Aminoglycoside nephrotoxicity: do time and frequency of administration matter?

MDR Tuberculosis Treatment

Multidrug-resistant (MDR) tuberculosis (TB), resistant to isoniazid and rifampicin, continues to be one of the most important threats to controlling the TB epidemic. Over the last few years, there have been promising pharmacological advances in the paradigm of MDR TB treatment: new and repurposed drugs have shown excellent bactericidal and sterilizing activity against Mycobacterium tuberculosis and several all-oral short regimens to treat MDR TB have shown promising results. The purpose of this comprehensive review is to summarize the most important drugs currently used to treat MDR TB, the recommended regimens to treat MDR TB, and we also summarize new insights into the treatment of patients with MDR TB.

The Mechanism of Drug Nephrotoxicity and the Methods for Preventing Kidney Damage

Acute kidney injury (AKI) is a global health challenge of vast proportions, as approx. 13.3% of people worldwide are affected annually. The pathophysiology of AKI is very complex, but its main causes are sepsis, ischemia, and nephrotoxicity. Nephrotoxicity is mainly associated with the use of drugs. Drug-induced AKI accounts for 19-26% of all hospitalized cases. Drug-induced nephrotoxicity develops according to one of the three mechanisms: (1) proximal tubular injury and acute tubular necrosis (ATN) (a dose-dependent mechanism), where the cause is related to apical contact with drugs or their metabolites, the transport of drugs and their metabolites from the apical surface, and the secretion of drugs from the basolateral surface into the tubular lumen; (2) tubular obstruction by crystals or casts containing drugs and their metabolites (a dose-dependent mechanism); (3) interstitial nephritis induced by drugs and their metabolites (a dose-independent mechanism). In this article, the mechanisms of the individual types of injury will be described. Specific groups of drugs will be linked to specific injuries. Additionally, the risk factors for the development of AKI and the methods for preventing and/or treating the condition will be discussed.

Exploration of Antibiotic Activity of Aminoglycosides, in Particular Ribostamycin Alone and in Combination With Ethylenediaminetetraacetic Acid Against Pathogenic Bacteria

The emergence of infections caused by bacterial pathogens that are resistant to current antibiotic therapy is a critical healthcare challenge. Aminoglycosides are natural antibiotics with broad spectrum of activity; however, their clinical use is limited due to considerable nephrotoxicity. Moreover, drug-resistant bacteria that cause infections in human as well as livestock are less responsive to conventional antibiotics. Herein, we report the in vitro antibacterial evaluation of five different aminoglycosides, including ribostamycin, against a panel of Gram-positive and Gram-negative pathogens. Eight of the tested bacterial strains are linked to gastrointestinal (GI) infections. The minimum inhibitory concentration (MIC) of ribostamycin against three different Escherichia coli strains is in the range of 0.9–7.2 μM and against a strain of Haemophilus influenzae is 0.5 μM. We also found that the MIC of ribostamycin was considerably enhanced from 57.2 to 7.2 μM, an 8-fold improvement, when bacteria were treated with a combination of ribostamycin and ethylenediaminetetraacetic acid (EDTA). These findings demonstrate a promising approach to enhance the clinical potential of ribostamycin and provide a rational for its antibiotic reclassification from special level to non-restricted level.

Chronotherapeutics: Recognizing the Importance of Timing Factors in the Treatment of Disease and Sleep Disorders

This review describes the characteristics of a number of pathologies, which are considered from the point of view of chronobiology, that is, the way in which biological processes are expressed throughout the 24-hour day. This perspective is a relatively new way of thinking about disease and additionally about how to treat diseases. It has called attention to the importance of not only the quantity of a drug that is administered but also when it is administered. In addition, the review presents an overview of the emerging clinical strategies known as chronotherapeutics, that is, the effects of the daily scheduling of drug administration and the consequences of the activity and efficacy of therapies that are applied in this manner. This article also reviews innovative ways in which physicians are applying time-specified drug treatment (chronopharmacology) for sleep disorders. Here, we present a systematic description of chronopharmacology as well as definitions of key terms that, we believe, will be helpful for newcomers to the field. It is hoped that greater awareness of this new perspective on pharmacology will promote its adoption by researchers and clinicians.

