CENTER FOR DRUG EVALUATION AND
`RESEARCH
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`APPLICATION NUMBER:
`050814Orig1s000
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`MICROBIOLOGY REVIEW(S)
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`Division of Anti-Infective and Ophthalmology Products
`Clinical Microbiology Review #2
`NDA 50-814 SN040
`
`Aztreonam Lysine
`
`Peter Coderre, PhD
`Gilead Sciences
`
`29 December 2009
`
`APPLICANT:
`Gilead Sciences, Inc.
`2025 1st Avenue, Suite 800
`Seattle, WA 98121
`
`CONTACT:
`Melissa Yeager, JD
`Vice President, Regulatory Affairs
`Tel: (206) 792-3015
`
`SUBMISSION REVIEWED: NDA 50-814 SN040
`
`PROVIDING FOR: The management of cystic fibrosis (CF) patients with
`Pseudomonas aeruginosa to improve respiratory symptoms.
`
`PRODUCT NAME:
`Proprietary: CAYSTON
`Non-proprietary: Aztreonam Lysine for Inhalation
`
`
`CHEMICAL NAME: (Z)-2-[[[(2-Amino-4-thiazolyl)[[(2S, 3S)-2 methyl-4-oxo-1-
`sulfo-3-azetidinyl]carbomoyl]methylene]amino]oxy]-2-ethylpropionic acid
`
`MOLECULAR FORMULA: C13H17N5O8S2, MW 453.43 (anhydrous, β-form)
`
`STRUCTURAL FORMULA:
`
`
`ROUTE OF ADMINISTRATION, DOSAGE AND FORMULATION:
`• Dosage Form: Aerosol (nebulization) NOTE: A device called the PARI eFlow
`will be used to deliver the dose. Patients will receive either 75 mg aztreonam
`for inhalation (AI) [1 ml] twice daily for 14 days.
`• Formulation: Aztreonam for inhalation (75 mg/ml pyrogen-free aztreonam
`lysinate) dissolved in sterile 0.17% saline to result in a pH of 4.2—7.0 and
`osmolarity of 300—550 mOsmol/kg
`
`
`PHARMACOLOGICAL CATEGORY: Antimicrobial
`
`DISPENSED: Rx
`
`INITIAL SUBMISSION DATES:
`
`Received by CDER:
`
`Received by Reviewer:
`
`Review Completed:
`
`11 August 2009
`13 August 2009
`29 December 2009
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`2 of 67
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`Division of Anti-Infective and Ophthalmology Products
`Clinical Microbiology Review #2
`NDA 50-814 SN040
`
`Aztreonam Lysine
`
`Peter Coderre, PhD
`Gilead Sciences
`
`29 December 2009
`
`REMARKS:
`The Applicant submits a resubmission intended to be a complete response to the
`deficiencies outlined by the Division in the Complete Response Letter (CRL). In
`addition, the Applicant requested this NDA 50-814 be presented to the Anti-Infective
`Drugs Advisory Committee as part of the review. This request was granted.
`
`On 10 December 2009, the Anti-Infective Drugs Advisory Committee convened to
`discuss aztreonam, the subject of this NDA. Presentations were made by the
`Applicant, the Agency and the Public. It should be noted that one of the three public
`speakers was a 44-year old attorney afflicted with cystic fibrosis who is being treated
`with AZLI via an EAP program. This speaker made a compelling, emotional plea for
`approval of AZLI due to the lack of antimicrobials available for cystic fibrosis.
`
`Following the presentations by the Applicant, the Agency and Public individuals, the
`committee addressed the following two questions posed by the Agency.
`
`
`1. Has the Applicant provided substantial evidence of the efficacy
`and safety of 75 mg three times daily of AZLI for the requested
`indication of improvement of respiratory symptoms and pulmonary
`function in cystic fibrosis patients with Pseudomonas aeruginosa?
`In your response, discuss the rationale for your answer.
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`a. If you voted YES, are there any specific issues that should be
`addressed in labeling?
`b. If you voted NO, what additional information is necessary?
