Aminoglycoside nephrotoxicity: modeling, simulation, and control

Circadian rhythms: mechanisms and therapeutic implications

The mammalian circadian system is organized in a hierarchical manner in that a central pacemaker in the suprachiasmatic nucleus (SCN) of the brain's hypothalamus synchronizes cellular circadian oscillators in most peripheral body cells. Fasting-feeding cycles accompanying rest-activity rhythms are the major timing cues in the synchronization of many, if not most, peripheral clocks, suggesting that the temporal coordination of metabolism and proliferation is a major task of the mammalian timing system. The inactivation of noxious food components by hepatic, intestinal, and renal detoxification systems is among the metabolic processes regulated in a circadian manner, with the understanding of the involved clock output pathways emerging. The rhythmic control of xenobiotic detoxification provides the molecular basis for the dosing time-dependence of drug toxicities and efficacy. This knowledge can in turn be used in improving or designing chronotherapeutics for the patients who suffer from many of the major human diseases.

Lack of effect of DX-619, a novel des-fluoro(6)-quinolone, on glomerular filtration rate measured by serum clearance of cold iohexol

DX-619 is a novel des-fluoro(6)-quinolone with activity against a broad range of bacterial strains, including methicillin-resistant Staphylococcus aureus. The effects of DX-619 on the glomerular filtration rate (GFR) were evaluated because drug-related increases in serum creatinine levels were observed in studies with healthy volunteers. Forty-one healthy subjects were randomized to receive intravenous DX-619 at 800 mg or placebo once daily for 4 days, and the GFR was directly measured by determination of the clearance of a bolus iohexol injection in 33 subjects who completed the study per protocol. DX-619 was noninferior to placebo for the GFR on the basis of a criterion for a clinically significant difference of -12 ml/min/1.73 m(2). The mean GFRs on day 4 were 101.1 +/- 14.2 ml/min/1.73 m(2) and 100.2 +/- 15.6 ml/min/1.73 m(2) for the volunteers receiving placebo and DX-619, respectively. On day 4 the mean serum creatinine concentration for volunteers receiving DX-619 increased by 30 to 40%, with a corresponding decrease in mean creatinine clearance. Both parameters normalized within 7 days after the cessation of DX-619 treatment. Nonclinical studies suggest that DX-619 increases the serum creatinine concentration by inhibiting excretory tubular transporters. In conclusion, DX-619 administered intravenously at 800 mg once a day for 4 days did not affect the GFR in healthy volunteers. Glomerular toxicity is not expected to present a risk to patients receiving DX-619 in clinical trials, but monitoring of the renal function, with an emphasis on the serum creatinine concentration, is still warranted.

Pharmacokinetic-pharmacodynamic relationship of arbekacin for treatment of patients infected with methicillin-resistant Staphylococcus aureus

Arbekacin is widely used in Japan for the treatment of patients infected with methicillin-resistant Staphylococcus aureus (MRSA). In this study, we have determined the optimal concentration targets of arbekacin for both efficacy and safety. A pharmacokinetic-pharmacodynamic analysis was performed to relate exposure to the drug and clinical cure/improvement or nephrotoxicity. Since we have reported the population pharmacokinetic parameters for arbekacin in the preceding paper (Y. Tanigawara, R. Sato, K. Morita, M. Kaku, N. Aikawa, and K. Shimizu, Antimicrob. Agents Chemother. 50:3754-3762, 2006), individual exposure parameters, such as area under the concentration-time curve (AUC), peak concentration (C(max)), AUC/MIC, C(max)/MIC, and trough concentration (C(min)) were estimated by the Bayesian method. Logistic regression was used to describe the relationship between exposure to the drug and the probability of clinical cure/improvement or nephrotoxicity. For the clinical efficacy analysis, 174 patients confirmed to have an MRSA infection were evaluated. The C(max), C(min), and AUC of arbekacin were associated with the probability of clinical cure/improvement during monotherapy. It was shown that the probability of cure/improvement rose when the C(max) of arbekacin was increased, with an odds ratio of 6.7 for a change in C(max) from 7.9 to 12.5 microg/ml (P = 0.037). For the nephrotoxic risk analysis, 333 patients were included, regardless of whether a pathogen was identified. Logistic regression analysis revealed C(min) and AUC as risk factors of nephrotoxicity (P < 0.005). The estimated probabilities of arbekacin-induced nephrotoxicity were 2.5, 5.2, and 13.1% when the C(min) values were 1, 2, and 5 microg/ml, respectively. The present findings are useful for optimizing the individual dose of arbekacin for the treatment of MRSA-infected patients.

