Prostatic Pharmacokinetic and Pharmacodynamic Analysis of Ceftazidime: Dosing Strategy for Bacterial Prostatitis.

This study aimed to develop a prostatic pharmacokinetic model of ceftazidime and suggest more effective dosing strategy for the bacterial prostatitis, based on a site-specific pharmacokinetic and pharmacodynamic perspective. Subjects were prostatic hyperplasia patients prophylactically receiving a 0.5-h infusion of 1.0 g or 2.0 g ceftazidime before transurethral resection of the prostate. Plasma and prostate samples were premeditatedly collected after the administration and the concentrations were measured by high-performance liquid chromatography. The prostate tissue/plasma ratio in area under the drug concentration-time curve was approximately 0.476. The prostatic population pharmacokinetic model incorporated creatinine clearance (CLcr) into ceftazidime clearance was developed, and adequately predicted prostate tissue concentrations by diagnostic scatter plots and visual predictive checks. Aiming for a bactericidal target of 70% of time above minimum inhibitory concentration (T > MIC) in prostate tissue, 2.0 g twice daily achieved ≥90% expected probability against main pathogens like Escherichia coli and Proteus species in patients regardless of renal function (CLcr = 60 and 90 mL/min). However, since the expected probability of attaining the bactericidal target of 0.5-h infusion dosing regimen did not achieve 90% against Pseudomonas aeruginosa in patients with CLcr = 60 and 90 mL/min, 4-h infusion dosing regimen of 2.0 g three times daily (6 g/day) might be required for empirical treatment. Based on site-specific simulations, the present study provides more effective dosing strategy for bacterial prostatitis.

Effects of High-Dose Cyclophosphamide on Ultrastructural Changes and Gene Expression Profiles in the Cardiomyocytes of C57BL/6J Mice.

The pathogenesis of cyclophosphamide (CY)-induced cardiotoxicity remains unknown, and methods for its prevention have not been established. To elucidate the acute structural changes that take place in myocardial cells and the pathways leading to myocardial damage under high-dose CY treatments, we performed detailed pathological analyses of myocardial tissue obtained from C57BL/6J mice subjected to a high-dose CY treatment. Additionally, we analysed the genome-wide cardiomyocyte expression profiles of mice subjected to the high-dose CY treatment. Treatment with CY (400 mg/kg/day intraperitoneally for two days) caused marked ultrastructural aberrations, as observed using electron microscopy, although these aberrations could not be observed using optical microscopy. The expansion of the transverse tubule and sarcoplasmic reticulum, turbulence in myocardial fibre travel, and a low contractile protein density were observed in cardiomyocytes. The high-dose CY treatment altered the cardiomyocyte expression of 1210 genes (with 675 genes upregulated and 535 genes downregulated) associated with cell-cell junctions, inflammatory responses, cardiomyopathy, and cardiac muscle function, as determined using microarray analysis (|Z-score| > 2.0). The expression of functionally important genes related to myocardial contraction and the regulation of calcium ion levels was validated using real-time polymerase chain reaction analysis. The results of the gene expression profiling, functional annotation clustering, and Kyoto Encyclopedia of Genes and Genomes pathway functional-classification analysis suggest that CY-induced cardiotoxicity is associated with the disruption of the Ca2+ signalling pathway.

Pulmonary Pharmacokinetic and Pharmacodynamic Evaluation of Ampicillin/Sulbactam Regimens for Pneumonia Caused by Various Bacteria, including Acinetobacter baumannii.

This study aimed to assess the dosing regimens of ampicillin/sulbactam for pneumonia based on pulmonary pharmacokinetic (PK)/pharmacodynamic (PD) target attainment. Using the literature data, we developed pulmonary PK models and estimated the probabilities of attaining PK/PD targets in lung tissue. Against bacteria other than A. baumannii (the general treatment), the PK/PD target was set as both 50% time above the minimum inhibitory concentration (T > MIC) for ampicillin and 50% T > 0.5 MIC for sulbactam. For the A. baumannii treatment, the PK/PD target was set as 60% T > MIC for sulbactam. The pulmonary PK/PD breakpoint was defined as the highest minimum inhibitory concentration (MIC) at which the target attainment probability in the lung tissue was ≥90%. The lung tissue/serum area under the drug concentration-time curve from 0 to 3 h (AUC0-3h) ratios for ampicillin and sulbactam were 0.881 and 0.368, respectively. The ampicillin/sulbactam AUC0-3h ratio in the lung tissue was 3.89. For the general treatment, the pulmonary PK/PD breakpoint for ampicillin/sulbactam at 3 g four times daily in typical patients with creatinine clearance (CLcr) of 60 mL/min was 2 µg/mL, which covered the MIC90s (the MICs that inhibited the growth of 90% of the strains) of most gram-positive and gram-negative bacteria. For the A. baumannii treatment, the pulmonary PK/PD breakpoint for ampicillin/sulbactam at 9 g 4-h infusion three times daily (27 g/day) in patients with a CLcr of 60 mL/min was 4 µg/mL, which covered the MIC90 of A. baumannii. A PK/PD evaluation for pneumonia should be performed in the lung tissue (the target site) rather than in the blood because sulbactam concentrations are lower in lung tissue. These findings should facilitate the selection of ampicillin/sulbactam regimens for pneumonia caused by various bacteria, including A. baumannii.