`
`2. Has the Applicant identified the correct dose and regimen for
`AZLI for the requested indication? In your response, discuss the
`rationale for your answer and discuss the rationale for your
`answer and discuss if there is any additional information that
`should be generated regarding the dose and regimen.
`
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`In response to question #1 regarding evidence of efficacy and safety, the committee
`voted as follows:
`
`YES—15 members
`NO — 2 members
`
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`The two dissenting voters did not elaborate on the rationale for their dissention other
`than saying the Applicant did not show sufficient data for efficacy, which did not
`show statistical significance. The other member believed that AZLI was not
`“durable” and that aztreonam resistance could be a potential safety problem.
`
`While there were a variety of reasons given, many of the 15 assenting voters gave
`similar rationale for their vote.
`• The bar should be low for approval for this drug due to the lack of alternative
`drugs for the treatment of this disease.
`• New drugs are needed for this disease.
`• The risk to benefit ratio is low for this drug.
`• There was overriding evidence for the safety and efficacy of this drug.
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`Division of Anti-Infective and Ophthalmology Products
`Clinical Microbiology Review #2
`NDA 50-814 SN040
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`Aztreonam Lysine
`
`Peter Coderre, PhD
`Gilead Sciences
`
`29 December 2009
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`• The CP-AI-006 study presented the necessary evidence to demonstrate safety
`and efficacy of this drug.
`
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`Some members of the committee did express concerns. One member was
`concerned about the time-to-need (TTN) data suffering from the lack of data. By far,
`the most common concern was the “durability” of AZLI compared to that of TOBI.
`
`Members expressed concerns about the approval of the drug that should be
`addressed in the labeling of the drug. Due to the concern regarding durability of
`AZLI, the development of AZLI resistance should be tracked over time. This is based
`on the belief that the 28 day treatment period was not sufficient to address the
`chronic effect on resistance. Another committee member stated that the label
`should be crafted such that only the device described in this application could be
`used to deliver AZLI to cystic fibrosis patients.
`
`In response to question #2 regarding identification of the correct dose and regimen
`for AZLI, the committee voted as follows:
`YES—17 members
`NO — 0 members
`
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`There was less discussion of the rationale for the answers given by the committee for
`this question as compared to the first question. Several members favored the TID
`regimen, due to the favorable time above MIC for the TID regimen versus the BID
`regimen. One member would consider the BID regimen as appropriate treatment
`while another member was skeptical that the BID regimen was an appropriate
`treatment.
`
`The recommendations of the Anti-Invective Advisory Committee were considered
`along with the microbiological outcomes in the determination of a recommendation
`by this Reviewer.
`
`This review describes the findings and recommendations of the Clinical Microbiology
`Reviewer. These recommendations are for evaluation by the Division Director for the
`determination of a decision regarding the approval of this new drug application.
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`CONCLUSION AND RECOMMENDATIONS:
`The Applicant seeks approval of AZLI for the improvement of respiratory symptoms
`and pulmonary function in CF patients with Pseudomonas aeruginosa.
`
`AI is intended as a suppressive therapy and is not expected to eradicate P.
`aeruginosa in CF patients with established airway infections. Consequently, in the
`Phase 2 and three Phase 3 clinical trials, there are no definitive endpoints for
`microbiological eradication or clinical cure. Under these circumstances, the objective
`of the review team is to determine what constitutes microbiological or clinical
`success? While it is not the place for this Reviewer to define clinical success, he
`shall attempt to define microbiological success.
`
`There are two ways to evaluate the data from this submission. First, the
`microbiological efficacy endpoints were compared to the most common clinical
`efficacy endpoint, improvement in FEV1. Second, the results of the microbiological
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`4 of 67
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`Division of Anti-Infective and Ophthalmology Products
`Clinical Microbiology Review #2
`NDA 50-814 SN040
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`Aztreonam Lysine
`
`Peter Coderre, PhD
`Gilead Sciences
`
`29 December 2009
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`and primary clinical efficacy endpoint data were compared to the corresponding data
`derived from the package insert for TOBI Solution for Inhalation (TSI), a drug for
`which AI is intended to be an alternative treatment for CF. TOBI is the only other
`Agency-approved drug for the management of cystic fibrosis and also is administered
`in a similar manner.
