David Sevillano

Micafungin pharmacokinetic/pharmacodynamic adequacy for the treatment of invasive candidiasis in critically ill patients on continuous venovenous haemofiltration

OBJECTIVES To explore the pharmacokinetics (PK) and pharmacodynamics (PD) of micafungin in patients undergoing continuous venovenous haemofiltration (CVVH). PATIENTS AND METHODS Ten patients receiving CVVH treated with 100 mg/day micafungin were included (April-December 2012). CVVH was performed using polyethersulphone or polysulphone haemofilters. Dialysis membranes were not changed on sampling days. On Days 1 and 2, blood samples from arterial pre-filter and venous post-filter ports and ultrafiltrate samples were collected at the start and end of the infusion and at 3, 5, 8, 18 and 24 h. Concentrations were determined using HPLC. Values for the area under the concentration-time curve (AUC0-24) were calculated. Monte Carlo simulations were performed using pre-filter and post-filter AUC0-24/MIC ratios on Days 1 and 2. The probability of target attainment (PTA) was calculated using AUC0-24/MIC cut-offs: 285 (C. parapsilosis), 3000 (all Candida spp.) and 5000 (non-parapsilosis Candida spp.). Cumulative fraction responses (CFRs) were calculated using EUCAST MIC distributions. RESULTS Mean post-filter AUC0-24 (mg·h/L) values were higher than pre-filter values on Day 1 (83.31 ± 15.87 versus 71.31 ± 14.24; P = 0.008) and Day 2 (119.01 ± 27.20 versus 104.54 ± 21.23; P = 0.005). PTAs were ≥90% for MICs of 0.125 mg/L (cut-off = 285), 0.016 mg/L (cut-off = 3000) and 0.008 mg/L (cut-off = 5000) on Day 1, and for MICs of 0.25 mg/L (cut-off = 285) and 0.016 mg/L (cut-off = 3000 and 5000) on Day 2, without differences between pre- and post-filter values. On Day 2, CFRs >90% were obtained for C. albicans (cut-off = 3000 and 5000) and C. glabrata (cut-off = 3000), but not for C. parapsilosis. CONCLUSIONS There was no removal of micafungin by CVVH or need for dose adjustment, and there was optimal PK/PD coverage for non-parapsilosis Candida and equivalence of pre- and post-filter PD.

Influence of the MBC/MIC ratio on the antibacterial activity of vancomycin versus linezolid against methicillin-resistant Staphylococcus aureus isolates in a pharmacodynamic model simulating serum and soft tissue interstitial fluid concentrations reported in diabetic patients

OBJECTIVES To explore serum and tissue pharmacodynamics of linezolid versus vancomycin against methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates with different MBC/MIC ratios. METHODS Five strains (vancomycin MIC/MBCs, mg/L) were used: TOL-1 (2/≥64), TOL-2 (1/16), LT-1 and LT-2 (1/8) and NT (1/2). The linezolid MIC/MBC for all strains was 2/≥64 mg/L. A two-compartment dynamic computerized device was used (inocula 10(7) cfu/mL). Free concentrations obtained in serum and interstitial fluid with twice-daily regimens of 1 g of vancomycin or 600 mg of linezolid were simulated over 48 h. ABBCs (differences between control growth curves and killing curves of bacteria exposed to antibiotics; log10 cfu × h/mL) and log10 reductions in initial inocula were calculated. RESULTS In serum simulations, vancomycin (AUC0-24/MIC = 251.8 for TOL-1 and 503.6 for the remaining strains) was bacteriostatic against strains with MBC/MIC ≥8, but bactericidal against NT. In interstitial fluid simulations (AUC0-24/MIC = 54.6 for TOL-1 and 109.2 for the remaining strains), initial inocula grew in all cases. Linezolid, both in serum (AUC0-24/MIC = 87.0) and in interstitial fluid (AUC0-24/MIC = 130.6) simulations, reduced initial inocula ≥2.2 log10 for all strains (apart from LT-1 in serum simulations that showed a bacteriostatic profile). ABBCs were similar in serum and interstitial fluid with linezolid, but significantly lower in interstitial fluid simulations with vancomycin. CONCLUSIONS From the pharmacodynamic perspective (serum concentrations), vancomycin tolerance should include MBC/MIC ≥8 since strains exhibiting this ratio showed bacteriostatic profiles similar to those obtained with isolates with MBC/MIC ratios of 16 or 32. Insufficient concentrations of vancomycin at the simulated infected site were linked to bacteriological failure. Free concentrations of linezolid at the infection site pharmacodynamically covered MRSA.

