Hybrid Hydrogels for Synergistic Periodontal Antibacterial Treatment with Sustained Drug Release and NIR-Responsive Photothermal Effect.

BACKGROUND: Periodontal pathogenic bacteria promote the destruction of periodontal tissues and cause loosening and loss of teeth in adults. However, complete removal of periodontal pathogenic bacteria, at both the bottom of the periodontal pocket and the root bifurcation area, remains challenging. In this work, we explored a synergistic antibiotic and photothermal treatment, which is considered an alternative strategy for highly efficient periodontal antibacterial therapy. METHODS: Mesoporous silica (MSNs) on the surface of Au nanobipyramids (Au NBPs) were designed to achieve the sustained release of the drug and photothermal antibacterials. The mesoporous silica-coated Au NBPs (Au NBPs@SiO2) were mixed with gelatin methacrylate (GelMA-Au NBPs@SiO2). Au NBPs@SiO2 and GelMA-Au NBPs@SiO2 hybrid hydrogels were characterized, and the drug content and photothermal properties in terms of the release profile, bacterial inhibition, and cell growth were investigated. RESULTS: The GelMA-Au NBPs@SiO2 hybrid hydrogels showed controllable minocycline delivery, and the drug release rates increased under 808 nm near-infrared (NIR) light irradiation. The hydrogels also exhibited excellent antibacterial properties, and the antibacterial efficacy of the antibiotic and photothermal treatment was as high as 90% and 66.7% against Porphyromonas gingivalis (P. gingivalis), respectively. Moreover, regardless of NIR irradiation, cell viability was over 80% and the concentration of Au NBPs@SiO2 in the hybrid hydrogels was as high as 100 µg/mL. CONCLUSION: We designed a new near-infrared light (NIR)-activated hybrid hydrogel that offers both sustained release of antibacterial drugs and photothermal treatment. Such sustained release pattern yields the potential to rapidly eliminate periodontal pathogens in the periodontal pocket, and the photothermal treatment maintains low bacterial retention after the drug treatment.

Use of Monte Carlo simulation to evaluate the efficacy of tigecycline and minocycline for the treatment of pneumonia due to carbapenemase-producing Klebsiella pneumoniae.

BACKGROUND: Pneumonia caused by carbapenemase-producing Klebsiella pneumoniae (CP-KP) are increasingly encountered in hospitals worldwide, causing high mortality due to lack of treatment options. The goal of this study was to assess the efficacy of tigecycline and minocycline for CP-KP hospital-acquired pneumonia (HAP) by using Monte Carlo simulation. METHODS: A total of 164 non-duplicated CP-KP strains were collected from sputum or blood in patients with HAP. The MICs for antimicrobials were determined by the agar dilution method. A 10,000-patient Monte Carlo Simulation based on a PK/PD model incorporating the MICs and population pharmacokinetic parameters were conducted to calculate probability of target attainment (PTA) at each MIC value and total cumulative fraction of response (CFR). RESULTS: The susceptibility rate of tigecycline and minocycline were 79.9% and 41.5%, respectively. At recommended doses, an optimal PTA of 90% was obtained for treating HAP caused by CP-KP with MICs of tigecycline ≤0.5 mg/L or minocycline ≤4 mg/L. The CFR of tigecycline at the recommended dose and double dose (100 mg q12h) were 71.2% and 90.2%, respectively. The CFR of minocycline at recommended dose and double dose (200 mg q12h) was 53.4% and 77.2%, respectively. CONCLUSIONS: The findings of this study suggest that the recommended dose of tigecycline was not effective in HAP caused by CP-KP, and a higher CFR indicating a better clinical efficacy can be gained by doubling the dose (100 mg q12h). minocycline (200 mg q12h) might be a potential alternative of tigecycline to against strains with MICs ≤ 8 mg/L.

Intraventricular administration of tigecycline for the treatment of multidrug-resistant bacterial meningitis after craniotomy: a case report.

