A retrospective analysis of pharmacokinetic/pharmacodynamic indices as indicators of the clinical efficacy of ciprofloxacin

Ciprofloxacin Pharmacokinetics/Pharmacodynamics against Susceptible and Low-Level Resistant Escherichia coli Isolates in an Experimental Ascending Urinary Tract Infection Model in Mice

The mouse ascending urinary tract infection model was used to study the pharmacokinetic/pharmacodynamic (PKPD) relationships of the effect of ciprofloxacin in subcutaneous treatment for 3 days with varying doses and dosing intervals against a susceptible Escherichia coli strain (MIC, 0.032 mg/liter). Further, a humanized dose of ciprofloxacin was administered for 3 days against three E. coli strains with low-level resistance, i.e., MICs of 0.06, 0.25, and 1 mg/liter, respectively. Against the susceptible isolate, ciprofloxacin was highly effective in clearing the urine with daily doses from 10 mg/kg, but the dosing regimen had to be divided into at least two doses for optimal effect. Ciprofloxacin could not clear the urine or kidneys for the low-level-resistant strains. PKPD correlations with all strains combined showed that for the AUC₂₄/MIC there was a slightly higher correlation with effect in urine and kidneys (R ², 0.71 and 0.69, respectively) than the %T_>MIC (R ², 0.41 and 0.61, respectively). Equal correlations for the two PKPD indices were found for reduction of colony counts (CFU) in the bladder tissue, but not even the highest dose of 28 mg/kg × 6 could clear the bladder tissue. In conclusion, ciprofloxacin is highly effective in clearing the urine and kidney tissue for fully susceptible E. coli, while even low-level resistance in E. coli obscures this effect. While the effect of ciprofloxacin is mostly AUC/MIC driven against E. coli infection in the urinary tract, the effect in urine depends on the presence of ciprofloxacin in the urine during most of a 24-h period.

Applications of physiologically based pharmacokinetic modeling for the optimization of anti-infective therapies

INTRODUCTION

The pharmacokinetic properties of anti-infective drugs are a determinant part of treatment success. Pathogen replication is inhibited if adequate drug levels are achieved in target sites, whereas excessive drug concentrations linked to toxicity are to be avoided. Anti-infective distribution can be predicted by integrating in vitro drug properties and mathematical descriptions of human anatomy in physiologically based pharmacokinetic models. This method reduces the need for animal and human studies and is used increasingly in drug development and simulation of clinical scenario such as, for instance, drug-drug interactions, dose optimization, novel formulations and pharmacokinetics in special populations.

AREAS COVERED

We have assessed the relevance of physiologically based pharmacokinetic modeling in the anti-infective research field, giving an overview of mechanisms involved in model design and have suggested strategies for future applications of physiologically based pharmacokinetic models.

EXPERT OPINION

Physiologically based pharmacokinetic modeling provides a powerful tool in anti-infective optimization, and there is now no doubt that both industry and regulatory bodies have recognized the importance of this technology. It should be acknowledged, however, that major challenges remain to be addressed and that information detailing disease group physiology and anti-infective pharmacodynamics is required if a personalized medicine approach is to be achieved.

Pharmacokinetic/ pharmacodynamic evaluation of anti-infective agents

Pharmacokinetic/pharmacodynamic modeling has become an extremely important tool in evaluating and optimizing anti-infective therapy. By systematically linking the pharmacokinetic and pharmacodynamic properties of the anti-infective agent, it is possible to make educated decisions about the correct drug to be used, correct dosing regimen and to estimate the probability of success with the selected dose regimen. This article gives an overview of the current pharmacokinetic/pharmacodynamic approaches for anti-infective agents and discusses their use in optimizing drug therapy.

An evaluation of ciprofloxacin pharmacokinetics in critically ill patients undergoing continuous veno-venous haemodiafiltration

Background

The study aimed to investigate the pharmacokinetics of intravenous ciprofloxacin and the adequacy of 400 mg every 12 hours in critically ill Intensive Care Unit (ICU) patients on continuous veno-venous haemodiafiltration (CVVHDF) with particular reference to the effect of achieved flow rates on drug clearance.

Methods

This was an open prospective study conducted in the intensive care unit and research unit of a university teaching hospital. The study population was seven critically ill patients with sepsis requiring CVVHDF.

Blood and ultrafiltrate samples were collected and assayed for ciprofloxacin by High Performance Liquid Chromatography (HPLC) to calculate the model independent pharmacokinetic parameters; total body clearance (TBC), half-life (t_1/2) and volume of distribution (Vd). CVVHDF was performed at prescribed dialysate rates of 1 or 2 L/hr and ultrafiltration rate of 2 L/hr. The blood flow rate was 200 ml/min, achieved using a Gambro blood pump and Hospal AN69HF haemofilter.

