Pharmacokinetics of cardiovascular drugs in children. Inotropes and vasopressors

Outcome of Extracorporeal Cardiopulmonary Resuscitation in Pediatric Patients Without Congenital Cardiac Disease: Extracorporeal Life Support Organization Registry Study

OBJECTIVES

To describe the use of extracorporeal cardiopulmonary resuscitation (ECPR) in pediatric patients without congenital heart disease (CHD) and identify associations with in-hospital mortality, with a specific focus on initial arrest rhythm.

DESIGN

Retrospective cohort study using data from pediatric patients enrolled in Extracorporeal Life Support Organization (ELSO) registry between January 1, 2017, and December 31, 2019.

SETTING

International, multicenter.

PATIENTS

We included ECPR patients under 18 years old, and excluded those with CHD. Subgroup analysis of patients with initial arrest rhythm.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We identified 567 patients: neonates (12%), infants (27%), children between 1 and 5 years old (25%), and children over 5 years old (36%). The patient cohort included 51% males, 43% of White race, and 89% not obese. Most suffered respiratory disease (26%), followed by acquired cardiac disease (25%) and sepsis (12%). In-hospital mortality was 59%. We found that obesity (adjusted odds ratio [aOR], 2.28; 95% CI, 1.21-4.31) and traumatic injury (aOR, 6.94; 95% CI, 1.55-30.88) were associated with greater odds of in-hospital mortality. We also identified lower odds of death associated with White race (aOR, 0.64; 95% CI, 0.45-0.91), ventricular tachycardia (VT) as an initial arrest rhythm (aOR, 0.36; 95% CI, 0.16-0.78), return of spontaneous circulation before cannulation (aOR, 0.56; 95% CI, 0.35-0.9), and acquired cardiac disease (aOR, 0.43; 95% CI, 0.29-0.64). Respiratory disease was associated with greater odds of severe neurologic complications (aOR, 1.64; 95% CI, 1.06-2.54).

CONCLUSIONS

In children without CHD undergoing ECPR, we found greater odds of in-hospital mortality were associated with either obesity or trauma. The ELSO dataset also showed that other variables were associated with lesser odds of mortality, including VT as an initial arrest rhythm. Prospective studies are needed to elucidate the reasons for these survival differences.

Effective dose of ephedrine for treatment of hypotension after induction of general anaesthesia in neonates and infants less than 6 months of age: a multicentre randomised, controlled, open label, dose escalation trial

BACKGROUND

The recommended dose of ephedrine in adults (0.1 mg kg^-1) frequently fails to treat hypotension after induction of general anaesthesia in neonates and infants less than 6 months of age. The aim of this study was to determine the optimal dose of ephedrine in this population for the treatment of hypotension after induction of general anaesthesia with sevoflurane.

METHODS

We conducted a multicentre, prospective, randomised, open-label, controlled, dose-escalation trial. Subjects were randomised if presenting a >20% change from baseline in MAP. Six cohorts of 20 subjects each were enrolled. Ten subjects in the first cohort received 0.1 mg kg^-1 i. v. (reference dose). For each subsequent cohort, 10 subjects were assigned to the next higher dose (consecutively 0.6, 0.8, 1, 1.2, and 1.4 mg kg^-1 i. v.), and the other subjects were assigned to one or more doses already investigated in previous cohorts. The primary outcome was the return of MAP to >80% of baseline at least once within 10 min after ephedrine administration.

RESULTS

A total of 119 infants (25% females), with a mean age (standard deviation) of 2.7 (1.3) months, received their allocated dose of ephedrine. The optimal dose of ephedrine was 1.2 mg kg^-1, with a percentage of success of 65.5% (95% confidence interval, 35.6-86.4). The doses of ephedrine investigated did not induce adverse events.

CONCLUSIONS

Doses of ephedrine much higher (∼10-fold) than those used in adults are necessary in neonates and infants for the treatment of hypotension after induction of general anaesthesia with sevoflurane.

CLINICAL TRIAL REGISTRATION

NCT02384876.

Influence of catecholamines at different dosages on the function of the LiDCO sensor in isoflurane anesthetized horses

OBJECTIVE

To compare the lithium dilution method for cardiac output (LiDCO) and bolus-thermo-dilution (BTD) measurements before and during infusion of dobutamine, dopamine, phenylephrine, or noradrenaline at 2 different doses in anesthetized horses and to examine the correlation between sensor voltages (saline-blood exposed) and possible measurement errors.

