Access to COVID-19 testing by individuals with housing insecurity during the early days of the COVID-19 pandemic in the United States: a scoping review.

Introduction: The COVID-19 pandemic focused attention on healthcare disparities and inequities faced by individuals within marginalized and structurally disadvantaged groups in the United States. These individuals bore the heaviest burden across this pandemic as they faced increased risk of infection and difficulty in accessing testing and medical care. Individuals experiencing housing insecurity are a particularly vulnerable population given the additional barriers they face. In this scoping review, we identify some of the barriers this high-risk group experienced during the early days of the pandemic and assess novel solutions to overcome these barriers. Methods: A scoping review was performed following PRISMA-Sc guidelines looking for studies focusing on COVID-19 testing among individuals experiencing housing insecurity. Barriers as well as solutions to barriers were identified as applicable and summarized using qualitative methods, highlighting particular ways that proved effective in facilitating access to testing access and delivery. Results: Ultimately, 42 studies were included in the scoping review, with 143 barriers grouped into four categories: lack of cultural understanding, systemic racism, and stigma; medical care cost, insurance, and logistics; immigration policies, language, and fear of deportation; and other. Out of these 42 studies, 30 of these studies also suggested solutions to address them. Conclusion: A paucity of studies have analyzed COVID-19 testing barriers among those experiencing housing insecurity, and this is even more pronounced in terms of solutions to address those barriers. Expanding resources and supporting investigators within this space is necessary to ensure equitable healthcare delivery.

RADx-UP Testing Core: Access to COVID-19 Diagnostics in Community-Engaged Research with Underserved Populations.

Research on the COVID-19 pandemic revealed a disproportionate burden of COVID-19 infection and death among underserved populations and exposed low rates of SARS-CoV-2 testing in these communities. A landmark National Institutes of Health (NIH) funding initiative, the Rapid Acceleration of Diagnostics-Underserved Populations (RADx-UP) program, was developed to address the research gap in understanding the adoption of COVID-19 testing in underserved populations. This program is the single largest investment in health disparities and community-engaged research in the history of the NIH. The RADx-UP Testing Core (TC) provides community-based investigators with essential scientific expertise and guidance on COVID-19 diagnostics. This commentary describes the first 2 years of the TC's experience, highlighting the challenges faced and insights gained to safely and effectively deploy large-scale diagnostics for community-initiated research in underserved populations during a pandemic. The success of RADx-UP shows that community-based research to increase access and uptake of testing among underserved populations can be accomplished during a pandemic with tools, resources, and multidisciplinary expertise provided by a centralized testing-specific coordinating center. We developed adaptive tools to support individual testing strategies and frameworks for these diverse studies and ensured continuous monitoring of testing strategies and use of study data. In a rapidly evolving setting of tremendous uncertainty, the TC provided essential and real-time technical expertise to support safe, effective, and adaptive testing. The lessons learned go beyond this pandemic and can serve as a framework for rapid deployment of testing in response to future crises, especially when populations are affected inequitably.

Exposure-safety relationship for acyclovir in the treatment of neonatal herpes simplex virus disease.

BACKGROUND: Neonatal herpes simplex virus (HSV) disease has been treated with high-dose (20 mg/kg/dose) acyclovir since 1991. AIMS: Determine the safety of acyclovir in infants with neonatal HSV treated with high-dose acyclovir; examine the association between acyclovir dose and exposure with adverse events (AEs). STUDY DESIGN: We obtained demographic information and acyclovir dosing via medical records. Acyclovir exposure was calculated using an established pharmacokinetic model. SUBJECTS: Infants <120 days of age with neonatal HSV discharged from four academic children's hospitals. OUTCOME MEASURES: We identified clinical and laboratory adverse events (AEs). RESULTS AND CONCLUSIONS: We identified 49 infants with neonatal HSV treated with acyclovir; 42 infants had complete 21-day dosing information. Median mean daily dose was 59 mg/kg/day. Clinical AEs were common among all gestational and postnatal age groups. Rash was the most common clinical AE (37 %). Mild laboratory AEs occurred in 2-37 % of infants. The median maximum doses (mg/kg/day) were higher among infants with hypokalemia, elevated blood urea nitrogen, and thrombocytosis. For all other laboratory AEs, the median maximum doses for infants without events were higher or equal to the median maximum dose of infants with the AE. The odds of experiencing any clinical or laboratory AE did not differ by predicted acyclovir exposure for either area under the curve (AUC) or maximum concentration (Cmax) (odds ratio [OR] = 1.00 [0.98, 1.03] and OR = 1.01 [0.93, 1.12], respectively). Although AEs were common with high-dose acyclovir exposure, severe AEs were rare. Acyclovir exposure was not associated with AEs.

