Therapeutic drug monitoring of tobramycin: once-daily versus twice-daily dosage schedules

Priorities for hearing loss prevention and estimates of global cause-specific burdens of hearing loss: a systematic rapid review

BACKGROUND

Hearing loss affects approximately 1·6 billion individuals worldwide. Many cases are preventable. We aimed to estimate the annual number of new hearing loss cases that could be attributed to meningitis, otitis media, congenital rubella syndrome, cytomegalovirus, and ototoxic medications, specifically aminoglycosides, platinum-based chemotherapeutics, and antimalarials.

METHODS

We used a targeted and a rapid systematic literature review to calculate yearly global incidences of each cause of hearing loss. We estimated the prevalence of hearing loss for each presumed cause. For each cause, we calculated the global number of yearly hearing loss cases associated with the exposure by multiplying the estimated exposed population by the prevalence of hearing loss associated with the exposure, accounting for mortality when warranted.

FINDINGS

An estimated 257·3 million people per year are exposed to these preventable causes of hearing loss, leading to an estimated 33·8 million new cases of hearing loss worldwide per year. Most hearing loss cases were among those with exposure to ototoxic medications (19·6 million [range 12·6 million-27·9 million] from short-course aminoglycoside therapy and 12·3 million from antimalarials). We estimated that 818 000 cases of hearing loss were caused by otitis media, 346 000 by meningitis, 114 000 by cytomegalovirus, and 59 000 by congenital rubella syndrome.

INTERPRETATION

The global burden of preventable hearing loss is large. Hearing loss that is attributable to disease sequelae or ototoxic medications contributes substantially to the global burden of hearing loss. Prevention of these conditions should be a global health priority.

FUNDING

The US National Institute on Deafness and Other Communication Disorders and the US National Institute on Aging.

High-Precision Control of Plasma Drug Levels Using Feedback-Controlled Dosing

By, in effect, rendering pharmacokinetics an experimentally adjustable parameter, the ability to perform feedback-controlled dosing informed by high-frequency in vivo drug measurements would prove a powerful tool for both pharmacological research and clinical practice. Efforts to this end, however, have historically been thwarted by an inability to measure in vivo drug levels in real time and with sufficient convenience and temporal resolution. In response, we describe a closed-loop, feedback-controlled delivery system that uses drug level measurements provided by an in vivo electrochemical aptamer-based (E-AB) sensor to adjust dosing rates every 7 s. The resulting system supports the maintenance of either constant or predefined time-varying plasma drug concentration profiles in live rats over many hours. For researchers, the resultant high-precision control over drug plasma concentrations provides an unprecedented opportunity to (1) map the relationships between pharmacokinetics and clinical outcomes, (2) eliminate inter- and intrasubject metabolic variation as a confounding experimental variable, (3) accurately simulate human pharmacokinetics in animal models, and (4) measure minute-to-minute changes in a drug's pharmacokinetic behavior in response to changing health status, diet, drug-drug interactions, or other intrinsic and external factors. In the clinic, feedback-controlled drug delivery would improve our ability to accurately maintain therapeutic drug levels in the face of large, often unpredictable intra- and interpatient metabolic variation. This, in turn, would improve the efficacy and safety of therapeutic intervention, particularly for the most gravely ill patients, for whom metabolic variability is highest and the margin for therapeutic error is smallest.

Comparison against current standards of a DNA aptamer for the label-free quantification of tobramycin in human sera employed for therapeutic drug monitoring

The use of DNA aptamers in biosensors for the quantification of pharmaceuticals in the clinics would help to overcome the limitations of antibody-based detection for small molecules. The interest for such systems is proven by the ever-increasing number of aptamer-based solutions for analytics proposed in the literature as proof-of-concept demonstrators. Despite such diversity, these platforms often lack a comparative assessment of their performances against the current standard of practice in the clinics when using real samples. We employed an aptamer against tobramycin discovered in our laboratory to quantify through surface plasmon resonance the concentration of the antibiotic in clinical samples obtained from patients treated with tobramycin and undergoing therapeutic drug monitoring. We then compared the performances of our detection strategy against the current standard of practice. Our results show how, using adequate calibration and matrix complexity reduction, DNA aptamer-based direct assays can assess clinically relevant concentrations of small molecules in patient serum and with good correlation to current standards used in the clinics.

Role of therapeutic drug monitoring in pulmonary infections: use and potential for expanded use of dried blood spot samples

Respiratory tract infections are among the most common infections in men. We reviewed literature to document their pharmacological treatments, and the extent to which therapeutic drug monitoring (TDM) is needed during treatment. We subsequently examined potential use of dried blood spots as sample procedure for TDM. TDM was found to be an important component of clinical care for many (but not all) pulmonary infections. For gentamicin, linezolid, voriconazole and posaconazole dried blood spot methods and their use in TDM were already evident in literature. For glycopeptides, β-lactam antibiotics and fluoroquinolones it was determined that development of a dried blood spot (DBS) method could be useful. This review identifies specific antibiotics for which development of DBS methods could support the optimization of treatment of pulmonary infections.

