Extended-interval dosing of tobramycin in neonates: implications for therapeutic drug monitoring

Targeting Lower Serum Trough Concentrations: A New Gentamicin Dosing Strategy for Suspected Neonatal Early-Onset Sepsis

OBJECTIVE

Neonatal gentamicin dosing algorithms are not designed to achieve serum trough concentrations ≤1 mcg/mL. The purpose of our study was to evaluate a new gentamicin algorithm based on serum creatinine (SCr) and gestational age (GA) designed to achieve serum gentamicin trough concentrations ≤1 mcg/mL.

METHODS

A retrospective cohort study was conducted in a level IIIB neonatal intensive care unit. The incidence of elevated serum gentamicin troughs for this study was compared with the center's previously published results to evaluate the proposed dosing algorithm. Patients were included if gentamicin was administered within the first 7 days of life and a serum gentamicin trough concentration and a baseline SCr concentration were obtained. Patients were further subdivided into groups based on GA for data analysis: ≤30 weeks (group 1), 30-34 weeks (group 2), and ≥35 weeks (group 3). The SCr was considered mildly elevated (0.81-0.99 mg/dL) or elevated (≥1 mg/dL). The respective outcomes between the post-algorithm and control groups were examined using intention-to-treat analysis and Bayesian modeling to calculate rate differences.

RESULTS

Of the 2377 patients evaluated, 366 met the inclusion criteria. Significantly lower percentages of elevated serum gentamicin troughs were noted in groups 2 and 3 subsequent to the implementation of the dosing algorithm with 16% and 15% lower rate differences, respectively. Regardless of GA, there were significantly fewer elevated serum troughs in the post-implementation groups than in the control with mildly elevated and elevated SCr p < 0.001.

CONCLUSIONS

Using a dosing algorithm based on SCr significantly reduced the number of elevated serum trough rates in neonates with a GA greater than 30 weeks.

Reviewing the WHO guidelines for antibiotic use for sepsis in neonates and children

Background Guidelines from 2005 for treating suspected sepsis in low- and middle-income countries (LMIC) recommended hospitalisation and prophylactic intramuscular (IM) or intravenous (IV) ampicillin and gentamicin. In 2015, recommendations when referral to hospital is not possible suggest the administration of IM gentamicin and oral amoxicillin. In an era of increasing antimicrobial resistance, an updated review of the appropriate empirical therapy for treating sepsis (taking into account susceptibility patterns, cost and risk of adverse events) in neonates and children is necessary. Methods Systematic literature review and international guidelines were used to identify published evidence regarding the treatment of (suspected) sepsis. Results Five adequately designed and powered studies comparing antibiotic treatments in a low-risk community in neonates and young infants in LMIC were identified. These addressed potential simplifications of the current WHO treatment of reference, for infants for whom admission to inpatient care was not possible. Research is lacking regarding the treatment of suspected sepsis in neonates and children with hospital-acquired sepsis, despite rising antimicrobial resistance rates worldwide. Conclusions Current WHO guidelines supporting the use of gentamicin and penicillin for hospital-based patients or gentamicin (IM) and amoxicillin (oral) when referral to a hospital is not possible are in accordance with currently available evidence and other international guidelines, and there is no strong evidence to change this. The benefit of a cephalosporin alone or in combination as a second-line therapy in regions with known high rates of non-susceptibility is not well established. Further research into hospital-acquired sepsis in neonates and children is required.

Bacterial sepsis in the neonate

Neonatal bacterial infections leading to sepsis occur frequently in the first few days or weeks of life. NPs must be able to recognize the early signs of sepsis and understand the need for rapid evaluation and treatment. This article discusses antibiotic treatments for various types and locations of bacterial infections and sepsis in the neonate.