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`There are three measures of microbiological outcome:
`1. Change in log10 P. aeruginosa CFUs/g sputum specimens from patients;
`2. Appearance of other pathogens, specifically S. aureus, B. cepacia, S.
`maltophilia or A. xylosoxidans in CF patients; and
`3. Changes in aztreonam MIC50s and MIC90s of P. aeruginosa isolates from CF
`patients.
`
`
`However, none of the data from the three microbiology outcomes correlated with
`clinical outcomes.
`
`In the original NDA submission, to investigate the possible correlation between
`microbiological and clinical endpoints, scatterplots were produced. Scatterplots
`examining these endpoints showed the following:
`• Changes in numbers of PA in sputum were not associated with changes in
`FEV1 or aztreonam concentrations in study CP-AI-003, CP-AI-005 and slightly
`negatively associated in study CP-AI-007.
`• Changes in numbers of PA in sputum were not associated with changes in
`aztreonam concentrations in study CP-AI-003.
`• Changes in aztreonam MIC for the PA isolate with the highest MIC from each
`patient were slightly positively associated with changes in FEV1 in study CP-
`AI-003 but slightly negatively associated in study CP-AI-007.
`• Changes in numbers of PA in sputum were not associated with changes in
`aztreonam MIC for the PA isolate with the highest MIC in study CP-AI-005 and
`CP-AI-007.
`• Changes in numbers of PA in sputum were not associated with changes in
`CFQ-R respiratory domain score in study CP-AI-007.
`• The Applicant did not present scattergrams to explain relationships between
`microbiological to clinical outcomes.
`
`
`The lack of correlation of microbiology outcomes with clinical outcomes for the
`treatment of cystic fibrosis with aztreonam is not unprecedented. In the
`Microbiology subsection of the package insert for TOBI for the management of cystic
`fibrosis patients with P. aeruginosa, the Agency states “The relationship between in
`vitro susceptibility test results and clinical outcome with TOBI therapy is not clear”.
`
`The efficacy of AZLI for CF caused by P. aeruginosa is not entirely clear in terms of
`clinical outcomes. While none of the three microbiology responses correlated with
`clinical responses, AZLI treated patients demonstrated positive microbiological
`outcomes by all three measures. In addition, the Applicant has demonstrated the
`safety of AZLI from the Microbiology standpoint as demonstrated by the lack of the
`development of aztreonam resistance in patients during therapy.
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`5 of 67
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`Division of Anti-Infective and Ophthalmology Products
`Clinical Microbiology Review #2
`NDA 50-814 SN040
`
`Aztreonam Lysine
`
`Peter Coderre, PhD
`Gilead Sciences
`
`29 December 2009
`
`This Reviewer recommends that CAYSTON be APPROVED for the treatment
`of cystic fibrosis in patients infected with Pseudomonas aeruginosa based on
`the following:
`(cid:190) the medical need for new antibiotics to treat cystic fibrosis,
`(cid:190) the demonstrated safety of the drug from the Microbiology standpoint, and
`(cid:190) the drug is efficacious from the Microbiology standpoint,
`(cid:190) the overwhelming vote by the Anti-Infective Advisory Committee for the
`approval of CAYSTON at the prescribed dose suggested this drug is needed by
`cystic fibrosis patients.
`
`
`One major concern expressed by the Advisory Committee was the potential for the
`development of aztreonam resistance in P. aeruginosa isolates harbored in cystic
`fibrosis patients. In vitro data does support this concern.
`
`Table A. Aztreonam Susceptibility Trends in CF Isolates of P. aeruginosa
`
`
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`Source: Table 6, NDA 50-814 Microbiology review.
`
`Notice in Table A that MIC90 values for P. aeruginosa isolates increased from 32
`µg/ml in 1995—96 to 64 µg/ml in 2004—05 to ≥ 32 µg/ml in 2006. While this in vitro
`data suggests the potential for development of resistance to aztreonam, patients did
`not develop aztreonam resistance during therapy.
`
`To address the concerns of the Advisory Committee, this Reviewer recommends the
`Applicant be subject to a Phase 4 commitment.