BACKGROUND: Intracranial infections, especially multidrug-resistant (MDR) bacterial meningitis, are one of the most severe complications after craniotomy and may greatly impact patient outcomes. CASE PRESENTATION: We report a case of severe MDR Klebsiella pneumonia meningitis after craniotomy that was treated with three different dosages of tigecycline (Pfizer, New York, NY, U.S.A.)via a combined intravenous (IV) and intracerebroventricular (ICV) administration. Here, we discuss the pharmacokinetics (PK) of a combined IV and ICV tigecycline administration for a patient with an intracranial infection after craniotomy. CONCLUSION: In the present case, three different dosages of tigecycline were administered: 49 mg IV plus 1 mg ICV q12 h, 45 mg IV plus 5 mg ICV q12 h, 40 mg IV plus 10 mg ICV q12 h. The combined IV and ICV administration might improve CSF tigecycline concentrations, and in this case, the methods of administration were safe and effective.

Population Pharmacokinetics of Tigecycline in Critically Ill Patients with Severe Infections.

We sought to describe the population pharmacokinetics of tigecycline in critically ill patients and to determine optimized dosing regimens of tigecycline for different bacterial infections. This prospective study included 10 critically ill patients given a standard dose of tigecycline. Blood samples were collected during one dosing interval and were analyzed using validated chromatography. Population pharmacokinetics and Monte Carlo dosing simulations were undertaken using Pmetrics. Three target exposures, expressed as ratios of the 24-h area under the curve to MICs (AUC0-24/MIC), were evaluated (≥17.9 for skin infections, ≥6.96 for intra-abdominal infections, ≥4.5 for hospital-acquired pneumonia). The median age, total body weight, and body mass index (BMI) were 67 years, 69.1 kg, and 24.7 kg/m2, respectively. A two-compartment linear model best described the time course of tigecycline concentrations. The parameter estimates (expressed as means ± standard deviations [SD]) from the final model were as follows: clearance (CL), 7.50 ± 1.11 liters/h; volume in the central compartment, 72.50 ± 21.18 liters; rate constant for tigecycline distribution from the central to the peripheral compartment, 0.31 ± 0.16 h-1; and rate constant for tigecycline distribution from the peripheral to the central compartment, 0.29 ± 0.30 h-1 A larger BMI was associated with increased CL of tigecycline. Licensed doses were found to be sufficient for Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, and methicillin-resistant Staphylococcus aureus for an AUC0-24/MIC target of 4.5 or 6.96. For a therapeutic target of 17.9, an increased tigecycline dose is required, especially for patients with higher BMI. The dosing requirements of tigecycline differ with the indication, with pathogen susceptibility, and potentially with patient BMI.

Pharmacokinetics and Pharmacodynamics of Minocycline against Acinetobacter baumannii in a Neutropenic Murine Pneumonia Model.

Multidrug-resistant (MDR) Acinetobacter baumannii is increasingly more prevalent in nosocomial infections. Although in vitro susceptibility of A. baumannii to minocycline is promising, the in vivo efficacy of minocycline has not been well established. In this study, the in vivo activity of minocycline was evaluated in a neutropenic murine pneumonia model. Specifically, we investigated the relationship between minocycline exposure and bactericidal activity using five A. baumannii isolates with a broad range of susceptibility (MIC ranged from 0.25 mg/liter to 16 mg/liter). The pharmacokinetics of minocycline (single dose of 25 mg/kg of body weight, 50 mg/kg, 100 mg/kg, and a humanized regimen, given intraperitoneally) in serum and epithelial lining fluid (ELF) were characterized. Dose linearity was observed for doses up to 50 mg/kg and pulmonary penetration ratios (area under the concentration-time curve in ELF from 0 to 24 h [AUCELF,0-24]/area under the concentration time curve in serum from 0 to 24 h [AUCserum,0-24]) ranged from 2.5 to 2.8. Pharmacokinetic-pharmacodynamics (PK-PD) index values in ELF for various dose regimens against different A. baumannii isolates were calculated. The maximum efficacy at 24 h was approximately 1.5-log-unit reduction of pulmonary bacterial burdens from baseline. The AUC/MIC ratio was the PK-PD index most closely correlating to the bacterial burden (r2 = 0.81). The required AUCELF,0-24/MIC for maintaining stasis and achieving 1-log-unit reduction were 140 and 410, respectively. These findings could guide the treatment of infections caused by A. baumannii using minocycline in the future. Additional studies to examine resistance development during therapy are warranted.

