Repurposing Drugs To Combat Antimicrobial Resistance

Fatima Begum^*
*Correspondence: Fatima Begum, Department of Antimicrobial Research, Bangladesh University of Health Sciences, Bangladesh, Email:

Introduction

Drug repurposing, a strategy involving the identification of new uses for existing approved drugs, is increasingly prominent in the battle against antimicrobial resistance. This approach offers a more rapid and economical pathway to new treatments compared to de novo drug discovery. Emerging research highlights the potential of various drug classes, including antiparasitics, antifungals, and even some psychiatric medications, to possess antimicrobial activity against a wide range of pathogens, including multi-drug resistant strains. The primary focus is on understanding the precise mechanisms by which these repurposed drugs interact with microbial targets and optimizing their efficacy and safety for antimicrobial applications. Current studies are actively exploring combinations of repurposed drugs with established antibiotics to effectively overcome resistance and enhance treatment outcomes. This field is experiencing rapid growth, evidenced by a continuously expanding number of preclinical and clinical investigations underway. Anthelmintics are emerging as promising candidates for drug repurposing against bacterial infections, particularly those caused by Gram-positive pathogens. Several investigations have demonstrated that drugs such as niclosamide and praziquantel exhibit potent in vitro activity against bacteria, including methicillin-resistant strains of Staphylococcus aureus (MRSA). The mechanisms of action are under investigation, with proposed pathways involving disruption of bacterial membrane integrity, interference with energy metabolism, or inhibition of essential enzyme pathways. This area is particularly relevant due to the urgent need for novel agents against resistant staphylococcal infections. Ongoing research is centered on optimizing drug delivery, understanding pharmacokinetic profiles, and conducting in vivo studies to validate their therapeutic potential. The repurposing of antifungal agents for antibacterial applications is an area of significant and active investigation. Fluconazole, a well-established antifungal medication, has demonstrated a degree of synergistic activity when administered in combination with traditional antibiotics against specific bacterial strains, including Pseudomonas aeruginosa. The proposed mechanisms involve the disruption of critical microbial cellular processes. While the direct antibacterial efficacy of fluconazole alone may be limited, its capacity to potentiate other antimicrobial agents warrants further comprehensive exploration. This research is crucial for the development of novel combination therapies designed to combat polymicrobial infections and overcome existing resistance mechanisms, especially in challenging environments such as biofilms. Antidepressants, particularly selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs), are being explored for their potential antimicrobial properties. Medications like sertraline and fluoxetine have exhibited activity against a variety of bacteria and fungi in vitro. The proposed mechanisms of action include the disruption of bacterial cell wall synthesis, interference with quorum sensing processes, and modulation of biofilm formation. This represents a significant development, as it could offer a dual therapeutic benefit: treating mental health conditions while simultaneously combating infections, particularly in immunocompromised patient populations. Research is actively progressing to determine optimal dosages and effective combinations for therapeutic use. Corticosteroids, widely utilized for their anti-inflammatory and immunosuppressive effects, are also undergoing investigation for their antimicrobial potential. Dexamethasone, for example, has shown some degree of activity against specific bacterial species and may play a role in modulating host-pathogen interactions. Although not directly potent bactericidal agents, their capacity to modulate immune responses and potentially synergize with other antimicrobial agents positions them as interesting candidates for repurposing, particularly in the management of severe infections where inflammation significantly contributes to pathology. A thorough understanding of these complex interactions is paramount for their effective clinical application. Anti-diabetic medications are emerging as an unexpected yet promising class for antimicrobial repurposing. Metformin, a widely prescribed drug for type 2 diabetes, has demonstrated inhibitory effects against a range of bacterial and fungal pathogens, including multidrug-resistant strains. Its proposed mechanisms involve influencing microbial metabolic pathways and potentially disrupting biofilm formation. The low cost and extensive availability of metformin render it an attractive candidate for further in-depth investigation, especially for the treatment of chronic or difficult-to-treat infections. Current research is focusing on its efficacy within combination therapies and its potential role in enhancing host immune responses. Proton pump inhibitors (PPIs), commonly prescribed for the management of acid reflux and related gastrointestinal conditions, are being evaluated for their role in combating bacterial infections, particularly those associated with gastric pathogens like Helicobacter pylori. While their primary pharmacological action is acid suppression, certain PPIs have exhibited direct or synergistic antimicrobial effects. This finding could be particularly relevant for infections that establish within or are influenced by the acidic environment of the stomach. Research is actively exploring the ways in which PPIs might interfere with bacterial virulence factors or create unfavorable conditions for bacterial proliferation, thereby opening a new avenue for the management of gastrointestinal infections. Antimalarial drugs represent another significant source for the repurposing of existing medications for antimicrobial applications. Chloroquine and hydroxychloroquine, despite their well-established roles in malaria treatment, have demonstrated in vitro activity against a diverse range of bacteria, viruses, and even certain parasites. Their proposed mechanisms of action include altering endosomal pH, interfering with pathogen replication processes, and modulating host immune responses. The broad-spectrum potential of these drugs, combined with their existing safety profiles (albeit with known side effects), makes them compelling candidates for further investigation, especially against emerging infectious diseases and drug-resistant pathogens. The repurposing of antihistamines for antimicrobial applications is an emerging area of significant scientific interest. Certain antihistamine compounds have demonstrated in vitro activity against bacterial pathogens, potentially through mechanisms involving the interference with bacterial growth or virulence factors. While their direct antimicrobial potency might be considered modest, their widespread availability and established safety profiles make them attractive candidates for integration into combination therapies or as valuable starting points for the development of novel antimicrobial agents. The ongoing research aims to precisely elucidate the specific mechanisms by which these drugs exert their effects on microbial cells. Cardiovascular drugs are also being actively explored for their repurposed antimicrobial potential. Specific calcium channel blockers and beta-blockers have exhibited inhibitory effects against various microbial species in vitro. These observed effects are thought to originate from their capacity to disrupt microbial cell membranes or interfere with essential cellular processes critical for microbial survival. Given the high prevalence of cardiovascular diseases and the extensive use of these medications, their potential to serve as antimicrobial agents, particularly within combination therapies, represents a significant and promising area of research for overcoming the global challenge of antimicrobial resistance.

