Clinical Antibiotic Use
β-Lactams
Drug
Penicillins
Penicillin G
(benzylpenicillin)
Mech of
action
General
specificity
Uses
resistance
CW
Gram (+)
*Streptococcus
-some low level resistance
S aureus
Coag (-) staph – most
methCN-resist.
Neisseria
-meningitidis (MC)
S pneumo
 altered PBPs
-gonorrhoeae (GC)
 sig minority have TEM β-lactamase
Ampicillin (IV)
Amoxicillin
(oral)
Gram (+)
streptococcus
-as above
SA
CNStaph – as above
*enterococcus
Neisseria – as above
H influenzae – sig minority w/ TEM βlactamase
E coli (EC) – activity, but large #s
resistant
Proteus mirabilis (PM) – most
susceptible
Semi-synthetic
PCNs
IV: methicillin,
oxacillin,
nafcillin
Gram (+)
SA – poor substrate
MSSA
MRSA
CNStaph – most MR
Some MS CNStaph
Strep – adequate activity, not preferred
Oral: cloxacillin,
dicloxacillin
Extended
Spectrum PCNs
IV: carbenicillin,
ticarcillin,
mezlocillin
Gram (+)
(Proteus mirabilis)
Strep – all but s pneumo
Enterococcus – piperacillin parallels
ampicillin
SA
CNStaph
S pneumo
E coli + enteroB – activity w/ special
emphasis on nosocomial pathogens
Oral:
piperacillin,
azlocillin
*Pseudomonas aeruginosa – optimal tx
for systemic PA infxn:
(anti-PA β-lactam, PCN or ceph, +
AMG)
piperacillin = PCN of choice
β-Lactamase Inactivator Combos
Amoxacillin/
Oral
clavulanic acid
(Augmentin)
Enhance activity against MSSA, GC,
HI, EC, Proteus, enteroB,
bacteroides fragilis
mixed soft tissue infxn
Ampicillin/
sulbactam
(Unasyn)
Ticarcillin/
clavulanic acid
(Timentin)
IV
Similar to above, also intra-abdominal
infxns
IV
Similar to above, but poor activity vs
enterococci & better vs nosocomial,
incl PA
Rarely used
Piperacillin/
tazobactam
(Zosyn)
Cephalosporins
1st generation
IV: cefazolin,
cephalothin,
cephradine
Oral:
cephradine,
cephalexin,
cefadroxil
IV
Similar to above, but adequate vs
enterococci & even better vs
nosocomials, incl PA
Gram (+)
Also some
gram (-)
MSSA (similar to nafcillin)
MS-CNStaph
MRSA
Strep – similar to PCN G, but not active
vs PCN-resist S pneumo
EC, PM – more strains EC than amp,
some resistance
Klebsiella – many susceptible
**clinical use:
1. surgical prophylaxis
2. PCN allergies w/o hx of
anaphylaxis
3. poor penetration of BBB
c-tetan & c-mzole have MTT
2nd generation
Cefoxin Gp:
cefoxin,
cefotetan,
cefmetazole
Staph – poor
S pneumo
strep – ok vs PCN-susceptible
GC – superb
enteroB – good vs EC, PM, kleb,
serratia, some citroB & enterobacter
anaerobes, including B frag
poor penetration of BBB
MSSA – fair
Strep – good
Cefuroxime Gp
MRSA
Poor-fair vs PCN-resis s
pneumo
*HI – good
enteroB – good vs EC, PM, kleb, more
**penetration of BBB!
MSSA – fair
Strep – good vs PCN-intermediate s
pneumo, fair vs some PCN-res strains
3rd generation
Standard:
cefotaxime,
ceftriaxone,
ceftizoxime
GC, MC – superb
HI – superb
enteroB – superb
penetration of BBB
MSSA – cefe > cefta
Strep – cefe > cefta
***incl. s pneumo
Ceftazidime,
cefepime
GC, MC – superb
HI – superb
EnteroB – superb
*PA – excellent
Penetration into BBB
Monobactams
Aztreonam
Pyelonephritis – some
ceftriaxone resistance probs
Broad
spectrum
gram (-)
Gram (-) similar to ceftazidime
NO activity vs gram (+) aerobes
NO activity vs anaerobes
NO cross-hypersens w/ PCNs or cephs
**can be used for PCN allergy w/ hx of
anaphylaxis
Some probs w/ resistance
MSSA – excellent
Strep – excellent
Enterococci – similar to amp
GC, MC, HI – superb
enteroB, PA – superb
anaerobes, incl B frag – superb
Carbapenems
Imipenem,
meropenem
Can be used w/ β-lactam
resistant bacteria
*imipenem admin w/ cilastatin
(inh imipenem inact by renal
dehydropeptidase)
Seizures: I >M, esp in pts w/
impaired renal fcn
Ertapenem
Glycopeptide
Drug
Mech of
action
Vancomycin
Parenteral (gen)
General
specificity
Uses
resistance
*all*
aerobic
gram (+)
All aerobic gram (+) cocci & bacilli
Staph
Strep
Enterococcus
Corynebacterium
Clostridium
˚˚can be used for MRSA!!
