Antibiotics

Antibiotics Guide

Quick reference for common antibiotics, indications, and key clinical pearls

Penicillins

Penicillin G/V
Narrow - Gram-positive cocci

Common Uses:

  • •Strep throat (Group A Strep)
  • •Syphilis
  • •Rheumatic fever prophylaxis

Typical Dosing:

Penicillin V: 250-500mg PO q6-8h

Key Clinical Pearl:

First-line for streptococcal infections. High S. aureus resistance.

Amoxicillin
Moderate - Better gram-negative coverage

Common Uses:

  • •Otitis media
  • •Sinusitis
  • •Community-acquired pneumonia
  • •UTI (uncomplicated)

Typical Dosing:

500mg PO q8h or 875mg PO q12h

Key Clinical Pearl:

Better absorbed than ampicillin. Add clavulanate for resistant organisms.

Augmentin (Amoxicillin-Clavulanate)
Broad - Extended coverage with beta-lactamase inhibitor

Common Uses:

  • •Animal/human bites
  • •Aspiration pneumonia
  • •Sinusitis (resistant)
  • •Diabetic foot infections

Typical Dosing:

875-125mg PO q12h

Key Clinical Pearl:

Clavulanate inhibits beta-lactamase. Higher diarrhea risk.

Nafcillin/Oxacillin
Narrow - Anti-staphylococcal (MSSA only)

Common Uses:

  • •MSSA infections
  • •Cellulitis (staph)
  • •Osteomyelitis (MSSA)

Typical Dosing:

1-2g IV q4-6h

Key Clinical Pearl:

Drug of choice for MSSA. No MRSA activity - use vancomycin instead.

Piperacillin-Tazobactam (Zosyn)
Very broad - Pseudomonas, anaerobes, many gram-negatives

Common Uses:

  • •Hospital-acquired pneumonia
  • •Intra-abdominal infections
  • •Febrile neutropenia
  • •Severe sepsis (empiric)

Typical Dosing:

3.375-4.5g IV q6-8h

Key Clinical Pearl:

Excellent empiric broad-spectrum for critically ill patients.

Ampicillin
Broad - Better gram-negative than penicillin V

Common Uses:

  • •Enterococcus infections
  • •Listeria meningitis
  • •Urinary tract infections

Typical Dosing:

250-500mg PO q6h or 1-2g IV q4-6h

Key Clinical Pearl:

Poor oral absorption. Use amoxicillin orally instead.

Piperacillin without Tazobactam
Gram-positive/negative, some anaerobes

Common Uses:

  • •Gram-negative infections (older)
  • •Pseudomonas (limited - use Zosyn)

Typical Dosing:

3-4g IV q4-6h

Key Clinical Pearl:

Usually given with tazobactam (Zosyn) for better coverage.

Cephalosporins (1st Gen)

Cefazolin
Narrow - Good gram-positive, limited gram-negative

Common Uses:

  • •Surgical prophylaxis
  • •Skin/soft tissue infections (MSSA)
  • •Osteomyelitis (MSSA)

Typical Dosing:

1-2g IV q8h

Key Clinical Pearl:

Most common cephalosporin for surgical prophylaxis.

Cephalexin
Narrow - Gram-positive, limited gram-negative

Common Uses:

  • •Skin/soft tissue infections
  • •Urinary tract infections
  • •Streptococcal infections

Typical Dosing:

500mg PO q6h

Key Clinical Pearl:

Oral first-generation cephalosporin. Poor gram-negative coverage.

Cephalosporins (2nd Gen)

Cefuroxime
Moderate - Better gram-negative than 1st gen

Common Uses:

  • •Community-acquired pneumonia
  • •Sinusitis
  • •Lyme disease (early disseminated)

Typical Dosing:

750mg-1.5g IV q8h

Key Clinical Pearl:

Good for respiratory infections. Better CNS penetration.

Cefoxitin
Good anaerobic coverage, gram-negative

Common Uses:

  • •Intra-abdominal infections
  • •Surgical prophylaxis (colorectal)
  • •Anaerobic infections

Typical Dosing:

1-2g IV q6-8h

Key Clinical Pearl:

Excellent anaerobic activity. Predicts for CDI risk.

Cephalosporins (3rd Gen)

Ceftriaxone
Broad - Excellent gram-negative, decent gram-positive

Common Uses:

  • •Meningitis (bacterial)
  • •Gonorrhea
  • •Pneumonia
  • •Pyelonephritis
  • •Sepsis (empiric)

Typical Dosing:

1-2g IV/IM q24h

Key Clinical Pearl:

Long half-life = once-daily dosing. Don't mix with calcium in neonates.