Pharmacokinetics of cefmetazole in plasma, peritoneal fluid, peritoneum, and subcutaneous adipose tissue of patients scheduled for lower gastrointestinal surgery: Dosing considerations based on site-specific pharmacodynamic target attainment.

INTRODUCTION: Cefmetazole (CMZ) has gained interest as a carbapenem-sparing alternative to the epidemic of extended-spectrum ß-lactamase (ESBL)-producing Enterobacterales (ESBL-E). In this study, we investigated the pharmacokinetics (PK) of CMZ in plasma, peritoneal fluid, peritoneum, and subcutaneous adipose tissue to assess the dosing regimen needed to achieve pharmacodynamic (PD) goals at the target site. METHODS: Patients scheduled for elective lower gastrointestinal surgery were intravenously administered CMZ. Plasma, peritoneal fluid, peritoneum, and subcutaneous adipose tissue samples were collected after CMZ infusion and during the surgery, and CMZ concentrations were measured. The non-compartmental and compartmental PK parameters were estimated and used to evaluate site-specific PD target attainment. RESULTS: A total of 38 plasma, 27 peritoneal fluid, 36 peritoneum, and 38 subcutaneous adipose tissue samples were collected from 10 patients. The non-compartmental PK analysis revealed the ratios of the mean area under the drug concentration-time curve (AUC0-3.5 h) of peritoneal fluid-to-plasma, peritoneum-to-plasma, and subcutaneous adipose tissue-to-plasma were 0.60, 0.36, and 0.11, respectively. The site-specific PD target attainment analyses based on the breakpoints for ESBL-E per the Japanese surgical site infection (SSI) surveillance (MIC90 = 8 mg/L) revealed that 2 g CMZ every 3.5 h achieved desired bactericidal effect at all sites and 2 g CMZ every 6 h achieved PD goals at peritoneum and peritoneal fluid. CONCLUSION: These findings clarify the PK of CMZ in abdominal tissues and could help decide optimal dosing regimens to treat intra-abdominal infection and prophylaxis of SSI.

Ceftolozane-Tazobactam Pharmacokinetics in the Abdominal Tissue of Patients Undergoing Lower Gastrointestinal Surgery: Dosing Considerations Based on Site-Specific Pharmacodynamic Target Attainment.

INTRODUCTION: Recently, complicated intra-abdominal infections (cIAI) have been caused not only by Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, and Pseudomonas aeruginosa, but also by extended-spectrum ß-lactamase-producing Enterobacterales members. Ceftolozane-tazobactam (CTLZ-TAZ) is considered to exhibit therapeutic effects against cIAI. Studies on the concentrations of antibiotics in abdominal tissues directly affected by cIAI are limited. Therefore, in this study, we investigated the pharmacokinetics of CTLZ-TAZ in abdominal tissue and simulated the administration regimen required to achieve the pharmacodynamic target for cIAI-causing bacteria. METHODS: Patients scheduled for elective lower gastrointestinal surgery were intravenously administered preoperative CTLZ-TAZ (1 g CTLZ and 0.5 g TAZ). Plasma, peritoneal fluid, peritoneum, and subcutaneous adipose tissue samples were collected during the surgery, and CTLZ as well as TAZ concentrations were measured. The noncompartmental and compartmental pharmacokinetic parameters were then estimated. Site-specific pharmacodynamic target attainment analysis using 1.5 g of CTLZ-TAZ was performed. RESULTS: CTLZ-TAZ was administered to nine patients (once to five patients and twice to four patients). The mean peritoneal fluid-to-plasma ratio (one dose/two doses) for CTLZ was 0.74/1.15, which was slightly higher than the mean peritoneal fluid-to-plasma ratio for TAZ (0.95/1.13). The ratio for subcutaneous adipose was lower than those for peritoneal fluid and peritoneum tissues. We also discovered that the average ratio of CTLZ and TAZ concentrations in all tissues was maintained at or above 2:1. In our investigation of pharmacodynamic target attainment in each tissue, the desired bactericidal effect was attained with all CTLZ-TAZ (1.5 g) administration regimens [q12h (3 g/day), q8h (4.5 g/day), and q6h (6 g/day)]. CONCLUSION: To the best of our knowledge, this is the first study investigating the optimal pharmacodynamic level of CTLZ-TAZ in the abdominal tissue against cIAI-causing bacteria. This study also serves as a guideline for designing an optimal administration regimen based on pharmacodynamic target attainment for cIAI-causing bacteria. DETAILS OF THE TRIAL REGISTRATION: The institutional review board of Hiroshima University Hospital, CRB6180006. The Japan Registry of Clinical Trials, jRCTs061190025.

