BACKGROUND:In breast cancer endocrine therapy, post-therapy Ki-67 assay of biopsy material predicts recurrence-free survival but is invasive and prone to sampling error. 18F]Fluorodeoxyglucose (FDG) positron emission tomography (PET) has shown an early agonist or 'flare' response to tamoxifen and estradiol, but has not been tested in response to estrogen-lowering aromatase inhibitors (AIs). We hypothesized that decreased agonistic response to AIs would result in early FDG uptake decline. We also measured early response to trastuzumab (T), another targeted agent for breast cancer with differing mechanisms of action. Our study was designed to test for an early decline in FDG uptake in response to AI or T and to examine association with Ki-67 measures of early response.METHODS:Patients with any stage of newly diagnosed or recurrent breast cancer were eligible and enrolled prior to initiation (or resumption) of AI or T therapy. FDG PET and tissue biopsy were planned before and after 2 weeks of AI or T therapy, with pretreatment archival tissue permitted. Cutoffs of greater than or equal to]20% decline in standardized uptake value (SUV) as FDG PET early response and less than or equal to]5% post-treatment expression as Ki-67 early response were defined prior to analysis.RESULTS:Forty-two patients enrolled, and 40 (28 AI, 12 T) completed serial FDG-PET imaging. Twenty-two patients (17 AI, 5 T) had newly diagnosed disease, and 23 (14 AI, 9 T) had metastatic disease (5 newly diagnosed). Post-treatment biopsy was performed in 25 patients (63%) and was either refused or not feasible in 15. Post-treatment biopsy yielded tumor in only 17/25 cases (14 AI, 3 T). Eleven of 14 AI patients with post-therapy tissue showed FDG PET early response, and there was 100% concordance of PET and post-therapy Ki-67 early response. For the T group, 6/12 showed an FDG PET early response, including 2/3 patients with post-therapy biopsy, all with Ki-67 >5%.CONCLUSIONS:Substantial changes in FDG PET SUV occurred over 2 weeks of AI therapy and were associated with low post-therapy proliferation. SUV decline was seen in response to T, but few tissue samples were available to test association with Ki-67. Our results support further investigation of FDG PET as a biomarker for early response to AI therapy.

Objetivo: O objetivo do presente estudo foi descrever a relação entre as concentrações plasmáticas totais e livres tumorais do etoposídeo (ETO) e a inibição do crescimento do tumor observada em ratos Wistar portadores de tumor Walker- 256 (W256) utilizando a modelagem farmacocinética/farmacodinâmica (PK/PD). Métodos: Os procedimentos com animais foram aprovados no CEUA/UFRGS sob o número 22302. Os experimentos de farmacocinética foram realizados para determinar concentrações plasmáticas e livres em duas regiões do tumor sólido W256 através de microdiálise. Após a administração do ETO nas doses de 10 ou 20 mg/kg i.v. bolus em ratos Wistar portadores de tumor W256, amostras de sangue e microdialisado de tecido do centro e periferia do tumor foram coletadas simultaneamente, até 7 h pós-dose, para determinar o fator de penetração no tumor. Um método analítico por CLAE-UV foi desenvolvido e validado para quantificação do etoposídeo nas amostras de plasma e dialisado. Os experimentos de farmacodinâmica foram conduzidos em ratos portadores de tumor W256 que receberam ETO 5 e 10 mg/kg i.v. bolus uma vez ao dia por 8 e 4 dias, respectivamente. O volume dos tumores foram monitorados diariamente durante 30 dias. Análise não-compartimental dos dados de PK foi realizada no WinNonlin®. A modelagem dos dados PK e PK/PD foi realizada no Monolix®, utilizando abordagem populacional. Os dados PK/PD foram analisados usando o modelo Simeoni TGI modificado através da introdução de uma função Emax para descrever a relação nãolinear entre a concentração plasmática e tumoral e o efeito. Resultados e Discussão: O método por CLAE-UV foi desenvolvido e validado para quantificar as amostras de ETO em plasma e tecido. A penetração do ETO no tumor foi maior na periferia (61 ± 15 % e 61 ± 29 %) do que no centro do tumor (34 ± 6 % e 28 ± 11 %) após administração das doses 10 e 20 mg/kg, respectivamente (ANOVA, α = 0.05). Um modelo de 4 compartimentos compreendendo uma distribuição saturável (cinética de Michaelis-Menten) nos compartimentos tumorais a partir do compartimento central modelou simultaneamente os perfis de concentração-tempo do ETO em plasma e em ambas regiões do tumor. O modelo populacional PK/PD Simeoni TGI–Emax foi capaz de descrever o efeito antitumoral dependente do regime de administração do ETO utilizando concentrações totais plasmáticas ou livres no tumor, resultando em um maior k2max (potência máxima) para as concentrações livres (25,8 mL.μg-1.dia-1 - intratumoral vs. 12,6 mL.