Unveiling a potential link: Do non-steroidal anti-inflammatory drugs modulate resistance-associated microbial pathways?

INTRODUCTION

Antibiotic resistance represents a major threat in low- and middle-income countries, where limited diagnostic settings, unregulated consumption, poor sanitation procedures, and inadequate waste management facilities promote the emergence and dissemination of antibiotic resistance.^[1] The increasing prevalence of antibiotic resistance is turning the world into a crisis, characterized by sharply rising mortality rates and unequal regional impacts. By 2050, it is projected to dismantle decades of infectious disease control and severely strain healthcare infrastructures. The declining effectiveness of antibiotics against bacterial infections complicates treatment and endangers global public health, prompting international health authorities to classify antimicrobial resistance (AMR) as an urgent crisis requiring immediate action.^[2,3] While the misuse and overuse of antibiotics remain the main drivers of resistance, growing evidence indicates that several non-antibiotic factors may also contribute to resistance. Encouraging prudent antibiotic use is essential to curb the rise of resistance. However, balancing widespread access to new antibiotics with safeguarding their sustained effectiveness poses a significant ongoing challenge.^[4] In this context, increasing research attention has turned to the influence of widely used non-steroidal anti-inflammatory drugs (NSAIDs) on microbial communities and their potential role in modulating antibiotic resistance mechanisms.

NSAIDs rank among the most frequently prescribed medications globally, approved for alleviating pain, reducing fever, and controlling inflammation. This category includes non-selective agents such as ibuprofen, diclofenac, and naproxen, as well as cyclooxygenase (COX)-2 selective inhibitors such as celecoxib and rofecoxib, underscoring their broad clinical relevance and widespread use.^[5,6] Their easy accessibility, over-the-counter availability, and frequent use for a variety of acute and long-term ailments have led to widespread exposure among humans and contamination of the environment.^[7] Besides, their recognized adverse events include gastrointestinal, renal, and cardiovascular complications. In higher doses, NSAIDs have also been associated with liver toxicity, acute kidney injury, and disturbances in fluid homeostasis, although their underlying mechanisms remain poorly understood.^[8] Common NSAIDs such as acetylsalicylic acid, diclofenac, and ibuprofen exhibit anti-biofilm activity at clinically relevant concentrations, suggesting potential adjunctive roles in managing biofilm-related infections. However, most supporting evidence is derived from in vitro studies using non-clinical isolates, and the clinical relevance of these findings remains uncertain, with current data linking NSAIDs to antibiotic resistance being largely experimental and inconclusive.^[9] Figure 1 presents a comparative schematic delineating traditional antibiotic-mediated resistance and NSAID-associated resistance-modulating mechanisms. It illustrates that classical resistance pathways generally entail drug-specific structural modification or enzymatic inactivation, whereas NSAID-associated stress responses may promote broader physiological adaptations, including the induction of bacterial DNA damage response (SOS response), enhanced horizontal gene transfer, and biofilm matrix remodeling, collectively facilitating resistance dissemination and cross-protection against diverse antimicrobial agents.

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Figure 1:

Comparative mechanisms of traditional antibiotic-driven resistance versus non-steroidal anti-inflammatory drugs-associated resistance-modulating pathways: (a) traditional antibiotic-driven resistance involving drug inactivation, target modification, efflux activation, and permeability reduction, (b) non-antibiotic-driven resistance characterized by systemic stress responses, including bacterial DNA damage response (SOS response) activation, enhanced horizontal gene transfer, quorum sensing modulation, efflux upregulation, and biofilm reinforcement. ROS: Reactive oxygen species.

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The primary objective of this narrative review is to critically evaluate experimental, clinical, and mechanistic evidence on interactions between NSAIDs and microbial systems, with particular emphasis on their influence on AMR mechanisms, adaptive microbial pathways, and biofilm modulation. Drawing on a structured synthesis of microbiologically relevant evidence from the existing biomedical literature, this review examines the emerging link between NSAIDs and antibiotic resistance, elucidates potential mechanistic pathways, and explores broader implications for global public health. It also identifies existing research gaps and proposes future investigative pathways to better understand the clinical significance of nonsteroidal anti-inflammatory drugs as potential modulators rather than direct drivers of antimicrobial resistance, fostering evidence-based strategies for scientific advancement and healthcare policy reform.