A Monte Carlo pharmacokinetic/pharmacodynamic simulation to evaluate the efficacy of minocycline, tigecycline, moxifloxacin, and levofloxacin in the treatment of hospital-acquired pneumonia caused by Stenotrophomonas maltophilia.

BACKGROUND: Stenotrophomonas maltophilia has emerged as an important opportunistic pathogen in recent years. Increasing antimicrobial resistance and other contraindications have greatly compromised trimethoprim/sulfamethoxazole (SXT) as the first-line therapeutic option. The objective of this study was to explore other options for treating hospital-acquired pneumonia (HAP) caused by S. maltophilia. METHODS: A total of 102 strains of S. maltophilia were isolated from sputum and bronchoalveolar lavage (BAL) specimens of patients with HAP in our institution. The minimum inhibitory concentration (MIC) values of minocycline, tigecycline, moxifloxacin, and levofloxacin were determined by the agar dilution method. Based on the MICs and the population pharmacokinetic parameters of the investigated antimicrobials, a Monte Carlo simulation was performed to simulate the pharmacokinetic/pharmacodynamic (PK/PD) indices of different regimens. The probability of target attainment (PTA) was estimated at each MIC value and the cumulative fraction of response (CFR) was calculated to evaluate the efficacy of these regimens. RESULTS: The susceptibility rates to minocycline, tigecycline, moxifloxacin, and levofloxacin were 96.1%, 80.4%, 74.5%, and 69.6%, respectively. The estimated CFRs were 96.2% for minocycline 100 mg twice daily; 50.8%/67.1%/75.4% for tigecycline 50/75/100 mg twice daily; 34.3%/48.0%/56.6% for levofloxacin 500/750/1000 mg once daily; and 45.7% for moxifloxacin 400 mg once daily. CONCLUSIONS: The simulation results suggest that minocycline may be a proper choice for treatment of HAP caused by S. maltophilia, while tigecycline, moxifloxacin, and levofloxacin may not be optimal as monotherapy.

Antimicrobial Effects of Novel Triple Antibiotic Paste-Mimic Scaffolds on Actinomyces naeslundii Biofilm.

INTRODUCTION: Actinomyces naeslundii has been recovered from traumatized permanent teeth diagnosed with necrotic pulps. In this work, a triple antibiotic paste (TAP)-mimic scaffold is proposed as a drug-delivery strategy to eliminate A. naeslundii dentin biofilm. METHODS: Metronidazole, ciprofloxacin, and minocycline were added to a polydioxanone (PDS) polymer solution and spun into fibrous scaffolds. Fiber morphology, mechanical properties, and drug release were investigated by using scanning electron microscopy, microtensile testing, and high-performance liquid chromatography, respectively. Human dentin specimens (4 × 4 × 1 mm(3), n = 4/group) were inoculated with A. naeslundii (ATCC 43146) for 7 days for biofilm formation. The infected dentin specimens were exposed to TAP-mimic scaffolds, TAP solution (positive control), and pure PDS (drug-free scaffold). Dentin infected (7-day biofilm) specimens were used for comparison (negative control). Confocal laser scanning microscopy was done to determine bacterial viability. RESULTS: Scaffolds displayed a submicron mean fiber diameter (PDS = 689 ± 312 nm and TAP-mimic = 718 ± 125 nm). Overall, TAP-mimic scaffolds showed significantly (P ≤ .040) lower mechanical properties than PDS. Within the first 24 hours, a burst release for all drugs was seen. A sustained maintenance of metronidazole and ciprofloxacin was observed over 4 weeks, but not for minocycline. Confocal laser scanning microscopy demonstrated complete elimination of all viable bacteria exposed to the TAP solution. Meanwhile, TAP-mimic scaffolds led to a significant (P < .05) reduction in the percentage of viable bacteria compared with the negative control and PDS. CONCLUSIONS: Our findings suggest that TAP-mimic scaffolds hold significant potential in the eradication/elimination of bacterial biofilm, a critical step in regenerative endodontics.

