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.

Standards of aminoglycoside therapeutic drug monitoring in a South African private hospital: perspectives and implications.

BACKGROUND: Therapeutic drug monitoring (TDM) is essential to ensure that aminoglycoside peak concentrations are high enough for effective antimicrobial treatment and trough levels are low enough to minimise toxicity. Inappropriate utilisation of TDM may lead to suboptimal therapy, toxicity and waste of resources. This study aimed to investigate the standard of aminoglycoside TDM performed in adult hospitalised patients. DESIGN: An observational, descriptive, cross-sectional study. SETTING: A 221-bed private hospital. PARTICIPANTS: All patients, older than 18 years, on intravenous aminoglycosides for more than 48 hours were included. INTERVENTIONS: None, was observational. A computerised database and patient files were used to obtain the information required for this study. Descriptive statistical analysis was used. MAIN OUTCOMES MEASURES: Aminoglycoside blood levels and estimated glomerular filtration rate (eGFR) in the patients. RESULTS: One hundred and three (103) patients were included: 65 on gentamicin and 38 on amikacin. Blood levels were performed in only 19 gentamicin (29.23%) and 22 amikacin (57.89%) patients. Trough levels were taken more than 2 hours before the next dose in 12 gentamicin (63.16%) and 12 amikacin (54.54%) patients. The majority of patients (96.92% on gentamicin and 84.21% on amikacin) received once daily doses. TDM was performed in all patients with an estimated glomerular filtration rate (eGFR) lower than 60 mL/min/1.73m2 and in 23.31% of gentamicin patients and 56.76% of amikacin patients with an eGFR higher than 60 mg/min/1.73m2. CONCLUSIONS: Incorrect sampling times and unnecessary levels taken in patients with normal renal function indicate a need for aminoglycoside treatment guidelines in the private hospital. FUNDING: None.

Development of a Paper-Based Luminescence Bioassay for Therapeutic Monitoring of Aminoglycosides: a Proof-of-Concept Study.

Aminoglycosides are widely used antibiotics that bind to the bacterial 30S ribosomal subunit to inhibit translation. Owing to their adverse side effects and narrow therapeutic index, monitoring blood levels of aminoglycosides is important to maximize their effectiveness and minimize their toxicity. Current monitoring techniques require a well-equipped diagnostic laboratory. The present study aimed to present a proof-of-concept for a simple, low-cost biochemical assay utilizing a paper platform for the detection of serum/whole blood aminoglycosides. A paper-based bioassay chip for the assay was developed by spotting and freeze-drying cell-free transcription/translation reaction machinery for a luminescent reporter protein (NanoLuc) within an array of wax circles printed on filter paper. The paper-based chip could be used to quantify serum/whole blood aminoglycosides within clinically relevant concentrations in 30-60 min by spotting minimal volumes of samples, followed by the NanoLuc substrate, in the wax circles and detecting the associated changes in luminescence signals, using a simple digital camera. Furthermore, a one-pot assay in which cell-free transcription/translation reaction machinery and NanoLuc substrate are mixed in advance and embedded in paper could be used to detect an aminoglycoside in serum. Overall, our paper-based bioassay can potentially provide a basic platform for the simple and low-cost therapeutic monitoring of aminoglycosides, especially in resource-limited regions.

A population pharmacokinetic model of intravenous telavancin in healthy individuals to assess tissue exposure.