Aminoglycosides against carbapenem-resistant Enterobacteriaceae in the critically ill: the pitfalls of aminoglycoside susceptibility

INTRODUCTION

The emergence of carbapenem-resistant Enterobacteriaceae (CRE) has brought aminoglycosides to the frontline since an aminoglycoside may be the only antimicrobial to which CRE isolates show in vitro susceptibility. The appropriateness of aminoglycoside-based therapies for severe infections by CRE is discussed considering the current breakpoints and recent pharmacokinetic (PK) studies in critically ill patients. Areas covered: Many aminoglycoside-susceptible CRE isolates present minimal inhibitory concentrations (MICs) at or slightly below the breakpoint of amikacin or gentamicin. However, recent PK studies with these aminoglycosides in critically ill have invariably shown that the PK/pharmacodynamic (PD) target is very unlikely attained even when high doses are administered, if the MICs are near the breakpoint. Expert commentary: While new antimicrobials are not widely available, the authors forecast an increasing use of aminoglycosides as backbone antibiotics against CRE isolates. However, the altered PK of aminoglycosides in critically ill patients severely impairs their predicted efficacy in these patients. Aminoglycoside breakpoints may hide 'aminoglycoside-susceptible' CRE isolates for that aminoglycosides will unlikely be effective if used in monotherapy. Therefore, these breakpoints may need to be revised due to the increasing use of aminoglycosides as backbone antibiotics to treat severe infections by CRE isolates in critically ill patients.

Severe infection, sepsis and acute kidney injury

Both severe infection and acute kidney injury (AKI) have a high, and rising incidence in critically ill patients admitted to the intensive care unit (ICU), and are associated with increased in-hospital mortality. Septic AKI patients are more severely ill compared to non-septic AKI patients and have worse outcome. Severe infection is a major cause of AKI in ICU patients, while conversely, AKI patients are at increased risk for infection. The dogma from the past relates the development of AKI in sepsis patients to decreased renal blood flow. However, current data suggest that there is no impairment of renal blood flow in patients with sepsis. The pathogenesis of AKI in sepsis is probably related to cytotoxic effects of inflammation, and impaired microcirculation. In addition, hyperglycaemia, and antimicrobial agent-induced drug nephrotoxicity may contribute to the development of AKI. On the other hand, AKI patients are at greater risk for infection as a result of volume overload, dialysis catheter insertion and secondary manipulation, inflammation of the kidneys leading to'organ cross talk', and impaired host immunity.

Survey on the Use of Gentamicin and Vancomycin in Adult Intensive Care Units

Aminoglycosides and glycopeptides are frequently used as empirical antibiotics in critically ill patients. Various nomograms are employed to monitor and adjust doses either as once daily or more frequent regimens. However, there is no universal guidance for their administration and monitoring. We conducted a survey, using an online questionnaire, of adult intensive care units (ICUs) across England, Wales and Northern Ireland, to ascertain prescribing and monitoring practices. ICUs listed on the Intensive Care National Audit and Research Centre (ICNARC) register were invited to participate. A total of 242 intensive care units were approached and 24.3% responded (n=59). Of those responding, 100% (n=59) used gentamicin to treat gram-negative infections, with 96.6% (n=57) of them using a once daily regimen and 11.9% (n=7) using multiple doses daily. An initial gentamicin dose of 5mg/kg was used by 53.4% (n=31), whereas 25.9% (n=15) used a concentration of 7 mg/kg. With regard to use of glycopeptides, vancomycin was used by 83.1% (n=49) of responders while 61% (n=36) used teicoplanin. Over two-thirds of responders (67.3%, n=35) indicated that they used vancomycin as an intermittent daily dose and 32.7% (n=17) used it as a continuous infusion. We conclude that diversity exists as to the use and monitoring of aminoglycosides and glycopeptides within the ICUs surveyed. Most of the clinicians stopped antibiotics based on clinical assessment rather than a predetermined duration (eg five days or seven days) and a small number of units used procalcitonin to guide antibiotic therapy.