Pharmacokinetics of Hydrochlorothiazide in Children: A Potential Surrogate for Renal Secretion Maturation.

Hydrochlorothiazide (HCTZ) is a thiazide diuretic used in adults and children for the treatment of hypertension and edema. The pharmacokinetic (PK) properties of HCTZ in children are not well characterized, particularly among children with obesity who frequently suffer from hypertension and may, therefore, benefit from HCTZ therapy. HCTZ is excreted in the kidney via organic anion transporters 1 and 3 (OAT1 and OAT3). The ontogeny of OAT1 and OAT3 remain unknown, but HCTZ clearance may serve as a surrogate marker of OAT1 and OAT3 maturation. Population PK modeling was performed in NONMEM, and the model was leveraged to conduct dose-exposure simulations. This study examined 83 plasma samples from 49 participants (69% male) taking enteral HCTZ. The median (range) postnatal age was 6.7 years (0.03-19.5 years), and 17 (34%) participants were obese or morbidly obese. The median (range) dose of HCTZ was 0.654 mg/kg (0.11-1.8 kg) and the median number of doses recorded per participant was 5 (1-8). HCTZ PK was well characterized by a 1-compartment PK model. Body weight and a maturation model based on postmenstrual age were significant covariates for apparent clearance, but the presence of obesity was not. Dosing simulations were performed with a standardized 1mg/kg. Simulated exposure (area under the curve and maximum HCTZ concentrations) decreased with age and was likely due to older children receiving the maximum absolute doses of HCTZ. Further studies with more patients in each age group are required to confirm these PK findings of HCTZ in the children.

Population Pharmacokinetics of Metoclopramide in Infants, Children, and Adolescents.

Metoclopramide is commonly used for gastroesophageal reflux. The aims of the present study were to develop a pediatric population pharmacokinetic (PopPK) model, which was applied to simulate the metoclopramide exposure following dosing used in clinical practice. Opportunistic pharmacokinetic data were collected from pediatric patients receiving enteral or parenteral metoclopramide per standard of care and these data were simultaneously fitted using NONMEM. Allometric scaling with body weight was included a priori in the model. Using the final model, the steady-state maximum concentrations (Css,max ) and the area under the metoclopramide plasma concentration-time curve at steady state from 0 to 6 hours (AUCss,0-6h ) were simulated following 0.1 or 0.15 mg/kg orally every 6 hours in virtual patients, and compared with previously reported ranges associated with toxicity or the efficacy for gastroesophageal reflux in infants. A two-compartment model with first-order absorption best characterized 87 concentration measurements from 50 patients (median [range] postnatal age of 8.89 years [0.01-19.13]). There were 20 infants (≤ 2 years), 9 children (2 years to age ≤ 12 years), and 21 adolescents (> 12 years). Body weight was the only covariate included in the final model. For > 75% of virtual patients, simulated Css,max and AUCss,0-6h estimates were within the range associated with efficacy for gastroesophageal reflux in infants; however, slightly lower exposures were predicted in virtual patients < 2 years. Our study suggests that a metoclopramide enteral dose of 0.1 mg/kg every 6 hours, which was previously recommended for pediatric patients, results in simulated exposure generally within suggested ranges for the treatment of gastroesophageal reflux.

Dosing of Continuous Fentanyl Infusions in Obese Children: A Population Pharmacokinetic Analysis.

