Tigecycline Spectrum of Activity Beyond MRSA
Tigecycline demonstrates broad-spectrum activity against numerous clinically important bacteria including multidrug-resistant Gram-positive organisms (vancomycin-resistant enterococci, methicillin-susceptible Staphylococcus aureus), Gram-negative bacteria (ESBL-producing Enterobacteriaceae, Acinetobacter baumannii), and anaerobes, though it lacks activity against Pseudomonas aeruginosa and certain Enterobacteriaceae species.
Gram-Positive Bacteria
According to FDA labeling, tigecycline is active against 1:
- Enterococci: Enterococcus faecalis (both vancomycin-susceptible and vancomycin-resistant isolates), E. faecium (vancomycin-susceptible and -resistant), E. avium, E. casseliflavus, E. gallinarum
- Staphylococci: Staphylococcus aureus (methicillin-susceptible isolates), S. epidermidis (methicillin-susceptible and -resistant), S. haemolyticus
- Streptococci: Streptococcus pneumoniae (penicillin-susceptible), S. pyogenes, S. agalactiae, Streptococcus anginosus group
- Other: Listeria monocytogenes
Clinical surveillance data confirm 100% susceptibility among enterococci and staphylococci to tigecycline, with no resistance detected among vancomycin-resistant enterococci (VRE) 2, 3, 4, 5. For VRE intra-abdominal infections specifically, tigecycline is recommended as the drug of choice 6.
Gram-Negative Bacteria
Enterobacteriaceae
Tigecycline demonstrates excellent activity against 1:
- Escherichia coli (including ESBL-producers)
- Klebsiella pneumoniae and K. oxytoca
- Enterobacter cloacae and E. aerogenes
- Citrobacter freundii and C. koseri
- Serratia marcescens
Among ESBL-producing Enterobacteriaceae, tigecycline maintains 97-99% susceptibility 7, 8, making it a carbapenem-sparing option for complicated intra-abdominal infections when MIC ≤1 mg/L 7. Surveillance data from Europe showed 99.3% susceptibility among E. coli and resistance rates ≤5.9% among ESBL-producing isolates 9, 5.
Non-Fermenting Gram-Negatives
Acinetobacter baumannii: Tigecycline inhibits 91-98% of isolates at ≤2 mg/L 10. However, resistance can develop during treatment via MDR efflux pumps 1. For A. baumannii infections, tigecycline is recommended for complicated skin/soft tissue and intra-abdominal infections when MIC ≤1 mg/L 10.
Stenotrophomonas maltophilia: Demonstrates in vitro susceptibility 1
Other Gram-Negatives
- Haemophilus influenzae (including ampicillin-resistant strains)
- Haemophilus parainfluenzae
- Legionella pneumophila (tigecycline shows bactericidal activity) 1
- Pasteurella multocida
- Aeromonas hydrophila
Anaerobic Bacteria
Tigecycline has favorable activity against 7, 8, 1:
- Bacteroides species (B. fragilis, B. thetaiotaomicron, B. uniformis, B. vulgatus, B. distasonis, B. ovatus)
- Clostridium perfringens
- Peptostreptococcus species
- Porphyromonas species
- Prevotella species
Mycobacteria
Tigecycline demonstrates in vitro activity against 11, 1:
- Mycobacterium abscessus
- Mycobacterium fortuitum
Though not FDA-approved for non-tuberculous mycobacterial infections, tigecycline has been used off-label at standard or reduced doses (50 mg daily for tolerability) 11.
Critical Limitations
Tigecycline lacks activity against:
- Pseudomonas aeruginosa 7, 8
- Certain Enterobacteriaceae: Proteus spp., Morganella morganii, Providencia stuartii 7
Important Clinical Caveats
Avoid tigecycline for bloodstream infections: Poor serum concentrations (Cmax 0.87 mg/L with standard dosing) result in treatment failure for bacteremia 10, 12. The FDA warns of higher mortality with tigecycline versus comparators.
Suboptimal for pneumonia: Low concentrations in endothelial lining fluid (0.01-0.02 mg/L) make standard-dose tigecycline inferior to comparators for hospital-acquired/ventilator-associated pneumonia 10. High-dose regimens (200 mg loading, then 100 mg q12h) may be considered for severe MDR infections including pneumonia 10, 13.
Combination therapy recommended: For non-approved indications (pneumonia, severe sepsis) or carbapenem-resistant organisms, tigecycline should be combined with another active agent 10, 6.
Monitor for resistance development: Particularly with A. baumannii, where MDR efflux pumps can emerge during therapy 1. More frequent monitoring and repeat cultures are suggested if clinical relapse occurs.