Pharmacokinetics of flomoxef in plasma, peritoneal fluid, peritoneum, and subcutaneous adipose tissue of patients undergoing lower gastrointestinal surgery: Dosing considerations based on site-specific pharmacodynamic target attainment.

INTRODUCTION: Flomoxef is generally used to treat abdominal infections and as antibiotic prophylaxis during lower gastrointestinal surgery. It is reportedly effective against extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae and an increasingly valuable alternative to carbapenems. However, its abdominal pharmacokinetics remain unclear. Herein, pharmacokinetic analysis of flomoxef in the abdominal tissue was conducted to simulate dosing regimens for pharmacodynamic target attainment in abdominal sites. METHODS: Flomoxef (1 g) was administered intravenously to a patient 30 min before commencing elective lower gastrointestinal surgery. Samples of plasma, peritoneal fluid, peritoneum, and subcutaneous adipose tissue were collected during surgery. The flomoxef tissue concentrations were measured. Accordingly, non-compartmental and compartmental pharmacokinetic parameters were calculated, and simulations were conducted to evaluate site-specific pharmacodynamic target values. RESULTS: Overall, 41 plasma samples, 34 peritoneal fluid samples, 38 peritoneum samples, and 41 subcutaneous adipose samples from 10 patients were collected. The mean peritoneal fluid-to-plasma ratio in the areas under the drug concentration-time curve was 0.68, the mean peritoneum-to-plasma ratio was 0.40, and the mean subcutaneous adipose tissue-to-plasma was 0.16. The simulation based on these results showed the dosing regimens (q8h [3 g/day] and q6h [4 g/day]) achieved the bactericidal effect (% T > minimum inhibitory concentration [MIC] = 40%) in all tissues at an MIC of 1 mg/L. CONCLUSIONS: We elucidated the pharmacokinetics of flomoxef and simulated pharmacodynamics target attainment in the abdominal tissue. This study provides evidence concerning the use of optimal dosing regimens for treating abdominal infection caused by strains like ESBL-producing bacteria.

Concentration-Dependent Activity of Pazufloxacin against Pseudomonas aeruginosa: An In Vivo Pharmacokinetic/Pharmacodynamic Study.

The bacterium Pseudomonas aeruginosa is known to be associated with nosocomial infections around the world. Pazufloxacin, a potent DNA gyrase inhibitor, is known to be an effective drug candidate. However, it has not been clarified whether the pharmacokinetic (PK)/pharmacodynamic (PD) of pazufloxacin was effective against P. aeruginosa. Herein, we demonstrated that the PK/PD index of pazufloxacin against P. aeruginosa infection is used to optimize the dosing regiments. We constructed an in vivo infection model by infecting P. aeruginosa into the thigh of a mouse to determine the PD, and we measured the serum concentration of pazufloxacin to construct the PK model using high-performance liquid chromatography. The therapeutic efficacy of pazufloxacin was correlated with the ratio of the area under the free concentration time curve at 24 h to the minimum inhibitory concentration (fAUC24/MIC), and the maximum free concentration to the MIC (fCmax/MIC). Each contribution rate (R2) was 0.72 and 0.65, respectively, whereas the time at which the free drug concentration remained above the MIC (R2 = 0.28). The target value of pazufloxacin fAUC24/MIC for stasis was 46.1, for 1 log10 it was 63.8, and for 2 log10 it was 100.8. Moreover, fCmax/MIC for stasis was 5.5, for 1 log10 it was 7.1, and for 2 log10 it was 10.8. We demonstrated that the in vivo concentration-dependent activity of pazufloxacin was effective against the P. aeruginosa infection, and successfully made the PK/PD model sufficiently bactericidal. The PK/PD model will be beneficial in preventing the spread of nosocomial infections.

