Exebacase in Addition to Standard-of-Care Antibiotics for Staphylococcus aureus Bloodstream Infections and Right-Sided Infective Endocarditis: A Phase 3, Superiority-Design, Placebo-Controlled, Randomized Clinical Trial (DISRUPT).

BACKGROUND: Novel treatments are needed for Staphylococcus aureus bacteremia, particularly for methicillin-resistant S. aureus (MRSA). Exebacase is a first-in-class antistaphylococcal lysin that is rapidly bactericidal and synergizes with antibiotics. METHODS: In DISRUPT, a superiority-design phase 3 study, patients with S. aureus bacteremia/endocarditis were randomly assigned to receive a single dose of IV exebacase or placebo in addition to standard-of-care antibiotics. The primary efficacy outcome was clinical response at Day 14 in the MRSA population. RESULTS: A total of 259 patients were randomized before the study was stopped for futility based on the recommendation of the unblinded Data Safety Monitoring Board. Clinical response rates at Day 14 in the MRSA population (n = 97) were 50.0% (exebacase + antibiotics; 32/64) vs. 60.6% (antibiotics alone; 20/33) (P = 0.392). Overall, rates of adverse events were similar across groups. No adverse events of hypersensitivity related to exebacase were reported. CONCLUSIONS: Exebacase + antibiotics failed to improve clinical response at Day 14 in patients with MRSA bacteremia/endocarditis. This result was unexpected based on phase 2 data that established proof-of-concept for exebacase + antibiotics in patients with MRSA bacteremia/endocarditis. In the antibiotics alone group, the clinical response rate was higher than that seen in phase 2. Heterogeneity within the study population and a relatively small sample size in either the phase 2 or phase 3 studies may have increased the probability of imbalances in the multiple components of Day 14 clinical outcome. This study provides lessons for future superiority studies in S. aureus bacteremia/endocarditis.

In vitro activity of exebacase against methicillin-resistant Staphylococcus aureus biofilms on orthopedic Kirschner wires.

Orthopedic foreign body-associated infection can be difficult to treat due to the formation of biofilms protecting microorganisms from both antimicrobials and the immune system. Exebacase is an antistaphylococcal lysin (cell wall hydrolase) under consideration for local treatment for biofilm-based infections caused by methicillin-resistant Staphylococcus aureus (MRSA). To determine the activity of exebacase, we formed MRSA biofilms on orthopedic Kirschner wires and exposed them to varying concentrations (0.098, 0.98, 9.8 mg/ml) of exebacase and/or daptomycin over 24 h. The biofilm consisted of 5.49 log10 colony forming units (cfu)/K-wire prior to treatment and remained steady throughout the experiment. Exebacase showed significant biofilm reduction at all timepoints (up to 5.78 log10 cfu/K-wire; P < 0.0495) compared to the controls at all concentrations and all time points with bactericidal activity (> 3 log10 cfu/K-wire reduction) observed for up to 12 h for the 0.098 and 0.98 mg/ml concentrations and at 24 h for 9.8 mg/ml. Daptomycin showed significant biofilm reduction, although non-bactericidal, at all time points for 0.98 and 9.8 mg/ml and at 4 and 8 h with 0.098 mg/ml (P < 0.0495). This study supports further evaluation of local administration of exebacase as a potential treatment for orthopedic implant infections.

Locally delivered antistaphylococcal lysin exebacase or CF-296 is active in methicillin-resistant Staphylococcus aureus implant-associated osteomyelitis.

