Incidence of amikacin ototoxicity: a sigmoid function of total drug exposure independent of plasma levels

Inoculum-Based Dosing: A Novel Concept for Combining Time with Concentration-Dependent Antibiotics to Optimize Clinical and Microbiological Outcomes in Severe Gram Negative Sepsis

Certain classes of antibiotics show "concentration dependent" antimicrobial activity; higher concentrations result in increased bacterial killing rates, in contrast to "time dependent antibiotics", which show antimicrobial activity that depends on the time that antibiotic concentrations remain above the MIC. Aminoglycosides and fluoroquinolones are still widely used concentration-dependent antibiotics. These antibiotics are not hydrolyzed by beta-lactamases and are less sensitive to the inoculum effect, which can be defined as an increased MIC for the antibiotic in the presence of a relatively higher bacterial load (inoculum). In addition, they possess a relatively long Post-Antibiotic Effect (PAE), which can be defined as the absence of bacterial growth when antibiotic concentrations fall below the MIC. These characteristics make them interesting complementary antibiotics in the management of Multi-Drug Resistant (MDR) bacteria and/or (neutropenic) patients with severe sepsis. Global surveillance studies have shown that up to 90% of MDR Gram-negative bacteria still remain susceptible to aminoglycosides, depending on the susceptibility breakpoint (e.g., CLSI or EUCAST) being applied. This percentage is notably lower for fluoroquinolones but depends on the region, type of organism, and mechanism of resistance involved. Daily (high-dose) dosing of aminoglycosides for less than one week has been associated with significantly less nephro/oto toxicity and improved target attainment. Furthermore, higher-than-conventional dosing of fluoroquinolones has been linked to improved clinical outcomes. Beta-lactam antibiotics are the recommended backbone of therapy for severe sepsis. Since these antibiotics are time-dependent, the addition of a second concentration-dependent antibiotic could serve to quickly lower the bacterial inoculum, create PAE, and reduce Penicillin-Binding Protein (PBP) expression. Inadequate antibiotic levels at the site of infection, especially in the presence of high inoculum infections, have been shown to be important risk factors for inadequate resistance suppression and therapeutic failure. Therefore, in the early phase of severe sepsis, effort should be made to optimize the dose and quickly lower the inoculum. In this article, the authors propose a novel concept of "Inoculum Based Dosing" in which the decision for antibiotic dosing regimens and/or combination therapy is not only based on the PK parameters of the patient, but also on the presumed inoculum size. Once the inoculum has been lowered, indirectly reflected by clinical improvement, treatment simplification should be considered to further treat the infection.

Amikacin nomogram for treatment of adult cystic fibrosis exacerbations based on an external evaluation of a population pharmacokinetic model

BACKGROUND

In patients with cystic fibrosis (CF), amikacin is the alternative for the treatment of acute pulmonary exacerbations associated with pathogens resistant to tobramycin. Population pharmacokinetic (PK) models of amikacin in adult patients with CF have been previously published. However, current dosing recommendations remain disputed (Illamola et al. Clin Pharmacokinet. 2018;57(10):1217-1228). We perform here the first external evaluation of a published amikacin adult CF population PK model and propose a dosing nomogram for initial dosing.

METHODS

We retrospectively collected demographic, biological, and clinical data from the medical records of adult patients who had received intravenous amikacin. To assess the predictive performance of this model we applied visual comparison of predictions to observations, calculation of bias and inaccuracy, and simulation-based diagnostics. Monte Carlo simulations from the evaluated model were used to compare maximum concentration/minimum inhibitory concentration achieved with different dosing regimens.

RESULTS

A total of 91 concentrations from 19 adult patients with CF were collected for external evaluation. The model predicted amikacin concentrations with reasonable bias (7.2% [95% confidence interval, CI: -0.7% to 15.0%]) and inaccuracy (18.2% [95% CI: 12.0%-24.4%]). Our simulations with this model suggest that administered amikacin doses must be adjusted to creatinine clearance and also adjusted to body weight (doses from 20 to 45 mg/kg/d). According to these simulations, we developed the Montreal amikacin nomogram to optimize amikacin dosing regimens in patients with CF.

