Pharmacokinetic/pharmacodynamic model-based combination therapy approach to target antibiotic resistant populations emerged from ciprofloxacin exposure.

BACKGROUND: Despite decades of antimicrobial usage, the relationship between antimicrobial drugs and the development of drug resistance has not been fully delineated. This has led to increased frequency of resistance with increased usage of antimicrobials. In recent years, new insights into the mechanisms of antibiotic resistance have been proposed, leading to a re-evaluation of novel pharmacokinetic/pharmacodynamic (PK/PD) models. We have developed a semi-mechanistic PK/PD model to describe drug-bacteria kill curve relationships using the compensatory mutation hypothesis. In addition, we explored the model-based combination therapy approach to combat the resistance population. METHODS: In vitro kill-curves of E. coli 204 up to 48 h following initial ciprofloxacin (CIP) treatment at 0.0, 0.1, 0.2, 0.5, 1.0, 2.0, 4.0, 8.0, 16.0, 32.0 and 125 times the minimum inhibitory concentration (MIC) totaling 193 data points were obtained with an in vitro system with a simulated CIP half-life of 4 h. The proposed antibiotic resistant mechanism mimics the sequential compensatory mutation hypothesis, in which mutations that acquire drug resistant traits are associated with fitness costs. Subsequent restoration of bacterial fitness is necessary for the population to be clinically relevant. Model parameters were estimated from simultaneous fitting of eleven dose groups using Adapt II software. Standard goodness of fit criteria used to obtain the final model included model convergence, Schwartz Criterion, Akaike Information Criterion, residuals versus predicted concentrations and time, and visual inspection. RESULTS/CONCLUSIONS: The eleven E. coli kill curves after CIP treatment were well described simultaneously by the compensatory mutation model. The emergence of bacterial population with drug resistance characteristics and bacterial fitness restored appears to dominate shortly following CIP treatment. The model suggests a subsequent dose of a different mechanisms of action should be considered for the emerged resistant population.

Bioavailability and pharmacokinetics of caffeoylquinic acids and flavonoids after oral administration of Artichoke leaf extracts in humans.

Extracts from artichoke leaves are traditionally used in the treatment of dyspeptic and hepatic disorders. Various potential pharmacodynamic effects have been observed in vitro for mono- and dicaffeoylquinic acids (e.g. chlorogenic acid, cynarin), caffeic acid and flavonoids (e.g. luteolin-7-O-glucoside) which are the main phenolic constituents of artichoke leaf extract (ALE). However, in vivo not only the genuine extract constituents but also their metabolites may contribute to efficacy. Therefore, the evaluation of systemic availability of potential bioactive plant constituents is a major prerequisite for the interpretation of in vitro pharmacological testing. In order to get more detailed information about absorption, metabolism and disposition of ALE, two different extracts were administered to 14 healthy volunteers in a crossover study. Each subject received doses of both extracts. Extract A administered dose: caffeoylquinic acids equivalent to 107.0 mg caffeic acid and luteolin glycosides equivalent to 14.4 mg luteolin. Extract B administered dose: caffeoylquinic acids equivalent to 153.8 mg caffeic acid and luteolin glycosides equivalent to 35.2 mg luteolin. Urine and plasma analysis were performed by a validated HPLC method using 12-channel coulometric array detection. In human plasma or urine none of the genuine target extract constituents could be detected. However, caffeic acid (CA), its methylated derivates ferulic acid (FA) and isoferulic acid (IFA) and the hydrogenation products dihydrocaffeic acid (DHCA) and dihydroferulic acid (DHFA) were identified as metabolites derived from caffeoylquinic acids. Except of DHFA all of these compounds were present as sulfates or glucuronides. Peak plasma concentrations of total CA, FA and IFA were reached within 1 h and declined over 24 h showing almost biphasic profiles. In contrast maximum concentrations for total DHCA and DHFA were observed only after 6-7 h, indicating two different metabolic pathways for caffeoylquinic acids. Luteolin administered as glucoside was recovered from plasma and urine only as sulfate or glucuronide but neither in form of genuine glucosides nor as free luteolin. Peak plasma concentrations were reached rapidly within 0.5 h. The elimination showed a biphasic profile.

Pharmacokinetic/pharmacodynamic (PK/PD) evaluation of a once-daily treatment using ciprofloxacin in an extended-release dosage form.

OBJECTIVE: To evaluate the suitability of a once-a-day dosing regimen of ciprofloxacin using a new extended-release dosage form based on PK/PD principles. METHODS: Ciprofloxacin's serum concentrations were measured after administration of 500 mg immediate-release twice-daily, and 1,000 mg extended-release once-daily to 19 healthy volunteers. Pharmacokinetic parameters were determined using non-compartmental and compartmental data analysis. Measured serum concentration profiles were linked to ciprofloxacin's effect against Escherichia coli (MIC 0.013 mg/l) from in vitro kill curve studies where the pharmacokinetics of ciprofloxacin were simulated and change in number of bacteria (CFU/ml) versus time was monitored. Resulting parameters were used to compare expected kill curves for the two dosing regimens based on measured ciprofloxacin concentrations. RESULTS: Fitting the data using an appropriate PK/PD model resulted in a set of mean pharmacodynamic parameters (bacterial growth rate constant, k0, maximum kill rate constant, Kmax, and EC50). The model included a novel term to account for a change in kill rate after approximately 4 h when Kmax decreased in concentration-dependent matter. The model allowed excellent curve fits of all ciprofloxacin concentrations investigated. Comparison of expected kill curves with the immediate-release versus extended-release treatments showed similar outcome. Both treatments resulted in a decrease in CFU/ml > 5 log units over 24 h. CONCLUSION: Results indicate that once-a-day dosing of equal total daily doses with the new and more compliance-friendly extended-release dosing form will be therapeutically equivalent to once-a-day dosing with traditional immediate-release dosage forms for treatment of infections with this microorganism.