Results

Seventeen profiles were obtained. CVVHDF resulted in a median ciprofloxacin t_1/2 of 13.8 (range 5.15-39.4) hr, median TBC of 9.90 (range 3.10-13.2) L/hr, a median V_dss of 125 (range 79.5-554) L, a CVVHDF clearance of 2.47+/-0.29 L/hr and a clearance of creatinine (Cl_cr) of 2.66+/-0.25 L/hr. Thus CVVHDF, at an average flow rate of ~3.5 L/hr, was responsible for removing 26% of ciprofloxacin cleared. At the dose rate of 400 mg every 12 hr, the median estimated C_pmax/MIC and AUC_0-24/MIC ratios were 10.3 and 161 respectively (for a MIC of 0.5 mg/L) and exceed the proposed criteria of >10 for C_pmax/MIC and > 100 for AUC_0-24/MIC. There was a suggestion towards increased ciprofloxacin clearance by CVVHDF with increasing effluent flow rate.

Conclusions

Given the growing microbial resistance to ciprofloxacin our results suggest that a dose rate of 400 mg every 12 hr, may be necessary to achieve the desired pharmacokinetic - pharmacodynamic (PK-PD) goals in patients on CVVHDF, however an extended interval may be required if there is concomitant hepatic impairment. A correlation between ciprofloxacin clearance due to CVVHDF and creatinine clearance by the filter was observed (r² = 0.76), providing a useful clinical surrogate marker for ciprofloxacin clearance within the range studied.

Trial Registration

Current Controlled Trials ISRCTN52722850

[Pharmacokinetic/pharmacodynamic analysis of antibiotic therapy in dentistry and stomatology]

INTRODUCTION

This study evaluates the efficacy of various antimicrobial treatments for orofacial infections on the basis of pharmacokinetic/pharmacodynamic (PK/PD) criteria.

METHODS

A complete a literature search was undertaken to establish the MIC90 values of the five microorganisms most frequently isolated in odontogenic infections and the pharmacokinetic parameters of 13 antibiotics used in these infections. Pharmacokinetic simulations were then carried out with mean population parameters and efficacy indexes were calculated for the 47 treatment regimens analyzed. For drugs showing time-dependent antibacterial killing, the time above MIC (t > MIC) was calculated. For drugs with concentration-dependent bactericidal activity, the AUC/MIC was calculated.

RESULTS

Amoxicillin-clavulanic (500 mg/8 h or 1000 mg/12 h) and clindamycin (300 mg/6 h) in the time-dependent killing group and moxifloxacin (400 mg/24 h) in the concentration-dependent group showed adequate efficacy indexes against the five pathogens considered to be the most commonly implicated in odontogenic infections. The spiramycin plus metronidazole combination, present in the commercial formulation Rhodogyl, did not reach satisfactory PK/PD indexes.

CONCLUSION

PK/PD indexes, which are useful predictors of the potential efficacy of antibacterial therapy, were used with ontogenic infections in the present study. The PK/PD simulations showed that amoxicillin-clavulanic, clindamycin and moxifloxacin were the most suitable antibiotics for this kind of infection. Clinical trials are required to confirm that this methodology is useful in these pathologic processes.

Pharmacokinetics of ciprofloxacin as a tool to optimise dosage schedules in community patients

OBJECTIVE

To evaluate the dosage regimens of ciprofloxacin prescribed for outpatients by applying the principles of antibacterial therapy.

DESIGN

Retrospective analysis of prescription and demographic data.

SETTING

Community pharmacy in Valladolid, Spain.

PATIENTS

Fifty male and female patients aged 18-93 years and with bodyweight 41-95kg.

METHODS

Prescribed dosage regimen, age, weight, height, type of infection, comorbidity and coadministered drugs were recorded for each patient. Plasma concentration curves were simulated from literature values of the pharmacokinetic parameters of the drug and the age and weight of the patients. Urine concentrations were estimated from simulated plasma concentrations, literature values of renal clearance and an average urinary flow rate of 2 L/day. The potential efficacy of the prescribed treatment was evaluated from the ratio of the simulated peak plasma concentration (C(max)) to the literature value of the minimum inhibitory concentration (MIC) for the bacterium most probably responsible for the infection (C(max) /MIC). The ratio of area under the plasma concentration-time curve over 24 hours to MIC (AUC24 /MIC) was also estimated for non-urinary infections.

RESULTS

Demographic variables such as age or bodyweight do not seem to be taken in consideration when ciprofloxacin is prescribed, at least in the patients considered here, leading to wide interindividual variability in plasma concentrations. This may not be relevant for urinary infections, since ciprofloxacin concentrates in the urine, leading to high Cmax /MIC ratios in all patients. Simulated plasma concentration-time curves revealed consistent underdosing for systemic infections in young patients over 60kg, for whom the plasma concentrations achieved led to Cmax /MIC and AUC24 /MIC ratios lower than those associated with clinical efficacy and minimal spread of bacterial resistance.

