Why might hydroxychloroquine and azithromycin be effective against the novel Coronavirus SARS-CoV-2/Covid-19?

Repurposing of older drugs such as chloroquine or hydroxychloroquine (HC) and more recently, azithromycin (AZ), has received much attention recently in the treatment of Covid-19. Both HC and AZ have immune modulating and antiviral activity that may potentially be effective in our fight against Covid-19.

Chloroquine/HC: Chloroquine is an old drug used for its antimalarial activity as well as for its immune modulation and anti-inflammatory properties. It is active in mice against a variety of viruses, including some enteroviruses, Zika virus, and influenza A H5N1 (1). Both chloroquine and HC are active in vitro against Covid-19, though HC appears to be more active (2).

Azithromycin: A macrolide often used for treatment of bacterial respiratory tract infections but also with anti-inflammatory and antiviral activity. Azithromycin has been shown to augment interferon response in rhinovirus-infected bronchial epithelial cells as well as in an experimental mouse model of asthma exacerbation (3,4). It also has activity against Zika virus (5). As recently as 2016, some authors opined that macrolides may be useful in pandemic influenza characterized by excessive inflammatory cytokine production because of their anti-inflammatory and interferon-boosting potential (6).

March 2020 French clinical trial: A small non-randomized clinical trial involving 36 confirmed Covid-19 patients (mean age 45 y) reported that HC (200 mg 3x/day x 10 days) was associated with rapid viral clearance from nasopharynx, often within 3-6 days (7). The effect was even more pronounced when AZ (500 mg 1st day, followed by 250 mg daily x 4 days) was added in 6 patients.

It’s worth emphasizing that most subjects in this study were either asymptomatic (17%) or had mild disease with upper respiratory tract infection symptoms only (61%). Pneumonia was diagnosed in only 6 patients.  A significant number of patients in the treatment arm also dropped out of the study, some due to ICU transfer.

Although such preliminary reports appear promising, the proof of the efficacy and safety of HC and/or AZ in the treatment of Covid-19 awaits larger properly designed clinical studies. Stay tuned!



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1. Touret F, de Lamballerie X. Of chloroquine and COVID-19. Antiviral Research 2020;177. 104762. https://www.ncbi.nlm.nih.gov/pubmed/32147496
2. Yao X, Ye F, Zhang M, et al. In vitro antiviral activity and projection of optimized dosing design of hydroxychloroquine for the treatment of severe acute respirartory syndrome coronavirus 2 (SARS-CoV-2). Clin Infect Dis 2020, March 9. https://www.ncbi.nlm.nih.gov/pubmed/32150618
3. Menzel M, Akbarshai H, Bjermer L, et al. Azithromycin induces anti-viral effects in cultured bronchial epithelial cells from COPD patients. Scientific Reports 2016;6:28698. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4923851/
4. Menzel M, Akbarshai H, Uller L. Azithromycin exhibits interferon-inducing properties in an experimental mouse model of asthma exacerbation. Eur Resp J 2015;46:PA5095. https://erj.ersjournas.com/content/46/suppl_59/PA5095
5. Retallack H, Di Lullo E, Knopp AC, et al. Zika virus cell tropism in the developing human brain and inhibition by azithromycin. Proc Nat Acad Sci USA 2016;113:14408-13. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5167169/
6. Porter JD, Watson J, Roberts LR, et al. Identification of novel macrolides with antibacterial, anti-inflammatory and type I and III-IFN-augmenting activity in airway epithelium. J Antimicrob Chemother 2016;71:2767-81. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5031920/
7. Gautret P, Lagier JC, Parola P, et al. Hydroxychloroquine and azithromycin as a treatment of COVID-19:results of an open-label non-randomized clinical trial. International Journal of Antimicrobial Agents—In Press 17 March 2020-DOI: 10.1016/j.ijantimicag.2020.105949 . https://www.sciencedirect.com/science/article/pii/S0924857920300996


Disclosures: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Massachusetts General Hospital, Harvard Catalyst, Harvard University, its affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

Why might hydroxychloroquine and azithromycin be effective against the novel Coronavirus SARS-CoV-2/Covid-19?

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