Antibiotic

Susceptibility criteria (MIC)

  Susceptible       Resistant

MIC₅₀

MIC₉₀

No. of isolates studied

Reference

Penicillins

Ampicillin

£8

³32

>64

>64

423

(4)

Carbenicillin

£16

³64

£16

>256

423

(4)

Piperacillin

£16

³128

£4

>64

423

(4)

b-lactam/b-lactamase inhibitor combinations

Amoxicillin/clavulanic

£8/4

³32/16

64

>64

78

(50)

Piperacillin/tazobactam

£16/4

³128/4

¡V

16

14

(28)

Cephalosporins

Cefaclor

£8

³32

>64

>64

78

(50)

Cefoperazone

£16

³64

2

16

44

(38)

Cefoxitin

£8

³32

³25

³100

78

(50)

Cefuroxime

£8

³32

>32

>32

423

(4)

>64

>64

78

(50)

Cefotaxime

£8

³64

0.5

32

326

(83)

1

16

423

(4)

Ceftriaxone

£8

³64

0.5

4

44

(38)

0.5

8

78

(50)

Ceftazidime

£8

³32

0.25

1

423

(4)

0.5

8

326

(83)

Cefepime

£8

³32

0.12

8

70

(79)

0.12

0.5

44

(38)

Cefpirome

¡V

¡V

0.11

¡V

400

(68)

¡V

0.06

14

(28)

Carbapenems

Imipenem

£4

³16

1

2

326

(83)

Meropenem

£4

³16

0.06

0.13

326

(83)

Fluoroquinolones

Ciprofloxacin

£1

³4

0.13

2

326

(83)

0.25

4.0

78

(50)

Norfloxacin

£4

³16

0.5

1

24

(23)

Ofloxacin

£2

³8

0.5

4.0

78

(50)

Levofloxacin

£2

³8

0.25

0.5

24

(23)

Aminoglycosides

Gentamicin

£4

³16

2

>32

423

(4)

1

128

326

(83)

Amikacin

£16

³64

4

8

423

(4)

Tobramycin

£4

³16

4

32

423

(4)

Miscellaneous

Aztreonam

£8

³32

¡V

1.6

113

(75)

Trimethoprim-sulfamethoxazole

£2/38

4/76

0.25

1.0

78

(50)

Antibiotic

Usual Dose

Comments

Third-generation

cephalosporins/b-

lactamase inhibitor

combinations

Inadvisable for treatment of infection where resistance is likely to develop.  Remain the treatment of choice for UTI and uncomplicated infection.  Often combined with aminoglycosides.

Cefotaxime

1¡V2 g q. 4¡V8 h

Ceftriaxone

1¡V2 g q. 24 h

Ceftazidime

1¡V2 g q. 8 h

Pip/ tazobactam

4-5 g  q 8 h

Fourth-generation cephalosporins

Effective treatment option where resistance to third-generation cephalosporins is evident or likely to develop.  Active against ESBL- and chromosomal b-lactamase-producing S. marcescens

Cefepime

1 g q. 12 h

Cefpirome

1¡V2 g q 12 h

Carbapenems

Considered the treatment of choice when third-generation cephalosporin resistance is evident or likely to develop. 

Imipenem

0.5¡V1 g q. 6 h

Meropenem

1g q. 8 h

Fluoroquinolones

Prudent to avoid for treatment of serious infection due to the ready development of resistance.  Can be used for the treatment of uncomplicated UTI

Ciprofloxacin

400¡V800 mg q. 12 h

Oral formulations can be used in UTI

Ofloxacin

200¡V400 mg q.12 h

Levofloxacin

500 mg q. 24 h

Norfloxacin

400 mg p.o b.i.d.

No i.v. formulation, only for UTI

Aminoglycosides

No longer treatment of choice.  Maybe combined with third-generation cephalosporins for the treatment UTI or combined with fourth-generation cephalosporins or carbapenems for the treatment of serious infection

Gentamicin

3¡V5 mg/kg/day x SD

Most frequently used of the aminoglycosides

Tobramycin

3¡V5 mg/kg/day x SD

Amikacin

15 mg/kg/day x SD

Frequently active against gentamicin-resistant S. marcescens

Netilmicin

4-6 mg/kg/day x SD

Miscellaneous

Aztreonam

1¡V2 g q. 6¡V8 h

Trimethoprim-

sulfamethoxazole

960 mg b.d. or 120 mg/kg 2¡V4 dose/24 h

Usually active; suitable for UTI but rarely used as sole agent for more serious infections

Rifampin

600mg q. 24 h

May be used in combination with other agents