Complete antibiotics classification function in which disease to give and dose

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Complete Antibiotic Classification: Function, Disease Indications & Doses

Sources: Katzung's Basic and Clinical Pharmacology 16th Ed, Goodman & Gilman's Pharmacological Basis of Therapeutics, Lippincott Illustrated Reviews Pharmacology

I. BETA-LACTAMS

A. Penicillins

All penicillins share a core beta-lactam ring fused to a thiazolidine ring. They inhibit cell-wall synthesis by binding penicillin-binding proteins (PBPs).

1. Natural Penicillins

Drug	Route	Dose	Key Indications
Penicillin G	IV/IM	2-4 million units IV q4h	Streptococcal pharyngitis, pneumococcal pneumonia, syphilis (neurosyphilis: 18-24 MU/day IV x 10-14 days), meningococcal meningitis, actinomycosis, gas gangrene
Penicillin V	Oral	250-500 mg q6-8h	Streptococcal pharyngitis, mild streptococcal skin infections, rheumatic fever prophylaxis
Benzathine Penicillin G	IM	1.2 MU IM single dose	Primary/secondary syphilis, rheumatic fever prophylaxis
Procaine Penicillin G	IM	600,000 units IM OD	Moderately severe pneumococcal pneumonia, uncomplicated gonorrhea

Spectrum: Gram-positive cocci (Streptococcus, Pneumococcus), Neisseria, Treponema pallidum, anaerobes (Clostridium, Actinomyces)

2. Antistaphylococcal Penicillins (Penicillinase-Resistant)

Drug	Route	Dose	Key Indications
Cloxacillin	Oral/IV	250-500 mg q6h PO; 1-2 g IV q6h	MSSA skin/soft tissue infections, osteomyelitis, septic arthritis, endocarditis
Dicloxacillin	Oral	250-500 mg q6h (fasting)	MSSA cellulitis, impetigo, wound infections
Nafcillin	IV	1-2 g IV q4-6h	MSSA bacteremia, endocarditis, osteomyelitis
Oxacillin	IV	1-2 g IV q4-6h	MSSA bacteremia, endocarditis
Methicillin	IV	(historical; now rarely used)	Introduced concept; replaced by nafcillin/oxacillin

Note: MRSA is resistant to all penicillinase-resistant penicillins - use vancomycin or daptomycin instead.

3. Aminopenicillins (Extended-Spectrum)

Drug	Route	Dose	Key Indications
Ampicillin	IV/IM	1-2 g IV q4-6h (up to 12 g/day for serious infections)	Listeria meningitis, enterococcal endocarditis, typhoid (if susceptible), UTI (susceptible E. coli), H. influenzae pneumonia
Amoxicillin	Oral	250-500 mg q8h; 875 mg q12h	Otitis media, sinusitis, community-acquired pneumonia (CAP), H. pylori eradication (triple therapy), dental abscess, urinary tract infections

Spectrum added over natural penicillins: H. influenzae, E. coli, Salmonella, Shigella (ampicillin > amoxicillin for Shigella), Listeria, Enterococcus

4. Beta-Lactam / Beta-Lactamase Inhibitor Combinations

Drug	Dose	Key Indications
Amoxicillin-Clavulanate	875/125 mg PO q12h; 500/125 mg q8h	Sinusitis, otitis media, animal bites, ABECB, UTIs with resistant organisms, pneumonia
Ampicillin-Sulbactam	1.5-3 g IV q6h	Intra-abdominal infections, aspiration pneumonia, pelvic inflammatory disease, skin/soft tissue infections
Piperacillin-Tazobactam	3.375 g IV q6h or 4.5 g IV q6-8h	Hospital-acquired pneumonia, febrile neutropenia, intra-abdominal sepsis, complicated UTI, Pseudomonas infections

5. Antipseudomonal Penicillins (Ureidopenicillins)

Drug	Dose	Key Indications
Piperacillin (alone)	3-4 g IV q4-6h	Pseudomonas aeruginosa infections, Klebsiella, Enterobacter; typically combined with tazobactam

B. Cephalosporins

Mechanism same as penicillins (PBP binding, cell wall synthesis inhibition). Classified by "generations."