DESIGN

Prospective experimental study.

SETTING

University teaching hospital.

ANIMALS

Nine Warmblood horses.

INTERVENTIONS

Following 90 minutes of equilibration, 3 different doses of dobutamine (0.5-3 μg/kg/min), dopamine (1-5 μg/kg/min), phenylephrine (0.5-3 μg/kg/min), or noradrenaline (0.1-0.5 μg/kg/min) were administered for 15 minutes in anesthetized horses, and measurements using the LiDCO were performed at the lowest and highest doses. Pairs of LiDCO and BTD measurements were collected and sensor voltages exposed to blood and saline were measured before and at the end of each infusion period. Agreement between LiDCO and BTD was assessed with the Bland-Altman method.

MEASUREMENT AND MAIN RESULTS

The biases (2 standard deviations) before infusion of dobutamine, dopamine, phenylephrine, and noradrenaline were 1.1 (5.7), 1.6 (7.3), 0.2 (6.6), and 1.5 (4.1) L/min, respectively, and minimally and nonsignificantly changed following low-dose catecholamine infusions. Following infusion of higher doses, biases were significantly higher compared to baseline with 10.7 (7.8), 11.2 (11.9), 6.9 (11.7), and 3.5 (3.8) L/min, respectively. The difference between saline- and blood-exposed sensor voltage decreased during infusion of high doses of catecholamines with correlations (r_s = 0.62) between cardiac output differences and sensor voltage differences (saline-blood).

CONCLUSIONS

This study demonstrated that catecholamines could lead to overestimation in a dose-dependent fashion in LiDCO measurements. Monitoring changes in sensor voltage differences (saline-blood) is a valuable and clinically applicable tool to predict errors in LiDCO measurements.

Non–Health Care Facility Cardiovascular Medication Errors in the United States

Background: Prior studies have not examined national trends and characteristics of unintentional non–health care facility (HCF) medication errors associated with cardiovascular drugs. Objective: To investigate non-HCF medication errors associated with cardiovascular drugs reported to poison control centers in the United States. Methods: A retrospective analysis of non-HCF medication errors associated with cardiovascular drugs from 2000 to 2012 was conducted using the National Poison Data System database. Results: There were 278 444 medication errors associated with cardiovascular drugs reported to US poison control centers during the study period, averaging 21 419 exposures annually. The overall rate of cardiovascular medication errors per 100 000 population increased 104.6% from 2000 to 2012 ( P < 0.001) and the highest rates were among older adults. Most cases (83.6%) did not require treatment at a HCF. Serious medical outcomes were reported in 4.0% of exposures. The cardiovascular drugs most commonly implicated in medication errors were β-blockers (28.2%), calcium antagonists (17.7%), and angiotensin-converting enzyme inhibitors (15.9%). Most of the 114 deaths were associated with cardiac glycosides (47.4%) or calcium antagonists (29.8%). Most medication errors involved taking or being given a medication twice (52.6%). Conclusions: This study describes characteristics and trends of non-HCF cardiovascular medication errors over a 13-year period in the United States. The number and rate of cardiovascular medication errors increased steadily from 2000 to 2012, with the highest error rates among older adults. Further research is needed to identify prevention strategies for these errors, with a particular focus on the older adult population.

A Literature Review of the Pharmacokinetics and Pharmacodynamics of Dobutamine in Neonates

Since its discovery in 1975 dobutamine has been used off-label for treating hemodynamic insufficiency in newborns and children. We present a structured literature review of pharmacokinetic and pharmacodynamic data for dobutamine in the pediatric population. Structured searches were conducted to identify relevant articles according to pre-defined inclusion criteria. Where possible, results for the pharmacodynamic and pharmacokinetic effect of dobutamine were reported as pooled data. Forty-six papers met the inclusion criteria. With regard to pharmacodynamic data a number of studies reported significant increases in a number of clinical parameters such as heart rate, blood pressure, cardiac output across a wide range of pediatric populations. With regard to pharmacokinetic data studies reported that the infusion rate was positively correlated to plasma dobutamine concentration. There was great variability with regard to dobutamine clearance between individuals and as to whether it followed first- or zero-order elimination kinetics. While the pharmacodynamic effects of dobutamine appear to reflect the pharmacological profile of the drug, the pharmacokinetic data are difficult to interpret due to inhomogeneity between study populations ages, comorbidities, dobutamine dosages and methodologies. High-quality prospective pharmacokinetic and pharmacodynamic data especially in newborns are urgently required prior to a large randomized study.