Non-compartmental analysis of telavancin microdialysis data indicated a sustained exposure in soft tissues and that unbound plasma concentrations were underestimated in vitro. The objective of the present evaluation was to develop a population pharmacokinetic model of telavancin to describe its plasma protein binding, its distribution into muscle, and subcutaneous tissue and to predict pharmacokinetic/-dynamic target attainment (PTA). Total plasma concentrations and microdialysate concentrations (plasma, subcutaneous, and muscle tissue) were available up to 24 h (plasma microdialysate, up to 8 h) post-dose from eight healthy subjects after a single intravenous infusion of 10 mg/kg telavancin. Population pharmacokinetic modeling and simulations were performed using NONMEM. A two-compartment model with saturable protein binding best described plasma concentrations. Plasma unbound fractions at steady state were 23, 15, and 11% at 100, 50, and 10% of the maximum predicted concentrations respectively. Distribution into muscle and subcutaneous tissue was non-linear and described appropriately by one additional compartment each. Based on total plasma concentrations, predicted median (95% confidence interval) values of AUC/MIC (MIC 0.125 mg/L, clinical breakpoint for MRSA) at steady state were 4009 [3421-4619] with a PTA of 96 [78-100] %. The fAUC/MIC in muscle was 496 [227-1232] with a PTA of 100 [98-100] %. The %fT>MIC was approximately 100% in plasma and interstitial space fluid of muscle and subcutaneous tissues up to an MIC of 0.25 mg/L. The model provided a new hypothesis on telavancin plasma protein binding in vivo. Proposed pharmacodynamic targets in plasma and muscle are achieved with currently approved doses of 10 mg/kg daily.

Integrated Microfluidic Devices Fabricated in Poly (Methyl Methacrylate) (PMMA) for On-site Therapeutic Drug Monitoring of Aminoglycosides in Whole Blood.

On-site therapeutic drug monitoring (TDM) is important for providing a quick and accurate dosing to patients in order to improve efficacy and minimize toxicity. Aminoglycosides such as amikacin, gentamicin, and tobramycin are important antibiotics that have been commonly used to treat infections of chronic bacterial infections in the urinary tract, lung, and heart. However, these aminoglycosides can lead to vestibular and auditory dysfunction. Therefore, TDM of aminoglycosides is important due to their ototoxicity and nephrotoxicity. Here, we have developed a hot embossed poly (methyl methacrylate) (PMMA) microfluidic device featuring an electrokinetic size and mobility trap (SMT) to purify, concentrate, and separate the aminoglycoside antibiotic drugs amikacin, gentamicin, and tobramycin. These drugs were separated successfully from whole blood within 3 min, with 30-fold lower detection limits compared to a standard pinched injection. The limit of detections (LOD) were 3.75 µg/mL for gentamicin, 8.53 µg/mL for amikacin, and 6.00 µg/mL for tobramycin. These are sufficient to cover the therapeutic range for treating sepsis of 6⁻10 µg/mL gentamicin and tobramycin and 12⁻20 µg/mL of amikacin. The device is simple and could be mass produced via embossing or injection molding approaches.

Reappraisal of Contemporary Pharmacokinetic and Pharmacodynamic Principles for Informing Aminoglycoside Dosing.

Therapeutic drug management is regularly performed for aminoglycosides in an effort to maximize their effectiveness and safety. The ratio of maximum plasma drug concentration to minimum inhibitory concentration (Cmax/MIC) has long been regarded as the primary pharmacokinetic/pharmacodynamic (PK/PD) index of clinical efficacy for aminoglycosides due to their concentration-dependent killing. In this review, however, we discuss why the area under the plasma concentration-time curve (AUC)/MIC ratio may be a more reliable indicator of bacterial killing and clinical efficacy for these agents. The definitive AUC/MIC efficacy targets for aminoglycosides are less clear, unlike those that exist for fluoroquinolones. Evaluation of available literature suggests that an AUC/MIC ratio of 30-50 for aminoglycoside therapy may provide optimal outcomes when targeting non-critically ill immunocompetent patients with low-bacterial burden gram-negative infections such as urinary tract infections or in patients receiving additional gram-negative therapy with good source control. However, an AUC/MIC target of 80-100 may be more prudent when treating patients with aminoglycoside monotherapy or in critically ill patients with high-bacterial burden infections, such as nosocomial pneumonia. Reappraisal of current antimicrobial susceptibility breakpoints for aminoglycosides against gram-negative bacteria may also be necessary to achieve these AUC/MIC targets and ensure that current empiric doses are not grossly suboptimal in critically ill patients. Although it has been historically difficult to calculate AUCs in clinical practice, equation-based and Bayesian approaches now can be used to estimate the AUC in clinical practice, with limited PK sampling. Additional research is needed to better define optimal AUC/MIC targets for efficacy, especially when drugs are used in combination, as well as PK/PD targets associated with suppression of resistance. It is also important to determine if AUC can predict nephrotoxicity of these agents or whether trough concentrations should be used instead.