Suppression of premature termination codons as a therapeutic approach

In this review, we describe our current understanding of translation termination and pharmacological agents that influence the accuracy of this process. A number of drugs have been identified that induce suppression of translation termination at in-frame premature termination codons (PTCs; also known as nonsense mutations) in mammalian cells. We discuss efforts to utilize these drugs to suppress disease-causing PTCs that result in the loss of protein expression and function. In-frame PTCs represent a genotypic subset of mutations that make up ~11% of all known mutations that cause genetic diseases, and millions of patients have diseases attributable to PTCs. Current approaches aimed at reducing the efficiency of translation termination at PTCs (referred to as PTC suppression therapy) have the goal of alleviating the phenotypic consequences of a wide range of genetic diseases. Suppression therapy is currently in clinical trials for treatment of several genetic diseases caused by PTCs, and preliminary results suggest that some patients have shown clinical improvements. While current progress is promising, we discuss various approaches that may further enhance the efficiency of this novel therapeutic approach.

Impact of combination therapy with aminoglycosides on the outcome of ICU-acquired bacteraemias

Pharmacodynamic studies report on the rapid bactericidal activity of aminoglycosides, conferring them as being of theoretical interest for bacteraemia treatment. We assessed this issue in a retrospective study of patients with intensive care unit (ICU)-acquired bacteraemias. To determine the impact of aminoglycosides in antimicrobial combination on the outcome of patients with bacteraemia, we performed a monovariate analysis and a logistic regression analysis comparing patients treated with or without aminoglycosides. Forty-eight bacteraemias in 48 patients were included. Eighteen patients received aminoglycosides. Baseline characteristics as well as adaptation and adequation of antibiotherapy did not differ in patients who did or did not receive aminoglycosides. Patients who received aminoglycosides had longer time alive away from the ICU (11.3 ± 8.9 (10 [0–20]) vs. 3.2 ± 6.6 (0 [0–2] days; p = 0.002) and free from mechanical ventilation (12.5 ± 9.3 (14 [0–21] vs. 5.5 ± 9.2 (0 [0–10] days; p = 0.02) on day 28. The ICU mortality was 16% in the aminoglycoside group versus 46% (p = 0.03). In the multivariate analysis, patients treated with aminoglycosides were 6 times less likely to die than those treated without aminoglycosides (confidence interval [CI] = [1.3–28.9]; p = 0.02). Our study supports the hypothesis that combination short-term antibiotherapy with an aminoglycoside for ICU-acquired bacteraemias could increase survival.

Management of aminoglycosides in the intensive care unit

Antibacterial resistance is increasing throughout the world, while the development of new agents is slowly progressing. In addition, the increasing prevalence of fluoroquinolone resistance may force many practitioners to choose an aminoglycoside agent in gram-negative regimens. Aminoglycosides are bactericidal agents with potent activity against gram-negative infections and activity against gram-positive infections when added to a cell wall active antimicrobial-based regimen. These agents may be dosed multiple times a day or consolidated as high-dose, extended-interval dosing to maximize pharmacokinetic and pharmacodynamic properties to achieve possible improved efficacy with reduced toxicity. Clinical application includes the treatment of bacteremia, endocarditis, health-care and nosocomial pneumonias, intra-abdominal infections, and others. Nephrotoxicity and ototoxicity are potential risks of aminoglycoside therapy that may be minimized with serum monitoring and short courses of therapy.

Enzymuria determination in children treated with aminoglycosides drugs

Although aminoglycosides antibiotics are used in children and adult commonly, they have serious side effects such as nephrotoxicity and ototoxicity. In clinical practice, for renal function, the levels of serum creatinine and blood urea nitrogen routinely are measured. Since these parameters have limitations such as unreliability, insensitivity, and nonspecificity, the rapid assessment of renal function based on these patients is very important. Increase in N-acetyl-β-D-glucosaminidase (NAG), a hydrolytic lysosomal enzyme, suggests proximal tubular cell damage. In this study, 32 children aged 2 months through 2 years, treated with gentamicin and amikacin for suspected infections at the pediatric ward of Alborz hospital from September 2006 to February 2007, were enrolled. Serum and fresh urine before and after drug infusion were obtained on the 1st, 3rd, and 5th days of antibiotic treatment. Serum urea and creatinine with urinary creatinine, albumin, NAG, lactate dehydrogenase (LDH) and alkaline phosphatase (AP) activity were then determined. A statistically significant increase in urinary NAG, LDH, and AP on 5th day was found compared with before gentamicin administration ( P < 0.001, P < 0.01, P < 0.05, respectively). The urinary NAG activity may be a useful indicator of renal injury in children treated with aminoglycosides drugs compared with other routine clinical indicators.

