GENERAL PRINCIPLES OF ANTIMICROBIAL THERAPY



GENERAL PRINCIPLES OF ANTIMICROBIAL THERAPY

Questions to ask before selecting an antibiotic:

Host factors:

1. Normal or abnormal immune status?
2. Underlying disease that will affect selection &/or dosing? (e.g. renal failure)
3. Seriousness of the infection?

Pathogen factors:

4. What are the most likely bugs based on the infection site?
5. Where was the infection acquired? (community or hospital setting?)
6. Local susceptibility patterns?

Drug factors:

7. Bioavailability at infected site? (e.g. blood-brain barrier)
8. Broad or narrow spectrum?
9. Bacteriocidal or bacteriostatic?
10. Side effect profile?

 General Principles:

1. Be elegant. Use the antibiotic with the narrowest spectrum that covers the pathogen.

2. Be smart. If a patient is very sick or immunocompromised, it’s OK to cover broadly for the first 1-3 days while you identify the pathogen as long as you narrow your choice as soon as possible.

3. Follow the 3 day rule: Broad spectrum antibiotics markedly alter the normal host flora about 3 days into therapy AND cultures should be back in 3 days so always reassess your antibiotic choices and narrow it when possible.

4. Assume nothing. If a patient needs IV antibiotics, then you need to make sure it is hanging within the time frame you determine reasonable.

5. New isn’t always better. When several antibiotics have similar coverage, select the least expensive.

 Antibiotic Classes by Coverage:

Gram positive coverage:

1. Penicillins (ampicillin, amoxicillin) penicillinase resistant (Dicloxacillin, Oxacillin)*
2. Cephalosporins (1st and 2nd generation)*
3. Macrolides (Erythromycin, Clarithromycin, Azithromycin)*
4. Quinolones (gatifloxacin, moxifloxacin, and less so levofloxacin)*
5. Vancomycin* (MRSA)
6. Sulfonamide/trimethoprim*(Increasing resistance limits use, very inexpensive)
7. Clindamycin*
8. Tetracyclines
9. Chloramphenicol (§causes aplastic anemia so rarely used)
10. Other: Linezolid, Synercid (VRE)

Gram negative coverage:

1. Broad spectrum penicillins (Ticarcillin-clavulanate, piperacillin-tazobactam)*
2. Cephalosporins (2nd, 3rd, and 4th generation)*
3. Aminoglycosides* (renal and ototoxicity)
4. Macrolides (Azithromycin)*
5. Quinolones (Ciprofloxacin)*
6. Monobactams (Azetreonam)*
7. Sulfonamide/trimethoprim*
8. Carbapenems (Imipenem)
9. Chloramphenicol§

Anaerobic coverage:

1. Metronidazole*
2. Clindamycin*
3. Broad spectrum penicillins*
4. Quinolones (Gatifloxacin, Moxifloxacin)
5. Carbapenems
6. Chloramphenicol§

Atypical coverage:

1. Macrolides (Legionella, Mycoplasma, chlamydiae)*
2. Tetracyclines (rickettsiae, chlamydiae)*
3. Quinolones (Legionella, Mycoplasma, Chlamydia)*
4. Chloramphenicol§ (rickettsiae, chlamydiae, mycoplasma)
5. Ampicillin (Listeria)

Pseudomonas coverage:

1. Ciprofloxacin
2. Aminoglycosides
3. Some 3rd generation cephalosporins
4. 4th generation cephalosporins
5. Broad spectrum penicillins
6. Carbapenems

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