CONCLUSIONS

The standard regimen of ciprofloxacin 250mg every 12 hours prescribed for urinary infections may not be the best choice, since a more convenient regimen of 500mg once daily leads to a higher Cmax /MIC ratio, which is associated with a more significant postantibiotic effect and higher efficacy of fluoroquinolones. For non-urinary infections, the age and weight of patients should be taken into account to achieve optimum plasma concentrations.

The pharmacokinetic-pharmacodynamic approach to a rational dosage regimen for antibiotics

Pharmacokinetic-pharmacodynamic (PK/PD) surrogate indices (AUIC, AUC/MIC, C(max)/MIC, T>MIC) for measuring antibiotic efficacy are presented and reviewed. As clinical trials are not sufficiently sensitive to establish a dosage regimen which guarantees total bacteriological cure (Pollyanna phenomenon), PK/PD indexes have been proposed from in vitro, ex vivo, and in vivo infection models and subsequently validated in retrospective or prospective human clinical trials. The target value for time-dependent antibiotics (beta-lactams, macrolides) is a time above the MIC (T>MIC) of 50-80% of the dosage interval, while for concentration-dependent antibiotics (quinolones and aminoglycosides), the area under the inhibitory curve (AUIC, or more simply AUC/MIC of about 125h) is the best surrogate indicator of activity. Using the latter drugs, high concentrations achieved early during therapy are desirable to prevent the development of resistance. A C(max)/MIC ratio greater than 10-12 seems to be an appropriate target for aminoglycosides.

Antibiotic pharmacodynamics in surgical prophylaxis: an association between intraoperative antibiotic concentrations and efficacy

The objective of this study was to characterize the relationship between gentamicin concentrations during surgery and the development of wound infection following colorectal operations. Despite decades of research in surgical prophylaxis, the relationship between intraoperative antibiotic concentrations and postoperative infection and the concentrations required for effective prophylaxis have not been established. A pharmacodynamic analysis was conducted using data from a previous prospective, randomized, double-blind clinical study which compared two dosage regimens of gentamicin plus metronidazole for prophylaxis in connection with elective colorectal surgery. Univariate and multivariate analyses of risk factors for postoperative wound infection were conducted, and the relationship between intraoperative gentamicin concentrations and surgical outcome was characterized. The gentamicin concentration at the time of surgical closure was one of the strongest independent risk factors for infection (P = 0.02), along with the presence of diabetes mellitus (P = 0.02), stoma (P = 0.04), and advanced age (P = 0.05). Gentamicin concentrations at closure of less than 0.5 mg/liter were associated with an infection rate of 80% (representing 8 of 10 patients with concentrations below that level) (P = 0.003). Receiver operating characteristic curve analysis identified a critical closure concentration of 1.6 mg/liter for effective surgical prophylaxis (P = 0.002; sensitivity, 70.8%; specificity, 65.9%). This study provides new and important information on antibiotic pharmacodynamics in surgical prophylaxis. It demonstrates the critical effect of the antibiotic concentration at closure on wound infection and suggests a significant association between the concentration and other well-established risk factors, like the timing of preoperative antibiotic administration and surgery duration.

A retrospective analysis of pharmacokinetic-pharmacodynamic parameters as indicators of the clinical efficacy of ceftizoxime

OBJECTIVE

To analyse the relationship between a series of estimated pharmacokinetic-pharmacodynamic parameters and the reported efficacy of ceftizoxime.

DESIGN

Retrospective literature search and analysis using different correlation models.

METHODS

The following parameters were calculated for each group of patients included in the study from the simulated plasma concentration curves corresponding to the dosage regimen administered: (i) peak concentration at steady state divided by the minimum inhibitory concentration (CmaxSS/MIC); (ii) the time that the plasma drug concentration exceeded the MIC scaled to 24 hours at steady state [(tSS)24h > MIC]; (iii) the total area under the concentration-time curve over 24 hours at steady state divided by the MIC [(AUC(SS))24h/MIC]; and (iv) the AUC at steady state for the period of time that the concentration is above the MIC over a period of 24 hours divided by the MIC [(AUIC(SS))24h]. A univariate correlation analysis was performed considering efficacy [rate (%) of clinical cure or bacterial eradication] as the dependent variable and the pharmacokinetic-pharmacodynamic parameter as the independent variable, using linear and nonlinear models.

RESULTS

(tSS)24h > MIC was the only parameter that was statistically correlated with efficacy, the linear model being the best choice among the 4 relationship approaches tested. A biased frequency distribution of reported efficacy data constricts the correlation analysis to a narrow range of efficacy and hinders interpretation of the results.

CONCLUSIONS

The reporting of cases with low efficacy rates as well as those with high efficacy rates, including information on patient idiosyncrasies and the infecting organisms, would be of great help in performing retrospective analyses of the use of antimicrobial agents, leading to the optimisation of therapy with this type of drug in clinical practice.