Inhibitory Effect on In Vitro Streptococcus oralis Biofilm of a Soda-Lime Glass Containing Silver Nanoparticles Coating on Titanium Alloy

This paper reports the effect of soda-lime-glass-nAg coating on the viability of an in vitro biofilm of Streptococcus oralis. Three strains (ATCC 35037 and two clinical isolates from periodontitis patients) were grown on coated with glass, glass containing silver nanoparticles, and uncoated titanium alloy disks. Two different methods were used to quantify biofilm formation abilities: crystal violet staining and determination of viable counts. The influence of the surface morphology on the cell attachment was studied. The surface morphology was characterized by scanning electron microscopy (SEM) and using a profilometer. SEM was also used to study the formation and the development of biofilm on the coated and uncoated disks. At least a >99.7% inocula reduction of biofilm respect to titanium disks and also to glass coated disks was observed in the glass-nAg coated disks for all the studied strains. A quantitative evaluation of the release of silver was conducted in vitro to test whether and to what extend the biocidal agent (silver) could leach from the coating. These findings suggest that the biofilm formation of S. oralis strains is highly inhibited by the glass-nAg and may be useful for materials which require durable antibacterial effect on their surfaces, as it is the case of dental implants.

Exposure–response analysis of tigecycline in pharmacodynamic simulations using different size inocula of target bacteria

This study explored tigecycline exposure-bacterial responses in pharmacodynamic simulations (in vitro kinetic model) using different inocula. One meticillin-resistant vancomycin-heteroresistant Staphylococcus aureus, one Enterococcus faecium and one extended-spectrum beta-lactamase-producing Escherichia coli with equal tigecycline minimum inhibitory concentrations/minimum bactericidal concentrations (MICs/MBCs) (0.12/0.25 microg/mL) were used. A computerised pharmacodynamic bicompartmental model simulated three tigecycline twice-daily dosing regimens over 48h: 50mg (100mg loading dose); 100mg; and 150 mg. Areas under bacterial growth curves were calculated, and differences between the growth curve used as control and the killing curve of bacteria exposed to tigecycline (ABBC) were determined. With standard inocula [ca. 1 x 10(6)colony-forming units (CFU)/mL], linear increases in area under the concentration-time curve (AUC)/MIC (25.6 for 50mg, 53.76 for 100mg and 79.52 for 150 mg) produced linear increases in activity against Gram-positive organisms (mean ABBCs of 120.60, 143.20 and 195.80 log CFU x h/mL for S. aureus and of 95.75, 172.55 and 216.90 log CFUxh/mL for E. faecium, respectively), with the activity of the 150 mg regimen being significantly higher (P<0.01) than that of the other two regimens. ABBCs obtained with the 100mg regimen using standard inocula were similar to those obtained with the 150 mg regimen when using high inocula (ca. 1 x 10(7)CFU/mL). Against E. coli, the highest dosing regimen was required to obtain significant antibacterial activity compared with control (mean ABBCs of 145.75 log CFU x h/mL with standard inocula and 63.33 log CFU x h/mL with high inocula). An increase in tigecycline dosing appears to be an interesting therapeutic option to maximise antibacterial activity owing to its linear pharmacokinetics and pharmacodynamics, especially when severe infections with high bacterial load are suspected.

