Antimicrobial Stewardship

Introduction

Antimicrobial stewardship is the coordinated set of actions taken to promote the appropriate use of antimicrobials - selecting the right drug, at the right dose, by the right route, for the right duration - in order to achieve the best clinical outcome while minimising toxicity, cost, and the emergence of resistance. It exists because antibiotics are a shared, finite resource: every inappropriate prescription contributes, in a small but real way, to a problem that affects every future patient who might need that drug to work.

Antimicrobial resistance (AMR) is now recognised as one of the leading global health threats of this century. It is driven overwhelmingly by the overuse and misuse of antimicrobials, in human medicine and in agriculture, and its consequences reach beyond infection itself: effective antibiotics underpin the safety of routine surgery, cancer chemotherapy and organ transplantation, all of which depend on being able to treat or prevent infection reliably.

Mechanisms of resistance

Bacteria become resistant either intrinsically (a species is naturally unaffected by a drug class) or through acquired resistance, gained by mutation or, very commonly, by horizontal gene transfer - the exchange of resistance genes between bacteria via plasmids, transposons or bacteriophages, which allows resistance to spread rapidly across and even between species.

• Enzymatic drug inactivation - for example beta-lactamases breaking down penicillins and cephalosporins
• Altered drug target - for example the altered penicillin-binding protein (PBP2a) that makes MRSA resistant to meticillin and other beta-lactams
• Reduced membrane permeability, limiting drug entry into the bacterial cell
• Efflux pumps, actively exporting the drug back out of the cell before it can act

Start Smart Then Focus

Start Smart Then Focus is the UK's national framework for hospital antimicrobial prescribing, and its two-phase logic underpins good stewardship practice everywhere.¹

Start Smart

Do not withhold or delay antibiotics in a genuinely unwell patient (sepsis remains a time-critical emergency, as covered in its own article). Start prompt, appropriately broad empirical therapy guided by local guidelines, the likely source, and any relevant microbiology history, and clearly document the indication, drug, dose, route and a review or stop date at the point of prescribing.

Then Focus

Formally review every antibiotic prescription at 48-72 hours, once clinical response and any culture results are available, and make an active decision: stop if there is no evidence of infection, switch to a narrower-spectrum or oral agent, continue with a clear ongoing indication, or change based on culture and sensitivity results. This structured review is what prevents broad-spectrum empirical therapy from silently continuing for far longer than it was ever needed.

The core principles in practice

• Right drug - the narrowest-spectrum agent likely to be effective, guided by local antimicrobial guidelines and microbiology advice, rather than defaulting to the broadest available option
• Right dose - adequate to achieve therapeutic levels; underdosing does not just risk treatment failure, it also promotes resistance by exposing bacteria to sub-lethal drug concentrations
• Right route - switch from IV to oral as soon as the patient is afebrile, clinically improving, and able to tolerate oral medication, reducing line-related infection risk, cost and length of stay without compromising outcome
• Right duration - the shortest effective course; evidence increasingly supports shorter courses than were traditionally taught for many common infections (for example 5 days rather than 7-10 for uncomplicated community-acquired pneumonia, or 3 days for uncomplicated UTI in women)
• Right time - prompt when genuinely needed (sepsis), but not prescribed reflexively for a self-limiting or likely viral illness, where no antibiotic is the correct answer
• Clear documentation of indication, route and a stop/review date on every prescription

The WHO AWaRe classification

The WHO groups antibiotics into three categories to guide and monitor prescribing at a system level, increasingly used as a UK stewardship metric as well as a global one.²

Practical stewardship tools

• Local antimicrobial guidelines, built from local resistance patterns rather than generic national defaults
• Microbiology ward rounds and OPAT (outpatient parenteral antibiotic therapy) services, allowing IV antibiotics to continue safely outside hospital rather than prolonging admission unnecessarily
• Restricted or "reserve" antibiotic policies, requiring microbiology approval for agents such as carbapenems or certain glycopeptides, protecting last-line drugs from unnecessary use
• Delayed or back-up prescribing in primary care for likely self-limiting infections (for example suspected otitis media or sinusitis) - giving a prescription to use only if symptoms fail to settle, reducing unnecessary antibiotic exposure while still safety-netting the patient
• Point-of-care CRP testing in primary care, used to guide antibiotic decisions in suspected lower respiratory tract infection where the clinical picture is otherwise equivocal
• Patient education - explaining clearly why an antibiotic is not indicated for a viral illness is itself a stewardship intervention, and one that reduces demand-driven prescribing over time

Consequences of poor stewardship

• Clostridioides difficile infection - a direct consequence of antibiotic disruption of normal gut flora, covered in its own article
• Selection and spread of resistant organisms - MRSA, ESBL and carbapenemase-producing Gram-negatives, vancomycin-resistant enterococci, and azole-resistant Candida, each covered where relevant in these notes
• Avoidable adverse drug reactions, allergic reactions and drug interactions from unnecessary prescribing
• Rising healthcare costs from treating resistant infections and their complications
• A shrinking pool of effective agents for future patients with genuinely resistant infections

Prognosis

For the individual patient, appropriate antimicrobial stewardship - the right drug, dose, route and duration - gives outcomes at least as good as, and often better than, indiscriminate broad-spectrum prescribing, while avoiding unnecessary side effects and complications such as C. difficile infection. At a population level, stewardship is one of the few interventions capable of slowing the trajectory of antimicrobial resistance, and its effectiveness depends on consistent application by every prescriber - not just specialist infection teams - which is exactly why it is examined as a core clinical skill rather than a niche subspecialty topic.