Antibiotic spectrum index

• Measures the spectrum of an antibiotic, with a range from 0 to 14
• One point for activity against each of the following:
  • Methicillin-sensitive Staphylococcus aureus (MSSA)
  • Methicillin-resistant Staphylococcus aureus (MRSA)
  • Enterococcus faecalis
  • Vancomycin-resistant Enterococcus faecalis (VRE)
  • Escherichia coli or Klebsiella
  • AmpC producers (Enterobacter, Serratia, and Citrobacter)
  • Extended-spectrum β-lactamase (ESBL) E. coli/Klebsiella
  • Pseudomonas aeruginosa
  • Penicillin-resistant pneumococcus (PRP)
  • Moraxella and Haemophilus influenzae
  • Mycoplasma and Chlamydophila (atypicals)
  • Anaerobes (in general)
  • Bacteriodes fragilis (specifically)
  • Multidrug-resistant organisms
• For each patient, the number of points for every antibiotic is added to give a total daily ASI

Working Ranking

• The following is a reasonable list of commonly-used antibiotics, order from broadest to narrowest, not based on the ASI
• Cefiderocol, Colistin, Polymyxin B, Meropenem-vaborbactam, Imipenem-relebactam, Ceftazidime-avibactam, Ceftolozane-tazobactam, Tigecycline, Meropenem, Doripenem, Ertapenem, Piperacillin-tazobactam, Ticarcillin-clavulanate, Fosfomycin, Moxifloxacin, Levofloxacin, Ciprofloxacin, Doxycycline, Amikacin, Tobramycin, Gentamicin, Cefipime, Ceftazidime, Trimethoprim-sulfamethoxazole, Ampicillin-sulbactam, Amoxicillin-clavulanate, Ceftaroline, Ceftriaxone, Cefuroxime, Cefazolin, Ampicillin, Amoxicillin

Sample Spectrum Index

Antibiotic	MSSA	E.faeca	Anaer	Bact	M/H.flu	E/K	AmpC	ESBL	Pseudo	MRSA	PRP	VRE	Atyp	MDRO	ASI
Dicloxacillin	+	–	–	–	–	–	–	–	–	–	–	–	–	–	1
Oxacillin	+	–	–	–	–	–	–	–	–	–	–	–	–	–	1
Amoxicillin	–	+	–	–	–	+	–	–	–	–	–	–	–	–	2
Ampicillin	–	+	–	–	–	+	–	–	–	–	–	–	–	–	2
Cephalexin	+	–	–	–	–	+	–	–	–	–	–	–	–	–	2
Erythromycin	–	–	–	–	+	–	–	–	–	–	–	–	+	–	2
Erythromycin	–	–	–	–	+	–	–	–	–	–	–	–	+	–	2
Metronidazole	–	–	+	+	–	–	–	–	–	–	–	–	–	–	2
Penicillin	–	+	+	–	–	–	–	–	–	–	–	–	–	–	2
Aztreonam	–	–	–	–	+	+	–	–	+	–	–	–	–	–	3
Cefazolin	+	–	–	–	+	+	–	–	–	–	–	–	–	–	3
Cefdinir	+	–	–	–	+	+	–	–	–	–	–	–	–	–	3
Cefixime	–	–	+	–	+	+	–	–	–	–	–	–	–	–	3
Cefpodoxime	+	–	–	–	+	+	–	–	–	–	–	–	–	–	3
Rifampin	+	–	–	–	+	–	–	–	–	+	–	–	–	–	3
Azithromycin	+	–	+	–	+	–	–	–	–	–	–	–	+	–	4
Cefprozil	+	–	+	–	+	+	–	–	–	–	–	–	–	–	4
Ceftazidime	–	–	+	–	+	+	–	–	+	–	–	–	–	–	4
Cefuroxime	+	–	+	–	+	+	–	–	–	–	–	–	–	–	4
Chloramphenicol	–	–	+	+	+	+	–	–	–	–	–	–	–	–	4
Clarithromycin	+	–	+	–	+	–	–	–	–	–	–	–	+	–	4
Clindamycin	+	–	+	+	–	–	–	–	–	+	–	–	–	–	4
Piperacillin	–	+	+	–	–	+	–	–	+	–	–	–	–	–	4
TMP-SMX	+	–	–	–	+	+	–	–	–	+	–	–	–	–	4
Cefotaxime	+	–	+	–	+	+	–	–	–	–	+	–	–	–	5
Cefoxitin	+	–	+	+	+	+	–	–	–	–	–	–	–	–	5
Ceftriaxone	+	–	+	–	+	+	–	–	–	–	+	–	–	–	5
Colistin	–	–	–	–	–	+	+	+	+	–	–	–	–	+	5
Daptomycin	+	+	–	–	–	–	–	–	–	+	–	+	–	+	5
Doxycycline	+	–	–	–	+	+	–	–	–	+	–	–	+	–	5
Gentamicin	+	–	–	–	+	+	–	–	+	+	–	–	–	–	5
Minocycline	+	–	–	–	+	+	–	–	–	+	–	–	+	–	5
Telavancin	+	+	–	–	–	–	–	–	–	+	+	–	–	+	5
Tobramycin	+	–	–	–	+	+	–	–	+	+	–	–	–	–	5
Vancomycin	+	+	–	–	–	–	–	–	–	+	+	–	–	+	5
Amikacin	+	–	–	–	+	+	–	–	+	+	–	–	–	+	6
Amoxicillin-clavulanic acid	+	+	+	+	+	+	–	–	–	–	–	–	–	–	6
Ampicillin-sulbactam	+	+	+	+	+	+	–	–	–	–	–	–	–	–	6
Cefepime	+	–	–	–	+	+	+	–	+	–	+	–	–	–	6
Linezolid	+	+	–	–	–	–	–	–	–	+	+	+	–	+	6
Ticarcillin-clavulanate	+	–	+	+	+	+	–	–	+	–	–	–	–	–	6
Ceftaroline	+	+	–	–	+	+	+	–	–	+	+	–	–	+	8
Ciprofloxacin	+	+	–	–	+	+	+	+	+	–	–	–	+	–	8
Piperacillin-tazobactam	+	+	+	+	+	+	+	–	+	–	–	–	–	–	8
Ertapenem	+	–	+	+	+	+	+	+	–	–	+	–	–	+	9
Levofloxacin	+	+	+	–	+	+	+	+	–	–	+	–	+	–	9
Meropenem	+	–	+	+	+	+	+	+	+	–	+	–	–	+	10
Moxifloxacin	+	+	+	+	+	+	+	–	–	+	+	–	+	–	10
Imipenem-cilastatin	+	+	+	+	+	+	+	+	+	–	+	–	–	+	11
Tigecycline	+	+	+	+	+	+	+	+	–	+	+	+	+	+	13

MSSA = methicillin-susceptible Staphylococcus aureus; E/K = Escherichia coli/Klebsiella; M/H.flu = Moraxella and Haemophilus influenzae; Pseudo = Pseudomonas aeruginosa; MRSA = methicillin-resistant Staphylococcus aureus; PRP = penicillin-resistant pneumococcus; VRE = vancomycin-resistant Enterococcus; atypicals = Mycoplasma pneumoniae and Chlamidophila; MDRO = multidrug-resistant organisms

Further Reading

• Development and Application of an Antibiotic Spectrum Index for Benchmarking Antibiotic Selection Patterns Across Hospitals. Infect Control Hosp Epidemiol. 2017;38(8):993-997. doi: 10.1017/ice.2017.94.