Marie Sandström

Semimechanistic Pharmacokinetic/Pharmacodynamic Model for Assessment of Activity of Antibacterial Agents from Time-Kill Curve Experiments

ABSTRACT Dosing of antibacterial agents is generally based on point estimates of the effect, even though bacteria exposed to antibiotics show complex kinetic behaviors. The use of the whole time course of the observed effects would be more advantageous. The aim of the present study was to develop a semimechanistic pharmacokinetic (PK)/pharmacodynamic (PD) model characterizing the events seen in a bacterial system when it is exposed to antibacterial agents with different mechanisms of action. Time-kill curve experiments were performed with a strain of Streptococcus pyogenes exposed to a wide range of concentrations of the following antibiotics: benzylpenicillin, cefuroxime, erythromycin, moxifloxacin, and vancomycin. Bacterial counts were monitored with frequent sampling during the experiment. A simultaneous fit of all data was accomplished. The degradation of the drugs was monitored and corrected for in the model, and a link model was used to account for an effect delay. In the final PK/PD model, the total bacterial population was divided into two subpopulations: one growing drug-susceptible population and one resting insusceptible population. The drug effect was included as an increase of the killing rate of bacteria in the susceptible state, according to a maximum-effect (Emax) model. An internal model validation showed that the model was robust and had good predictability. In conclusion, for all drugs, the final PK/PD model successfully described bacterial growth and killing kinetics when the bacteria were exposed to different antibiotic concentrations. The semimechanistic model that was developed might, after further refinement, serve as a tool for the development of optimal dosing strategies for antibacterial agents.

Population pharmacokinetic modelling of unbound and total plasma concentrations of paclitaxel in cancer patients.

The aim of this study was to validate and further develop a mechanism-based population pharmacokinetic model for paclitaxel (Taxol; Bristol-Myers Squibb Co, Princeton, NJ, USA) based on the knowledge of Cremophor EL (CrEL) micelle entrapment and to evaluate the exposure/toxicity relationships. Paclitaxel (total and unbound) and CrEL concentrations were obtained according to a sparse sampling scheme with on average only 3.5 samples per course from 45 patients with solid tumours who received 3-hour infusions of paclitaxel (final dose range 112-233 mg/m(2)). The present data were predicted well by the mechanism-based model. In addition, bilirubin and body size were found to be significant as covariates. A change in body surface area (BSA) of 0.1 m(2) typically caused a change in clearance (CL) of 22.3 l/h and an increase in bilirubin of 10 microM typically caused a decrease in CL of 41 l/h. Toxicity was best described by a threshold model. In conclusion, even with a sparse sampling scheme, the same mechanism-based binding components as in the previously developed model could be identified. Once the CrEL and total paclitaxel plasma concentrations are known, the unbound concentrations, which are more closely related to the haematological toxicity, can be predicted.

Model Describing the Relationship Between Pharmacokinetics and Hematologic Toxicity of the Epirubicin-Docetaxel Regimen in Breast Cancer Patients

PURPOSE The aims of the present study were (1) to characterize the pharmacokinetics of both component drugs and (2) to describe the relationship between the pharmacokinetics and the dose-limiting hematologic toxicity for the epirubicin (EPI)/docetaxel (DTX) regimen in breast cancer patients. PATIENTS AND METHODS Forty-four patients with advanced disease received EPI and DTX every 3 weeks for up to nine cycles. The initial doses (EPI/DTX) were 75/70 mg/m(2). Based on leukocyte (WBC) and platelet counts, the subsequent doses were, stepwise, either escalated (maximum, 120/100 mg/m(2)) or reduced (minimum, 40/50 mg/m(2)). Hematologic toxicity was monitored in all patients, whereas pharmacokinetics was studied in 16 patients. A semiphysiological model, including physiological parameters as well as drug-specific parameters, was used to describe the time course of WBC count following treatment. RESULTS In the final pharmacokinetic model, interoccasion variability was estimated to be less than interindividual variability in the clearances for both drugs. The sum of the individual EPI and DTX areas under concentration-time curve correlated stronger to WBC survival fraction than did the corresponding sum of doses. A pharmacokinetic-pharmacodynamic (PK-PD) model with additive effects of EPI and DTX could adequately describe the data. CONCLUSION The final PK-PD model might provide a tool for calculation of WBC time course, and hence, for prediction of nadir day and duration of leukopenia in breast cancer patients treated with the EPI/DTX regimen.

Lack of relationship between systemic exposure for the component drug of the fluorouracil, epirubicin, and 4-hydroxycyclophosphamide regimen in breast cancer patients.