`
`This commitment shall include the monitoring of Pseudomonas aeruginosa isolates
`from cystic fibrosis patients for aztreonam and tobramycin resistance for a period of
`not less than three years. The aztreonam and tobramycin susceptibilities from these
`isolates should be taken from the Cystic Fibrosis Foundation Registry and reported to
`the Agency on a yearly basis.
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`
`Division of Anti-Infective and Ophthalmology Products
`Clinical Microbiology Review #2
`NDA 50-814 SN040
`
`Aztreonam Lysine
`
`Peter Coderre, PhD
`Gilead Sciences
`
`29 December 2009
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`TABLE OF CONTENTS
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`
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`Executive Summary
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`Microbiology Subsections of the Package Insert
`
`Introduction
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`Preclinical Efficacy
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`Clinical Susceptibility Test Methods
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`Clinical Microbiology Methods
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`Quality Control Studies
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`Provisional Susceptibility Interpretive Criteria
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`Clinical Efficacy
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`Study AI-006
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` Clinical Protocols
` Correlation of In Vitro Susceptibility and Clinical Outcome
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`Breakpoint Discussion
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`Microbiology Subsections of the Package Insert
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`Review References
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`Division of Anti-Infective and Ophthalmology Products
`Clinical Microbiology Review #2
`NDA 50-814 SN040
`
`Aztreonam Lysine
`
`Peter Coderre, PhD
`Gilead Sciences
`
`29 December 2009
`
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`7 of 67
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`EXECUTIVE SUMMARY
`
`
`Aztreonam is a synthetic bactericidal monobactam antibiotic that was originally
`isolated from Chromobacterium violaceum. Aztreonam (Azactam®) is the only
`monobactam approved for clinical use in the US.
`
`The Applicant seeks the use of Aztreonam for Inhalation (AI) for the improvement of
`respiratory symptoms and pulmonary function in cystic fibrosis (CF) patients over 6
`years of age with Pseudomonas aeruginosa.
`
`What follows is a summary of the in vitro preclinical, in vivo preclinical and clinical
`efficacy data for the use of aztreonam for the improvement of symptoms of CF.
`
`The in vitro preclinical efficacy is determined by: the mechanism of action,
`spectrum of activity, mechanism of resistance, cross-resistance, post-antibiotic effect
`and other miscellaneous studies.
`
`Mechanism of Action. Aztreonam, like beta-lactam antibiotics, inhibits bacterial cell
`wall biosynthesis, resulting in cell lysis and death through irreversible inhibition of
`penicillin-binding proteins (PBPs), enzymes that catalyze the elongation and
`crosslinking of the peptidoglycan chains. Aztreonam binds preferentially and with
`high affinity to PBP3 of aerobic Gram-negative bacteria, accounting for its potent
`antibacterial activity against P. aeruginosa, Escherichia coli, Proteus mirabilis,
`Proteus vulgaris, Enterobacter cloacae and Klebsiella pneumoniae. In contrast,
`aztreonam has poor affinity for the PBP3 of Gram-positive and anaerobic bacteria
`and consequently is inactive against these bacteria. Binding of aztreonam to PBP3
`results in filamentation and cell lysis, an effect similar to that observed with
`cephalosporins.
`
`Aztreonam, like beta-lactam antibiotics, demonstrates time-dependent killing against
`sensitive Gram-negative bacteria; increasing the concentration of aztreonam above
`the minimum inhibitory concentration (MIC) of the test organism does not
`substantially increase the speed or degree of bacterial killing.
`
`Spectrum of Activity. Aztreonam is active against several aerobic Gram-negative
`pathogens, including many Enterobacteriaceae as well as P. aeruginosa, but is
`relatively inactive against Gram-positive and anaerobic organisms.
