Hexylresorcinol lozenges demonstrated rapid antibacterial activity against a broad range of organisms implicated in acute sore throat, including Gram-positive species (S. aureus and S. pyogenes) and Gram-negative species (M. catarrhalis, H. influenzae and F. necrophorum). Across all test organisms, bactericidal activity was seen from the 1-min time point. For S. aureus, M. catarrhalis, H. influenzae and F. necrophorum, the decrease at 1 min exceeded 3log10 (99.9% reduction). For S. pyogenes, the most common cause of bacterial acute sore throat [3], the decrease was 2.9log10 at 1 min and greater than 3log10 reductions were recorded by 5 min. To the best of our knowledge, these are the first published data indicating that hexylresorcinol-containing lozenges have bactericidal activity in vitro.
The study was designed to simulate the clinical setting as far as possible, including the time taken for a lozenge to dissolve in the mouth (mean ± standard deviation: 6.77 ± 2.01 min) [22]. Furthermore, the method was designed to replicate the expected concentration of hexylresorcinol that would be achieved when a lozenge is dissolved in the mouth, assuming a volume of 5 mL of saliva.
The findings in this study are consistent with previously reported antibacterial effects of hexylresorcinol in solution against a range of organisms, including Streptococcus spp. and S. aureus [18]. In addition, these data are in line with studies of other over-the-counter acute sore throat treatments. In a similar in vitro study, Matthews et al. (2018) reported that lozenges containing 0.6 mg amylmetacresol and 1.2 mg 2,4-dichlorobenzyl alcohol had broad antibacterial activity against a similar range of oropharyngeal organisms associated with acute sore throat. Specifically, reductions in bacterial counts exceeded 99.9% by 1 min for S. pyogenes, H. influenzae, F. necrophorum and A. haemolyticum, by 5 min for M. catarrhalis and S. dysgalactiae and by 10 min for S. aureus [21]. The antibacterial effects of hexylresorcinol lozenges reported here add to existing knowledge of their activity, which include numbing effects [13, 14] and antiviral activity [16, 17], resulting in relief of sore throat symptoms [13].
In conclusion, hexylresorcinol lozenges demonstrated bactericidal activity against medically relevant oropharyngeal organisms associated with acute sore throat from 1 min and achieved a > 99.9% reduction in cfu/mL for all test organisms within 5 min, which is in line with the duration for a lozenge to dissolve in the mouth. Thus, hexylresorcinol lozenges represent an effective over-the-counter treatment option for acute sore throat, offering rapid antibacterial, antiviral and local anesthetic effects, and may help to avoid unnecessary antibiotic prescribing, which is associated with the development of antibiotic resistance.