Mechanism of enhanced activity of liposome-entrapped aminoglycosides against resistant strains of Pseudomonas aeruginosa

Pseudomonas aeruginosa is inherently resistant to most conventional antibiotics. The mechanism of resistance of this bacterium is mainly associated with the low permeability of its outer membrane to these agents. We sought to assess the bactericidal efficacy of liposome-entrapped aminoglycosides against resistant clinical strains of P. aeruginosa and to define the mechanism of liposome-bacterium interactions. Aminoglycosides were incorporated into liposomes, and the bactericidal efficacies of both free and liposomal drugs were evaluated. To define the mechanism of liposome-bacterium interactions, transmission electron microscopy (TEM), flow cytometry, lipid mixing assay, and immunocytochemistry were employed. Encapsulation of aminoglycosides into liposomes significantly increased their antibacterial activity against the resistant strains used in this study (MICs of > or =32 versus < or =8 microg/ml). TEM observations showed that liposomes interact intimately with the outer membrane of P. aeruginosa, leading to the membrane deformation. The flow cytometry and lipid mixing assays confirmed liposome-bacterial membrane fusion, which increased as a function of incubation time. The maximum fusion rate was 54.3% +/- 1.5% for an antibiotic-sensitive strain of P. aeruginosa and 57.8% +/- 1.9% for a drug-resistant strain. The fusion between liposomes and P. aeruginosa significantly enhanced the antibiotics' penetration into the bacterial cells (3.2 +/- 2.3 versus 24.2 +/- 6.2 gold particles/bacterium, P < or = 0.001). Our data suggest that liposome-entrapped antibiotics could successfully resolve infections caused by antibiotic-resistant P. aeruginosa through an enhanced mechanism of drug entry into the bacterial cells.

Transdermal delivery of aminoglycosides: Amikacin transport and iontophoretic non-invasive monitoring

The aim of this paper was to try to single out new administration strategies for aminoglycoside antibiotics. The objectives of the work were to reduce the systemic absorption in the case of topical application and to achieve plasma levels within the therapeutic window in case of systemic administration. Amikacin (AK) was chosen as a model aminoglycoside, as it has a broad spectrum of activity against Gram-negative bacteria. Additionally, since the therapeutic use of aminoglycosides requires careful monitoring, the feasibility of noninvasive monitoring of AK by reverse iontophoresis was explored in preliminary experiments. Permeation experiments were performed in vitro using rabbit ear skin as barrier. From the results obtained, it can be concluded that topical delivery of amikacin is possible for the treatment of local diseases, both using a commercial gel formulation and an innovative transdermal film, the latter being able to reduce in a significant way the risks of systemic absorption. When anodal iontophoresis at pH 4.0 was applied, amikacin transport and, to a limited extent, accumulation were increased. Reverse iontophoresis gave promising results, since AK could be extracted across the skin at the cathode, and this can be taken as a reference point to develop and optimize the technique.

