What is the best mouthrinse against coronaviruses?

Dear editor,

The person‐to‐person transmission of SARS‐CoV‐2 may occur directly or indirectly through saliva, and a pre‐operational use of antimicrobial mouthwash is considered to reduce the number of oral microbes . Chlorhexidine mouthwash has been a common antiseptic agent used in dentistry, both pre‐operative and post‐operative use reducing post‐surgical infectious complications . Since chlorhexidine compounds are also effective against lipid‐enveloped viruses, it has been examined as a possible alternative antiseptic effective against the novel coronavirus .

Peng et al. (2020) suggested that chlorhexidine may not be effective to kill 2019‐nCoV, and since 2019‐nCoV is vulnerable to oxidation, pre‐procedural mouthrinse containing 1% hydrogen peroxide or 0.2% povidone is recommended. Anterior studies evaluated the use of chlorhexidine against Human Coronavirus 229E (HCOV), and it proved ineffective , . However, these studies evaluated chlorhexidine concentrations below 0.12% (Table 1).

Table 1

Chlorhexidine and its efficacy against HCOV and SARS‐COV‐2 (adapted from Geller et al. ; Kampf et al. and Yoon et al. )

Mouthwashes	Reference	pH at used concentration	Efficacy against HCOV	Efficacy against SARS‐CoV‐2
Chlorhexidine gluconate (0.008%) + cetrimide (0.08%)	Geller et al. 4	5	No	–
Chlorhexidine gluconate (0.05%) + cetrimide (0.5%) + ethanol (70%)	Geller et al. 4	4.5	Yes	–
Chlorhexidine gluconate (0.02%)	Kampf et al. 5	–	No	–
Chlorhexidine gluconate (0.12%)	Yoon et al. 3	–	–	Yes

Notwithstanding, it was observed that concentrations of chlorhexidine 0.05%, with ethanol and cetrimide added to the mouthwash demonstrated effective results against HCOV . A recent study conducted by Yoon et al. (2020) that prescribed chlorhexidine (0.12%, 15 mL) mouthwash demonstrated viral suppression for 2 h after using the mouthwash once. This study suggested that chlorhexidine mouthwash might be beneficial for the oral antisepsis and control of SARS‐CoV‐2 transmission in both community and hospital/ambulatory settings. Nevertheless, there are several limitations to this study, such as a small number of patients and the lack of a control group for comparison.

There is insufficient evidence on the efficacy of chlorhexidine and hydrogen peroxide in diminishing the possibility of SARS‐CoV‐2 transmission. Only one article regarding the efficacy of hydrogen peroxide as oral antiseptic rinses against SARS Cov‐2 was found. This article compared in vitro inactivation of SARS CoV‐2 with hydrogen peroxide and povidone‐iodine oral antiseptic rinses (Table 2). It demonstrated minimal viricidal activity against SARSCoV‐2 after 30 s of contact time of 1.5% and 3% of hydrogen peroxide. Meanwhile, SARSCoV‐2 virus was completely inactivated by povidone after the 15‐ and 30‐s contact times in concentrations of 0.5%, 1.25%, and 1.5% . However, further studies proving the efficacy of 1% of hydrogen peroxide against SARS CoV‐2 as mentioned by Peng et al. (2020) were not found.

Table 2

Hydrogen peroxide and povidone‐iodine regarding its efficacy against SARS‐COV‐2 in vitro (adapted from Bidra et al. 2020)

Mouthwashes	Concentration (%)	Time of viricidal effect after contact (seconds)	Efficacy against SARS‐CoV‐2
Hydrogen peroxide	1.5	30	Minimal viricidal activity
Hydrogen peroxide	3	30	Minimal viricidal activity
Povidone‐iodine	0.5	15	Complete inactivation
Povidone‐iodine	1.25	15	Complete inactivation
Povidone‐iodine	1.5	15	Complete inactivation

Likewise, there is insufficient evidence regarding the efficacy of pre‐operative 1% hydrogen peroxide to prevent infectious complications on the post‐operative period, unlike chlorhexidine. Even assuming that 1% of hydrogen peroxide is the best alternative to prevent transmission during oral procedures, its use on post‐operative does not seem to be necessary. Rinsing with 1% of hydrogen peroxide should not be done as a treatment for COVID‐19. The purpose of rinsing 1% hydrogen peroxide is to protect the professional from avoiding transmission during the procedure from patients already infected by SARS‐CoV‐2 .

Besides, the frequent use of hydrogen peroxide can be harmful to the tissue and its effectiveness in reducing post‐operative infectious complications has not been proven . Although povidone has been used as an antiseptic in preventing infections, it is not a primary choice for mouthwash because of its possibility of pigmentate restorations, tooth darkening and allergenic potential . Povidone is not recommended either in pregnant or for patients with active thyroid disease or undergoing radioactive iodine therapy .

Large‐scale in vitro and in vivo studies, including control subjects, sampling errors, are required to help clarify the possibility of the use of chlorhexidine as an effective antiseptic against SARS‐CoV‐2. We suggest additional studies to evaluate the effectiveness of chlorhexidine using other concentrations such as 0.12%, 0.2% or even less, e.g. 0.05%, if it is an alcoholic solution considering the efficacy of ethanol 70% against SARS‐CoV‐2 . Furthermore, studies to clarify the efficacy of 1% hydrogen peroxide against SARS‐CoV‐2 and for the prevention of infectious complications in post‐operatory are imperative, since Ortega et al. (2020) reported that there is only one study showing the SARS inactivation efficacy of hydrogen peroxide and it occurred using vapour form at a 35% concentration. Then, those future studies could be useful for health professionals to use one solution to prevent SARS‐CoV‐2 transmission during procedures and future infectious post‐operative complications.

Conflicts of interest

Authors declare that there is no conflict of interest.

Author contributions

Conceptualisation: Gercina AC, Amorim KS and Groppo FC; Writing – original draft preparation: Gercina AC, Pagaduan R, Amorim KS; Writing – review & editing: Souza LMA and Groppo FC.