Pharmacokinetic and pharmacodynamic simulation for the quantitative risk assessment of linezolid-associated thrombocytopenia.

WHAT IS KNOWN AND OBJECTIVE: Linezolid (LZD) may cause thrombocytopenia, which can result in discontinuation of treatment. In this study, the blood LZD trough concentration was estimated based on population pharmacokinetic (PK) parameters derived from two previously published models in the Japanese population to determine the rate of achieving the target trough value when the risk of thrombocytopenia is low and to clarify its relationship with the onset of thrombocytopenia. METHODS: This study included adult patients hospitalized at Shimane University Hospital, who received LZD treatment for at least 4 days from January 2010 to December 2017. Patients whose platelet count fell below 70% before LZD administration were categorized as the thrombocytopenic group. Patient PK parameters were calculated based on the population PK models described by Matsumoto et al. and Sasaki et al., and these parameters were designated A and B, respectively. Based on these parameters, the rate of achieving an LZD trough concentration of less than 8 µg/ml, which is the safety target achievement rate, was calculated using a random simulation for each patient. We further analysed the association between the incidence of thrombocytopenia and patient factors, including safety target achievement rate, through univariate, multivariate, and receiver operating characteristic (ROC) analyses. RESULTS AND DISCUSSION: Patients (n = 77) aged 72 ± 11 years and weighing 56.7 ± 10.9 kg, with a creatinine clearance (CLcr ) of 60.5 ± 47.2 ml/min and a cirrhosis prevalence of 9.1%, were analysed. All patients received LZD at a dose of 600 mg twice daily for a total of 10.9 ± 8.9 days. Univariate analyses revealed significant differences (p < 0.05) in the duration of LZD therapy, serum creatinine, creatinine clearance, LZD clearance, and the safety target achievement rate for parameters A and B between the thrombocytopenic and non-thrombocytopenic groups. A multivariate analysis of these factors stratified with the cutoff values obtained by ROC analysis revealed that the duration of LZD therapy and the safety target achievement rates for parameters A and B were significant factors (odds ratios for duration of LZD therapy: 7.436 [95% confidence interval (CI): 1.918-28.831] and 4.712 [95% CI: 1.567-14.163]; odds ratio for safety target achievement rate: 0.060 [95% CI: 0.016-0.232] and 0.167 [95% CI: 0.056-0.498] for parameters A and B, respectively). When the safety target achievement rates for patients treated with LZD were compared between the thrombocytopenic and non-thrombocytopenic groups, the safety target achievement rate was higher in the non-thrombocytopenic group in both the patients treated with LZD for less than 10 days and those for 10 days or more. Therefore, the safety target achievement rate estimated by the PK/PD simulation may represent to be an important index for risk assessment of LZD-induced thrombocytopenia. WHAT IS NEW AND CONCLUSION: The risk of LZD-induced thrombocytopenia, which increased with the duration of LZD therapy, may be predicted using the safety target achievement rate obtained by the blood concentration simulation.

Pharmacodynamic Evaluation of Ampicillin-sulbactam in Pediatric Patients Using Plasma and Urine Data.

BACKGROUND: We aimed to develop population pharmacokinetic (PK) models of ampicillin and sulbactam using pooled data analysis and to optimize dosing regimens of ampicillin-sulbactam (combination ratio of 2:1) in pediatric patients. METHODS: Population PK models of ampicillin and sulbactam were separately developed by simultaneously fitting plasma and urine data from pediatric patients in 14 published studies. Based on these models, we estimated the probability of attaining a pharmacodynamic (PD) target [50% of time that free drug concentrations above the minimum inhibitory concentration, 50% fT > minimum inhibitory concentration (MIC)] against MIC90 [MIC that blocked the growth of 90% of the strains] of common bacteria in community-acquired pneumonia. RESULTS: The analysis included 54 pediatric patients (0.083-16.42 years of age, 4.0-77.0 kg of body weight). A total of 284 plasma concentrations and 90 urinary excretions from 0 to 6 hours after administration were used for population PK modeling. The data were adequately described by 2-compartment models for ampicillin and sulbactam. Age was not a statistically significant covariate in the PK of either drug. The PK/PD breakpoint MICs for 45 mg/kg 3 times daily and 75 mg/kg 4 times daily (q.i.d.) were 0.25 and 1 µg/mL, respectively. For empiric therapy of community-acquired pneumonia, because MIC90 values for the main target pathogens is high (MIC90 = 2 µg/mL for Streptococcus pneumoniae and MIC90 = 4 µg/mL for Haemophilus influenzae), 75 mg/kg q.i.d. (Food and Drug Administration-approved maximum dosage in United States) might be better than 45 mg/kg 3 times daily (within approved dosage in Japan) to cover many pathogens. CONCLUSIONS: From the results of this PK/PD approach, 75 mg/kg q.i.d. (Food and Drug Administration-approved maximum dosage) should be recommended in the empiric therapy of community-acquired pneumonia.