Differences in fentanyl pharmacokinetics (PK) between obese and nonobese adults have previously been reported; however, the impact of childhood obesity on fentanyl PK is relatively unknown. We developed a population pharmacokinetic (PopPK) model using opportunistically collected samples from a cohort of predominately obese children receiving fentanyl per the standard of care. Using a probability-based approach, we evaluated the ability of different continuous infusion strategies to provide steady-state concentrations (Css ) within an analgesic concentration range (1-3 ng/mL). Fifty-three samples from 32 children were used for PopPK model development. Median (range) age and body weight of study participants were 13 years (2-19 years) and 52 kg (16-164 kg), respectively. The majority of children (94%) were obese. A 2-compartment model allometrically scaled by total body weight provided an appropriate fit to the data. Estimated typical clearance was 32.5 L/h (scaled to 70 kg). A fixed dose rate infusion of 1 µg/kg/h was associated with probabilities between 49% and 58% for achieving Css within target; however, the risk of achieving Css > 3 ng/mL increased with increasing body weight (15% at 16 kg vs 43% at 164 kg). A proposed model-based infusion strategy maintained consistent probabilities across the examined weight range for achieving Css within (58%) and above (20%) target. Use of an allometric relationship between weight and clearance was appropriate for describing the PK of intravenous fentanyl in our cohort of predominately obese children. Our proposed model-derived continuous infusion strategy maximized the probability of achieving target Css in children of varying weights.

Population Pharmacokinetics of Doxycycline in Children.

Doxycycline is a tetracycline-class antimicrobial labeled by the United States (U.S.) Food and Drug Administration for children >8 years of age for many common childhood infections. Doxycycline is not labeled for children ≤8 years of age, due to the association between tetracycline class antibiotics and tooth staining, although doxycycline may be used off-label in severe conditions. Accordingly, there is a paucity of pharmacokinetic (PK) data to guide dosing in children 8 years and younger. We leveraged opportunistically-collected plasma samples after intravenous (IV) and oral doxycycline doses received per standard of care to characterize the PK of doxycycline in children of different ages, and evaluated the effect of obesity and fasting status on PK parameters.We developed a population PK model of doxycycline using data collected from 47 patients 0-18 years of age, including 14 participants ≤8 years. We developed a 1 compartment PK model and found doxycycline clearance to be 3.32 L/h/70 kg and volume to be 96.8 L/70kg for all patients; comparable to values reported in adults. We estimated a bioavailability of 89.6%, also consistent with adult data. Allometrically scaled clearance and volume of distribution did not differ between children 2 to ≤8 years of age and children >8 to ≤18 years of age, suggesting that younger children may be given the same per kg dosing. Obese and fasting status were not selected for inclusion in the final model. Additional doxycycline PK samples collected in future studies may be used to improve model performance and maximize its clinical value.

Population Pharmacokinetics of Milrinone in Infants, Children, and Adolescents.

Milrinone is a type 3 phosphodiesterase inhibitor used to improve cardiac output in critically ill infants and children. Milrinone is primarily excreted unchanged in the urine, raising concerns for toxic accumulation in the setting of renal dysfunction of critical illness. We developed a population pharmacokinetic model of milrinone using nonlinear mixed-effects modeling in NONMEM to perform dose-exposure simulations in children with variable renal function. We included children aged <21 years who received intravenous milrinone per clinical care. Plasma milrinone concentrations were measured using a validated liquid chromatography-tandem mass spectrometry assay (range 1-5000 ng/mL). We performed dose-exposure simulations targeting steady-state therapeutic concentrations of 100-300 ng/mL previously established in adults and children with cardiac dysfunction. We simulated concentrations over 48 hours in typical subjects with decreasing creatinine clearance (CrCl), estimated using the updated bedside Schwartz equation. Seventy-four patients contributed 111 plasma samples (concentration range, 4-634 ng/mL). The median (range) postmenstrual age (PMA) was 3.7 years (0-18), and median weight (WT) was 13.1 kg (2.6-157.7). The median serum creatinine and CrCl were 0.5 mg/dL (0.1-3.1) and 117.2 mL/min/1.73 m2 (13.1-261.3), respectively. A 1-compartment model characterized the pharmacokinetic data well. The final model parameterization was: Clearance (L/h) = 15.9*(WT [kg] / 70)0.75 * (PMA1.12 / (67.71.12 +PMA1.12 )*(CrCl / 117)0.522 ; and Volume of Distribution (L) = 32.2*(WT [kg] / 70). A loading dose of 50 µg/kg followed by a continuous infusion of 0.5 µg/kg/min resulted in therapeutic concentrations, except when CrCl was severely impaired at ≤30 mL/min/1.73 m2 . In this setting, a 25 µg/kg loading dose and 0.25 µg/kg/min continuous infusion resulted in therapeutic exposures.