`
`Other aerobic Gram-negative bacteria show in vitro susceptibility to aztreonam,
`although the clinical significance of these organisms in CF is unknown, and data
`regarding clinical efficacy is not available. Susceptible bacteria are typically killed at
`concentrations one to four times their MICs. However, in some cases, the
`concentration of aztreonam required to achieve bactericidal killing of P. aeruginosa
`has been reported to be 4 to 16 times the MIC. Aztreonam exhibits MICs of ≤ 8
`µg/mL against at least 90% of the following aerobic Gram-negative bacteria:
`Aeromonas hydrophila, Morganella morganii, Neisseria gonorrhoeae (including
`penicillinase-producing strains), Pasteurella multocida, Proteus vulgaris, Providencia
`stuartii, Providencia rettgeri, and Yersinia enterocolitica. The safety and efficacy of
`aztreonam in treating clinical infections due to these microorganisms, however, have
`not been established in clinical trials.
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`8 of 67
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`Division of Anti-Infective and Ophthalmology Products
`Clinical Microbiology Review #2
`NDA 50-814 SN040
`
`Aztreonam Lysine
`
`Peter Coderre, PhD
`Gilead Sciences
`
`29 December 2009
`
` Recent data regarding the activity of aztreonam compared with other antibiotics
`commonly used to treat Gram-negative infections has been examined. Overall,
`aztreonam is less active than other commonly used antibiotics in Asia, Europe, Latin
`America and North America.
`
`Antibiotic susceptibility trends in bacterial isolates collected from CF patients may
`differ from the general patient population due to the chronic nature of antibiotic
`therapy in CF patients. In the US, susceptibility of P. aeruginosa to aztreonam has
`gradually decreased within both the CF and non-CF populations over the last 10
`years with 80% of P. aeruginosa isolates susceptible (MIC ≤ 8 µg/mL) to aztreonam
`in 1995, 78.9 % susceptible in 2004,and 68.6% susceptible in 2006. Aztreonam has
`been shown to have in vitro activity against tobramycin-resistant and multidrug-
`resistant P. aeruginosa isolates from CF patients.
`
`Mechanisms of Resistance. Multiple mechanisms of bacterial resistance to
`aztreonam and beta-lactam antibiotics have been identified. These mechanisms
`include the derepression of chromosomal beta-lactamases, the acquisition of beta-
`lactamase encoding plasmids, overexpression of efflux pump systems,
`impermeability of the outer membrane, and alteration of the drug target (PBPs).
`
`In Gram-negative bacteria the prevalence of various resistance mechanisms varies
`by organism and two or more mechanisms may contribute to the overall resistance
`profile. In contrast, for P. aeruginosa isolated from CF patients, resistance to beta-
`lactam antibiotics was primarily due to overproduction of a constitutive
`cephalosporinase (18.6%), and rarely due to production of a transferable beta-
`lactamase (1.4%). However, researchers also reported that susceptibility to
`aminoglycosides and fluoroquinolones was lower in isolates producing beta-
`lactamases, thereby suggesting involvement of other mechanisms.
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`Aztreonam is a poor inducer of beta-lactamase production and, although not used as
`such, is an inhibitor of many beta-lactamases.
`
`The beta-lactamases are classified using the Ambler system into four groups (A, B,
`C, and D) according to their amino acid sequences. Classes A, C, and D beta-
`lactamases use a catalytically active serine molecule for inactivation of the beta-
`lactam drug, while Class B enzymes are metallo-enzymes requiring zinc for activity.
`
`Of most concern among the Class A beta-lactamases are the clavulanic acid-inhibited
`Ambler Class A ESBLs that are broadly active against most beta-lactams, as well as
`aztreonam. The TEM- and SHV-type ESBLs have been extensively reported in
`Enterobacteriaceae but have been only rarely reported from P. aeruginosa.
`
`The class B metallo-beta-lactamases (MBLs) hydrolyze a wide variety of beta-
`lactams, including carbapenems, but do not hydrolyze aztreonam. While there have
`been rare reports of organisms with MBLs that are also resistant to aztreonam [VIM-
`5 (K. pneumoniae and P. aeruginosa-Turkey), VIM-6 (P. putida-Singapore) and VIM-
`7 (P. aeruginosa-United States)], it is possible that these organisms were expressing
`multiple resistance mechanisms.
