Amparo Sánchez Navarro

Development and validation of an HPLC method for vancomycin and its application to a pharmacokinetic study.

A rapid and simple method of high performance liquid chromatography with UV detection for the quantification of vancomycin in artificial perfusion fluid and lung tissue samples has been developed and validated. Chromatographic separation was carried out in a Nucleosil 120 C(18) 5 microm column (length, 15 cm; inner diameter, 0.4 cm) using a mixture of 0.05 M NH(4)H(2)PO(4) (pH 4)-acetonitrile (92:8, v/v) as the mobile phase at a flow rate of 1 mL/min, with UV detection at 220 nm. The method used for the vancomycin quantification showed linearity for concentration ranges of 0.1-2, 2-15 and 15-250 microg/mL, with r(2)=0.9985, 0.9996 and 0.9985, respectively. The limit of quantification of the method was 0.1 microg/mL and the coefficients of variation of the between- and within-day precision showed values between 0.6% and 7.0%. The retention time of vancomycin was 8.5 min. The method was used successfully to study the pharmacokinetics of vancomycin in isolated rat lung after its administration through the systemic and inhalatory routes.

New Formulations of Amoxicillin/ Clavulanic Acid A Pharmacokinetic and Pharmacodynamic Review

The pharmacokinetic properties of amoxicillin and clavulanic acid when used alone or in combination are extensively reviewed and discussed in this article. The reported data support a nonlinear absorption process for amoxicillin. Saturable transport mechanisms, limited solubility and the existence of an absorption window are possibly involved in the gastrointestinal absorption of this antibacterial, all leading to a decrease in the peak plasma concentration (Cmax)/dose ratio, a prolongation of the time to reach Cmax, and broad variability for high doses of amoxicillin. Data available in the literature also suggest a possible interaction between amoxicillin and clavulanic acid that might decrease the absolute bioavailability of clavulanic acid. In the present review the intrinsic pharmacodynamics of each drug, together with the synergism produced by the amoxicillin/clavulanic acid association, are also reviewed and analysed. Not only β-lactamase-producing strains, but also Streptococcus pneumoniae strains, seem to be more efficiently eradicated by the association of amoxicillin and clavulanic acid, and a relevant post-antibacterial effect and post-β-lactamase inhibitor effect are likely to operate when amoxicillin is administered together with clavulanic acid.The principles of pharmacokinetic/pharmacodynamic analysis applied to amoxicillin are reviewed, with special emphasis being placed on the results obtained from in vitro studies and animal models regarding the new pharmacokinetically enhanced formulation. Theoretical considerations concerning the efficacy of this formulation provided by the application of pharmacokinetic/pharmacodynamic analysis to the scarce pharmacokinetic data available are also included. The broad pharmacokinetic variability of both amoxicillin and clavulanic acid, particularly when administered together and at high doses of amoxicillin, is highlighted and the interest in considering this aspect to improve predictions based on pharmacokinetic/pharmacodynamic analyses for the new formulations is indicated. Methodological recommendations such as the Monte Carlo simulation are proposed in order to obtain more realistic predictions in clinical practice.

In vitro study of the interaction between quinolones and polyvalent cations.

The aim of the present study was to evaluate the influence of aluminium and iron on the in vitro dissolution kinetics of ciprofloxacin and ofloxacin as well as the usefulness of this type of in vitro data to predict modifications in in vivo absorption processes as a consequence of different factors, such as the widely documented in vivo interaction between quinolones and cations. Fitting of experimental data to different theoretical in vitro dissolution profiles was performed by non-linear regression methods and the statistical moments were calculated from raw experimental data. Analysis of residuals applied to dissolution curves as well as statistical comparison of the estimated parameters were carried out to evaluate the in vitro interaction. The results reveal significative modifications of the dissolution profiles of these quinolones as a consequence of the presence of cations, especially for Fe2+ which decreases 34.7% the maximum amount dissolved for ciprofloxacin and 29.1% for ofloxacin. Al3+ also produces a decrease of the total amount of quinolone dissolved although less relevant than Fe2+. Analysis of residuals proved to be the best statistical method to evaluate differences between whole dissolution profiles, at least under the experimental conditions used.

