» (15 RCTs, 5,099 participants) showed that second-generation H1 antagonists (cetirizine, loratadine) do not reduce nasal symptoms. A weak effect on rhinorrhoea is seen only with first-generation H1 agents (chlorpheniramine, diphenhydramine) via their anticholinergic component, which cetirizine largely lacks. AAP, NICE, and CDC do not recommend antihistamines for the common cold. Widespread prescribing in post-Soviet practice is inconsistent with international evidence.

Cetirizine is not used in non-allergic rhinitis (vasomotor, idiopathic, infectious URI-related, medication-induced). ARIA 2020 and EAACI explicitly separate allergic and non-allergic rhinitis: systemic H1 blockers are not useful in the latter because histamine plays no or minimal role in pathogenesis. Topical azelastine and topical corticosteroids work for vasomotor rhinitis. Oral cetirizine or loratadine «for a runny nose» is an incorrect choice.

Routine cetirizine before planned vaccination in healthy individuals without allergy history is not supported by international societies. CDC Pink Book, ACIP 2023, WHO Vaccine Safety and Immunization Action Group: antihistamine premedication does not reduce anaphylaxis risk because the anaphylactic cascade is faster and stronger than H1-receptor blockade. Some data indicate reduced vaccine immunogenicity with antihistamine and paracetamol premedication (Prymula R et al. Lancet 2009, Saleh E et al. Pediatr Infect Dis J 2017) – antibody responses are 10–25 % lower for HIB, pneumococcal, and rotavirus vaccines. Patients with confirmed allergy to vaccine components are managed individually by an allergist, not «just in case».