Clinical pharmacokinetics of newer cephalosporins

Examining the combination of cefixime and amoxicillin/clavulanate against extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli isolates

INTRODUCTION

Community-acquired urinary tract infections (UTIs) caused by extended spectrum beta-lactamase (ESBL)-producing Escherichia coli have limited oral therapeutic options and pose significant clinical challenges. The goal of this study was to evaluate the in vitro synergy between CFM and AMC against ESBL E. coli with aims to identify an oral treatment option for UTIs.

METHODS

Minimum inhibitory concentrations (MICs) of CFM in the presence of AMC were determined for 46 clinical isolates by placing a CFM Etest on a plate with AMC impregnated in the agar. Isolates with CFM MIC ≤1 µg/ml in the presence of AMC were considered susceptible to the CFM and AMC combination. Five isolates were then selected for further testing using time-kill analysis in the presence of CFM, AMC, and CFM with AMC. Time-kill curves were plotted to determine synergy over 24 hours.

RESULTS

AMC improved the activity of CFM against ESBL E. coli isolates by 128-fold in the Etest analysis with 85% of tested isolates being susceptible to the combination. Four-fold or greater reduction in CFM MIC was exhibited in 44 of 46 (96%) isolates when in the presence of AMC. Synergy and bactericidal activity between CFM and AMC were exhibited in each of the five isolates tested by time-kill analysis.

DISCUSSION/CONCLUSION

This study found that AMC improves the activity of CFM against ESBL E. coli and that this antibiotic combination has potential as an oral therapeutic option to treat ESBL E. coli UTIs.

Drug-Dosing Adjustment in Dogs and Cats with Chronic Kidney Disease

Chronic kidney disease is a common kidney disorder in adult and aged dogs and cats; the management of associated complications and comorbidities generally requires a life-long medical treatment to ensure a good quality of life of affected patients. However, indications and the literature on drug dosing in dogs and cats with chronic kidney disease are often lacking. The aim of this review is to revise the current literature on drug dosing in canine and feline patients with renal impairment, with a special focus on the most commonly used medications to manage chronic kidney disease and possible comorbidities.

Clavulanate combinations with mecillinam, cefixime or cefpodoxime against ESBL-producing Enterobacterales frequently associated with blaOXA-1 in a paediatric population with febrile urinary tract infections

OBJECTIVES

Oral treatment of febrile urinary tract infections (FUTIs) can be impaired by MDR Enterobacterales often combining ESBL and inhibitor-resistant genes. We studied the impact of β-lactamases and Enterobacterales' genotypes on the cefixime, cefpodoxime and mecillinam ± amoxicillin/clavulanate MICs.

MATERIALS AND METHODS

In this multicentric study, we included 251 previously whole-genome-sequenced ESBL-producing Enterobacterales, isolated in French children with FUTIs. The MICs of cefixime, cefpodoxime, mecillinam alone and combined with amoxicillin/clavulanate were determined and analysed with respect to genomic data. We focused especially on the isolates' ST and their type of β-lactamases. Clinical outcomes of patients who received cefixime + amoxicillin/clavulanate were also analysed.

RESULTS

All isolates were cefixime and cefpodoxime resistant. Disparities depending on blaCTX-M variants were observed for cefixime. The addition of amoxicillin/clavulanate restored susceptibility for cefixime and cefpodoxime in 97.2% (MIC50/90 of 0.38/0.75 mg/L) and 55.4% (MIC50/90 of 1/2 mg/L) of isolates, respectively, whatever the ST, the blaCTX-M variants or the association with inhibitor-resistant β-lactamases (34.2%). All isolates were susceptible to mecillinam + amoxicillin/clavulanate with MIC50/90 of 0.19/0.25 mg/L, respectively. Neither therapeutic failure nor any subsequent positive control urine culture were reported for patients who received cefixime + amoxicillin/clavulanate as an oral relay therapy (n = 54).

CONCLUSIONS

Despite the frequent association of ESBL genes with inhibitor-resistant β-lactamases, the cefixime + amoxicillin/clavulanate MICs remain low. The in vivo efficacy of this combination was satisfying even when first-line treatment was ineffective. Considering the MIC distributions and pharmacokinetic parameters, mecillinam + amoxicillin/clavulanate should also be an alternative to consider when treating FUTIs in children.

