A simulation study on model-informed precision dosing of amikacin for achieving target area under the concentration-time curve.

AIMS: Amikacin requires therapeutic drug monitoring for optimum efficacy; however, the optimal model-informed precision dosing strategy for the area under the concentration-time curve (AUC) of amikacin is uncertain. This simulation study aimed to determine the efficient blood sampling points using the Bayesian forecasting approach for early achievement of the target AUC range for amikacin in critically ill patients. METHODS: We generated a virtual population of 3000 individuals using 2 validated population pharmacokinetic models identified using a systematic literature search. AUC for each blood sampling point was evaluated using the probability of achieving a ratio of estimated/reference AUC at steady state in the 0.8-1.2 range. RESULTS: On day 1, the 1-point samplings for population pharmacokinetic models showed a priori probabilities of 26.3 and 45.6%, which increased to 47.3 and 94.4% at 23 and 15 h, respectively. Using 2-point sampling at the peak (3 and 4 h) and trough (24 h) on day 1, these probabilities further increased to 72.3 and 99.5%, respectively. These probabilities were comparable on days 2 and 3, regardless of 3 and 6 sampling points or estimated glomerular filtration rate. These results indicated the higher predictive accuracy of 2-point sampling than 1-point sampling on day 1 for amikacin AUC estimation. Moreover, 2-point sampling was a more reasonable approach than rich sampling. CONCLUSIONS: This study contributes to the development of an efficient model-informed precision dosing strategy for early targeting of amikacin AUC in critically ill patients.

Population Pharmacokinetics of Amikacin Administered Once Daily in Patients with Different Renal Functions.

The aim of this work was to evaluate the pharmacokinetics of amikacin in Mexican patients with different renal functions receiving once-daily dosing regimens and the influence of clinical and demographical covariates that may influence the optimization of this antibiotic. A prospective study was performed in a total of 63 patients with at least one determination of amikacin plasma concentration. Population pharmacokinetic (PK) parameters were estimated by nonlinear mixed-effects modeling; validations were performed for dosing recommendation purposes based on PK/pharmacodynamic simulations. The concentration-versus-time data were best described by a one-compartment open model with proportional interindividual variability associated with amikacin clearance (CL) and volume of distribution (V); residual error followed a homoscedastic trend. Creatinine clearance (CLCR) and ideal body weight (IBW) demonstrated significant influence on amikacin CL and V, respectively. The final model [CL (liters/h) = 7.1 × (CLCR/130)0.84 and V (liters) = 20.3 × (IBW/68)2.9] showed a mean prediction error of 0.11 mg/liter (95% confidence interval, -3.34, 3.55) in the validation performed in a different group of patients with similar characteristics. There is a wide variability in amikacin PK parameters in Mexican patients. This leads to inadequate dosing regimens, especially in patients with augmented renal clearance (CLCR of >130 ml/min). Optimization based on the final population PK model in Mexican patients may be useful, since reliability and clinical applicability have been demonstrated in this study.

Evaluation of Assays to Measure Aminoglycosides in Serum: Comparison of Accuracy and Precision Based on External Quality Assessment.

BACKGROUND: Aminoglycosides require highly accurate therapeutic drug monitoring owing to their narrow therapeutic windows and toxic side effects. Therapeutic drug monitoring varies in different laboratories, and this difference is mainly due to the use of different analytical techniques. This study aimed to compare the accuracy and precision of immunoassays for the measurement of gentamicin, tobramycin, and amikacin in serum. METHODS: Human plasma samples were spiked with known concentrations of amikacin, gentamicin, and tobramycin and dispatched to laboratories worldwide. The percentage deviation and coefficient of variation were calculated to compare the accuracy and precision among immunoassays and among antibiotics. RESULTS: We analyzed 273, 534, and 207 amikacin, gentamicin, and tobramycin measurement results, obtained satisfactory rates of 83.9%, 86.3%, and 93.7%, and coefficients of variation ranging from 1.1% to 15.6%, 2.9% to 25.2%, and 1.8% to 27.0%, respectively. The percentage deviation ranged from -7.5% to 6.6%, -20.8% to 18.7%, and -33.2% to 41.5% for amikacin, gentamicin, and tobramycin, respectively. Significant differences were observed in accuracy and precision among assays for all antibiotics. CONCLUSIONS: This study demonstrated high variations in results obtained from antibiotic assays conducted at different laboratories worldwide.