CONCLUSION

In conclusion, we developed the first nomogram to optimize initial amikacin dosing regimens in patients with CF based on this external evaluation of a recently published amikacin population PK model.

Optimizing Antibiotic Drug Therapy in Pediatrics: Current State and Future Needs

The selection of the right antibiotic and right dose necessitates clinicians understand the contribution of pharmacokinetic variability stemming from age-related physiologic maturation and the pharmacodynamics to optimize drug exposure for clinical response. The complexity of selecting the right dose arises from the multiplicity of pediatric age groups, from premature neonates to adolescents. Body size and age (which relate to organ function) must be incorporated to optimize antibiotic dosing in this vulnerable population. In the effort to optimize and individualize drug dosing regimens, clinical pharmacometrics that incorporate population-based pharmacokinetic modeling, Bayesian estimation, and Monte Carlo simulations are utilized as a quantitative approach to understanding and predicting the pharmacology and clinical and microbiologic efficacy of antibiotics. In addition, opportunistic study designs and alternative blood sampling strategies can serve as practical approaches to ensure successful conduct of pediatric studies. This review article examines relevant literature on optimization of antibiotic pharmacotherapy in pediatric populations published within the last decade. Specific pediatric antibiotic data, including beta-lactam antibiotics, aminoglycosides, and vancomycin, are critically evaluated.

Estimation of once-daily amikacin dose in critically ill adults

This study aimed at investigating variables affecting amikacin pharmacokinetics in order to propose optimal initial dosing in critically ill adult patients treated with once-daily amikacin regimen. Amikacin pharmacokinetics was calculated based on plasma concentrations using one compartmental analysis. Relationships between pharmacokinetic parameters and demographic/clinical data were explored in linear regression models. Simulated dose and dosing intervals were derived from body size descriptors and estimated creatinine clearances for each patient. Amikacin volume of distribution best correlated with body surface area, while amikacin clearance was best predicted by CKD-EPI creatinine clearance. Our study suggests that dose of 517 mg per m² of body surface area leads to amikacin levels most approaching target peak concentration. Dosing interval calculated as 228.7 × e^{-3.08× CKD-EPI creatinine clearance (mL s-1)} + 15.84 most closely approximated optimal dosing intervals based on individual pharmacokinetics. The dosing nomogram based on CKD-EPI creatinine clearance was designed.

Towards the Prevention of Aminoglycoside-Related Hearing Loss

Aminoglycosides are potent antibiotics deployed worldwide despite their known side-effect of sensorineural hearing loss. The main etiology of this sensory deficit is death of inner ear sensory hair cells selectively triggered by aminoglycosides. For decades, research has sought to unravel the molecular events mediating sensory cell demise, emphasizing the roles of reactive oxygen species and their potentials as therapeutic targets. Studies in recent years have revealed candidate transport pathways including the mechanotransducer channel for drug entry into sensory cells. Once inside sensory cells, intracellular targets of aminoglycosides, such as the mitochondrial ribosomes, are beginning to be elucidated. Based on these results, less ototoxic aminoglycoside analogs are being generated and may serve as alternate antimicrobial agents. In this article, we review the latest findings on mechanisms of aminoglycoside entry into hair cells, their intracellular actions and potential therapeutic targets for preventing aminoglycoside ototoxicity.

