Gerber et al proposed the Antibiotic Spectrum Index (ASI) to classify an antibiotic based on activity against important pathogens. The index is reported to give insights into a hospital's antibiotic use. The authors are from Children's Hospital of Philadelphia, the University of Pennsylvania, the University of Utah, Seattle Children's Hospital and Washington University.
Each antibiotic is scored against a list of clinically relevant bacteria (14 groups in Table 1), with 0 indicating ineffective and 1 effective.
Organisms evaluated:
(1) MSSA
(2) MRSA
(3) Enterococcus faecalis
(4) vancomycin resistant Enterococcus faecalis (VRE)
(5) E. coli/Klebsiella
(6) ampC producer
(7) extended spectrum beta-lactamase producing (ESBL) E. coli or Klebsiella
(8) Pseudomonas aeruginosa
(9) penicillin-resistant Streptococcus pneumoniae
(10) Hemophilus influenzae/Moraxella
(11) Mycoplasma and Chlamydophila
(12) anaerobe not B. fragilis (1 point)
(13) Bacteroides fragilis (2 points)
An additional point is given for multi-drug-resistant organism (MDRO).
The antibiotic spectrum index for an antibiotic is the sum of scores with a range from 0 to 14. A broad-spectrum antibiotic will have a higher ASI.
If a person is receiving more than 1 antibiotic per day, then the total ASI is the sum of the individual ASI's for antibiotics received. If two antibiotics are effective against the same organism, then 2 points are assigned. The maximum total ASI is the number of antibiotics times the number of organisms evaluated.
Supposedly the index can aid in antibiotic stewardship. In theory the ASI per antibiotic day should decrease with an effective intervention to reduce antibiotic use.
Possible issues:
(1) The scores are 0 or 1 with no apparent intermediate scores.
(2) There appears to be no account for bacterial strain variation, and some categories include multiple genera.
(3) Comparison between hospitals would require a standardized list of organisms.
