The use of benzalkonium chloride in topical glaucoma treatment: An investigation of the efficacy and safety of benzalkonium chloride-preserved intraocular pressure-lowering eye drops and their effect on conjunctival goblet cells.

ENGLISH SUMMARY: Glaucoma is a leading cause of the global prevalence of irreversible blindness. The pathogenesis of glaucoma is not entirely known, but the major risk factors include advancing age, genetic predisposition, and increased intraocular pressure (IOP). The only evidence-based treatment is a lowering of IOP through the use of eye drops, laser procedures, or surgical interventions. Although laser treatment is gaining recognition as a first-choice treatment option, the most common approach for managing glaucoma is IOP-lowering eye drops. A major challenge in the treatment is the occurrence of adverse events and poor adherence. In this context, the ocular surface is an area of great concern, as most glaucoma patients have dry eye disease (DED), which is largely caused by eye drops. Preservation with benzalkonium chloride (BAK) is a controversial topic due to its potential role as a significant cause of DED. A systematic review and meta-analyses investigate potential differences in efficacy and safety between BAK-preserved and BAK-free anti-glaucomatous eye drops (I). Many of the included studies report on ocular surface damage caused by the application of BAK-preserved eye drops. However, the meta-analyses addressing hyperemia, number of ocular adverse events, and tear break-up time did not identify any significant differences. The latter is likely due to varying measurement methods, different endpoints, and study durations. It is, therefore, possible that the large variations between the studies conceal differences in the safety profiles. The efficacy meta-analysis finds that there are no differences in the IOP-lowering effect between BAK-preserved and BAK-free eye drops, indicating that BAK is not necessary for the effectiveness of eye drops. To promote more homogeneous choices of endpoints and methods when evaluating BAK-preserved and BAK-free glaucoma treatments, a Delphi consensus statement was performed. In this study, glaucoma experts and ocular surface disease experts reached consensus on the key factors to consider when designing such studies (II). The hope is to have more studies with comparable endpoints that can systematically show the potentially adverse effects of BAK. The preclinical studies in the current Ph.D. research focus on conjunctival goblet cells (GCs). GCs are important for the ocular surface because they release the mucin MUC5AC, which is an essential component of the inner layer of the tear film. BAK preservation may damage the GCs and result in a low GC density, leading to an unstable tear film and DED. The most commonly used IOP-lowering drugs are prostaglandin analogs (PGAs). Thus, the conducted studies investigate the effect of PGAs preserved in different ways on GCs. BAK-preserved latanoprost is cytotoxic to primary cultured human conjunctival GCs and results in a scattered expression of MUC5AC, in contrast to negative controls, where MUC5AC is localized around the cell nucleus (III). Preservative-free (PF) latanoprost is not cytotoxic and does not affect the MUC5AC expression pattern. Furthermore, BAK-preserved travoprost is found to be cytotoxic in a time-dependent manner, while Polyquad®-preserved travoprost does not affect GC survival at any measured time point (IV). Both Polyquad and BAK induce scattered expression of MUC5AC. The cytotoxicity of BAK-preserved PGA eye drops is higher compared to the safer profile of PF and Polyquad-preserved PGA eye drops (V). Additionally, PF latanoprost does not increase the release of the inflammatory markers interleukin (IL)-6 and IL-8, unlike BAK-preserved latanoprost. A review highlights the active and inactive components of IOP-lowering eye drops (VI). Several preclinical and clinical studies have identified adverse effects of BAK. Although other components, such as the active drug and phosphates, can also cause adverse events, the review clearly states that BAK alone is a major source of decreased tolerability. The conclusion of this thesis is that BAK preservation is unnecessary and harmful to the ocular surface. The preclinical studies demonstrate that GCs die when exposed to BAK. Furthermore, they find that BAK induces a pro-inflammatory response. The review included in the thesis concludes that BAK should be phased out of eye drops for chronic use. Overall, the inclusion of BAK poses a risk of developing DED and poor adherence, which can ultimately lead to disease progression and blindness.

Efficacy, safety and acceptability of a benzalkonium chloride spermicide cream in women aged 40 years and over needing contraception: A prospective multicentre study.

