Chapter 9: Antibiotics Properties, Classes, and Nursing Considerations

General Concepts: * Bactericidal: Kills the bacteria directly. * Bacteriostatic: Inhibits the reproduction of the bacteria. * Narrow Spectrum: Effective against specific microorganisms with specific metabolic pathways. * Broad Spectrum: Effective against a wide variety of pathogens but increases the risk of superinfections (e.g., Clostridioides difficile).
Clostridioides difficile (C. diff): A bacterium causing severe diarrhea and intestinal inflammation when normal flora is destroyed. Symptoms include foul-smelling diarrhea, fever, abdominal cramps, and leukocytosis. Spread occurs via contaminated surfaces; hygiene and isolation are essential.
Beta-lactamase Resistance: Bacteria produce enzymes like penicillinase to break the beta-lactam ring. Drugs like Augmentin (amoxicillin + clavulanic acid) include beta-lactamase inhibitors to counteract this.

Penicillins: * Prototype: Amoxicillin. * Mechanism: Bactericidal; inhibits cell-wall synthesis causing the cell to burst. * Key Issues: Allergic reactions occur in $0.7\%$ to $4\%$ of courses; cross-sensitivity exists with cephalosporins. * Interactions: Decreases oral contraceptive (OC) effectiveness. Aminoglycosides cannot be mixed in the same IV line/syringe as they will crystallize.
Cephalosporins: * Prototypes: cefazolin, cefaclor. * Generations: As generations increase ( $1^{st}$ through $5^{th}$ ), they gain more Gram-negative coverage and better CNS penetration. * Special Note: Ceftaroline ( $5^{th}$ Gen) is the only one effective against MRSA. * Side Effects: Nephrotoxicity and disulfiram-like reactions when consumed with alcohol (ETOH).
Carbapenems: * Prototypes: ertapenem, meropenem, imipenem/cilastatin. * Details: Broadest spectrum available. Meropenem carries a risk for seizure activity.

Macrolides: * Prototypes: erythromycin, azithromycin, clarithromycin. * Adverse Effects: QT interval prolongation and hepatotoxicity. Fidaxomicin is used specifically for C. diff colitis.
Tetracyclines: * Prototypes: tetracycline, doxycycline, tigecycline. * Contraindications: Avoid in children under $8$ years old and pregnancy due to bone growth disruption and permanent tooth discoloration. * Nursing: Avoid dairy, antacids, and iron (prevents absorption). Causes significant photosensitivity.
Aminoglycosides: * Prototypes: gentamicin, amikacin, neomycin, tobramycin. * Toxicities: Highly nephrotoxic (renal failure) and ototoxic (damage to CN VIII). * Monitoring: Requires close tracking of peak and trough serum levels due to a narrow therapeutic window.

Fluoroquinolones: * Prototypes: ciprofloxacin, levofloxacin. * Adverse Effects: Black box warnings for tendonitis and Achilles tendon rupture (risk increased in older adults). May cause QT interval prolongation. * Nursing: Avoid in patients under $18$ yo; separate from antacids/minerals by $4$ hours.
Sulfonamides: * Prototype: cotrimoxazole (Bactrim). * Mechanism: Inhibits folic acid synthesis. * Adverse Effects: Stevens-Johnson syndrome, bone marrow depression, and crystalluria. * Nursing: Increase fluid intake to $2\text{ to }3\,dm^3$ per day to prevent renal crystals.

Vancomycin: Treatment of choice for MRSA. Rapid infusion can cause Red man syndrome (idiopathic erythroderma) and hypotension. Monitor renal function and blood levels.
Clindamycin: Highly associated with the development of Clostridioides difficile infection.
Metronidazole: Used for anaerobic and protozoal infections. Causes severe acute alcohol intolerance (disulfiram-like reaction).
General Nursing Implications: * Complete the full course of therapy to prevent resistance. * Monitor for superinfections (thrush, vaginal discharge). * Antibiotics (penicillins, tetracyclines, sulfonamides) interfere with the enterohepatic recirculation of estrogen, reducing oral contraceptive effectiveness.