CETIRIZINE

What is cetirizine?

Cetirizine is an over-the-counter antihistamine used to relieve allergy symptoms such as watery or itchy/red eyes, an itchy nose, sneezing, and hives. While it is a non-drowsy antihistamine, it is considered more sedating than fexofenadine (Allegra) or loratadine (Claritin) and is typically taken at 10 mg once a day.

How can cetirizine help alleviate certain long COVID symptoms? 

Histamine is a chemical our immune system releases that causes allergy symptoms. Cells in our body called mast cells release histamine, and in some patients, after COVID, they may release too much, leading to a prolonged inflammatory response.

Long COVID is believed to be caused by a persistent hyper-inflammatory state that results in symptoms such as fatigue, arthralgia, myalgia, shortness of breath, chest pain, and rash. Two types of drugs can block histamine in the body, which we call our H1- and H2-antihistamines. Cetirizine is an H1-antihistamine believed to reduce inflammatory effects associated with long COVID.

What evidence supports cetirizine’s use for long COVID?

Several studies have shown a benefit in combining an H1- and H2-antihistamine for long COVID symptoms; however, studies need to study cetirizine in long COVID specifically. Loratadine is an H1-antihistamine that works like cetirizine to block histamine in the body. Studies with loratadine in combination with an H2-antihistamine such as famotidine have shown a reduction in long COVID symptoms such as brain fog and headaches, chest pain, and fatigue.¹ Given their similarities in mechanism, cetirizine may have similar effects in long COVID patients, but more studies are needed to confirm this.

Cetirizine has been studied in hospitalized patients with an acute COVID infection. A study done with 110 hospitalized COVID-19 patients who received cetirizine 10 mg twice a day plus famotidine (an H2-antihistamine) 20 mg twice a day for at least 48 hours showed a reduction in inpatient mortality and progression of pulmonary symptoms (such as shortness of breath or cough) compared to published reports of COVID-19 patients in 2020.²

What should you be aware of when taking cetirizine?

Cetirizine can be more sedating than fexofenadine and loratadine, so you may feel more drowsiness or fatigue, especially if you are taking other potentially sedating medications. Some side effects of cetirizine may include headaches, dry mouth, and dizziness. 

References:

1)      Glynne P, Tahmasebi N, Gant V, Gupta R. Long COVID following mild SARS-CoV-2 infection: characteristic T cell alterations and response to antihistamines. J Investig Med. 2022 Jan;70(1):61-67. doi: 10.1136/jim-2021-002051

2)      Hogan RB, Cannon T, Rappai M, Studdard J, Paul D, Dooley TP. Dual-histamine receptor blockade with cetirizine-famotidine reduces pulmonary symptoms in COVID-19 patients. Pulm Pharmacol Ther. 2020 Aug;63:101942. doi: 10.1016/j.pupt.2020.101942

Active Clinical Trials: Long COVID, antihistamines | Card Results | ClinicalTrials.gov