Dosing and Safety of Off-label Use of Caffeine Citrate in Premature Infants.

OBJECTIVE: To characterize the dosing and safety of off-label caffeine citrate in a contemporary cohort of extremely premature infants. STUDY DESIGN: We used electronic health records (2010-2013) from 4 neonatal intensive care units to identify infants of ≤28 weeks of gestational age exposed to caffeine citrate. Safety outcomes included death, bronchopulmonary dysplasia, necrotizing enterocolitis, spontaneous intestinal perforation, intraventricular hemorrhage, patent ductus arteriosus ligation, seizures, and arrhythmias. We used multivariable logistic regression to evaluate the association of caffeine citrate exposure with clinical events. RESULTS: Of 410 infants with a median (IQR) gestational age of 26 (24-27) weeks, 95% received caffeine citrate for >0 days. Infants received a median (IQR) daily dose of 8 (5-10) mg/kg/day. Incidences of clinical events on day of caffeine citrate exposure were death 2%, patent ductus arteriosus ligation 12%, and medical and surgical necrotizing enterocolitis 5% and 4%, respectively. Bronchopulmonary dysplasia occurred in 37% of infants and was not associated with caffeine dose. Increased caffeine citrate dose was associated with lower odds of patent ductus arteriosus ligation and necrotizing enterocolitis. CONCLUSIONS: Caffeine citrate was used in extremely premature infants at younger gestation, at higher doses, and for longer durations than recommended on the drug label. Increased caffeine citrate exposure, dose, or therapy duration was not associated with increased risk of necrotizing enterocolitis.

Pharmacokinetics of ticarcillin-clavulanate in premature infants.

Ticarcillin-clavulanate covers a broad spectrum of pathogens that are common in premature infants. In infants <30 weeks gestational age, pharmacokinetic data to guide ticarcillin-clavulanate dosing are lacking. We enrolled 15 premature infants <30 weeks gestational age, determined pharmacokinetic parameters, and performed dosing simulations to determine optimal dosing for ticarcillin-clavulanate. The infants had a median (range) postnatal age (PNA) of 18 days (6-44 days) and gestational age of 25 weeks (23-28 weeks). Clearance was lower in infants with a PNA <14 days (0.050 L/kg/h [range 0.043-0.075]) compared with a PNA ≥14-45 days (0.078 L/kg/h [0.047-0.100]), consistent with maturation of renal function. Dosing simulations determined that ticarcillin 75 mg/kg q12h (PNA <14 days) or q8h (PNA ≥ 14-45 days) achieved the target exposure for organisms with a minimum inhibitory concentration ≤16 µ/mL in >90% of simulated infants. For highly resistant organisms (minimum inhibitory concentration 32 µg/mL), increased dosing frequency or extended infusion are necessary.

Population Pharmacokinetics and Exploratory Exposure-Response Relationships of Diazepam in Children Treated for Status Epilepticus.

