Girth-based administered activity for pediatric 99m Tc-DMSA SPECT

BACKGROUND

Pediatric molecular imaging requires a balance between administering an activity that will yield sufficient diagnostic image quality while maintaining patient radiation exposure at acceptable levels. In current clinical practice, this balance is arrived at by the current North American Consensus Guidelines in which patient weight is used to recommend the administered activity (AA).

PURPOSE

We have previously demonstrated that girth (waist circumference at the level of the kidneys) is better at equalizing image quality than patient weight for pediatric Tc-99m DMSA renal function imaging. However, the correlation between image quality (IQ), AA, and patient girth has not been rigorously and systematically developed. In this work, we generate a series of curves showing the tradeoff between AA and IQ as a function of patient girth, providing the data for standards bodies to develop the next generation of dosing guideline for pediatric DMSA SPECT.

METHODS

An anthropomorphic phantom series that included variations in age (5, 10, and 15 years), gender (M, F), local body morphometry (5, 10, 50, 90, and 95th girth percentiles), and kidney size (±15% standard size), was used to generate realistic SPECT projections. A fixed and clinically challenging defect-to-organ volume percentage (0.49% of renal cortex value) was used to model a focal defect with zero uptake (i.e., full local loss of renal function). Task-based IQ assessment methods were used to rigorously measure IQ in terms of renal perfusion defect detectability. This assessment was performed at multiple count levels (corresponding to various AAs) for groups of patients that had similar girths and defect sizes. Receiver-operating characteristics (ROC) analysis was applied; the area under the ROC curve (AUC) was used as a figure-of-merit for task performance. Curves showing the tradeoff between AUC and AA were generated for these groups of phantoms.

RESULTS

Overall, the girth-based dosing method suggested different amounts of AA compared to weight-based dosing for the phantoms that had a relatively large body weight but a small girth or phantoms with relatively small bodyweight but large girth. Reductions of AA to 62.9% compared to weight-based dosing guidelines can potentially be realized while maintaining a baseline (AUC = 0.80) IQ for certain 15-year-olds who have a relatively small girth and large defect size. Note that the task-based IQ results are heavily dependent on the simulated defect size for the defect detection task and the appropriate AUC value must be decided by the physicians for this diagnostic task. These results are based purely on simulation and are subject to future clinical validation.

CONCLUSIONS

The study provides simulation-based IQ-AA data for a girth-based dosing method for pediatric renal SPECT, suggesting that patient waist circumference at the level of kidneys should be considered in selecting the AA needed to achieve an acceptable IQ. This data may be useful for standards bodies to develop girth-based dosing guidelines.

Pharmacogenomics and the Management of Mood Disorders-A Review

Due to the chronic relapsing nature of mental disorders and increased life expectancy, the societal burden of these non-communicable diseases will increase even further. Treatments for mental disorders, such as depression, are available, but their effect is limited due to patients' (genetic) heterogeneity, low treatment compliance and frequent side effects. In general, only one-third of the patients respond to treatment. Today, medication selection in psychiatry relies on a trial-and-error approach based mainly on physicians' experience. Pharmacogenetic (PGx) testing can help in this process by determining the person-specific genetic factors that may predict clinical response and side effects associated with genetic variants that impact drug-metabolizing enzymes, drug transporters or drug targets. PGxis a discipline that investigates genetic factors that affect the absorption, metabolism, and transport of drugs, thereby affecting therapy outcome. These genetic factors can, among other things, lead to differences in the activity of enzymes that metabolize drugs. Studies in depressed patients show that genotyping of drug-metabolizing enzymes can increase the effectiveness of treatment, which could benefit millions of patients worldwide. This review highlights these studies, gives recommendations and provides future perspectives on how to proceed with PGx testing. Finally, it is recommended to consider genotyping for CYP2D6 and CYP2C19, when there is an indication (side effects or inefficacy).

Azole antifungals and inter-individual differences in drug metabolism: the role of pharmacogenomics and precision medicine

INTRODUCTION

Azole antifungal drugs are commonly prescribed to treat invasive fungal infections in various disease conditions. However, these drugs are substrates and inhibitors of cytochrome P450 (CYP) enzymes, UGT1A4, and P-gp. The genetic variants of CYP3A4/5, CYP2C9, CYP2C19, ABCB1, or UGT1A4 can modify the safety or effectiveness of azole antifungals.