Oral cephalosporin and β-lactamase inhibitor combinations for ESBL-producing Enterobacteriaceae urinary tract infections

ESBL-producing Enterobacteriaceae as uropathogens have given rise to a sizeable amount of global morbidity. Community and hospital surveillance studies continue to report increasing proportions of these organisms as causes of urinary tract infection (UTI). Due to limited treatment options and the presence of cross-resistance amongst oral antibiotics of different classes, patients often require IV therapy, thereby increasing healthcare costs and reducing the effectiveness of delivering healthcare. Oral cephalosporin antibiotics are well known for their ability to achieve high urinary concentrations, in addition to achieving clinical success for treatment of uncomplicated UTI with a drug-susceptible pathogen. Novel cephalosporin/β-lactamase inhibitor combinations have been developed and demonstrate good in vitro activity against ESBL-producing isolates. A pooled analysis of in vitro activity of existing oral cephalosporin/clavulanate combinations in ESBL-producing Enterobacteriaceae has shown MIC50s of 0.5-1, 0.125-1 and 0.25 mg/L for cefpodoxime, ceftibuten and cefixime, respectively. A novel cyclic boronic acid β-lactamase inhibitor, QPX7728, was able to produce MIC50 values of 0.5 and ≤0.06 mg/L when paired with cefpodoxime and ceftibuten, respectively. Other novel combinations, cefpodoxime/ETX0282 and ceftibuten/VNRX7145, have also demonstrated excellent activity against ESBL producers. Clinical trials are now awaited.

Pharmacokinetic and pharmacodynamic considerations of cephalosporin use in children

Introduction: Cephalosporins are a major class of antibiotics, frequently used in children because of their remarkable antibacterial activity and excellent safety profile. Time above the minimal inhibitory concentration of the non-protein-bound fraction (fT>MIC) is the pharmacokinetic/pharmacodynamic parameter that correlates with the therapeutic efficacy. In the pediatric population, the inter-individual variability in cephalosporin pharmacokinetics is large because of maturational changes. However, the prescription of cephalosporins promotes emergence of Enterobacteriaceae producing broad-spectrum ß-lactamases.Areas covered: Here we describe in vitro activities and the main pharmacokinetic characteristics of cephalosporins in children. On the basis of these characteristics, we propose an estimation of the fT>MIC for each molecule as a tool to help optimize the use of cephalosporins. We also provide an inventory of the clinical use of cephalosporins and present prospects for the development of new molecules or associations to address the emergence of resistant strains.Expert opinion: Cephalosporins represent a heterogeneous group of antibiotics with various pharmacokinetics and in vitro antimicrobial activity that the clinician needs to master to optimize their use. However, their broad use plays a role in the emergence of broad-spectrum ß-lactamase-producing strains and must thus be restricted to probabilistic broad-spectrum therapy and situations without therapeutic alternatives.

Pharmacological properties of oral antibiotics for the treatment of uncomplicated urinary tract infections

The therapeutic management of uncomplicated bacterial urinary tract infections (UTIs) is based on short-term courses of oral antibiotics. The preferred drugs are nitrofurantoin trimethoprim-sulfamethoxazole, fosfomycin trometamol, fluoroquinolones and β-lactam agents. The choice of agent for treating uncomplicated UTIs should be based on the pharmacokinetic characteristics of the molecule so that clinical benefit is optimized and the risk of antibacterial resistance is minimized. This article discusses the general pharmacokinetic-pharmacodynamic (PK/PD) aspects of antimicrobial chemotherapy, the PK/PD characteristics of oral antimicrobial agents for the treatment of uncomplicated UTIs and the pharmacological and therapeutic strategies for limiting or preventing bacterial resistance.