METHODOLOGY

This narrative review seeks to synthesize current evidence about the effects of nonsteroidal anti-inflammatory drugs on antimicrobial resistance-associated microbiological activity. Literature review was carried out utilizing publicly accessible scientific databases such as “PubMed”, “Scopus,” and “Google Scholar,” with the goal of capturing peer-reviewed publications available as free full-text sources. Publications published between 1990 and 2025 were considered to provide both historical background and current relevance. The search strategy incorporated topic-specific keywords and their combinations, including “non-antibiotic drug resistance,” “non-steroidal anti-inflammatory drugs,” “microbial stress adaptation,” and “biofilm modulation and antimicrobial tolerance.” Search results were refined through manual screening of titles and abstracts to identify studies relevant to NSAID–microbe interactions. Full-text assessment was subsequently performed to confirm relevance and scientific rigor. Studies eligible for inclusion comprised experimental, clinical, and mechanistic investigations that explored microbial responses to NSAID exposure in relation to resistance-associated outcomes. Articles were excluded if they were non-English, inaccessible as full text, lacked microbiological endpoints, or did not address antimicrobial resistance-related mechanisms. Following the study selection process, an interpretive qualitative synthesis was performed to consolidate findings from heterogeneous experimental models. Instead of quantitative data aggregation, the studies underwent comparative appraisal to discern convergent biological motifs and mechanistic principles. Particular focus was directed toward elucidating the modulatory effects of NSAIDs on microbial responses amid antibiotic exposure and non-antibiotic stressors. An inductive thematic framework emerged organically from the analysis, categorizing the evidence into three core domains: microbial adaptation mechanisms, clinical and therapeutic ramifications, and persisting research voids. Key mechanistic subthemes encompassed stress-response cascades, efflux pump modulation, biofilm formation dynamics, oxidative stress cascades, and horizontal gene transfer processes. The clinical ramifications were contextualized with respect to antibiotic susceptibility profiles, therapeutic efficacy, and antimicrobial stewardship imperatives. Research voids were pinpointed through scrutiny of methodological constraints, inter-study discrepancies, and the paucity of translational or in vivo investigations.

ANTIBIOTIC RESISTANCE

Antibiotic resistance represents the evolutionary adaptation of the microorganism to resist various antimicrobial agents, diminishing therapeutic efficacy and threatening global healthcare through escalating economic strain, illness, or even death.^[10] It emerges from the interplay of multiple factors, including the level of resistance determinant expression in bacterial strains and their ability to endure through diverse molecular and physiological resistance mechanisms.^[11] Resistance develops through intrinsic genetic mutations coupled with horizontal gene transfer through mobile genetic elements such as plasmids, integrons, and transposons, which rapidly propagate resistance genes across bacterial populations and throughout clinical settings. This dynamic interplay accelerates the evolutionary adaptation of pathogens, thus enabling resilient strains to emerge and dominate under selective pressures.^[12-14] Resistant bacteria deploy sophisticated defense mechanisms, encompassing enzymatic inactivation of antibiotics (such as β-lactamase-mediated hydrolysis), structural modifications to drug targets, and heightened expression of efflux pumps that diminish intracellular antibiotic accumulation strategies, particularly prominent among Gram-negative pathogens.^[12,15] In addition to these mechanisms, bacteria can attenuate antibiotic ingress by modifying outer membrane porins, thereby curtailing drug permeation and undermining therapeutic efficacy. Concurrently, biofilm formation constitutes a pivotal resistance strategy, establishing a fortified microenvironment that impedes antibiotic diffusion, induces metabolic quiescence, and fosters horizontal gene transfer within bacterial consortia.^[16,17]