Diazepam is labeled for status epilepticus (SE) in children, but there are limited data characterizing its disposition in pediatric patients. We developed a population pharmacokinetic (PK) model of i.v. diazepam in children with SE. We evaluated relationships between PK parameters and both safety and efficacy, and simulated exposures using dosing regimens from the product label and clinical practice. The model was developed using prospective data from a pediatric clinical trial comparing diazepam to lorazepam for treatment of SE. Altogether, 87 patients aged ≥ 3 months to < 18 years contributed 162 diazepam concentrations. Diazepam PKs were well characterized by a two-compartment model scaled by body size. No significant or clinically important relationships were observed between diazepam PKs and safety or efficacy. Simulations demonstrated that, compared with label dosing, the study dose (0.2 mg/kg i.v., maximum 8 mg) resulted in greater frequency in rapidly achieving the target therapeutic range of 200-600 ng/mL.

Population Pharmacokinetics of Intramuscular and Intravenous Ketamine in Children.

Ketamine is an N-methyl D-aspartate receptor antagonist used off-label to facilitate dissociative anesthesia in children undergoing invasive procedures. Available for both intravenous and intramuscular administration, ketamine is commonly used when vascular access is limited. Pharmacokinetic (PK) data in children are sparse, and the bioavailability of intramuscular ketamine in children is unknown. We performed 2 prospective PK studies of ketamine in children receiving either intramuscular or intravenous ketamine and combined the data to develop a pediatric population PK model using nonlinear mixed-effects methods. We applied our model by performing dosing simulations targeting plasma concentrations previously associated with analgesia (>100 ng/mL) and anesthesia awakening (750 ng/mL). A total of 113 children (50 intramuscular and 63 intravenous ketamine) with a median age of 3.3 years (range 0.02 to 17.6 years), and median weight of 14 kg (2.4 to 176.1) contributed 275 plasma samples (149 after intramuscular, 126 after intravenous ketamine). A 2-compartment model with first-order absorption following intramuscular administration and first-order elimination described the data best. Allometrically scaled weight was included in the base model for central and peripheral volume of distribution (exponent 1) and for clearance and intercompartmental clearance (exponent 0.75). Model-estimated bioavailability of intramuscular ketamine was 41%. Dosing simulations suggest that doses of 2 mg/kg intravenously and 8 mg/kg or 6 mg/kg intramuscularly, depending on age, provide adequate sedation (plasma ketamine concentrations >750 ng/mL) for procedures lasting up to 20 minutes.

A pharmacokinetic model for amiodarone in infants developed from an opportunistic sampling trial and published literature data.

Amiodarone is a first-line antiarrhythmic for life-threatening ventricular fibrillation or ventricular tachycardia in children, yet little is known about its pharmacokinetics (PK) in this population. We developed a population PK (PopPK) model using samples collected via an opportunistic study design of children receiving amiodarone per standard of care supplemented by amiodarone PK data from the literature. Both study data and literature data were predominantly from infants < 2 years old, so our analysis was restricted to this group. The final combined dataset consisted of 266 plasma drug concentrations in 45 subjects with a median (interquartile range) postnatal age of 40.1 (11.0-120.4) days and weight of 3.9 (3.1-5.1) kg. Since the median sampling time after the first dose was short (study: 95 h; literature: 72 h) relative to the terminal half-life estimated in adult PopPK studies, values of the deep compartment volume and flow were fixed to literature values. A 3-compartment model best described the data and was validated by visual predictive checks and non-parametric bootstrap analysis. The final model included body weight as a covariate on all volumes and on both inter-compartmental and elimination clearances. The empiric Bayesian estimates for clearance (CL), volume of distribution at steady state, and terminal half-life were 0.25 (90% CL 0.14-0.36) L/kg/h, 93 (68-174) L/kg, and 266 (197-477) h, respectively. These studies will provide useful information for future PopPK studies of amiodarone in infants and children that could improve dosage regimens.

Comparative Analysis of Ampicillin Plasma and Dried Blood Spot Pharmacokinetics in Neonates.