A pharmacodynamic simulation to evaluate tigecycline in treatment of nosocomial pneumonia caused by multidrug-resistant Acinetobacter baumannii.

The shortage of effective antibiotics against multidrug-resistant Acinetobacter baumannii (MDR-Ab) has posed great threat to the public health. But the advent of tigecycline gives us new hope. The goal of our research was to assess the clinical efficacy of tigecycline at different doses by using a pharmacokinetic/pharmacodynamic (PK/PD) model which can incorporate pharmacokinetic data of tigecycline from patients with pneumonia and MICs of MDR-Ab from a tertiary hospital. A 10000-patient Monte-Carlo Simulation based on the PK/PD model was conducted to calculate the probability of target attainment (PTA) and the cumulative fraction of response (CFR) of tigecycline. 97% isolates displayed susceptibility and 3% were tigecycline-intermediate strains and the values of MIC ranged from 0.125 to 4 µ g/ml. A CFR of 61.62% was predicted for tigecycline at current dosage (50 mg q12h). When the dosage was increased, the predicted CFRs for 75 mg q12h, 100 mg q12h, 125 mg q12h, 150 mg q12h were 81.00%, 89.86%, and 94.57%, 96.77%, respectively. Despite presented higher susceptibility, the CFR obtained was not optimal at current dosage. A higher CFR indicating a better clinical efficacy can be gained by the increased dosage.

Effectiveness and safety of high-dose tigecycline-containing regimens for the treatment of severe bacterial infections.

Here we review the effectiveness and safety of high-dose tigecycline (200mg daily). A systematic search was performed in PubMed and Scopus databases as well as of abstracts presented at scientific conferences. Eight studies (263 patients; 58% critically ill) were included, comprising one randomised controlled trial (RCT), four non-randomised cohorts and three case reports. Klebsiella pneumoniae was the most commonly isolated pathogen (reported in seven studies). In the RCT, response in the clinically evaluable patients was 85.0% (17/20) in the 100mg every 12h (q12h) group and 69.6% (16/23) in the 75mg q12h group (P=0.4). More episodes of diarrhoea, treatment-related nausea and vomiting developed in the high-dose group (14.3% vs. 2.8%, 8.6% vs. 2.8% and 5.7% vs. 2.8%, respectively; P>0.05 for all comparisons). Three (8.6%) and 7 (19.6%) patients died in the 200mg and 150mg daily dose groups, respectively. The cohort studies enrolled patients with severe infections, including ventilator-associated pneumonia and complicated intra-abdominal infections. Mortality with high-dose tigecycline (100mg q12h) in the cohort studies ranged from 8.3% to 26%; mortality in the low-dose groups (50mg q12h) ranged from 8% to 61% and depended on the severity of the underlying infection. There are limited available data regarding the effectiveness and safety of high-dose tigecycline. Most of the data come from critically ill patients with difficult-to-treat infections. Pharmacokinetic/pharmacodynamic properties of tigecycline suggest that high-dose regimens may be more effective than low-dose regimens. Candidates for administration of high-dose tigecycline should be also defined.

The therapeutic effect of tigecycline, unlike that of Ceftazidime, is not influenced by whether the Klebsiella pneumoniae strain produces extended-spectrum ß-lactamases in experimental pneumonia in rats.

The efficacies of tigecycline and ceftazidime against fatal pneumonia in rats caused by an extended-spectrum ß-lactamase (ESBL)-positive Klebsiella pneumoniae strain or its wild-type (WT) progenitor were compared. Ceftazidime at 12.5 or 50 mg/kg of body weight twice daily (b.i.d.) was effective (50% or 100% rat survival) in pneumonia caused by the WT isolate but unsuccessful (100% rat mortality) in pneumonia caused by the ESBL-positive variant. In contrast, tigecycline at 6.25, 12.5, or 25 mg/kg b.i.d. showed dosage-dependent efficacy up to 100% rat survival irrespective of the ESBL character of the infecting organism.