NSAIDs’ EFFECTS ON MICROBIAL PHYSIOLOGY AND MICROBIOMES

NSAIDs exert profound effects on microbial physiology and microbiomes, particularly within the complex ecosystem of the GI tract.^[18] The gut microbiota comprises a vast and diverse community of bacteria, archaea, viruses, fungi, and parasites that inhabit the GI tract and contribute to host physiology through numerous metabolic and immunological pathways.^[19] The composition and function of these microbial communities vary markedly along the gut’s regions due to differences in environmental parameters such as pH, oxygen concentration, epithelial physiology, and nutrient availability.^[20] For example, the small intestine harbors relatively low microbial biomass dominated by facultative anaerobes such as Lactobacillaceae owing to higher oxygen content, rapid transit times, and specialized immune activity, whereas the colon provides a more anaerobic, nutrient-rich habitat that supports dense populations of strict anaerobes including Lachnospiraceae, Bacteroidaceae, Ruminococcaceae and Prevotellaceae ^[21,22] NSAIDs, extensively employed for their pain-relieving and anti-inflammatory actions, can modulate microbial composition and function through both direct antimicrobial effects and host-mediated mechanisms.^[23] Directly, NSAIDs can inhibit or facilitate the growth of specific bacterial taxa, induce microbial cell death, and interfere with bacterial metabolism.^[24,25] For instance, in vitro studies have demonstrated antimicrobial activity of commonly used NSAIDs such as indomethacin and diclofenac against pathogens including Salmonella Typhimurium and Staphylococcus epidermidis ^[26,27] However, it remains unclear whether these effects are achieved at therapeutic doses in vivo and whether such antibacterial activity contributes to NSAID-induced dysbiosis and enteropathy. Indirect effects of NSAIDs upon the gut microbiota derive from their influence on host physiology. NSAIDs disrupt the integrity of the intestinal mucosa, increasing permeability (“leaky gut”) and promoting mucosal inflammation by upregulating pro-inflammatory cytokines such as interleukin-1β and tumor necrosis factor-alpha.^[28] These changes alter the ecological niche and immune environment, facilitating expansion of proinflammatory Gram-negative bacteria such as Proteobacteria and Bacteroidetes and reducing beneficial Firmicutes such as Lachnospiraceae. ^[29,30] Animal studies highlight variable effects of different NSAIDs on microbial diversity and composition. Naproxen causes jejunal ulceration and alters the balance between Lachnospiraceae and Bacteroides.^[31] Such variability likely reflects drug-specific pharmacodynamic properties and localized mucosal exposure, emphasizing the complexity of host–microbiome–drug interactions.^[32] Variation in NSAID-induced dysbiosis is influenced by age and sex; older individuals on NSAIDs show reduced beneficial microbes like Lactobacilli and increased microbial abundance compared to younger subjects, while women exhibit greater microbial diversity but heightened sensitivity to NSAID effects on permeability and community structure relative to men.^[33,34] Furthermore, microbial imbalance-driven neuroimmune activation and hypothalamic–pituitary–adrenal axis dysregulation appear to underlie the bidirectional relationship between gut dysbiosis and cognitive dysfunction in bipolar disorder, underscoring the therapeutic potential of microbiota-targeted interventions in neuropsychiatric management.^[35]

MOLECULAR MECHANISMS DRIVING NSAID-ASSOCIATED ANTIBIOTIC RESISTANCE

NSAIDs have recently been implicated in modulating bacterial responses associated with reduced antibiotic susceptibility through multiple molecular pathways.^[36] Studies show that common NSAIDs such as ibuprofen, diclofenac, naproxen, and salicylate can significantly enhance horizontal gene transfer and plasmid conjugation among clinically relevant pathogens, particularly Escherichia coli and Pseudomonas aeruginosa ^[37] This process is often triggered by NSAID-induced oxidative stress, which disrupts cell membranes and promotes DNA uptake and recombination.^[38] Elevated levels of reactive oxygen species activate the bacterial SOS response, leading to DNA repair errors and increased mutagenesis, which accelerate resistance gene expression.^[39] In addition, NSAIDs modulate the function of efflux pump systems such as AcrAB–TolC in E. coli and MexAB–Opr M in P. aeruginosa, enhancing bacterial survival under antibiotic pressure.^[22] Salicylates have been shown to upregulate MarA and AcrB transcription, reducing susceptibility to β-lactams, quinolones, and aminoglycosides.^[40] Such efflux-mediated effects may contribute to cross-resistance phenotypes even in the absence of direct antibiotic pressure.^[41] Furthermore, prolonged NSAID exposure alters outer membrane permeability and interferes with quorum-sensing regulation, which supports biofilm formation and persistence of resistant phenotypes.^[42] Experimental findings also demonstrate that NSAIDs can affect both planktonic and biofilm-associated cells. Diclofenac and ibuprofen inhibit early biofilm formation but later induce adaptive resistance by upregulating multidrug efflux and stress response pathways.^[43,44] These effects are not limited to E. coli; Pseudomonas similar phenomena have been observed in Staphylococcus aureus, Klebsiella pneumoniae, and Acinetobacter baumannii ^[45] Such alterations may complicate infection management, especially in immunocompromised or hospitalized patients with high NSAID usage. Collectively, these findings suggest that NSAIDs, while pharmacologically safe and widely prescribed, may facilitate resistance-associated adaptive mechanisms rather than directly cause antimicrobial resistance, posing emerging challenges for antimicrobial stewardship.^[46,47]

The frequent use of NSAIDs among patients with infections, especially in populations already at risk, such as those with chronic illness or weakened immunity, raises important clinical concerns. A large UK cohort study showed that patients prescribed NSAIDs during acute respiratory or urinary infections had significantly higher hospitalization and mortality rates compared to those not given NSAIDs. This pattern suggests that NSAID use remains widespread even among individuals who might experience adverse infection outcomes, underlining the need for cautious prescribing in high-risk cases.^[48] Evidence from a meta-analysis comparing NSAIDs and antibiotics for urinary tract infections revealed that NSAID-treated patients had slower recovery and prolonged symptoms compared to those who received antibiotics.^[49]

