Serum and blister fluid pharmacokinetics and bactericidal activities of ampicillin-sulbactam, cefotetan, cefoxitin, ceftizoxime, and ticarcillin-clavulanate

Foetal and neonatal exposure prediction and dosing evaluation for ampicillin using a physiologically-based pharmacokinetic modelling approach

AIMS

Ampicillin is frequently used in neonates for the treatment of sepsis and as an intrapartum prophylaxis option for Group B Streptococcus. Pharmacokinetic data to guide ampicillin dosing in neonates and during the intrapartum period are limited. The objective of this study was to build a physiologically-based pharmacokinetic (PBPK) model to characterize the disposition of ampicillin in neonates and foetuses and to inform corresponding optimal dosing regimens.

METHODS

An adult ampicillin PBPK model was first developed using the Simcyp® simulator. The adult model was then scaled to neonates by accounting for maturational changes in physiological parameters and age-dependent drug disposition or extended to a pregnancy model for mothers and foetuses. Models were verified using collected mean or individual-level concentration data from the literature.

RESULTS

The developed adult PBPK model included elimination via glomerular filtration, OAT3-mediated tubular secretion and biliary excretion as well as hepatic metabolism, and 89.8% of the observed mean concentrations in adults were within a 2-fold range of model mean predictions. Most of the observed individual-level observations in neonates (78.4%) and foetuses (about 65% in two studies) were within the 90% prediction intervals. The recommended 50 mg/kg every 8 h (q8h) ampicillin regimen achieved the 75% fraction time of total drug concentration above minimum inhibitory concentration (T > MIC) target for an MIC ≤8 mg/L in >90% virtual neonates, and 1 g ampicillin for pregnant women provided adequate foetal exposure (>0.25 mg/L) for 4 h prior to delivery.

CONCLUSIONS

A PBPK model was developed to characterize ampicillin's disposition in neonates, pregnant women, and foetuses, and the model supported optimal dosing evaluation in these vulnerable populations.

In vitro Antibacterial Activity and Resistance Prevention of Antimicrobial Combinations for Dihydropteroate Synthase-Carrying Stenotrophomonas maltophilia

Background

Stenotrophomonas maltophilia (S. maltophilia) is a multidrug-resistant gram-negative bacillus that is known to be an opportunistic pathogen, particularly in a hospital environment. The infection has a high morbidity and mortality. Sulfamethoxazole-trimethoprim (SXT) is the first-line agent recommended for its treatment. The global spread of dihydropteroate synthase (sul) genes has resulted in an increased resistance rate. However, the appropriate therapy for infections caused by sul-carrying S. maltophilia has not yet been established.

Objective

Our study aimed to identify the optimal antibiotic combinations that could both show high antibacterial activity against sul-carrying S. maltophilia and the ability to prevent the emergence of resistance at clinical dosage regimens.

Methods

Time-killing experiments and mutant prevention concentration (MPC) experiments were conducted to evaluate the antibacterial effect and ability to prevent resistance to minocycline, tigecycline, moxifloxacin, and ticarcillin/clavulanic acid (T/K), both alone and in combination, at clinically relevant antimicrobial concentrations.

Results

Minocycline, tigecycline, and T/K all exhibited bacteriostatic activity to sul-carrying S. maltophilia. The combination of minocycline plus T/K and tigecycline plus T/K neither enhanced the bactericidal ability nor prevented drug-resistant mutations. Moxifloxacin, at 2 mg/L, showed good bactericidal activity to most S. maltophilia, but bacterial regrowth at 24 h was observed in two strains. When combined with T/K, moxifloxacin showed good bactericidal activity in all moxifloxacin-sensitive strains. The concentrations of moxifloxacin alone were lower than most MPCs of the tested sul-carrying strains. When combined with T/K, the mean steady-state concentrations (MSC) of moxifloxacin could prevent 70% of resistance, and the peak concentration (C_max) prevented 95% of resistance.

Conclusion

The combination of moxifloxacin and T/K can achieve a good in vitro bactericidal effect and prevent the emergence of resistance at clinical dosage regimens, and may be an optimal therapeutic strategy for S. maltophilia infections, especially for vulnerable immunocompromised and critically ill patients.

New insights in Staphylococcus pseudintermedius pathogenicity: antibiotic-resistant biofilm formation by a human wound-associated strain

BACKGROUND

Staphylococcus pseudintermedius is an opportunistic pathogen recognized as the leading cause of skin, ear, and post-operative bacterial infections in dogs and cats. Zoonotic infections have also recently been reported causing endocarditis, infection of surgical wounds, rhinosinusitis, and catheter-related bacteremia. The aim of the present study is to evaluate, for the first time, the pathogenic potential of S. pseudintermedius isolated from a human infection. To this end, strain DSM 25713, which was recently isolated from a wound of a leukemic patient who underwent a bone marrow transplantation, was investigated for biofilm formation and antibiotic-resistance under conditions relevant for wound infection.

RESULTS

The effect of pH (5.5, 7.1, and 8.7) and the presence of serum (diluted at 1:2, 1:10, and 1:100) on biofilm formation was assessed through a crystal violet assay. The presence of serum significantly reduced the ability to form biofilm, regardless of the pH value tested. In vitro activity of eight antibiotics against biofilm formation and mature 48 h-old biofilms was comparatively assessed by crystal violet assay and viable cell count, respectively. Antibiotics at sub-inhibitory concentrations reduced biofilm formation in a dose-dependent manner, although cefoxitin was the most active, causing a significant reduction already at 1/8xMIC. Rifampicin showed the highest activity against preformed biofilms (MBEC90: 2xMIC). None of the antibiotics completely eradicated the preformed biofilms, regardless of tested concentrations. Confocal and electron microscopy analyses of mature biofilm revealed a complex "mushroom-like" architecture consisting of microcolonies embedded in a fibrillar extracellular matrix.