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`9 of 67
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`Division of Anti-Infective and Ophthalmology Products
`Clinical Microbiology Review #2
`NDA 50-814 SN040
`
`Aztreonam Lysine
`
`Peter Coderre, PhD
`Gilead Sciences
`
`29 December 2009
`
`Recently, a strain of P. aeruginosa was found to express an ESBL, GES-9 which
`differs from GES-1 by a Gly243Ser substitution. This ESBL hydrolyzes aztreonam
`but is inhibited by clavulanic acid and imipenem. The gene for GES-9 is located
`inside a class 1 integron structure containing two copies of an insertion sequence.
`
`AmpC, the best characterized enzyme of Class C beta-lactamases, is normally
`produced at low levels in clinical isolates of P. aeruginosa and Enterobacteriaceae but
`production can be induced to high levels by the presence of beta-lactams, especially
`cefoxitin and imipenem. High-level production of both chromosomal- and plasmid-
`encoded AmpC is responsible for cross-resistance to aztreonam and to multiple beta-
`lactam antibiotics.
`
`The OXA-type carbapenemases (Class D beta-lactamases) generally have little or no
`activity against aztreonam, but there have been rare reports of oxacillinases from
`clinical isolates of P. aeruginosa (OXA-11 [Turkey] and OXA-45 [United States] that
`have hydrolyzed aztreonam.
`
`Some porins provide entry for a wide variety of drugs and others are specific for a
`single drug allowing permeation through the outer membrane. In P. aeruginosa,
`porins have extremely low permeability to most beta-lactams and thereby play a
`major role in intrinsic resistance. Due to variability in porin specificity, alterations
`may lead to resistance to one or more antibiotics. An example of specific drug
`resistance is seen in loss of the OprD porin, which can result in resistance of P.
`aeruginosa to carbapenems but does not confer cross-resistance to non-carbapenem
`beta-lactams or aztreonam.
`
`Several chromosomally-encoded efflux systems play an important role in P.
`aeruginosa antibiotic resistance. The MexAB-OprM, MexCD-OprJ, MexEF-OprN, and
`MexXY-OprM systems extrude a wide variety of antibiotics including beta-lactams.
`Most beta-lactams, (e.g., penicillins, cephems, and meropenem) are pump
`substrates for all of these efflux systems. In contrast, aztreonam can only be
`extruded by the MexAB-OprM pump system.
`
`Clinical resistance associated with alteration of PBPs is exceedingly rare in P.
`aeruginosa, but cannot be ruled out.
`
`In vitro resistance frequencies for P. aeruginosa ATCC 27853 were low, less than 1 x
`10-8 in the presence or absence of aztreonam (500 µg/mL). A modified Szybalski
`method was used to demonstrate that aztreonam, at four times the MIC, selected
`resistant variants of 10 P. aeruginosa isolates (two lab isolates, eight isolated from
`blood of cancer patients) in vitro. Mutants resistant to aztreonam were generated at
`a frequency of approximately 1 x 10-6 to 1 x 10-7. Some mutants produced large
`amounts of cephalosporinase; however, aztreonam was stable to hydrolysis by this
`enzyme.
`
`Cross resistance. Aztreonam is not antagonistic with the antibiotics commonly
`used on- and off-label to treat respiratory infections in CF patients, suggesting that
`clinical use of aztreonam lysine in conjunction with another antibiotic to treat CF
`respiratory infections will not reduce the antibacterial activity of either drug due to
`antagonistic interactions.
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`Division of Anti-Infective and Ophthalmology Products
`Clinical Microbiology Review #2
`NDA 50-814 SN040
`
`Aztreonam Lysine
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`Peter Coderre, PhD
`Gilead Sciences
`
`29 December 2009
`
`When P. aeruginosa or Enterobacteriaceae are treated with aztreonam in
`combination with beta-lactam antibiotics, the interactions are typically indifferent or
`synergistic. In a study of 14 multidrug-resistant isolates of Enterobacteriaceae (N =
`10) and P. aeruginosa (N = 4 [ATCC 27853 and three clinical isolates]), synergy was
`noted with 42% (6 of 14) of the organisms when aztreonam was combined with any
`of the beta-lactam antibiotics tested (piperacillin, moxalactam, cefotaxime, or
`cefperazone); indifferent effects were observed with all other organisms.