Dosing antibiotics in neonates: review of the pharmacokinetic data

Antibiotics are often used in neonates despite the absence of relevant dosing information in drug labels. For neonatal dosing, clinicians must extrapolate data from studies for adults and older children, who have strikingly different physiologies. As a result, dosing extrapolation can lead to increased toxicity or efficacy failures in neonates. Driven by these differences and recent legislation mandating the study of drugs in children and neonates, an increasing number of pharmacokinetic studies of antibiotics are being performed in neonates. These studies have led to new dosing recommendations with particular consideration for neonate body size and maturation. Herein, we highlight the available pharmacokinetic data for commonly used systemic antibiotics in neonates.

Therapeutic drug monitoring in neonates

Therapeutic drug monitoring (TDM) aims to integrate drug measurement results into clinical decision making. The basic rules apply when using TDM in neonates (aminoglycosides, vancomycin, phenobarbital, digoxin), but additional factors should also be taken into account. First, due to both pharmacokinetic variability and non-pharmacokinetic factors, the correlation between dosage and concentration is poor in neonates, but can be overcome with the use of more complex, validated dosing regimens. Second, the time to reach steady state is prolonged, especially when no loading dose is used. Consequently, the timing of TDM sampling is important in this population. Third, the target concentration may be uncertain (vancomycin) or depend on specific factors (phenobarbital during whole body cooling). Finally, because of differences in matrix composition (eg, protein, bilirubin), assay-related inaccuracies may be different in neonates. We anticipate that complex validated dosing regimens, with subsequent TDM sampling and Bayesian forecasting, are the next step in tailoring pharmacotherapy to individual neonates.

Pharmacometric Approaches to Personalize Use of Primarily Renally Eliminated Antibiotics in Preterm and Term Neonates

Sepsis remains a major cause of mortality and morbidity in neonates, and, as a consequence, antibiotics are the most frequently prescribed drugs in this vulnerable patient population. Growth and dynamic maturation processes during the first weeks of life result in large inter- and intrasubject variability in the pharmacokinetics (PK) and pharmacodynamics (PD) of antibiotics. In this review we (1) summarize the available population PK data and models for primarily renally eliminated antibiotics, (2) discuss quantitative approaches to account for effects of growth and maturation processes on drug exposure and response, (3) evaluate current dose recommendations, and (4) identify opportunities to further optimize and personalize dosing strategies of these antibiotics in preterm and term neonates. Although population PK models have been developed for several of these drugs, exposure-response relationships of primarily renally eliminated antibiotics in these fragile infants are not well understood, monitoring strategies remain inconsistent, and consensus on optimal, personalized dosing of these drugs in these patients is absent. Tailored PK/PD studies and models are useful to better understand relationships between drug exposures and microbiological or clinical outcomes. Pharmacometric modeling and simulation approaches facilitate quantitative evaluation and optimization of treatment strategies. National and international collaborations and platforms are essential to standardize and harmonize not only studies and models but also monitoring and dosing strategies. Simple bedside decision tools assist clinical pharmacologists and neonatologists in their efforts to fine-tune and personalize the use of primarily renally eliminated antibiotics in term and preterm neonates.

Bayesian pharmacokinetic analysis of a gentamicin nomogram in neonates: a retrospective study

BACKGROUND

Although gentamicin is used extensively within the first week of life for suspected sepsis in neonates, little is known about the performance of gentamicin dosing nomograms in this population.

OBJECTIVE

The goal of our study was to retrospectively assess the performance of a gentamicin dosing nomogram in neonates given gentamicin during the first week after birth.

METHODS

In this retrospective study, gentamicin therapeutic drug monitoring data were collected during routine clinical care for all neonates who were born in St. Boniface General Hospital (Winnipeg, Manitoba, Canada) between January 1999 and April 2001 and given gentamicin during the first week after birth. We used Bayesian pharmacokinetic analysis to retrospectively assess the performance of our gentamicin dosing nomogram in neonates born at gestation ages <32 weeks, between 32 and 34 weeks, and >34 weeks. Bayesian pharmacokinetic values for parameters within groups were compared and used to explore predicted peak and trough serum gentamicin concentrations based on the institutional dosing nomogram.