Population Pharmacokinetics of Teicoplanin and Its Dosing Recommendations for Neutropenic Patients With Augmented Renal Clearance for Hematological Malignancies.

BACKGROUND: Plasma teicoplanin concentrations do not reach the therapeutic range in several patients with hematological malignancies. Nevertheless, the characteristics of the population pharmacokinetic (PPK) models have not been clarified for malignancy. The decrease in the teicoplanin concentration in patients with cancer has been attributed to augmented renal clearance (ARC). It is essential to identify the causative factors of ARC to construct a PPK model to optimize the administration method. The authors aimed to establish a PPK model and develop an appropriate dosing regimen for teicoplanin in patients with hematological malignancies. METHODS: PPK analysis was performed using therapeutic drug monitoring (TDM) data from 119 patients with hematological malignancies. The developed model was verified by predictive performance. RESULTS: The covariates affecting systemic clearance were serum creatinine, presence or absence of neutropenia (<500/µL), and body size descriptor. Patients with hematologic malignancies and neutropenia showed a 25% increase in clearance compared with those with a normal neutrophil count. The PPK model was constructed based on the presence or absence of neutropenia. This model allowed the selection of the most appropriate dosage regimen out of those recommended by the TDM guidelines for patients with eGFR of >60 mL/min/1.73 m2. The PPK model predicted a dosing regimen for achieving a 10% improvement in the coverage probability of the target concentration range during the loading and maintenance phases. CONCLUSIONS: The PPK model may help optimize dose regimens and evaluate dosing methods, using comparative simulations, in patients with hematological malignancies.

Dosing Optimization of Ampicillin-Sulbactam Based on Cystatin C in Elderly Patients with Pneumonia.

Ampicillin-sulbactam is a first-line therapy for pneumonia and is mainly excreted by the kidney. It is important to optimize the dose and dosing interval of ampicillin-sulbactam because in patients with decreased renal function and low skeletal muscle mass, such as the elderly, excess drug may burden renal function. In this study, we evaluated indices of renal function and optimized the dose and dosing interval of ampicillin-sulbactam based on pharmacokinetics (PK) and pharmacodynamics theory in elderly patients. The serum concentrations of ampicillin and sulbactam were measured by HPLC, and PK parameters were calculated. Correlations between the clearance of ampicillin or sulbactam and renal function were evaluated, and dosing optimization was calculated based on PK parameters. The PK parameters of ampicillin were CL = 6.5 ± 4.0 L/h, Vd = 19.3 ± 0.2 L, Ke = 0.4 ± 0.2, and t1/2 = 2.7 ± 1.6 h. The most correlated renal function index was estimated glomerular filtration rate (eGFRcys-c) calculated by serum cystatin-c (r = 0.7374, correlation formula; CL of ampicillin = 0.1937 × eGFRcys-c-0.6726). Based on this formula, we calculated the clearance of ampicillin and developed dosing regimens for the elderly. Serum cystatin-c concentration is an ideal index to optimize ampicillin-sulbactam antimicrobial therapy in elderly patients with pneumonia.

[Assessment of Renal Function and Simulation Using Serum Cystatin-C in an Elderly Patient with Uncontrollable Plasma Vancomycin Levels Due to Muscular Dystrophy: A Case Report].

Herein, we describe a case of an elderly patient with muscular dystrophy for whom control of the plasma vancomycin (VCM) concentration proved difficult when he developed a catheter-related bloodstream infection. The pharmacist initially carried out therapeutic drug monitoring using an estimate of the creatinine clearance (CLcr) level, which was based on the serum creatinine (SCr) and serum cystatin-C (CysC) levels, but was ultimately unable to control the plasma VCM concentration. Therefore, the plasma VCM concentration was predicted ex post facto using population pharmacokinetic parameters as a covariate; that is, directly including the glomerular filtration rate (GFRCysC) estimated from the CysC level, which is not affected by the muscle mass. As a result, the estimated VCM concentration was closer to the actual concentration than that predicted using CLcr. Furthermore, the results of examining the predictive accuracy according to the assessment of renal function at the time of initial VCM administration suggested that estimation of the trough concentration using GFRCysC might be useful in elderly patients with muscular dystrophy.