Amikacin Pharmacokinetics in Terminal Stage of Hematological Malignancy.

BACKGROUND: The influence of cancer cachexia on the pharmacokinetics of and kidney injury caused by amikacin remains unclear. This study investigated whether the pharmacokinetics of amikacin and the risk of kidney injury are altered with the progression of cancer cachexia. METHODS: A retrospective analysis was conducted using therapeutic drug monitoring data obtained from 52 cancer patients who received amikacin intravenously for infection(s). The patients were classified into 2 groups based on the status of cachexia using a consensus definition: noncachexia group (n = 31) and cachexia group (n = 21). Differences in amikacin pharmacokinetics and occurrence of kidney injury were compared between the 2 groups. Amikacin pharmacokinetics was calculated based on a 1-compartment model using peak and trough concentrations measured clinically for therapeutic drug monitoring. In addition, intrapatient analysis was conducted based on patients who received amikacin treatments more than once during the study period to examine the alteration in amikacin pharmacokinetics with the progression of cancer cachexia. RESULTS: Systemic clearance of amikacin [median (range)] was significantly (P < 0.05) lower in the cachexia group [37.3 (11.2-87.3) (mL/min)] than in the noncachexia group [52.0 (19.1-133.4) (mL/min)]. In contrast, volume of distribution was significantly (P < 0.05) increased in the cachexia group [0.47 (0.20-1.45) L/kg] compared with the noncachexia group [0.32 (0.21-1.00) L/kg]. There was no difference in the occurrence of kidney injuries between the 2 groups. In an intrapatient analysis of the longitudinal alteration of amikacin pharmacokinetics, an approximately 50% reduction in clearance and 30% increase in volume of distribution were observed as cancer cachexia progressed. CONCLUSIONS: The present study suggests that progression of cancer cachexia may reduce amikacin clearance and increase the volume of distribution, but cancer cachexia does not increase amikacin-induced kidney injury.

Relationship between amikacin blood concentration and ototoxicity in low birth weight infants.

Amikacin (AMK) is used as empiric therapy for severe infections such as sepsis in low birth weight (LBW) infants. AMK administered once daily (OD) in adults is reported to be therapeutically effective and prevent side effects, however, evidence on AMK administration in LBW infants is limited, with no clear indications of effectiveness. We performed therapeutic drug monitoring analysis of 20 infants treated with AMK OD for severe infections such as bacteremia. Treatment effectiveness was admitted by the patients' medical records, and side effects of renal dysfunction and ototoxicity were investigated. The mean gestational age was 30.4 ± 5 weeks and mean body weight (Bw) was 1280.2 ± 809.8 g. The mean AMK dose was 14.1 ± 2.6 mg/kg and mean administration period was 10.1 ± 4.1 days. Blood concentration was measured 6.3 ± 2.3 days after AMK administration; mean peak and trough concentrations were 29.1 ± 7.5 µg/mL and 7.6 ± 6.9 µg/mL, respectively. Additionally, therapeutic effect was observed in all patients, and no significant change in serum creatinine (CRE) concentration (a marker of renal dysfunction) was observed, suggesting no renal dysfunction. Ototoxicity was observed in 4 patients, 3 of whom had trough concentrations ≥10 µg/mL. When we categorized patients into two groups using a trough cut-off value of 10 µg/mL, no difference in AMK dose was observed. However, there were significant differences in peak concentration, Bw, volume of distribution and CRE. Our findings suggest AMK trough concentration ≥10 µg/mL significantly affects ototoxicity in neonates.

Predictors of insufficient peak amikacin concentration in critically ill patients on extracorporeal membrane oxygenation.