Gaps in Drug Dosing for Obese Children: A Systematic Review of Commonly Prescribed Emergency Care Medications

PURPOSE

Approximately 1 of 6 children in the United States is obese. This has important implications for drug dosing and safety because pharmacokinetic (PK) changes are known to occur in obesity due to altered body composition and physiologic mechanisms. Inappropriate drug dosing in an emergency setting can limit therapeutic efficacy and increase drug-related toxic effects for obese children. Few systematic reviews examining PK properties and drug dosing in obese children have been performed.

METHODS

We identified 25 emergency care drugs from the Strategic National Stockpile and Acute Care Supportive Drugs List and performed a systematic review for each drug in 3 study populations: obese children (2-18 years of age), normal weight children, and obese adults (aged >18 years). For each study population, we first reviewed a drug's Food and Drug Administration label and then performed a systematic literature review. From the literature, we extracted drug PK data, biochemical properties, and dosing information. We then reviewed data in 3 age subpopulations (2-7 years, 8-12 years, and 13-18 years) for obese and normal weight children and by route of drug administration (intramuscular, intravenous, oral, and inhaled). If sufficient PK data were not available by age and route of administration, a data gap was identified.

FINDINGS

Only 2 of 25 emergency care drugs (8%) contained dosing information on the Food and Drug Administration label for obese children and adults compared with 22 of 25 (88%) for normal weight children. We found no sufficient PK data in the literature for any of the emergency care drugs in obese children. Sufficient PK data were found for 7 of 25 emergency care drugs (28%) in normal weight children and 3 of 25 (12%) in obese adults.

IMPLICATIONS

Insufficient information exists to guide dosing in obese children for any of the emergency care drugs reviewed. This knowledge gap is alarming, given the known PK changes that occur in the setting of obesity. Future clinical trials examining the PK properties of emergency care medications in obese children should be prioritized.

Population pharmacokinetics and haemodynamic effects of norepinephrine in hypotensive critically ill children

AIM

The aim of the study was to investigate the pharmacokinetics and pharmacodynamics of norepinephrine in hypotensive critically ill children, including associated variability factors.

METHODS

This was a prospective study in an 18-bed neonatal and paediatric intensive care unit. All children were aged less than 18 years, weighed more than 1500 g and required norepinephrine for systemic arterial hypotension. The pharmacokinetics and haemodynamic effects were described using the non-linear mixed effect modelling software MONOLIX.

RESULTS

Norepinephrine dosing infusions ranging from 0.05 to 2 μg kg(-1)  min(-1) were administered to 38 children whose weight ranged from 2 to 85 kg. A one compartment open model with linear elimination adequately described the norepinephrine concentration-time courses. Bodyweight (BW) was the main covariate influencing norepinephrine clearance (CL) and endogenous norepinephrine production rate (q0) via an allometric relationship: CL(BWi) = θCL × (BWi)(3/4) and q0(BWi) = θq0 × (BWi)(3/4) . The increase in mean arterial pressure (MAP) as a function of norepinephrine concentration was well described using an Emax model. The effects of post-conceptional age (PCA) and number of organ dysfunctions were significant on basal MAP level (MAP0i = MAP0 × PCA/9i (0.166) ) and on the maximal increase in MAP (32 mmHg and 12 mmHg for a number of organ dysfunctions ≤3 and ≥4, respectively).

CONCLUSION

The pharmacokinetics and haemodynamic effects of norepinephrine in hypotensive critically ill children highlight the between-subject variability which is related to the substantial role of age, BW and severity of illness. Taking into account these individual characteristics may help clinicians in determining an appropriate initial a priori dosing regimen.

Drug Dosing and Pharmacokinetics in Children With Obesity: A Systematic Review

IMPORTANCE

Obesity affects nearly one-sixth of US children and results in alterations to body composition and physiology that can affect drug disposition, possibly leading to therapeutic failure or toxic side effects. The depth of available literature regarding obesity's effect on drug safety, pharmacokinetics, and dosing in obese children is unknown.

OBJECTIVE

To perform a systematic literature review describing the current evidence of the effect of obesity on drug disposition in children.