N-Substituted Prodrugs of Mebendazole Provide Improved Aqueous Solubility and Oral Bioavailability in Mice and Dogs

Mebendazole (MBZ) was developed as a broad-spectrum anthelmintic but has recently shown efficacy as an anticancer agent. The use of MBZ for cancer, however, is challenging due to its poor solubility leading to poor bioavailability. Herein, we developed a prodrug approach with various N-linked promoieties including acyloxymethyl, aminoacyloxymethyl, and substituted phosphonooxymethyl in attempt to improve these characteristics. Compound 12, containing an (((((isopropoxycarbonyl)oxy)methoxy)phosphoryl)oxy)methyl promoiety, showed a >10 000-fold improvement in aqueous solubility. When evaluated in mice, 12 displayed a 2.2-fold higher plasma AUC_{0- t} and a 1.7-fold improvement in brain AUC_{0- t} with a calculated oral bioavailability of 52%, as compared to 24% for MBZ-polymorph C (MBZ-C), the most bioavailable polymorph. In dogs, 12 showed a 3.8-fold higher plasma AUC_{0- t} with oral bioavailability of 41% compared to 11% for MBZ-C. In summary, we have identified a prodrug of MBZ with better physicochemical properties and enhanced bioavailability in both mice and dog.

Randomised trial of oral versus sequential intravenous/oral cephalosporins in children with pyelonephritis

The hypothesis was tested that oral antibiotic treatment in children with acute pyelonephritis and scintigraphy-documented lesions is equally as efficacious as sequential intravenous/oral therapy with respect to the incidence of renal scarring. A randomised multi-centre trial was conducted in 365 children aged 6 months to 16 years with bacterial growth in cultures from urine collected by catheter. The children were assigned to receive either oral ceftibuten (9 mg/kg once daily) for 14 days or intravenous ceftriaxone (50 mg/kg once daily) for 3 days followed by oral ceftibuten for 11 days. Only patients with lesions detected on acute-phase dimercaptosuccinic acid (DMSA) scintigraphy underwent follow-up scintigraphy. Efficacy was evaluated by the rate of renal scarring after 6 months on follow-up scintigraphy. Of 219 children with lesions on acute-phase scintigraphy, 152 completed the study; 80 (72 females, median age 2.2 years) were given ceftibuten and 72 (62 females, median age 1.6 years) were given ceftriaxone/ceftibuten. Patients in the intravenous/oral group had significantly higher C-reactive protein (CRP) concentrations at baseline and larger lesion(s) on acute-phase scintigraphy. Follow-up scintigraphy showed renal scarring in 21/80 children treated with ceftibuten and 33/72 with ceftriaxone/ceftibuten (p = 0.01). However, after adjustment for the confounding variables (CRP and size of acute-phase lesion), no significant difference was observed for renal scarring between the two groups (p = 0.2). Renal scarring correlated with the extent of the acute-phase lesion (r = 0.60, p < 0.0001) and the grade of vesico-ureteric reflux (r = 0.31, p = 0.03), and was more frequent in refluxing renal units (p = 0.04). The majority of patients, i.e. 44 in the oral group and 47 in the intravenous/oral group, were managed as out-patients. Side effects were not observed. From this study, we can conclude that once-daily oral ceftibuten for 14 days yielded comparable results to sequential ceftriaxone/ceftibuten treatment in children aged 6 months to 16 years with DMSA-documented acute pyelonephritis and it allowed out-patient management in the majority of these children.

Decrease in bacterial load versus resistance selection of pneumococcal subpopulations by beta-lactam physiological concentrations over time: an in vitro pharmacodynamic simulation

To investigate beta-lactam effects on Streptococcus pneumoniae-mixed cultures, a computerized pharmacodynamic model simulating over 24-hr concentrations obtained after several beta-lactam regimens was used. Strain 1 (no penicillin binding protein [PBP] mutations) and strain 2 (mutation in pbp1a) were penicillin/amoxicillin susceptible. Strain 3 (mutations in pbp1a, pbp2x, and pbp2b) and strain 4 (mutations in pbp1a, pbp2x, and pbp2b [10 changes]) were penicillin/amoxicillin resistant. Initial inoculum was approximately 6 x 10(6) CFU (colony forming units)/ml (with a 1:1:1:1 proportion of each strain). Population analysis profile was performed pre- and post-simulations. Strain 1 exhibited the best fitness (growth over 24 hr) in individual cultures, and strain 2 did so in mixed cultures in antibiotic-free simulations. In antibiotic simulations with the mixed inocula, penicillin/amoxicillin-susceptible strains were eradicated with all study drugs (time that concentrations exceed the minimal inhibitory concentration [T>MIC >or= 43%]). Penicillin-resistant strains showed different evolution depending on the antibiotic: (a) cefditoren produced >2 log(10) reduction of initial inocula at 12-24 hr (T>MIC >or=45%), with a remaining population growing in plates with >or=4 mg/L amoxicillin; (b) cefuroxime, cefixime, and cefaclor did not decrease initial inocula at 12-24 hr (T>MIC=0%), with minor subpopulations growing in plates with 4 mg/L amoxicillin; (c) amoxicillin produced 2.6 log(10) decrease of initial inocula at 12 hr (T>MIC=47.5%), but 1.1 log(10) increase of initial inocula at 24 hr, with a significant population growing in plates with 4 mg/L amoxicillin. Antibiotic activity against mixed inocula (susceptible and resistant strains) depends on intrinsic activity (as well as its subsequent pharmacodynamic activity: T>MIC against resistant strains), and on possible selection of intra-strain-resistant subpopulations.