β-Lactam Effects on Mixed Cultures of Common Respiratory Isolates as an Approach to Treatment Effects on Nasopharyngeal Bacterial Population Dynamics

Background Streptococcus pneumoniae, Streptococcus pyogenes and Haemophilus influenzae are bacteria present in the nasopharynx as part of normal flora. The ecological equilibrium in the nasopharynx can be disrupted by the presence of antibiotics. Methodology/Principal Findings A computerized two-compartment pharmacodynamic model was used to explore β-lactam effects on the evolution over time of a bacterial load containing common pharyngeal isolates by simulating free serum concentrations obtained with amoxicillin (AMX) 875 mg tid, amoxicillin/clavulanic acid (AMC) 875/125 mg tid and cefditoren (CDN) 400 mg bid regimens over 24 h. Strains and MICs (µg/ml) of AMX, AMC and CDN were: S. pyogenes (0.03, 0.03 and 0.015), S. pneumoniae (2, 2 and 0.25), a β-lactamase positive H. influenzae (BL+; >16, 2 and 0.06) and a β-lactamase positive AMC-resistant H. influenzae (BLPACR, >16, 8 and 0.06). Mixture of identical 1∶1∶1∶1 volumes of each bacterial suspension were prepared yielding an inocula of ≈4×106 cfu/ml. Antibiotic concentrations were measured both in bacterial and in bacteria-free antibiotic simulations. β-lactamase production decreased AMX concentrations and fT>MIC against S. pneumoniae (from 43.2% to 17.7%) or S. pyogenes (from 99.9% to 24.9%), and eradication was precluded. The presence of clavulanic acid countered this effect of co-pathogenicity, and S. pyogenes (but not BL+ and S. pneumoniae) was eradicated. Resistance of CDN to TEM β-lactamase avoided this co-pathogenicity effect, and CDN eradicated S. pyogenes and H. influenzae strains (fT>MIC >58%), and reduced in 94% S. pneumoniae counts (fT>MIC ≈25%). Conclusions/Significance Co-pathogenicity seems to be gradual since clavulanic acid countered this effect for strains very susceptible to AMX as S. pyogenes but not for strains with AMX MIC values in the limit of susceptibility as S. pneumoniae. There is a potential therapeutic advantage for β-lactamase resistant cephalosporins with high activity against streptococci.

Enhanced In Vivo Activity of Cefditoren in Pre-Immunized Mice against Penicillin-Resistant S. pneumoniae (Serotypes 6B, 19F and 23F) in a Sepsis Model

Background Specific antibodies are likely to be present before S. pneumoniae infection. We explored cefditoren (CDN) total and free values of serum concentrations exceeding the MIC (t>MIC) related to efficacy in a mice sepsis model, and the effect of specific gammaglobulins on in-vitro phagocytosis and in-vivo efficacy. Methodology/Principal Findings We used three pneumococcal isolates (serotype, MIC of CDN): Strain 1 (6B, 1 µg/ml), Strain 2 (19F, 2 µg/ml) and Strain 3 (23F, 4 µg/ml). Hyperimmune serum (HS) was obtained from mice immunized with heat-inactivated strains. In-vitro, phagocytosis by HS diluted 1/10 in presence/absence of sub-inhibitory concentrations was measured by flow cytometry including fluorescent bacteria and a neutrophil cell line. In-vivo dose-ranging experiments with HS (dilutions 1/2–1/16) and CDN (6.25 mg/kg–100 mg/kg tid for 48 h) were performed to determine the minimal protective dilution/dose (highest survival) and the non-protective highest dilution/dose (highest mortality: HS-np dilution and CDN-np dose) over 7 days. Efficacy of CDN-np in animals pre-immunized with HS-np (combined strategy) was explored and blood bacterial clearance determined. The CDN measured protein binding was 86.9%. In-vitro, CDN significantly increased phagocytosis (vs. HS 1/10). In non pre-immunized animals, t>MIC values for CDN of ≈35% (total) and ≈19% (free) were associated with 100% survival. Significant differences in survival were found between HS-np alone (≤20%) or CDN-np alone (≤20%) vs. the combined strategy (90%, 60% and 60% for Stains 1, 2 and 3), with t>MIC (total/free) of 22.8%/14.3%, 26.8%/16.0%, and 22.4%/12.7% for Strains 1, 2 and 3, respectively. Prior to the second dose (8 h), median bacterial counts were significantly lower in animals surviving vs. dead at day 7. Conclusions/Significance In mice (CDN protein binding similar to humans) total t>MIC values of ≈35% (≈19% free) were efficacious, with a decrease in the required values in pre-immunized animals. This reinforces that immunoprotection to overcome resistance may provide lifesaving strategies.