Pharmacokinetic-pharmacodynamic evaluation of daptomycin, tigecycline, and linezolid versus vancomycin for the treatment of MRSA infections in four western European countries.

PURPOSE: To evaluate the usefulness of daptomycin, tigecycline, and linezolid for the treatment of MRSA infection compared with vancomycin in Belgium, the United Kingdom/Ireland, and Spain. METHODS: The methodology included the following steps: acquisition of microbiological and pharmacokinetic data, Monte Carlo simulation, estimation of the probability of target attainment (PTA), and calculation of the cumulative fraction of response (CFR). RESULTS: We showed that differences in the susceptibility of MRSA strains among countries may justify differences in the antibiotic dose selection. Two, 3, and 4 g daily of vancomycin seem be adequate in Belgium, Spain, and United Kingdom/Ireland respectively. The CFR obtained with 50 mg tigecycline every 12 h was higher in Spain than in Belgium and the United Kingdom/Ireland, but with the highest dose (100 mg q12h) the CFR was always 100%. At least 8 mg/kg daptomycin is necessary in United Kingdom/Ireland, but 4 mg/kg may be sufficient in Spain, and probably in Belgium. Six hundred mg q12h linezolid may be adequate in the four countries. CONCLUSION: Our study reinforces the idea that the local MIC distribution must be considered in order to increase the probability of success of empirical treatment and must be periodically updated.

Efficacies of colistin and tigecycline in mice with experimental pneumonia due to NDM-1-producing strains of Klebsiella pneumoniae and Escherichia coli.

New Delhi metallo-ß-lactamase-1 (NDM-1)-producing Enterobacteriaceae have emerged as a global threat. The aim of this study was to assess the efficacies of colistin and tigecycline in an experimental model of pneumonia caused by NDM-1-producing Escherichia coli and Klebsiella pneumoniae. The susceptibilities of K. pneumoniae NDM, E. coli NDM and K. pneumoniae ATCC 29665 were determined using the broth microdilution technique. The pharmacokinetics of colistin and tigecycline in an experimental model of pneumonia were performed using immunocompetent C57BL/6 mice. Mice were treated with colistin (60 mg/kg/day) or tigecycline (10 mg/kg/day). Mortality, bacteraemia and lung bacterial concentrations were recorded. The strains were susceptible to colistin and tigecycline. The ratio of area under the concentration-time curve/minimum inhibitory concentration (AUC/MIC) for colistin was 158.5 (all three strains) and that for tigecycline was 18.5 (K. pneumoniae NDM) and 37 (K. pneumoniae ATCC 29665 and E. coli NDM). In vivo, colistin decreased bacterial lung concentrations of K. pneumoniae NDM and K. pneumoniae ATCC 29665 by 1.16 log colony-forming units (CFU)/g and 2.23 logCFU/g, respectively, compared with controls (not significant). Tigecycline reduced K. pneumoniae NDM and K. pneumoniae ATCC 29665 load by 2.67 logCFU/g and 4.62 logCFU/g (P<0.05). Colistin and tigecycline decreased lung concentrations of E. coli NDM by 2.27 logCFU/g and 4.15 logCFU/g (P<0.05), respectively, compared with controls, and was more active than colistin (P<0.05). In conclusion, these results suggest that colistin is inappropriate for treating pneumonia due to NDM-1-producing K. pneumoniae and its efficacy was suboptimal against NDM-1-producing E. coli. A high tigecycline dose was efficacious for treating experimental pneumonia due to NDM-1-producing E. coli and K. pneumoniae.

Pharmacological and patient-specific response determinants in patients with hospital-acquired pneumonia treated with tigecycline.