RESULTS

In a total of 58 neonates, those neonates born at ≤34 weeks' gestation had a weight-normalized apparent volume of gentamicin distribution 1.6 times larger than infants born after 34 weeks' gestation (P<0.001), as identified by Bayesian analysis. Weight-normalized gentamicin clearance was 22% lower in the youngest age category (P<0.01). Only 33% of predicted peak serum gentamicin concentrations were >6 mg/L for neonates born at ≤34 weeks' gestation, whereas 90% were therapeutic in neonates born at >34 weeks' gestation (P<0.001). With the present nomogram, the likelihood of an indication for adjustment of the dosing regimen was 12.4-fold higher (95% CI, 3.5-43.7) for those neonates born at ≤34 weeks' gestation.

CONCLUSIONS

These results have important clinical implications with regard to the advisability of determining peak serum gentamicin concentrations in neonates born at ≤34 weeks' gestation. Sampling of peak serum concentrations is indicated in this population to avoid underdosing and potential loss of therapeutic efficacy.

How to optimize the evaluation and use of antibiotics in neonates

Early and late-onset neonatal sepsis has specific pathogen distribution and infection rates in neonates with different gestational and postnatal ages. Despite the fact that early-onset sepsis is relatively rare (<1% of total deliveries), it is a major cause of mortality and morbidity. The known immunological immaturity of the neonate combined with non-specific clinical symptoms of infection has resulted in the frequent overuse of antibiotics in neonatal intensive care units (NICUs). In addition to this overuse there is a huge variability in the choice of antibacterial agents and dosing regimens used in NICUs across the world. Therefore, a more rational approach in the neonatal use of antibiotics is needed because of two major reasons: the emergence of multi-resistant bacteria in NICUs, and short- and long-term side effects of frequently used antibacterial agents in the neonatal population. This paper will focus on the optimal use of aminoglycosides (both used in early and late onset sepsis) and vancomycin (primarily used in late onset infections) in NICUs, and will underscore the need for specialists in neonatal medicine and pediatric pharmacology to work closely together to reach the most effective and safe way of using medicines in the NICU.

Validation of a dosage individualization table for extended-interval gentamicin in neonates

BACKGROUND

Extended-interval aminoglycoside dosing is increasingly used in neonates; however, guidance on how to monitor concentrations and adjust dosages accordingly is limited.

OBJECTIVE

To prospectively validate the use of a 22-hour gentamicin concentration dosing table for the individualization of extended-interval dosing in the neonatal population by examining the peak and trough concentrations achieved through its use.

METHODS

A prospective observational study was carried out on gentamicin concentrations achieved using a 22-hour post-first-dose gentamicin concentration dosing table for determining dosing intervals in neonates. Neonates (N = 104) in the first week of life, gestational age 23 weeks to full term, in level II and III neonatal intensive care units were included. Neonates were given gentamicin 5 mg/kg intravenously; a table using 22-hour post-first-dose gentamicin concentrations was then used to individualize dosing intervals. Pre- and post-serum gentamicin concentrations on the dosing interval indicated were measured with the second or third doses and used to calculate the peak and trough concentrations achieved.

RESULTS

Use of the 22-hour post-first-dose gentamicin concentration dosing table resulted in dosing intervals that provided appropriate peak (mean 10.55 mg/L) and trough (mean 0.75 mg/L) concentrations (with second or third doses) in all neonates. All patients had trough concentrations less than 2 mg/L, and 73% had a trough concentration less than 1 mg/L. No peak concentrations were less than 5 mg/L, 82% of patients had a peak concentration from 5 to 12 mg/L, and the remaining 18% had concentrations from 12.1 to 16 mg/L. Peak and trough concentrations were similar across all gestational ages.

CONCLUSIONS

Use of a 22-hour post-first-dose gentamicin concentration dosing table to individualize extended-interval gentamicin dosages in neonates resulted in appropriate peak and trough concentrations in all neonates studied. Use of this table will result in appropriate extended-interval aminoglycoside dosages in neonates early in treatment, using a single serum concentration.