Prostatic Pharmacokinetic/Pharmacodynamic Evaluation of Ampicillin-Sulbactam for Bacterial Prostatitis and Preoperative Prophylaxis.

This study aims to define the penetration of ampicillin and sulbactam into prostate tissue, develop a prostatic pharmacokinetic model of each drug, and assess the appropriateness of ampicillin-sulbactam regimens for the treatment of prostatitis and the prophylaxis of postoperative infection, based on a pharmacokinetic and pharmacodynamic simulation. Subjects were prostatic hyperplasia patients prophylactically receiving a 0.5-hour infusion of 1.5 g (1:0.5 g) or 3 g (2:1 g) ampicillin-sulbactam before transurethral resection of the prostate. Ampicillin and sulbactam concentrations in plasma and prostate tissue were measured. The prostate tissue/plasma ratios of both ampicillin and sulbactam were approximately 0.37 (area under the drug concentration-time curve), and penetration was similar. The prostatic population pharmacokinetic model, which included a covariate analysis, adequately predicted prostate tissue concentrations in our patient population. For therapeutic use, aiming for a bactericidal target of 50% of time above minimum inhibitory concentration (T > MIC) in prostate tissue, 3 g ampicillin-sulbactam 4 times daily achieved ≥90% expected probability against only Enterococcus faecalis in typical patients with a creatinine clearance (CLcr ) of 30 mL/min. For prophylactic use, aiming for a bacteriostatic target of 30% T > MIC, 3 g ampicillin-sulbactam 4 times daily achieved ≥90% expected probability of attaining the bacteriostatic target against E. faecalis and Proteus species when CLcr was 30 mL/min. Based on prostatic simulations, the present study provides helpful recommendations for the treatment of bacterial prostatitis and preoperative prophylaxis in prostatectomy.

Pharmacokinetic/pharmacodynamic evaluation of teicoplanin against Staphylococcus aureus in a murine thigh infection model.

OBJECTIVES: Pharmacokinetic/pharmacodynamic (PK/PD) analysis using murine infection models is a well-established methodology for optimising antimicrobial therapy. Therefore, we investigated the PK/PD indices of teicoplanin againstStaphylococcus aureus using a murine thigh infection model. METHODS: Mice were rendered neutropenic by administration of a two-step dosing of cyclophosphamide. Then, isolates of methicillin-susceptibleS. aureus (MSSA) or methicillin-resistant S. aureus (MRSA) were inoculated into the thighs of neutropenic mice. PK/PD analyses were performed by non-linear least-squared regression using the MULTI program. RESULTS: Target values offCmax/MIC (r2 = 0.94) of teicoplanin for static effect and 1 log10 kill against MSSA were 4.44 and 15.44, respectively. Target values of fAUC24/MIC (r2 = 0.92) of teicoplanin for static effect and 1 log10 kill against MSSA were 30.4 and 70.56, respectively. Target values of fCmax/MIC (r2 = 0.91) of teicoplanin for static effect and 1 log10 kill against MRSA were 8.92 and 14.16, respectively. Target values of fAUC24/MIC (r2 = 0.92) of teicoplanin for static effect and 1 log10 kill against MRSA were 54.8 and 76.4, respectively. CONCLUSION: These results suggest thatfCmax/MIC and fAUC24/MIC are useful PK/PD indices of teicoplanin against MSSA and MRSA.

Population Pharmacokinetic Modeling and Pharmacodynamic Target Attainment Simulation of Piperacillin/Tazobactam for Dosing Optimization in Late Elderly Patients with Pneumonia.

The aim of this study was to develop a population pharmacokinetic model for piperacillin (PIPC)/tazobactam (TAZ) in late elderly patients with pneumonia and to optimize the administration planning by applying pharmacokinetic/pharmacodynamic (PK/PD) criteria. PIPC/TAZ (total dose of 2.25 or 4.5 g) was infused intravenously three times daily to Japanese patients over 75 years old. The plasma concentrations of PIPC and TAZ were determined using high-performance liquid chromatography and modeled using the NONMEM program. PK/PD analysis with a random simulation was conducted using the final population PK model to estimate the probability of target attainment (PTA) profiles for various PIPC/TAZ-regimen-minimum-inhibitory-concentration (MIC) combinations. The PTAs for PIPC and TAZ were determined as the fraction that achieved at least 50% free time > MIC and area under the free-plasma-concentration-time curve over 24 h ≥ 96 µg h/mL, respectively. A total of 18 cases, the mean age of which was 86.5 ± 6.0 (75-101) years, were investigated. The plasma-concentration-time profiles of PIPC and TAZ were characterized by a two-compartment model. The parameter estimates for the final model, namely the total clearance, central distribution volume, peripheral distribution volume, and intercompartmental clearance, were 4.58 + 0.061 × (CLcr - 37.4) L/h, 5.39 L, 6.96 L, and 20.7 L/h for PIPC, and 5.00 + 0.059 × (CLcr - 37.4) L/h, 6.29 L, 7.73 L, and 24.0 L/h for TAZ, respectively, where CLcr is the creatinine clearance. PK/PD analysis using the final model showed that in drug-resistant strains with a MIC > 8 µg/mL, 4.5 g of PIPC/TAZ every 6 h was required, even for the patients with a CLcr of 50-60 mL/min. The population PK model developed in this study, together with MIC value, can be useful for optimizing the PIPC/TAZ dosage in the over-75-year-old patients, when they are administered PIPC/TAZ. Therefore, the findings of present study may contribute to improving the efficacy and safety of the administration of PIPC/TAZ therapy in late elderly patients with pneumonia.