The histopathology of septic acute kidney injury: a systematic review

Introduction

Sepsis is the most common trigger of acute kidney injury (AKI) in critically ill patients; understanding the structural changes associated with its occurrence is therefore important. Accordingly, we systematically reviewed the literature to assess current knowledge on the histopathology of septic AKI.

Methods

A systematic review of the MEDLINE, EMBASE and CINHAL databases and bibliographies of the retrieved articles was performed for all studies describing kidney histopathology in septic AKI.

Results

We found six studies reporting the histopathology of septic AKI for a total of only 184 patients. Among these patients, only 26 (22%) had features suggestive of acute tubular necrosis (ATN). We found four primate studies. In these, seven out of 19 (37%) cases showed features of ATN. We also found 13 rodent studies of septic AKI. In total, 23% showed evidence of ATN. In two additional studies performed in a dog model and a sheep model there was no evidence of ATN on histopathologic examination. Overall, when ATN was absent, studies reported a wide variety of kidney morphologic changes in septic AKI – ranging from normal (in most cases) to marked cortical tubular necrosis.

Conclusion

There are no consistent renal histopathological changes in human or experimental septic AKI. The majority of studies reported normal histology or only mild, nonspecific changes. ATN was relatively uncommon.

Designer aminoglycosides: the race to develop improved antibiotics and compounds for the treatment of human genetic diseases

Aminoglycosides are highly potent, broad-spectrum antibiotics that exert their bactericidal therapeutic effect by selectively binding to the decoding aminoacyl site (A-site) of the bacterial 16 S rRNA, thereby interfering with translational fidelity during protein synthesis. The appearance of bacterial strains resistant to these drugs, as well as their relative toxicity, have inspired extensive searches towards the goal of obtaining novel molecular designs with improved antibacterial activity and reduced toxicity. In the last few years, a new, aminoglycoside dependent therapeutic approach for the treatment of certain human genetic diseases has been identified. These treatments rely on the ability of certain aminoglycosides to induce mammalian ribosomes to readthrough premature stop codon mutations. This new and challenging task has introduced fresh research avenues in the field of aminoglycoside research. Recent observations and current challenges in the design of aminoglycosides with improved antibacterial activity and the treatment of human genetic diseases are discussed.

Drug-induced acute kidney injury

PURPOSE OF REVIEW

The purpose of this review is to describe the most prevalent mechanisms of drug-induced acute kidney injury, to define the risk factors for nephrotoxicity, and to analyze the available evidence for preventive measures.

RECENT FINDINGS

Drug toxicity remains an important cause of acute kidney injury that, in many circumstances, can be prevented or at least minimized by vigilance and early intervention. Recent studies have resulted in increased insight into the subcellular mechanisms of drug nephrotoxicity. Further improvement is to be expected from the identification of early markers of nephrotoxicity and an increasing involvement of a clinical pharmacist.

SUMMARY

The main mechanisms of nephrotoxicity are vasoconstriction, altered intraglomerular hemodynamics, tubular cell toxicity, interstitial nephritis, crystal deposition, thrombotic microangiopathy, and osmotic nephrosis. Before prescribing a potentially nephrotoxic drug, the risk-to-benefit ratio and the availability of alternative drugs should be considered. Modifiable risk factors should be corrected. The correct drug dosage should be prescribed. Patients should be pre-hydrated and the glomerular filtration rate should be frequently monitored during the administration of a potentially nephrotoxic drug. Studies are needed to further elucidate the mechanisms of nephrotoxicity to design more-rational prevention and treatment strategies. Computer-based prescriber-order entry and an appropriately trained intensive care unit pharmacist are particularly helpful to minimize medication errors and adverse drug events.