Introduction: Staphylococcus aureus is the most common cause of orthopedic infections and can be challenging to treat, especially in the presence of a foreign body. The antistaphylococcal lysins exebacase and CF-296 have rapid bactericidal activity, a low propensity for resistance development, and synergize with some antibiotics. Methods: Rabbit implant-associated osteomyelitis was induced by drilling into the medial tibia followed by locally delivering exebacase, CF-296, or lysin carrier. A titanium screw colonized with methicillin-resistant S. aureus (MRSA) IDRL-6169 was inserted. Intravenous daptomycin or saline was administered and continued daily for 4 d. On day 5, rabbits were euthanized, and the tibiae and implants were collected for culture. Results were reported as log 10 colony forming units (cfu) per gram of bone or log 10  cfu per implant, and comparisons among the six groups were performed using the Wilcoxon rank sum test. Results: Based on implant and bone cultures, all treatments resulted in significantly lower bacterial counts than those of controls ( P ≤ 0.0025 ). Exebacase alone or with daptomycin as well as CF-296 with daptomycin were more active than daptomycin alone ( P ≤ 0.0098 ) or CF-296 alone ( P ≤ 0.0154 ) based on implant cultures. CF-296 with daptomycin was more active than either CF-296 alone ( P = 0.0040 ) or daptomycin alone ( P = 0.0098 ) based on bone cultures. Conclusion: Local delivery of either exebacase or CF-296 offers a promising complement to conventional antibiotics in implant-associated infections.

Direct Lytic Agents: Novel, Rapidly Acting Potential Antimicrobial Treatment Modalities for Systemic Use in the Era of Rising Antibiotic Resistance.

Direct lytic agents (DLAs) are novel antimicrobial compounds with unique mechanisms of action based on rapid cell wall destabilization and bacteriolysis. DLAs include two classes of purified polypeptides-lysins (peptidoglycan hydrolase enzymes) and amurins (outer membrane targeting peptides). Their intended use is to kill bacteria in a manner that is complimentary to and synergistic with traditional antibiotics without selection for DLA resistance. Lysins were originally described as having activity against Gram-positive pathogens and of those, exebacase, is the first to have advanced into Phase 3 of clinical development. Recently, both engineered and native DLAs have now been described with potent bactericidal activity against a range of Gram-negative pathogens, including multidrug-resistant (MDR) and extensively drug-resistant (XDR) Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii. Importantly, novel DLAs targeting Gram-negatives, including the lysin CF-370 and the amurin peptides, are active in biological matrices (blood/serum) and, as such, offer promise for therapeutic use as systemically administered agents for the treatment of life-threatening invasive infections. In this review, DLAs are discussed as potential new classes of antimicrobial biologics that can be used to treat serious systemic infections.

Safety and Pharmacokinetics of Exebacase in an Infant With Disseminated Staphylococcus aureus Infection.

Exebacase, an antistaphylococcal lysin produced from a bacteriophage-encoded gene, is a promising adjunctive therapy for severe methicillin-resistant Staphylococcus aureus infections. We describe the first infant to receive exebacase, dosing, and pharmacokinetics. Exebacase may be safe and efficacious in children; however, further clinical trials are needed to optimize dosing.

Efficacy assessment of lysin CF-296 in addition to daptomycin or vancomycin against Staphylococcus aureus in the murine thigh infection model.