Generation Overview Table

Generation	Examples	Gram+ Coverage	Gram- Coverage	Key Uses
1st Gen	Cefazolin, Cephalexin	Excellent (MSSA, Strep)	Limited (E. coli, Proteus, Klebsiella)	Surgical prophylaxis, skin/soft tissue (MSSA), UTI
2nd Gen	Cefuroxime, Cefaclor, Cefoxitin, Cefotetan	Good	Broader (H. influenzae, Moraxella)	Respiratory tract infections, otitis media, anaerobes (cephamycins: cefoxitin/cefotetan)
3rd Gen	Ceftriaxone, Cefotaxime, Ceftazidime	Reduced	Excellent (Enterobacteriaceae)	Meningitis, gonorrhea, CAP, sepsis, typhoid
4th Gen	Cefepime	Good	Very broad including Pseudomonas	Febrile neutropenia, hospital-acquired pneumonia, Pseudomonas
5th Gen	Ceftaroline	Includes MRSA	Gram-negative	MRSA skin/soft tissue, CAP

Detailed Cephalosporin Doses

Drug	Generation	Route	Dose	Indications
Cephalexin	1st	PO	250-500 mg q6h	Skin/soft tissue (MSSA), uncomplicated UTI, dental prophylaxis
Cefazolin	1st	IV/IM	1-2 g IV q8h	Surgical prophylaxis (standard), MSSA bacteremia, cellulitis
Cefaclor	2nd	PO	250-500 mg q8h	Otitis media, sinusitis, bronchitis, UTI
Cefuroxime	2nd	PO/IV	250-500 mg q12h PO; 750 mg-1.5 g IV q8h	Respiratory tract infections, Lyme disease (mild), UTI
Cefoxitin	2nd (cephamycin)	IV	1-2 g IV q6-8h	Intra-abdominal infections, pelvic infections, surgical prophylaxis (colorectal)
Cefotetan	2nd (cephamycin)	IV	1-2 g IV q12h	Pelvic inflammatory disease, intra-abdominal infections
Ceftriaxone	3rd	IV/IM	1-2 g IV/IM OD (2 g IV q12h for meningitis)	Meningitis, CAP, gonorrhea (500 mg IM single dose), typhoid fever, sepsis, Lyme disease, spontaneous bacterial peritonitis
Cefotaxime	3rd	IV	1-2 g IV q8h (2 g q4-6h for meningitis)	Meningitis, neonatal sepsis, CAP, gram-negative sepsis
Ceftazidime	3rd	IV	1-2 g IV q8h	Pseudomonas aeruginosa, nosocomial infections, cystic fibrosis pulmonary exacerbations
Cefixime	3rd	PO	400 mg OD or 200 mg BD	UTI, typhoid, gonorrhea, otitis media
Cefpodoxime	3rd	PO	100-200 mg q12h	RTI, UTI, sinusitis, gonorrhea
Cefepime	4th	IV	1-2 g IV q8-12h	Febrile neutropenia, nosocomial pneumonia, Pseudomonas, complicated UTI
Ceftaroline	5th	IV	600 mg IV q12h	MRSA skin/soft tissue infections, CAP
Ceftolozane-Tazobactam	Novel	IV	1.5 g IV q8h	MDR Pseudomonas, complicated UTI, HAP/VAP
Ceftazidime-Avibactam	Novel	IV	2.5 g IV q8h	KPC-producing Klebsiella, MDR gram-negatives

C. Carbapenems

Broadest spectrum beta-lactams; highly resistant to beta-lactamases.