Developmental pharmacology

Understanding the pharmacokinetics and pharmacodynamics of drugs used in psychopharmacology across the pediatric age spectrum from infants to adolescents represents a major challenge for clinicians. In pediatrics, treatment protocols use either standard dose reductions for these drugs for children below a certain age or use less conventional parameters such as weight for allometric dosing. The rationale behind this, however, is often lacking. In this review current available data on the developmental changes in absorption, distribution, metabolism, and elimination of drugs are presented with a specific focus on metabolic pathways, indicating significant differences in the development of enzymes involved in the biotransformation of drugs used in psychopharmacology. Major emphasis will be given to the genetic variation in CYP2D6 activity, the most important enzyme for the metabolism of many psychotropic medications. Finally, this review will summarize the role of the developmental pharmacologist in ensuring rational use of drugs in children with developmental disabilities and in translating pharmacological concepts from the bench to the clinic.

Developmental pharmacokinetics

The advances in developmental pharmacokinetics during the past decade reside with an enhanced understanding of the influence of growth and development on drug absorption, distribution, metabolism, and excretion (ADME). However, significant information gaps remain with respect to our ability to characterize the impact of ontogeny on the activity of important drug metabolizing enzymes, transporters, and other targets. The ultimate goal of rational drug therapy in neonates, infants, children, and adolescents resides with the ability to individualize it based on known developmental differences in drug disposition and action. The clinical challenge in achieving this is accounting for the variability in all of the contravening factors that influence pharmacokinetics and pharmacodynamics (e.g., genetic variants of ADME genes, different disease phenotypes, disease progression, and concomitant treatment). Application of novel technologies in the fields of pharmacometrics (e.g., in silico simulation of exposure-response relationships; disease progression modeling), pharmacogenomics and biomarker development (e.g., creation of pharmacodynamic surrogate endpoints suitable for pediatric use) are increasingly making integrated approaches for developmentally appropriate dose regimen selection possible.

Clinical Pharmacokinetics of Penicillins, Cephalosporins and Aminoglycosides in the Neonate: A Review

Bacterial infections are common in the neonates and are a major cause of morbidity and mortality. Sixty percent of preterm infants admitted to neonatal intensive care units received at least one antibiotic during the first week of life. Penicillins, aminoglycosides and cephalosporins comprised 53, 43 and 16%, respectively. Kinetic parameters such as the half-life (t1/2), clearance (Cl), and volume of distribution (Vd) change with development, so the kinetics of penicillins, cephalosporins and aminoglycosides need to be studied in order to optimise therapy with these drugs. The aim of this study is to review the pharmacokinetics of penicillins, cephalosporins and aminoglycosides in the neonate in a single article in order to provide a critical analysis of the literature and thus provide a useful tool in the hands of physicians. The bibliographic search was performed electronically using PubMed, as the search engine, until February 2nd, 2010. Medline search terms were as follows: pharmacokinetics AND (penicillins OR cephalosporins OR aminoglycosides) AND infant, newborn, limiting to humans. Penicillins, cephalosporins and aminoglycosides are fairly water soluble and are mainly eliminated by the kidneys. The maturation of the kidneys governs the pharmacokinetics of penicillins, cephalosporins and aminoglycosides in the neonate. The renal excretory function is reduced in preterms compared to term infants and Cl of these drugs is reduced in premature infants. Gestational and postnatal ages are important factors in the maturation of the neonate and, as these ages proceed, Cl of penicillins, cephalosporins and aminoglycosides increases. Cl and t1/2 are influenced by development and this must be taken into consideration when planning a dosage regimen with these drugs. More pharmacokinetic studies are required to ensure that the dose recommended for the treatment of sepsis in the neonate is evidence based.