μg-1.dia-1 - plasma total). Conclusões: Os resultados mostram que a utilização das concentrações livres do fármaco no tumor para a modelagem PK/PD pode fornecer um melhor entendimento da relação farmacocinética e farmacodinâmica e melhoram a capacidade de previsão do modelo, considerando que a eficácia dos fármacos antineoplásicos no tratamento de tumores sólidos é dependente da capacidade do fármaco em se distribuir no tecido tumoral. / Objective: The aim of this study was to describe the relationship between total plasma and free interstitial tumor etoposide (ETO) concentrations and the drug tumor growth inhibition observed in a Walker-256 (W256) tumor-bearing Wistar rat model using the pharmacokinetic/pharmacodynamic (PK/PD) modeling. Methods: The experiments with animals were approved by CEUA/UFRGS (protocol number 22302). Pharmacokinetic experiments were conducted to determine total plasma and free intratumoral concentrations in two regions of W256 solid tumor by microdialysis. After administration of ETO 10 or 20 mg/kg i.v. bolus to W256 tumorbearing Wistar rats, blood and tissue microdialysate samples from tumor center and periphery were simultaneously collected up to 7h to determine the tumor penetration factor. An analytical HPLC-UV method was developed and validated for quantification of ETO in plasma and microdialysate samples. The pharmacodynamic experiments were conducted in W256 tumor-bearing rats that received ETO 5 or 10 mg/kg i.v. bolus every day for 8 and 4 days, respectively. Tumor volumes were monitored daily for 30 days. Non-compartmental analysis of PK data was performed in WinNonlin®. The PK and PK/PD modeling by population approach were performed using Monolix®. PK/PD data were analyzed using a modification of Simeoni TGI model by introducing an Emax function to describe the nonlinear relationship between tumor and plasma concentrations and effect. Results and Discussion: The HLPCUV method was developed and validated to determine plasma and tissue samples of ETO. ETO tumor penetration was higher in the tumor periphery (61 ± 15 % and 61 ± 29 %) than center (34 ± 6 % and 28 ± 11 %) following 10 and 20 mg/kg doses, respectively (ANOVA, α = 0.05). A 4-compartment structural model comprising a saturable distribution (Michaelis-Menten kinetics) into the tumor compartments from the central compartment simultaneously described the ETO concentration–time profiles in plasma and both tumor regions. The PK/PD population Simeoni TGI–Emax model was capable of describing the schedule-dependent antitumor effects of ETO using total plasma or free tumor concentrations obtained in a W256-tumor bearing Wistar rat model, resulting in higher k2max (maximal potency) for free concentrations (25.8 mL.μg-1.day-1 - intratumoral vs. 12.6 mL.μg-1.day-1 total plasma). Conclusions: The results showed that the use of free intratumoral drug concentrations in the PK/PD modeling can provide a better understanding of the pharmacokinetics and pharmacodynamics relationship and improve the forecasting ability of the models considering that the efficacy of antineoplastic drugs in the treatment of solid tumors is dependent on the drug ability to distribute into the tumor.

Depot intramuscularly administered testosterone cypionate (TC) is indicated for treatment of hypogonadism in males. However, illegal use of TC and other anabolic steroids in athletic competition has been occurring for over 50 years. A randomized three-arm clinical trial was conducted to investigate side effects of long-term abuse of testosterone cypionate. The objective of the thesis is to apply modeling approach to characterize pharmacokinetics of long-term TC injections as well as identify its side effects on healthy male volunteers. A linear one-compartment model with first-order absorption best described the concentration-time profile of testosterone obtained from 31 healthy males. The population clearance estimates for total and free testosterone were 2.42*103 and 6.03*105 L/day, respectively. Weight and albumin were identified as significant covariates for total testosterone. Given the known inhibitory effect of testosterone on HPG axis, an indirect effect model was applied to describe the suppression of luteinizing hormone and spermatogenesis. The estimated potency of total testosterone with respect to LH suppression was 9.38ng/ml. Model simulation showed that suppression of luteinizing hormone and spermatogenesis after TC injection was more severe and of greater duration in the highest dose level. A polynomial change point mixed effects model was successfully built to describe the change in weight and lipid profiles after weekly injection of testosterone cypionate. Model simulation showed that both 250mg and 500mg would incur an average increase of body weight of 3.5kg at 8 weeks after dosing. A polynomial change point model also identifies that there is a tendency for lipid decrease after TC administration. However, no difference was found in the lipid change between three dose groups, which precludes any definite conclusion on the effect of long-term TC administration on lipid profiles.