Clinical doses of amikacin provide more effective suppression of the human CFTR-G542X stop mutation than gentamicin in a transgenic CF mouse model

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause the disease cystic fibrosis. We previously reported that gentamicin administration suppressed a CFTR premature stop mutation in a Cftr-/- mouse model carrying a human CFTR-G542X (hCFTR-G542X) transgene, resulting in the appearance of hCFTR protein and function. However, the high doses used in that study resulted in peak serum levels well beyond the levels typically administered to humans. To address this problem, we identified doses of both gentamicin and amikacin that resulted in peak serum levels within their accepted clinical ranges. We then asked whether these doses could suppress the hCFTR-G542X mutation in the Cftr-/- hCFTR-G542X mouse model. Our results indicate that low doses of each compound restored some hCFTR protein expression and function, as shown by immunofluorescence and short-circuit current measurements. However, we found that amikacin suppressed the hCFTR-G542X premature stop mutation more effectively than gentamicin when administered at these clinically relevant doses. Because amikacin is also less toxic than gentamicin, it may represent a superior choice for suppression therapy in patients that carry a premature stop mutation in the CFTR gene.

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.

Renal failure secondary to acute tubular necrosis: epidemiology, diagnosis, and management

Acute tubular necrosis (ATN) is a form of acute renal failure (ARF) that is common in hospitalized patients. In critical care units, it accounts for about 76% of cases of ARF. Despite the introduction of hemodialysis > 30 years ago, the mortality rates from ATN in hospitalized and ICU patients are about 37.1% and 78.6%, respectively. The purpose of this review is to discuss briefly the cause, diagnosis, and epidemiology of ARF, and to review in depth the clinical trials performed to date that have examined the influence of growth factors, hormones, antioxidants, diuretics, and dialysis. In particular, the role of the dialysis modality, dialyzer characteristics, and dosing strategies are discussed.

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.

Molecular Aspects of Renal Handling of Aminoglycosides and Strategies for Preventing the Nephrotoxicity

Aminoglycosides such as gentamicin and amikacin are the most commonly used antibiotics worldwide in the treatment of Gram-negative bacterial infections. However, serious complications like nephrotoxicity and ototoxicity are dose-limiting factors in the use of aminoglycosides. A relatively large amount of the intravenously administered dose is accumulated in the kidney (about 10% of dose), whereas little distribution of aminoglycosides to other tissues is observed. Aminoglycosides are taken up in the epithelial cells of the renal proximal tubules and stay there for a long time, resulting in nephrotoxicity. Acidic phospholipids are considered as a binding site for aminoglycosides in the brush-border membrane of the proximal tubular cells. More recently, it has been reported that megalin, a giant endocytic receptor abundantly expressed at the apical membrane of renal proximal tubules, plays an important role in binding and endocytosis of aminoglycosides in the proximal tubular cells. The elucidation of the aminoglycoside-binding receptor would help design a strategy to prevent against aminoglycoside-induced nephrotoxicity. In this review, we summarize recent advances in the understandings of the molecular mechanisms responsible for renal accumulation of aminoglycosides, especially megalin-mediated endocytosis. In addition, approaches toward prevention of aminoglycoside-induced nephrotoxicity are discussed, based on the molecular mechanisms of the renal accumulation of aminoglycosides.

Agents ameliorating or augmenting experimental gentamicin nephrotoxicity: some recent research

Despite its nephrotoxic potential, the aminoglycoside antibiotic gentamicin (GM) is still considered to be an important agent against life-threatening infections. The goal of reducing or protecting against its nephrotoxicity has attracted much effort and attention during the last decade. This article reviews some of the literature published during the last decade on the effects of agents that ameliorate or augment GM nephrotoxicity. Notable among the ameliorating agents are antioxidant agents. These include different classes of compounds that include beta blockers (e.g. carvedilol), superoxide dismutase mimetic agents (e.g. M40403), hormones (e.g. melatonin), iron chelators (e.g. deferrioxamine), vitamins (vitamin C and E) and medicinal plants (e.g. garlic). Other ameliorating agents include antibiotics (e.g. ceftriaxone), antiplatelet drugs (e.g. trapidil) and Ca++ agents that may augment GM nephrotoxicity include cyclosporin and the Ca++-channel blocker verapamil.

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.

[PK/PD modeling of aminoglycoside nephrotoxicity]

Aminoglycosides are bactericidial antibiotics with a serum concentration-dependent activity. They are mainly eliminated by the kidneys and the main difficulty arising in clinical use is their uptake by the renal cortex which leads to nephrotoxicity. An ototoxicity is also reported. We propose a PK/PD modelling of aminoglycoside nephrotoxicity which unifies more fourty years of physiological knowledge. This deterministic model successively describes the pharmacokinetics of aminoglycosides, their storage into renal cortex, their effect on renal cells, their consequences on the renal function through tubuloglomerular feedback and the changes in the serum concentrations of creatinine that is considered as a toxicity marker. The simulation of the model displays the leading effect of the shape and daily-time of administration schedule on the search for minimizing toxicity.