Therapeutic Drug Monitoring of Beta-Lactams and Other Antibiotics in the Intensive Care Unit: Which Agents, Which Patients and Which Infections?

Antibiotics are among the medications most frequently administered to the critically ill, a population with high levels of intra- and inter-individual pharmacokinetic variability. Our knowledge of the relationships among antibiotic dosing, exposure and clinical effect in this population has increased in recent decades. Therapeutic drug monitoring (TDM) of serum antibiotic concentrations is the most practical means of assessing adequate antibiotic exposure, though until recently, it has been underutilised for this end. Now TDM is becoming more widespread, particularly for the beta-lactam antibiotics, a class historically thought to have a wide therapeutic range. We review the basic requirements, indications, and targets for effective TDM of the glycopeptides, aminoglycosides, quinolones and beta-lactam antibiotics in the adult intensive-care setting, with a special focus on TDM of the beta-lactam antibiotics, the most widely used antibiotic class.

Safety and Pharmacokinetic Study of Fidaxomicin in Children With Clostridium difficile-Associated Diarrhea: A Phase 2a Multicenter Clinical Trial.

BACKGROUND: Fidaxomicin is an approved therapy for Clostridium difficile-associated diarrhea (CDAD) in adults. The safety of fidaxomicin in children has not been reported. METHODS: In this study (ClinicalTrials.gov identifier NCT01591863), pediatric patients with CDAD received twice-daily oral fidaxomicin at a dose of 16 mg/kg per day (up to 200 mg) for 10 days in an open-label study. Plasma and fecal samples were collected for pharmacokinetic assessments. The primary outcome measure was safety, which was assessed by adverse-event (AE), laboratory, and physical examination/vital-sign monitoring. Efficacy was determined through early and sustained clinical response rates (clinical response without recurrence of CDAD). RESULTS: The study enrolled 40 patients (11 months to 17 years of age), many with underlying comorbidity, including neoplasm (23.7%), gastrointestinal disorder (78.9%), and history of CDAD (60.5%). Plasma fidaxomicin and OP-1118 (the major fidaxomicin metabolite) 3- to 5-hour postdose concentrations were 0.6 to 87.4 and 2.4 to 882.0 ng/mL, respectively, and no age-related trends were seen. Fecal fidaxomicin concentrations within 24 hours of the last dose averaged 3228 µg/g, and higher concentrations and greater variability in the youngest age group were found. AEs were reported in 73.7% of the patients; most of them were mild (44.7%) to moderate (21.1%) and were considered treatment-related in 15.8% of the patients. Overall, the early clinical response rate was 92.1%. The rate of sustained clinical response (clinical response without recurrence through 28 days after treatment) was 65.8% overall. CONCLUSIONS: Fidaxomicin was well tolerated in children with CDAD and has a pharmacokinetic profile in children similar to that in adults. The clinical response rate was high.

Development and validation of a sensitive LC-MS/MS method without derivatization/ion-pairing agents for etimicin quantification in rat plasma, internal ear and kidney.