BACKGROUND: Amikacin infusion requires targeting a peak serum concentration (Cmax) 8-10 times the minimal inhibitory concentration, corresponding to a Cmax of 60-80 mg/L for the least susceptible bacteria to theoretically prevent therapeutic failure. Because drug pharmacokinetics on extracorporeal membrane oxygenation (ECMO) are challenging, we undertook this study to assess the frequency of insufficient amikacin Cmax in critically ill patients on ECMO and to identify relative risk factors. METHODS: This was a prospective, observational, monocentric study in a university hospital. Patients on ECMO who received an amikacin loading dose for suspected Gram-negative infections were included. The amikacin loading dose of 25 mg/kg total body weight was administered intravenously and Cmax was measured 30 min after the end of the infusion. Independent predicators of Cmax < 60 mg/L after the first amikacin infusion were identified with mixed-model multivariable analyses. Various dosing simulations were performed to assess the probability of reaching 60 mg/L < Cmax < 80 mg/L. RESULTS: A total of 106 patients on venoarterial ECMO (VA-ECMO) (68%) or venovenous-ECMO (32%) were included. At inclusion, their median (1st; 3rd quartile) Sequential Organ-Failure Assessment score was 15 (12; 18) and 54 patients (51%) were on renal replacement therapy. Overall ICU mortality was 54%. Cmax was < 60 mg/L in 41 patients (39%). Independent risk factors for amikacin under-dosing were body mass index (BMI) < 22 kg/m2 and a positive 24-h fluid balance. Using dosing simulation, increasing the amikacin dosing regimen to 30 mg/kg and 35 mg/kg of body weight when the 24-h fluid balance is positive and the BMI is ≥ 22 kg/m2 or < 22 kg/m2 (Table 3), respectively, would have potentially led to the therapeutic target being reached in 42% of patients while reducing under-dosing to 23% of patients. CONCLUSIONS: ECMO-treated patients were under-dosed for amikacin in one third of cases. Increasing the dose to 35 mg/kg of body weight in low-BMI patients and those with positive 24-h fluid balance on ECMO to reach adequate targeted concentrations should be investigated.

Penetration of Ciprofloxacin and Amikacin into the Alveolar Epithelial Lining Fluid of Rats with Pulmonary Fibrosis.

We determined the concentration-time profiles of ciprofloxacin and amikacin in serum and alveolar epithelial lining fluid (ELF) of rats with or without pulmonary fibrosis and investigated the effect of pulmonary fibrosis on the capacity for penetration of antimicrobials into the ELF of rats. Pulmonary fibrosis was induced in rats with a single intratracheal instillation of bleomycin. After intravenous injection of ciprofloxacin or amikacin, blood and bronchoalveolar lavage fluid samples were collected. Urea concentrations in serum and lavage fluid were determined using an enzymatic assay. Ciprofloxacin and amikacin concentrations were determined by high-performance liquid chromatography and liquid chromatography-tandem mass spectrometry, respectively. The mean ratio of ELF to plasma concentrations of ciprofloxacin at each time point in the normal group did not significantly differ from that in the pulmonary fibrosis group. However, the ratio of the ciprofloxacin area under the concentration-time curve from 0 to 24 h (AUC0-24) in ELF to the AUC0-24 in plasma was 1.02 in the normal group and 0.76 in the pulmonary fibrosis group. The mean ELF-to-plasma concentration ratios of amikacin at each time point in the normal group were higher than those in the pulmonary fibrosis group, reaching a statistically significant difference at 1, 2, and 4 h. The ratio of the AUC0-24 in ELF to the AUC0-24 in plasma was 0.49 in the normal group and 0.27 in the pulmonary fibrosis group. In conclusion, pulmonary fibrosis can influence the penetration of antimicrobials into the ELF of rats and may have a marked effect on the penetration of amikacin than that of ciprofloxacin.

Reduced Chance of Hearing Loss Associated with Therapeutic Drug Monitoring of Aminoglycosides in the Treatment of Multidrug-Resistant Tuberculosis.

Hearing loss and nephrotoxicity are associated with prolonged treatment duration and higher dosage of amikacin and kanamycin. In our tuberculosis center, we used therapeutic drug monitoring (TDM) targeting preset pharmacokinetic/pharmacodynamic (PK/PD) surrogate endpoints in an attempt to maintain efficacy while preventing (oto)toxicity. To evaluate this strategy, we retrospectively evaluated medical charts of tuberculosis (TB) patients treated with amikacin or kanamycin in the period from 2000 to 2012. Patients with culture-confirmed multiresistant or extensively drug-resistant tuberculosis (MDR/XDR-TB) receiving amikacin or kanamycin as part of their TB treatment for at least 3 days were eligible for inclusion in this retrospective study. Clinical data, including maximum concentration (Cmax), Cmin, and audiometry data, were extracted from the patients' medical charts. A total of 80 patients met the inclusion criteria. The mean weighted Cmax/MIC ratios obtained from 57 patients were 31.2 for amikacin and 12.3 for kanamycin. The extent of hearing loss was limited and correlated with the cumulative drug dose per kg of body weight during daily administration. At follow-up, 35 (67.3%) of all patients had successful outcome; there were no relapses. At a median dose of 6.5 mg/kg, a correlation was found between the dose per kg of body weight during daily dosing and the extent of hearing loss in dB at 8,000 Hz. These findings suggest that the efficacy at this lower dosage is maintained with limited toxicity. A randomized controlled trial should provide final proof of the safety and efficacy of TDM-guided use of aminoglycosides in MDR-TB treatment.

