Study On Population Pharmcokinetics And Population Pharmacokinetics/Pharmacodynamics Of Norvancomycin

A significant challenge to treat infections with antibiotic-resistant bacteria, like highly resistant methicillin-resistant Staphylococcus aureus (MRSA) and other gram-positive bacteria, remains in the field of the current diagnosis and treatment of infectious diseases. Norvancomycin, vancomycin and other glycopeptide antibiotics are vital drugs to treat MRSA infections. However, the class of glycopeptide antibiotics has lower therapeutic index, a narrow therapeutic window associated with their nephrotoxicity and ototoxicity. Patients with special physiologic and pathogenic alternations, such as elderly patients and patients with renal function impairment, are extremely vulnerable to the adverse effects of the drugs. A study desire to investigate the variability of pharmacokinetics of norvancomycin in different populations of patients with the special physiology, pathology, and underlying disease that may lead variable kinetic behaves of this drug, so called population pharmacokinetics (PPK). PPK based on clinical pharmacokinetics to determine a rational regimen for drugs with the low therapeutic index has been widely conducted in developed countries. Our institute has established a population pharmacokintic model of norvancomycin, based on study of our previous clinical pharmacokinetic practices of norvancomycin and more than ten other drugs. This study was a project of scheduled applications of new techniques from foreign counties. The model can be applied to estimate or predict an effective and safe regimen of norvancomycin for different subgroups of patients. The target population of this pharmacokinetic research was the patient with the infection caused by gram-position bacteria resistant to antibiotics and the patients treated with norvancomycin. An assay to determine serum concentrations of norvancomycin was requested to establish for PPK studies. Since the study carried out vast samples which were collected from patients who may have different underlying diseases and severe infections as well as receive multiple drugs. A high rapid, accurate, and specific assay was demanded, while a small volume of samples was essential for the assay. Thus, we set up a rapid assay to measure serum concentrations of norvancomycin: fluorescence polarization immunoassay (FPIA). Moreover, the assay was strictly tested andvalidated. After obtaining PPK parameters, combined with the study of the pharmacodynamics (PD) of norvancomycin and the norvancomycin MIC of bacteria which caused this patient's infection, PPK was linked to PD in order to design an optimized regimen for different subgroups of patients with infections caused by various Gram-positive bacteria resistant to antibiotics. This approach finally assured the efficacy and safety of anti-infection therapy. The thesis is composed of three parts.First part: Establishment and validation of a rapid assay to determine serum concentrations of norvancomycinAlthough norvancomycin has clinically been used over decades, a rapid assay to measure serum concentrations of norvancomycin is not available to monitor therapeutic drug concentrations in patients with infections. Even if bioassay for norvancomycin is sensitive and accurate, it is time-consuming and non-specific. Results of the assay may be influenced by other drugs which are co-administered to patients. Thus the bioassay is not appropriate for use of the therapeutic drug monitoring (TDM) practices. A FPLA assay commercially used for vancomycin was chosen to establish an assay for norvancomycin, based on the very similarity of the chemical structures of norvancomycin and vancomycin, and availability for the kit and instrument (TDx). The assay was tested and validated in 20 healthy volunteers in comparison with a traditional bioassay and high pressure liquid chromatography (HPLC) to determine its accuracy, stability, sensitivity, and specificity. The relevance of this assay with other two assays was also evaluated. The establishment procedure of the FPIA method for norvancomycin was to assay drug concentrations of 239 different time-point serum samples from 10 young and 10 elderly volunteers; following an intravenous infusion of norvancomycin at a dose of 800 mg. simultaneously these samples were measured via the bioassay. The results of bioassay were used as the measurement standard to establish a lineal regression of two assays: Y= 0.7534X-0.5948, where X was the value from the FPIA method