EVIDENCE REVIEW

We searched the MEDLINE, Cochrane, and EMBASE databases (January 1, 1970-December 31, 2012) and included studies if they contained data on drug clearance, volume of distribution, or drug concentration in obese children (aged ≤18 years). We compared exposure and weight-normalized volume of distribution and clearance between obese and nonobese children. We explored the association between drug physicochemical properties and clearance and volume of distribution.

FINDINGS

Twenty studies met the inclusion criteria and contained pharmacokinetic data for 21 drugs. The median number of obese children studied per drug was 10 (range, 1-112) and ages ranged from newborn to 29 years (1 study described pharmacokinetics in children and adults together). Dosing schema varied and were either a fixed dose (6 [29%]) or based on body weight (10 [48%]) and body surface area (4 [19%]). Clinically significant pharmacokinetic alterations were observed in obese children for 65% (11 of 17) of the studied drugs. Pharmacokinetic alterations resulted in substantial differences in exposure between obese and nonobese children for 38% (5 of 13) of the drugs. We found no association between drug lipophilicity or Biopharmaceutical Drug Disposition Classification System class and changes in volume of distribution or clearance due to obesity.

CONCLUSIONS AND RELEVANCE

Consensus is lacking on the most appropriate weight-based dosing strategy for obese children. Prospective pharmacokinetic trials in obese children are needed to ensure therapeutic efficacy and enhance drug safety.

Prediction of Hemodynamic Response to Epinephrine via Model-Based System Identification

In this study, we present a system identification approach to the mathematical modeling of hemodynamic responses to vasopressor-inotrope agents. We developed a hybrid model called the latency-dose-response-cardiovascular (LDC) model that incorporated 1) a low-order lumped latency model to reproduce the delay associated with the transport of vasopressor-inotrope agent and the onset of physiological effect, 2) phenomenological dose-response models to dictate the steady-state inotropic, chronotropic, and vasoactive responses as a function of vasopressor-inotrope dose, and 3) a physiological cardiovascular model to translate the agent's actions into the ultimate response of blood pressure. We assessed the validity of the LDC model to fit vasopressor-inotrope dose-response data using data collected from five piglet subjects during variable epinephrine infusion rates. The results suggested that the LDC model was viable in modeling the subjects' dynamic responses: After tuning the model to each subject, the r (2) values for measured versus model-predicted mean arterial pressure were consistently higher than 0.73. The results also suggested that intersubject variability in the dose-response models, rather than the latency models, had significantly more impact on the model's predictive capability: Fixing the latency model to population-averaged parameter values resulted in r(2) values higher than 0.57 between measured versus model-predicted mean arterial pressure, while fixing the dose-response model to population-averaged parameter values yielded nonphysiological predictions of mean arterial pressure. We conclude that the dose-response relationship must be individualized, whereas a population-averaged latency-model may be acceptable with minimal loss of model fidelity.

Phenylephrine eye drops in pediatric patients undergoing ophthalmic surgery: incidence, presentation, and management of complications during general anesthesia

BACKGROUND

Phenylephrine eye drops are widely used as mydriatic agent to reach the posterior segment of the eye. In literature, many reports suggest a systemic absorption of this agent as a source of severe adverse drug reactions. Hence, we reviewed our experience with topical phenylephrine in ophthalmic surgery.

METHODS

In May 2006, following US guidelines publication, a standard operating procedure was issued in our operating rooms to standardize the use of phenylephrine eye drops in our practice. Two years later, after the occurrence of a cluster of serious adverse drug reactions in infants undergoing surgery, a review of phenylephrine safety and systemic complications incidence was performed.

RESULTS

We observed 451 pediatric patients, and 187 met the inclusions criteria: Among them, 4 experienced hemodynamic complications due to phenylephrine eye drops. The incidence of major complications was 2.1%.

CONCLUSIONS

Two different patterns of side effects occurred. The first one was a cardiovascular derangement with severe hypertension and heart rate alterations; the other one involved exclusively pulmonary circuit causing early edema. These clinical manifestations, their duration, and treatment responses are all explainable by alfa1-adrenergic action of phenylephrine. This hypothetic pathogenesis has been confirmed also by the usefulness of direct vasodilators (anesthetic agents) and by the negative outcome occurred in the past with the use of beta-blockers.