Amikacin use and therapeutic drug monitoring in adults: do dose regimens and drug exposures affect either outcome or adverse events? A systematic review.

OBJECTIVES: The objectives of this study were to identify the amikacin dosage regimens and drug concentrations consistent with good outcomes and to determine the drug exposures related to nephrotoxicity and ototoxicity. METHODS: A literature review was conducted in Medline, EMBASE and the Cochrane Central Register of Controlled Trials. Full journal articles reporting randomized controlled trials, controlled clinical trials, interrupted time series trials, and controlled before and after studies involving amikacin therapeutic drug monitoring (TDM) and dose adjustment were considered for inclusion. RESULTS: Seventeen studies for inclusion were identified, comprising 1677 participants. Amikacin doses ranged from 11 to 15 mg/kg/day with 13 studies using 15 mg/kg/day. Studies were generally designed to compare different aminoglycosides rather than to assess concentration-effect relationships. Only 11 papers presented data on target concentrations, rate of clinical cure and toxicity. Target peak concentrations ranged from 15 to 40 mg/L and target troughs were typically <10 or <5 mg/L. It was not clear whether these targets were achieved. Measured peaks averaged 28 mg/L for twice-daily dosing and 40-45 mg/L for once-daily dosing; troughs averaged 5 and 1-2 mg/L, respectively. Fifteen of the included studies reported rates of nephrotoxicity; auditory and vestibular toxicities were reported in 12 and 8 studies. CONCLUSIONS: This systematic review found little published evidence to support an optimal dosage regimen or TDM targets for amikacin therapy. The use of alternative approaches, such as consensus opinion and a review of current practice, will be required to develop guidelines to maximize therapeutic outcomes and minimize toxicity with amikacin.

Evaluating renal function and age as predictors of amikacin clearance in neonates: model-based analysis and optimal dosing strategies.

AIMS: We aimed to compare the performance of renal function and age as predictors of inter-individual variability (IIV) in clearance of amikacin in neonates through parallel development of population pharmacokinetic (PK) models and their associated impact on optimal dosing regimens. METHODS: Amikacin concentrations were retrospectively collected for 149 neonates receiving amikacin (post-natal age (PNA) between 4-89 days). Two population PK models were developed in parallel, considering at least as predictors current body weight (WT), in combination with either creatinine clearance (CLcr ) or age descriptors. Using stochastic simulations for both renal function or age-based dosing, we identified optimal dosing strategies that were based on attainment of optimal peak- (PCC) and trough target concentration coverage (TCC) windows associated with efficacy and toxicity. RESULTS: The CLcr and age-based population PK models both included current body weight (WT) on CL, central distribution volume and intercompartmental clearance, in combination with either CLcr or PNA as predictors for IIV of clearance (CL). The WT-CLcr model explained 6.9% more IIV in CL compared with the WT-PNA model. Both models successfully described an external dataset (n = 53) of amikacin PK. The simulation analysis of optimal dose regimens suggested similar performance of either CLcr or PNA based dosing. CONCLUSION: CLcr predicted more IIV in CL, but did not translate into clinically relevant improvements of target concentrations. Our optimized dose regimens can be considered for further evaluation to optimize initial treatment with amikacin.

Prospective Evaluation of a Model-Based Dosing Regimen for Amikacin in Preterm and Term Neonates in Clinical Practice.