Drug dosing in chronic kidney disease

Patients with chronic kidney disease (CKD) are at high risk for adverse drug reactions and drug-drug interactions. Drug dosing in these patients often proves to be a difficult task. Renal dysfunction-induced changes in human pathophysiology regularly results may alter medication pharmacodynamics and handling. Several pharmacokinetic parameters are adversely affected by CKD, secondary to a reduced oral absorption and glomerular filtration; altered tubular secretion; and reabsorption and changes in intestinal, hepatic, and renal metabolism. In general, drug dosing can be accomplished by multiple methods; however, the most common recommendations are often to reduce the dose or expand the dosing interval, or use both methods simultaneously. Some medications need to be avoided all together in CKD either because of lack of efficacy or increased risk of toxicity. Nevertheless, specific recommendations are available for dosing of certain medications and are an important resource, because most are based on clinical or pharmacokinetic trials.

Current use for old antibacterial agents: polymyxins, rifampin, and aminoglycosides

This article discusses three classes of antibacterial agents that are uncommonly used in bacterial infections (other than mycobacterial infections) and can be thought of as special-use agents. These are the polymyxins, rifampin, and the aminoglycosides.

Principles of use of antibacterial agents

The selection of an antimicrobial regimen is based on a number of factors, including the nature of the infection, the identity and susceptibility of the pathogens, host characteristics, and the pharmacokinetics and pharmacodynamics of antimicrobial agents. This article provides a comprehensive overview of these factors, with particular attention to pharmacokinetics and monitoring for efficacy and toxicity. A brief summary is also provided of some other topics discussed in detail elsewhere in this issue, such as susceptibility testing, pharmacodynamics, and pharmacokinetics-pharmacodynamics parameters.

Artificial neural network modeling to predict the plasma concentration of aminoglycosides in burn patients

The goal was to use an artificial neural network model to predict the plasma concentration of aminoglycosides in burn patients and identify patients whose plasma antibiotic concentration would be sub-therapeutic based on the patients' physiological data and taking into account burn severity. Physiological data and some indicators of burn severity were collected from 30 burn patients who received arbekacin. A three-layer artificial neural network with five neurons in the hidden layer was used to predict the plasma concentration of arbekacin. Linear modeling for prediction of plasma concentration and logistic regression modeling for the classification of patients were also used and the predictive performance was compared to results from the artificial neural network model. Dose, body mass index, serum creatinine concentration and amount of parenteral fluid were selected as covariates for the plasma concentration of arbekacin. Area of burn after skin graft was a good covariate for indicating burn severity. Predictive performance of the artificial neural network model including burn severity was much better than linear modeling and logistic regression analysis. An artificial neural network model should be helpful for the prediction of plasma concentration using patients' physiological data, and burn severity should be included for improved prediction in burn patients. Because the relationship between burn severity and plasma concentration of aminoglycosides is thought to be nonlinear, it is not surprising that the artificial neural network model showed better predictive performance compared to the linear or logistic regression models.

Pharmacokinetic and pharmacodynamic issues in the treatment of bacterial infectious diseases

This review outlines some of the many factors a clinician must consider when selecting an antimicrobial dosing regimen for the treatment of infection. Integration of the principles of antimicrobial pharmacology and the pharmacokinetic parameters of an individual patient provides the most comprehensive assessment of the interactions between pathogen, host, and antibiotic. For each class of agent, appreciation of the different approaches to maximize microbial killing will allow for optimal clinical efficacy and reduction in risk of development of resistance while avoiding excessive exposure and minimizing risk of toxicity. Disease states with special considerations for antimicrobial use are reviewed, as are situations in which pathophysiologic changes may alter the pharmacokinetic handling of antimicrobial agents.

Pharmacodynamics and dosing of aminoglycosides

Aminoglycosides are concentration-dependent killing agents whose pharmacodynamic predictors of efficacy are the area-under-the-curve to minimum inhibitory concentration ratio and the peak to minimum inhibitory concentration ratio. Prospective studies have shown that these agents can be given once-daily or less frequently in most clinical settings, with equal efficacy and possible reduced toxicity. Dosages for different clinical settings have been studied and methods are available to monitor once-daily dosing.