Pharmacokinetic modelling of a once-daily dosing regimen for intravenous tobramycin in paediatric cystic fibrosis patients

Review of Tobramycin Dosing in Pediatric Patients With Cystic Fibrosis

OBJECTIVE

An institution's tobramycin pharmacokinetics (PK) database was reviewed to evaluate the efficacy and safety of empiric tobramycin dosing and monitoring strategies used in pediatric patients with cystic fibrosis (CF). The relationship between patient age and tobramycin dosing needed to achieve the area under the curve (AUC) goal was investigated.

METHODS

Retrospective chart review was performed for patients who received tobramycin during a CF exacerbation from 2009 to 2019 who received PK monitoring by pediatric pharmacists. Tobramycin dosing needed to achieve an AUC of 100 mg·hr/L was calculated for each patient. Serum creatinine and concomitant nephrotoxin use were collected as surrogate nephrotoxicity endpoints to evaluate safety.

RESULTS

Goal AUC (100 ± 15 mg·hr/L) was achieved based on initial or repeat PK calculations in 43.5% (95% CI, 37.7-49.3) of 85 unique patients across 326 encounters. Patients with calculated recommended doses of 9.5 to 11.9 mg/kg every 24 hours empirically achieved goal AUC in 77% (78/101) of encounters. The odds of achieving goal AUC were 56% higher for children aged 10 vs 5 years (OR = 1.56; 95% CI, 1.04-2.34; p = 0.033) and 32% higher for children aged 15 vs 10 years (OR = 1.32; 95% CI, 1.07-1.61; p = 0.008). Overall rates of acute kidney injury and concomitant nephrotoxin use were 10.8% (95% CI, 6.2-15.5) and 80.7% (95% CI, 74.3-87.1), respectively.

CONCLUSIONS

Desired AUC was achieved by 43.5% of pediatric patients with CF using tobramycin 10 mg/kg every 24 hours. Older patient age was associated with higher initial AUC attainment and fewer dose modifications. Younger children may require higher weight-based dosing to meet AUC goals.

Pharmacokinetic and Pharmacodynamic Optimization of Antibiotic Therapy in Cystic Fibrosis Patients: Current Evidences, Gaps in Knowledge and Future Directions

Antibiotic therapy is one of the main treatments for cystic fibrosis (CF). It aims to eradicate bacteria during early infection, calms down the inflammatory process, and leads to symptom resolution of pulmonary exacerbations. CF can modify both the pharmacokinetic (PK) and pharmacodynamic (PD) profiles of antibiotics, therefore specific PK/PD endpoints should be determined in the context of CF. Currently available data suggest that optimal PK/PD targets cannot be attained in sputum with intravenous aminoglycosides. Continuous infusion appears preferable for β-lactam antibiotics, but optimal concentrations in sputum are unlikely to be reached, with some possible exceptions such as meropenem and ceftolozane. Usual doses are likely suboptimal for fluoroquinolones and linezolid, whereas daily doses of 45-60 mg/kg and 200 mg could be convenient for vancomycin and doxycycline, respectively. Weekly azithromycin doses of 22-30 mg/kg could also be appropriate for its anti-inflammatory effect. The difficulty with achieving optimal concentrations supports the use of combined treatments and the inhaled administration route, as very high local concentrations, concomitantly with low systemic exposure, can be obtained with the inhaled route for aminoglycosides, colistin, and fluoroquinolones, thus minimizing the risk of toxicity.