and Y was the value from the bioassay method, R² = 0.9703. This approach indirectly determined serum concentrations of norvancomycin, resulted from values derived from FPIA and the regression equation. Intraday and interday precision (RSD) of the FPLA method for norvancomycin was ≤ 6.08 % and ≤ 4.75, respectively. The range of the recoveries of this assay was from 87.74% to 114.34%. This assay was not influenced by serum concentrations of beta-lactam and aminoglycoside antibiotics when they were co-administered to patients. The assay was compared with HPLC via simultaneously determining 371 serum samples from patients in TDM practices. The comparison showed serumconcentrations determined by the FPIA method plus use of regression equation was very similar to those by the HPLC method. Y= 1.016X+0.0041, where X was the value from the FPIA method plus use of regression equation and Y was the value from the HPLC method, R² = 0.9782. Therefore, the FPIA method was able to be a major approach for TDM procedures. Eventually, it was utilized to measure serum concentrations of norvancomycin from patients in the PPK study and from healthy volunteers in clinical studies.Part two: Population pharmacokinetics (PPK) of norvancomycinThe objective of the PPK study is to completely illustrate the variability of pharmacokinetic of therapeutic drugs in a diverse population, and thus it provides a reliable approach to design a rational regimen in different groups of patients. Nonlinear mixed effect model (NONMEM) is utilized to PPK analysis. The advantages of this method requires sparse samples from each patient and suitable for the PPK modeling, although it demands a large number of patients to enroll a study. Moreover, the POSTHOC program of the NONMEM software allows estimating individual PK parameters and thus can be used to establish an individualized regimen. Therefore, NONMEM approach was chosen to establish a PPK model for patients given norvancomycin in this investigation. Data came from 146 patients diagnosed and suspected with the infection caused by staphylococcus aureus and other gram-positive bacteria resistant to antibiotics. Norvancomycin was administered to all of the patients. The data included TDM, demography, and clinical information associated with these patients. Simultaneously, the study also used different concentration-time-points data derived from volunteers of 10 young and 10 elderly men, following a single intravenous infusion of norvancomycin at 800 mg. All of a data set consisted of 166 cases. Among them, 110 cases were randomly selected to establish the model. The gender, age, body weight, liver function, and renal function (values of Ccr) and the administration of multiple drugs (like aminoglycoside and diuretics) were initially evaluated to search fixed factors that could alter pharmacokinetic parameters and cause interindividual and intraindividual variability in pharmacokinetic parameters. Fixed factors obtained from the screening were applied to establish PPK model. The model was validated via other 56 cases. After confirming the stabilities and effectiveness of the model, all of 166 subjects were pooled to obtain final PPK parameters. The results demonstrated a two compartmental model fit well the PPK model of norvancomycin via the NONMEM approach. The final PPK parameters were found: CL (Ccr ≤ 85 ml/min, CL (Ccr > 85 ml/min). V₁, Q, and V₂ of norvancomycin was 2.54 L/h, 5.66 L/h, 23.89L. 8.50 L/h. and 21.70L, respectively. Interindividual variability in CL , V₁, Q and V₂ was35.92 %, 11.40%, 0 and 79.75%, respectively. Residual variability was 3.05 mg/L.The findings of the PPK study were followings as: â‘  the significant impact of renal function impairment on PK parameters of norvancomycin. Among 146 patients: the mean of the drug clearance (CL) and eliminate half-life (T_1/2β was (0.23 ± 0.09) L/h and (154.26 ± 74.28) h in 14 patients with severe renal impairment, (2.17 ± 0.95) L/h and (22.86 ± 20.73)h in 16 patients with moderate renal impairment, and (4.01 ± 1.27) L/h and (9.57 ± 4.34) h in 45 patients with mild renal impairment, respectively. The results of the study strongly suggested that the elimination of norvancomycin decreased in subjects with mild, moderate, and severe renal impairment. â‘¡ the important impact of age on PK parameters of norvancomycin. A comparison of 59 elderly patients (≥ 65 years) versus non-elderly patients (18～< 65 years) showed (3.94 ± 1.73 L/h ) versus (5.89 ± 2.08) L/h for CL, (12.07 ± 12.19 )h versus (6.79 ± 5.18) h for