CONCLUSIONS

For the first time, our results show that human wound-associated S. pseudintermedius is able to form inherently antibiotic-resistant biofilms, suggestive of its pathogenic potential, and consistent with recent reports of zoonotic infections.

Determination of third-generation cephalosporins by high-performance liquid chromatography in connection with pharmacokinetic studies

The third-generation cephalosporins are semisynthetic beta-lactam antibiotics, including several oral and parental agents with extended activity against Gram-negative pathogens. They are generally determined either by microbiological techniques or by high-performance liquid chromatography (HPLC). The major drawback or bioassays is the lack of specificity, especially when a biotransformation of the cephalosporin molecule leads to active metabolites, or when the antibacterial therapy is based on association with drugs. Thus, for many years, numerous reversed-phase HPLC procedures have been proposed to overcome these difficulties. This review presents different HPLC methods proposed for the quantification in biological fluids of fourteen third-generation cephalosporins, ranged between parenteral and oral compounds. The sensitivity and specificity of these chromatographic procedures are discussed with regard to the pharmacokinetic properties of the antibiotics studied.

Activities of oral and parenteral agents against penicillin-susceptible and -resistant pneumococci

This study examined bacteriostatic and bactericidal activities of oral and parenteral antibiotics for penicillin-susceptible and intermediately and fully penicillin-resistant pneumococci. beta-Lactamase inhibitors did not affect beta-lactam results. The activities of ampicillin, amoxicillin +/- clavulanate, WY-49605, cefuroxime, cefpodoxime, cefdinir, cefixime, and cefaclor against two penicillin-susceptible, two intermediately penicillin-resistant, and two fully penicillin-resistant pneumococcal strains were tested. For all three groups, bacteriostatic values of amoxicillin and WY-49605 were lower than were those of other beta-lactams tested. Of the cephalosporins, cefdinir, cefuroxime, and cefpodoxime yielded the lowest bacteriostatic values. All beta-lactams were bactericidal (reduced original counts by > or = 3 log10 CFU/ml) at 1 dilution above bacteriostatic values, except for cefpodoxime (bactericidal at 2 dilutions above bacteriostatic values for one susceptible strain and one intermediately resistant strain), cefuroxime (bactericidal at 2 dilutions above bacteriostatic values for one intermediately resistant strain), and ampicillin (bactericidal at 2 dilutions above bacteriostatic values for one intermediately resistant strain). The activities of piperacillin, piperacillin-tazobactam, ticarcillin, ticarcillin-clavulanate, ampicillin, ampicillin-sulbactam, ceftriaxone, ceftazidime, and ciprofloxacin against four penicillin-susceptible, two intermediately penicillin-resistant, and four fully penicillin-resistant pneumococcal strains were evaluated. Bacteriostatic values of piperacillin, ampicillin, and ceftriaxone for all groups were lower than were those of ticarcillin and ceftazidime. Bacteriostatic values of ciprofloxacin were unaffected by penicillin susceptibility. All beta-lactams were bactericidal at 1 dilution above the bacteriostatic value, except for piperacillin (bactericidal at 2 dilutions above the bacteriostatic value for one intermediately resistant strain), ticarcillin (bactericidal at 2 dilutions above the bacteriostatic value for one susceptible strain and one resistant strain), ampicillin (bactericidal at 2 dilutions above the bacteriostatic value for two resistant strains), ceftriaxone (bactericidal at 2 dilutions above the bacteriostatic value for one resistant strain), and ceftazidime (bactericidal at 2 dilutions above the bacteriostatic value for one susceptible strain).

Multiple-dose pharmacokinetics of ceftibuten after oral administration to healthy volunteers

The pharmacokinetics of ceftibuten in plasma and urine were investigated after oral administration. Twelve healthy subjects were treated orally twice daily with 400 mg of the drug for 7 days; on day 8, the subjects received a last dose of 400 mg of ceftibuten. Ceftibuten and its metabolite, the trans isomer of ceftibuten, were assayed in plasma and urine by a specific HPLC method with UV detection. Ceftibuten was rapidly absorbed, as evidenced by the mean time to the maximum observed cis-ceftibuten concentration of 2.4 h. To describe the drug intake process, a Weibull model was used. For the metabolite, the mean time to maximum concentration in plasma was 3.25 h. Mean values for the terminal half-life in plasma were 2.17 h for cis-ceftibuten and 3.19 h for trans-ceftibuten. The overall elimination half-life, tmax, and total and renal clearances of cis-ceftibuten were invariant with respect to duration of dosing. The area under the plasma concentration versus time curve from 0 to infinity and the Cmax of this drug were significantly higher on day 8 than the values predicted from the elimination half-life computed on day 1 of treatment and the dosing interval. The pharmacokinetic parameters of trans-ceftibuten were invariant with respect to duration of dosing. Ceftibuten was well tolerated; there were no clinically significant adverse clinical events. The results from the present study indicate that the levels of cis-ceftibuten in plasma as well as in urine remain above the MICs for susceptible organisms over the dosing interval.