AREAS COVERED

This review has collated the recent advances in the pharmacogenomics of azole antifungals pertaining to their metabolism and the safety or effectiveness of their use. A literature search was performed in PubMed from inception to the 5^th of December 2022 to retrieve articles focusing on pharmacogenomics of azole antifungals.

EXPERT OPINION

Optimizing the safety or effectiveness of most azole antifungals, excluding voriconazole, through pharmacogenomics remains largely theoretical, pending laboratory assessment in future studies. However, the ample evidence of the clinically significant pharmacogenetic impacts of voriconazole, due to the CYP2C19 genetic variability, favors clinical implementation. The inconsistencies of the pharmacogenomics-based dosing guidelines for voriconazole, from different international pharmacogenomics working groups, may hinder clinicians in assimilating and applying such pharmacogenetic information into clinical practice. Consideration of drug-drug interactions along with the pharmacogenetic effects may advance the precision medicine of azole antifungals and allow greater effectiveness in clinical practice.

Refinement of a pharmacogenomics app for dosing guidelines for oncology: findings from the usability evaluation

Background

This study extended a precision medicine clinical decision support mobile application (app) for use with oncology medications. Two gene variants (CYP2D6 and DPYD) associated with pharmacogenomic dosing algorithms in oncology was added to a prototype app. Usability of the app was evaluated. The use of smartphones and mobile apps for prescribing medications has exponentially increased since the introduction of physician order entry. Decision support apps have improved provider performance and studies have shown broader adoption is crucial for the success of these tools. Therefore, successful use of mobile apps will depend on perceptions of users. Rogers' Diffusion of Innovation theory will be the guiding framework for this study.

Methods

The main research variable is usability as measured by effectiveness, efficiency, and satisfaction. A mixed method design was used. The setting was inpatient and outpatient oncology practices within North Carolina. The sample included registered nurses and nurse practitioners within the oncology field. A functioning mobile app was extended based on the Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines to address the most common gene variants seen in oncology patients. Usability testing is divided into two main categories, inspection and testing methods. Prior to the field study, a heuristic evaluation was conducted. This evaluation inspected the user interface, comparing the elements and aspects of it to a set of principles, heuristics, as a guideline to evaluate the usability of the mobile app.

Results

The testing evaluation was conducted with a sample of 51 health care providers to evaluate usability, measured by the System Usability Scale and open-ended questions. Descriptive statistics was used to summarize usefulness and end-user perceived ease of use. In addition, a thematic analysis of the open-ended questions was conducted.

Conclusions

The development of this mobile app is relevant to nurses who have prescriptive privileges, as well as an educational tool for nurses to understand the rationale behind prescribing certain medications and alternate dosages by providing specific recommendations. Translation of precision medicine into practice will benefit patients by improving care, reducing adverse reactions, and lowering costs.

International Consensus Guidelines for the Optimal Use of the Polymyxins: Endorsed by the American College of Clinical Pharmacy (ACCP), European Society of Clinical Microbiology and Infectious Diseases (ESCMID), Infectious Diseases Society of America (IDSA), International Society for Anti-infective Pharmacology (ISAP), Society of Critical Care Medicine (SCCM), and Society of Infectious Diseases Pharmacists (SIDP)

The polymyxin antibiotics colistin (polymyxin E) and polymyxin B became available in the 1950s and thus did not undergo contemporary drug development procedures. Their clinical use has recently resurged, assuming an important role as salvage therapy for otherwise untreatable gram-negative infections. Since their reintroduction into the clinic, significant confusion remains due to the existence of several different conventions used to describe doses of the polymyxins, differences in their formulations, outdated product information, and uncertainties about susceptibility testing that has led to lack of clarity on how to optimally utilize and dose colistin and polymyxin B. We report consensus therapeutic guidelines for agent selection and dosing of the polymyxin antibiotics for optimal use in adult patients, as endorsed by the American College of Clinical Pharmacy (ACCP), Infectious Diseases Society of America (IDSA), International Society of Anti-Infective Pharmacology (ISAP), Society for Critical Care Medicine (SCCM), and Society of Infectious Diseases Pharmacists (SIDP). The European Society for Clinical Microbiology and Infectious Diseases (ESCMID) endorses this document as a consensus statement. The overall conclusions in the document are endorsed by the European Committee on Antimicrobial Susceptibility Testing (EUCAST). We established a diverse international expert panel to make therapeutic recommendations regarding the pharmacokinetic and pharmacodynamic properties of the drugs and pharmacokinetic targets, polymyxin agent selection, dosing, dosage adjustment and monitoring of colistin and polymyxin B, use of polymyxin-based combination therapy, intrathecal therapy, inhalation therapy, toxicity, and prevention of renal failure. The treatment guidelines provide the first ever consensus recommendations for colistin and polymyxin B therapy that are intended to guide optimal clinical use.