Mechanistic Approaches to Volume of Distribution Predictions: Understanding the Processes

PURPOSE

To use recently developed mechanistic equations to predict tissue-to-plasma water partition coefficients (Kpus), apply these predictions to whole body unbound volume of distribution at steady state (Vu(ss)) determinations, and explain the differences in the extent of drug distribution both within and across the various compound classes.

MATERIALS AND METHODS

Vu(ss) values were predicted for 92 structurally diverse compounds in rats and 140 in humans by two approaches. The first approach incorporated Kpu values predicted for 13 tissues whereas the second was restricted to muscle.

RESULTS

The prediction accuracy was good for both approaches in rats and humans, with 64-78% and 82-92% of the predicted Vu(ss) values agreeing with in vivo data to within factors of +/-2 and 3, respectively.

CONCLUSIONS

Generic distribution processes were identified as lipid partitioning and dissolution where the former is higher for lipophilic unionised drugs. In addition, electrostatic interactions with acidic phospholipids can predominate for ionised bases when affinities (reflected by binding to constituents within blood) are high. For acidic drugs albumin binding dominates when plasma protein binding is high. This ability to explain drug distribution and link it to physicochemical properties can help guide the compound selection process.

Pharmacokinetic and pharmacodynamic aspects of antimicrobial agents for the treatment of uncomplicated urinary tract infections

Uncomplicated urinary tract infections (UTI) are treated with beta-lactams, co-trimoxazole, quinolones and fosfomycin tromethamine. Due to increasing resistance of causative pathogens, antibiotics should be used by considering their pharmacodynamic and pharmacokinetic characteristics. beta-lactams have time-dependent activity and should not be used once-daily. Co-trimoxazole should be restricted due to increasing chemoresistance. Fluoroquinolones play a primary role in the treatment of serious and complicated infections. Fosfomycin tromethamine is active against most urinary tract pathogens. In vitro time-kill kinetics of fosfomycin against Escherichia coli and Proteus mirabilis showed primarily concentration-dependent activity, with a prolonged post-antibiotic effect (3.4 to 4.7h). Based on these results a single 3g dose of fosfomycin guarantees optimal efficacy against common uropathogens with an AUC(urine)/MIC ratio of 500.

Prodrug forms of N-[(4-deoxy-4-amino-10-methyl)pteroyl]glutamate-gamma-[psiP(O)(OH)]-glutarate, a potent inhibitor of folylpoly-gamma-glutamate synthetase: synthesis and hydrolytic stability

Ester prodrugs of the phosphinate pseudopeptide N-[(4-deoxy-4-amino-10-methyl)pteroyl]glutamate-gamma-[psiP(O)(OH)]-glutarate (1a) were synthesized. H-phosphinic acids derived from N-Cbz vinyl glycine esters were converted to the desired pseudopeptides by Michael addition to alpha-methyleneglutarate esters. Pivaloyloxymethyl (POM) ester moieties were incorporated in both the N-terminal and C-terminal fragments prior to formation of either C-P bond. N-Alkylation of the corresponding amides derived from p-(N-methyl)aminobenzoic acid with 2,4-diamino-6-(bromomethyl)pteridine gave the target compounds. POM esters of methotrexate and the corresponding gamma-glutamyl conjugate were also synthesized using the same strategy. All prodrugs were evaluated in Chinese hamster ovary cells. Although the pseudopeptide prodrugs were ineffective, prodrugs of methotrexate and the corresponding gamma-glutamyl conjugate were equipotent with the parent compounds. Stability of the prodrugs was investigated in both phosphate buffer and cell line medium to provide a rationale for the observed biological data.