BACKGROUND: Dried blood spot (DBS) is a practical sampling strategy for pharmacokinetic studies in neonates. The utility of DBS to determine the population pharmacokinetics (pop-PK) of ampicillin, as well as accuracy versus plasma samples, was evaluated. METHODS: An open-label, multicenter, opportunistic, prospective study was conducted in neonates. Ampicillin concentrations from plasma and DBS (CONCPlasma and CONCDBS) were measured by liquid chromatographic tandem mass spectrometry and analyzed using pop-PK and statistical (including transformation) approaches. RESULTS: A total of 29 paired plasma and DBS samples from 18 neonates were analyzed. The median (range) gestational age and postnatal age were 37 (27-41) weeks and 8 (1-26) days, respectively. The geometric mean of CONCDBS to CONCPlasma ratio was 0.56. Correlation analysis demonstrated strong association between CONCPlasma and CONCDBS (r = 0.902, analysis of variance P < 0.001). Using linear regression transformation, the estimated CONCPlasma (eCONCPlasma) was derived using (CONCDBS - 3.223)/0.51. The median bias and geometric mean ratio improved to -11% and 0.88 (Wilcoxon signed-rank test, P < 0.001), respectively, when comparing eCONCPlasma to CONCPlasma. Furthermore, using pop-PK modeling, the median bias (interquartile range) for clearance and individual predicted concentrations improved to 8% (-11 to 50) and -8% (-34 to 11), respectively, when eCONCPlasma was used. CONCLUSIONS: After transformation, DBS sampling accurately predicted ampicillin exposure in neonates.

Population Pharmacokinetics of Trimethoprim-Sulfamethoxazole in Infants and Children.

Trimethoprim (TMP)-sulfamethoxazole (SMX) is used to treat various types of infections, including community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) and Pneumocystis jirovecii infections in children. Pharmacokinetic (PK) data for infants and children are limited, and the optimal dosing is not known. We performed a multicenter, prospective PK study of TMP-SMX in infants and children. Separate population PK models were developed for TMP and SMX administered by the enteral route using nonlinear mixed-effects modeling. Optimal dosing was determined on the basis of the matching adult TMP exposure and attainment of the surrogate pharmacodynamic (PD) target for efficacy, a free TMP concentration above the MIC over 50% of the dosing interval. Data for a total of 153 subjects (240 samples for PK analysis) with a median postnatal age of 8 years (range, 0.1 to 20 years) contributed to the analysis for both drugs. A one-compartment model with first-order absorption and elimination characterized the TMP and SMX PK data well. Weight was included in the base model for clearance (CL/F) and volume of distribution (V/F). Both TMP and SMX CL/F increased with age. In addition, TMP and SMX CL/F were inversely related to the serum creatinine and albumin concentrations, respectively. The exposure achieved in children after oral administration of TMP-SMX at 8/40 mg/kg of body weight/day divided into administration every 12 h matched the exposure achieved in adults after administration of TMP-SMX at 320/1,600 mg/day divided into administration every 12 h and achieved the PD target for bacteria with an MIC of 0.5 mg/liter in >90% of infants and children. The exposure achieved in children after oral administration of TMP-SMX at 12/60 and 15/75 mg/kg/day divided into administration every 12 h matched the exposure achieved in adults after administration of TMP-SMX at 640/3,200 mg/day divided into administration every 12 h in subjects 6 to <21 years and 0 to <6 years of age, respectively, and was optimal for bacteria with an MIC of up to 1 mg/liter.

An anthropometric survey of US pre-term and full-term neonates.

BACKGROUND: Anthropometric data prove valuable for screening and monitoring various medical conditions. In young infants, however, only weight, length and head circumference are represented in publicly accessible databases. AIM: To characterise length and circumferential measures in pre-term and full-term infants up to 90 days post-natal. SUBJECTS AND METHODS: In eight US medical centres, trained raters recorded humeral, ulnar, femoral, tibial and fibular lengths along with mid-upper arm, mid-thigh, chest, abdominal and neck circumference. Data were pooled by post-menstrual age into 1-week intervals and population curves created using the lambda, mu and sigma (LMS) method. Goodness-of-fit was assessed by examining de-trended quantile-quantile plots, Q statistics and fitted centiles overlaid on empirical centiles. RESULTS: In total, 2097 infants were enrolled in this study with a mean ± SD gestational age and post-natal age of 37.1 ± 3.3 weeks and 27.3 ± 25.3 days, respectively. A re-scale option was used to describe all curves. The resultant models reliably characterised anthropometric measures from 33-52 weeks PMA, with less certainty at the extremes (27-55 weeks). CONCLUSION: The population curves generated under this investigation expand existing reference data on a comprehensive set of anthropometric traits in infants through the first 90 days post-natal.