Background: Infections caused by carbapenem-resistant Enterobacteriaceae (CRE) such as Escherichia coli and Klebsiella pneumoniae are among the most urgent threats of the infectious disease realm. The incidence of these infections has been increasing over the years and due to very limited treatment options, mortality is estimated at about 50%. By 2050, mortality from antimicrobial resistant infections is expected to surpass cancer at 10 million deaths annually. Methods: We evaluated 18 contemporary antimicrobials against 122 carbapenem-resistant Enterobacteriaceae using a variety of antimicrobial susceptibility testing methods according to Clinical Laboratory Standards Institute guidelines. Time-kill studies were performed on clinical isolates with variable resistance to meropenem, amikacin, and polymyxin B. Phenotypic expression assays were performed on all isolates and whole genome sequencing was performed on 8 isolates to characterize molecular resistance mechanisms. Pharmacodynamic modeling of meropenem and polymyxin B was also conducted. Results: CRE were primarily K. pneumoniae, and Enterobacter spp. 60% expressed Klebsiella pneumoniae carbapenemase (KPC) only, 16% expressed Verona Integron-encoded Metallo-beta-lactamase (VIM) only, 5% expressed KPC and VIM, and 20% expressed other mechanisms of resistance. Antimicrobial susceptibility testing indicated the most active antimicrobials against CRE were ceftazidime/avibactam, imipenem/relebactam, amikacin, tigecycline, and the polymyxins. Etest® strips did not reliably measure polymyxin B resistance. The automated testing system, BD Phoenix™, consistently reported lower MICs than the gold standard broth microdilution. Time-kill studies showed regrowth at clinically achievable concentrations of meropenem alone (4, 16, and 64 mg/L), polymyxin B alone (0.25 and 1 mg/L), or amikacin alone (8 and 16 mg/L), but combinations of meropenem with either polymyxin B or amikacin were bactericidal and synergistic. Meropenem administered simultaneously or prior to polymyxin B exhibited superior activity to polymyxin B administered first. Conclusions: Novel carbapenemase-inhibitor combinations (ceftazidime/avibactam and imipenem/relebactam) exhibit the best activity against KPC-producing CRE. The polymyxins, amikacin, and tigecycline exhibit the best activity against VIM-producing CRE. Meropenem in combination with polymyxin B is bactericidal and synergistic when the meropenem MIC is ≤32 mg/L, and meropenem should never be administered after polymyxin B. Meropenem and amikacin is bactericidal and synergistic when the amikacin MIC is ≤16 mg/L. Etest® strips should not be used for characterizing polymyxin B or colistin activity. Clinicians should be aware that automated testing systems may produce biased susceptibility results relative to the gold standard method, broth microdilution, which may influence interpretation of in vitro results.