Pharmacokinetics, hemodynamic and metabolic effects of epinephrine to prevent post-operative low cardiac output syndrome in children

Introduction

The response to exogenous epinephrine (Ep) is difficult to predict given the multitude of factors involved such as broad pharmacokinetic and pharmacodynamic between-subject variabilities, which may be more pronounced in children. We investigated the pharmacokinetics and pharmacodynamics of Ep, co-administered with milrinone, in children who underwent open heart surgical repair for congenital defects following cardiopulmonary bypass, including associated variability factors.

Methods

Thirty-nine children with a high risk of low cardiac output syndrome were prospectively enrolled. Ep pharmacokinetics, hemodynamic and metabolic effects were analyzed using the non-linear mixed effects modeling software MONOLIX. According to the final model, an Ep dosing simulation was suggested.

Results

Ep dosing infusions ranged from 0.01 to 0.23 μg.kg^-1.min^-1 in children whose weight ranged from 2.5 to 58 kg. A one-compartment open model with linear elimination adequately described the Ep concentration-time courses. Bodyweight (BW) was the main covariate influencing clearance (CL) and endogenous Ep production rate (q0) via an allometric relationship: CL(BWi) = θ_CL x (BWi)^3/4 and q0(BWi) = θ_q0 x (BWi )^3/4. The increase in heart rate (HR) and mean arterial pressure (MAP) as a function of Ep concentration were well described using an Emax model. The effect of age was significant on HR and MAP basal level parameters. Assuming that Ep stimulated the production rate of plasma glucose, the increases in plasma glucose and lactate levels were well described by turnover models without any significant effect of age, BW or exogenous glucose supply.

Conclusions

According to this population analysis, the developmental effects of BW and age explained a part of the pharmacokinetic and pharmacodynamics between-subject variabilities of Ep administration in critically ill children. This approach ultimately leads to a valuable Ep dosing simulation which should help clinicians to determine an appropriate a priori dosing regimen.

The Effect of Epinephrine on Coronary Flow in the Setting of a Systemic-to-Pulmonary Artery Shunt

Background:

Indirect clinical evidence suggests that coronary blood flow (CBF) is altered in patients palliated with systemic-to-pulmonary artery shunts (SPSs). The addition of epinephrine may exert additional effects.

Methods:

A total of 11 newborn piglets underwent placement of a 3.5- to 4-mm graft between the innominate artery and the pulmonary artery. Doppler probes measured flow continuously in the aorta (aortic flow [AoF]), pulmonary artery and left coronary artery at baseline (SPS closed), SPS open, and during epinephrine administration (SPS closed and open). Each animal served as its own control. Systolic and diastolic CBF, resistance (coronary vascular resistance index [CVRI]), and myocardial oxygen supply demand ratio were calculated.

Results:

Opening the SPS increased AoF and decreased systolic and diastolic pressure from baseline, with and without the presence of epinephrine. The CBF and CVRI decreased on opening the SPS in the presence of epinephrine. The decrease occurred only in diastole and was proportional to pulmonary-to-systemic flow ratio (Qp/Qs). Epinephrine infusion itself reduced CVRI with SPS closed, but there was little further decrease on opening SPS. Myocardial oxygen supply–demand ratio decreased on opening SPS at baseline and with epinephrine.

Conclusions:

This study suggests that SPS decreases CBF, especially in the presence of a higher Qp/Qs and epinephrine. The mechanism is largely due to the decrease in diastolic pressure and the inability of the coronary arteries to compensate with vasodilation.

Principles of therapeutic drug monitoring

Therapeutic drug monitoring (TDM) is central to optimize drug efficacy in children, because the pharmacokinetics and pharmacodynamics of most drugs differ greatly between children and adults. Many factors should be analyzed to implement TDM in the pediatric population, including a validated pharmacological parameter and an analytical method adapted to children as limited sampling volumes and high sensitivity are required. The use of population approaches, new analytical methods such as saliva and dried blood spots, and pharmacodynamic monitoring give attractive options to improve TDM, individualize therapy in order to optimize efficacy and reduce adverse drug reactions.