The safety and tolerability of the second-line injectable antituberculosis drugs in children

INTRODUCTION

A growing number of children globally are being treated for multidrug-resistant tuberculosis (MDR-TB). The second-line injectable antituberculosis medications amikacin, kanamycin and capreomycin, traditionally a mainstay of MDR-TB treatment, cause important adverse effects including permanent sensorineural hearing loss, nephrotoxicity, electrolyte abnormalities, injection pain and local injection site complications. Areas covered: To characterize the safety and tolerability of the second-line injectables in children treated for MDR-TB, we reviewed data on the mechanism of injectable associated adverse effects, risk factors for their development, and the incidence of injectable-associated adverse effects in adults and children treated for MDR-TB. Expert opinion: Despite a substantial evidence base in adults demonstrating the frequent and potentially serious adverse effects of second-line injectables, important knowledge gaps remain. Improved characterization of the incidence of injectable-associated adverse effects will inform rational guidance on monitoring children with TB on injectables. Eliminating the need for injectables in MDR-TB treatment regimens is a high priority, and will rely on the use of novel antituberculosis TB drugs. Strategies to reduce the risk of adverse effects of injectables, if used, deserve evaluation. This includes evaluation of potentially otoprotective medications N-acetylcysteine or aspirin, high frequency hearing screening for earlier detection of ototoxicity and therapeutic drug monitoring.

Dose optimisation of antibiotics in children: application of pharmacokinetics/pharmacodynamics in paediatrics

The judicious use of antibiotics to combat infections in children relies upon appropriate selection of an agent, dose and duration to maximise efficacy and to minimise toxicity. Critical to dose optimisation is an understanding of the pharmacokinetics and pharmacodynamics of available drugs. Optimal dosing strategies may take advantage of pharmacokinetic/pharmacodynamic (PK/PD) principles so that antibiotic dosing can be individualised to assure effective bacterial killing in patients who have altered pharmacokinetics or who have infections with less susceptible or resistant organisms. This review will outline the fundamentals of antimicrobial pharmacokinetics/pharmacodynamics through discussion of antibacterial agents most often used in children. We aim to highlight the importance of dose optimisation in paediatrics and describe non-conventional dosing strategies that can take advantage of PK/PD principles at the bedside.

Guidelines for aminoglycoside use and applicability to geriatric patients

OBJECTIVES

The authors had for objective to evaluate the applicability of AFSSAPS guidelines for aminoglycoside use to geriatric patients.

METHODS

Theoretical doses and dosing regimens allowing reaching target concentrations in this population were calculated by applying a pharmacokinetic model to 30 geriatric patients treated by amikacin.

RESULTS

The dose allowing reaching a maximum concentration of 60 mg/L was 1.217 mg on average. The time required to reach a blood concentration lower than or equal to 2.5mg/L was 62.5±70.4 hours. Forty-six percent of patients had a trough concentration greater than 2.5 mg/L, 48 hours after administration. For these patients, the time between critical minimum inhibitory concentration (MIC) and toxicity threshold concentration was 21.9±14.9 hours.

CONCLUSION

Reaching a target concentration can be problematic in geriatric patients. It is frequently necessary to use dosing intervals greater than 48 hours. The effectiveness and safety of these regimens remain uncertain.

Sudden irreversible sensory-neural hearing loss in a patient with diabetes receiving amikacin as an antibiotic-heparin lock

Gram-negative septicemia due to central venous catheter-related infection is a leading cause of mortality and morbidity among patients who undergo hemodialysis. Antibiotic-heparin locks are valuable for preserving access sites and lowering the cost and inconvenience associated with central venous catheter replacement and surgical interventions. The optimal duration of use of an antibiotic-heparin lock is unknown. Prolonged use of an amikacin-heparin lock may lead to severe irreversible sensory-neural hearing loss. Patients at risk for this complication should be monitored for its emergence to facilitate early detection. A 43-year-old man with diabetic end-stage renal disease received hemodialysis through a permanent catheter. After 16 weeks of using an amikacin-heparin lock, he suddenly developed sensory-neural hearing loss of 40 dB, which affected high frequencies. His condition progressed relentlessly within 1 week despite immediate discontinuation of the amikacin-heparin lock. The patient developed severe irreversible hearing loss below 80 dB for both high and low frequencies.

Once daily aminoglycoside therapy. Is it less toxic than multiple daily doses and how should it be monitored?