Drug	Dose	Key Indications
Imipenem-Cilastatin	500 mg IV q6h	Serious polymicrobial infections, ESBL-producing organisms, febrile neutropenia, Acinetobacter
Meropenem	1-2 g IV q8h (2 g q8h for meningitis)	Meningitis (preferred carbapenem), intra-abdominal, HAP/VAP, ESBL infections
Ertapenem	1 g IV/IM OD	Community-acquired intra-abdominal infections, complicated UTI, skin/soft tissue; NOT active against Pseudomonas
Doripenem	500 mg IV q8h	Complicated UTI, HAP, IAI

D. Monobactams

Drug	Dose	Key Indications
Aztreonam	1-2 g IV q6-8h	Gram-negative infections (aerobic only) in penicillin-allergic patients; UTI, intra-abdominal (with metronidazole), Pseudomonas; Safe in true penicillin allergy

II. PROTEIN SYNTHESIS INHIBITORS

A. Aminoglycosides (30S subunit inhibitors)

Drug	Dose	Key Indications
Gentamicin	5-7 mg/kg/day IV OD (once-daily dosing) or 1.5-2 mg/kg q8h	Gram-negative sepsis, synergy for endocarditis, plague, tularemia; UTI, pyelonephritis
Tobramycin	5-7 mg/kg/day IV OD	Pseudomonas (preferred aminoglycoside), cystic fibrosis (inhaled form), HAP/VAP
Amikacin	15-20 mg/kg/day IV OD	MDR gram-negatives resistant to gentamicin/tobramycin, NTM infections, TB (2nd line)
Streptomycin	15 mg/kg/day IM	TB (2nd line), brucellosis (+ doxycycline), plague, tularemia, endocarditis (synergy)
Neomycin	Oral/topical	Hepatic encephalopathy (oral, non-absorbed), bowel prep, topical wound infections
Spectinomycin	2 g IM single dose	Gonorrhea (penicillin/cephalosporin-allergic patients)

Toxicity: Nephrotoxicity, ototoxicity (irreversible). Monitor levels. Contraindicated in myasthenia gravis.

B. Tetracyclines (30S subunit inhibitors)

Drug	Dose	Key Indications
Doxycycline	100 mg PO/IV q12h	Chlamydia, atypical pneumonia (Mycoplasma, Chlamydophila), Rickettsia, RMSF, malaria prophylaxis, Lyme disease, brucellosis (+ streptomycin), Q fever, anthrax, MRSA skin infections, PID
Tetracycline	250-500 mg PO q6h	H. pylori (quadruple therapy), acne, Chlamydia, Rickettsia
Minocycline	100 mg PO/IV q12h	Acne, MRSA skin infections, Nocardia, atypical mycobacteria
Tigecycline	100 mg IV load, then 50 mg IV q12h	MDR gram-negatives, MRSA, intra-abdominal infections, skin/soft tissue; Not for bacteremia/pneumonia (high mortality)

Avoid in: Pregnancy (category D), children < 8 years (permanent tooth staining/bone effects).

C. Macrolides (50S subunit inhibitors)

Drug	Dose	Key Indications
Azithromycin	500 mg day 1, then 250 mg days 2-5 (Z-pack); 500 mg OD x 3 days	CAP, atypical pneumonia (Mycoplasma, Legionella, Chlamydophila), pharyngitis (pen-allergic), Chlamydia (1 g single dose), MAC prophylaxis (HIV), pertussis, traveler's diarrhea
Clarithromycin	250-500 mg q12h	H. pylori (triple therapy), CAP, MAC treatment, H. influenzae sinusitis, endocarditis prophylaxis
Erythromycin	250-500 mg q6h	Streptococcal pharyngitis (penicillin-allergic), atypical pneumonia, Chlamydia, Campylobacter, pertussis, diphtheria (adjunct), gastroparesis (prokinetic)

D. Chloramphenicol (50S subunit inhibitor)

Drug	Dose	Key Indications
Chloramphenicol	50-100 mg/kg/day IV q6h; max 4 g/day	Typhoid fever, bacterial meningitis (penicillin-allergic, developing world), RMSF in pregnancy/children where tetracyclines contraindicated, brain abscess

Toxicity: Gray baby syndrome, aplastic anemia (idiosyncratic), dose-dependent bone marrow suppression.