Description

Drug repurposing, the strategy of identifying novel therapeutic uses for existing approved drugs, is gaining considerable momentum in the global effort to combat antimicrobial resistance. This approach offers a considerably faster and more cost-effective route to developing new treatments compared to the traditional de novo drug discovery process. Recent scientific endeavors have highlighted the potential of diverse drug classes, including antiparasitics, antifungals, and even certain psychiatric medications, to exhibit antimicrobial activity against a broad spectrum of pathogens, notably including multi-drug resistant strains. The current research emphasis is on thoroughly understanding the intricate mechanisms of action of these repurposed drugs against microbial targets and subsequently optimizing their efficacy and safety profiles for antimicrobial applications. Furthermore, studies are actively exploring the synergistic effects of combining repurposed drugs with existing antibiotics to overcome resistance and improve overall treatment outcomes. This field is characterized by its rapid evolution, with a continuously growing number of preclinical and clinical investigations being conducted. Anthelmintics are emerging as particularly promising candidates for drug repurposing initiatives targeting bacterial infections, especially those caused by Gram-positive pathogens. A growing body of research demonstrates that established anthelmintic drugs such as niclosamide and praziquantel possess potent in vitro activity against a range of bacteria, including methicillin-resistant Staphylococcus aureus (MRSA) strains. The precise mechanisms underlying this antimicrobial activity are currently under intensive investigation, with hypotheses suggesting disruption of bacterial membrane integrity, interference with vital energy metabolism pathways, or inhibition of essential enzyme functions. This avenue of research is of paramount importance given the urgent and critical need for new therapeutic agents capable of combating resistant staphylococcal infections. Further research efforts are specifically focused on optimizing drug delivery systems, elucidating detailed pharmacokinetic profiles, and conducting robust in vivo studies to rigorously validate their therapeutic potential. The repurposing of established antifungal agents for direct antibacterial applications represents another significant and dynamic area of active investigation. Fluconazole, a widely recognized and utilized antifungal medication, has demonstrated a notable level of synergistic activity when employed in combination with conventional antibiotics against specific bacterial strains, including the opportunistic pathogen Pseudomonas aeruginosa. The proposed mechanisms of action primarily involve the disruption of critical microbial cellular processes. While the direct antibacterial efficacy of fluconazole when used as a monotherapy might be relatively limited, its demonstrated potential to enhance the activity of other antimicrobial agents warrants extensive and further exploration. This line of research is critically important for the development of innovative combination therapies aimed at addressing complex polymicrobial infections and effectively overcoming existing bacterial resistance mechanisms, particularly in challenging microenvironments such as biofilms. Antidepressant medications, particularly those belonging to the classes of selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCAs), are currently being explored for their potential antimicrobial properties. Compounds such as sertraline and fluoxetine have shown demonstrable activity against various bacterial and fungal pathogens in in vitro settings. The proposed mechanisms of action encompass a range of effects, including the disruption of bacterial cell wall synthesis, interference with quorum sensing signaling pathways, and the modulation of biofilm formation processes. This represents a significant advancement, as it holds the potential to provide a dual therapeutic benefit: simultaneously addressing underlying mental health conditions and combating microbial infections, especially in vulnerable patient populations such as the immunocompromised. Research is ongoing to meticulously determine optimal dosages and effective combinations for successful therapeutic application. Corticosteroids, a class of drugs primarily known for their potent anti-inflammatory and immunosuppressive effects, are also being investigated for their potential antimicrobial capabilities. Dexamethasone, for instance, has exhibited some level of activity against specific bacterial species and may contribute to modulating complex host-pathogen interactions. While these agents may not act as directly potent bactericidal compounds, their inherent ability to modulate immune responses and potentially synergize with other antimicrobial agents makes them highly interesting candidates for repurposing strategies. This is particularly relevant in the context of treating severe infections where inflammation plays a major role in disease pathology. A comprehensive understanding of these intricate biological interactions is key to unlocking their effective application in antimicrobial therapy. Anti-diabetic medications are emerging as an unexpected yet highly promising class of drugs