After 50 years of clinical experience with the aminoglycoside agents, there is continuing debate over the most appropriate administration regimen for these drugs. In recent years, once daily administration has been used increasingly, in the hope of both improving efficacy and reducing toxicity. At least 30 controlled clinical trials have compared once versus conventional multiple daily administration. Efficacy was assessed in some, but not all, studies using clinical and/or bacteriological cure. Toxicity was generally determined using rather nonsensitive end-points such as measurement of serum creatinine for nephrotoxicity and clinically detectable hearing loss for ototoxicity. The results of individual clinical trials and subsequent meta-analyses have been variable. However, 5 of 9 meta-analyses found clinical efficacy to be significantly better with once daily administration, and in 3 of the 9 there were significantly less nephrotoxicity with once daily administration. The results were not significant for ototoxicity in any of the meta-analyses. There is debate about how therapeutic drug monitoring should be performed, and whether it is still required with once daily administration. Previous experience with the aminoglycosides, especially in patients with impaired drug clearance caused by renal impairment, suggests that monitoring is still prudent. Results from the once daily administration trials appear to support this. Various methods of monitoring and dose adjustment have been proposed. The most common is to measure a 24-hour trough concentration and to adjust the dose to maintain the trough concentration below a value of 2, 1 or 0.5 mg/L. However, this method allows for greater total aminoglycoside exposure than has been permitted with conventional dosages, increasing the likelihood of toxicity in patients with impaired aminoglycoside clearance. Other methods measure drug concentrations at a time-point or points within the dose interval (when the concentration is still measurable), and adjust the dose according to concentration-time curve nomograms or to a target area under the concentration-time curve. This allows the use of higher doses in those with high drug clearance. Furthermore, in patients with impaired clearance, drug exposure is limited to the same extent as, or less than, that with conventional multiple daily administration. To date no controlled trials have compared methods of dose-individualisation. In summary, in addition to a slight overall improvement in efficacy, once daily administration has resulted in a small reduction in nephrotoxicity. In the studies using more sensitive measures of toxicity, the differences in toxicity were greater, strengthening the case for once daily administration. Therapeutic drug monitoring is probably required with once daily administration. Methods which use mid-dosage interval concentrations to gauge drug exposure would seem to be preferable over trough concentration measurement.

Validation and nephrotoxicity of a simplified once-daily aminoglycoside dosing schedule and guidelines for monitoring therapy

There is no established dosing schedule for once-daily aminoglycoside dosing regimens, and accepted guidelines for monitoring therapy are lacking. We derived a simplified schedule from the Hull and Sarubbi (J. H. Hull and F. A. Sarubbi, Ann. Intern. Med. 85:183-189, 1976) nomogram, for which efficacy and safety in a once-daily dosing regimen were previously demonstrated, and prospectively followed serum aminoglycoside levels in patients. The standard treatment was gentamicin or tobramycin at 4 mg/kg of body weight given intravenously once daily. When the renal function was decreased, the daily dose was reduced, as follows: for an estimated creatinine clearance of between 50 and 80 ml/min, the daily dose was 3.25 mg/kg, for an estimated creatinine clearance of between 30 and 50 ml/min, the daily dose was 2.5 mg/kg, and for an estimated creatinine clearance of below 30 ml/min, the daily dose was 2 mg/kg. A total of 221 patients were studied (184 received gentamicin and 37 received tobramycin). First trough levels above 2 mg/liter were recorded in 11% of the patients, and they all had a baseline creatinine clearance below 50 ml/min, or a substantial decrease in clearance between enrollment and the day that the trough level was obtained. A peak level below 6 mg/liter was recorded in 6% of the patients, and half of them received the lowest daily dose. Twenty-five of the 179 evaluable patients (14%; 95% confidence interval, 9 to 19%) fulfilled the criteria for nephrotoxicity. In a multiple regression analysis, the duration of treatment and the use of other nephrotoxic antibiotics or high-dose furosemide, but not trough levels, were significant risk factors. Since the meaning of low peak levels is unclear and since most studies with multiple daily regimens confirm the lack of an association between trough levels and toxicity, we believe that monitoring of serum drug levels can be restricted to monitoring of trough levels in patients with a creatinine clearance below 50 ml/min or with a deteriorating renal function.