E. Lincosamides (50S subunit inhibitors)

Drug	Dose	Key Indications
Clindamycin	300-600 mg PO/IV q8h; 600-900 mg IV q8h	Anaerobic infections (aspiration pneumonia, lung abscess, intra-abdominal), MRSA skin/soft tissue, osteomyelitis, pelvic inflammatory disease, Toxoplasma (with pyrimethamine), Pneumocystis (with primaquine), dental infections, BV

Toxicity: C. difficile-associated colitis (pseudomembranous colitis) - highest risk.

F. Oxazolidinones (50S - 30S bridge inhibitors)

Drug	Dose	Key Indications
Linezolid	600 mg PO/IV q12h	MRSA pneumonia, MRSA bacteremia/endocarditis (vancomycin-resistant), VRE infections, drug-resistant TB (XDR-TB)

Toxicity: Thrombocytopenia, serotonin syndrome (MAO inhibitor activity), optic/peripheral neuropathy with prolonged use.

G. Streptogramins

Drug	Dose	Key Indications
Quinupristin-Dalfopristin	7.5 mg/kg IV q8h	VRE faecium (not faecalis), MRSA (limited use)

III. DNA / RNA SYNTHESIS INHIBITORS

A. Fluoroquinolones (DNA gyrase / Topoisomerase IV inhibitors)

Drug	Dose	Key Indications
Ciprofloxacin	250-750 mg PO q12h; 200-400 mg IV q12h	UTI/pyelonephritis, typhoid fever, traveler's diarrhea, anthrax (drug of choice), gonorrhea (if susceptible), Pseudomonas, bone/joint infections, prostatitis
Levofloxacin	500-750 mg PO/IV OD	CAP (respiratory fluoroquinolone), UTI, prostatitis, pyelonephritis, TB (2nd line), nosocomial pneumonia, sinusitis
Moxifloxacin	400 mg PO/IV OD	CAP, sinusitis, acute exacerbation of bronchitis, TB (2nd line); Not for UTI (poor urinary excretion)
Norfloxacin	400 mg PO q12h	Uncomplicated UTI, prostatitis, traveler's diarrhea
Ofloxacin	200-400 mg PO/IV q12h	UTI, Chlamydia, PID, otitis externa, leprosy (MDT)
Gemifloxacin	320 mg PO OD x 5-7 days	CAP, acute bacterial exacerbation of chronic bronchitis

Avoid in: Children (< 18 years, cartilage toxicity), pregnancy. Risk of tendon rupture (especially Achilles), QT prolongation.

B. Nitroimidazoles

Drug	Dose	Key Indications
Metronidazole	500 mg PO/IV q8h; 2 g PO single dose	Anaerobic infections (B. fragilis), C. difficile (oral, not IV), BV (500 mg BD x 7 days or 2 g single dose), trichomoniasis, amoebiasis, giardiasis, H. pylori (quadruple therapy)
Tinidazole	2 g PO single dose or 500 mg BD	Trichomoniasis, amoebiasis, giardiasis, BV

C. Sulfonamides + Trimethoprim (Folate Synthesis Inhibitors)

Drug	Dose	Key Indications
TMP-SMX (Co-trimoxazole)	1 DS tab (160/800 mg) PO q12h; 15-20 mg/kg/day IV (PCP dose)	UTI, Pneumocystis jirovecii pneumonia (PCP - treatment and prophylaxis), MRSA skin/soft tissue, Nocardia, Toxoplasma (alternative), Isospora, Stenotrophomonas, Whipple's disease
Sulfadiazine	1-4 g/day divided	Toxoplasmosis (+ pyrimethamine), nocardiosis
Dapsone	100 mg PO OD	Leprosy (MDT), PCP prophylaxis (pentamidine-allergic), dermatitis herpetiformis

