Antimicrobials and Their Mechanisms

Antimicrobials

• Bactericidal: Kills bacteria, disrupting cell membrane/wall stability or essential proteins/enzymes.
• Bacteriostatic: Prevents bacterial replication, often by obstructing essential protein/enzyme systems involved in reproduction.
• Prophylaxis: Prevents infection before it occurs, typically for high-risk patients.
• Resistance: Pathogens adapt over time to become less susceptible to anti-infectives.
• Spectrum: Range of bacteria an antibiotic effectively targets; broad spectrum (wide range) or narrow spectrum (specific types).
• Superinfection: Opportunistic pathogens proliferate due to destruction of normal flora by antibiotics.

Mode of Action of Antibiotics

• Cell Wall Synthesis Inhibitors: β-lactams, glycopeptides, fosfomycin, bacitracin, vancomycin.
• Cell Membrane Synthesis Disruptors: Lipopeptides, polymyxins.
• Folate Synthesis Inhibitors: Sulfonamides.
• Protein Synthesis Inhibitors: Tetracyclines, aminoglycosides, macrolides, lincosamides , oxazolidinones.
• DNA Synthesis Inhibitors: Quinolones, Fluoroquinolones.
• RNA Synthesis Inhibitors: Rifampicin, ansamycins.

Bactericidal vs. Bacteriostatic

• Bactericidal: Irreversible, kills the bacteria directly, inhibits cell wall formation. Requires no immune response to destroy bacteria.
• Bacteriostatic: Reversible, prevents bacteria from reproducing. Relies on the host's immune system to eliminate the bacteria, inhibits DNA replication/protein synthesis.
• MBC: Minimum Bactericidal Concentration - drug concentration that eliminates 99.99% of bacteria.
• MIC: Minimum Inhibitory Concentration - drug concentration that inhibits bacterial growth.

Antibiotic Resistance

• Restriction of antibiotic access: Bacteria make changes or limits of entry points into cells.
• Antibiotic elimination: Bacteria pump antibiotics out of cells.
• Antibiotic modification: Enzymes (breaking down the antibiotic).
• Target alteration: Bacteria modify the target's structure, antibiotic can't bind anymore.
• Antibiotic bypass: Bacteria find and utilize alternative pathways.

Core Elements of Antibiotic Stewardship

• Prescribing antibiotics when truly needed.
• Prescribing appropriate antibiotics, with adequate dosages.
• Using the shortest duration of antibiotics based on available evidence.
• Using culture results to reassess the treatment.

Gram Stains of Bacteria

• Gram-positive: Thicker cell walls, stain purple.
• Gram-negative: Outer membrane, thinner cell walls, stain pink.

Nursing Considerations for Antibiotic Therapy

• Infection site and type of organisms.
• Determine the antibiotic spectrum.
• Consider the patient's health status.
• Antibiotic choice, common and dangerous side effects, contraindications, monitoring labs.
• Monitor for superinfections, renal function (e.g., urine output and kidney labs, etc.), hydration status.

Culture and Sensitivity Report

• Important Data (from report): Collected date & time, source (e.g., urine, blood), estimated pathogen concentration
• Organism Identification: Bacteria type or name
• Anitbiotic susceptibilities: Results of testing different antibiotics to evaluate if bacteria is sensitive or resistant to the antibiotic.
• Interpretation: Determine if bacteria is susceptible (S), intermediate (I), resistant (R). Focus on selecting the lowest MIC (minimum inhibitory concentration) of available antibiotics.

Antibiotic Drug Families

• Aminoglycosides: Often used against gram-negative bacteria. Can cause hearing loss / kidney damage.
• Carbapenems: Broad-spectrum, often used for severe infections; use with caution in patients with seizure disorders.
• Cephalosporins: Vary widely in their spectrum (first-generations effective gram +, later generations more gram -)
• Fluoroquinolones: Broad-spectrum, can affect the musculoskeletal system.
• Penicillins: Often for bacterial infections; allergy is very common, causing anaphylaxis.
• Sulfonamides: Broad spectrum, typically for urinary tract infections and skin infections.
• Tetracyclines: Broad-spectrum, but use should be avoided in children as it affects bone/teeth development
• Lincosamides: Often for skin, bone, or respiratory infections; can trigger Clostridium difficile colitis.
• Lipoglycopeptides (e.g., vancomycin): Primarily used against gram-positive bacteria, including MRSA.
• Macrolides: Broad spectrum, effective in people who are allergic to penicillin. Can cause severe stomach issues and interactions with other medications.
• Antiseptics: (e.g., nitrofurantoin): Often used for urinary tract infections; broad spectrum.

Nursing Considerations for Antibiotic Adminstration

• Monitor for adverse reactions such as allergic reactions, kidney or liver problems. Always assess for drug interactions with other medications the patient may be taking.
• Patient education: Instruct patient about side effects, to avoid unnecessary use and importance of finishing the entire medication course to avoid antibiotic resistance.