OBJECTIVES: CF-296 is a lysin in pre-clinical development for the treatment of MSSA and MRSA infections, used in addition to standard-of-care (SOC) antibiotics. We evaluated the efficacy of CF-296 alone and in addition to daptomycin or vancomycin against Staphylococcus aureus in the neutropenic mouse thigh infection model. METHODS: Eight isolates (one MSSA and seven MRSA) were studied. Mice were administered five CF-296 monotherapy doses ranging from 0.5 to 50 mg/kg intravenously. To assess adjunctive therapy, mice received sub-therapeutic daptomycin alone, sub-therapeutic vancomycin alone, or the five CF-296 doses in addition to either daptomycin or vancomycin. RESULTS: Relative to starting inoculum (5.80 ± 0.31 log10 cfu/thigh), bacterial density in vehicle controls increased by +2.49 ± 0.98 across all eight strains. Relative to 24 h controls, a dose-response in bacterial killing (range -0.22 ± 0.87 to -2.01 ± 1.71 log10 cfu/thigh) was observed with increasing CF-296 monotherapy against the eight isolates. Daptomycin and vancomycin resulted in -1.36 ± 0.77 and -1.37 ± 1.01 log10 cfu/thigh bacteria reduction, respectively, relative to 24 h controls. Escalating CF-296 exposures (0.5-50 mg/kg) in addition to daptomycin resulted in an enhanced dose-response, ranging from bacterial killing of -0.69 to -2.13 log10 cfu/thigh, relative to daptomycin alone. Similarly, in addition to vancomycin, escalating CF-296 exposures resulted in bacterial reduction ranging from -1.37 to -2.29 log10 cfu/thigh, relative to vancomycin alone. CONCLUSIONS: Relative to SOC antibiotics (daptomycin or vancomycin), addition of CF-296 resulted in robust and enhanced antibacterial dose-response, achieving ≥1 log10 cfu/thigh decrease across most doses, highlighting a potential role for CF-296 adjunctive therapy against MSSA and MRSA isolates.

Exebacase Is Active In Vitro in Pulmonary Surfactant and Is Efficacious Alone and Synergistic with Daptomycin in a Mouse Model of Lethal Staphylococcus aureus Lung Infection.

Exebacase (CF-301) is a novel antistaphylococcal lysin (cell wall hydrolase) in phase 3 of clinical development for the treatment of Staphylococcus aureus bacteremia, including right-sided endocarditis, used in addition to standard-of-care antibiotics. In the current study, the potential for exebacase to treat S. aureus pneumonia was explored in vitro using bovine pulmonary surfactant (Survanta) and in vivo using a lethal murine pneumonia model. Exebacase was active against a set of methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains, with an MIC90 of 2 µg/ml (n = 18 strains), in the presence of a surfactant concentration (7.5%) inhibitory to the antistaphylococcal antibiotic daptomycin, which is inactive in pulmonary environments due to specific inhibition by surfactant. In a rigorous test of the ability of exebacase to synergize with antistaphylococcal antibiotics, exebacase synergized with daptomycin in the presence of surfactant in vitro, resulting in daptomycin MIC reductions of up to 64-fold against 9 MRSA and 9 MSSA strains. Exebacase was also observed to facilitate the binding of daptomycin to S. aureus and the elimination of biofilm-like structures formed in the presence of surfactant. Exebacase (5 mg/kg of body weight 1 time every 24 h [q24h], administered intravenously for 3 days) was efficacious in a murine model of staphylococcal pneumonia, resulting in 50% survival, compared to 0% survival with the vehicle control; exebacase in addition to daptomycin (50 mg/kg q24h for 3 days) resulted in 70% survival, compared to 0% survival in the daptomycin-alone control group. Overall, exebacase is active in pulmonary environments and may be appropriate for development as a treatment for staphylococcal pneumonia.

Arthroscopic "Debridement and Implant Retention" With Local Administration of Exebacase (Lysin CF-301) Followed by Suppressive Tedizolid as Salvage Therapy in Elderly Patients for Relapsing Multidrug-Resistant S. epidermidis Prosthetic Knee Infection.