Etimicin (ETM), which belongs to the newest generation of aminoglycosides (AGs), has been proven to not only maintain but also strengthen the advantages of former AGs with relatively less toxicity. Now, it is widely applied for the treatment of bacterial infections in the clinic. Nevertheless, nephrotoxicity and ototoxicity are unavoidable issues for AGs, and while ETM is no exception, the seriousness of these issues is different. To explore the reason why ETM exhibits less toxicity and to better direct the optimization and development of new AGs, it is of great necessity and importance to monitor the pharmacokinetic behaviors of ETM in its potential toxicity target organs, the kidney and internal ear, as well as in plasma. Therefore, a novel, sensitive and efficient LC-MS/MS method without derivatization or ion-pairing agents had been developed and validated for quantification of ETM in rat plasma, kidney and internal ear for the first time. This method showed good linearity over the range of 50-2000ng/mL for rat plasma/internal ear and 100-5000ng/mL for rat kidney. The precision was less than 4.4% and the accuracy was below 4.8%. Recovery and matrix effects were 71.3%-82.8% and 97.6%-108.5%, respectively. After intravenous administration of a single dose of ETM, plasma drug concentrations fit well with a two-compartmental model, and the AUC0-∞, t1/2α, t1/2ß, MRT and CL were 127.96±5.52µg*h/mL, 0.53±0.03h, 3.32±1.11h, 1.01±0.03h and 234.80±10.05mL/h/kg, respectively. Particularly, ETM showed a considerably long half-life in kidney and internal ear, up to 155.96±19.95h and 83.11±26.60h, respectively, which might contribute greatly to its toxicity.

High throughput LSPR and SERS analysis of aminoglycoside antibiotics.

Aminoglycoside antibiotics are used in the treatment of infections caused by Gram-negative bacteria, and are often dispensed only in severe cases due to their adverse side effects. Patients undergoing treatment with these antibiotics are therefore commonly subjected to therapeutic drug monitoring (TDM) to ensure a safe and effective personalised dosage. The ability to detect these antibiotics in a rapid and sensitive manner in human fluids is therefore of the utmost importance in order to provide effective monitoring of these drugs, which could potentially allow for a more widespread use of this class of antibiotics. Herein, we report on the detection of various aminoglycosides, by exploiting their ability to aggregate gold nanoparticles. The number and position of the amino groups of aminoglycoside antibiotics controlled the aggregation process. We investigated the complementary techniques of surface enhanced Raman spectroscopy (SERS) and localized surface plasmon resonance (LSPR) for dual detection of these aminoglycoside antibiotics and performed an in-depth study of the feasibility of carrying out TDM of tobramycin using a platform amenable to high throughput analysis. Herein, we also demonstrate dual detection of tobramycin using both LSPR and SERS in a single platform and within the clinically relevant concentration range needed for TDM of this particular aminoglycoside. Additionally we provide evidence that tobramycin can be detected in spiked human serum using only functionalised nanoparticles and SERS analysis.

Appropriateness of aminoglycoside prescriptions in a French university hospital.

INTRODUCTION: Aminoglycosides are a major class of antibiotics. Their use is particularly interesting in the treatment of severe infections but their toxicity is well known. They are mostly prescribed combined with other agents and as first-line treatments. We aimed to assess the appropriateness of aminoglycoside prescriptions in a French university hospital on the basis of the latest French recommendations published in 2011. METHOD: We conducted a prospective study between January 17th and February 4th, 2014 to assess prescription modalities of aminoglycosides on the basis of the following criteria: indication, duration of treatment, dosing schedule, administration modalities, and drug level monitoring. Prescriptions were then compared to the 2011 national guidelines. RESULTS: A total of 68 consecutive prescriptions were analyzed and only 47.8% complied with guidelines. Most physicians complied with recommendations, particularly with the indication for severe infections (95.6%), the administration of a single daily dose (92.6%), and the slow intravenous infusion (30minutes) administration (84%). However, physicians tended to prescribe lower doses than recommended (40.3%), especially to patients presenting with renal insufficiency, and drug level monitoring was not optimal. CONCLUSION: Although new and accurate national recommendations were recently published, aminoglycoside prescription is still not optimal, in particular for dosing and plasma concentration monitoring.

