Indirect adverse effects
Indirect adverse effects of antimicrobials include effects on both human commensal and environmental flora.
Clostridioides difficile (formerly known as Clostridium difficile) is a common cause of healthcare-associated and antibiotic-associated diarrhoea. Impairment of the normal defence mechanisms (including the disruption of host gastrointestinal tract flora by most antibiotics, proton pump inhibitors, or immunosuppressive drugs) may result in colonisation of the gastrointestinal tract with C. difficile. A proportion of colonised patients progress to develop C. difficile infection secondary to toxin production. Minimising exposure to antibiotics reduces the risk of developing C. difficile infection.
Candida species1 are normal flora in the gastrointestinal (including oral) and genitourinary tracts. Antimicrobial therapy disrupts the normal flora and can lead to an increased Candida burden and subsequent infection by Candida species (eg oropharyngeal or vulvovaginal candidiasis, or invasive infection in patients with immune compromise or patients who are critically ill).
Colonisation or infection with a drug-resistant pathogen is associated with antimicrobial use (see Antimicrobial resistance). For example, acquisition of vancomycin-resistant enterococci (VRE) has been associated with previous treatment with antimicrobials, particularly vancomycin and cephalosporins. The risk of colonisation with methicillin-resistant Staphylococcus aureus (MRSA) has been correlated with the frequency and duration of prior antibiotic therapy, particularly quinolones and cephalosporins. Gram-negative organisms are at increased risk of acquired resistance following antimicrobial therapy (eg extended-spectrum beta-lactamases [ESBLs] and cephalosporin use, Pseudomonas aeruginosa and carbapenem use)Kim, 2021Tacconelli, 2020Zhu, 2019.
The microbiome is an ecological community of commensal, symbiotic and pathogenic organisms found in (and on) all multicellular organisms, including humans. Emerging data suggest that changes to the human microbiome following antimicrobial use may have implications for patient health. An intact microbiome is part of the body’s defence against infection.