Calcium induces tobramycin resistance in Pseudomonas aeruginosa by regulating RND efflux pumps

Pseudomonas aeruginosa is an opportunistic multidrug resistant pathogen causing severe chronic infections. Our previous studies showed that elevated calcium (Ca²⁺) enhances production of several virulence factors and plant infectivity of the pathogen. Here we show that Ca²⁺ increases resistance of P. aeruginosa PAO1 to tobramycin, antibiotic commonly used to treat Pseudomonas infections. LC-MS/MS-based comparative analysis of the membrane proteomes of P aeruginosa grown at elevated versus not added Ca²⁺, determined that the abundances of two RND (resistance-nodulation-cell division) efflux pumps, MexAB-OprM and MexVW-OprM, were increased in the presence of elevated Ca²⁺. Analysis of twelve transposon mutants with disrupted RND efflux pumps showed that six of them (mexB, muxC, mexY, mexJ, czcB, and mexE) contribute to Ca²⁺-induced tobramycin resistance. Transcriptional analyses by promoter activity and RT-qPCR showed that the expression of mexAB, muxABC, mexXY, mexJK, czcCBA, and mexVW is increased by elevated Ca²⁺. Disruption of mexJ, mexC, mexI, and triA significantly decreased Ca²⁺-induced plant infectivity of the pathogen. Earlier, our group showed that PAO1 maintains intracellular Ca²⁺ (Ca²⁺_in) homeostasis, which mediates Ca²⁺ regulation of P. aeruginosa virulence, and identified four putative Ca²⁺ transporters involved in this process (Guragain et al., 2013). Here we show that three of these transporters (PA2435, PA2092, PA4614) play role in Ca²⁺-induced tobramycin resistance and one of them (PA2435) contributes to Ca²⁺ regulation of mexAB-oprM promoter activity. Furthermore, mexJ, czcB, and mexE contribute to the maintenance of Ca²⁺_in homeostasis. This provides the first evidence that Ca²⁺_in homeostasis mediates Ca²⁺ regulation of RND transport systems, which contribute to Ca²⁺-enhanced tobramycin resistance and plant infectivity in P. aeruginosa.

Extended-Interval Aminoglycoside Use in Cystic Fibrosis Exacerbation in Children and Young Adults: A Prospective Quality Improvement Project

This is a prospective quality improvement project for patients with cystic fibrosis who are 5 years of age and older who were admitted for intravenous antibiotic administration as part of treatment of cystic fibrosis exacerbation. The goal of this project was to compare the pharmacokinetics of once-daily versus thrice-daily aminoglycoside use when treating cystic fibrosis exacerbation in different age groups. Of the total of 119 patient encounters, 82.4% were started on once-daily dosing, and the remainder were started on thrice-daily dosing. Patients with pharmacokinetics allowing the continuation of once-daily dosing differed from patients who required a switch to thrice-daily dosing in terms of baseline forced expiratory volume in 1 second, forced expiratory flow from 25% to 75% of vital capacity, age, and body mass index (BMI) but were similar in BMI percentiles. The once-daily dosing group had higher mean 18-hour level, higher mean half-life, higher mean area under the curve, and lower mean elimination constant. This study showed that aminoglycoside clearance is higher in younger children.

Cystic Fibrosis and Its Management Through Established and Emerging Therapies

Cystic fibrosis (CF) is the most common life-shortening autosomal recessive disorder in the Caucasian population and occurs in many other ethnicities worldwide. The daily treatment burden is substantial for CF patients even when they are well, with numerous pharmacologic and physical therapies targeting lung disease requiring the greatest time commitment. CF treatments continue to advance with greater understanding of factors influencing long-term morbidity and mortality. In recent years, in-depth understanding of genetic and protein structure-function relationships has led to the introduction of targeted therapies for patients with specific CF genotypes. With these advances, CF has become a model of personalized or precision medicine. The near future will see greater access to targeted therapies for most patients carrying common mutations, which will mandate individualized bench-to-bedside methodologies for those with rare genotypes.

Dose derivation of once-daily dosing guidelines for gentamicin in critically ill pediatric patients

OBJECTIVES

To determine dose and eligibility criteria for once-daily dosing (ODD) of gentamicin in critically ill pediatric patients.