T_1/2β, and (490.16 ± 564.36) mg.h/L versus (283.92 ±161.66) mg.h/L for values of AUC₂₄ Thus, the reduced drug clearance, prolonged T_1/2β, and increased values of AUC₂₄ were found in the elderly patients. â‘¢ the increased volume of a peripheral distribution as coadministration of norvancomycin with diuretics. It suggested that the coadministration may accelerate the elimination of the former drug and thus decrease its serum concentrations. â‘£ non-influence of hepatic impairment and coadministration with aminoglycoside antibiotics on PK parameters of norvancomycin.Diverse regimens of norvancomycin were finally established to different patients on the basis of important PPK parameters generated from different groups of patients in this study.Part three: PPK/PD Study of norvancomycinInfectious diseases may differ from other diseases, since they are caused by invasion of microorganisms. Therefore, clinicians who prescribe antibiotics should have knowledge of the kinetics of drugs in body (clinical pharmacokinetics or PPK) and the effects and characteristics of antimicrobial activity against pathogens (Pharmacodynamics, PD). The design of an effective and safe anti-infection regimen should integrate both principles. The last objective of the present study was to accurately calculate individual PPK/PD parameters in order to predict clinical and microbiologic outcomes in patients after the treatment of norvancomycin, and further to optimize the regimen, based on individual pharmacokinetic parameters generated from the PPK model and norvancomycin MIC values of the pathogens in this patient. The norvancomycin MICs of 78 clinically isolated strains from 71 patients were determined by an agar dilution method. The ratios (AUC₂₄/MIC) were calculated in 68 patients, where data of the area under time-concentration curve (AUC₂₄) and the value of MIC were derived from the individual patient. At the same time, calculations were conducted for the percentage of the time of serum concentrations above MIC during the interval of administration. The possibilities of the influence of underlying conditions and coadministration on efficacy of norvancomycin were excluded. The present study was performed in patients with infections caused by Staphylococcus aureus and Enterococcus species and treated with norvancomycin. The group of patients who had the outcomes of cure after the treatment was compared with the group of patients who had the outcomes of non-cure. The statistical study revealed that there were significant differences in the age, daily norvancomycin dose, AUC₂₄ and AUC₂₄/MIC between two group for patients with Staphylococcus aureus (p<0.05).There was a significant difference in the AUC₂₄ and AUC₂₄/MIC between two group for patients with Enterococcus infections (p<0.05). The logistic stepwise analyses for multiple factors on clinical outcome revealed only the ratio of AUC₂₄/MIC was the major factor which could significantly determine the clinical outcomes and bacterial eradication for patients with Staphylococcus aureus and enterococcal infections. As the ratio of AUC₂₄/MIC yielded >579.90 for Staphylococcus aureus infections or > 637.67 for enterococcal infections, would predict approximately 95% of patients with Staphylococcus aureus and enterococcal infections to achieve improved clinical outcomes and bacterial eradication, respectively. The study demonstrated that the value of AUIC was a major PPK/PD parameter to evaluate the efficacy of norvancomycin. Therefore, this value can be applied to design an optimal regimen as an important reference. Finally, an individualized regimen can be established for different subgroups of patients on the basis of the results of the PPK/PD study.In summary, the rapid assay to determine serum concentrations of norvancomycin was established. It provided a robust technique approach to conduct TDM of this drug. The population pharmacokinetic model of norvancomycin in patients with infections was successfully generated and validated, using the NONMEM method. The model was effectively applied to design the regimen for patients with variable renal function. Using the novel PPK/PD theory that was developed in this study, the regimen was further optimized in order to assure the efficacy safe regimen for different subgroups of patients with the infection. In the future, it offers promises of a rational use of norvancomycin to reduce the toxicity and enhance the greatest bactericidal effect and to assure efficacy and safety use of norvancomycin in clinical practices.