This is a summary for the major uses of antibiotics regarding the type of infection. Extracted from KAPLAN lecture notes and other sources. I stressed on stuff like “1st choice” and “2nd choice” items being a question key in the USMLE Step 2 CK. So if you’re having a hard time knowing which AB is for which infection, this list will considerably help. Of course, there are some exceptions for some infections, but in general, this list would be good as a scheme.

¶ For GM +VE COCCI (mainly)

¤ SEMISYNTHETIC PENICILLINASE RESISTANT PENICILLINS
» e.g. oxacillin, nafcillin, cloxacillin, dicloxacillin
• 1st choice in; sensitive Staph. without concurrent Gm -ve infection.
• Also useful in; other Gm +ve org. like Strept.
• In MSRA; use Vancomycin instead.

¤ PENICILLIN-G, PENICILLIN VK, AMPICILLIN, AMOXICILLIN
• 1st choice in; Strep. infection
• Also useful in; Listeria, Gm -ve org.
• Preferably combined with beta-lactamase inhibitors as sulbactam or clavulanate — such combinations may be useful in empiric ttt of HAP (hospital acquired pneumonia)

¤ CEPHALOSPORINS
» e.g. 1st gen; cefozalin, cefadroxil, cephalexin, 2nd gen; cefoxitin, cefuroxime, cefprozil
• 1st choice in; sensitive Staph. inf. when Penicillins are contraindicated (e.g. allergy)
• 2nd generation drugs cover more Gm -ve drugs as well
• Don’t use 3rd gen. in Gm +ve inf. (useless)

¤ MACROLIDES (» e.g. erythromycin, clarithromycin, azithromycin), FLUOROQUINOLONES (» e.g. levofloxacin, gatifloxacin, moxifloxacin)
• 3rd choice after penicillins and cephalosporins in Staph. inf.
• 1st choice in; Atypical pneumonia, OUTPAITENT CA-pneumonia (i.e. minor inf.)

¤ VANCOMYCIN, LINEZOLID
• 1st choice in; major infection with severe allergy to penicillin (Vancomycin IV), MSRA (Vancomycin IV, or Linezolid PO)

¶ For GRAM -VE BACILLI (mainly)

¦ P.S. ¦ all drugs below are effective ag. ALL Gm -ve bacilli.

¤ PENICILLINS
» e.g. piperacillin, ticarcillin, mezlocillin
• 1st choice in Pseudomonas
• Also eff. ag. ALL Gm -ve bacilli incl. Enterobacteriaceae (E. coli, Proteus, Enterobacter, Citrobacter, Klebsiella, Morganella, Serratia)

¤ CEPHALOSPORINS
» e.g. 3rd gen (ceftazidime “brain abscess”, cefotaxime, cefixime, ceftriaxone); 4th gen (cefepime)
• 1st choice (among others) in “empiric” treatment of hospital acquired pneumonia (HAP)
• 2nd choice in INPATIENT CA-pneumonia
• 1st choice in penicillin-insensitive meningitis

¤ FLUOROQUINOLONES
» e.g. ciprofloxacin, ofloxacin, (levofloxacin, gatifloxacin, moxifloxacin) « NEW ones
• 1st choice (the NEW ones) in INPATIENT community acquired pneumonia (CAP)
• 2nd choice (the NEW ones, after Macrolides) in OUTPATIENT community acquired pneumonia (CAP)

¤ AMINOGLYCOSIDES (» e.g. gentamycin, tobramycin, amikacin)/MONOBACTAMS (» e.g. aztreonam)
• Mainly in Gm -ve only

¤ CARBAPENEMS
» e.g. imipenem, meropenem
• Mainly in Gm -ve only
• Fully active ag. Enterobact. & Pseudomonas
• May be used instead of Cephalosp. in empiric ttt of HAP

¶ For ANAEROBES

• 1st choice is Metronidazole (Flagyl) – best for Bowel inf.
• Equivalent alternatives;
Clindamycin – best for Mouth inf.
Carbapenems
Beta-lactam/beta-lactamase