Describe the mechanisms of antimicrobial resistance, its spread and the principles of antimicrobial stewardship.

Definition and Types of Resistance

Mechanisms of Resistance

Important Resistant Organisms

Containment and Stewardship

• Prescribe only when there is a bacterial infection — the largest single source of unnecessary use is antibiotics for viral upper respiratory illness
• Use the narrowest effective agent, and de-escalate once cultures are available
• Correct dose and duration — subtherapeutic doses select resistance, and unnecessarily long courses do the same; short courses are as effective for most infections
• Take cultures before starting, and use local antibiograms to guide empirical choice
• Infection control is as important as prescribing — hand hygiene, isolation, device care and environmental cleaning limit the spread of resistant organisms
• Restrict reserve agents — carbapenems, colistin, linezolid — by formulary control and specialist approval
• Vaccination reduces antibiotic use, both by preventing bacterial disease and by preventing the viral illnesses for which antibiotics are wrongly given
• Reduce agricultural use — a large share of global antibiotic consumption is in animals, much of it for growth promotion

Preventing the Emergence of Resistance in the Individual Patient

• Use an adequate dose — subtherapeutic levels select resistant mutants most efficiently, since they inhibit the sensitive without killing them
• Use combinations where resistance emerges readily — tuberculosis, leprosy, HIV, Helicobacter; the chance of an organism carrying resistance to two drugs is the product of the separate probabilities
• Complete the course where a defined duration is established, but equally do not extend it — the evidence increasingly favours shorter courses, and the old advice to "always finish the course" is being revised
• Avoid using a drug topically that is needed systemically — topical use over large areas selects resistance without therapeutic benefit
• Rotate or restrict agents at unit level, guided by local resistance data rather than by textbook spectra
• Treat the infection, not the colonisation — positive cultures from a catheter, a wound swab or sputum in a stable patient often need no antibiotic at all

Applied Aspects

• India has among the highest rates of antimicrobial resistance in the world, driven by over-the-counter sale without prescription, incomplete courses, widespread use of third-generation cephalosporins and fluoroquinolones, and agricultural use
• NDM-1 was first described from this region, and carbapenem-resistant organisms are now common in Indian hospitals — a problem that will not be solved by new drugs alone
• The National Action Plan on AMR and the Schedule H1 restriction on sale of certain antibiotics are steps toward control, but enforcement remains the difficulty
• Explain to patients why an antibiotic is not being given — expectation drives a great deal of unnecessary prescribing, and a clear explanation with safety-netting advice is usually accepted
• Very few genuinely new antibiotic classes are in development, because the commercial return is poor; the drugs we have may be the drugs we keep, which makes preserving them a matter of real consequence
• Resistance is reversible in principle — where antibiotic use has been reduced, resistance rates have fallen, because resistance usually carries a fitness cost; this is a reason for optimism about stewardship
• Rapid diagnostics shorten the period of empirical broad therapy, and are among the more promising practical measures
• Ask at every ward round whether the antibiotic can be stopped, narrowed or switched to oral; this single habit does more than any policy document
• Intravenous to oral switch as soon as the patient is improving and absorbing reduces line infections, cost and length of stay, and is one of the easiest gains available
• Procalcitonin and clinical review can guide when to stop, and shorten courses safely in pneumonia and sepsis
• Hand hygiene prevents the transmission that spreads resistance, and no prescribing policy compensates for its absence — the two must go together
• Resistance is not confined to hospitals — community ESBL-producing E. Coli now causes ordinary urinary infection, so the empirical choices taught a decade ago may no longer work
• Antibiotics in animal feed contribute substantially, and resistant organisms reach humans through food, water and the environment; this is a public health problem beyond clinical prescribing
• Explain to the patient why no antibiotic is being given, with clear advice on what would prompt review — this is more effective than refusal and is usually accepted
• Delayed prescriptions — giving a prescription to be filled only if symptoms worsen — substantially reduce antibiotic consumption without harming outcomes in respiratory illness
• Every clinician contributes to a collective problem; resistance is not created by other people’s prescribing alone, and the individual decision to withhold an unnecessary course is the whole of the solution repeated many times