Exebacase, a recombinantly produced lysin has recently (i) reported proof-of-concept data from a phase II study in S. aureus bacteremia and (ii) demonstrated antibiofilm activity in vitro against S. epidermidis. In patients with relapsing multidrug-resistant (MDR) S. epidermidis prosthetic knee infection (PKI), the only surgical option is prosthesis exchange. In elderly patients who have undergone several revisions, prosthesis explantation could be associated with definitive loss of function and mortality. In our BJI reference regional center, arthroscopic debridement and implant retention with local administration of exebacase (LysinDAIR) followed by suppressive tedizolid as salvage therapy is proposed for elderly patients with recurrent MDR S. epidermidis PKI with no therapeutic option or therapeutic dead end (for whom revision or transfemoral amputation is not feasible and no other oral option is available). Each use was decided in agreement with the French health authority and in accordance with the local ethics committee. A written consent was obtained for each patient. Exebacase (75 mg/mL; 30 mL) was administered directly into the joint during arthroscopy. Four patients (79-89 years old) were treated with the LysinDAIR procedure. All had several previous prosthetic knee revisions without prosthesis loosening. Three had relapsing PKI despite suppressive antibiotics following open DAIR. Two had clinical signs of septic arthritis; the two others had sinus tract. After the LysinDAIR procedure, no adverse events occurred during arthroscopy; all patients received daptomycin 8 mg/kg and linezolid 600 mg bid (4-6 weeks) as primary therapy, followed by tedizolid 200 mg/day as suppressive therapy. At 6 months, recurrence of the sinus tract occurred in the two patients with sinus tract at baseline. After >1 year follow up, the clinical outcome was favorable in the last two patients with total disappearance of clinical signs of septic arthritis even if microbiological persistence was detected in one of them. Exebacase has the potential to be used in patients with staphylococci PKI during arthroscopic DAIR as salvage therapy to improve the efficacy of suppressive antibiotics and to prevent major loss of function.

Development of a Broth Microdilution Method for Exebacase Susceptibility Testing.

Exebacase (CF-301) belongs to a new class of protein-based antibacterial agents, known as lysins (peptidoglycan hydrolases). Exebacase, a novel lysin with antistaphylococcal activity, is in phase 3 of clinical development. To advance into the clinic, it was necessary to develop an accurate and reproducible method for exebacase MIC determination. The Clinical and Laboratory Standards Institute (CLSI) reference broth microdilution (BMD) method using cation-adjusted Mueller-Hinton broth (CAMHB) produced trailing MIC endpoints, and exebacase activity was diminished when frozen BMD panels were used. A modified BMD method was developed using CAMHB supplemented with 25% horse serum and 0.5 mM dl-dithiothreitol (CAMHB-HSD). Preliminary quality control (QC) ranges for Staphylococcus aureus ATCC 29213 of 0.25 to 1 µg/ml and for Enterococcus faecalis ATCC 29212 of 16 to 64 µg/ml were determined based on the results of a CLSI M23-defined MIC QC tier 1 study. These preliminary QC ranges validated the MIC data generated from a systematic study testing a discrete S. aureus strain collection using CAMHB-HSD to investigate the impact of parameters known to influence susceptibility test results and to evaluate the exebacase MIC distribution against clinical S. aureus isolates. Presentation of these data led to the CLSI Subcommittee on Antimicrobial Susceptibility Testing (AST) approval of the use of CAMHB-HSD to determine exebacase susceptibility and commencement of a multilaboratory (tier 2) QC study. Use of a standard BMD method and concomitant QC testing provides confidence in the assessment of test performance to generate accurate and reproducible susceptibility data during antibacterial drug development.

Effect of the Lysin Exebacase on Cardiac Vegetation Progression in a Rabbit Model of Methicillin-Resistant Staphylococcus aureus Endocarditis as Determined by Echocardiography.