Vancomycin dosage optimization in patients with malignant haematological disease by pharmacokinetic/pharmacodynamic analysis.

Abstract:Background: The use of vancomycin against Staphylococcus aureus is currently debated because of the increasing resistance developed by this pathogen. Nevertheless, antibacterial effectiveness is a limited resource that must be protected and restored. Novel dosage strategies based on pharmacokinetic/pharmacodynamic analyses are needed to retain effectiveness that could improve drug exposure in patients infected with such pathogens. Objective: The aim of this study was to assess whether standard or higher vancomycin dosages are required to increase the probability of attaining a target pharmacokinetic/pharmacodynamic index for several staphylococcal strains and thus to estimate the minimum vancomycin daily dose related to a high probability of effective treatment in patients with malignant haematological disease. Methods: Monte Carlo simulation was performed to calculate the cumulative fraction of response (CFR) for different vancomycin daily dosages, using a population pharmacokinetic model previously defined in patients with malignant haematological disease and the minimum inhibitory concentration (MIC) distribution for vancomycin against several staphylococcal species (vancomycin-susceptible S. aureus and vancomycin-intermediate S. aureus [VISA], S. epidermidis, S. haemolyticus and coagulase-negative Staphylococcus [CNS] species) obtained from the European Committee on Antimicrobial Susceptibility Testing (EUCAST) in order to predict the dose that would achieve the pharmacokinetic/pharmacodynamic index value associated with efficacy (the area under the concentration-time curve from 0 to 24 hours divided by the MIC [AUC24/MIC ≥400]). Results: CFR values showed dependence on the renal function of the patient and the causative pathogen. Only in patients with a creatinine clearance (CLCR) <60 mL/min did the standard vancomycin dosage (2000 mg/day) induce CFRs > 60% for all staphylococci, except the VISA strains. CFRs for S. aureus of 90.6%, 47.3% and 31.2% for CLCR values of <60, 60–120 and > 120 mL/min, respectively, were obtained, whereas for the VISA strains, the corresponding values were only 14.0%, 0.3% and 0%.The impact of potential pathogens on CFRs is also significant. According to our pharmacokinetic/pharmacodynamic analysis, in patients with normal renal function (CLCR between 60 and 120 mL/min) vancomycin 2000 mg/day leads to a risk of not achieving the recommended AUC24/MIC breakpoint of 52.7%, 70.4%, 74.9% and 80.3% for S. aureus, S. haemolyticus, CNS and S. epidermidis, respectively. Application of our results to clinical practice graphically allows us to obtain the recommended dose for any a priori-selected probability of attaining the AUC24/MIC ratio of ≥400 and to evaluate the CFRs for any dosing regimen used in this population group, depending on the patients’ renal function. Conclusions: Application of pharmacokinetic/pharmacodynamic analysis based on Monte Carlo simulation offers an excellent tool for selecting the therapeutic option with the highest probability of clinical success in patients with malignant haematological disease. Thus, for vancomycin-susceptible S. aureus, if a CFR ≥80 is assumed as clinically acceptable, vancomycin doses of 1500, 3000 and 4000 mg/day for a CLCR of <60, 60–120 and >120 mL/min, respectively, will be required.

Pulmonary versus systemic delivery of antibiotics : Comparison of vancomycin dispositions in the isolated rat lung

ABSTRACT Vancomycin dispositions in the respiratory system were compared after systemic and inhalatory administration under two respiratory conditions using the isolated-lung model. Inhalatory delivery led to much higher drug levels in pulmonary tissue and fluids. The respiratory pattern affects vancomycin disposition in the pulmonary system regardless of the administration route.