D. Rifamycins (RNA polymerase inhibitors)

Drug	Dose	Key Indications
Rifampin (Rifampicin)	600 mg PO/IV OD (TB); 600 mg BD x 2 days (prophylaxis)	Tuberculosis (HRZE regimen), leprosy (MDT), H. influenzae/meningococcal prophylaxis (close contacts), staphylococcal prosthetic valve endocarditis (adjunct), brucellosis (+ doxycycline)
Rifabutin	300 mg PO OD	MAC prophylaxis/treatment (HIV patients), TB in HIV (fewer drug interactions than rifampin)
Rifaximin	200 mg PO TID x 3 days or 550 mg PO BD	Traveler's diarrhea (E. coli, non-invasive), hepatic encephalopathy (prophylaxis/treatment), IBS-D

IV. CELL MEMBRANE DISRUPTORS

Drug	Dose	Key Indications
Vancomycin	15-20 mg/kg IV q8-12h (AUC-guided dosing); 125 mg PO q6h x 10 days (C. diff)	MRSA infections (bacteremia, pneumonia, endocarditis, meningitis, osteomyelitis), VRE, C. difficile colitis (oral only), penicillin-allergic gram-positive coverage
Daptomycin	4-6 mg/kg IV OD (skin); 6-10 mg/kg OD (bacteremia/endocarditis)	MRSA bacteremia, right-sided MRSA endocarditis, VRE, MRSA skin/soft tissue; NOT for pneumonia (inactivated by surfactant)
Polymyxin B	1.25-2.5 mg/kg/day IV divided q12h	MDR Acinetobacter baumannii, MDR Pseudomonas, KPC-producing Klebsiella (last resort)
Colistin (Polymyxin E)	2.5-5 mg/kg/day IV (as CBA) divided q12h	Same as polymyxin B; carbapenem-resistant gram-negative bacteria (last-resort)

V. CELL WALL SYNTHESIS - OTHER MECHANISMS

Glycopeptides / Lipoglycopeptides

Drug	Dose	Key Indications
Teicoplanin	400 mg IV/IM OD (or BD for severe)	MRSA, CNS infections, endocarditis, C. difficile (oral)
Oritavancin	1200 mg IV single dose	Acute bacterial skin/soft tissue infections (ABSSSI) due to MRSA or Streptococcus
Dalbavancin	1500 mg IV single dose (or 1000 mg then 500 mg 1 week later)	ABSSSI due to gram-positive organisms including MRSA
Telavancin	10 mg/kg IV OD	MRSA HAP/VAP, ABSSSI

VI. ANTI-MYCOBACTERIAL DRUGS

Standard TB Regimen (HRZE)

Phase	Drugs	Duration
Intensive	Isoniazid (H) + Rifampicin (R) + Pyrazinamide (Z) + Ethambutol (E)	2 months
Continuation	Isoniazid (H) + Rifampicin (R)	4 months

Drug	Dose	Notes
Isoniazid (INH)	5 mg/kg/day (max 300 mg) PO	Latent TB (9 months); give pyridoxine to prevent peripheral neuropathy
Rifampicin	10 mg/kg/day (max 600 mg) PO	Powerful CYP450 inducer
Pyrazinamide	25-35 mg/kg/day (max 2 g) PO	Hepatotoxic, hyperuricemia, only active in acidic pH
Ethambutol	15-25 mg/kg/day PO	Optic neuritis (check visual acuity/color vision)
Streptomycin	15 mg/kg/day IM	2nd line; 8th nerve toxicity

Leprosy MDT (WHO Regimen)

Type	Drugs	Duration
Paucibacillary	Dapsone 100 mg OD + Rifampicin 600 mg once monthly	6 months
Multibacillary	Dapsone 100 mg OD + Rifampicin 600 mg monthly + Clofazimine 50 mg OD + 300 mg monthly	12 months