Isoproterenol stimulates 5'-AMP-activated protein kinase and fatty acid oxidation in neonatal hearts

Isoproterenol increases phosphorylation of LKB, 5'-AMP-activated protein kinase (AMPK), and acetyl-CoA carboxylase (ACC), enzymes involved in regulating fatty acid oxidation. However, inotropic stimulation selectively increases glucose oxidation in adult hearts. In the neonatal heart, fatty acid oxidation becomes a major energy source, while glucose oxidation remains low. This study tested the hypothesis that increased energy demand imposed by isoproterenol originates from fatty acid oxidation, secondary to increased LKB, AMPK, and ACC phosphorylation. Isolated working hearts from 7-day-old rabbits were perfused with Krebs solution (0.4 mM palmitate, 11 mM glucose, 0.5 mM lactate, and 100 mU/l insulin) with or without isoproterenol (300 nM). Isoproterenol increased myocardial O(2) consumption (in J·g dry wt(-1)·min(-1); 11.0 ± 1.4, n = 8 vs. 7.5 ± 0.8, n = 6, P < 0.05), and the phosphorylation of LKB (in arbitrary density units; 0.87 ± 0.09, n = 6 vs. 0.59 ± 0.08, n = 6, P < 0.05), AMPK (0.82 ± 0.08, n = 6 vs. 0.51 ± 0.06, n = 6, P < 0.05), and ACC-β (1.47 ± 0.14, n = 6 vs. 0.97 ± 0.07, n = 6, P < 0.05), with a concomitant decrease in malonyl-CoA levels (in nmol/g dry wt; 0.9 ± 0.9, n = 8 vs. 7.5 ± 1.3, n = 8, P < 0.05) and increase in palmitate oxidation (in nmol·g dry wt(-1)·min(-1); 272 ± 45, n = 8 vs. 114 ± 9, n = 6, P < 0.05). Glucose and lactate oxidation were increased (in nmol·g dry wt(-1)·min(-1); 253 ± 75, n = 8 vs. 63 ± 15, n = 9, P < 0.05 and 246 ± 43, n = 8 vs. 82 ± 11, n = 6, P < 0.05, respectively), independent of alterations in pyruvate dehydrogenase phosphorylation, but occurred secondary to a decrease in acetyl-CoA content and acetyl-CoA-to-free CoA ratio. As acetyl-CoA levels decrease in response to isoproterenol, despite an acceleration of the rates of palmitate and carbohydrate oxidation, these data suggest net rates of acetyl-CoA utilization exceed the net rates of acetyl-CoA generation.

Childhood obesity and survival after in-hospital pediatric cardiopulmonary resuscitation

OBJECTIVE

We hypothesized that childhood obesity would be associated with decreased likelihood of survival to hospital discharge after in-hospital, pediatric cardiopulmonary resuscitation (CPR).

METHODS

We reviewed 1477 consecutive, pediatric, CPR index events (defined as the first CPR event during a hospitalization in that facility for a patient <18 years of age) reported to the American Heart Association National Registry of Cardiopulmonary Resuscitation between January 2000 and July 2004. The primary outcome was survival to hospital discharge. A total of 1268 index subjects (86%) with complete registry data were included for analysis. Children were classified as obese (> or =95th weight-for-length percentile if <2 years of age or > or =95th BMI-for-age percentile if > or =2 years of age) or underweight (<5th weight-for-length percentile if <2 years of age or <5th BMI-for-age percentile if > or =2 years of age), with adjustment for gender.

RESULTS

Obesity was noted for 213 (17%) of 1268 subjects and underweight for 571 (45%) of 1268 subjects. Obesity was more likely to be associated with male gender, noncardiac medical illness, and cancer and inversely associated with heart failure. Underweight was more likely to be associated with male gender, cardiac surgery, and prematurity and inversely associated with age and cancer. Self-reported, process-of-care, CPR quality was generally worse for obese children. With adjustment for important potential confounding factors, obesity was independently associated with worse odds of event survival (adjusted odds ratio: 0.58 [95% confidence interval: 0.35-0.76]) and survival to hospital discharge (adjusted odds ratio: 0.62 [95% confidence interval: 0.38-0.93]) after in-hospital, pediatric CPR. Underweight was not associated with worse outcomes.

CONCLUSIONS

Childhood obesity is associated with a lower rate of survival to hospital discharge after in-hospital, pediatric CPR.

