Correction
for
Horn et al., Ann Pharmacother 41 (4) 674-680.
Published Online, 30 September 2008, www.theannals.com, DOI 10.1345/aph.1L171b.
The Annals of Pharmacotherapy: Vol. 42, No. 11, pp. 1718. DOI 10.1345/aph.1L171b
© 2008 Harvey Whitney Books Company.
Authors' Reply
Jason C Gallagher, PharmD BCPS
Clinical Assistant Professor School of Pharmacy Temple University
3307 North Broad Street Philadelphia, Pennsylvania 19140 fax 215/707-8326
jason.gallagher{at}temple.edu
Heather M Rouse, PharmD
Pharmacy Practice Resident Allegheny General Hospital Pittsburgh,
Pennsylvania
Published Online, September 30, 2008. www.theannals.com, DOI 10.1345/aph.1L171b
We thank Dr. Curcio for his interest in our article and for the points that
he raises. Regarding the issue of susceptibility testing, in our retrospective
study, we are constrained to report the data that were generated by the
treating clinicians, namely tigecycline MICs by E-test. One lab found higher
MIC90 values with E-tests than with broth microdilution.
However, the isolates tested were in different batches in different
laboratories; hence, the methods were not tested against each
other.1 While
another paper by the same group showed differences in MIC90
values of tigecycline when both methods were used in a central
laboratory,2
these results contrast with other articles that noted strong correlations
between testing methods for
tigecycline.3,4
Thus, it seems that consensus does not exist regarding the reproducibility by
various methods for testing tigecycline susceptibility in
Acinetobacter infections. This issue is confounded by the lack of a
standardized susceptibility breakpoint, as neither the Clinical and Laboratory
Standards Institute nor the Food and Drug Administration has issued guidelines
for laboratories. More concerning for us is the fact that no isolates tested
as being fully susceptible to tigecycline in our study, preventing us from
comparing outcomes between patients with susceptible and
intermediate-to-resistant isolates. For this reason, we can only speculate as
to whether the high MICs observed in our study were related to negative
outcomes.
Secondly, Dr. Curcio inquires about the incidence of prior antibiotic use
in our patients. As might be expected in a population where tigecycline was
started a median of 30 days into the hospital stay and the majority of
patients were in intensive care units, all of the patients received
antibiotics prior to receiving tigecycline. Only once was tigecycline alone
used as empiric therapy before Acinetobacter spp. were identified,
and this patient received antibiotics prior to receiving tigecycline. It is
quite possible that this prior antibiotic use contributed to tigecycline
resistance, and our report serves as a caution to evaluate tigecycline
susceptibility in Acinetobacter infections in which a history of
prior antibiotic use and a long hospital stay are present.
We do not believe that the proposed suggestion to divide our patients into
groups is plausible given the small sample size of our study. We invite others
to research and publish their experiences with tigecycline for
Acinetobacter infections. Our study was performed to evaluate our own
experience and was published to be shared with others. In the absence of
prospective trial data, we believe that studies such as ours serve as useful
data for others to evaluate and consider. Tigecycline was recently compared
with imipenem/cilastatin in a prospective, comparative study of
hospital-acquired and ventilator-associated
pneumonia.5
Tigecycline had lower cure rates than imipenem/cilastatin in the subset of
patients with ventilator-associated pneumonia in this study. Since the most
common indication in our study was Acinetobacter pneumonia, we await
with interest the publication of this study and hope that a sufficient number
of patients with Acinetobacter pneumonia were enrolled to answer some
of the questions that our study and Curcio's letter raise more definitely.
Footnotes
Letters are subject to review prior to acceptance. They should address
areas related to pharmacy practice, research, or education, or articles
recently published. Corrections of previously published material also are
accepted. Letters are limited to no more than five authors. In cases where
adverse effects or drug interactions are described, the Naranjo ADR
probability scale (Clin Pharmacol Ther 1981;30:239-45) or DIPS scale (Ann
Pharmacother 2007;41:674-80. DOI
10.1345/aph.1H423), respectively, should be used to determine the likelihood
that the adverse effect or interaction was drug-related.
References
- Sahm DF, Dowzicky MJ, Draghi DC, Tench S, Thornsberry C.
Surveillance of tigecycline activity; discordance between national profiles
associated with testing protocol and methods. In: Program and Abstracts
of the 46th Interscience Conference on Antimicrobial Agents and
Chemotherapy, San Francisco, CA. American Society for Microbiology,
Washington, DC, 2006: D-701.
- Pillar CM, Draghi DC, Dowzicky MJ, Sahm DF. In vitro activity of
tigecycline against gram-positive and gram-negative pathogens as evaluated by
broth microdilution and E-test. J Clin Microbiol2008;46:2862-7.
Epub 2 Jul 2008.[Abstract/Free Full Text]
- Bolmstrom A, Karlsson A, Engelhardt A, et al. Validation and
reproducibility assessment of tigecycline MIC determinations by Etest. J Clin Microbiol 2007;45:2474-9.[Abstract/Free Full Text]
- Hope R, Parsons T, Mushtaq S, James D, Livermore DM. Determination
of disc breakpoints and evaluation of Etests for tigecycline susceptibility
testing by the BSAC method. J Antimicrob Chemother2007;60:770-4.[Abstract/Free Full Text]
- Wyeth to file for FDA approval of Tygacil for the treatment
of patients with community-acquired pneumonia. Wyeth Press Releases.
www.wyeth.com/news?nav=display&navTo=/wyeth_html/home/news/pressreleases/2007/1184074360162.html
(accessed 2008 Aug 1).