Somatotype, the risk of hydroxychloroquine retinopathy, and safe daily dosing guidelines

Purpose

The aim of this study was to determine whether somatotype influences the risk of hydroxychloroquine (HC) retinopathy (HCR) and whether dosing by real body weight (RBW), ideal body weight (IBW), or the lesser of these better predicts the risk of HCR.

Patients and methods

A total of 565 patients taking HC for whom height and weight were recorded and a sensitive ancillary testing modality was used including 10-2 visual fields, spectral domain optical coherence tomography, fundus autofluorescence imaging, and multifocal electroretinography were enrolled. Body mass index (BMI) was compared for patients without and with HCR. Logistic regression models of age, cumulative dose, and daily dosing based on RBW, IBW, or lesser of these were compared. Area under the curve (AUC) of receiver operating characteristic plots was used to assess the diagnostic accuracy of RBW, IBW, and lesser of these guidelines for safe dosing. Probability plots for the risk of retinopathy versus BMI were compared for the different recommended guidelines on safe dosing.

Results

A total of 41 patients had HCR. The median BMI was 27.6 (interquartile range [IQR] 24.3, 32.6) and 24.0 (IQR 21.0, 31.6) for patients without and with HCR (P=0.0102), respectively. AUC for univariate receiver operating characteristic plots of retinopathy versus dosing by RBW, IBW, and lesser of these was 0.71, 0.72, and 0.76, respectively. AUC for multivariate receiver operating characteristic plots of retinopathy versus models incorporating gender, age, cumulative dose, and BMI and differing by including dosing by RBW, IBW, and lesser of these was 0.82, 0.82, and 0.83, respectively. For all of the multivariate logistic models, the risk of retinopathy was higher for lower BMIs.

Conclusion

Short, asthenic women are at higher risk for HCR. The 2011 American Academy of Ophthalmology (AAO) guidelines are safer for short, obese women. The 2016 AAO guidelines are safer for short, asthenic patients. Choosing daily dosing based on the lesser of the RBW and IBW guidelines is safer for all patients.

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

AIMS

We aimed to compare the performance of renal function and age as predictors of inter-individual variability (IIV) in clearance of amikacin in neonates through parallel development of population pharmacokinetic (PK) models and their associated impact on optimal dosing regimens.

METHODS

Amikacin concentrations were retrospectively collected for 149 neonates receiving amikacin (post-natal age (PNA) between 4-89 days). Two population PK models were developed in parallel, considering at least as predictors current body weight (WT), in combination with either creatinine clearance (CLcr ) or age descriptors. Using stochastic simulations for both renal function or age-based dosing, we identified optimal dosing strategies that were based on attainment of optimal peak- (PCC) and trough target concentration coverage (TCC) windows associated with efficacy and toxicity.

RESULTS

The CLcr and age-based population PK models both included current body weight (WT) on CL, central distribution volume and intercompartmental clearance, in combination with either CLcr or PNA as predictors for IIV of clearance (CL). The WT-CLcr model explained 6.9% more IIV in CL compared with the WT-PNA model. Both models successfully described an external dataset (n = 53) of amikacin PK. The simulation analysis of optimal dose regimens suggested similar performance of either CLcr or PNA based dosing.

CONCLUSION

CLcr predicted more IIV in CL, but did not translate into clinically relevant improvements of target concentrations. Our optimized dose regimens can be considered for further evaluation to optimize initial treatment with amikacin.

Population pharmacokinetic study of gentamicin in a large cohort of premature and term neonates

AIM

This study aims to investigate the clinical and demographic factors influencing gentamicin pharmacokinetics in a large cohort of unselected premature and term newborns and to evaluate optimal regimens in this population.

