Chlorpheniramine for long COVID

CHLORPHENIRAMINE

What is chlorpheniramine?

Chlorpheniramine is an antihistamine that relieves symptoms of allergies, hay fever, or a cold, such as red, itchy, or watery eyes, sneezing, and runny nose. Compared to other antihistamines, chlorpheniramine is more sedating and can help you fall asleep. It is typically taken as a 4 mg tablet every 4-6 hours for adults and children ages 12 years and older.

How can chlorpheniramine help alleviate certain long COVID symptoms? 

Histamine is a chemical our immune system releases that causes our allergy symptoms. Cells in our body called mast cells release histamine, and in some patients after COVID, they may release too much, leading to some of the symptoms of long COVID. Long COVID is believed to be a state of prolonged hyper-inflammation that follows the infection. Chlorpheniramine can block histamine type 1 receptors and help alleviate nasal congestion and inflammatory symptoms of long COVID.

What evidence supports chlorpheniramine’s use for long COVID?

In vitro, chlorpheniramine has been found to have antiviral properties by blocking viral replication and directly inactivating the COVID virus and other respiratory viruses such as influenza.¹ While a chlorpheniramine nasal spray is not currently available over-the-counter in the US, it has been studied in patients treated outpatient with mild to moderate COVID and was found to reduce symptoms by day seven and specifically improve nasal congestion.² In this study, 136 patients were randomized to chlorpheniramine nasal spray for ten days or placebo. It is important to note that chlorpheniramine nasal spray results may differ from oral chlorphenamine tablets because the medications are absorbed differently and applied at different sites of action.

Antihistamines are effective in managing long COVID symptoms.³ Other H1-antihistamines such as fexofenadine, loratadine, and cetirizine have beneficial effects on long COVID symptoms, and chlorpheniramine would likely show similar effects.^4,5 However, more studies that look specifically at chlorpheniramine for long COVID are needed.

What are some things to watch out for with chlorpheniramine?

Because chlorpheniramine can cause drowsiness, it should not be taken during the day, while driving, or while operating heavy machinery. Depending on what other medications you take, chlorpheniramine can worsen some side effects, such as constipation, dry mouth, and dry eyes. While chlorpheniramine has sedating effects, it should not be routinely used for insomnia.  

References:

1)      Elshaier YAMM, Mostafa A, Valerio-Pascua F, et al. Chlorpheniramine maleate displays multiple modes of antiviral action against SARS-CoV-2: a mechanistic study. bioRxiv. 2023 Aug 29. doi: 10.1101/2023.08.28.554806

2)      Pascua FRV, Pineda E, Vargas-Pineda M, et al. Chlorpheniramine intranasal spray (0.4%) to accelerate COVID-19 clinical recovery in an outpatient setting: Accros III. AJRCCM. 2023;207:A5619. doi: 10.1164/ajrccm-conference.2023.207.1_MeetingAbstracts.A5619

3)      Mashauri HL. Covid-19 Histamine theory: Why antihistamines should be incorporated as the basic component in Covid-19 management? Health Sci Rep. 2023 Feb 7;6(2):e1109. doi: 10.1002/hsr2.1109

4)      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

5)      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