METHODS

Retrospective chart review of patients admitted to the Pediatric Intensive Care Unit or Cardiac Critical Care Unit at The Hospital for Sick Children (SickKids) who received traditionally dosed intravenous (IV) gentamicin (January 2008 to June 2010). Statistically significant patient characteristics associated with gentamicin pharmacokinetic (PK) parameters were determined by multiple linear regression. Binary partitioning was used to set critical values for these characteristics to derive dose for ODD of gentamicin. Feasibility of implementing ODD of gentamicin in critically ill children was assessed using individualized PK parameters to simulate area under the concentration-time curves and drug-free intervals while targeting a maximum concentration (C(max)) of 16-20 mg/L. Eligibility criteria were determined by patient characteristics that had a statistically significant impact on gentamicin PK.

RESULTS

Volume of distribution (V(d)) and elimination rate constant (k(e)) were calculated for 140 patients. Weight and admission unit were significantly associated with weight-normalized V(d) (Vd/kg), whereas age and serum creatinine (SCr) were significantly associated with k(e). Weight <5 kg and SCr ≥20% over age-specific upper normal limit before gentamicin initiation were associated with prolonged gentamicin elimination. Gentamicin 6 mg/kg IV every 24 hours, the dose at which the highest percentage of patients achieved C(max), area under the curve, and drug-free interval within target ranges simultaneously, was selected as the proposed ODD regimen.

CONCLUSIONS

A regimen of gentamicin 6 mg/kg IV every 24 hours for Pediatric Intensive Care Unit/Cardiac Critical Care Unit patients at SickKids weighing ≥5 kg with SCr <20% above age-specific upper normal limit before initiation of gentamicin is proposed.

Pharmacokinetic/pharmacodynamic modelling approaches in paediatric infectious diseases and immunology

Pharmacokinetic/pharmacodynamic (PKPD) modelling is used to describe and quantify dose-concentration-effect relationships. Within paediatric studies in infectious diseases and immunology these methods are often applied to developing guidance on appropriate dosing. In this paper, an introduction to the field of PKPD modelling is given, followed by a review of the PKPD studies that have been undertaken in paediatric infectious diseases and immunology. The main focus is on identifying the methodological approaches used to define the PKPD relationship in these studies. The major findings were that most studies of infectious diseases have developed a PK model and then used simulations to define a dose recommendation based on a pre-defined PD target, which may have been defined in adults or in vitro. For immunological studies much of the modelling has focused on either PK or PD, and since multiple drugs are usually used, delineating the relative contributions of each is challenging. The use of dynamical modelling of in vitro antibacterial studies, and paediatric HIV mechanistic PD models linked with the PK of all drugs, are emerging methods that should enhance PKPD-based recommendations in the future.

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

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

Clinical pharmacist impact on care, length of stay, and cost in pediatric cystic fibrosis (CF) patients

BACKGROUND

Cystic fibrosis (CF) patients are often treated with aminoglycoside (AG) antibiotics during infective pulmonary exacerbations. Achieving pharmacokinetic and pharmacodynamic (PK/PD) targets to improve outcomes and counteract resistance is paramount.

PURPOSE

The primary objective was to compare the number of pediatric CF patients achieving AG PK/PD targets when a clinical pharmacist (CP) managed therapeutic drug monitoring (TDM) compared with usual care (UC).

METHODS

A retrospective cohort study was conducted on the records of 40 CF patients that received AGs and ≥2 serum samples between 1/2007 and 5/2009. Chi-square and Student's t-test were used to analyze nominal and continuous variables, respectively.

RESULTS

Twenty-nine patients with 52 courses of AGs were included the CP group, and 22 patients with 42 courses were included the UC group. Ninety-eight percent of patients in the CP group reached AG PK/PD targets compared with 71% in the UC group, P < 0.001. Patients in the CP group reached the AG PK/PD target in a mean of 1.9 ± 0.8 days compared with 4.8 ± 3.4 days in the UC group, P < 0.0001. The average LOS in the CP group was 9 ± 5 days compared with 12 ± 7.5 days in the UC group, P = 0.033. The mean number of levels per patient was 2.7 in the CP group compared with 5.2 (range of 2-20) in the UC group, P < 0.001. Resource utilization associated with drug levels, dosing adjustments and LOS were $26,549, $14,069, and $1,680,000 in the CP group as compared with $40,683, $27,812, and $1,940,000, respectively, in the UC group.