OBJECTIVE: This multicenter prospective study (BZK40+) aims to determine the efficacy and tolerance of a benzalkonium chloride-containing spermicide as contraceptive among women aged 40 and over. PROCEDURE: Fertile women enrolled in this open single-arm study were instructed to systematically use the benzalkonium chloride spermicide before each intercourse. At the end of a 6-month mandatory period, participants were given the option of continuing the study for a further 6 months. The primary endpoint for contraceptive efficacy was the Pearl Index (PI) up to 12 months of typical use. MAIN FINDINGS: A total of 151 women (mean age: 45.9 years) were enrolled, 144 (95.4%) completed the initial 6-month period and 63 (41.7%) completed the optional 6-month period. The median number of intercourses ranged from 3 to 5 per month. The spermicide was applied before 96.3% of the 5,895 sexual intercourses. The PI up to 12 months of typical use was 0 pregnancies (95% confidence interval: 0-2.88). The cumulative treatment exposure was 1249.7 women-months. CONCLUSION: This first study in women aged 40 years and over shows that benzalkonium chloride spermicide (Pharmatex®) is effective, well tolerated and well accepted in this population. Although very interesting, these results with a PI equal to zero are surprising and not in accordance with the low efficacy of spermicides in the overall population according to the WHO. So, our results should be interpreted with caution and confirmed by future research. Clinical trial registration number (EudraCT): 2016-004,188-38.

[Cell cultures - model object for experimental studies in ophthalmology]. / Kletochnye kul'tury ­ model'nyi ob"ekt dlya eksperimental'nykh issledovanii v oftal'mologii.

The article presents results obtained on several types of model cultures. Primary cultures of corneal epithelial cells and fibroblast-like cells from the limbus were obtained from the tissues of the anterior eye segment. Tests were performed on these cultures to determine the cytotoxicity of antiglaucoma drugs and to trial a protection method. In addition, a comparative analysis of the regenerative potential of various blood derivatives was carried out. An in vitro culture of endotheliocytes showed a correlation between the degree of damaging effects of antiglaucoma drugs of various groups and the content of the preservative benzalkonium chloride in their composition. Corneal keratocytes were used to create a cell sheet reflecting the main structural features of the stroma and suitable for biomechanical tests. The antifibrotic activity of the drugs was tested on the culture of fibroblasts from the nasolacrimal duct. The conducted studies demonstrate that cell cultures can be used as an informative model object for researching the pathogenesis of ophthalmic diseases and for testing drugs.

Influence of BAKs on tear film lipid layer: In vitro and in silico models.

Benzalkonium chloride (BAK) compounds are commonly used in topical ophthalmic products as preservatives and stabilizers. BAK mixtures containing several compounds with different alkyl chain lengths are typically used. However, in chronic eye conditions, such as dry eye disease and glaucoma, the accumulation of adverse effects of BAKs was observed. Hence, preservative-free eye drops formulations are preferred. On the other hand, selected long-chain BAKs, particularly cetalkonium chloride, exhibit therapeutic functions, promoting epithelium wound healing and tear film stability. Nevertheless, the mechanism of BAKs influence on the tear film is not fully understood. By employing in vitro experimental and in silico simulation techniques, we elucidate the action of BAKs and demonstrate that long-chain BAKs accumulate in the lipid layer of the tear film model, stabilizing it in a concentration-dependent fashion. In contrast, short-chain BAKs interacting with the lipid layer compromise the tear film model stability. These findings are relevant for topical ophthalmic drug formulation and delivery in the context of selecting proper BAK species and understanding the dose dependency for tear film stability.

Tobramycin and antiglaucoma agents as increasing culprits of periorbital allergic contact dermatitis from topical ophthalmic medications: A 24-year study from Turkey.

BACKGROUND: Allergic contact dermatitis (ACD) from topical ophthalmic medications (TOMs) poses an additional disease burden to patients who already suffer from eye problems. OBJECTIVES: To investigate the epidemiological/clinical profile of patients with periorbital ACD from TOMs in Turkey. PATIENTS AND METHODS: This was a retrospective, cross-sectional, single tertiary centre study based on files of 75 patch tested patients with suspected periorbital ACD from TOMs among a total of 2801 consecutively patch tested patients with suspected ACD of any origin between 1996 and 2019. RESULTS: Periorbital ACD was diagnosed in 25 of 75 (33.3%) patients (female:male = 1.8:1; age range: 6-85 years) with suspected ACD from TOMs showing an overall prevalence of 0.9% (25/2801) among the whole patch test population. Atopy was not present. Tobramycin-containing TOMs were the most frequent culprits, followed by antiglaucoma preparations. Their frequency increased, whereas no new cases of neomycin-induced ACD were observed after 2011. Positivities with thimerosal were of unknown clinical relevance, while benzalkonium chloride (BAC) caused ACD in two patients. The diagnosis would be missed in each 20% of patients without performing day (D) 4 and D7 readings and strip-patch testing. Ten culprits were identified only by testing with patients' own TOMs in eight (32%) patients. CONCLUSIONS: Aminoglycosides, particularly tobramycin, were the leading cause of ACD from TOMs. The frequency of ACD from tobramycin and antiglaucoma medications increased after 2011. BAC was a rare but important allergen. Additional D4 and D7 readings, strip-patch testing, and testing with patients' own TOMs seem essential when patch testing with eye medications.