Optimizing pediatric dosing: a developmental pharmacologic approach

Many physiologic differences between children and adults can result in age-related differences in pharmacokinetics. Understanding the effects of age on bioavailability, volume of distribution, protein binding, hepatic metabolic isoenzymes, and renal elimination can provide insight into optimizing doses for pediatric patients. We performed a search of English-language literature using the MEDLINE database regarding age and pharmacokinetics (1979-July 2008). We then evaluated the literature with an emphasis on drugs with one primary elimination pathway, such as renal clearance or a pathway involving a single metabolic isoenzyme. Our mechanistic-based analysis revealed that children need weight-corrected doses that are substantially higher than adult doses for drugs that are metabolically eliminated solely by the specific cytochrome P450 (CYP) isoenzymes CYP1A2, CYP2C9, and CYP3A4. In contrast, weight-corrected doses for drugs eliminated by renal excretion or metabolism involving CYP2C19, CYP2D6, N-acetyltransferase 2, or uridine diphosphate glucuronosyltransferases are similar in children and adults. In children, bioavailability of drugs with high first-pass metabolism is decreased for drugs metabolized by CYP1A2, CYP2C9, and CYP3A4. Limited data suggest that by age 5 years, bioavailability of drugs affected by efflux transporters should be equivalent to that of adults. Using a pharmacokinetics-based approach, rational predictions can be made for the effects of age on drugs that undergo similar pathways of elimination, even when specific pharmacokinetic data are limited or unavailable.

Therapeutic drug monitoring of aminoglycosides in neonates

The efficacy and toxicity of aminoglycosides show a strong direct positive relationship with blood drug concentrations, therefore, therapy with aminoglycosides in adults is usually guided by therapeutic drug monitoring. Dosing regimens in adults have evolved from multiple daily dosing to extended-interval dosing. This evolution has also taken place in neonates. Neonates, however, display large interindividual differences in the pharmacokinetics of aminoglycosides due to developmental differences early in life. The volume of distribution of aminoglycosides shows a strong relationship with bodyweight, which tends to be larger (corrected for bodyweight) in more premature infants and those with sepsis. Renal clearance of aminoglycosides increases with gestational age and accelerates immediately after birth. Because of these developmental influences, there is great inter- and intraindividual variability in the volume of distribution and clearance of these drugs, and investigators have established aminoglycoside dosing regimens based on bodyweight and/or gestational age. Widely practised dosing regimens comprise 4-5 mg/kg bodyweight of gentamicin every 24-48 hours as a first dose, followed by dose adjustment based on therapeutic drug monitoring. Although formal toxicity studies are scarce, there is no evidence that aminoglycoside toxicity in neonates differs from that in adults. Monitoring of blood drug concentrations and intelligent reconstruction of individual pharmacokinetic behaviour using a population pharmacokinetic model, optimally chosen blood sampling times and appropriate pharmacokinetic software, help clinicians to quickly optimize aminoglycoside dosing regimens to maximize the clinical effect and minimize the toxicity of these drugs.

Two nomograms for determining extended-dosing intervals for gentamicin in neonates

PURPOSE

The development of two nomograms to predict dosing intervals for gentamicin in neonates based on one gentamicin concentration is described.

METHODS

Pooled data from three retrospective studies on neonates age seven days or younger were used to create nomograms that would predict dosing intervals for gentamicin. The population volume of distribution (0.45 L/kg) and a determined half-life were used to create nomogram cutoff concentrations that could select a dosing interval for neonates to achieve steady-state trough concentrations of < or =0.5 or < or =1 mg/L. A dose of 4 mg/kg was used to simulate concentration-versus-time profiles for included neonates based on their individual pharmacokinetic data. Predicted concentrations from hours 6 to 22, at one-hour intervals, for each neonate were compared against the nomograms and evaluated for the number of correct interval predictions. The nomograms were considered to have failed at any time point where they indicated an interval that would not have achieved the desired trough concentration of < or =0.5 or < or =1 mg/L or if the interval chosen was longer than necessary.

RESULTS

The 0.5- and 1-mg/L nomograms predicted correct dosing intervals for 81-92% of neonates for postinfusion hours between 15 to 21 and 86-93% for postinfusion hours of 13 and 21, respectively. Accuracy of the nomograms to predict correct dosing intervals improved as the postinfusion time before the next concentration measurement increased.