Pharmacokinetic and clinical data from tigecycline-treated patients with hospital-acquired pneumonia (HAP) who were enrolled in a phase 3 clinical trial were integrated in order to evaluate pharmacokinetic-pharmacodynamic (PK-PD) relationships for efficacy. Univariable and multivariable analyses were conducted to identify factors associated with clinical and microbiological responses, based on data from 61 evaluable HAP patients who received tigecycline intravenously as a 100-mg loading dose followed by 50 mg every 12 h for a minimum of 7 days and for whom there were adequate clinical, pharmacokinetic, and response data. The final multivariable logistic regression model for clinical response contained albumin and the ratio of the free-drug area under the concentration-time curve from 0 to 24 h (fAUC(0-24)) to the MIC (fAUC(0-24):MIC ratio). The odds of clinical success were 13.0 times higher for every 1-g/dl increase in albumin (P < 0.001) and 8.42 times higher for patients with fAUC(0-24):MIC ratios of ≥0.9 compared to patients with fAUC(0-24):MIC ratios of <0.9 (P = 0.008). Average model-estimated probabilities of clinical success for the albumin/fAUC(0-24):MIC ratio combinations of <2.6/<0.9, <2.6/≥0.9, ≥2.6/<0.9, and ≥2.6/≥0.9 were 0.21, 0.57, 0.64, and 0.93, respectively. For microbiological response, the final model contained albumin and ventilator-associated pneumonia (VAP) status. The odds of microbiological success were 21.0 times higher for every 1-g/dl increase in albumin (P < 0.001) and 8.59 times higher for patients without VAP compared to those with VAP (P = 0.003). Among the remaining variables evaluated, the MIC had the greatest statistical significance, an observation which was not surprising given the differences in MIC distributions between VAP and non-VAP patients (MIC(50)and MIC(90) values of 0.5 and 0.25 mg/liter versus 16 and 1 mg/liter for VAP versus non-VAP patients, respectively; P = 0.006). These findings demonstrated the impact of pharmacological and patient-specific factors on the clinical and microbiological responses.

Efficacy of tigecycline alone and with rifampin in foreign-body infection by methicillin-resistant Staphylococcus aureus.

OBJECTIVES: Tigecycline appears as an alternative therapy against methicillin-resistant Staphylococcus aureus (MRSA) with limited clinical experience. We evaluate the efficacy of tigecycline and its combination with rifampin in comparison to that for vancomycin in a rat model of foreign-body infection by MRSA. METHODS: A tissue-cage infection model were used; therapy with tigecycline, vancomycin, rifampin, tigecycline plus rifampin and vancomycin plus rifampin was administered intraperitoneally for 7 days. The antibiotic efficacy was evaluated in the tissue-cage fluid and in the coverslips (attached bacteria); the emergence of resistance was screened. RESULTS: Among monotherapies rifampin was the best treatment (decrease in log CFU/ml of tissue-cage fluid, 2.75) (P < 0.05). The addition of rifampin improved the efficacy of vancomycin (decrease, 2.28) and tigecycline (decrease, 1.56) in solitary; there were not significantly differences between tigecycline-rifampin (decrease, 3.39) and vancomycin-rifampin (decrease, 3.70), but only the latter was better than rifampin alone (P < 0.05). Resistant strains were only detected using rifampin alone. CONCLUSIONS: tigecycline alone was the least effective treatment. Tigecycline-rifampin prevented the emergence of rifampin resistance, thus allowing the benefits of rifampin over time against staphylococcal foreign-body infections, but its efficacy needs to be evaluated in comparison with other anti-MRSA combined therapies.

Tigecycline for the treatment of severe Clostridium difficile infection.