Clinical pharmacokinetics of flomoxef in prostate tissue and dosing considerations for prostatitis based on site-specific pharmacodynamic target attainment.

Flomoxef is used to treat bacterial prostatitis; however, its prostatic pharmacokinetics have not been fully clarified. Flomoxef (500 or 1000 mg) was administered to patients with benign prostatic hypertrophy (n = 54). After a 0.5-h infusion, venous blood samples were drawn at time points of 0.5-5 h, and prostate tissue samples were collected at time points of 0.5-1.5 h during transurethral resection of the prostate. The drug concentrations in plasma and prostate tissue were analyzed pharmacokinetically and used for a stochastic simulation to predict the probability of attaining pharmacodynamic target in prostate tissue. Showing dose linearity in the prostatic pharmacokinetics, flomoxef rapidly penetrated into prostate tissue, with a prostate/plasma ratio of 0.48-0.50 (maximum drug concentration) and 0.42-0.55 (area under the drug concentration-time curve). Against the tested populations of Escherichia coli, Klebsiella and Proteus species isolates, 0.5-h infusion of 1000 mg three times daily achieved a ≥90% expected probability of attaining the bactericidal target (70% of the time above the minimum inhibitory concentration [MIC]) in prostate tissue. The site-specific pharmacodynamic-based breakpoint (the highest MIC at which the target-attainment probability in prostate tissue was >90%) values were 0.25 mg/L (MIC for 90th percentile of E. coli and Klebsiella species) for 500 mg four times daily and 0.5 mg/L (MIC90 of Proteus species) for 1000 mg four times daily. These results help to fully characterize the prostatic pharmacokinetics of flomoxef, while also helping to rationalize and optimize the dosing regimens for prostatitis based on site-specific pharmacodynamic target attainment.

The pharmacokinetics of oral metronidazole in patients with metronidazole-induced encephalopathy undergoing maintenance hemodialysis.

BACKGROUND: Metronidazole-induced encephalopathy (MIE) is a rare disease caused by an adverse reaction to metronidazole (MNZ). Furthermore, the pharmacokinetics of MNZ during hemodialysis (HD) treatment have not been revealed. CASE PRESENTATION: In a 70-year-old woman undergoing maintenance HD, MNZ was administered intermittently for the treatment of recurrent hepatic cyst infections. She complained of vomiting, dizziness, and dysarthria after 65 consecutive days of MNZ administration. In brain fluid-attenuated inversion recovery (FLAIR) magnetic resonance imaging (MRI), we found a high signal intensity in the cerebellar dentate nuclei and splenium of the corpus callosum. We diagnosed the patient with MIE. MNZ administration was withdrawn immediately, and HD treatment was performed for 3 consecutive days. Accompanying the remarkable decrease in serum MNZ levels, MIE symptoms were attenuated after three consecutive days of HD. In a brain MRI at 9 days, the high-intensity areas in the cerebellar dentate nuclei and splenium of the corpus callosum had disappeared. CONCLUSION: In this patient, we diagnosed MIE in the early stage using MRI, and 3 consecutive days of HD rapidly attenuated the symptoms associated with MIE, accompanied by a significant decrease in serum MNZ levels.

Clinical pharmacokinetics of oral azithromycin in epididymal tissue.