Methicillin-resistant Staphylococcus aureus (MRSA) poses significant therapeutic challenges related to its frequency in clinical infections, innate virulence properties, and propensity for multiantibiotic resistance. MRSA is among the most common causes of endovascular infections, including infective endocarditis (IE). Our objective was to employ transthoracic echocardiography (TTE) to evaluate the effect of exebacase, a novel direct lytic agent, in experimental aortic valve MRSA IE. TTE was utilized to evaluate the in vivo effect of exebacase on MRSA-infected vegetation progression when combined with daptomycin (versus daptomycin alone). Primary intravegetation outcomes were maximum size, weights at sacrifice, and MRSA counts at infection baseline versus after 4 days of daptomycin treatment (alone or in addition to exebacase administered once on treatment day 1). A single dose of exebacase in addition to daptomycin cleared significantly more intravegetation MRSA than daptomycin alone. This was associated with a statistical trend toward reduced maximum vegetation size in the exebacase plus daptomycin versus the daptomycin alone therapy groups (P = 0.07). Also, mean vegetation weights in the exebacase-treated group were significantly lower than those of the daptomycin alone group (P < 0.0001). Maximum vegetation size by TTE correlated with vegetation weight (P = 0.005). In addition, intravegetation MRSA counts in the combination group were significantly lower than those of untreated controls (P < 0.0001) and the daptomycin alone group (P < 0.0001). This study suggests that exebacase has a salutary impact on MRSA-infected vegetation progression when combined with daptomycin, especially in terms of vegetation MRSA burden, size, and weight. Moreover, TTE appears to be an efficient noninvasive tool to assess therapeutic efficacies in experimental MRSA IE.

Exebacase for patients with Staphylococcus aureus bloodstream infection and endocarditis.

BACKGROUNDNovel therapeutic approaches are critically needed for Staphylococcus aureus bloodstream infections (BSIs), particularly for methicillin-resistant S. aureus (MRSA). Exebacase, a first-in-class antistaphylococcal lysin, is a direct lytic agent that is rapidly bacteriolytic, eradicates biofilms, and synergizes with antibiotics.METHODSIn this superiority-design study, we randomly assigned 121 patients with S. aureus BSI/endocarditis to receive a single dose of exebacase or placebo. All patients received standard-of-care antibiotics. The primary efficacy endpoint was clinical outcome (responder rate) on day 14.RESULTSClinical responder rates on day 14 were 70.4% and 60.0% in the exebacase + antibiotics and antibiotics-alone groups, respectively (difference = 10.4, 90% CI [-6.3, 27.2], P = 0.31), and were 42.8 percentage points higher in the prespecified exploratory MRSA subgroup (74.1% vs. 31.3%, difference = 42.8, 90% CI [14.3, 71.4], ad hoc P = 0.01). Rates of adverse events (AEs) were similar in both groups. No AEs of hypersensitivity to exebacase were reported. Thirty-day all-cause mortality rates were 9.7% and 12.8% in the exebacase + antibiotics and antibiotics-alone groups, respectively, with a notable difference in MRSA patients (3.7% vs. 25.0%, difference = -21.3, 90% CI [-45.1, 2.5], ad hoc P = 0.06). Among MRSA patients in the United States, median length of stay was 4 days shorter and 30-day hospital readmission rates were 48% lower in the exebacase-treated group compared with antibiotics alone.CONCLUSIONThis study establishes proof of concept for exebacase and direct lytic agents as potential therapeutics and supports conduct of a confirmatory study focused on exebacase to treat MRSA BSIs.TRIAL REGISTRATIONClinicaltrials.gov NCT03163446.FUNDINGContraFect Corporation.

Exebacase Demonstrates In Vitro Synergy with a Broad Range of Antibiotics against both Methicillin-Resistant and Methicillin-Susceptible Staphylococcus aureus.

In vitro synergy between an antimicrobial protein lysin (cell wall hydrolase) called exebacase and each of 12 different antibiotics was examined against Staphylococcus aureus isolates using a nonstandard medium approved for exebacase susceptibility testing by the Clinical and Laboratory Standards Institute. In the checkerboard assay format, fractional inhibitory concentration index values of ≤0.5, consistent with synergy, were observed for the majority of interactions tested. Synergy was further confirmed in time-kill assays.

In vitro activity of Exebacase (CF-301) against clinical Staphylococcus aureus surveillance isolates from the United States, Europe, and Latin America, 2015-2017.