Ceftazidime
Broad - Pseudomonas, gram-negative

Common Uses:

  • •Pseudomonas infections
  • •Cystic fibrosis patients
  • •Hospital-acquired pneumonia

Typical Dosing:

1-2g IV q8h

Key Clinical Pearl:

Anti-pseudomonal 3rd gen. Better pseudo coverage than ceftriaxone.

Cephalosporins (4th Gen)

Cefepime
Very broad - Pseudomonas, extended gram-negatives

Common Uses:

  • •Febrile neutropenia
  • •Hospital-acquired pneumonia
  • •Complicated UTI
  • •Pseudomonas infections

Typical Dosing:

1-2g IV q8-12h

Key Clinical Pearl:

Anti-pseudomonal activity. Watch for neurotoxicity in renal impairment.

Fluoroquinolones

Ciprofloxacin
Broad - Excellent gram-negative, Pseudomonas

Common Uses:

  • •Complicated UTI/Pyelonephritis
  • •Pseudomonas infections
  • •Traveler's diarrhea
  • •Anthrax (post-exposure)

Typical Dosing:

500-750mg PO q12h or 400mg IV q8-12h

Key Clinical Pearl:

BLACK BOX: Tendon rupture, nerve damage. Avoid in pregnancy/children.

Levofloxacin
Broad - Better gram-positive than cipro, good atypicals

Common Uses:

  • •Community-acquired pneumonia
  • •Acute bacterial sinusitis
  • •Complicated UTI

Typical Dosing:

500-750mg PO/IV q24h

Key Clinical Pearl:

Good respiratory pathogen coverage. BLACK BOX warnings like cipro.

Gemifloxacin
Gram-negative, some gram-positive

Common Uses:

  • •Community-acquired pneumonia
  • •Acute exacerbation COPD

Typical Dosing:

320mg PO q24h

Key Clinical Pearl:

Rash common (especially in women). BLACK BOX warnings apply.

Fluoroquinolones - Ofloxacin
Broad - Gram-positive/negative, some atypicals

Common Uses:

  • •Complicated UTI
  • •Prostatitis
  • •Respiratory infections

Typical Dosing:

300-400mg PO/IV q12h

Key Clinical Pearl:

Balanced gram-positive/negative. Same BLACK BOX concerns.

Macrolides

Azithromycin (Z-pack)
Moderate - Atypicals, some gram-positives/negatives

Common Uses:

  • •Community-acquired pneumonia (atypical)
  • •Pharyngitis (PCN allergic)
  • •Pertussis
  • •Chlamydia

Typical Dosing:

500mg day 1, then 250mg days 2-5

Key Clinical Pearl:

Long half-life = short course. Covers atypicals (Mycoplasma, Chlamydia).

Tetracyclines

Doxycycline
Broad - Atypicals, rickettsia, some gram-pos/neg

Common Uses:

  • •Lyme disease
  • •Rocky Mountain spotted fever
  • •Malaria prophylaxis
  • •Acne
  • •Chlamydia/Mycoplasma

Typical Dosing:

100mg PO q12h

Key Clinical Pearl:

Drug of choice for tick-borne illnesses. Avoid in pregnancy/children <8.

Minocycline
Broad - Similar to doxycycline

Common Uses:

  • •Atypical infections
  • •Acne
  • •Malaria prophylaxis alternative

Typical Dosing:

100mg PO q12h

Key Clinical Pearl:

Better CNS penetration than doxycycline. Same pregnancy/age restrictions.

Aminoglycosides

Gentamicin
Narrow - Gram-negatives, synergy with beta-lactams

Common Uses:

  • •Sepsis (gram-negative)
  • •Endocarditis (synergy)
  • •Pyelonephritis (severe)

Typical Dosing:

5-7mg/kg IV q24h

Key Clinical Pearl:

Monitor troughs and renal function. Nephrotoxic and ototoxic.

Glycopeptides

Vancomycin
Narrow - Gram-positive only (MRSA, Enterococcus)

Common Uses:

  • •MRSA infections
  • •C. difficile (oral only)
  • •Endocarditis (MRSA)
  • •Meningitis (resistant gram-positive)

Typical Dosing:

15-20mg/kg IV q8-12h or 125mg PO q6h (C. diff)

Key Clinical Pearl:

Drug of choice for MRSA. Oral form ONLY for C. diff.

Lipopeptides

Daptomycin
Narrow - Gram-positive (MRSA, VRE)

Common Uses:

  • •MRSA bacteremia/endocarditis
  • •Complicated skin infections (MRSA)
  • •VRE infections

Typical Dosing:

4-8mg/kg IV q24h

Key Clinical Pearl:

NOT for pneumonia (inactivated by surfactant). Monitor CPK weekly.