Thiolated chitosans: development and in vitro evaluation of a mucoadhesive, permeation enhancing oral drug delivery system

It was the aim of this study to develop a mucoadhesive, permeation enhancing delivery system for orally administered poorly absorbed drugs. Chitosan was modified by the immobilisation of thiol groups utilising 2-iminothiolane (Traut's reagent). The permeation enhancing effect of the resulting chitosan-4-thio-butylamidine conjugate (chitosan-TBA conjugate) in combination with the permeation mediator glutathione (GSH) was evaluated in Ussing chambers on freshly excised small intestinal mucosa from guinea pigs using rhodamine 123 as marker for passive drug uptake. The mucoadhesive properties of the chitosan-TBA conjugate adjusted to pH 3, 5 and 7 were evaluated via the rotating cylinder method and via tensile studies. Release studies were performed with tablets comprising 10% cefadroxil used as model drug, 10% GSH and 80% chitosan-TBA conjugate pH 3 in 100 mM phosphate buffer pH 6.8 at 37 degrees C. Results showed a 3-fold higher permeation enhancing effect of the chitosan-TBA conjugate/GSH system in comparison to unmodified chitosan. Mucoadhesion studies revealed that the lower the pH of the thiolated chitosan is, the higher are its mucoadhesive properties. Release studies showed a sustained release of both cefadroxil and GSH over several hours. This delivery system might represent a promising novel tool in order to improve the therapeutic efficacy of various drugs which are poorly absorbed from the gastrointestinal tract.

Multiple-dose pharmacokinetics and safety of a novel broad-spectrum cephalosporin (BAL5788) in healthy volunteers

BAL5788 is the water-soluble prodrug of BAL9141, a novel broad-spectrum cephalosporin with potent bactericidal activity against methicillin-resistant Staphylococcus aureus (MRSA) and penicillin-resistant Streptococcus pneumoniae. Safety and pharmacokinetic data from a multiple-dose study with 16 healthy male volunteers are reported. Subjects were randomized to receive BAL5788 at 500 or 750 mg (as BAL9141 equivalents; n = 6 subjects per dose) or placebo (n = 2 subjects per dose). The doses were given as 200-ml infusions over 30 min once daily on days 1 and 8 and twice daily on days 2 to 7. BAL5788 was well tolerated, with no severe or serious adverse events (AEs) or dosing-related changes in laboratory parameters, electrocardiographic findings, or vital signs. Drug accumulation in plasma was negligible during the dosing period. The results of pharmacokinetic analyses agreed well with data reported from a previous single-ascending-dose study. The elimination half-life of BAL9141 was about 3 h. The volume of distribution at steady state was equal to the volume of the adult extracellular water compartment. BAL9141 was predominantly eliminated in urine, and renal clearance of the free drug corresponded to the normal glomerular filtration rate in adults. After multiple infusions of 750 mg, the mean concentrations of BAL9141 in plasma exceeded the MIC at which 100% of MRSA isolates are inhibited (4 microg/ml) for approximately 7 to 9 h, corresponding to 58 to 75% of a 12-h dosing interval.

Single-dose pharmacokinetics and safety of a novel broad-spectrum cephalosporin (BAL5788) in healthy volunteers

BAL5788 is the water-soluble prodrug of BAL9141, a novel broad-spectrum cephalosporin with potent bactericidal activities against methicillin-resistant Staphylococcus aureus (MRSA) and penicillin-resistant Streptococcus pneumoniae. We investigated the safety and pharmacokinetics of BAL5788 in a double-blind, single-ascending-dose study with 40 healthy male subjects. The subjects were randomized to receive placebo (n = 2 subjects per dose) or BAL5788 (n = 6 subjects per dose) as a 200-ml intravenous infusion over 30 min. The BAL5788 doses used were 125, 250, 500, 750, and 1,000 mg (BAL9141 equivalents). All doses were well tolerated, with no severe or serious adverse events (AEs). The most frequent AE was taste disturbance. No electrocardiographic abnormalities and no trends or clinically significant changes in laboratory parameters or vital signs were observed. The maximum concentration of drug in serum and the area under the concentration-time curve for BAL9141 were dose proportional over the dosing range. The elimination half-life of BAL9141 was about 3 h. The volume of distribution at steady state was equal to the volume of the adult extracellular water compartment, and the rate of renal clearance of free drug corresponded to the normal glomerular filtration rate for adults. More than 70% of the administered dose was excreted as BAL9141 in the urine, and almost no prodrug was detected. After the infusion of 750 mg, the mean plasma BAL9141 concentrations exceeded the MIC at which 100% of MRSA isolates are inhibited (4 microg/ml) for approximately 7 h, or 58% of a 12-h dosing interval. These results indicate that infusions of 750 mg twice a day should be adequate for the treatment of infections caused by MRSA.