VII. QUICK REFERENCE - DISEASE TO ANTIBIOTIC GUIDE

Disease / Condition	Drug of Choice	Alternative
Streptococcal pharyngitis	Penicillin V 500 mg q12h x 10 days	Amoxicillin, Azithromycin (if PCN allergy)
MSSA bacteremia	Nafcillin/Oxacillin or Cloxacillin	Cefazolin, Vancomycin (PCN allergy)
MRSA bacteremia	Vancomycin 15-20 mg/kg IV q8-12h	Daptomycin 6-10 mg/kg IV OD
MRSA pneumonia	Vancomycin or Linezolid 600 mg IV q12h	Ceftaroline
MRSA skin infection	TMP-SMX or Doxycycline 100 mg q12h	Clindamycin, Linezolid
Community-acquired pneumonia (mild)	Amoxicillin 500-1000 mg TID or Azithromycin	Doxycycline
CAP (severe/hospitalized)	Ceftriaxone 1-2 g OD + Azithromycin 500 mg OD	Levofloxacin 750 mg OD
Atypical pneumonia (Mycoplasma/Chlamydia)	Doxycycline 100 mg q12h or Azithromycin	Levofloxacin
Legionella pneumonia	Azithromycin 500 mg OD or Levofloxacin 750 mg OD	Doxycycline
Bacterial meningitis (empiric, adult)	Ceftriaxone 2 g IV q12h + Vancomycin	+ Ampicillin if Listeria suspected (> 50 yrs)
Meningococcal meningitis	Penicillin G 4 MU IV q4h	Ceftriaxone 2 g IV q12h
Pneumococcal meningitis	Ceftriaxone 2 g IV q12h + Vancomycin	Meropenem
UTI (uncomplicated)	TMP-SMX DS q12h x 3 days or Nitrofurantoin 100 mg BD x 5 days	Fosfomycin 3 g single dose
Pyelonephritis	Ciprofloxacin 500 mg BD x 7-14 days or Ceftriaxone 1 g OD IV	Levofloxacin 750 mg OD x 5-7 days
Gonorrhea	Ceftriaxone 500 mg IM single dose	Cefixime 400 mg single dose
Chlamydia	Doxycycline 100 mg BD x 7 days	Azithromycin 1 g single dose
Syphilis (primary/secondary)	Benzathine Penicillin G 2.4 MU IM single dose	Doxycycline 100 mg BD x 14 days
Neurosyphilis	Penicillin G 18-24 MU/day IV x 10-14 days	Ceftriaxone 2 g IV OD x 10-14 days
PID	Ceftriaxone 500 mg IM + Doxycycline 100 mg BD + Metronidazole 400 mg BD x 14 days	Ampicillin-Sulbactam + Doxycycline
H. pylori eradication (1st line)	Amoxicillin 1 g + Clarithromycin 500 mg + PPI BD x 14 days (CAC)	Bismuth quadruple therapy
Typhoid fever	Azithromycin 500 mg OD x 7 days (uncomplicated) or Ceftriaxone 2 g IV OD x 7-10 days	Ciprofloxacin (if susceptible)
Intra-abdominal infection	Pip-Tazo 3.375 g q6h or Ertapenem 1 g OD	Ampicillin-Sulbactam + Metronidazole
Anaerobic infection / aspiration	Amoxicillin-Clavulanate or Clindamycin + Ceftriaxone	Metronidazole + Cephalosporin
C. difficile (mild)	Vancomycin 125 mg PO QID x 10 days	Fidaxomicin 200 mg BD x 10 days
C. difficile (severe/fulminant)	Vancomycin 500 mg PO QID + Metronidazole 500 mg IV q8h	Fidaxomicin
Febrile neutropenia	Piperacillin-Tazobactam 4.5 g IV q6h	Cefepime 2 g IV q8h, Meropenem
Pseudomonas infection	Pip-Tazo or Ceftazidime or Cefepime + Tobramycin	Meropenem, Ciprofloxacin
Acinetobacter (MDR)	Imipenem or Meropenem	Colistin, Polymyxin B
Tuberculosis (sensitive)	HRZE x 2 months then HR x 4 months	Standardized regimen
Leprosy (paucibacillary)	Dapsone + Rifampicin x 6 months	WHO MDT
Malaria prophylaxis	Doxycycline 100 mg PO OD (start 1-2 days before, continue 4 weeks after)	Mefloquine, Atovaquone-Proguanil
Anthrax	Ciprofloxacin 500 mg BD or Doxycycline 100 mg BD x 60 days	Amoxicillin if susceptible
Brucellosis	Doxycycline 100 mg BD x 6 weeks + Streptomycin 1 g/day IM x 2-3 weeks	Doxycycline + Rifampicin x 6 weeks
Lyme disease (early localized)	Doxycycline 100 mg BD x 10-21 days	Amoxicillin 500 mg TID x 14-21 days
Lyme disease (disseminated/CNS)	Ceftriaxone 2 g IV OD x 14-28 days	Penicillin G IV
Rickettsia / RMSF	Doxycycline 100 mg BD x 5-7 days	Chloramphenicol (pregnancy)
Tularemia	Streptomycin 1 g IM BD x 10 days or Gentamicin 5 mg/kg IV OD	Doxycycline x 14-21 days
Plague	Streptomycin 1 g IM BD or Gentamicin 5 mg/kg OD	Doxycycline, Ciprofloxacin
Actinomycosis	Penicillin G 18-24 MU/day IV x 2-6 weeks then Amoxicillin x 6-12 months	Doxycycline
Nocardia	TMP-SMX or Imipenem + Amikacin	Linezolid
PCP (Pneumocystis)	TMP-SMX 15-20 mg/kg/day IV or PO (based on TMP) x 21 days	Pentamidine, Clindamycin + Primaquine
Toxoplasmosis	Pyrimethamine + Sulfadiazine + Folinic acid	Pyrimethamine + Clindamycin
BV (Bacterial vaginosis)	Metronidazole 500 mg BD x 7 days or 0.75% gel intravaginally x 5 days	Clindamycin 2% cream
Surgical prophylaxis (clean/clean-contaminated)	Cefazolin 1-2 g IV within 60 min before incision	Clindamycin + Gentamicin (PCN allergy)