Rodent models for dry eye syndrome: Standardization using benzalkonium chloride and scopolamine hydrobromide.

Dry eye disease is a highly prevalent ocular condition that significantly affects the quality of life and presents a major challenge in ophthalmology. Animal models play a crucial role in investigating the pathophysiology and developing effective treatments. The goal of this study was to compare and standardize two dry eye disease rodent models and explore their recovery aspects. We have standardized benzalkonium chloride and scopolamine-induced dry eye disease models which represents two different classes of the dry eye i.e., evaporative dry eye and aqueous deficient dry eye, respectively. After the development of dry eye conditions, a self-recovery period of seven days was granted to assess the reversal of the induced changes. The dry eye condition was assessed by measuring tear volume, corneal slit lamp imaging, and histological examination of the cornea, the lacrimal and the harderian gland. The study indicated the development of chronic inflammation of the cornea and lacrimal gland in the case of benzalkonium after five days of the treatment, while the scopolamine treated group showed chronic inflammation of the lacrimal gland after five days and corneal inflammation after seven days of administration. The recovery study suggested that after discontinuation of inducing agent, the dry eye symptoms were still persistent suggesting the utility of the model in evaluating dry eye treatments. The study highlights the comparative changes in both models along with recovery which can serve as a base for drug discovery and development against dry eye disease.

Effectiveness and Safety of Albuterol Solutions With and Without Benzalkonium Chloride.

INTRODUCTION: Continuous aerosolized ß2 agonist, namely albuterol, is the most commonly used therapy for critical asthma. Benzalkonium chloride is a preservative present in some formulations of aerosolized albuterol solutions that can induce bronchospasm. Recent studies have shown that inhalation of albuterol containing benzalkonium chloride might induce unintended bronchoconstriction and poor outcomes. This study aimed to investigate whether using albuterol solutions containing benzalkonium chloride results in prolonged hospital length of stay (LOS). METHODS: This was a retrospective cohort study of pediatric subjects admitted to the pediatric ICU (PICU) and treated with continuous albuterol. Data were collected and compared before and after a change to benzalkonium chloride-containing solutions. Subjects who were treated with preservative-free solutions were used as control. The primary outcome was PICU and hospital LOS; secondary outcomes included the duration of continuous albuterol and use of adjunctive therapies. RESULTS: A total of 266 admissions were included in the study. One hundred forty subjects (52.6%) were exposed to benzalkonium chloride. Median age and severity of illness scoring were similar between groups. The initial dose of continuous albuterol was significantly higher in the benzalkonium chloride group (median 15 interquartile range [IQR] 10-20 mg/h) compared to the preservative-free group (median 10 IQR 10-20 mg/h) (P < .001). PICU LOS was longer for the preservative-free group, 2.5 (IQR 1.4-4.6) d vs 1.8 (IQR 1.1-2.9) d for benzalkonium chloride group (P = .002). There was no significant difference in duration of continuous albuterol therapy (P = .16) or need for adjunctive respiratory support (heliox [P = .32], noninvasive ventilation [P = .81], and invasive mechanical ventilation [P = .57]). CONCLUSIONS: In contrast to published literature showing that benzalkonium chloride may be associated with a longer duration of continuous albuterol nebulization and hospital LOS, our study demonstrated that benzalkonium chloride-containing albuterol is safe for continuous nebulization in critically ill children and not associated with worse outcomes.

Allergic contact dermatitis to chlorhexidine-containing antiseptics and their excipients in children: A series of six cases.

Contact allergy to skin disinfectants is not often recognized in children. We report the cases of six children (1-16.5 years old) with allergic contact dermatitis to ingredients commonly contained in commercial antiseptic and cosmetic products. Patch test responses to chlorhexidine, benzyl alcohol, and benzalkonium chloride varied from one child to another one, but most children were sensitized to at least two components. In several of the cases, exposure had initially occurred in the neonatal period, but diagnosis occurred only after multiple reactions of increasing severity.