Based on a previously derived population pharmacokinetic model, a novel neonatal amikacin dosing regimen was developed. The aim of the current study was to prospectively evaluate this dosing regimen. First, early (before and after second dose) therapeutic drug monitoring (TDM) observations were evaluated for achieving target trough (<3 mg/liter) and peak (>24 mg/liter) levels. Second, all observed TDM concentrations were compared with model-predicted concentrations, whereby the results of a normalized prediction distribution error (NPDE) were considered. Subsequently, Monte Carlo simulations were performed. Finally, remaining causes limiting amikacin predictability (i.e., prescription errors and disease characteristics of outliers) were explored. In 579 neonates (median birth body weight, 2,285 [range, 420 to 4,850] g; postnatal age 2 days [range, 1 to 30 days]; gestational age, 34 weeks [range, 24 to 41 weeks]), 90.5% of the observed early peak levels reached 24 mg/liter, and 60.2% of the trough levels were <3 mg/liter (93.4% ≤5 mg/liter). Observations were accurately predicted by the model without bias, which was confirmed by the NPDE. Monte Carlo simulations showed that peak concentrations of >24 mg/liter were reached at steady state in almost all patients. Trough values of <3 mg/liter at steady state were documented in 78% to 100% and 45% to 96% of simulated cases with and without ibuprofen coadministration, respectively; suboptimal trough levels were found in patients with postnatal age <14 days and current weight of >2,000 g. Prospective evaluation of a model-based neonatal amikacin dosing regimen resulted in optimized peak and trough concentrations in almost all patients. Slightly adapted dosing for patient subgroups with suboptimal trough levels was proposed. This model-based approach improves neonatal dosing individualization.

Plasma drug activity in patients on treatment for multidrug-resistant tuberculosis.

Little is known about plasma drug concentrations relative to quantitative susceptibility in patients with multidrug-resistant tuberculosis (MDR-TB). We previously described a TB drug activity (TDA) assay that determines the ratio of the time to detection of plasma-cocultured Mycobacterium tuberculosis versus control growth in a Bactec MGIT system. Here, we assess the activity of individual drugs in a typical MDR-TB regimen using the TDA assay. We also examined the relationship of the TDA to the drug concentration at 2 h (C2) and the MICs among adults on a MDR-TB regimen in Tanzania. These parameters were also compared to the treatment outcome of sputum culture conversion. Individually, moxifloxacin yielded superior TDA results versus ofloxacin, and only moxifloxacin and amikacin yielded TDAs equivalent to a -2-log killing. In the 25 patients enrolled on a regimen of kanamycin, levofloxacin, ethionamide, pyrazinamide, and cycloserine, the C2 values were found to be below the expected range for levofloxacin in 13 (52%) and kanamycin in 10 (40%). Three subjects with the lowest TDA result (<1.5, a finding indicative of poor killing) had significantly lower kanamycin C2/MIC ratios than subjects with a TDA of ≥1.5 (9.8 ± 8.7 versus 27.0 ± 19.1; P = 0.04). The mean TDAs were 2.52 ± 0.76 in subjects converting to negative in ≤2 months and 1.88 ± 0.57 in subjects converting to negative in >2 months (P = 0.08). In Tanzania, MDR-TB drug concentrations were frequently low, and a wide concentration/MIC range was observed that affected plasma drug activity ex vivo. An opportunity exists for pharmacokinetic optimization in current MDR-TB regimens, which may improve treatment response.

[Spectrophotometric method for aminoglycoside concentration measurement in blood plasma].

The aim of the research was to develop a simple, available and rapid spectrophotometric method for measuring aminoglycoside concentration in blood plasma and to evaluate the antibiotic efficacy and susceptibility. The method is based on the ability of aminoglycosides, in particular amikacin, to change the color of Fast Blue B Salt Dye (SIGMA-ALDRICH). An antibiotic at various concentrations and the dye were added to blood plasma. The resulting mixture was filtered to separate the insoluble residue. After that the optical density of the filtrate were measured spectrophotometrically against the control specimen with no antibiotic at the wavelength of 450 nm. It was demonstrated that an increase in the plasma antibiotic concentration led to a directly proportional increase of the antibiotic solution extinction. This is a simple, precise and rapid method.

Pharmacokinetics of amikacin after intravenous, intra-articular, and combined intravenous and intra-articular administration in healthy neonatal foals.