Prospective Analysis of Various Dosing Methods for Aminoglycosides and Vancomycin Therapy in Chronic Spinal Cord Injury Patients.

BACKGROUND/AIM: Several methods have been proposed for the better estimation of creatinine clearance (CLCR) in spinal cord injury (SCI); however, there is no standard method to date. In 2011, Lee-Dang derived an equation to predict CLCR more accurately, although it was limited by problems inherent in any retrospective study of previously collected data. Thus, a prospective investigation was conducted to evaluate the feasibility of clinical implementation and accuracy of the Lee-Dang method against 5 other methods while controlling sources of bias and confounding. METHODS: A prospective investigation included 100 patients who met the inclusion criteria, given as follows: a diagnosis of SCI and administration of intravenous aminoglycosides (AG) or vancomycin with their dosing regimen determined by the Lee-Dang equation. The percentage of patients achieving therapeutic goal was determined, and the measured AG and vancomycin drug clearance (mCL(DRUG)) values were compared with the results that were estimated from 6 equations. RESULTS: The Lee-Dang equation was found to be more accurate, with a smaller magnitude of variance from mCL(DRUG) and smaller residuals and bias compared with the alternatives. The Lee-Dang method resulted in >90% of patients achieving the steady state serum concentrations within the pre-defined goal for AG and vancomycin. All other predictive methods grossly overestimated CLCR and produced markedly lower frequency (<50%) of achieving the goal for both antimicrobials (p < 0.05). CONCLUSION: The prospective data shows that the Lee-Dang method for predicting CLCR is more accurate relative to the alternative methods in the study population with SCI, thus recommend using the Lee-Dang method for pharmacokinetic dosing of AG and vancomycin in SCI.

Development of spectrofluorimetric method for determination of certain aminoglycoside drugs in dosage forms and human plasma through condensation with ninhydrin and phenyl acetaldehyde.

A simple and sensitive spectrofluorimetric method has been developed and validated for determination of amikacin sulfate, neomycin sulfate and tobramycin in pure forms, pharmaceutical formulations and human plasma. The method was based on condensation reaction of cited drugs with ninhydrin and phenylacetaldehyde in buffered medium (pH 6) resulting in formation of fluorescent products which exhibit excitation and emission maxima at 395 and 470nm, respectively. The different experimental parameters affecting the development and stability of the reaction products were carefully studied and optimized. The calibration plots were constructed with good correlation coefficients (0.9993 for tobramycin and 0.9996 for both neomycin and amikacin). The proposed method was successfully applied for the analysis of cited drugs in dosage forms with high accuracy (98.33-101.7)±(0.80-1.26)%. The results show an excellent agreement with the reference method, indicating no significant difference in accuracy and precision. Due to its high sensitivity, the proposed method was applied successfully for determination of amikacin in real human plasma.

Serum inhibitory and bactericidal activity of telavancin in non-infected subjects with severe renal impairment or end-stage renal disease.

Telavancin biological activity, determined by serum titers against a reference strain of Staphylococcus aureus, was maintained in the serum of subjects with severe renal impairment or end-stage renal disease suggesting that there is no apparent effect of renal function on in vitro activity of telavancin.

Variability in telavancin cross-reactivity among vancomycin immunoassays.