The Importance of Preventing and Managing Tear Dysfunction Syndrome in Allergic Conjunctivitis and How to Tackle This Problem

Tear dysfunction syndrome, also known as dry eye disease (DED), is a multifactorial disease of the ocular surface characterized by the loss of tear film homeostasis. DED shows a significant clinical overlap with ocular allergy (OA), which alters tear film homeostasis, thus predisposing the patient to DED. Both conditions constitute the most common ocular surface disorders and have a potentially severe impact on patients’ quality of life. Clinical practice guidelines recommend topical therapies as first-line treatment for OA. However, eye drop formulations may contain additional substances that can contribute to ocular surface damage and the development of DED. Therefore, physicians treating ocular allergy should be aware of problems affecting the tear film, the role of tear film disruption in OA, and topical treatment to prevent or minimize DED. The aim of this review is to present an updated overview of the topic. (AU)

El síndrome de disfunción lagrimal, también denominado enfermedad del ojo seco (EOS), es una enfermedad multifactorial de la superficie ocular caracterizada por la pérdida de la homeostasis de la película lagrimal. La EOS y la alergia ocular (AO) son patologías que comparten un abanico de signos y síntomas, y pueden aparecer simultáneamente; además, la AO altera la homeostasis de la película lagrimal, predisponiendo a la EOS. Estas dos afecciones constituyen los trastornos más frecuentes de la superficie ocular y pueden afectar notablemente la calidad de vida de los pacientes. Las guías de práctica clínica recomiendan terapias tópicas como tratamiento de primera línea para la alergia ocular. Sin embargo, las fórmulas de los colirios pueden contener aditivos y conservantes que pueden contribuir al daño de la superficie ocular y a la aparición de EOS. Por lo tanto, los facultativos que tratan la alergia ocular deben conocer las implicaciones que conlleva la alteración de la película lagrimal en la conjunctivitis alérgica, el potencial daño que pueden provocar los conservantes incluidos en los colirios empleados en el tratamiento tópico de esta patología, así como los tratamientos disponibles para manejar la EOS y la AO cuando la disfunción de la película lacrimal ya está establecida. El objetivo de esta revisión es presentar una visión general actualizada del tema. (AU)

Prevalence of Ocular Surface Disease and Associated Risk Factors in Glaucoma Patients: A Survey Study of Ophthalmologists.

Objectives: This survey study of ophthalmologists investigated the prevalence and clinical manifestations of ocular surface disease (OSD) in glaucoma patients, assessment methods used, risk factors, glaucoma drugs considered responsible, and treatment approaches. Materials and Methods: A questionnaire prepared jointly by the Turkish Ophthalmological Association Cornea and Ocular Surface Society and Glaucoma Society using SurveyMonkey was sent to ophthalmologists via e-mail. The distribution of parameters was compared with chi-square test and p<0.05 was considered statistically significant. Results: Forty-five percent of the ophthalmologists reported that OSD was evident in least 25% of their patients. The most common symptom was redness (91.9%), while the most common ocular surface finding was conjunctival hyperemia (75.6%). The tests considered to be the most important in ocular surface assessment were ocular staining (38.7%) and tear film break-up time (TBUT) (21.9%). Ninety percent of the physicians stated that the main cause of OSD was benzalkonium chloride (BAC) in medications. Prostaglandin analogs and alpha-2 agonists were reported to be the most common medications causing OSD. In case of OSD, the ophthalmologists often switch to a glaucoma drug from a different group (38%), a non-preservative glaucoma drug (33.7%) or a drug with a preservative other than BAC (20.4%). Most physicians prescribed artificial tears (84.6%). Conclusion: In this cross-sectional survey study, ophthalmologists detected varying rates of OSD in glaucoma patients depending on chronic drug use and BAC exposure. Although ocular surface examination was performed by physicians, tests such as TBUT and ocular surface staining were rarely used. Detecting OSD in glaucoma patients and planning personalized treatment increase patient comfort, drug compliance, and treatment effectiveness. For this reason, it is important to prepare an algorithm for the management of comorbid OSD in glaucoma patients.

Hyperkeratotic flexural erythema (more commonly known as granular parakeratosis) with use of laundry sanitizers containing benzalkonium chloride.