Lysins are direct lytic agents which act through enzymatic cell-wall-hydrolysis and represent a potential new class of antimicrobial agents in development to treat antibiotic-resistant bacterial infections. Exebacase (CF-301) is a first-in-class lysin now in clinical development for the treatment of Staphylococcus aureus (S. aureus) bacteremia and infective endocarditis (IE) when used in addition to conventional antibiotics. Exebacase and comparator antibiotics were tested by broth microdilution against a set of 535 clinical MSSA and MRSA isolates collected from 2015 to 2017 throughout the United States, Europe and South America. All S. aureus isolates were inhibited by ≤1 mg/L exebacase (MIC50/90, 0.5/1 mg/L) with a range of 0.25-1 mg/L. No difference in susceptibility was observed between the MSSA and MRSA isolates. Exebacase was uniformly and equivalently active against all recent clinical MSSA and MRSA surveillance isolates from a broad survey across 3 continents.

Exebacase in Addition to Daptomycin Is More Active than Daptomycin or Exebacase Alone in Methicillin-Resistant Staphylococcus aureus Osteomyelitis in Rats.

Bacteriophage-derived lysins are being developed as anti-infective agents. In an acute osteomyelitis methicillin-resistant Staphylococcus aureus (MRSA) model, rats receiving no treatment or treatment with daptomycin, exebacase (CF-301), or daptomycin plus exebacase had means of 5.13, 4.09, 4.65, and 3.57 log10 CFU/gram of bone, respectively. All treated animals had fewer bacteria than did untreated animals (P ≤ 0.0001), with daptomycin plus exebacase being more active than daptomycin (P = 0.0042) or exebacase (P < 0.001) alone.

Antimicrobial Activity of Exebacase (Lysin CF-301) against the Most Common Causes of Infective Endocarditis.

Exebacase, a recombinantly produced lysin (cell wall hydrolase), and comparator antibiotics were tested by the broth microdilution method against strain sets of Staphylococcus and Streptococcus spp., which are the most common causes of infective endocarditis in humans. Exebacase was active against all Staphylococcus spp. tested, including S. aureus and coagulase-negative staphylococci (MIC50/90, 0.5/1 µg/ml). Activity against Streptococcus spp. was variable, with S. pyogenes, S. agalactiae, and S. dysgalactiae (MIC50/90, 1/2 µg/ml) among the most susceptible.

Postantibiotic and Sub-MIC Effects of Exebacase (Lysin CF-301) Enhance Antimicrobial Activity against Staphylococcus aureus.

CF-301 (exebacase) is a recombinantly produced bacteriophage-derived lysin (cell wall hydrolase) and is the first agent of this class to enter clinical development in the United States for treating bacteremia including endocarditis due to Staphylococcus aureus Whereas rapid bactericidal activity is the hallmark in vitro and in vivo response to CF-301 at exposures higher than the MIC, prolonged antimicrobial activity, mediated by cell wall damage, is predicted at concentrations less than the MIC. In the current study, a series of in vitro pharmacodynamic parameters, including the postantibiotic effect (PAE), postantibiotic sub-MIC effect (PA-SME), and sub-MIC effect (SME), were studied to determine how short-duration and sub-MIC CF-301 exposures affect the growth of surviving staphylococci and extend its antimicrobial activity. Mean PAE, PA-SME, and SME values up to 4.8, 9.3, and 9.8 h, respectively, were observed against 14 staphylococcal strains tested in human serum; growth delays were extended by 6 h in the presence of daptomycin. Exposures to CF-301 at sub-MIC levels as low as 0.001× to 0.01× MIC (∼1 to 10 ng/ml) resulted in aberrant cell wall ultrastructure, increased membrane permeability, dissipation of membrane potential, and inhibition of virulence phenotypes, including agglutination and biofilm formation. A mouse thigh infection model designed to study the PAE was used to confirm our findings and demonstrate in vivo growth delays of ≥19.3 h. Our findings suggest that at CF-301 concentrations less than the MIC during therapeutic use, sustained reductions in bacterial fitness and virulence may substantially enhance efficacy.