CONCLUSION

CP managed TDM resulted in a significantly higher percentage of pediatric CF patients achieving AG PK/PD targets 3 days sooner with an average LOS that was 3 days shorter. CP managed TDM resulted in significantly fewer dosage adjustments, drug levels, and cost associated with serum sampling, drug wastage, and LOS.

Population pharmacokinetics of tobramycin in patients with and without cystic fibrosis

BACKGROUND AND OBJECTIVES

While several studies have examined the pharmacokinetics of tobramycin in patients with cystic fibrosis (CF), there is no consensus on whether they differ in patients with and without CF. The objectives of this study were to identify covariates which explain pharmacokinetic variability and to examine whether having the disease CF in itself alters these relationships and drug dose requirements.

METHODS

To investigate this issue, a population pharmacokinetic meta-analysis of data from eight centres was undertaken. NONMEM(®) 7.2 was used to analyse the data, which comprised 4,514 concentration-time measurements from 465 adults and children with CF and 1,095 concentration-time measurements from 267 adults and children without CF.

RESULTS

Tobramycin disposition was well described by a two-compartment model with first-order elimination. Patient age, fat-free mass, serum creatinine concentration and sex were identified as significant covariates in the final model. Fat-free mass was superior to total bodyweight as a descriptor of clearance, volume of distribution of the central and peripheral compartments and inter-compartmental clearance. CF as an independent disease-specific factor had no significant influence on the pharmacokinetics of tobramycin at any stage during covariate model building. An optimal dose of 11 mg/kg every 24 h was defined for CF patients using a utility function approach.

CONCLUSION

The pharmacokinetics of tobramycin do not differ significantly in CF patients compared with patients without CF when subject age, fat-free mass, sex and renal function are taken into consideration. Variations in tobramycin dosing between CF and non-CF patients should therefore reflect target concentrations or exposures based on differences in expected pathogen sensitivity and not the presence of CF.

Evaluation of serum concentrations achieved with an empiric once-daily tobramycin dosage regimen in children and adults with cystic fibrosis

OBJECTIVES

To assess the ability of an empiric once-daily dosing (ODD) tobramycin regimen to achieve desired serum concentrations in patients with cystic fibrosis (CF); to determine an optimal dosage regimen, using pharmacodynamic parameters; and to evaluate clinical response, adverse effects, and patient/parent satisfaction with ODD.

METHODS

This was a prospective single-center trial in patients with CF who are 5 years of age and older requiring intravenous antibiotics. Tobramycin, 10 mg/kg every 24 hours, was infused over 60 minutes, and two serum concentrations were analyzed using 1-compartment pharmacokinetic modeling. Simulations were performed to identify dosage regimens that maximized desired pharmacodynamic parameters. Other data included demographics, symptoms, spirometry, adverse events, and satisfaction with ODD.

RESULTS

A total of 14 children and 11 adults completed the study. Empiric doses resulted in mean peak tobramycin concentrations of 28.7 ± 5.5 mg/L and undetectable trough concentrations. Only 42% of patients achieved desired peak serum concentrations (20-30 mg/L) with the empiric regimen. A regimen of 12 mg/kg every 24 hours would achieve modified pharmacodynamic goals with an acceptable peak range of 20 to 35 mg/L. Forced expiratory volume in 1 second improved in 15 of 20 (75%) patients with ODD. Two patients experienced reversible vestibular adverse effects attributed to tobramycin. All patients were satisfied or very satisfied with ODD because of convenience and ease of use.

CONCLUSIONS

An empiric tobramycin regimen of 10 mg/kg every 24 hours did not achieve desired serum concentrations for most patients, although all patients demonstrated clinical improvement. Desired tobramycin concentrations with modified pharmacodynamic goals could be achieved by using an empiric dosage of 12 mg/kg every 24 hours. Prospective evaluation of this regimen with individualized patient monitoring is needed to ensure safety and efficacy and to monitor the effects on microbial resistance patterns.