Pharmacokinetics and Pharmacodynamics of Levofloxacin in Intensive Care Patients

AbstractObjective: A prospective pharmacokinetic study was performed in Caucasian patients from an intensive care unit with respiratory support to evaluate the influence of this circumstance on the pharmacokinetic behaviour of levofloxacin. Patients and methods: A standard dosage regimen of 500 mg/day was administered to nine Caucasian patients included in the study, irrespective of their demographic characteristics. The experimental data on plasma concentrations were analysed by independent-modelling techniques to estimate the following pharmacokinetic parameters: area under the plasma concentration-time curve (AUC), volume of distribution at steady state (Vss), plasma clearance (CL), maximum plasma concentration at steady state (Cmax,ss) and elimination half-life (t½β). Multiple regression analysis was applied to establish the type of correlation between the pharmacokinetic parameters and patient characteristics; the Monte Carlo simulation technique was implemented for the pharmacokinetic/pharmacodynamic analysis based on the probability distribution of the values of AUC/ minimum inhibitory concentration (MIC) and Cmax,ss/MIC observed in this group of patients. Results and conclusion: The results show that for AUC the simplest linear model with creatinine clearance as the only independent variable fits the data at a 99% confidence level, explaining more than 85% of the observed variability in this parameter. The volume of distribution, however, showed a statistical correlation with the severity of the illness (Simplified Acute Physiology Score II), although total bodyweight also explains a high percentage of variability of these parameters. Since the group of patients included in the study was small and also included obese individuals, it is difficult to estimate with precision the contribution of each circumstance (overweight or illness severity) to the pharmacokinetic behaviour of levofloxacin.

Comparative study of the disposition of levofloxacin, netilmicin and cefepime in the isolated rat lung.

An experimental model of artificially perfused and mechanically ventilated lung has been applied to compare the kinetic behaviour of levofloxacin, cefepime and netilmicin in this body tissue. The study has been performed to explore the usefulness of the isolated lung technique in the pharmacokinetic field, particularly to study the disposition of antibiotics in pulmonary tissue. The lung was perfused with Krebs‐Henseleit medium containing 3% bovine albumin at a flow rate of 5 mL min−1. It was ventilated at 60 respirations/min with a 2‐mL tidal volume of air previously humidified and warmed to 37°C. The concentrations of the above antibiotics were determined by HPLC techniques and the outflow curves were analysed by stochastic, as well as by model‐dependent, methods. The results show pharmacokinetic differences among these antibiotics, which are in accordance with previously reported data, levofloxacin being the drug with the highest distribution coefficient in this tissue (1.25 ± 0.14 vs 0.39 ± 0.07 and 0.41 ± 0.06 mL g−1 for netilmicin and cefepime, respectively). Accordingly, the isolated lung of the rat, under the experimental conditions used here, constitutes an alternative model to be incorporated to pharmacokinetic studies with a great potential use for those drugs that show a pharmacological or toxicological action depending on the kinetic profile in the lung tissue.

Albumin micro/nanoparticles entrapping liposomes for itraconazole green formulation

Abstract Itraconazole‐loaded micro/nanoparticles containing albumin and liposomes were prepared by a technological process that avoids the use of organic solvents and crosslinker agents. The particles were characterized, lyophilized and formulated as tablets. Dynamic light scattering was used to determine the hydrodynamic diameter and zeta potential of the particles; optical and scanning‐electron microscopy was used to evaluate their morphology. Spherical shaped particles of different sizes and zeta potential were obtained. An exponential relationship between the zeta potential and the albumin/cationic lipid molar ratio was established. Drug entrapment efficiency values were in the range of 51–68%, with no statistical differences among albumin feeding concentrations. Mannitol was used as lyophilization additive and the freeze‐dried cake was directly compressed into tablets, suitable for vaginal administration. The results from the in vitro drug delivery assay show the influence of albumin on the itraconazole delivery profile; a rapid release was observed for particles with higher albumin amount compared to those with lower protein content. According to the results of this study, albumin particles entrapping liposomes prove to be a green pharmaceutical vehicle with a high potential for delivery of hydrophobic and highly albumin‐bound drugs. Graphical abstract Figure. No Caption available.