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`Investigators have demonstrated that combinations of aztreonam plus cefepime,
`piperacillin or imipenem resulted in indifference against P. aeruginosa isolates.
`Interactions with cephalosporins were predominantly partially synergistic.
`
`Combinations of aztreonam with quinolones sometimes result in synergy, but
`indifferent or additive effects are more commonly observed. Combinations of
`aztreonam plus ciprofloxacin generally resulted in indifference against P. aeruginosa
`isolates. However, one investigator examined interactions between aztreonam and
`ciprofloxacin, levofloxacin, gatifloxacin or moxifloxacin using the checkerboard
`method. Interactions were evaluated against four isolates each of P. aeruginosa, B.
`cepacia, E. cloacae, K. pneumoniae, E. coli and P. mirabilis. All combinations
`demonstrated uniformly additive activity against P. aeruginosa.
`
` A
`
` recent report by Gasink et al. concluded that curbing the use of fluoroquinolones
`and antimicrobials with activity against anaerobes may be an effective strategy to
`limit the emergence of aztreonam-resistant P. aeruginosa. These investigators
`identified risk factors for infection or colonization with aztreonam-resistant P.
`aeruginosa. Nosocomial morality was greater among patients infected or colonized
`with aztreonam-resistant P. aeruginosa compared with those infected with
`aztreonam-susceptible P. aeruginosa.
`
`In vitro interactions between aztreonam and aminoglycosides have been shown to be
`synergistic against P. aeruginosa, Enterobacteriaceae, and other Gram-negative
`aerobic bacilli. These aminoglycosides included: amikacin, gentamicin, tobramycin or
`netilmicin.
`
`PAE. Post antibiotic effect (PAE) refers to the suppression of bacterial growth that
`persists after short-term exposure to an antibiotic. Aztreonam, like beta-lactam
`antibiotics, has minimal or no persistent effects on most organisms. The duration of
`PAE for aztreonam against P. aeruginosa ATCC 27853 is less than 0.5 hour when
`tested at concentrations equivalent to four times the MIC. Because aztreonam does
`not have a demonstrable PAE for P. aeruginosa, the dosing schedule was determined
`on the basis of the pharmacokinetic (PK) parameters.
`
`Miscellaneous Studies. A number of miscellaneous studies were conducted to
`examine the effects of aztreonam in a pharmacodynamic model, effects on
`phagocytic cells, effects on gastrointestinal flora, effects on biofilms and the effects
`of nebulization on aztreonam potency.
`
` A
`
` pharmacodynamic model was developed to facilitate evaluation of aztreonam
`activity when delivered to an in vitro, mucin-covered epithelial cell surface. Although
`the model’s reproducibility limited its utility, a significant decrease in CFUs was
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`11 of 67
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`Division of Anti-Infective and Ophthalmology Products
`Clinical Microbiology Review #2
`NDA 50-814 SN040
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`Aztreonam Lysine
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`Peter Coderre, PhD
`Gilead Sciences
`
`29 December 2009
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`observed by 6 to 12 hours for both aztreonam and tobramycin with regrowth at 24
`hours.
`
`Exposure of bacteria to aztreonam can modify the interactions between Gram-
`negative bacteria and phagocytic cells, resulting in enhanced phagocytic killing due
`to aztreonam-induced alterations in the bacterial cells. Sub-MIC concentrations of
`aztreonam enhanced the phagocytosis and killing of P. aeruginosa K1 by a murine
`macrophage cell line. Enhanced phagocytic killing was attributed to modification of
`bacterial cell surface structures upon exposure to aztreonam.
`
`Aztreonam has the potential to alter the normal gastrointestinal flora, thereby
`decreasing patients’ resistance to colonization with other pathogens such as Candida
`and Clostridium spp. However, in the clinical trials conducted for this NDA, systemic
`exposure to aztreonam is very low and is unlikely to lead to pseudomembranous
`colitis.