Telavancin is a semisynthetic lipoglycopeptide with a dual mechanism of action against Gram-positive pathogens. Two brief reports have suggested potential cross-reactivity of telavancin with the vancomycin particle-enhanced turbidometric immunoassay (PETIA). The purpose of this study was to evaluate several commercially available vancomycin immunoassays (fluorescence polarization [FPIA], enzyme-multiplied immunoassays [EMIT], PETIA, and chemiluminescent immunoassay [CMIA]) for cross-reactivity with telavancin. Seven sites were selected to analyze serum samples for vancomycin. Each site received a set of samples (n = 18) which combined drug-free serum with telavancin, 7-OH telavancin metabolite, or vancomycin. Immunoassays demonstrating potential cross-reactivity were further evaluated by sending a duplicate sample set to multiple laboratories. Cross-reactivity was defined as the percent theoretical concentration (reported concentration/theoretical concentration × 100). No cross-reactivity was seen with FPIA or EMIT. Within the theoretical concentration range of 5 to 120 µg/ml of telavancin, the Synchron PETIA system reported vancomycin concentrations ranging from 4.7 to 54.2 µg/ml compared to vancomycin concentrations from 1.1 to 5.6 µg/ml for the Vista PETIA system. The Architect CMIA system reported vancomycin concentrations in the range of 0.27 to 0.97 µg/ml, whereas Advia Centaur XP CMIA reported vancomycin concentrations between 1.6 and 31.6 µg/ml. The Architect CMIA immunoassay had the lowest percent cross-reactivity (0.8 to 5.4%), while the Synchron PETIA immunoassay demonstrated the highest percent cross-reactivity (45.2 to 53.8%). Telavancin samples measured by liquid chromatography-mass spectroscopy were within 93.9 to 122% of theoretical concentrations. Vancomycin concentrations were not measured in any 7-OH telavancin-spiked sample. Vancomycin concentrations measured by liquid chromatography-mass spectroscopy were within 57.2 to 113% of theoretical concentrations. PETIA and CMIA measured vancomycin concentrations in telavancin-spiked samples. Significant variability in percent cross-reactivity was observed for each platform regardless of immunoassay method.

Quantitative determination of telavancin in pregnant baboon plasma by solid-phase extraction and LC-ESI-MS.

The increasing incidence and severity of methicillin- and vancomycin-resistant infections during pregnancy prompted further development of telavancin. The understanding of the pharmacokinetics of telavancin during pregnancy is critical to optimize dosing. Due to ethical and safety concerns the study is conducted on the pregnant baboons. A method using solid-phase extraction coupled with liquid chromatography-single quadrupole mass spectrometry for the quantitative determination of telavancin in baboon plasma samples was developed and validated. Teicoplanin was used as an internal standard. Telavancin was extracted from baboon plasma samples by using Waters Oasis(®) MAX 96-Well SPE plate and achieved extraction recovery was >66% with variation <12%. Telavancin was separated on Waters Symmetry C18 column with gradient elution. Two SIM channels were monitored at m/z 823 and m/z 586 to achieve quantification with simultaneous confirmation of telavancin identification in baboon plasma samples. The linearity was assessed in the range of 0.188µg/mL to75.0µg/mL, with a correlation coefficient of 0.998. The relative standard deviation of this method was <11% for within- and between-run assays, and the accuracy ranged between 96% and 114%.

A survey of extended-interval aminoglycoside dosing practices in United States adult cystic fibrosis programs.

INTRODUCTION: The Cystic Fibrosis Foundation recently deemed the use of extended-interval dosing (EID) of aminoglycosides acceptable for the treatment of cystic fibrosis (CF) pulmonary exacerbations. However, current practice across United States adult CF programs and affiliate programs is unknown. The objectives of this research are to characterize the practice trends, dosing strategies, therapeutic drug-monitoring practices, and adverse effect monitoring of the EID of aminoglycosides in the treatment of pulmonary exacerbations across United States adult CF programs. METHODS: A 34-question online survey instrument was distributed on behalf of the author by the United States Cystic Fibrosis Foundation to all United States adult CF programs and affiliate programs. RESULTS: Of the 68 participating adult CF programs (44.4% survey response rate), 64 (94.1%) reported using EID of aminoglycosides (as once-daily or twice-daily dosing). More than 95% of programs reported frequently or always using this dosing method. Tobramycin dosed 10 mg/kg/d every 24 h, infused over 30-60 min, was the most commonly cited regimen. Monitoring of aminoglycoside serum concentrations was reported by all programs, with a tobramycin peak of 25-30 mg/L and trough of < 1 mg/L targeted most frequently. Nephrotoxicity was commonly monitored through serum creatinine measurements, while ototoxicity was monitored by audiometry in approximately one-half of programs. CONCLUSIONS: This study indicates that the use of EID of aminoglycosides across United States adult CF programs has increased considerably since the publication of the CF pulmonary exacerbation guidelines and now appears to be the most common method for dosing aminoglycosides in adults with CF.

