Antibiotics
Key Points
- Antibiotics are either bactericidal (kill bacteria) or bacteriostatic (suppress growth)
- Antibiotics do not kill viruses and should not be used to treat viral infections
- Antibiotics are also not primary treatment for helminthic parasitic infections, which require antihelmintic agents
- If side effects occur, clients should contact the prescriber rather than stopping therapy on their own
- Culture and sensitivity must be collected BEFORE starting antibiotics to ensure accurate results
- Gram stain: gram-positive = violet, gram-negative = red/pink
- Most serious adverse effect: anaphylaxis — monitor closely for first dose
- Broad-spectrum antibiotics risk superinfection (C. diff); use soap/water, not hand sanitizer, for C. diff patients
- Vancomycin and aminoglycosides require renal function monitoring and therapeutic drug level monitoring
Drug Class Overview
Antibiotics are drugs used to treat infections caused by bacteria, either by directly killing bacteria (bactericidal) or by suppressing their growth and multiplication (bacteriostatic). Antibiotics are among the most commonly prescribed medications — careful stewardship is essential to prevent antibiotic resistance, a major global public health threat.
Broad-spectrum antibiotics cover many bacterial types; narrow-spectrum agents target specific organisms. Selection is guided by culture and sensitivity results, gram stain, and institutional antibiograms.
Pre-Administration: Culture and Sensitivity
Culture collects samples (blood, urine, sputum, wound) to identify the causative pathogen. Sensitivity analysis identifies which antibiotics will effectively treat the organism. Gram stain rapidly classifies bacteria as gram-positive (violet staining) or gram-negative (red/pink staining), enabling empiric antibiotic selection before culture results return (takes 1–5 days).
Collect Culture BEFORE Starting Antibiotics
Administering antibiotics before collecting culture samples causes inaccurate results, complicates recovery, and delays identification of resistant organisms. The nurse is responsible for collecting cultures promptly.
Major Antibiotic Classes
Beta-Lactams
Mechanism: Inhibit penicillin-binding protein → block bacterial cell wall cross-linking → cell wall holes → cellular death.
| Subclass | Agents | Common Indications |
|---|---|---|
| Penicillins | Amoxicillin, ampicillin, nafcillin, piperacillin | Strep pharyngitis, otitis media, endocarditis |
| Beta-lactamase inhibitor combinations | Amoxicillin-clavulanate (Augmentin), piperacillin-tazobactam (Zosyn) | Broader coverage including resistant organisms |
| Cephalosporins (1st gen) | Cephalexin, cefazolin | UTIs, skin infections, surgical prophylaxis |
| Cephalosporins (3rd gen) | Ceftriaxone, cefotaxime | Meningitis, pneumonia, neonatal sepsis |
| Cephalosporins (4th-5th gen) | Cefepime, ceftaroline | Pseudomonas (cefepime); MRSA (ceftaroline) |
Protein Synthesis Inhibitors
| Subclass | Agents | Key Notes |
|---|---|---|
| Macrolides | Azithromycin, clarithromycin, erythromycin | CYP3A4 inhibitors — many drug interactions; atypical pneumonia, Legionella, Chlamydia |
| Aminoglycosides | Gentamicin, tobramycin, amikacin | Gram-negative coverage including Pseudomonas; renally eliminated; monitor levels and renal function |
| Tetracyclines | Doxycycline, minocycline | Lyme disease, acne, anthrax; avoid in pregnancy and children <8 years |
| Lincosamides | Clindamycin | MRSA, anaerobes, skin/soft tissue infections |
| Oxazolidinones | Linezolid | Vancomycin-resistant organisms (VRSA); last resort for resistant gram-positive |
Cell Wall / DNA Disruptors
| Subclass | Agents | Key Notes |
|---|---|---|
| Glycopeptides | Vancomycin | IV: MRSA, gram-positive infections; Oral: C. diff colitis only; monitor renal function and serum levels (therapeutic range: trough 10–20 mcg/mL) |
| Fluoroquinolones | Ciprofloxacin, levofloxacin, moxifloxacin | Inhibit DNA gyrase → DNA strand breakage; respiratory and UTI infections; avoid in pregnancy |
| Sulfonamides | Sulfamethoxazole/trimethoprim (Bactrim) | Folic acid pathway inhibition; UTIs, MRSA skin infections, PCP prophylaxis |
| Nitroimidazoles | Metronidazole | Anaerobes, protozoa, C. diff, STIs; alcohol interaction (disulfiram-like reaction) |
For selected regimens, deep IM administration is used (for example penicillin or ceftriaxone) when oral therapy is not appropriate or adherence is a concern; larger required doses may be split across sites per site-volume limits.