Preparation and in vitro characterization of poly(acrylic acid)–cysteine microparticles

The purpose of the present study was to prepare and characterize a novel mucoadhesive microparticulate drug delivery system. Microparticles were prepared by the solvent evaporation emulsion technique using a poly(acrylic acid)-cysteine conjugate of an average molecular mass of 450 kDa with an amount of 308 micromol thiol groups per gram polymer. The cross-linking of thiol groups via the formation of disulfide bonds during this preparation process was pH-controlled. The resulting microparticles were characterized with regard to the degree of cross-linking and the amount of remaining free thiol groups, shape, size distribution and stability. Furthermore, the drug release behaviour using bromelain as model drug and the mucoadhesive properties were evaluated.Results demonstrated that the higher the pH of the aqueous phase was during the preparation process, the higher was the degree of cross-linking within the particles. However, even at pH 9, 8.9+/-2.2% of free thiol groups remained on the microparticles. Particles were of spherical and partially porous structure and had a main size in the range of 20-60 microm with a center at 35 microm. Because of the formation of disulfide bonds within the particles, they did not disintegrate under physiological conditions within 48 h. In addition, a controlled drug release of bromelain was achieved. Due to the immobilization of thiol groups on poly(acrylic acid), the mucoadhesive properties of the corresponding microparticles were improved threefold. These features should render poly(acrylic acid)-cysteine conjugate microparticles useful as drug delivery system providing a prolonged residence time on mucosal epithelia.

Pharmacological properties of parenteral cephalosporins: rationale for ambulatory use

Parenteral cephalosporins are among the most frequently used antibiotics in hospital therapy. They are characterised by an extended spectrum of activity against gram-positive and gram-negative bacteria, and some also have good activity against anaerobes. They kill proliferating bacterial cells rapidly, and generally show only a low tendency to select resistant mutants. However, there are cephalosporin compounds which induce cephalosporinases very rapidly in certain microorganisms. Together with other beta-lactam antibiotics, parenteral cephalosporins interfere with bacterial cell wall synthesis by inhibiting peptidoglycan cross-linkage. Because of this specific target, they are nontoxic to mammalian cells, and have a very favourable adverse effect profile. The chemical stability of parenteral cephalosporins in aqueous solution is good. After intravenous injection, high concentrations of these agents are achieved in serum and tissue. Most cephalosporins are eliminated unchanged via the kidney, with a half-life of 1 to 2 hours. But there are also derivatives with a serum half-life of more than 2 and up to 8 hours, allowing 12- or 24-hour dosage intervals. Because of their reliable efficacy and low risk of adverse effects, the parenteral cephalosporins offer a high degree of tolerability even in the setting of outpatient antibiotic therapy. In particular, the derivatives of the third generation are characterised by unique pharmacological properties.

Novel oral cephalosporins

The therapeutic use of oral cephalosporins to treat infectious diseases continues to challenge clinicians; many attempts have been made over recent years to improve the efficacy and spectrum of these anti-infectives. Many oral cephalosporins are in development and include cefdinir, cefprozil, cefetamet pivoxil, cefcapene pivoxil, cefcanel daloxate hydrochloride in Phase II trials, S-1090 in Phase III trials and the novel compounds E1100, E1101 and BRL-57347. Differences between these drugs are sometimes subtle and the improvement over existing compounds modest, although recent cephalosporins have shown greater activity against Gram-negative bacterial infections. A better knowledge of the pharmacodynamic and pharmacokinetic interrelationships of existing oral cephalosporins is demanded for a more rational use of these compounds and to avoid the subsequent development of resistance. Perhaps with such an approach, the perceived need for new cephalosporins will diminish.