Carbapenems

Meropenem
Extremely broad - ESBL, Pseudomonas, anaerobes (NOT MRSA)

Common Uses:

  • •Severe sepsis/septic shock
  • •Meningitis (bacterial)
  • •Hospital-acquired pneumonia
  • •Multi-drug resistant organisms

Typical Dosing:

1-2g IV q8h

Key Clinical Pearl:

Broadest spectrum available. Reserve for serious infections.

Ertapenem
Broad - ESBL, gram-negative/positive, anaerobes (NOT Pseudomonas)

Common Uses:

  • •Intra-abdominal infections
  • •Diabetic foot infections
  • •Community-acquired pneumonia (resistant)

Typical Dosing:

1g IV q12h

Key Clinical Pearl:

Once-daily dosing. No pseudomonal activity - use meropenem if needed.

Imipenem-Cilastatin
Extremely broad - Pseudomonas, anaerobes, ESBL

Common Uses:

  • •Febrile neutropenia
  • •Severe sepsis with multi-resistant organisms
  • •Meningitis (bacterial)

Typical Dosing:

500mg-1g IV q6-8h

Key Clinical Pearl:

CNS penetration. Cilastatin prevents renal metabolism. More seizure risk.

Sulfonamides

Trimethoprim-Sulfamethoxazole (Bactrim)
Moderate - Some gram-pos/neg, MRSA, PCP

Common Uses:

  • •UTI (uncomplicated)
  • •MRSA skin infections
  • •Pneumocystis pneumonia (PCP)
  • •Nocardia

Typical Dosing:

1-2 DS tablets PO q12h

Key Clinical Pearl:

Check renal function and K+. Avoid in pregnancy (1st trimester).

Nitroimidazoles

Metronidazole (Flagyl)
Narrow - Anaerobes only

Common Uses:

  • •C. difficile infection
  • •Bacterial vaginosis
  • •Intra-abdominal infections (anaerobic)
  • •Brain abscess

Typical Dosing:

500mg PO/IV q8h

Key Clinical Pearl:

NO ALCOHOL (disulfiram reaction). Excellent anaerobic coverage.

Oxazolidinones

Linezolid (Zyvox)
Narrow - Gram-positive (MRSA, VRE)

Common Uses:

  • •MRSA pneumonia
  • •VRE infections
  • •Complicated skin infections (MRSA)

Typical Dosing:

600mg PO/IV q12h

Key Clinical Pearl:

Excellent oral bioavailability. Monitor CBC weekly. Avoid tyramine foods.

Tedizolid
Gram-positive (MRSA, VRE)

Common Uses:

  • •MRSA skin infections
  • •Complicated skin infections

Typical Dosing:

200mg PO/IV q24h

Key Clinical Pearl:

Newer linezolid analog. Shorter duration therapy (6 days).

Lincosamides

Clindamycin
Gram-positive cocci, anaerobes

Common Uses:

  • •MRSA (limited - increased resistance)
  • •Anaerobic infections
  • •Aspiration pneumonia
  • •Toxoplasmosis (PCP prophylaxis alternative)

Typical Dosing:

300-450mg PO q6-8h or 600-900mg IV q6-8h

Key Clinical Pearl:

Risk of C. difficile infection. Excellent anaerobic coverage.

Phenicols

Chloramphenicol
Broad - Good CNS penetration

Common Uses:

  • •Bacterial meningitis (resistant organisms)
  • •Aplastic anemia association limits use

Typical Dosing:

12.5-25mg/kg IV q6h

Key Clinical Pearl:

Excellent meningitis penetration. RARELY used due to aplastic anemia risk.

Nitrofurans

Nitrofurantoin
Gram-positive/negative (NOT Pseudomonas)

Common Uses:

  • •Uncomplicated UTI
  • •UTI prophylaxis

Typical Dosing:

100mg PO q12h (short course: 5-7 days)

Key Clinical Pearl:

Safe in pregnancy. Avoid in renal failure (eGFR <30).

Phosphonic Acids

Fosfomycin
Gram-positive/negative

Common Uses:

  • •Uncomplicated cystitis
  • •Single-dose UTI treatment

Typical Dosing:

3g PO single dose

Key Clinical Pearl:

Single-dose option for uncomplicated UTI. Safe in pregnancy.

Fluoroquinolones (Respiratory)

Fluoroquinolones - Moxifloxacin
Broad - Atypicals, gram-positive/negative

Common Uses:

  • •Community-acquired pneumonia
  • •Acute exacerbation COPD
  • •Sinusitis

Typical Dosing:

400mg PO/IV q24h

Key Clinical Pearl:

Enhanced respiratory pathogen coverage. Same BLACK BOX as cipro/levo.