A reliable and safe method of collecting blood samples from implantable central venous catheters for determination of plasma gentamicin concentrations

STUDY OBJECTIVE

To evaluate the extent of agreement between plasma gentamicin concentrations determined from samples collected by using implantable subcutaneous central venous catheters (ports) with the push-pull method and those collected by finger lancet punctures in children with febrile neutropenia.

DESIGN

Prospective, randomized study.

SETTING

University-affiliated, tertiary care hospital.

PATIENTS

Sixty-two children with cancer who had single- or double-lumen ports and who received gentamicin for treatment of febrile neutropenia between February 2008 and October 2009.

INTERVENTION

One blood sample was collected from the port by using the push-pull method at the same time one blood sample was collected by finger lancet puncture for determination of plasma gentamicin concentrations.

MEASUREMENTS AND MAIN RESULTS

Forty-four pairs of samples were available for assessment of agreement, and 43 were available for pharmacokinetic analysis. Agreement between plasma gentamicin concentrations determined from blood samples from ports and finger lancet punctures was assessed by the intraclass correlation coefficient (ICC), Bland-Altman analysis, and comparison of simulated dosage adjustments. Changes in port patency were monitored for 1 week after port sampling. Differences in simulated dosage adjustments calculated by using either the port or finger lancet puncture samples that differed by greater than 20% were considered clinically significant. Agreement between the 44 finger lancet puncture and port sample pairs was excellent (ICC 0.991, 95% confidence interval 0.984-0.995). Port plasma gentamicin concentrations were 4.7% lower than those concentrations determined in blood from finger lancet punctures. The observed limits of agreement ranged from -20.5% to 11%. Differences in dosage adjustments calculated by using port and finger lancet puncture plasma gentamicin concentrations were not clinically significant in 38 (88%) of 43 cases. No changes in port patency were observed in the week after port sampling.

CONCLUSION

The push-pull method of blood sampling is a reliable and safe option for determining plasma gentamicin concentrations in children with ports.

Cystic fibrosis pulmonary guidelines: treatment of pulmonary exacerbations

The natural history of cystic fibrosis lung disease is one of chronic progression with intermittent episodes of acute worsening of symptoms frequently called acute pulmonary exacerbations These exacerbations typically warrant medical intervention. It is important that appropriate therapies are recommended on the basis of available evidence of efficacy and safety. The Cystic Fibrosis Foundation therefore established a committee to define the key questions related to pulmonary exacerbations, review the clinical evidence using an evidence-based methodology, and provide recommendations to clinicians. It is hoped that these guidelines will be helpful to clinicians in the treatment of individuals with cystic fibrosis.

A survey of once-daily dosage tobramycin therapy in patients with cystic fibrosis

The purpose of this study was to quantify the prevalence of once-daily dosage of tobramycin (ODDT) among Cystic Fibrosis Foundation-accredited care centers and affiliated programs (CFFACCs) and characterize the ODDT approaches used by these institutions. An anonymous cross-sectional survey of CFFACCs was performed using an electronic survey tool. This tool was electronically mailed to the program directors. Eighty-four out of 195 institutions completed the survey (response rate = 43%). Fifty-one (61%) of 84 centers reported using ODDT. Of those 51 institutions, 34 (67%) use a dosage of 10 mg/kg/dose. Serum creatinine was measured routinely in 51 centers (100%) with weekly monitoring being used in 40 centers (78%). Audiometric evaluation was performed routinely in 22 (43%) centers with annual assessment performed in 14 (64%) of these 22 centers. In conclusion, a majority of responding institutions use ODDT. The most common reported dosage is 10 mg/kg. Serum creatinine was routinely measured in all institutions with weekly assessment being the most common frequency. Audiometic assessment is routinely performed in <50% of centers. Of the institutions performing audiograms routinely, annual assessment is the most common frequency.