BACKGROUND: Pharmacokinetics of amikacin administered IV to neonatal foals are described, but little data are available regarding the plasma concentrations contributed by concurrent intra-articular (IA) administration. HYPOTHESIS/OBJECTIVES: Compare the pharmacokinetics of amikacin when the total dose is administered IV compared to being divided between IV and IA routes of administration in neonatal foals and predict the plasma concentrations from various combined IV and IA dosing regimens. ANIMALS: Eight healthy neonatal foals. METHODS: Foals received 3 amikacin treatment protocols: (1) IV-only (25 mg/kg q24h IV), (2) concurrent IV and IA (16.7 mg/kg q24h IV and 8.3 mg/kg q24h into 1 tarsocrural joint), and (3) IA-only (8.3 mg/kg q24h into 1 tarsocrural joint). Protocols were administered for 3 days beginning at 7, 14, and 21 days of age. Plasma concentrations ≥53 µg/mL at 30 minutes were considered therapeutic for isolates with intermediate susceptibility. RESULTS: Foal age was a significant variable. The IV-only protocol met or exceeded the 30-minute plasma concentrations considered therapeutic (mean µg/mL [95% confidence interval, CI]) in 7- to 9-day-old (54.0 [52.2-56.9]), 14- to 16-day-old (58.1 [55.2-61.0]), and 21- to 23-day-old (66.6 [63.7-69.6]) foals. Concurrent IV and IA protocol did not reach the 30-minute concentration considered therapeutic in 7- to 9-day-old foals (46.5 [43.6-49.4]) but did in 14- to 16-day-old (62.9 [60.0-65.8]) and 21-to 23-day-old (62.6 [59.7-65.6]) foals. CONCLUSIONS AND CLINICAL IMPORTANCE: Concurrent IV and IA administration of amikacin produces 30-minute plasma concentrations considered therapeutic in foals 14 to 23 days old, but concentrations observed in younger foals might be below those considered therapeutic for isolates with intermediate susceptibility to amikacin.

Subcutaneous amikacin administration in red-eared sliders (Trachemys scripta elegans) produces prolonged detectable plasma concentrations without biochemistry evidence of impaired renal function.

OBJECTIVE: To establish pilot data on the plasma concentrations of SC amikacin at 2 doses in red-eared sliders and evaluate concurrent plasma biochemistry parameters. ANIMALS: 8 adult red-eared sliders (Trachemys scripta elegans). METHODS: Amikacin was administered SC at target doses of 5 and 10 mg/kg with a 3-week washout period. Blood samples were collected at 0, 24, 48, 72, and 96 hours postadministration. Plasma amikacin concentrations were quantified using liquid chromatography tandem mass spectrometry. Plasma biochemistry analyses were performed before amikacin administration, 1 week post 5-mg/kg administration, and 1 week post 10-mg/kg administration. RESULTS: Mean maximum amikacin plasma concentrations were recorded 24 hours after 5-mg/kg and 10-mg/kg dosing and were 17.5 ± 2.32 µg/mL and 23.6 ± 2.92 µg/mL, respectively. Mean plasma concentrations after 5-mg/kg dosing steadily decreased to 9.1 ± 0.92 µg/mL by 96 hours postadministration. Amikacin remained detectable in all plasma samples 3 weeks post 5-mg/kg dosing with a mean plasma concentration of 1.04 ± 0.22 µg/mL. Mean plasma concentrations after 10-mg/kg dosing did not decrease over the 96-hour study period. There were no clinically relevant changes in biochemistry parameters. CLINICAL RELEVANCE: Amikacin persists at detectable plasma levels for at least 3 weeks after SC administration of a 5-mg/kg dose in red-eared sliders, which has not previously been reported in any species. No biochemistry changes consistent with renal toxicity occurred after either dose. Use caution with repeated amikacin dosing in this species until further studies can better characterize cumulative amikacin pharmacokinetics and toxic threshold.

Therapeutic drug monitoring of amikacin in septic patients.