OBJECTIVE: To evaluate the evidence for the use of tigecycline in the treatment of Clostridium difficile infection (CDI). DATA SOURCES: Searches were performed (2004 to June 2011), using the EMBASE and MEDLINE databases, with the terms tigecycline, Tygacil, Clostridium difficile, C. difficile, Clostridium difficile infection, and CDI. STUDY SELECTION: Six case reports that described the use of tigecycline for treatment of CDI were included for review. No clinical trials were identified. DATA SYNTHESIS: In all case reports except 1, tigecycline (alone or in combination with other CDI therapies) was used for the treatment of CDI that was refractory to metronidazole and/or vancomycin. In 6 of the cases, treatment success was reported following initiation of tigecycline therapy; 1 patient died following a complicated hospitalization. The treatment duration with tigecycline was 2-4 weeks. In the cases with successful outcomes, symptoms began to improve within 1 week. None of these patients experienced recurrence during follow-up of various lengths. In vitro studies demonstrated a 90% minimum inhibitory concentration range for tigecycline of 0.016-0.25 mg/L for all C. difficile isolates. Tigecycline exhibited good fecal penetration because of primary biliary excretion of unchanged drug. Up to 59% of the dose is recovered in feces following administration over 4 days in healthy volunteers. CONCLUSIONS: Case reports have suggested that tigecycline may be successful for treatment of severe or severe complicated CDI, when prior therapy has failed. Data demonstrating tigecycline use as initial therapy for CDI are limited; therefore, this option should be reserved for patients in whom other therapeutic options, including metronidazole and vancomycin, have failed. A randomized controlled trial is needed to assess the safety and efficacy of tigecycline in this patient population and better define the drug's role in the treatment of CDI.

Comparison of tigecycline with imipenem/cilastatin for the treatment of hospital-acquired pneumonia.

To compare efficacy and safety of a tigecycline regimen with an imipenem/cilastatin regimen in hospital-acquired pneumonia patients, a phase 3, multicenter, randomized, double-blind, study evaluated 945 patients. Coprimary end points were clinical response in clinically evaluable (CE) and clinical modified intent-to-treat (c-mITT) populations at test-of-cure. Cure rates were 67.9% for tigecycline and 78.2% for imipenem (CE patients) and 62.7% and 67.6% (c-mITT patients), respectively. A statistical interaction occurred between ventilator-associated pneumonia (VAP) and non-VAP subgroups, with significantly lower cure rates in tigecycline VAP patients compared to imipenem; in non-VAP patients, tigecycline was noninferior to imipenem. Overall mortality did not differ between the tigecycline (14.1%) and imipenem regimens (12.2%), although more deaths occurred in VAP patients treated with tigecycline than imipenem. Overall, the tigecycline regimen was noninferior to the imipenem/cilastatin regimen for the c-mITT but not the CE population; this difference appears to have been driven by results in VAP patients.

Guideline: appropriate use of tigecycline.

INTRODUCTION: Tigecycline, the first of a new class of antibiotics, the glycylcyclines, was licensed in South Africa for the parenteral treatment of adult patients with complicated intra-abdominal infections (cIAIs) and complicated skin and soft-tissue infections (cSSTIs). METHODS: A multidisciplinary meeting representative of the Association of Surgeons of South Africa, the Critical Care Society of Southern Africa, the Federation of Infectious Diseases Societies of Southern Africa, the South African Thoracic Society and the Trauma Society of South Africa was held to draw up a national guideline for the appropriate use of tigecycline. Background information reviewed included randomised controlled trials, other relevant publications and local antibiotic susceptibility patterns. The initial document was drafted at the meeting. Subsequent drafts were circulated to members of the working group for modification. OUTPUT: The guideline addresses several important aspects of the new agent, summarising key clinical data and highlighting important considerations with the use of the drug. The recommendations in this guideline are based on currently available scientific evidence together with the consensus opinion of the authors. CONCLUSION: This statement was written out of concern regarding the widespread misuse of antibiotics. Its primary intention is to facilitate heterogeneous use of antibiotics as a component of antibiotic stewardship and to highlight the appropriate use of tigecycline in particular.

Pharmacodynamic evaluation of tigecycline against Acinetobacter baumannii in a murine pneumonia model.