Pharmacokinetics and bioavailability of quercetin glycosides in humans.

Due to its potentially beneficial impact on human health, the polyphenol quercetin has come into the focus of medicinal interest. However, data on the bioavailability of quercetin after oral intake are scarce and contradictory. Previous investigations indicate that the disposition of quercetin may depend on the sugar moiety of the glycoside or the plant matrix. To determine the influence of the sugar moiety or matrix on the absorption of quercetin, two isolated quercetin glycosides and two plant extracts were administered to 12 healthy volunteers in a four-way crossover study. Each subject received an onion supplement or quercetin-4'-O-glucoside (both equivalent to 100 mg quercetin), as well as quercetin-3-O-rutinoside and buckwheat tea (both equivalent to 200 mg quercetin). Samples were analyzed by HPLC with a 12-channel coulometric array detector. In human plasma, only quercetin glucuronides, but no free quercetin, could be detected. There was no significant difference in the bioavailability and pharmacokinetic parameters between the onion supplement and quercetin-4'-O-glucoside. Peak plasma concentrations were 2.3 +/- 1.5 microg x mL(-1) and 2.1 +/- 1.6 microg x mL(-1) (mean +/- SD) and were reached after 0.7 +/- 0.2 hours and 0.7 +/- 0.3 hours, respectively. After administration of buckwheat tea and rutin, however, peak plasma levels were--despite the higher dose-only 0.6 +/- 0.7 microg x mL(-1) and 0.3 +/- 0.3 microg x mL(-1), respectively. Peak concentrations were reached 4.3 +/- 1.8 hours after administration of buckwheat tea and 7.0 +/- 2.9 hours after ingestion of rutin. The terminal elimination half-life was about 11 hours for all treatments. Thus, the disposition of quercetin in humans primarily depends on the sugar moiety. To a minor extent, the plant matrix influences both the rate and extent of absorption in the case of buckwheat tea administration compared with the isolated compound. The site of absorption seems to be different for quercetin-4'-O-glucoside and quercetin-3-O-rutinoside. The significance of specific carriers on the absorption of quercetin glycosides, as well as specific intestinal beta-glucosidases, needs to be further evaluated.

Pharmacokinetic-pharmacodynamic modeling of the antibiotic effect of piperacillin in vitro.

PURPOSE: It was the aim of the present study to investigate the in vitro antimicrobial effects of the beta-lactam antibiotic piperacillin on Escherichia coli using concentration-time profiles similar to those encountered in vivo. METHODS: An in vitro dilution model was used to expose E. coli to various piperacillin concentration profiles. The antimicrobial effect was evaluated by determination of the number of bacteria over time. RESULTS: A modified Emax-model was found appropriate to describe the pharmacodynamic effect. This model was linked with the respective piperacillin concentrations to provide a suitable pharmacokinetic-pharmacodynamic (PK-PD) model. The average growth half-life in absence of piperacillin was 28 min and the maximum kill half-life was 25 min. The EC50 for the various dosing regimens averaged 5.2 micrograms/mL and was independent of dose. These parameters were used the simulate the bacterial effects of commonly administered doses or dosing regimens in humans. CONCLUSIONS: Based on the in vitro data a more frequent administration of piperacillin will be more efficacious. The proposed PK-PD-model allows a more detailed evaluation of dosing regimens than the use of minimum inhibitory concentrations.

[Pharmacokinetics and pharmacodynamics of prednisolone following extremely high dosage as prednisolone hemisuccinate]. / Zur Pharmakokinetik und Pharmakodynamik von Prednisolon nach extrem hoher Dosierung als Prednisolonhemisuccinat.

Plasma levels of prednisolone and prednisolone hemisuccinate of volunteers were measured with HPLC following i.v. injections of 1200 and 75 mg of prednisolone, given as the water-soluble hemisuccinate ester. The hemisuccinate ester is hydrolyzed relatively quickly with a plasma half-life between 18 and 25 min, and the resulting prednisolone has a plasma half-life of 3.5-3.7 h. The dose dependency of the pharmacokinetic parameters indicates a partial saturation of the metabolizing enzymes as consequence of the application of the high dose of prednisolone. In saliva no hemisuccinate could be detected. The prednisolone saliva concentration corresponds with those of non-protein-bound prednisolone in plasma measured at the same time. Only minor quantities of intact ester (1-8%) or intact prednisolone (2-4%) are excreted in urine. Following the application of 1200 mg prednisolone the endogenous cortisol level is partially suppressed only 24 h after the i.v. injection; 48 h later the difference from the basis value is not statistically significant. Leukocytosis and granulocytosis are at maximum 24 h after the injection of the high dose, and after 48 h normal values are observed. Lymphocytes and monocytes fall below normal levels for a longer time after 1200 mg compared to 75 mg, the minimum is between 4 and 8 h. Glucose levels are enhanced dose-dependently. They are normalized even after the extremely high dose at 24 h. Sodium, potassium, calcium, plasma proteins, urea, creatinine, hematocrit and hemoglobin showed no significant differences within 48 h following the injections.