Paterson and Doi described extreme drug resistance (XDR) in Gram-negative bacteria. This is antibiotic resistance beyond panresistance, indicating an organism for which there may be few if any therapeutic options. The authors are from the University of Pittsburgh, the University of Queensland and Royal Brisbane and Women's Hospital in Brisbane, Australia.


Extreme-drug resistance indicates resistance to all of the following:

(1) ceftazidime, cefepime and other antipseudomonal cephalosporins

(2) beta-lactam and beta-lactamase inhibitor combinations (ampicillin + sulbactam, ticarcillin + clavulanate, piperacillin + tazobactam)

(3) imipenem, meropenem and other antipseudomonal carbapenems

(4) levofloxacin, ciprofloxacin and other fluoroquinolones with antipseudomonal activity

(5) gentamicin, tobramycin, amikacin and other aminoglycosides

(6) tigecycline

(7) polymyxin B, colistin and other polymyxins



• Susceptibility testing is not done against all of these antibiotics; it is limited for an agent that is representative for the group.

• Testing must be performed in accordance with standard guidelines.

• Resistance to all 4 items 1, 2, 3 and 4 indicates panresistance.


To read more or access our algorithms and calculators, please log in or register.