INTRODUCTION: Use of higher than standard doses of amikacin (AMK) has been proposed during sepsis, especially to treat less susceptible bacterial strains. However, few data are available on drug concentrations during prolonged therapy and on potential adverse events related to this strategy. METHODS: Sixty-three critically ill patients who required AMK administration for the treatment of severe infection were included in this study. After a loading dose (LD, 18 to 30 mg/kg), the daily regimen was adapted using therapeutic drug monitoring (TDM) of both peak (Cpeak) and trough (Cmin) concentrations. Target concentrations had to give a ratio of at least 8 between Cpeak and the minimal inhibitory concentration (MIC) of the isolated pathogen. A Cmin >5 mg/L was considered as potentially nephrotoxic. We recorded clinical and microbiological responses, the development of acute kidney injury (AKI) during therapy and ICU mortality. RESULTS: The median AMK LD was 1500 (750 to 2400) mg, which resulted in a Cpeak/MIC ≥8 in 40 (63%) patients. Increasing the dose in the 23 patients with a Cpeak/MIC <8 resulted in optimal Cpeak/MIC in 15 of these patients (79%). In 23 patients (37%), Cmin was >5 mg/L after the LD, notably in the presence of altered renal function at the onset of therapy, needing prolongation of drug administration. Overall, only 11 patients (17%) required no dose or interval adjustment during AMK therapy. Clinical cure (32/37 (86%) vs. 16/23 (70%), P = 0.18)) and microbiological eradication (29/35 (83%) vs. 14/23 (61%), P = 0.07) were higher in patients with an initial optimal Cpeak/MIC than in the other patients. The proportion of patients with clinical cure significantly improved as the Cpeak/MIC increased (P = 0.006). Also, increased time to optimal Cpeak was associated with worse microbiological and clinical results. AKI was identified in 15 patients (24%) during AMK therapy; 12 of these patients already had altered renal function before drug administration. Survivors (n = 47) had similar initial Cpeak/MIC ratios but lower Cmin values compared to nonsurvivors. CONCLUSIONS: TDM resulted in adjustment of AMK therapy in most of our septic patients. Early achievement of an optimal Cpeak/MIC ratio may have an impact on clinical and microbiological responses, but not on outcome. In patients with impaired renal function prior to treatment, AMK therapy may be associated with a further decline in renal function.

Lack of a relationship between the serum concentration of aminoglycosides and ototoxicity in neonates.

INTRODUCTION: Gentamicin and the other aminoglycosides are toxic antibiotics, but they are urgently needed to treat newborns with neonatal sepsis. Aminoglycosides are well known for their nephrotoxicity and ototoxicity. The aminoglycoside dosage currently applied in Indonesia is derived from studies done in Caucasian populations. The safety and efficacy of this dosage regimen, however, has never been evaluated to date. The pharmacokinetic profile of drugs may vary between populations and this may be influenced by genetic factors, lifestyle, drug interactions, etc. The detection of aminoglycoside toxicity in newborns is usually problematic. The present study aims to know the proportion of ototoxicity in newborns in the Cipto Mangunkusumo Hospital treated with gentamicin or amikacin in relation to their trough serum concentration. METHODS: The serum level of gentamicin and amikacin were quantified using Liquid Chromatography Tandem Mass Spectrometry (LC-MSMS), and is assumed to be safe if the trough serum concentrations are < 2 mcg/ml and effective if it is between 5 - 12 mcg/ml. For amikacin the desired trough serum concentrations are < 10 mcg/ml and the peak is between 20 - 30 mcg/ml. The hearing function was assessed by Distortion Product Otoacoustic Emission (DPOAE) instrument. This study is registered with the www.clinicaltrials.gov NCT01624324. CONCLUSION: Our study indicated that there was no relationship between aminoglycosides serum trough concentration and ototoxicity in neonates with neonatal sepsis.

Once-daily amikacin dosing in burn patients treated with continuous venovenous hemofiltration.

Amikacin clearance can be increased in burn injury, which is often complicated by renal insufficiency. Little is known about the impact of renal replacement therapies, such as continuous venovenous hemofiltration (CVVH), on amikacin pharmacokinetics. We retrospectively examined the clinical pharmacokinetics, bacteriology, and clinical outcomes of 60 burn patients given 15 mg/kg of body weight of amikacin in single daily doses. Twelve were treated with concurrent CVVH therapy, and 48 were not. The pharmacodynamic target of ≥10 for the maximum concentration of drug in serum divided by the MIC (C(max)/MIC) was achieved in only 8.5% of patients, with a small reduction of C(max) in patients receiving CVVH and no difference in amikacin clearance. Mortality and burn size were greater in patients who received CVVH. Overall, 172 Gram-negative isolates were recovered from the blood cultures of 39 patients, with amikacin MIC data available for 82 isolates from 24 patients. A 10,000-patient Monte Carlo simulation was conducted incorporating pharmacokinetic and MIC data from these patients. The cumulative fraction of response (CFR) was similar in CVVH and non-CVVH patients. The CFR rates were not significantly improved by a theoretical 20 mg/kg amikacin dose. Overall, CVVH did not appear to have a major impact on amikacin serum concentrations. The low pharmacodynamic target attainment appears to be primarily due to higher amikacin MICs rather than more rapid clearance of amikacin related to CVVH therapy.