OBJECTIVES: Tigecycline is an extended-spectrum antibiotic with activity against Acinetobacter spp. (ACB), an increasingly common cause of nosocomial pneumonia. Although this compound is under investigation for this indication, supportive pharmacodynamic data are not yet available at this infection site. The objective of this study was to characterize the exposure-response relationship of tigecycline with ACB in an established murine pneumonia model. METHODS: The pharmacokinetic profile of tigecycline was evaluated in infected neutropenic mice. Tigecycline 6.25, 12.5, 25, 50, 100, 200, 300 and 400 mg/kg, in single or two to six divided subcutaneous doses, were tested against all ACB isolates. Efficacy, defined as the log(10) change in bacterial cfu/mL, was assessed after a 24 h course of therapy. Tigecycline exposures in serum were corrected for dose-specific protein binding. The relationship between the area under the free concentration-time curve to MIC (fAUC/MIC) and change in bacterial density was determined using the sigmoid E(max) model. RESULTS: Tigecycline displayed linear pharmacokinetics with a mean half-life of 11.3 +/- 1.4 h. Efficacy correlated well with fAUC/MIC (R(2) = 0.96). The mean 80%, 50% effective and stasis exposures (fAUC/MIC) were 17, 8 and 6, respectively. Maximal efficacy for the five Acinetobacter baumannii studied was 3.4 log kill. CONCLUSIONS: Tigecycline efficacy in this murine ACB pneumonia model was well predicted by fAUC/MIC. Requisite tigecycline exposures for efficacy appear to be higher for ACB pneumonia than for other pathogens reported of non-respiratory infections.

Pharmacodynamics of tigecycline against phenotypically diverse Staphylococcus aureus isolates in a murine thigh model.

Tigecycline is a currently marketed antimicrobial agent with activity against resistant gram-positive cocci, including methicillin-resistant Staphylococcus aureus (MRSA). Despite the proven efficacy of tigecycline in the treatment of infections caused by these pathogens, questions remain as to the exposure-response relationship best associated with its efficacy. The purpose of this study was to define this relationship against seven distinct S. aureus isolates by using a neutropenic murine thigh model. Single-dose pharmacokinetics were evaluated, and free drug exposures were calculated after determination of protein binding. Doses of 1.56 to 400 mg/kg of body weight divided 1 to 8 times daily were administered against two methicillin-susceptible S. aureus isolates, two hospital-associated MRSA (HA-MRSA) isolates, and three community-associated (CA-MRSA) isolates. Tigecycline pharmacokinetics were best described by a two-compartment model, with a mean half-life of 9.9 h. Protein binding was dose dependent (range, 92.9 to 81.2%). MICs were 0.25 microg/ml for all isolates, except for HA-MRSA 56 (MIC, 0.5 microg/ml) and CA-MRSA 156 (MIC, 0.125 microg/ml). Tigecycline displayed efficacy against all isolates, producing maximum decreases in log(10) numbers of CFU/ml of 1.8 to 2.3 from 0-h controls. Mean correlation coefficients for free-drug (f) concentration exposures derived from the parameters fT>MIC (the percentage of time during which the concentration of f remains above the MIC), fC(max)/MIC (the ratio of the maximum concentration of f to the MIC), and fAUC/MIC (the ratio of the area under the concentration-time curve of f to the MIC) were 0.622, 0.812, and 0.958, respectively. Values for the mean effective exposure index at 80% (EI(80)) and 50% (EI(50)) for fAUC/MIC were 5.4 microg/ml (range, 2.8 to 13 microg/ml) and 2.6 microg/ml (range, 0.6 to 5.1 microg/ml), respectively. Experiments with nonneutropenic mice infected with CA-MRSA 156 resulted in maximum kill at all fAUC/MIC exposures tested (1.8 to 8.8 microg/ml). The fAUC/MIC ratio is the pharmacodynamic parameter most predictive of tigecycline efficacy. Furthermore, the presence of a functioning immune system markedly reduces the required exposure.

Tigecycline in critical care.

The emergence and spread of multidrug resistance in many pathogenic bacterial species is increasing at an alarming rate, especially with hospital-acquired infections in the critical care setting. Deaths associated with hospital-acquired infections have exceeded the number attributable to several of the top 10 leading causes of death reported in the United States. The emerging resistance limits the use of older antibiotics. Tigecycline is a new agent, and this article explores its role in the treatment of adults in the critical care setting.