CLINICAL IMPLICATIONS OF NSAID-DRIVEN RESISTANCE

NSAIDs constitute one of the most extensively prescribed and widely utilized pharmacological classes globally. They are routinely employed for the management of pain, pyrexia, and inflammatory conditions, particularly among clinically vulnerable populations such as oncology patients, individuals with autoimmune pathologies, organ transplant recipients, and those suffering from chronic infections or immunocompromised states.^[8,50] Increasing evidence now demonstrates that certain NSAIDs, including acetylsalicylic acid, salicylic acid, and ibuprofen, possess measurable antimicrobial activity at therapeutic or slightly elevated concentrations, affecting a range of bacterial, fungal, and viral pathogens. These effects appear to be mediated through inhibition of nuclear factor-κB signaling, modulation of mitogen-activated protein kinase pathways, and disruption of microbial adhesion and motility structures, indicating biological actions beyond classic anti-inflammatory roles.^[51] Experimental studies further show that ibuprofen and diclofenac can inhibit Enterococcus faecalis at concentrations ≥ 50 µg/mL, producing significantly larger inhibition zones compared with calcium hydroxide (p < 0.05), although still inferior to antibiotics such as amoxicillin and gentamicin.^[52] In addition, both NSAIDs have demonstrated the ability to interfere with early biofilm formation by S . aureus and E. coli, reducing cell adhesion and colony-forming units, suggesting these agents may modulate microbial persistence and virulence rather than solely planktonic growth.^[44] These findings suggest modulation of microbial persistence and virulence rather than direct eradication, raising concerns that repeated or unsupervised NSAID exposure may inadvertently promote adaptive tolerance and altered susceptibility patterns.

FUTURE PERSPECTIVES AND INTEGRATION INTO STEWARDSHIP PROGRAMS

NSAID exposure warrants rigorous investigation beyond traditional antibiotic-centric frameworks to determine its potential contribution to AMR at molecular, clinical, and population levels. Emerging evidence indicates that these agents may influence bacterial efflux regulation, biofilm communication networks, and adaptive stress responses in ways that resemble sub-inhibitory antibiotic effects, suggesting a broader pharmacological footprint than previously recognized.^[9] Essential next steps include prospective longitudinal studies employing metagenomic, metabolomic, and resistome profiling to assess whether sustained or intensive NSAID use drives alterations in susceptibility patterns, pathogen virulence, and microbiome architecture among heterogeneous patient cohorts.^[53]

Antimicrobial stewardship initiatives may consider incorporating NSAIDs utilization monitoring into electronic health record systems, real-time alerting mechanisms, and risk-assessment protocols, with targeted application to vulnerable populations such as oncology patients, those with recurrent infections, and individuals on extended analgesic regimens.^[54] Medicinal chemistry advancements must concurrently pursue microbiome-sparing analgesics, isoform-selective COX inhibitors, hybrid molecular entities, and optimized delivery formulations that preserve therapeutic efficacy without provoking microbial signaling perturbations.^[23,55,56] Innovations in nanomedicine, such as precision-targeted carriers and biofilm-penetrating vehicles, offer additional promise for neutralizing selective pressures or enabling synergistic NSAID-antimicrobial combinations.^[57,58] Effective incorporation into stewardship practices demands unified clinical guidelines, artificial intelligence-driven forecasting models, microbiome-integrated pharmacovigilance, and cross-disciplinary partnerships among pharmacologists, infectious disease experts, microbiome scientists, and policymakers.^[59,60] This strategic evolution in surveillance and research priorities will protect current antimicrobial assets while ensuring sustained availability of vital anti-inflammatory therapies.

CONCLUSION

Current evidence suggests that NSAIDs may influence AMR dynamics through mechanisms that extend beyond their intended actions. Certain NSAIDs, including diclofenac, ibuprofen, and acetaminophen, have been shown under specific conditions to modulate bacterial stress responses, enhance oxidative stress, alter DNA repair pathways, and upregulate efflux pump systems. These microbial effects extend the drivers of AMR beyond antibiotic misuse alone. Given their broad clinical use and environmental presence, NSAIDs may inadvertently accelerate the evolution and spread of resistant bacterial strains in both hospitals and communities. This evolving evidence underscores the need for interdisciplinary investigation and supports the expansion of conventional antibiotic stewardship toward a broader “drug–microbiome stewardship” framework that considers the resistance-modulating potential of non-antibiotic medications. Addressing these interactions will be essential for preserving antimicrobial efficacy and strengthening long-term strategies to mitigate the global resistance burden.