Lyophilized tablets for focal delivery of fluconazole and itraconazole through vaginal mucosa, rational design and in vitro evaluation

&NA; The present work deals with the rational design and in vitro evaluation of vaginal tablets for focal delivery of fluconazole (FLZ) and itraconazol (ITZ). Drug loaded liposomes with and without d‐alpha‐tocopheryl polyethylene glycol 1000 succinate (vit E TPGS) were prepared by direct sonication of the components and mixed with albumin to obtain albusomes. Tablets were obtained by direct compression of the lyophilized cake. The influence of vit E TPGS on size, zeta potential and entrapment efficiency (EE%) of liposomes and albusomes was evaluated. Tablet swelling and drug release were studied by in vitro assays. Vit E TPGS neither affected the zeta potential nor the EE% of liposomes and albusomes, but affected the liposomes size and the tablet disintegration time. A rapid erosion was observed for the tablets with the highest content of vitamin, while a slow swelling for those lacking the vitamin (swelling index = 57.76 ± 13.51%). A faster drug release profile was obtained for the former compared to the latter. The in vitro assay showed that FLZ diffused and solved in the vaginal fluid simulant while ITZ remained into the albusomes, which slowly released ITZ‐albumin complex and ITZ‐loaded liposomes, both suitable carriers for drug transport to deeper vaginal endothelium. Graphical abstract Figure. No caption available.

Therapeutic Drug Monitoring and Pharmacokinetics/Pharmacodynamics of Antibiotics as Useful Tools for Translational Research and Personalized Medicine

Antibiotic dosage optimization in special population groups is a desirable task in clinical practice since product label recommendations rely on drug information from a reduced number of individuals receiving the product. Clinical use involves patients showing relevant differences in ethnic, genetic, age, weight, and health/illness states that may affect drug response. In the case of antibiotics, this topic is of particular relevance due to the high risk of emerging resistance when non-appropriate dosage schedules are used. Fortunately, knowledge of pharmacokinetics and pharmacodynamics, together with application of drug plasma curve simulation techniques, allows for determining the best dosage schedule in terms of achieving the recommended valued for the particular pharmacokinetic/ pharmacodynamic index related to clinical efficacy. Literature information regarding the pharmacokinetics/ pharmacodynamics of antibiotics has progressively increased over the last 30 years, revealing an increased interest in this subject. Although these theoretical considerations are not always applied in the clinical arena, translational research involving application of the ‘knowhow’ of the practice is being able for anti-infective drugs. The work performed by Pai et al. [1] is an example of this. These authors reviewed medical records of critically ill patients treated with meropenem administered by continuous infusion, both empirically and for documented Gram-negative infections, from a hospital where therapeutic drug monitoring of this antibiotic has been routinely performed. Those subjects with a body mass index [25 kg/m were included in the study in order to evaluate the influence of body weight on the pharmacokinetic parameters determining the pharmacokinetic/pharmacodynamic index predictive of meropenem clinical efficacy, i.e. the time above minimum inhibitory concentration (t[MIC). The selection of overweight and obese patients for the study was an excellent choice due to the worldwide increase of this population group, and also because there was no consensus on the best body size descriptor to be used for creatinine clearance (CLCR) estimation for this population group. For antibiotics mainly eliminated via renal excretion, such as aminoglycosides, vancomycin and meropenem dosage was based on CLCR values since this is a surrogate marker of renal function. However, estimation of CLCR was carried out according to body size, and methods using total body weight (TBW) significantly overestimated CLCR in overweight and obese individuals. An extensive analysis of this topic has been previously carried out for aminoglycoside antibiotics [2], and adjusted body weight (ABW) seems to be the variable that best predicts CLCR in overweight patients. Regarding the above-mentioned meropenem study [1], the results of the body size descriptors (TBW, ABW, body surface area) marginally affecting CLCR estimation are interesting, as is the conclusion that point estimates of CLCR can provide a reasonable estimate of meropenem clearance (CL), even in patients with changing kidney function. These unexpected findings might be related to a ‘flip-flop’ pharmacokinetic phenomenon; in that case not the renal function but the slow infusion rate would mainly control the elimination rate. From the meropenem CL to CLCR relationship obtained, the authors estimate drug serum concentrations for & Amparo Sánchez Navarro asn@usal.es