METHODS

All gentamicin concentration data, along with clinical and demographic characteristics, were retrieved from medical charts in a Neonatal Intensive Care Unit over 5 years within the frame of a routine therapeutic drug monitoring programme. Data were described using non-linear mixed-effects regression analysis ( nonmem®).

RESULTS

A total of 3039 gentamicin concentrations collected in 994 preterm and 455 term newborns were included in the analysis. A two compartment model best characterized gentamicin disposition. The average parameter estimates, for a median body weight of 2170 g, were clearance (CL) 0.089 l h(-1) (CV 28%), central volume of distribution (Vc ) 0.908 l (CV 18%), intercompartmental clearance (Q) 0.157 l h(-1) and peripheral volume of distribution (Vp ) 0.560 l. Body weight, gestational age and post-natal age positively influenced CL. Dopamine co-administration had a significant negative effect on CL, whereas the influence of indomethacin and furosemide was not significant. Both body weight and gestational age significantly influenced Vc . Model-based simulations confirmed that, compared with term neonates, preterm infants need higher doses, superior to 4 mg kg(-1) , at extended intervals to achieve adequate concentrations.

CONCLUSIONS

This observational study conducted in a large cohort of newborns confirms the importance of body weight and gestational age for dosage adjustment. The model will serve to set up dosing recommendations and elaborate a Bayesian tool for dosage individualization based on concentration monitoring.

Considerations for rare variants in drug metabolism genes and the clinical implications

INTRODUCTION

Large-scale whole genome and exome resequencing studies have revealed that humans have a high level of deleterious rare variation, which has important implications for the design of future pharmacogenetics studies.

AREAS COVERED

Current pharmacogenetic guidelines focus on the implementation of common variation into dosing guidelines. However, it is becoming apparent that rare variation may also play an important role in differential drug response. Current sequencing technologies offer the opportunity to examine rare variation, but there are many challenges associated with such analyses. Nonetheless, if a comprehensive picture of the role that genetic variants play in treatment outcomes is to be obtained, it will be necessary to include the entire spectrum of variation, including rare variants, into pharmacogenetic research.

EXPERT OPINION

In order to implement pharmacogenetics in the clinic, patients should be genotyped for clinically actionable pharmacogenetic variants and patients responding unfavourably to treatment after pharmacogenetics-based dosing should be identified and resequenced to identify additional functionally relevant variants, including rare variants. All derived information should be added to a central database to allow for the updating of existing dosing guidelines. By routinely implementing such strategies, pharmacogenetics-based treatment guidelines will continue to improve.

Implications of serum creatinine measurements on GFR estimation and vancomycin dosing in children

BACKGROUND

Different serum creatinine (sCr) assays may obtain different values in the same patient, causing discrepancies in estimated glomerular filtration rate (eGFR) and sCr-based vancomycin dosing calculations.

OBJECTIVE

To identify potential discrepancies in sCr concentrations obtained by different assays, the compensated Jaffe (sCr-Jaffe) and the enzymatic (sCr-enz), and to compare between the eGFR and vancomycin daily dose, based on these sCr values.

METHOD

sCr-Jaffe and, sCr-enz concentrations of 890 healthy children, aged 1-18 years, were available from the Canadian Laboratory Initiative in Pediatric Reference Intervals study in Ontario. For each subject, eGFR (eGFR-Jaffe, eGFR-enz) was calculated using the revised Schwartz equation, and vancomycin daily dose (Vdose-Jaffe, Vdose-enz) was calculated using a sCr-based pharmacokinetic model.

RESULT

Significant, age-related differences were found in sCr concentrations, and in subsequent eGFR and Vdose, between the two assays. In children aged 1-5 years, mean sCr-Jaffe was higher than sCr-enz (44.0 ± 5.0 vs. 27.7 ± 7.3 μmol/L, P < 0.001), leading to lower eGFR-Jaffe (83.2 ± 9.0 vs. 137.9 ± 27.1 mL/min/1.73m2, P < 0.001) and lower Vdose-Jaffe (44.7 ± 2.5 vs. 53.5 ± 5.1 mg/kg/24 h, P < 0.001).

CONCLUSION

Based on these findings, young children may be at risk for vancomycin under-treatment. Further research is needed to define the more accurate sCr assay in young children treated with renally excreted drugs.