<p>To increase the proportion of patients with successful drug treatment, dose individualisation on the basis of one or several patient characteristics, <i>a priori</i> individualisation, and/or on the basis of feedback observations from the patient following an initial dose, <i>a posteriori</i> individualisation, is an option. Efficient tools in optimising individualised dosing strategies are population models describing pharmacokinetics (PK) and the relation between pharmacokinetics and pharmacodynamics (PK/PD).</p><p>Methods for estimating optimal dosing strategies, with a discrete number of doses, for dose individualisation <i>a priori</i> and <i>a posteriori</i> were developed and explored using simulated data. The methods required definitions of (<i>i</i>) the therapeutic target, <i>i.e. </i>the value of the target variable and a risk function quantifying the seriousness of deviation from the target, (<i>ii</i>) a population PK/PD model relating dose input to the target variable in the patients to be treated, and (<i>iii</i>) distributions of relevant patient factors. Optimal dosing strategies, in terms of dose sizes and individualisation conditions, were estimated by minimising the overall risk. Factors influencing the optimal dosing strategies were identified. Consideration of those will have implications for study design, data collection, population model development and target definition.</p><p>A dosing strategy for <i>a priori</i> individualisation was estimated for NXY-059, a drug under development. Applying the estimated dosing strategy in a clinical study resulted in reasonable agreement between observed and expected outcome, supporting the developed methodology.</p><p>Estimation of a dosing strategy for <i>a posteriori</i> individualisation for oxybutynin, a drug marketed for the treatment of overactive bladder, illustrated the implementation of the method when defining the therapeutic target in terms of utility and responder probability, that is, as a combination of the desired and adverse effects.</p><p>The proposed approach provides an estimate of the maximal benefit expected from individualisation and, if individualisation is considered clinically superior, the optimal conditions for individualisation. The main application for the methods is in drug development where the methods can be generally employed in the establishment of dosing strategies for individualisation with relevant extensions regarding population model complexity and individualisation conditions.</p>

To increase the proportion of patients with successful drug treatment, dose individualisation on the basis of one or several patient characteristics, a priori individualisation, and/or on the basis of feedback observations from the patient following an initial dose, a posteriori individualisation, is an option. Efficient tools in optimising individualised dosing strategies are population models describing pharmacokinetics (PK) and the relation between pharmacokinetics and pharmacodynamics (PK/PD). Methods for estimating optimal dosing strategies, with a discrete number of doses, for dose individualisation a priori and a posteriori were developed and explored using simulated data. The methods required definitions of (i) the therapeutic target, i.e. the value of the target variable and a risk function quantifying the seriousness of deviation from the target, (ii) a population PK/PD model relating dose input to the target variable in the patients to be treated, and (iii) distributions of relevant patient factors. Optimal dosing strategies, in terms of dose sizes and individualisation conditions, were estimated by minimising the overall risk. Factors influencing the optimal dosing strategies were identified. Consideration of those will have implications for study design, data collection, population model development and target definition. A dosing strategy for a priori individualisation was estimated for NXY-059, a drug under development. Applying the estimated dosing strategy in a clinical study resulted in reasonable agreement between observed and expected outcome, supporting the developed methodology. Estimation of a dosing strategy for a posteriori individualisation for oxybutynin, a drug marketed for the treatment of overactive bladder, illustrated the implementation of the method when defining the therapeutic target in terms of utility and responder probability, that is, as a combination of the desired and adverse effects. The proposed approach provides an estimate of the maximal benefit expected from individualisation and, if individualisation is considered clinically superior, the optimal conditions for individualisation. The main application for the methods is in drug development where the methods can be generally employed in the establishment of dosing strategies for individualisation with relevant extensions regarding population model complexity and individualisation conditions.

The aim of this work is to evaluate the fuzzy system for different types of patients for levodopa infusion in Parkinson Disease based on simulation experiments using the pharmacokinetic-pharmacodynamic model. Fuzzy system is to control patient’s condition by adjusting the value of flow rate, and it must be effective on three types of patients, there are three different types of patients, including sensitive, typical and tolerant patient; the sensitive patients are very sensitive to drug dosage, but the tolerant patients are resistant to drug dose, so it is important for controller to deal with dose increment and decrement to adapt different types of patients, such as sensitive and tolerant patients. Using the fuzzy system, three different types of patients can get useful control for simulating medication treatment, and controller will get good effect for patients, when the initial flow rate of infusion is in the small range of the approximate optimal value for the current patient’ type.