OBJECTIVES: Chlamydia trachomatis is one of the major pathogens causing acute epididymitis. Azithromycin (AZM) has a good efficacy against C. trachomatis; however, the ability of AZM to penetrate into human epididymal tissue has not yet been fully elucidated. Here, we examined the appropriate dosage of oral AZM for human epididymal tissue by site-specific pharmacokinetic/pharmacodynamic (PK/PD) analysis. METHODS: Patients with prostate cancer who underwent orchiectomy were included in this study. All patients received a 1-g dose of AZM before orchiectomy. Both epididymal tissue and blood samples were collected during surgery, and the drug concentrations were measured by high-performance liquid chromatography. All concentration-time data were analyzed with a three-compartment model with first-order absorption and elimination processes to simulate AZM concentrations in serum and epididymal tissue. RESULTS: A total of 10 patients were enrolled in the current study. For the observed values, the ratio of the epididymal concentration to the serum concentration was 5.13 ± 3.71 (mean ± standard deviation). For the simulated values, the maximum concentrations were 0.64 µg/mL at 2.42 h in serum and 1.96 µg/g at 4.10 h in epididymal tissue. The 24-h concentrations were 0.239 µg/mL in serum and 0.795 µg/g in epididymal tissue. CONCLUSIONS: The penetration of oral AZM into human epididymal tissue was examined to assess the potential application of AZM for the treatment of acute epididymitis. Based on the previous reports mentioning drug-susceptibility of C. trachomatis, multiple doses of oral AZM 1 g would be recommended for epididymitis based on the site-specific PK/PD.

Influence of GST polymorphisms on busulfan pharmacokinetics in Japanese children.

BACKGROUND: Fatal adverse effects or relapse can occur with excessive or insufficient busulfan exposure in hematopoietic stem cell transplantation. Given that busulfan is mainly metabolized by glutathione S-transferase (GST), we investigated the influence of GST polymorphisms on busulfan pharmacokinetics in Japanese pediatric patients. METHODS: Blood samples were taken from patients receiving high-dose i.v. busulfan as the first dose. Plasma busulfan concentration was measured using high-performance liquid chromatography. The area under the plasma busulfan concentration-time curve (AUC) was calculated. The genotype of GSTA1 was determined on polymerase chain reaction (PCR)-restriction fragment length polymorphism. Multiplex PCR was used to detect the presence or absence of GSTM1 and GSTT1 in the genomic DNA samples. RESULTS: Twenty patients were consecutively enrolled. Phenotype prediction was defined as follows: poor metabolizer (n = 4), one or more GSTA1*B haplotype or GSTM1/GSTT1 double-null genotypes; and extensive metabolizer (n = 16), other genotypes. GSTA1, M1, and T1 independently had no significant differences in AUC0-∞ , clearance or elimination rate constant. For the infant with unexpectedly high AUC0-∞ (2,591 µmol/L min), the GSTA1, M1, and T1 polymorphisms were wild type. On further analysis, the poor metabolizer group had lower clearance and higher AUC0-∞, except for the aforementioned patient, compared with the extensive metabolizer group (1,531 vs 1,010 µmol/L min; P < 0.01). CONCLUSIONS: GST polymorphisms may have affected busulfan pharmacokinetics, but these effects were obscured by other factors, such as underlying disease, systemic conditions, treatment history, and race.

Population pharmacokinetics/pharmacodynamics of linezolid in sepsis patients with and without continuous renal replacement therapy.

PURPOSE: The purpose of this study was to identify the optimum dosing regimen of linezolid in sepsis patients with and without renal dysfunction and sepsis patients on low-dose continuous renal replacement therapy (CRRT) using a pharmacokinetics/pharmacokinetics (PK/PD) approach. METHODS: Sepsis patients with and without renal dysfunction (creatinine clearance < 50 mL/min), and sepsis patients on low-dose CRRT (dose: 800 mL/h) were studied. The PK data were modeled using a two-compartment model, and then used for simulation. The target PK/PD was the 24-h area under the concentration-time curve to minimum inhibitory concentration ratio of ≥ 80. Dosing regimens were evaluated using cumulative fraction of response (CFR) and safety probability (trough level < 7 µg/mL) by Monte Carlo simulation. RESULTS: Twenty-seven patients, including 8 patients with preserved renal function, 9 patients with renal dysfunction, and 10 patients on CRRT, were studied. The proposed regimen to attain CFR ≥ 90% was 800 mg every 12 h (safety probability 82.4%) for patients with preserved renal function. By contrast, the target CFR was attained with a decreased regimen in patients with renal dysfunction and those on CRRT [600 mg every 24h (safety probability 68.6%) and 800 mg every 24h (42.1%)]. CONCLUSIONS: We identified different dosage strategies to achieve target linezolid concentrations according to renal function and use of CRRT in sepsis patients. Because of unassured safety probability in patients without preserved renal function, dosing regimens should be adjusted based on the therapeutic drug monitoring.