`
`In chronic airway infections in CF patients, P. aeruginosa is likely to exist in both
`planktonic and biofilm phases. The presence of a biofilm in CF helps to explain why
`P. aeruginosa lung infections are rarely eradicated with antibiotic therapy, regardless
`of the organism’s reported in vitro susceptibility. Recently a methodology to test
`antibiotic susceptibility within a biofilm was developed with the hope that it might be
`more predictive. As with beta-lactams, biofilm inhibitory concentrations (BICs) for
`aztreonam are much higher than conventionally determined MICs. Against 85
`clinical isolates of P. aeruginosa from the US, the aztreonam, the MIC90 was 32
`µg/mL, whereas the BIC90 was > 128 µg/mL.
`
`To determine whether nebulization impacts the potency of aztreonam, the in vitro
`activity of aztreonam lysine was tested before and after nebulization against 161
`clinical isolates of B. cepacia complex, S. maltophilia, A. xylosoxidans, S. aureus, and
`P. aeruginosa from CF patients. In aggregate, these results support the physical
`finding that the antimicrobial activity of aztreonam is not significantly reduced during
`nebulization by the eFlow device.
`
`Pharmacokinetics. AI is delivered using the PARI eFlow electronic nebulizer
`(eFlow) which produces an aerosol with a relatively monodispersed particle spectrum
`which is well-suited for lower airway drug deposition. Thus, this drug is essentially a
`topical antibiotic and does not have the same pharmacokinetic properties of a
`paternally administered antibiotic.
`
`Sputum provides a growth environment for bacteria and can significantly inhibit the
`activity of antibiotics. Investigators evaluated aztreonam lysine time-kill kinetics for
`P. aeruginosa ATCC 27853 using aztreonam concentrations equivalent to 0.1 times,
`1 time, and 10 times the MIC. No killing was observed at 0.1 times the aztreonam
`MIC. Bactericidal levels of killing (= 3 log10) were reached by five hours, and the
`speed and degree of killing were comparable at aztreonam concentrations of 1 time
`and 10 times the MIC. The killing kinetics of aztreonam against P. aeruginosa ATCC
`27853 in the presence of 1% CF sputum and 10% porcine mucin were nearly
`identical to those conducted in media alone. By comparison, the activity of
`aminoglycosides is known to be antagonized by sputum.
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`12 of 67
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`Division of Anti-Infective and Ophthalmology Products
`Clinical Microbiology Review #2
`NDA 50-814 SN040
`
`Aztreonam Lysine
`
`Peter Coderre, PhD
`Gilead Sciences
`
`29 December 2009
`
`Similar time-kill studies were conducted with 20 CF P. aeruginosa isolates using 10%
`porcine gastric mucin as a model for the protein-binding component of sputum.
`Similar results were found with the gastric mucin model. The sputum and mucin kill-
`curve data suggest that aztreonam administered as an aerosol to the CF lungs will
`not be significantly inhibited by sputum.
`
`Clinical Laboratory Susceptibility Testing. The approved antimicrobial
`susceptibility test methods and quality control parameters used for parenteral
`aztreonam therapy were used to monitor the activity of AI against P. aeruginosa
`isolates from CF patients. It should be noted that susceptibility testing of P.
`aeruginosa isolates from CF patients, in some cases, required extended incubation
`up to 24 hours for accurate determination of MIC values.
`
`Quality Control. Aztreonam has been approved by the Agency for other indications.
`In addition, as AI is a topically administered antibiotic, interpretive criteria will not be
`determined. Therefore, quality control parameters were not determined.
`
`Provisional Interpretive Criteria. Aztreonam has been approved by the Agency
`for other indications. Therefore, provisional interpretive criteria were not
`determined.
`
`Clinical Efficacy. The Applicant presents the protocols and results from four clinical
`trials: one phase 2 trial, Study AI-003, and three phase 3 trials. Among the three
`phase 3 trials were two pivotal studies, Study AI-005 and Study AI-007, as well as a
`follow-on study, AI-006, which will not be discussed in detail.
`
`Study AI-003 was a blinded, multicenter, randomized, placebo-controlled phase 2
`trial with aztreonam for inhalation (AI) in CF patients with lung disease due to P.
`ae