Bactericidal activity of daptomycin versus vancomycin in the presence of human albumin against vancomycin-susceptible but tolerant methicillin-resistant Staphylococcus aureus (MRSA) with daptomycin minimum inhibitory concentrations of 1–2 μg/mL

This study explored the influence of vancomycin tolerance and protein binding on the bactericidal activity of vancomycin versus daptomycin (protein binding 36.9% vs. 91.7%, respectively) against four vancomycin-tolerant methicillin-resistant Staphylococcus aureus (MRSA) [minimum inhibitory concentration/minimum bactericidal concentration (MIC/MBC)=0.5/16, 1/32, 2/32 and 1/32microg/mL for vancomycin and 1/1, 1/2, 2/2 and 2/4microg/mL for daptomycin]. Killing curves were performed with vancomycin/daptomycin concentrations equal to serum peak concentrations (C(max)) (65.70/98.60microg/mL) and trough concentrations (C(min)) (7.90/9.13microg/mL) in the presence and absence of a physiological human albumin concentration (4g/dL), controlled with curves with the theoretical free drug fraction of vancomycin/daptomycin C(max) (41.45/8.18microg/mL) and C(min) (4.98/0.76microg/mL). Vancomycin C(max) and C(min) concentrations, regardless of the media, showed a bacteriostatic profile not reaching a reduction of 99% or 99.9% of the initial inocula during the 24-h experimental time period. Daptomycin antibacterial profiles significantly differed when testing C(max) and C(min). C(max) was rapidly bactericidal (< or =4h) with >5 log(10) reduction in the initial inocula for all strains, regardless of the presence or not of albumin or the use of concentrations similar to free C(max). C(min) exhibited similar final colony counts at 0h and 24h in curves with albumin, but with >3 log colony-forming units (CFU)/mL reduction at < or =4h for strains with an MIC of 1microg/mL and ca. 2 logCFU/mL reduction at < or =6h for strains with an MIC of 2microg/mL. This activity was significantly higher than the activity of the free C(min) fraction. The results of this study reinforce the idea that pharmacodynamics using concentrations calculated using reported protein binding are unreliable. Daptomycin exhibited rapid antibacterial activity against vancomycin-tolerant MRSA isolates even against those with high daptomycin MICs in the presence of physiological albumin concentrations.

High Protein Binding and Cidal Activity against Penicillin-Resistant S. pneumoniae: A Cefditoren In Vitro Pharmacodynamic Simulation

Background Although protein binding is a reversible phenomenon, it is assumed that antibacterial activity is exclusively exerted by the free (unbound) fraction of antibiotics. Methodology/Principal Findings Activity of cefditoren, a highly protein bound 3rd generation cephalosporin, over 24h after an oral 400 mg cefditoren-pivoxil bid regimen was studied against six S. pneumoniae strains (penicillin/cefditoren MICs; µg/ml): S1 (0.12/0.25), S2 (0.25/0.25), S3 and S4 (0.5/0.5), S5 (1/0.5) and S6 (4/0.5). A computerized pharmacodynamic simulation with media consisting in 75% human serum and 25% broth (mean albumin concentrations = 4.85±0.12 g/dL) was performed. Protein binding was measured. The cumulative percentage of a 24h-period that drug concentrations exceeded the MIC for total (T>MIC) and unbound concentrations (fT>MIC), expressed as percentage of the dosing interval, were determined. Protein binding was 87.1%. Bactericidal activity (≥99.9% initial inocula reduction) was obtained against strains S1 and S2 at 24h (T>MIC = 77.6%, fT>MIC = 23.7%). With T>MIC of 61.6% (fT>MIC = 1.7%), reductions against S3 and S4 ranged from 90% to 97% at 12h and 24h; against S5, reduction was 45.1% at 12h and up to 85.0% at 24h; and against S6, reduction was 91.8% at 12h, but due to regrowth of 52.9% at 24h. Cefditoren physiological concentrations exerted antibacterial activity against strains exhibiting MICs of 0.25 and 0.5 µg/ml under protein binding conditions similar to those in humans. Conclusions/Significance The results of this study suggest that, from the pharmacodynamic perspective, the presence of physiological albumin concentrations may not preclude antipneumococcal activity of highly bound cephalosporins as cefditoren.