Preclinical and clinical evaluation of once-daily aminoglycoside chemotherapy

The rationale for and effectiveness of extended dosage intervals for aminoglycosides are reviewed. Aminoglycoside antibiotics have a prolonged postantibiotic effect against a variety of common Gram-negative and Gram-positive organisms: higher serum aminoglycoside levels are associated with a longer postantibiotic effect and increased bactericidal activity. Moreover once daily aminoglycoside administration may reduce the potential for adaptive postexposure resistance by allowing less contact time between bacteria and antibiotic. A longer dosage interval may decrease the risk of nephro- and ototoxicity. At least 33 published clinical trials suggest that once-daily administration of aminoglycosides and conventional regimens involving shorter dosage intervals are equally effective in patients with normal renal function and Gram-negative infections: besides, once-daily administration may reduce the frequency of aminoglycoside toxicity or delay it.

Toxicodynamics and toxicokinetics of amikacin in the guinea pig cochlea

An extensive overview of the relationship between cochlear toxicity and amikacin blood concentrations in the guinea pig is provided which should assist in the clinical application of this class of antibiotic. A data set previously used to relate the incidence of amikacin ototoxicity to dosing rates and blood concentrations was re-examined to assess the toxicodynamics of amikacin in terms of decibels of hearing loss across dosing rate, hearing frequency and time following drug exposure. Animals in this data set had received continuously i.v. infused amikacin over an 8-fold range of dosing rates. Preliminary analysis indicated that the data were consistent with a sigmoid relationship between hearing loss (decibels) and area under the amikacin plasma concentration vs time curve cumulated over the entire course of drug administration (cAUC). The sigmoid model was therefore used as the backbone of a far more comprehensive toxicodynamic model which described all the data with a single equation. Testing with this model showed that the cAUC required to produce half-maximum hearing loss (cAUC-1/2) was related to dosing rate (P < 0.01), to hearing frequency (P < 0.00001), and to post-drug interval (P < 0.00001). Maximum hearing loss (difference between upper and lower sigmoid asymptotes) was less than total and was significantly related to frequency (P < 0.00001). No effects could be detected on the sigmoid slope. Further modelling of the significant effects detected by the comprehensive toxicodynamic model was done to determine if they could be described by simple relationships or by biologically relevant sub-models. Modelling of maximum hearing loss (postulated to represent loss of mainly outer hair cell function) indicated that this parameter was constant at about 61 decibels for 2-12 kHz and linearly decreased with log frequency for frequencies > 12 kHz. Modelling of cAUC-1/2 on frequency indicated that there was a strong inverse linear relationship to log frequency. Modelling of cAUC-1/2 on post-drug interval indicated that delayed ototoxicity continued at progressively slower rates for at least 56 days after drug administration had ceased. Modelling of cAUC-1/2 on dosing rate showed an increased requirement for drug as the dosing rate decreased. However, cAUC-1/2 changed no more than 20% across the range of dosing rates compared to the 8-fold difference in mean steady-state plasma concentrations, suggesting that plasma concentration is not a primary determinant of ototoxicity. A toxicokinetic model was developed which explained the dosing rate effect on cAUC-1/2 very successfully.(ABSTRACT TRUNCATED AT 400 WORDS)

Once-daily administration of aminoglycosides

OBJECTIVE

To provide an overview of the efficacy and adverse effects associated with once-daily administration of aminoglycosides.

DATA SOURCES

An extensive MEDLINE search and review of journals was conducted to identify information for this review.

DATA SYNTHESIS

Aminoglycosides alone or in combination with beta-lactams are commonly used for their activity against gram-negative microorganisms. Numerous studies have been performed comparing efficacy and toxicity of once-daily administration of aminoglycosides with multiple-daily dosing. Two studies have found a significant difference in clinical efficacy between once-daily and multiple-daily dosing of aminoglycosides. Several studies have observed a lower incidence of toxicity with once-daily than multiple-daily dosing, but others have found no difference.