for antimicrobial repurposing. Metformin, a widely used and well-established medication for the management of type 2 diabetes, has demonstrated notable inhibitory effects against a diverse range of bacterial and fungal pathogens, including multidrug-resistant strains. Its proposed mechanisms of action involve influencing crucial microbial metabolic pathways and potentially disrupting biofilm formation processes. The inherent low cost and widespread availability of metformin make it an exceptionally attractive candidate for further in-depth investigation, particularly for the treatment of chronic or otherwise difficult-to-treat infections. Current research efforts are primarily focused on evaluating its efficacy in combination therapies and exploring its potential role in enhancing the host's immune responses. Proton pump inhibitors (PPIs), a class of drugs commonly prescribed for the management of acid reflux and other gastrointestinal acid-related disorders, are currently being evaluated for their potential role in combating bacterial infections. This is particularly relevant for infections caused by gastric pathogens, such as Helicobacter pylori. While their primary mechanism of action is the suppression of gastric acid production, certain PPIs have demonstrated direct or synergistic antimicrobial effects. This characteristic could prove highly significant for treating infections that establish within or are adversely affected by the acidic gastric environment. Ongoing research is actively exploring how PPIs might interfere with bacterial virulence factors or create unfavorable conditions for bacterial growth, thereby opening a novel therapeutic avenue for the management of specific gastrointestinal infections. Antimalarial drugs represent another significant and valuable source for antimicrobial drug repurposing efforts. Chloroquine and hydroxychloroquine, despite their established efficacy in malaria treatment, have shown in vitro activity against a broad spectrum of bacteria, viruses, and even certain parasitic organisms. Their proposed mechanisms of action include the alteration of endosomal pH within host cells, interference with pathogen replication processes, and modulation of host immune responses. The broad-spectrum potential exhibited by these drugs, coupled with their generally known safety profiles (although they do possess known side effects), renders them compelling candidates for further rigorous investigation. This is especially pertinent in the context of emerging infectious diseases and the persistent challenge posed by drug-resistant pathogens. The repurposing of antihistamines for antimicrobial applications is an emerging area that is attracting considerable scientific interest. Certain antihistamine compounds have demonstrated promising in vitro activity against bacterial pathogens, potentially by interfering with essential bacterial growth processes or key virulence factors. Although their direct antimicrobial potency might be considered modest in some cases, their widespread availability and established safety profiles make them attractive candidates for incorporation into combination therapies or as valuable starting points for the development of novel antimicrobial agents. The ongoing research endeavors are focused on precisely elucidating the specific molecular and cellular mechanisms by which these drugs exert their effects on microbial cells. Cardiovascular drugs are also being actively investigated for their potential as repurposed antimicrobial agents. Specific classes, such as certain calcium channel blockers and beta-blockers, have exhibited inhibitory effects against various microbial species in in vitro studies. These observed antimicrobial effects are hypothesized to stem from their ability to disrupt microbial cell membranes or interfere with essential cellular processes critical for microbial survival and proliferation. Considering the high global prevalence of cardiovascular diseases and the extensive use of these medications, their potential to serve as adjunctive antimicrobial agents, particularly within combination therapeutic strategies, represents a significant and promising area of research for addressing the growing challenge of antimicrobial resistance.

Conclusion

Drug repurposing, a strategy utilizing existing approved drugs for new therapeutic applications, is gaining prominence in combating antimicrobial resistance due to its speed and cost-effectiveness over de novo discovery. Various drug classes, including antiparasitics, antifungals, psychiatric medications, anthelmintics, antidepressants, corticosteroids, anti-diabetic drugs, proton pump inhibitors, antimalarials, antihistamines, and cardiovascular drugs, are being explored for their antimicrobial potential. These repurposed agents exhibit activity against a wide range of pathogens, including multi-drug resistant strains, through mechanisms such as disrupting cell membranes, interfering with metabolic pathways, or affecting virulence factors. Research is focused on understanding these mechanisms, optimizing efficacy and safety, and exploring combination therapies to overcome resistance. The field is rapidly evolving with ongoing preclinical and clinical investigations.

Acknowledgement

None

Conflict of Interest

None

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