Aminoglycoside nephrotoxicity: modeling, simulation, and control

The main constraints on the administration of aminoglycosides are the risks of nephrotoxicity and ototoxicity, which can lead to acute, renal, vestibular, and auditory toxicities. In the present study we focused on nephrotoxicity. No reliable predictor of nephrotoxicity has been found to date. We have developed a deterministic model which describes the pharmacokinetic behavior of aminoglycosides (with a two-compartment model), the kinetics of aminoglycoside accumulation in the renal cortex, the effects of aminoglycosides on renal cells, the resulting effects on renal function by tubuloglomerular feedback, and the resulting effects on serum creatinine concentrations. The pharmacokinetic parameter values were estimated by use of the NPEM program. The estimated pharmacodynamic parameter values were obtained after minimization of the least-squares objective function between the measured and the calculated serum creatinine concentrations. A simulation program assessed the influences of the dosage regimens on the occurrence of nephrotoxicity. We have also demonstrated the relevancy of modeling of the circadian rhythm of the renal function. We have shown the ability of the model to fit with 49 observed serum creatinine concentrations for a group of eight patients treated for endocarditis by comparison with 49 calculated serum creatinine concentrations (r(2) = 0.988; P < 0.001). We have found that for the same daily dose, the nephrotoxicity observed with a thrice-daily administration schedule appears more rapidly, induces a greater decrease in renal function, and is more prolonged than those that occur with less frequent administration schedules (for example, once-daily administration). Moreover, for once-daily administration, we have demonstrated that the time of day of administration can influence the incidence of aminoglycoside nephrotoxicity. The lowest level of nephrotoxicity was observed when aminoglycosides were administered at 1:30 p.m. Clinical application of this model might make it possible to adjust aminoglycoside dosage regimens by taking into account both the efficacies and toxicities of the drugs.

Principles and Clinical Application of Assessing Alterations in Renal Elimination Pathways

Drugs and metabolites are eliminated from the body by metabolism and excretion. The kidney makes the major contribution to excretion of unchanged drug and also to excretion of metabolites. Net renal excretion is a combination of three processes - glomerular filtration, tubular secretion and tubular reabsorption. Renal function has traditionally been determined by measuring plasma creatinine and estimating creatinine clearance. However, estimated creatinine clearance measures only glomerular filtration with a small contribution from active secretion. There is accumulating evidence of poor correlation between estimated creatinine clearance and renal drug clearance in different clinical settings, challenging the 'intact nephron hypothesis' and suggesting that renal drug handling pathways may not decline in parallel. Furthermore, it is evident that renal drug handling is altered to a clinically significant extent in a number of disease states, necessitating dosage adjustment not just based on filtration. These observations suggest that a re-evaluation of markers of renal function is required. Methods that measure all renal handling pathways would allow informed dosage individualisation using an understanding of renal excretion pathways and patient characteristics. Methodologies have been described to determine individually each of the renal elimination pathways. However, their simultaneous assessment has only recently been investigated. A cocktail of markers to measure simultaneously the individual renal handling pathways have now been developed, and evaluated in healthy volunteers. This review outlines the different renal elimination pathways and the possible markers that can be used for their measurement. Diseases and other physiological conditions causing altered renal drug elimination are presented, and the potential application of a cocktail of markers for the simultaneous measurement of drug handling is evaluated. Further investigation of the effects of disease processes on renal drug handling should include people with HIV infection, transplant recipients (renal and liver) and people with rheumatoid arthritis. Furthermore, changes in renal function in the elderly, the effect of sex on renal function, assessment of living kidney donors prior to transplantation and the investigation of renal drug interactions would also be potential applications. Once renal drug handling pathways are characterised in a patient population, the implications for accurate dosage individualisation can be assessed. The simultaneous measurement of renal function elimination pathways of drugs and metabolites has the potential to assist in understanding how renal function changes with different disease states or physiological conditions. In addition, it will further our understanding of fundamental aspects of the renal elimination of drugs.