In vitro activity of tigecycline and other tetracyclines against carbapenem-resistant acinetobacter species: Report from a tertiary care centre in Karachi, Pakistan

Background: The Aga Khan University Hospital is a tertiary care centre in Karachi, Pakistan, where tigecycline has not been used previously. We report findings of a pre-use in vitro study to evaluate sensitivity of nosocomial Acinetobacter spp. Tigecycline minimum inhibitory concentration (MIC) was correlated with that of other tetracyclines to assess their predictive potential. Methods: Acinetobacter spp. were collected from hospitalized inpatients admitted to Aga Khan University Hospital from April to November 2007. Tigecycline, tetracycline, doxycycline, and minocycline MICs were determined by E-test. Results: One hundred isolates of Acinetobacter spp. were tested. Ninety-eight percent of Acinetobacter spp. were carbapenem-resistant. Tigecycline MIC₅₀ and MIC₉₀ were 1.5 and 2.0 μg/ml, respectively. Unavailability of standard breakpoints hindered categorization of these values. Minocycline was highly active, with MIC₉₀ of 2.0 μg/ml. Conclusions: Tigecycline breakpoints for Acinetobacter spp. should be established to prevent injudicious use of this antibiotic based on misleading in vitro results. The therapeutic potential of minocycline needs more in-depth study.