A Weight Estimation Strategy for Preterm and Full-Term Infants.

Weight is the foremost marker of health outcomes in infants; however, the majority of community workers and health care providers in remote, resource-constrained settings have limited access to functional scales. This study develops and validates a simple weight estimation strategy for infants that addresses the limitations of current approaches. Circumferential and segmental anthropometric measures were evaluated for their relationship to infant weight and length. Data derived from 2097 US infants (n = 1681 for model development, n = 416 for validation). Statistical and practical considerations informed final measurement selection. Head circumference and chest circumference demonstrated the best correlations with weight (r = 0.89) and length (r = 0.94 and 0.93), and were among the most reproducible as reflected by intraclass correlation coefficients (>0.98). The head circumference and chest circumference combination offered better goodness-of-fit and smaller limits of agreement than did either measure alone. The final model predicted weight within 10% and 15% of actual for 84% and 94% of infants, respectively, with no bias for postnatal age (P = .76), gestational age (P = .10), and sex (P = .25). The model requires simple summation to generate a weight estimate and can be embodied as a low-cost, paper-based device.

Population Pharmacokinetics and Exploratory Pharmacodynamics of Lorazepam in Pediatric Status Epilepticus.

BACKGROUND: Lorazepam is one of the preferred agents used for intravenous treatment of status epilepticus (SE). We combined data from two pediatric clinical trials to characterize the population pharmacokinetics of intravenous lorazepam in infants and children aged 3 months to 17 years with active SE or a history of SE. METHODS: We developed a population pharmacokinetic model for lorazepam using the NONMEM software. We then assessed exploratory exposure-response relationships using the overall efficacy and safety study endpoints, and performed dosing simulations. RESULTS: A total of 145 patients contributed 439 pharmacokinetic samples. The median (range) age and dose were 5.4 years (0.3-17.8) and 0.10 mg/kg (0.02-0.18), respectively. A two-compartment pharmacokinetic model with allometric scaling described the data well. In addition to total body weight (WT), younger age was associated with slightly higher weight-normalized clearance (CL). The following relationships characterized the typical values for the central compartment volume (V1), CL, peripheral compartment volume (V2), and intercompartmental CL (Q), using individual subject WT (kg) and age (years): V1 (L) = 0.879*WT; CL (L/h) = 0.115*(Age/4.7)0.133*WT0.75; V2 (L) = 0.542*V1; Q (L/h) = 1.45*WT0.75. No pharmacokinetic parameters were associated with clinical outcomes. Simulations suggest uniform pediatric dosing (0.1 mg/kg, to a maximum of 4 mg) can be used to achieve concentrations of 50-100 ng/mL in children with SE, which have been previously associated with effective seizure control. CONCLUSIONS: The population pharmacokinetics of lorazepam were successfully described using a sparse sampling approach and a two-compartment model in pediatric patients with active SE.

Simultaneous determination of trimethoprim and sulfamethoxazole in dried plasma and urine spots.

BACKGROUND: Trimethoprim-sulfamethoxazole (TMP-SMX) is an antimicrobial drug combination commonly prescribed in children and adults. The study objectives were to validate and apply an HPLC-MS/MS method to quantify TMP-SMX in dried plasma spots (DPS) and dried urine spots (DUS), and perform a comparability analysis with liquid matrices. RESULTS: For TMP the validated range was 100-50,000 ng/ml for DPS and 500-250,000 ng/ml for DUS; for SMX, the validated range was 1000-500,000 ng/ml for both DPS and DUS. Good agreement was noted between DPS/DUS and liquid plasma and urine samples for TMP, while only modest agreement was observed for SMX in both matrices. CONCLUSION: A precise, accurate and reproducible method was developed to quantify TMP-SMX in DPS and DUS samples.