Pharmacokinetics of amikacin in plasma and selected body fluids of healthy horses after a single intravenous dose.

REASONS FOR PERFORMING STUDY: No studies have determined the pharmacokinetics of low-dose amikacin in the mature horse. OBJECTIVES: To determine if a single i.v. dose of amikacin (10 mg/kg bwt) will reach therapeutic concentrations in plasma, synovial, peritoneal and interstitial fluid of mature horses (n=6). METHODS: Drug concentrations of amikacin were measured across time in mature horses (n=6); plasma, synovial, peritoneal and interstitial fluid were collected after a single i.v. dose of amikacin (10 mg/kg bwt). RESULTS: The mean±s.d. of selected parameters were: extrapolated plasma concentration of amikacin at time zero 144±21.8 µg/ml; extrapolated plasma concentration for the elimination phase 67.8±7.44 µg/ml, area under the curve 139±34.0 µg*h/ml, elimination half-life 1.34±0.408 h, total body clearance 1.25±0.281 ml/min/kg bwt; and mean residence time (MRT) 1.81±0.561 h. At 24 h, the plasma concentration of amikacin for all horses was below the minimum detectable concentration for the assay. Selected parameters in synovial and peritoneal fluid were maximum concentration (Cmax) 19.7±7.14 µg/ml and 21.4±4.39 µg/ml and time to maximum concentration 65±12.2 min and 115±12.2 min, respectively. Amikacin in the interstitial fluid reached a mean peak concentration of 12.7±5.34 µg/ml and after 24 h the mean concentration was 3.31±1.69 µg/ml. Based on a minimal inhibitory concentration (MIC) of 4 µg/ml, the mean Cmax:MIC ratio was 16.9±1.80 in plasma, 4.95±1.78 in synovial fluid, 5.36±1.10 in peritoneal fluid and 3.18±1.33 in interstitial fluid. CONCLUSIONS: Amikacin dosed at 10 mg/kg bwt i.v. once a day in mature horses is anticipated to be effective for treatment of infection caused by most Gram-negative bacteria. POTENTIAL RELEVANCE: Low dose amikacin (10 mg/kg bwt) administered once a day in mature horses may be efficacious against susceptible microorganisms.

Assessment of the Effects of a High Amikacin Dose on Plasma Peak Concentration in Critically Ill Children.

OBJECTIVES: This study aimed to assess the incidence of amikacin plasma peak concentration (Cmax) below 60 mg·L-1 in critically ill children receiving an amikacin dosing regimen of 30 mg kg-1·day-1. Secondary objectives were to identify factors associated with low Cmax and to assess the incidence of acute kidney injury (AKI). METHODS: A retrospective observational study was performed in two French pediatric intensive care units. All admitted children who received 30 mg·kg-1 amikacin and had a Cmax measurement were eligible. Clinical and biological data, amikacin dose, and concentrations were collected. RESULTS: In total, 30 patients were included, aged from 3 weeks to 7 years. They received a median amikacin dosage of 30 mg kg-1·day-1 (range 29-33) based on admission body weight (BW), corresponding to 27 mg kg-1·day-1 (range 24-30) based on actual BW. Cmax was < 60 mg·L-1 in 21 (70%) children and none had a Cmax ≥ 80 mg·L-1. Among the 15 patients with a measured minimum inhibitory concentration (MIC), 13 (87%) had a Cmax/MIC ratio > 8. Univariate analysis showed that factors associated with Cmax < 60 mg·L-1 were high estimated glomerular filtration rate (p = 0.015) and low blood urea concentration (p = 0.001). AKI progression or occurrence was observed after amikacin administration in two (7%) and six (21%) patients, respectively. CONCLUSIONS: Despite the administration of the maximal recommended amikacin dose, Cmax was below the pharmacokinetic target in 70% of our pediatric population. Further studies are needed to develop a pharmacokinetic model in a population of critically ill children to optimize target attainment.