How do we use therapeutic drug monitoring to improve outcomes from severe infections in critically ill patients?

High mortality and morbidity rates associated with severe infections in the critically ill continue to be a significant issue for the healthcare system. In view of the diverse and unique pharmacokinetic profile of drugs in this patient population, there is increasing use of therapeutic drug monitoring (TDM) in attempt to optimize the exposure of antibiotics, improve clinical outcome and minimize the emergence of antibiotic resistance. Despite this, a beneficial clinical outcome for TDM of antibiotics has only been demonstrated for aminoglycosides in a general hospital patient population. Clinical outcome studies for other antibiotics remain elusive. Further, there is significant variability among institutions with respect to the practice of TDM including the selection of patients, sampling time for concentration monitoring, methodologies of antibiotic assay, selection of PK/PD targets as well as dose optimisation strategies. The aim of this paper is to review the available evidence relating to practices of antibiotic TDM, and describe how TDM can be applied to potentially improve outcomes from severe infections in the critically ill.

Aminoglycoside-induced nephrotoxicity--a focus on monitoring: a review of literature

The use of aminoglycoside (AG) antibiotics has declined over the past 15 years primarily due to comparable potency of other antimicrobials and the nephrotoxicity potential of AG drugs. However, resurgence in the use of AG antimicrobials is occurring due to multidrug-resistant gram-negative nosocomial infections. Multidrug-resistant Pseudomonas and Acinetobacter isolates as well as extended-spectrum beta-lactamase-producing Enterobacteriaceae continue to force clinicians to consider AG therapy for nosocomial infections in hospitalized patients and enterococcal endocarditis. Additionally, AGs are still indicated in the treatment of pulmonary exacerbations of cystic fibrosis. Along with the use of AG antibiotics is the associated renal insufficiency complication. This review discusses the mechanism for AG-induced nephrotoxicity. Patient- and drug-related risk factors are discussed to help identify patients at increased risk. The issue of serum-level monitoring is discussed relative to the development of nephrotoxicity.

Advances in antibiotic measurement

Antibiotics are most commonly prescribed drugs in clinical practice. Therapeutic drug monitoring of these medications is typically associated with a select group of antibiotics such as aminoglycosides and vancomycin. Outside this group, other antibiotics such as chloramphenicol and antituberculosis agents may also require monitoring. Due to their wide therapeutic index, other classes of antibiotics such as penicillins, cephalosporin, sulfonamides, quinolones, and macrolides do not generally require routine therapeutic drug monitoring. Determination of serum or plasma concentration of these drugs, however, may be beneficial in those patients with compromised renal function. As can be expected, immunoassays for routine monitoring of aminoglycosides and vancomycin have been developed and are widely commercially available. Tests for other antibiotics, due to their infrequent use and low clinical application, are generally limited to in-house developed methods.

Optimizing therapy with antibacterial agents: use of pharmacokinetic-pharmacodynamic principles in pediatrics

The appropriate dosage of antibacterial agents is essential in achieving both clinical and microbiologic success in the treatment of infections in children. By using in vitro experimental data and animal model outcome data, the pharmacokinetic-pharmacodynamic (PK-PD) parameters predictive of antibacterial effect have been elucidated. For time-dependent drugs such as beta-lactams, the PK-PD parameter of interest is the percentage of time in a dosage interval for which drug concentrations remain above the minimum inhibitory concentration (MIC) of the infecting organism. For concentration-dependent drugs such as aminoglycosides, the PK-PD parameter of interest is the ratio of the area under the plasma concentration-time curve to the MIC. Recent studies using data on clinical and microbiologic outcomes from infected adults and children, combined with data on drug exposure, have confirmed the importance of these parameters and provided estimates of the PK-PD goals of therapy for various antibacterial agents. Application of these PK-PD principles allows rational dosage regimen selection, both for serious infections in critically ill children and for non-life-threatening community-acquired infections.

Pharmacokinetic profile of once daily intravenous tobramycin in children with cystic fibrosis

AIM

Once-daily tobramycin in patients with cystic fibrosis (CF) is a more convenient dosing regimen than thrice daily dosing. There are limited data on the pharmacokinetic (PK) profile for once-daily tobramycin in patients with CF. The aim of this study was to define the PK parameters for once-daily tobramycin in children with CF and develop an algorithm for therapeutic drug monitoring dosing.