Oral vanco for c diff but
metranidazole preferred for
resistance reasons
Oral (≠ absorb)
Slightly less efficacious than βlactams
(eg. MSSA)
Resistance w/ enterococci
(VRE), some VRSA…
Little toxicity by itself, but
synergistic effect of
nephrotoxicity w/ AMG
***use restricted to situations when βlactams can’t be used
Aminoglycosides
Drug
Streptomycin
Gentamycin
Mech of
action
General
specificity
Uses
Broad
gram (+) &
gram (-)
aerobes
2nd line agent for M tuberculosis (MTB)
Adjunctive therapy w/ amp or vanco for
systemic enterococcal infxns
**Gram (+) aerobes – adjunctive w/
anti-CW for systemic enterococcal
infxns
Hardware associated infxns (SA)
Gram (-) aerobes – excellent vs
enteroB and PA (use w/ β-lactam)
Tobramycin
Gram (-) aerobes – similar to gent
More active vs PA (use w/ β-lactam)
Amikacin
2nd line agent for MTB, gen active vs
streptomycin-resistant strains
Gram (-) aerobes – similar to gent and
tobra, but active vs more strains (use
w/ β-lactam)
resistance
Clindamycin
Drug
Mech of
action
General
specificity
Uses
resistance
Clindamycin
IV or oral
Aerobic
gram (+)
Most strep
Many staph
SA – only if susceptible to BOTH clinda
AND erythro
MRSA
PCN-resist s pneumo
Anaerobes, incl B frag
Good penetration into bone and
abscesses
**MUST check for erythro
resistance b/c mech of
resistance for erythro can also
confer resistance to clinda!!
Diarrhea probs
canNOT cross BBB
Trimethoprim/Sulfamethoxazole
Drug
Mech of
action
TMP/SMX
Oral & IV
General
specificity
Uses
resistance
Staph – many strains, incl some MRSA
(good oral alternative)
Strep – fair/poor
NO activity vs enterococcus
Enterococcus – humans take
exogenous folate
20-25% EC are resistant
HI – fair
enteroB – excellent
pneumocystis carinii
nocardia
Probs w/ hypersens (esp in
HIV/AIDS pts)
toxoplasmosis
UTIs – EC resis precludes empiric use
for pyelo
**penetrates into prostate (TMP)
Macrolides
Drug
Mech of
action
Erythromycin
Oral & IV
Clarithromycin
Oral
General
specificity
Uses
resistance
Strep – alt to PCN
Legionella
Mycoplasma pneumoniae
Campylobacter
Similar to erythro, fewer GI side effects
S pneumo
H pylori
Mycobacterium avium complex (MAC)
Azithromycin
Oral, IV
Similar to erythro, fewer GI side effects
Chlamydia trachomatis (1x dose)
 used w/ ceftriaxone to tx gono/clap
MAC
Diarrhea, cramping
Fluoroquinolones
Drug
Mech of
action
General
specificity
Uses
Norfloxacin
Oral
UTIs
Aerobic gram (-) rods, incl PA
Ciprofloxacin
Levofloxacin
Oral & IV
Aerobic gram (-) rods, incl PA
(cipro>levo for PA)
Aerobic gram (+) cocci, incl S pneumo
(levo >cipro)
MTB (levo)
GC
M pneumo
Legionella
C pneumo
Gatifloxacin
Oral & IV
Moxifloxacin
Oral
Similar to levofloxacin, but MORE
active vs S pneumo
Similar to gati, but better against
anaerobes, incl B frag
Resistance
POOR vs gram (-), incl PA
NOT for UTIs
Community-acquired pneumonia
Better for S pneumo than levo
Only FQ w/ indication for intraabdominal infxn
New Agents
Drug
Mech of
action
Synercid
IV
Linezolid
Daptomycin
Tigecycline
Glycylcycline
(NEW CLASS)
Oral, IV
IV only
IV only
General
specificity
Uses
resistance
Synergy of 2 streptogramins
Broad spectrum gram (+)
MRSA
VRSA
VRE faecium
Rx-resistant S pneumo
Broad spectrum gram (+)
MRSA
VRSA
VRE
Rx-resistant S pneumo
BacterioSTATIC
Broad spectrum gram (+)
MRSA
VRSA
VRE
Rx-resistant S pneumo
Broad spectrum
Staph
Strep
Enterococcus
enteroB
anaerobes, incl B frag
acinobacter
indicated for complicated skin/soft
tissue & intra-abdom infxns
used for sulbactam resistance
Arthralgia-myalgia syndrome
Resistance w/ enterococcus
and SA strains
bacterioSTATIC
reversible thrombocytopenia
w/ tx 2+ weeks
resistance w/ enterococcus
and SA
bacterioCIDAL
NOT indicated for pneumonia
binds surfactant
Resistance??
bacterioSTATIC
side effects : nausea,
vomiting