In vitro antibacterial activity of newly combined povidone–iodine plus lidocaine throat spray against Streptococcus pyogenes

Abstract

Background: In clinical practice, streptococcal pharyngitis is difficult to distinguish from self-limited viral pharyngitis, resulting in overuse of antibacterial agents in patients with acute pharyngitis. Povidone–iodine (PVP-I) oral preparation could be a treatment option for throat infection, sparing the risk of antibiotic resistance of throat microflora. However, research on the antibacterial effect of PVP-I throat sprays, which typically contain lower concentrations of PVP-I compared to other PVP-I oral preparations, against Streptococcus pyogenes is limited and most commercial PVP-I oral preparations contain no ingredients with analgesic activity. Thus, few studies have focused on the effect of analgesics on antibacterial activity of PVP-I oral preparations.

Objectives: This study aimed to demonstrate in vitro bactericidal activity of a newly developed, combined antiseptic–analgesic oral throat spray of PVP-I plus lidocaine against S. pyogenes.

Methods: Antibacterial activity of combined 0.45% PVP-I plus 0.3% lidocaine throat spray against a reference strain of S. pyogenes was demonstrated using the bactericidal quantitative suspension test EN13727:2012 + A2:2015. The test product was serially diluted to 0.09%, 0.045%, 0.009%, 0.0045%, 0.00045% and 0.000045% PVP-I solution. Suspensions of the reference strain were added to the PVP-I test solutions for 30 seconds under dirty conditions and then spread on blood agar plates. Colony growth on each plate was counted and compared with a negative control sample to evaluate the antibacterial effect of the tested solutions.

Results: On 0.45%, 0.09%, 0.045% and 0.009% PVP-I plates, no surviving S. pyogenes colonies were observed after 24 h of incubation at 37°C. On those plates with visible bacterial colonies, colony count was inversely correlated with concentration of PVP-I. Compared with negative control plates, 0.0045% and 0.00045% PVP-I plates showed 97.45% and 93.33% colony growth reduction, respectively.

Conclusion: PVP-I, at concentrations of at least 0.009%, has demonstrated effective antibacterial activity against S. pyogenes in vitro. Therefore, a throat spray formulation containing 0.45% PVP-I, which is 50 times more concentrated than 0.009% PVP-I, is capable of inhibiting bacterial growth. This concentration may also alleviate concerns regarding clinical use, as the PVP-I concentration could be reduced through physiological dilution or clearance mechanisms in vivo.