Basis of anti-infective therapy: pharmacokinetic-pharmacodynamic criteria and methodology for dual dosage individualisation

Antimicrobial therapy should be designed on the basis of microbiological, as well as pharmacokinetic, criteria; microbiological parameters provide information about the susceptibility of the pathogen responsible for the infectious process while pharmacokinetic parameters give information about the potential ability of the drug in question to reach and remain at the sites of infection in the body. Microbiological parameters such as the minimum inhibitory concentration, minimum bactericidal concentration, bacterial titre, bactericidal rate and 'post-antibiotic effect' (PAE) must be considered. Among the pharmacokinetic parameters, the maximum serum concentration at steady state (CmaxSS), area under the concentration-time curve (AUC) and length of time that the serum concentrations exceed a particular value are the most useful in this context. Different relationships between these parameters, known as efficacy indices, have been established to predict the potential efficacy of antibacterial therapy. Antimicrobial dosage individualisation should be based on the optimisation of the efficacy index that best correlates with patient response. It seems appropriate to establish the degree of correlation among the different efficacy indices and clinical response observed in patients by means of a correlation analysis. This type of analysis can be either retrospective or prospective and may be based on linear or maximum response models. Simulation of the plasma concentration curves obtained with the particular regimen administered offers a methodology which is easy to apply and provides the pharmacokinetic information necessary to calculate the different efficacy indices. Information about the susceptibility of the pathogen to the antibacterial in question and about the response to the treatment used is also necessary for the correlation analysis. This type of analysis determines which of the indices is best correlated with efficacy and, hence, is the index to be optimised when attempting to individualise antibacterial therapy for different situations.

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.

Human variability and noncancer risk assessment- An analysis of the default uncertainty factor

A 10-fold uncertainty factor is used for noncancer risk assessments to allow for possible interindividual differences between humans in the fate of the chemical in the body (kinetics) and target organ sensitivity (dynamics). Analysis of a database on the variability in each of these aspects is consistent with an even subdivision of the 10-fold factor into 10(0.5) (3.16) for kinetics and 10(0.5) (3.16) for dynamics. Analysis of the number of subjects in a normally and log-normally distributed population which would not be covered by factors of 3.16 supports this subdivision and also the use of a 10-fold factor to allow for both aspects. Analysis of kinetic data for subgroups of the population indicates that the standard default value of 3.16 for kinetics will not be adequate for all routes of elimination and all groups of the population. A scheme is proposed which would allow the selection of appropriate default uncertainty factors based on knowledge of the biological fate and effects of the chemical under review. Copyright 1998 Academic Press.

Influence of lipophilicity on the diffusion of cephalosporins into the cerebrospinal fluid

The aim of this quantitative structure-activity relationship (QSAR) study was to investigate the influence of lipophilicity on the diffusion of cephalosporins into the cerebrospinal fluid (CSF). The lipophilicity was expressed as the chromatographic capacity factor (log k'w) determined by high-performance liquid chromatography in a reversed-phase system. The penetration of eight cephalosporins into CSF was studied in male Wistar rats receiving the drugs intramuscularly (1.5 mg/kg). One hour after administration, CSF and blood samples were collected, and concentrations of free drug were measured in CSF (CCSF) and in plasma (CP). A significant parabolic relationship was sought between lipophilicity (log k'w) and the capacity of diffusion across the blood-brain barrier expressed as log (CCSF/CP). The cephalosporins exhibiting a moderate lipophilicity diffused well into CSF. A pharmacokinetic study was performed at 1, 2 and 4 h after administration of three cephalosporins: cefazolin, ceftriaxone and cefsulodin. These compounds were choosen according to their lipophilicities (low, moderate and high values, respectively). The AUC0-4h for both free plasma (AUCP) and cerebrospinal fluid (AUCCSF) concentrations were determined. The AUCCSF/AUCP ratio presented a maximum value for a strongly albumin bound cephalosporin, ceftriaxone. In our experimental conditions, the ideal lipophilicity (log k'w) range for diffusion of cephalosporins from plasma into CSF was between 1.6 and 1.8.