METHODS

CF patients admitted to hospital were commenced on once-daily intravenous tobramycin (12 mg/kg/day) and ticarcillin/clavulinic acid. Serum tobramycin levels were taken at 30 min, 2-4 h and 12 h post dose. Data points for the PK model included: age, sex, weight, tobramycin dose, time of tobramycin doses and levels, tobramycin levels. WinNonMix was used to obtain the PK parameters.

RESULTS

Forty-four children with 86 admissions who were aged 9 months-20 years were included. A one-compartment intravenous infusion model with first order elimination kinetics produced the best model. Population parameters were: volume of distribution (V(d)) = 0.267 L/kg (95% confidence interval (CL) 0.260-0.272), clearance (CL) 0.103 L/kg/h (95% CI 0.098-0.107) and half-life (t(1/2)) 1.82 (95% CI 1.77-1.88) h. Once the population model was established post hoc analysis was used to calculate individual subject predictions. Plots of individual prediction curves agreed well with observed values.

CONCLUSION

This study has established an algorithm for routine monitoring of once-daily tobramycin in children with CF. Satisfactory serum levels of tobramycin were obtained with a dose of 12 mg/kg/day and a regimen algorithm that uses only one measurement to monitor the plasma concentration is suggested.

Evaluation of four once-daily aminoglycoside dosing nomograms

STUDY OBJECTIVE

To evaluate the accuracy of four once-daily aminoglycoside dosing nomograms in producing the desired gentamicin peak concentration (Cmax) target of 20 microg/ml in patients with varying degrees of renal function.

DESIGN

Retrospective analysis using prospectively collected pharmacokinetic data.

SETTING

Rural teaching hospital.

PATIENTS

Ninety patients receiving intravenous gentamicin divided into three groups (30 patients each) determined by estimated renal function: group 1, creatinine clearance (Cl(cr),) 60 ml/minute or greater; group 2, Cl(cr) 40-59 ml/minute; group 3, Cl(cr) 20-39 ml/minute. Intervention. Serum gentamicin concentrations were collected for a 2-point (two consecutive infusions and one predose and one postdose concentration sampled during steady state) or 3-point (single infusion and one predose and two postdose concentrations at least 1.5 estimated half-lives apart) pharmacokinetic study for determination of patient-specific pharmacokinetic parameters (elimination rate constant, volume of distribution at steady state, and clearance) after 30-minute infusions of gentamicin 2.8 +/- 1.6 mg/kg.

MEASUREMENTS AND RESULTS

The four nomograms evaluated were from Hartford Hospital, Barnes-Jewish Hospital, University of Rochester, and the Sanford Guide. With a pharmacokinetic analysis program and the patient-specific pharmacokinetic parameters, Cmax and minimum concentration (Cmin) were determined with use of the recommended doses and dosing intervals of the four nomograms. Also, the gentamicin dose and interval needed to achieve a Cmax and Cmin of 20 microg/ml and 0.2 microg/ml, respectively, were determined. Dosing was based on total body weight unless that weight was more than 25% of ideal body weight, in which case, an adjusted body weight was used. In general, the recommended dosages and resultant Cmax produced by the nomograms were significantly less (p < 0.05) than the dosage and Cmax actually needed to achieve a Cmax:minimum inhibitory concentration (MIC) ratio of 10 or greater for bacteria with an MIC of 2 microg/ml.

CONCLUSION

Once-daily aminoglycoside dosing using the four nomograms resulted in inaccurate dosing, and because of the large variability in human pharmacokinetics, dosing nomograms such as these should be abandoned in favor of individualizing dosages with therapeutic drug monitoring.

A multicenter evaluation of gentamicin therapy in the neonatal intensive care unit

STUDY OBJECTIVE

To evaluate traditional nomogram (TN) versus individualized pharmacokinetic gentamicin dosing practices in neonatal intensive care units, focusing on achieving target therapeutic concentrations (peak > 8 microg/ml, trough < 2 microg/ml), number of dosing changes, number of concentrations obtained, and evidence of nephrotoxicity.

DESIGN

Retrospective chart review.

SETTING

Three neonatal intensive care units.

PATIENTS

Three hundred nine infants prescribed gentamicin.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

Sixty-seven percent of patients receiving pharmacokinetic dosing had initial peak concentrations of 8 microg/ml or greater compared with 7% of patients receiving TN dosing (p<0.001). Trough concentrations exceeding 2 microg/ml were reported in 23% of patients receiving TN dosing compared with 2% of pharmacokinetic-dosed patients (p<0.001). Forty-two percent and 6%, respectively, required dosage adjustments (p<0.01). The mean number of concentrations obtained per patient was 2.8 and 2.1, respectively (p<0.01). Neither group had evidence of gentamicin-related nephrotoxicity.

CONCLUSION

Compared with TN dosing, administering gentamicin loading doses and performing initial pharmacokinetic analysis resulted in rapid attainment of desired concentrations and fewer dosage adjustments, and allowed for a decrease in the number of gentamicin concentrations.