VIII. MECHANISM OF ACTION SUMMARY

Mechanism	Class	Examples
Inhibit cell wall synthesis (PBP binding)	Beta-lactams	Penicillins, Cephalosporins, Carbapenems, Monobactams
Inhibit cell wall synthesis (D-Ala-D-Ala binding)	Glycopeptides	Vancomycin, Teicoplanin
Disrupt cell membrane	Polymyxins, Daptomycin	Polymyxin B, Colistin, Daptomycin
Inhibit 30S ribosomal subunit	Aminoglycosides, Tetracyclines	Gentamicin, Doxycycline
Inhibit 50S ribosomal subunit	Macrolides, Chloramphenicol, Lincosamides, Streptogramins	Azithromycin, Clindamycin, Linezolid (30S-50S bridge)
Inhibit DNA gyrase / Topoisomerase IV	Fluoroquinolones	Ciprofloxacin, Levofloxacin
Inhibit RNA polymerase	Rifamycins	Rifampicin, Rifabutin
Inhibit folate synthesis	Sulfonamides, Trimethoprim	TMP-SMX, Sulfadiazine
Inhibit DNA synthesis (nitroreduction)	Nitroimidazoles	Metronidazole, Tinidazole

Key mnemonics:

"VEST CaMP" for 50S inhibitors: Vancomycin (actually glycopeptide), Erythromycin/macrolides, Streptogramins, Tetracyclines (30S), Chloramphenicol, azithromycin, Macrolides, Lincosamides, Protein synthesis
"ESKAPE" pathogens needing special antibiotic consideration: Enterococcus faecium, S. aureus (MRSA), Klebsiella, Acinetobacter, Pseudomonas, Enterobacter

Sources: Katzung's Basic and Clinical Pharmacology 16th Ed | Goodman & Gilman's Pharmacological Basis of Therapeutics | Lippincott Illustrated Reviews: Pharmacology | Jawetz Medical Microbiology 28th Ed

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