CONCLUSIONS

Review of the literature suggests that once-daily administration of aminoglycosides may be as safe and effective as multiple-daily dosing regimens for the treatment of certain infections caused by gram-negative bacteria.

Eustachian tube function tests and their diagnostic potential in normal and diseased ears

We have summarized various methods for testing Eustachian tube function since the 1980's. There have been numerous contributions to our knowledge on Eustachian tube and middle ear functions, and the pathophysiology of disorders of the middle ear has been clarified. Understanding of the Eustachian tube function and controlling the Eustachian tube dysfunction are mandatory for adequate clinical management and for improvement of the prognosis.

Effect of isepamicin dosing scheme on concentration in cochlear tissue

To investigate the possible effect of the dosing scheme of aminoglycosides on their concentration in the cochlear tissue, we gave two groups of 12 guinea pigs subcutaneous doses of 45 mg of isepamicin (ca. 30 mg of active product) per kg of body weight daily for eight consecutive days. The first group received the drug by continuous infusion, while the second group received it by single daily injection. On the final day of administration, the animals were sacrificed and the cochlear tissue was removed. The tissues from the cochleas of pairs of guinea pigs were pooled. The isepamicin concentrations in the cochlear duct tissue (organ of Corti plus lateral wall) and the cochlear nerve tissue were determined separately. Hearing levels before and after treatment were assessed by means of frequency-specific auditory brain stem responses (ABR). The creatinine level in serum was determined on the last day of the administration. None of the animals in either group showed signs of renal insufficiency or of hearing impairment. The median isepamicin concentration in the cochlear duct was 2.40 micrograms/mg of protein after continuous administration and 2.50 micrograms/mg of protein after once-daily administration, compared with the concentration in the cochlear nerve, where it was 1.93 micrograms/mg of protein after continuous administration and 2.59 micrograms/mg of protein after once-daily administration. These differences are statistically insignificant. The results give evidence for linear uptake kinetics of isepamicin in the inner ear tissue and may be directly relevant to the clinical dosing of the drug.

Evidence that amikacin ototoxicity is related to total perilymph area under the concentration-time curve regardless of concentration

Previous studies have failed to fully establish whether ototoxicity is related in any way to the levels of an aminoglycoside antibiotic in the perilymph. To study this we exposed guinea pigs to continuously infused amikacin at four different dosing rates under conditions parallel to those used in our previous study which related ototoxicity to total plasma area under the concentration-time curve regardless of the level in plasma. It was found that at all dosing rates, levels in the perilymph and ratios of levels in perilymph/plasma remained constant as the dosing duration increased from nonototoxic to strongly ototoxic. Plasma and perilymph amikacin levels were found to be linear functions of the dosing rate even at ototoxic dosing exposures, and ratios of levels in perilymph/plasma did not differ between dosing rates. The total perilymph area under the concentration-time curve was not different between dosing rates either for a total dose associated with threshold ototoxicity or for one associated with severe ototoxicity. The results suggest that amikacin ototoxicity is related to the integral of the concentration in the perilymph over the total time of amikacin exposure regardless of the level in the perilymph.

Delay in hearing loss following drug administration. A consistent feature of amikacin ototoxicity

The time course of threshold increase in the VIII nerve compound action potential was studied in guinea pigs following amikacin administration at four different constant infusion rates. Despite the wide range of dosing durations required to achieve drug ototoxicity (2-24 days), the full development of both high and low frequency hearing loss was invariably found to be delayed with respect to the time of drug removal. The greatest degree of delayed hearing loss generally occurred within the first 7 days after drug removal, with smaller losses occurring during later time intervals. The delay showed a tendency to decrease as the ototoxic dose was increased. Using the data from the two highest dosing rates, it was estimated that a minimum of 4 days had to elapse before any hearing loss could be detected, once an ototoxic amount of drug had been administered. These data suggest that hearing loss is always substantially delayed with respect to the receipt of an ototoxic dose of amikacin, and that this must be taken into account when conducting animal experiments and when monitoring hearing in patients for the early detection of ototoxicity.