olism of drugs metabolized by these enzymes. In addition, because tigecycline is not extensively metabolized, clearance of tigecycline is not expected to be affected by drugs that inhibit or induce the activity of these CYP450 isoforms.
12.4 Microbiology
Mechanism of Action
Tigecycline, a glycylcycline, inhibits protein translation in bacteria by binding to the 30S ribosomal subunit and blocking entry of amino-acyl tRNA molecules into the A site of the ribosome. This prevents incorporation of amino acid residues into elongating peptide chains. Tigecycline carries a glycylamido moiety attached to the 9-position of minocycline. The substitution pattern is not present in any naturally occurring or semisynthetic tetracycline and imparts certain microbiologic properties to tigecycline. In general, tigecycline is considered bacteriostatic; however, TYGACIL has demonstrated bactericidal activity against isolates of S. pneumoniae and L. pneumophila.
Mechanism(s) of Resistance
To date there has been no cross-resistance observed between tigecycline and other antibacterials. Tigecycline is not affected by the two major tetracycline-resistance mechanisms, ribosomal protection and efflux. Additionally, tigecycline is not affected by resistance mechanisms such as beta-lactamases (including extended spectrum beta-lactamases), target-site modifications, macrolide efflux pumps or enzyme target changes (e.g. gyrase/topoisomerases). Tigecycline resistance in some bacteria (e.g. Acinetobacter calcoaceticus-Acinetobacter baumannii complex) is associated with multi-drug resistant (MDR) efflux pumps.
Interaction with Other Antimicrobials
In vitro studies have not demonstrated antagonism between tigecycline and other commonly used antibacterials.
Tigecycline has been shown to be active against most of the following bacteria, both in vitro and in clinical infections [see Indications and Usage (1)].
Facultative Gram-positive bacteria
Enterococcus faecalis (vancomycin-susceptible isolates)
Staphylococcus aureus (methicillin-susceptible and -resistant isolates)
Streptococcus agalactiae
Streptococcus anginosus grp. (includes S. anginosus, S. intermedius, and S. constellatus)
Streptococcus pneumoniae (penicillin-susceptible isolates)
Streptococcus pyogenes
Facultative Gram-negative bacteria
Citrobacter freundii
Enterobacter cloacae
Escherichia coli
Haemophilus influenzae (beta-lactamase negative isolates)
Klebsiella oxytoca
Klebsiella pneumoniae
Legionella pneumophila
Anaerobic bacteria
Bacteroides fragilis
Bacteroides thetaiotaomicron
Bacteroides uniformis
Bacteroides vulgatus
Clostridium perfringens
Peptostreptococcus micros
At least 90% of the following bacteria exhibit in vitro minimum inhibitory concentrations (MICs) that are at concentrations that are achievable using the prescribed dosing regimens. However, the clinical significance of this is unknown because the safety and effectiveness of tigecycline in treating clinical infections due to these bacteria have not been established in adequate and well-controlled clinical trials.
Facultative Gram-positive bacteria
Enterococcus avium
Enterococcus casseliflavus
Enterococcus faecalis (vancomycin-resistant isolates)
Enterococcus faecium (vancomycin-susceptible and -resistant isolates)
Enterococcus g |