Cephalosporins (3rd Gen oral)

Cefpodoxime
Moderate - Better gram-negative than 1st/2nd gen

Common Uses:

  • •Community-acquired pneumonia (oral)
  • •Otitis media
  • •Sinusitis

Typical Dosing:

200-400mg PO q12h

Key Clinical Pearl:

Oral 3rd generation option. Good bioavailability.

Monobactams

Aztreonam
Gram-negative only (NO gram-positive, NO anaerobes)

Common Uses:

  • •Gram-negative infections (PCN-allergic patients)
  • •Pseudomonas infections
  • •Alternative to beta-lactams in allergy

Typical Dosing:

1-2g IV q6-8h

Key Clinical Pearl:

Safe in penicillin-allergy (different beta-lactam structure). Gram-negative only.

Tetracyclines (Glycylcyclines)

Tigecycline
Extremely broad - MRSA, VRE, ESBL, anaerobes

Common Uses:

  • •Multi-drug resistant organisms
  • •Intra-abdominal infections
  • •Skin/soft tissue infections (resistant)

Typical Dosing:

100mg IV loading, then 50mg q12h

Key Clinical Pearl:

Broadest tetracycline. Increased mortality - reserve for serious infections.

Glycopeptides (Long-acting)

Dalbavancin
Gram-positive (MRSA, Streptococcus)

Common Uses:

  • •Skin/soft tissue infections (MRSA)
  • •Bacteremia (MRSA)
  • •Outpatient IV therapy

Typical Dosing:

1.5g IV single dose (or 1g day 1, 0.5g day 8)

Key Clinical Pearl:

Long half-life = weekly dosing. Expensive but convenient outpatient option.

Cephalosporins (5th Gen)

Ceftaroline
Broad - MRSA coverage, gram-positive/negative

Common Uses:

  • •MRSA skin/soft tissue infections
  • •MRSA pneumonia
  • •Streptococcal infections

Typical Dosing:

600mg IV q12h

Key Clinical Pearl:

First cephalosporin with MRSA activity. Good for serious infections.

Cephalosporin/Beta-lactamase inhibitor

Ceftriaxone-Sulbactam
Broad - Gram-positive/negative, anaerobes

Common Uses:

  • •Intra-abdominal infections
  • •Mixed aerobic/anaerobic infections

Typical Dosing:

3g IV q4-6h

Key Clinical Pearl:

Good anaerobic coverage with cephalosporin spectrum.

Penicillins/Beta-lactamase inhibitor

Amoxicillin-Sulbactam (Unasyn)
Ampicillin + anaerobic coverage

Common Uses:

  • •Intra-abdominal infections (anaerobic)
  • •Bite wounds (animal/human)
  • •Aspiration pneumonia

Typical Dosing:

3g (2g ampicillin/1g sulbactam) IV q6h

Key Clinical Pearl:

IV version of Augmentin. Good anaerobic/aerobic combo.

Polymyxins

Colistin
Gram-negative (pan-resistant organisms)

Common Uses:

  • •Pseudomonas (colistin-resistant)
  • •Acinetobacter (multi-drug resistant)
  • •Last-resort for XDR organisms

Typical Dosing:

2.5-5mg/kg/day IV divided

Key Clinical Pearl:

HIGH NEPHROTOXICITY. Reserve for truly resistant gram-negative infections.

Macrolides (Non-systemic)

Fidaxomicin
Anaerobes only (Gram-positive anaerobes)

Common Uses:

  • •C. difficile infection (preferred over vancomycin)
  • •Fulminant CDI

Typical Dosing:

200mg PO q12h x 10 days

Key Clinical Pearl:

Minimal systemic absorption = ideal for CDI. Very expensive.

Ansamycins

Rifampin
Broad - Used as adjunct only

Common Uses:

  • •Tuberculosis (always with other agents)
  • •Staph infections (as adjunct therapy)
  • •Meningitis prophylaxis

Typical Dosing:

10mg/kg IV/PO q24h

Key Clinical Pearl:

NEVER monotherapy (resistance develops rapidly). Many drug interactions.

Topical Antibiotics

Bacitracin/Polymyxin B (Topical)
Gram-positive/negative (limited depth)

Common Uses:

  • •Minor wound infections
  • •Ophthalmologic infections
  • •Topical prophylaxis

Typical Dosing:

Apply topically q6-8h

Key Clinical Pearl:

Topical only. Poor systemic absorption - not for serious infections.

Mupirocin
Gram-positive (MRSA)

Common Uses:

  • •Nasal MRSA colonization decolonization
  • •Minor skin infections
  • •Impetigo

Typical Dosing:

Apply topically q8h x 5-10 days

Key Clinical Pearl:

Excellent for intranasal MRSA. Topical only.

Created by Safana Abdullah

For educational purposes only. Always consult a medical professional for diagnosis and treatment.

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