PURPOSE The aim of this study was to investigate the covariance between the pharmacokinetics of the three components of the FEC regimen, epirubicin (EPI), fluorouracil (5-FU), and the cyclophosphamide (CP) metabolite 4-hydroxycyclophosphamide (4-OHCP), in breast cancer patients. PATIENTS AND METHODS Data from 21 women were collected over a total of 35 cycles. 5-FU (300 to 600 mg/m2) and CP (300 to 600 mg/m2) were administered as bolus injections, whereas EPI (15 to 60 mg/m2) was administered either as a bolus injection or as an infusion. The pharmacokinetics of the component drugs were monitored using a limited sampling scheme. Population pharmacokinetic models for each of the three drugs were developed using the program NONMEM. RESULTS The data for 5-FU were best described by a one-compartment model with nonlinear elimination, where the maximal rate of elimination (Vmax) and the concentration at which the elimination was half-maximal (Km) were 105 mg/L.h and 27 mg/L, respectively. EPI concentration-time profiles showed a triexponential decline, with a mean terminal half-life of 24 hours and a clearance (CL) of 59 L/h. The elimination of 4-OHCP was monoexponential, with a mean half-life of 7 hours. The interindividual coefficients of variation (CVs) in CL were 30%, 22%, and 41% for 5-FU, EPI, and 4-OHCP, respectively. The corresponding values for intrapatient course-to-course variability in CL were 11%, 8%, and 27%. No significant correlation in any of the pharmacokinetic parameters between the drugs was found. CONCLUSION Individualization of dosing of the FEC regimen using therapeutic drug monitoring and attempts to find concentration-response relationships may be successful, but requires that the exposure of all three drugs is considered simultaneously.

Cytotoxic activity of a new paclitaxel formulation, Pacliex, in vitro and in vivo.

BackgroundThe paclitaxel formulation, Taxol (Bristol-Myers Squibb), is one of the most effective anticancer agents used today. However; it is associated with serious side effects believed to be caused by the Cremophor EL used for its formulation.AimTo evaluate the cytotoxic activity of a new paclitaxel formulation, Pacliex (developed by Oasmia Pharmaceutical, Uppsala, Sweden), a mixed micelles preparation in which an amphiphilic synthetic derivative of retinoic acid replaced Cremophor EL/ethanol vehicle.MethodIn this study, three model systems were used to evaluate the cytotoxic activity of Pacliex and other paclitaxel preparations. The cytotoxic activities of Pacliex, Taxol and paclitaxel in ethanol were investigated against a panel of ten human tumor cell lines using the fluorometric microculture cytotoxicity assay (FMCA). Low- and high- proliferating in vitro hollow fiber model of two cell lines, the leukemia CCRF-CEM and the myeloma RPMI 8226/S cell lines, were used to assess the cytotoxic activity of the three formulations. The in vivo hollow fiber model of the two cell lines was used for assessment of Pacliex and Taxol activity. The [3-4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay was utilized to analyze the in vitro and in vivo hollow fiber data.ResultPacliex was somewhat more effective than Taxol in the more sensitive cell lines. The activity of Taxol was more pronounced in the resistant cell lines due to an additive effect of the vehicle used. The three formulations showed similar activity in both the low- and high-proliferating in vitro hollow fiber cultures. The in vivo hollow fiber cytotoxic activity of Pacliex was similar to that of Taxol. Putting all the results together, it was found that all the three formulations had similar in vitro and in vivo activity.ConclusionThe three in vitro and in vivo models confirmed the similarity of the cytotoxic activities of Pacliex and Taxol. Considering the above, Pacliex could be an interesting alternative Cremophor EL-free formulation of paclitaxel.

The time course of body temperature, serum amyloid A protein, C-reactive protein and interleukin-6 in patients with bacterial infection during the initial 3 days of antibiotic therapy

The accuracy of using body temperature, serum amyloid A (SAA), C-reactive protein (CRP) and interleukin-6 (IL-6) in the work-up for early or late step-down therapy after an initial course of intravenous cefuroxime was investigated. Eighty-one hospitalized patients with an initial course of cefuroxime were retrospectively classified with one of the following diagnoses: bacterial infection without known focus, pneumonia, bronchitis, pyelonephritis, skin and soft-tissue infections or fever of other origin. The majority of the patients had sepsis (91% or 74/81) of whom 6 patients had severe sepsis. The inter-individual variability of body temperature, SAA, CRP and IL-6 was considerable. The time course of SAA and CRP during the first 24 h in patients with sepsis with a short duration of illness but without septic shock showed increasing levels during the initial course of intravenous therapy. In contrast, body temperature and IL-6 decreased, regardless of illness duration. Beyond 24 h, all 4 biomarkers declined, again regardless of the duration of illness. After the initial course of cefuroxime, biomarkers were non-distinguishing in terms of guidance in the judgement of early or late step-down therapy. Further studies are proposed for biomarker guidance antibiotic therapy in sepsis patients without septic shock.