Cefditoren and Ceftriaxone Enhance Complement-Mediated Immunity in the Presence of Specific Antibodies against Antibiotic-Resistant Pneumococcal Strains

Background Specific antibodies mediate humoral and cellular protection against invading pathogens such as Streptococcus pneumoniae by activating complement mediated immunity, promoting phagocytosis and stimulating bacterial clearance. The emergence of pneumococcal strains with high levels of antibiotic resistance is of great concern worldwide and a serious threat for public health. Methodology/Principal Findings Flow cytometry was used to determine whether complement-mediated immunity against three antibiotic-resistant S. pneumoniae clinical isolates is enhanced in the presence of sub-inhibitory concentrations of cefditoren and ceftriaxone. The binding of acute phase proteins such as C-reactive protein and serum amyloid P component, and of complement component C1q, to pneumococci was enhanced in the presence of serum plus either of these antibiotics. Both antibiotics therefore trigger the activation of the classical complement pathway against S. pneumoniae. C3b deposition was also increased in the presence of specific anti-pneumococcal antibodies and sub-inhibitory concentrations of cefditoren and ceftriaxone confirming that the presence of these antibiotics enhances complement-mediated immunity to S. pneumoniae. Conclusions/Significance Using cefditoren and ceftriaxone to promote the binding of acute phase proteins and C1q to pneumococci, and to increase C3b deposition, when anti-pneumococcal antibodies are present, might help reduce the impact of antibiotic resistance in S. pneumoniae infections.

In vitro effect of physiological concentrations of human albumin on the antibacterial activity of tigecycline

OBJECTIVES To determine C(max) tigecycline activity in the presence/absence of physiological concentrations of human albumin with free fraction concentrations as controls. METHODS Killing curves (final inoculum: 1.0-5.0 x 10(7) cfu/mL) were performed with 0.88 mg/L final concentrations (serum C(max) after a 100 mg 1 h infusion) in Mueller-Hinton broth supplemented with Ca(2+) and Mg(2+) (MH) and in MH with 4 g/dL human albumin. Controls were curves in MH with concentrations similar to the free fraction (fC(max) = 0.17 mg/L) calculated using protein binding. Activity was measured as log(10) initial inoculum reduction (log(10) initial inoculum-log(10) at 12 h/24 h). Target strains (tigecycline MIC/MBC; mg/L) were: methicillin-resistant Staphylococcus aureus heteroresistant to vancomycin (0.12/0.25); Enterococcus faecium (0.12/0.25); Escherichia coli producing extended-spectrum beta-lactamase (0.12/0.25); and Acinetobacter baumannii (0.25/1). RESULTS At 24 h the fC(max) produced mean decreases of < or =0.1 cfu/mL for all strains, in contrast to the bactericidal activity (mean >3 log(10) reduction) provided by C(max) concentrations in the presence or absence of albumin for E. coli and E. faecium, and an activity nearly bactericidal for S. aureus (mean approximately 2.8 log(10) reduction). In the case of the A. baumannii isolate the C(max) in the presence or absence of albumin produced a mean reduction of 2.56 log(10) cfu/mL at 12 h (time of one dosing interval), with a bacteriostatic profile when considering 24 h colony counts (similar counts at 0 and 24 h). CONCLUSIONS Correcting the total concentration for the reported literature binding values is unreliable since tigecycline antibacterial activity was greater than that suggested by the free fraction of the drug.