BACKGROUND: Hyperkeratotic flexural erythema (HKFE), also known as granular parakeratosis, is a scaly, erythematous or brown eruption, which usually occurs in the intertriginous and flexural areas. It has been linked to the use of benzalkonium chloride (BAK). AIM: To review the clinical presentation of patients diagnosed with HKFE who had been exposed to laundry sanitizer containing BAK, and the therapies trialled to treat these patients. METHODS: This was a retrospective cases series of 45 patients seen by dermatologists in Victoria, Australia. Information was collected on clinical presentation, investigation and management. RESULTS: The patients varied in age from 18 months to 89 years. The rash typically presented as a symmetrical erythema with characteristic multilayered brownish epidermal scaling. The most common location of the rash was the inguinal/anogenital area (32 of 45 patients; 71.1%) and there was a female predominance. Regarding treatment, topical corticosteroids were frequently prescribed and antibiotics were trialled in 11 patients; however, the condition resolved spontaneously over time in all patients with use of emollients, along with cleaning of the washing machine by running an empty wash, and repeated washing or sometimes disposal of BAK-contaminated clothing. CONCLUSION: This large case series highlighted the characteristic clinical presentation of HKFE in the setting of BAK used in laundry sanitizer, demonstrating a potential causal link. Further studies are required to evaluate the role of the skin microbiome.

Noninferiority Study Comparing Latanoprost 0.005% Without Versus With Benzalkonium Chloride in Open-Angle Glaucoma or Ocular Hypertension.

OBJECTIVES: To evaluate the noninferiority of intraocular pressure (IOP)-lowering latanoprost without benzalkonium chloride (BAK) versus latanoprost with BAK (for treatment of open-angle glaucoma or ocular hypertension). METHODS: Overall, 578 patients were randomized 1:1 to latanoprost without BAK or latanoprost with BAK once daily in the affected eye(s) for 12 weeks. The primary efficacy endpoint was IOP, measured on days 0, 7, 28, 56, and 84 (8 am, 10 am, and 4 pm). Noninferiority was established if the following criteria were met: 95% confidence interval (CI) of the mean difference between treatments included 0 mm Hg for all time points (N1), 95% CI upper limit less than 1.5 mm Hg (N2), and less than 1 mm Hg for≥7 of 12 time points (N3). Primary efficacy analysis was performed on the intent-to-treat population. Safety measurements included ocular and systemic adverse event (AE). RESULTS: The 95% CI included 0 mm Hg for 7/12 time points (N1), 95% CI upper limit was less than 1.5 mm Hg for 12/12 time points (N2), and less than 1.0 mm Hg for 4/7 time points (N3). AEs were mild and similarly distributed between groups. CONCLUSIONS: Latanoprost without BAK did not meet two of three criteria for noninferiority and showed a similar safety profile relative to latanoprost with BAK.

Ocular benzalkonium chloride exposure: problems and solutions.

Preservatives in multidose formulations of topical ophthalmic medications are crucial for maintaining sterility but can be toxic to the ocular surface. Benzalkonium chloride (BAK)-used in approximately 70% of ophthalmic formulations-is well known to cause cytotoxic damage to conjunctival and corneal epithelial cells, resulting in signs and symptoms of ocular surface disease (OSD) including ocular surface staining, increased tear break-up time, and higher OSD symptom scores. These adverse effects are more problematic with chronic exposure, as in lifetime therapy for glaucoma, but can also manifest after exposure as brief as seven days. Multiple strategies are available to minimize or eliminate BAK exposure, among them alternative preservatives, preservative-free formulations including sustained release drug delivery platforms, and non-pharmacological therapies for common eye diseases and conditions. In this paper, we review the cytotoxic and clinical effects of BAK on the ocular surface and discuss existing and emerging options for ocular disease management that can minimize or eliminate BAK exposure.

Anti-glaucoma agents-induced pseudodendritic keratitis presumed to be herpetic simplex keratitis: a clinical case series.

Anti-glaucoma agents-induced corneal toxicity may be misdiagnosed as herpetic simplex keratitis (HSK). In our study, nineteen glaucoma patients were presumed to have HSK before referral. Corneal lesions were classified into (I) linear pseudodendritic lesions formed by elevated opacified cells, (II) linear pseudodendritic lesions formed by grouped superficial punctate keratitis (SPK), (III) satellite full-thickness epithelial defects, (IV) satellite lesions formed by elevated opacified cells, and (V) geographic lesions formed by grouped SPK. We observed thirty-one events, with 15 in the lower and 16 in the central corneas. There were 21 (67.7%) type II, five (16.1%) type V, two (6.5%) of each for types III and IV, and one (3.2%) type I events. Among linear lesions (types I and II), 17 (77.3%) had horizontal and 5 (22.7%) had curvilinear orientations. Exposure duration to the last-added anti-glaucoma agent was three days to 14.5 years. About half of the events (16/31, 51.6%) used prostaglandin analogues, and 30/31 (96.8%) applied benzalkonium chloride (BAK)-containing agents. All lesions resolved within two months after decreasing offending medications or enhancing protection of ocular surface. In conclusion, anti-glaucoma agents-induced pseudodendritic keratitis presents majorly in central-lower cornea as horizontally linear lesions, and BAK-containing agents are observed in the most events.