Στην παρούσα διπλωματική εργασία, πραγματοποιείται μία εκτεταμένη βιβλιογραφική αναφορά των πιο γνωστών και ευρέως χρησιμοποιούμενων μεθόδων για τον έλεγχο του βάθους της αναισθησίας (DoA) σε ασθενείς. Αν και ο χειροκίνητος έλεγχος της αναισθησίας παραμένει ο πιο διαδεδομένος τρόπος κατά τη διάρκεια των χειρουργικών επεμβάσεων, έχει πραγματοποιηθεί μία πληθώρα ερευνών και δοκιμών προκειμένου να αυτοματοποιηθεί η συγκεκριμένη διαδικασία. Στις περισσότερες μάλιστα από αυτές χρησιμοποιούνται μοντέλα PID ελεγκτών. Προκειμένου να επιτευχθούν καλύτερα επίπεδα εμπιστοσύνης και ακρίβειας, έχουν προταθεί διαφορετικοί τρόποι αντιμετώπισης που εφαρμόζονται πλέον σε ρεαλιστικά μοντέλα ασθενών. Επομένως, στη συγκεκριμένη εργασία γίνεται αναφορά στα διάφορα υπολογιστικά συστήματα που χρησιμοποιούνται επί του παρόντος για την υλοποίηση αλγορίθμων προβλεπτικού ελέγχου, περιγράφεται με λεπτομέρειες ο τρόπος εξαγωγής των Φαρμακοκινητικών και Φαρμακοδυναμικών μοντέλων, καθώς και επίσης μελετάται ο τρόπος λειτουργίας και η απόδοση διάφορων ελεγκτών, όπως απλός PID, MPC, RTDA και ενός deadbeat ελεγκτή, με σκοπό την εξομάλυνση της ύπνωσης έχοντας ως κύρια μεταβλητή ελέγχου την προποφόλη. / In this diploma thesis, there is an extended literature review of the most known and used methods for the depth of anesthesia (DoA) control systems. Although manual control of anesthesia is still the dominant practice during surgery, an increasing number of studies have been conducted to investigate the possibility of automating this procedure. These studies used proportional−integral−derivative (PID) controllers, as well as model-based controllers. However, there is a need for a comprehensive evaluation of closed-loop systems, to establish their safety, reliability, and efficacy for anesthesia regulation. This requires a detailed evaluation of promising and/or recent controllers for a range of patients and conditions via simulation. The present study investigates the different computational systems that are used to implement the appropriate algorithms for MPC ,the mathematic model of Pharmacokinetics and Pharmacodynamics models and the performance of single-loop PID, MPC, RTDA (Robustness, set point Tracking, Disturbance rejection, Aggressiveness) and deadbeat controllers for closed-loop regulation of hypnosis using propofol with bi spectral index (BIS) as the controlled variable

PURPOSE: This phase I dose-escalation study was undertaken to establish the maximum tolerated dose of the sequence-selective minor groove DNA binding agent SJG-136 in patients with advanced solid tumors. The study also investigated antitumor activity and provided pharmacokinetic and pharmacodynamic data. EXPERIMENTAL DESIGN: Sixteen patients were assigned sequentially to escalating doses of SJG-136 (15-240 microg/m(2)) given as a 10-minute i.v. infusion every 21 days. The dose was subsequently reduced in incremental steps to 45 microg/m(2) due to unexpected toxicity. RESULTS: The maximum tolerated dose of SJG-136 was 45 microg/m(2). The main drug-related adverse event was vascular leak syndrome (VLS) characterized by hypoalbuminemia, pleural effusions, ascites, and peripheral edema. Other unexpected adverse events included elevated liver function tests and fatigue. The VLS and liver toxicity had delayed onset and increased in severity with subsequent cycles. Disease stabilization was achieved for >6 weeks in 10 patients; in 2 patients this was maintained for >12 weeks. There was no evidence of DNA interstrand cross-linking in human blood lymphocytes with the use of the comet assay. Evidence of DNA interaction in lymphocytes and tumor cells was shown through a sensitive gamma-H2AX assay. SJG-136 had linear pharmacokinetics across the dose range tested. CONCLUSIONS: SJG-136 was associated with dose-limiting VLS and hepatotoxicity when administered by short injection every 21 days. DNA damage was noted, at all dose levels studied, in circulating lymphocytes. The etiology of the observed toxicities is unclear and is the subject of further preclinical research. Alternative clinical dosing strategies are being evaluated.