Therapeutic drug monitoring of once daily aminoglycoside dosing: comparison of two methods and investigation of the optimal blood sampling strategy.

PURPOSE: Therapeutic drug monitoring of patients receiving once daily aminoglycoside therapy can be performed using pharmacokinetic (PK) formulas or Bayesian calculations. While these methods produced comparable results, their performance has never been checked against full PK profiles. We performed a PK study in order to compare both methods and to determine the best time-points to estimate AUC0-24 and peak concentrations (C max). METHODS: We obtained full PK profiles in 14 patients receiving a once daily aminoglycoside therapy. PK parameters were calculated with PKSolver using non-compartmental methods. The calculated PK parameters were then compared with parameters estimated using an algorithm based on two serum concentrations (two-point method) or the software TCIWorks (Bayesian method). RESULTS: For tobramycin and gentamicin, AUC0-24 and C max could be reliably estimated using a first serum concentration obtained at 1 h and a second one between 8 and 10 h after start of the infusion. The two-point and the Bayesian method produced similar results. For amikacin, AUC0-24 could reliably be estimated by both methods. C max was underestimated by 10-20% by the two-point method and by up to 30% with a large variation by the Bayesian method. CONCLUSIONS: The ideal time-points for therapeutic drug monitoring of once daily administered aminoglycosides are 1 h after start of a 30-min infusion for the first time-point and 8-10 h after start of the infusion for the second time-point. Duration of the infusion and accurate registration of the time-points of blood drawing are essential for obtaining precise predictions.

Modeling nikkomycin Z dosing and pharmacology in murine pulmonary coccidioidomycosis preparatory to phase 2 clinical trials.

Nikkomycin Z (NikZ) is a chitin synthase inhibitor with activity against Coccidioides species that is being developed as a first-in-class orphan product for treatment of coccidioidomycosis. It has previously been shown to reduce lethal respiratory infections in mice to undetectable levels when treatment is begun 48 hours after infection. The studies described here focus on bracketing NikZ doses for phase 2 and 3 clinical trials, using an established mouse respiratory infection as a model and starting treatment 120 hours after infection. A dose of 80 mg/kg/day, divided into 2 doses, nearly eradicated infection, and larger doses did not improve fungal clearance. Increasing the duration of treatment from 1 week to 3 weeks resulted in a greater percentage of culture-negative mice. Comparative data show that plasma levels of NikZ that nearly eradicate Coccidioides in mice are achievable in patients and provide a plausibly effective dose range for initial phase 2 clinical studies.

PK of immunoconjugate anticancer agent CMD-193 in rats: ligand-binding assay approach to determine in vivo immunoconjugate stability.

BACKGROUND: Antibody-drug conjugates (ADCs) are a new generation of anticancer therapeutics. The objective of this manuscript is to propose a methodology that can be used to assess the stability of the ADCs by using the PK data obtained by ligand-binding assays that measure various components of ADCs. RESULTS: The ligand-binding assays format of different components of ADCs provided unique valuable PK information. The mathematical manipulation of the bioanalytical data provided an insight into the in vivo integrity, indicating that the loading of the calicheamicin on the G193 antibody declines in an apparent slow first-order process. CONCLUSION: This report demonstrates the value of analyzing various components of the ADC and their PK profiles to better understand the disposition and in vivo stability of ADCs.