The pharmacokinetics of cefepime in 31 young, healthy volunteers were assessed after the administration of single and multiple 250-, 500-, 1,000-, or 2,000-mg intravenous doses. Each subject received a single dose of cefepime via a 30-min intravenous infusion on day 1 of the study. Starting from day 2, subjects received multiple doses of cefepime every 8 h for 9 days, and on the morning of day 11, they received the last dose. Serial blood and urine samples were collected after administration of the first dose and on days 1, 6, and 11. Cefepime concentrations in plasma and urine were assayed by using reverse-phase high-performance liquid chromatography with UV detection. Data were evaluated by noncompartmental methods to determine pharmacokinetic parameters. The mean half-life of cefepime was approximately 2 h and did not vary with the dose or duration of dosing. The regression analyses of peak levels (Cm.) in plasma at the end of the 30-min intravenous infusion and the area under the plasma concentration-versus-time curve (AUC>o.) showed a dose-proportional response. The steady-state volume of distribution (V,,) was approximately 18 liters and was independent of the administered dose. The multiple-dose pharmacokinetic data are suggestive of a lack of accumulation or change in clearance of cefepime on repeated dosing. Cefepime was excreted primarily unchanged in urine. The recovery of intact cefepime in urine was invariant with respect to the dose and accounted for over 80%o of the dose. The values for renal clearance ranged from 99 to 132 ml/min and were suggestive of glomerular filtration as the primary excretion mechanism. It is concluded that cefepime exhibits linear phannacokinetics in healthy subjects.
The kinetics of aminoglycoside binding to renal brush border and basolateral membrane vesicles from rat renal cortex were studied by using [3H]amikacin.[3H]amikacin binding to renal membranes was found to be a rapid, saturable process with a fourfold greater affinity for basolateral membranes than for brush border membranes (Kd basolateral = 607 ,uM; Kd brush border = 2,535 ,uM). Renal membranes prepared from immature rats (2 to 3 weeks old) exhibited a significantly lower affinity compared with membranes from adults (Kd basolateral = 2,262 ,uM; Kd brush border = 6,216 ,uM). Additionally, the inhibitory behavior of several aminoglycosides versus [3H]amikacin binding to brush border membranes revealed the following rank order of potency: neomycin > tobramycin gentamicin netilmicin > amikacin neamine > streptomycin. The relative insensitivity of immature rats to aminoglycoside-induced nephrotoxicity in vivo and the comparative nephrotoxicity of the various aminoglycosides suggest that renal membrane-binding affinity is closely correlated to the nephrotoxic potential of these antibiotics.Aminoglycoside antibiotics are nephrotoxic in humans and experimental animals, in which they induce necrosis of the proximal tubule (4,13,26). The nephrotoxicity of these drugs is associated with selective accumulation of aminoglycosides in the kidney, with cortical levels reaching as high as 20 times the circulating levels in serum (10, 40). Aminoglycosides are known to accumulate in renal tissue via tubular reabsorption as well as by extraction from the circulation at the basolateral surface of the kidney, although brush border uptake is thought to contribute more on a quantitative basis (6,7,17,34). However, it remains to be established whether the nephrotoxicity is a consequence of accumulated drug or relates to an interaction at the initial point of contact between the renal cell and the aminoglycoside, the plasma membrane. Williams et al. (43) recently reported the inhibition of aminoglycoside nephrotoxicity by polyamino acids associated with decreased renal brush border and basolateral membrane binding without inhibition of total cortical accumulation. Effects of aminoglycosides on plasma membrane structure and function have been reported (11,20,29,36,44).To examine the possible correlation between renal membrane binding and the nephrotoxicity of aminoglycosides, it is appropriate to compare the relative affinity of the various aminoglycosides for the membrane-binding site. Renal membrane-binding kinetics have been described for gentamicin (18,28,42)
Abstract. Multiplex ligand binding assays (LBAs) are increasingly being used to support many stages of drug development. The complexity of multiplex assays creates many unique challenges in comparison to single-plexed assays leading to various adjustments for validation and potentially during sample analysis to accommodate all of the analytes being measured. This often requires a compromise in decision making with respect to choosing final assay conditions and acceptance criteria of some key assay parameters, depending on the intended use of the assay. The critical parameters that are impacted due to the added challenges associated with multiplexing include the minimum required dilution (MRD), quality control samples that span the range of all analytes being measured, quantitative ranges which can be compromised for certain targets, achieving parallelism for all analytes of interest, cross-talk across assays, freeze-thaw stability across analytes, among many others. Thus, these challenges also increase the complexity of validating the performance of the assay for its intended use. This paper describes the challenges encountered with multiplex LBAs, discusses the underlying causes, and provides solutions to help overcome these challenges. Finally, we provide recommendations on how to perform a fit-forpurpose-based validation, emphasizing issues that are unique to multiplex kit assays.
A collaborative international trial was conducted to evaluate the reproducibility and transferability of an in vivo mutation assay based on the enumeration of CD59-negative rat erythrocytes, a phenotype that is indicative of Pig-a gene mutation. Fourteen laboratories participated in this study, where anti-CD59-PE, SYTO 13 dye, and flow cytometry were used to determine the frequency of CD59-negative erythrocytes (RBC(CD59-)) and CD59-negative reticulocytes (RET(CD59-)). To provide samples with a range of mutant phenotype cell frequencies, male rats were exposed to N-ethyl-N-nitrosourea (ENU) via oral gavage for three consecutive days (Days 1-3). Each laboratory studied 0, 20, and 40 mg ENU/kg/day (n = 5 per group). Three sites also evaluated 4 mg/kg/day. At a minimum, blood samples were collected three times: predosing and on Days 15 and 30. Blood samples were processed according to a standardized sample processing and data acquisition protocol, and three endpoints were measured: %reticulocytes, frequency of RET(CD59-) , and frequency of RBC(CD59-) . The methodology was found to be reproducible, as the analysis of technical replicates resulted in experimental coefficients of variation that approached theoretical values. Good transferability was evident from the similar kinetics and magnitude of the dose-related responses that were observed among different laboratories. Concordance correlation coefficients showed a high level of agreement between the reference site and the test sites (range: 0.87-0.99). Collectively, these data demonstrate that with adequate training of personnel, flow cytometric analysis is capable of reliably enumerating mutant phenotype erythrocytes, thereby providing a robust in vivo mutation assay that is readily transferable across laboratories.
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