The pharmacokinetics of epirubicin and docetaxel in combination in rats.

Purpose: The aim of the present study was to investigate possible pharmacokinetic interactions between epirubicin (EPI) and docetaxel (DTX) in rats. Methods: Male Sprague Dawley rats (n = 36) were used in the study. They received either DTX (5 mg/kg, n = 9), EPI (3.5 mg/kg, n = 13), or a combination (5 mg/kg + 3.5 mg/kg, n = 14), administered as intravenous bolus doses. Blood samples were collected at various time-points between 3 min and 45 h after dose administration. DTX and EPI plasma concentrations were determined by HPLC analysis. Pharmacokinetic evaluation was carried out using the NONMEM program. Results: A three-compartment model best described the concentration-time profiles for EPI. Clearance (CL), intercompartmental clearances (Q2 and Q3), central (V1) and peripheral (V2 and V3) volumes of distribution were estimated as 3.57 l/h per kg, 5.01 l/h per kg, 12.48 l/h per kg, 0.805 l/kg, 3.67 l/kg and 158 l/kg, respectively. A two-compartment model was sufficient to describe the DTX data. CL, intercompartmental clearance (Q), V1 and V2 for DTX were estimated as 7.3 l/h per kg, 4.6 l/h per kg, 0.69 l/kg and 2.6 l/kg, respectively. No significant change in the disposition of either drug was found when they were administered in combination compared to when they were given singly. Conclusion: Concurrent treatment with EPI and DTX does not appear to cause any changes in the pharmacokinetics of the drugs in rats.

Fall-related self-efficacy in instrumental activities of daily living is associated with falls in older community-living people

ABSTRACT Introduction: The aim of this study was to identify fall risk factors in community-living people 75 years or older. Methods: From a random selection of 525 older adults, a total of 378 (72%) individuals participated in the study. Mean age was 81.7 years (range 75–101 years). A study-specific questionnaire including self-reported fall history for the past 6 months, the Falls-Efficacy Scale (Swedish version: FES(S)) and EuroQol 5 Dimensions (EQ5D) was used. Logistic regression analysis was conducted to find risk factors for falls. Results: The strongest significant predictor of falls was scoring low on FES(S) in instrumental activities of daily living (IADL), with an odds ratio of 7.89 (95% confidence interval 2.93–21.25). One fifth had experienced one or more falls during the past 6 months. Both fall-related self-efficacy and health-related quality of life were significantly lower among fallers. Conclusion: Our results imply that identifying community-living older adults with an increased risk of falling should include a measure of fall-related self-efficacy in IADL.

Evaluation of drug interactions in the established FEC regimen in primary cultures of tumour cells from patients

BACKGROUND Chemotherapy using multi-drug regimens is considered more active than single-agent therapy. This may be due to synergistic interactions or, simply, a higher probability of administering an active agent. We investigated in vitro the type of drug interactions in a recognized regimen in relationship to tumour type and drug sensitivity. PATIENTS AND METHODS The possibility of synergistic and additive interactions between individual cytotoxic drugs was investigated for the component drugs of the established FEC regimen, i.e., 5-fluorouracil, epirubicin and cyclophosphamide, in 243 patient tumour samples representing various drug sensitivity using the non-clonogenic fluorometric microculture cytotoxicity assay. RESULTS Using a cell survival of < or = 50% as a limit for drug activity and sample sensitivity, the overall response rates to the most active single drug (Dmax) and the combination were 56% and 64%, respectively, with a distribution among diagnoses similar to that in the clinic. For 86% of the samples there was concordance with respect to judgement of activity using either Dmax or the combination. For samples being sensitive to at least one single drug, 95% were also sensitive to the combination whereas for samples with insignificant Dmax effect, only 2% were sensitive to the combination. In samples with modest Dmax effects, i.e., cell survival in the range > 50%- < or = 80%, 45% responded to the combination. The effect of the combination was generally well predicted from the Dmax effect. CONCLUSIONS The superior antitumour effect of drug combinations compared with single drugs may be due to the higher chance of selecting an active agent. However, for intermediately sensitive tumours, additional interaction effects of a combination may be of clinical significance.