CONCLUSION

Using the two nomograms may help predict the correct extended-dosing intervals of gentamicin administration for neonates. Prospective evaluation and validation of the nomograms may be necessary for their wider use as a clinical tool.

Population pharmacokinetics of oxycodone in children 6 months to 7 years old

Young children are often undertreated for pain. One barrier to effective pain treatment is understanding the pharmacokinetic behavior of analgesics in this age group. Oxycodone is a commonly prescribed opioid for severe pain, yet little is known about its pharmacokinetics in young children. This article used population pharmacokinetic modeling to synthesize pharmacokinetic data from several studies into a model. A single population model that described the observed pharmacokinetics was developed. The combined data were best described with a 2-compartment linear model with different first-order absorption rates depending on route of administration. Weight was found to significantly influence both clearance (CL) and volume of distribution (Vd). The following model adequately describes the population pharmacokinetic profile of oxycodone where absolute bioavailability (F) is estimated for each administration route: CL/F=55x(body weight/70)0.87; V/F=86x(body weight/70)1.16. The interindividual coefficients of variation in CL and Vd were 20.2 and 19.7%, respectively. This finding confirms that the allometric scaling using the above model explained most of the variability in exposure observed among children. This model confirms using a weight-based dose for oxycodone without adjustment for age between 6 months and 7 years and is valuable for evaluating dosing schedules and dosing routes.

Prediction of gentamicin peak and trough concentrations from six extended-interval dosing protocols for neonates

PURPOSE

The ability of six extended-interval gentamicin dosing protocols to achieve desired peak and trough concentrations in neonates was evaluated using simulated calculations based on pooled patient data.

METHODS

The demographic and pharmacokinetic data of 293 neonates age one week or less from three previously published studies were pooled and applied in each of six published protocols. The data collected, including weight, dosage, dosing interval, and measured serum or plasma gentamicin concentrations, were used to determine gentamicin clearance, elimination-rate constant, and distribution volume. Peak and trough gentamicin concentrations were calculated and compared with several therapeutic ranges that aim to achieve high peak concentrations for maximum efficacy and low trough concentrations for minimum toxicity.

RESULTS

All protocols resulted in more than 95% of peak concentrations exceeding 5 mg/L. Peaks exceeded 10 mg/L in 26-42% of the simulations. Most of the protocols resulted in high trough concentrations (0.5-1.5 mg/L). Trough concentrations were below 1 mg/L in 51-83% of the simulations.

CONCLUSION

Simulated calculations based on pooled patient data found that six gentamicin dosing protocols for neonates would likely yield acceptable peak concentrations and a trough concentration of < or = 1 mg/L for at least 50% of patients. It may be sufficient to monitor only the trough concentrations when applying these protocols.

New dosing strategies for antibacterial agents in the neonate

Dosing of antibiotics in neonates requires finding a delicate balance between maximal efficacy and minimal toxicity. There is a lack of data on efficacy of currently used antibiotics in neonates, and rational dosing therefore needs to be based on gestational- and postnatal-age-dependent pharmacokinetics in combination with surrogate markers. These surrogate markers are: (i) the area-under-the serum concentration time curve to minimum inhibitory concentration ratio (AUC/MIC); (ii) peak concentration to MIC ratio (Cmax/MIC); and (iii) the time the concentration remains above the MIC (T>MIC). Whereas the efficacy of beta-lactam antibiotics (including carbapenems) depends on T>MIC, the efficacy of most other antimicrobials (including aminoglycosides and fluoroquinolones) is related to AUC/MIC and Cmax/MIC. Most modern dosing regimens are adequate when these concentration effect relationships are taken into account. Dosing adjustments in neonates are suggested, based on these relationships. Several antimicrobial combinations for treatment of meningitis and necrotizing enterocolitis exist. Empiric treatment should be based on efficacy, concerns about resistance as well as information from institutional microbiological surveillance.