Antibiotic Resistance
Mechanisms: Bacteria mutate to modify antibiotic targets, produce beta-lactamases (cleave beta-lactam ring), or pump drugs out of cells. Resistant bacteria can also share resistance genes between strains.
Practice-linked resistance drivers: Overprescribing for nonbacterial illness, selecting agents that do not match the pathogen, and failing to complete the prescribed course all increase resistance pressure.
Superinfection: Broad-spectrum antibiotic use destroys normal flora → resistant organisms (especially C. diff) proliferate → new, harder-to-treat infection develops.
Key resistant organisms: MRSA (methicillin-resistant S. aureus), VRSA (vancomycin-resistant), C. diff, Pseudomonas aeruginosa.
Nursing Assessment
Before Administration:
- Obtain baseline: temperature, HR, BP, RR, WBC count
- Review culture and sensitivity results — ensure correct antibiotic coverage
- Assess site of infection (wound, respiratory, urinary) and focused system assessment
- Review allergy history — cross-reactivity possible between antibiotic classes (penicillins ↔ cephalosporins)
- Ensure cultures collected before first dose is given
- For IM antibiotic dosing, confirm landmark/site plan (often ventrogluteal for deep IM preparations) and volume split strategy when needed
Monitoring for Adverse Effects:
- Anaphylaxis (highest risk: first dose): Urticaria, angioedema, dyspnea, hypotension, dizziness → stop drug, notify provider immediately, prepare epinephrine
- GI upset: Nausea, diarrhea — common with most antibiotics; take with food if permitted
- Adherence risk from side effects: If intolerance develops, contact the prescriber for management instead of self-stopping early
- C. diff superinfection: Frequent, foul-smelling stools → contact precautions + notify provider + soap and water hand hygiene (alcohol hand rub does NOT kill C. diff spores)
- Renal toxicity: Vancomycin and aminoglycosides — monitor BUN, creatinine, urine output, and serum drug levels
- Therapeutic drug monitoring: Follow ordered peak/trough timing because dose administration may need adjustment to keep serum concentration within therapeutic range
- Hepatotoxicity: Macrolides — monitor liver function tests
Evaluate Effectiveness:
- Declining fever, heart rate, and WBC count indicate clinical improvement
- Worsening signs (increasing WBC, temperature, HR, RR) → may indicate sepsis → notify provider immediately
Related Concepts
- infection-control — Isolation precautions that accompany antibiotic therapy
- susceptible-host — Host factors that determine infection risk and antibiotic need
- blood-culture-collection-in-suspected-sepsis — Blood culture collection procedure before antibiotic initiation
- sepsis — Life-threatening infection requiring urgent antibiotic therapy
- high-alert-medications — Select antibiotics (aminoglycosides, amphotericin B) classified as high-alert
- mode-of-transmission — Transmission routes that antibiotics help interrupt
- antimicrobial-stewardship — Coordinated framework for appropriate antibiotic use and resistance reduction
Self-Check
- Why must cultures be collected before administering the first dose of antibiotics?
- A patient on broad-spectrum antibiotics develops frequent, foul-smelling stools. What infection do you suspect, and what hand hygiene intervention is required?
- Which two antibiotic classes require therapeutic drug level monitoring and renal function assessment?