The Antistaphylococcal Lysin, CF-301, Activates Key Host Factors in Human Blood To Potentiate Methicillin-Resistant Staphylococcus aureus Bacteriolysis.

Bacteriophage-derived lysins are cell-wall-hydrolytic enzymes that represent a potential new class of antibacterial therapeutics in development to address burgeoning antimicrobial resistance. CF-301, the lead compound in this class, is in clinical development as an adjunctive treatment to potentially improve clinical cure rates of Staphylococcus aureus bacteremia and infective endocarditis (IE) when used in addition to antibiotics. In order to profile the activity of CF-301 in a clinically relevant milieu, we assessed its in vitro activity in human blood versus in a conventional testing medium (cation-adjusted Mueller-Hinton broth [caMHB]). CF-301 exhibited substantially greater potency (32 to ≥100-fold) in human blood versus caMHB in three standard microbiologic testing formats (e.g., broth dilution MICs, checkerboard synergy, and time-kill assays). We demonstrated that CF-301 acted synergistically with two key human blood factors, human serum lysozyme (HuLYZ) and human serum albumin (HSA), which normally have no nascent antistaphylococcal activity, against a prototypic methicillin-resistant S. aureus (MRSA) strain (MW2). Similar in vitro enhancement of CF-301 activity was also observed in rabbit, horse, and dog (but not rat or mouse) blood. Two well-established MRSA IE models in rabbit and rat were used to validate these findings in vivo by demonstrating comparable synergistic efficacy with standard-of-care anti-MRSA antibiotics at >100-fold lower lysin doses in the rabbit than in the rat model. The unique properties of CF-301 that enable bactericidal potentiation of antimicrobial activity via activation of "latent" host factors in human blood may have important therapeutic implications for durable improvements in clinical outcomes of serious antibiotic-resistant staphylococcal infections.

Tiotropium induced bronchodilation and protection from dynamic hyperinflation is independent of extent of emphysema in COPD.

BACKGROUND: The magnitude of tiotropium (1) induced bronchodilation and (2) protection against dynamic hyperinflation in COPD phenotypes has not been studied. METHODS: We studied moderate to severe COPD patients with varying extent of emphysema as evaluated by high-resolution thin-section lung CT. Spirometry including inspiratory capacity (IC) was measured before and immediately after metronome paced hyperventilation (MPH) at 2 times resting respiratory rate for 20s to induce dynamic hyperinflation. Spirometry was obtained at baseline and pre- and 1.5h post-18 microg tiotropium via HandiHaler after 30 day tiotropium treatment period in a single blind, open label intervention. RESULTS: In 29 COPD patients (15M), age 70+/-9 years (mean+/-SD) with smoking history of 53+/-37 pack years, baseline forced expiratory volume in 1s (FEV(1)) post-180 microg albuterol MDI was 1.6+/-0.4 L (61+/-8% predicted) and FEV(1)/FVC 59+/-6%. Lung CT emphysema score (LCTES) was 23+/-20 (mean+/-SD) on a scale of 0-100 (none to most severe emphysema). After 30-day tiotropium, FEV(1) increased 101+/-124 mL (mean+/-SD) (p<0.001) and Spearman correlation (r)=-0.04, p=0.8 with LCTES; IC increased 163+/-232 mL (p<0.001), and r=-0.2, p=0.3 with LCTES. Results following MPH induced DH before and after 30-day tiotropium were significant (p<0.001) and similar: IC decreased 340+/-280 mL before and 337+/-270 mL after tiotropium, and r=-0.3, p=0.9 with LCTES. CONCLUSION: Tiotropium significantly increased FEV(1) (L) and inspiratory capacity in moderate-severe COPD, independent of extent of lung CT emphysema score. Despite bronchodilation and lower resting lung volume, tiotropium did not abbreviate induced dynamic hyperinflation, which was also independent of underlying emphysema.