Ocular Surface Disease in Glaucoma Patients Randomized to Benzalkonium Chloride-Containing Latanoprost and Preservative-Free Bimatoprost.

Purpose: To investigate the influence of benzalkonium chloride (BAK) on ocular surface disease (OSD) in glaucoma patients receiving ocular-hypotensive agent. Methods: Patients were randomized to receive BAK-containing latanoprost (Xalatan) or preservative-free bimatoprost (Lumigan PF). Intraocular pressure (IOP), basal Schirmer's test, noninvasive keratograph tear-breakup time (TBUT), conjunctival redness score (R score), OSD index (OSDI), and corneal Oxford staining were recorded and compared between the 2 groups at 1-month and 4-month visits. The influence of BAK was analyzed by a generalized estimating equation model. Results: We enrolled 74 and 76 eyes treated with latanoprost and bimatoprost, respectively. The IOP decreased in both groups, although greater reduction was observed for latanoprost (13.95 vs. 15.42 mmHg, P = 0.0264). There was a significantly negative association between tear flow and latanoprost use (ß = -0.763, P = 0.0243). The first and average TBUT did not show intergroup differences, but the area with unstable tear film increased with latanoprost use and showed marginal significance at 4-month visit (9.33% vs. 5.94% P = 0.055). In both groups, OSDI decreased, whereas Oxford stain increased over time, and R scores showed improvement after transient increase in the first month. The bimatoprost group had significantly worse conjunctival hyperemia, whereas a negative association with conjunctival hyperemia was revealed for latanoprost use (R score-bulbar nasal: ß = -0.045, P = 0.0423). Conclusions: BAK-containing latanoprost was associated with decreased tear secretion and may be associated with tear-film instability, whereas bimatoprost was associated with worse conjunctival hyperemia. Ocular surface side effects should be considered when prescribing BAK-containing medication to glaucoma patients.

Benzalkonium chloride antagonises aminoglycoside antibiotics and promotes evolution of resistance.

BACKGROUND: Biocide disinfectants are essential tools in infection control, but their use can inadvertently contribute to emergence of antibiotic-resistant bacteria. In this study we systematically examine the effect of the biocide benzalkonium chloride, which is primarily used for surface disinfection but is also present as a preservative in many consumer products, on the activity of aminoglycoside antibiotics in Acinetobacter baumannii. METHODS: The effect of subinhibitory BAC on aminoglycoside treatment of A. baumannii ATCC17978 was investigated using time-to-kill assays, MIC determination, directed evolution experiments, fluctuation tests and labelled gentamicin accumulation assays. Further MIC determinations and directed evolution experiments were performed with additional Gram-negative ESKAPE pathogens. FINDINGS: In A. baumannii ATCC17978, BAC prevents gentamicin killing and drastically increases the frequency at which resistant mutants emerge, through reducing intracellular antibiotic accumulation. BAC also increases the MIC of multiple aminoglycoside antibiotics (kanamycin, tobramycin, streptomycin, gentamicin and amikacin). BAC promotes the emergence of mutants with reduced gentamicin susceptibility in other Gram-negative ESKAPE pathogens but does not always alter the MIC. These effects occur at BAC concentrations which are similar to residual levels in high-use environments, and just below the concentration range for BAC when used as a preservative in eye drops and ear drops. INTERPRETATION: Our results suggest that subinhibitory BAC has the potential to antagonise aminoglycoside activity and promote the emergence of bacterial mutants with reduced susceptibility. We suggest that the extremely widespread use of BAC in clinical and home settings and its long half-life mean there is potential for these interactions to occur in the environment, or in patients who use BAC-containing products while taking aminoglycosides to treat skin, eye or ear infections, although such co-exposure is likely to be rare. We suggest that biocide stewardship is needed to prevent the types of exposure that can contribute to antibiotic resistance. FUNDING: This work was funded by the National Health and Medical Research Council of Australia. The funders had no role in study design, interpretation or decision to publish.