Objetivo: O objetivo do presente estudo foi descrever a relação entre as concentrações plasmáticas totais e livres tumorais do etoposídeo (ETO) e a inibição do crescimento do tumor observada em ratos Wistar portadores de tumor Walker- 256 (W256) utilizando a modelagem farmacocinética/farmacodinâmica (PK/PD). Métodos: Os procedimentos com animais foram aprovados no CEUA/UFRGS sob o número 22302. Os experimentos de farmacocinética foram realizados para determinar concentrações plasmáticas e livres em duas regiões do tumor sólido W256 através de microdiálise. Após a administração do ETO nas doses de 10 ou 20 mg/kg i.v. bolus em ratos Wistar portadores de tumor W256, amostras de sangue e microdialisado de tecido do centro e periferia do tumor foram coletadas simultaneamente, até 7 h pós-dose, para determinar o fator de penetração no tumor. Um método analítico por CLAE-UV foi desenvolvido e validado para quantificação do etoposídeo nas amostras de plasma e dialisado. Os experimentos de farmacodinâmica foram conduzidos em ratos portadores de tumor W256 que receberam ETO 5 e 10 mg/kg i.v. bolus uma vez ao dia por 8 e 4 dias, respectivamente. O volume dos tumores foram monitorados diariamente durante 30 dias. Análise não-compartimental dos dados de PK foi realizada no WinNonlin®. A modelagem dos dados PK e PK/PD foi realizada no Monolix®, utilizando abordagem populacional. Os dados PK/PD foram analisados usando o modelo Simeoni TGI modificado através da introdução de uma função Emax para descrever a relação nãolinear entre a concentração plasmática e tumoral e o efeito. Resultados e Discussão: O método por CLAE-UV foi desenvolvido e validado para quantificar as amostras de ETO em plasma e tecido. A penetração do ETO no tumor foi maior na periferia (61 ± 15 % e 61 ± 29 %) do que no centro do tumor (34 ± 6 % e 28 ± 11 %) após administração das doses 10 e 20 mg/kg, respectivamente (ANOVA, α = 0.05). Um modelo de 4 compartimentos compreendendo uma distribuição saturável (cinética de Michaelis-Menten) nos compartimentos tumorais a partir do compartimento central modelou simultaneamente os perfis de concentração-tempo do ETO em plasma e em ambas regiões do tumor. O modelo populacional PK/PD Simeoni TGI–Emax foi capaz de descrever o efeito antitumoral dependente do regime de administração do ETO utilizando concentrações totais plasmáticas ou livres no tumor, resultando em um maior k2max (potência máxima) para as concentrações livres (25,8 mL.μg-1.dia-1 - intratumoral vs. 12,6 mL.μg-1.dia-1 - plasma total). Conclusões: Os resultados mostram que a utilização das concentrações livres do fármaco no tumor para a modelagem PK/PD pode fornecer um melhor entendimento da relação farmacocinética e farmacodinâmica e melhoram a capacidade de previsão do modelo, considerando que a eficácia dos fármacos antineoplásicos no tratamento de tumores sólidos é dependente da capacidade do fármaco em se distribuir no tecido tumoral. / Objective: The aim of this study was to describe the relationship between total plasma and free interstitial tumor etoposide (ETO) concentrations and the drug tumor growth inhibition observed in a Walker-256 (W256) tumor-bearing Wistar rat model using the pharmacokinetic/pharmacodynamic (PK/PD) modeling. Methods: The experiments with animals were approved by CEUA/UFRGS (protocol number 22302). Pharmacokinetic experiments were conducted to determine total plasma and free intratumoral concentrations in two regions of W256 solid tumor by microdialysis. After administration of ETO 10 or 20 mg/kg i.v. bolus to W256 tumorbearing Wistar rats, blood and tissue microdialysate samples from tumor center and periphery were simultaneously collected up to 7h to determine the tumor penetration factor. An analytical HPLC-UV method was developed and validated for quantification of ETO in plasma and microdialysate samples. The pharmacodynamic experiments were conducted in W256 tumor-bearing rats that received ETO 5 or 10 mg/kg i.v. bolus every day for 8 and 4 days, respectively. Tumor volumes were monitored daily for 30 days. Non-compartmental analysis of PK data was performed in WinNonlin®. The PK and PK/PD modeling by population approach were performed using Monolix®. PK/PD data were analyzed using a modification of Simeoni TGI model by introducing an Emax function to describe the nonlinear relationship between tumor and plasma concentrations and effect. Results and Discussion: The HLPCUV method was developed and validated to determine plasma and tissue samples of ETO. ETO tumor penetration was higher in the tumor periphery (61 ± 15 % and 61 ± 29 %) than center (34 ± 6 % and 28 ± 11 %) following 10 and 20 mg/kg doses, respectively (ANOVA, α = 0.05). A 4-compartment structural model comprising a saturable distribution (Michaelis-Menten kinetics) into the tumor compartments from the central compartment simultaneously described the ETO concentration–time profiles in plasma and both tumor regions. The PK/PD population Simeoni TGI–Emax model was capable of describing the schedule-dependent antitumor effects of ETO using total plasma or free tumor concentrations obtained in a W256-tumor bearing Wistar rat model, resulting in higher k2max (maximal potency) for free concentrations (25.8 mL.μg-1.day-1 - intratumoral vs. 12.6 mL.μg-1.day-1 total plasma). Conclusions: The results showed that the use of free intratumoral drug concentrations in the PK/PD modeling can provide a better understanding of the pharmacokinetics and pharmacodynamics relationship and improve the forecasting ability of the models considering that the efficacy of antineoplastic drugs in the treatment of solid tumors is dependent on the drug ability to distribute into the tumor.