Pediatric models for adult target-controlled infusion pumps

Target-controlled infusion (TCI) pumps currently do not satisfactorily cater for the pediatric population, particularly for those under 5 years. Growth and development are two major aspects of children not readily apparent in adults, and these two aspects influence clearance (CL) and volume of distribution (V). In simple terms, V determines initial dose, and CL determines infusion rate at steady state. Three major covariates (size, age, and organ function) contribute to parameter variability in children. Size can be standardized for clearance in a 70-kg person using the allometric (3/4) power model. Remifentanil, a drug cleared by hydrolysis, can be modeled in all age groups by simple application of this model using a standardized clearance of 2790 ml x min(-1) for a 70-kg person. Allometry alone is insufficient to predict clearance in neonates and infants from adult parameters for most drugs used in anesthesia. The addition of a model describing maturation is required. The sigmoid Emax or Hill model has been found useful for describing this maturation process. Propofol maturation has been described with a mature clearance of 1.83 l x min(-1) x 70 kg(-1), a maturation half-time (TM(50)) of 44 weeks and a Hill coefficient of 4.9. Organ function also affects clearance, and propofol clearance is reduced in neonates and infants after cardiac surgery. Although pharmacokinetics (PK) in children is receiving increasing attention and is eminently programmable into a TCI device, pharmacodynamic (PD) measures in children remain poorly defined, partly because the depth of anesthesia monitoring are inadequate. Both PK and PD are necessary for safe use of TCI pumps.

Population pharmacokinetics and dosing regimen design of milrinone in preterm infants

AIMS

To define the pharmacokinetics of milrinone in very preterm infants and determine an optimal dose regimen to prevent low systemic blood flow in the first 12 h after birth.

METHODS

A prospective open-labelled, dose-escalation pharmacokinetic study was undertaken in two stages. In stage one, infants received milrinone at 0.25 microg/kg/min (n = 8) and 0.5 microg/kg/min (n = 11) infused from 3 to 24 h of age. Infants contributed 4-5 blood samples for concentration-time data which were analysed using a population modelling approach. A simulation study was used to explore the optimal dosing regimen to achieve target milrinone concentrations (180-300 ng/ml). This milrinone regimen was evaluated in stage two (n = 10).

RESULTS

Infants (n = 29) born before 29 weeks gestation were enrolled. Milrinone pharmacokinetics were described using a one-compartment model with first-order elimination rate, with a population mean clearance (CV%) of 35 ml/h (24%) and volume of distribution of 512 ml (21%) and estimated half-life of 10 h. The 0.25 and 0.5 microg/kg/min dosage regimens did not achieve optimal milrinone concentration-time profiles to prevent early low systemic blood flow. Simulation studies predicted a loading infusion (0.75 microg/kg/min for 3 h) followed by maintenance infusion (0.2 microg/kg/min until 18 h of age) would provide an optimal milrinone concentration profile. This was confirmed in stage two of the study.

CONCLUSION

Population pharmacokinetic modelling in the preterm infant has established an optimal dose regimen for milrinone that increases the likelihood of achieving therapeutic aims and highlights the importance of pharmacokinetic studies in neonatal clinical pharmacology.

Application of two-point assay of digoxin serum concentration in studying population pharmacokinetics in Egyptian pediatric patients with heart failure: does it make sense?

Digoxin pharmacokinetics (PK) was studied among a selected group of Egyptian pediatric patients (n = 40) with an age range of 0.33 to 15 years. All the patients had heart failure and were maintained on i.v. digoxin (10 microg/kg/d in 2 equal doses). For population PK analysis, 2 serum samples of digoxin were taken per patient. From 30 patients' trough (before the next dose) and 4 hours postdose samples were obtained, while in the other 10 patients, 0.5- and 6-hour postdose samples were taken. Serum concentrations were measured by fluorescence polarization immunoassay. PK modeling was performed using NONMEM software on log-transformed serum digoxin data. The best structural covariate-free model was a linear 2-compartment model with an exponential error model for intersubject variability and an additive model for intrasubject variability. Serum creatinine (SCR) was a significant covariate for clearance. The final population PK parameters were CL (L/h) = 0.388 - [0.78 x (SCR-0.6)], V1 (L/kg) = 1.38, Q (L/h/kg) = 0.48, V2 (L/kg) = 9.11, where CL is the total body clearance, V1 and V2 are the apparent volumes of distribution in the central and peripheral compartments, and Q is intercompartment clearance. A bootstrap resampling for internal validation achieved excellent agreement with the original data sets for PK parameters. In conclusion, 2 points of digoxin concentration allow good regression analysis for clearance-covariate relationship. The inclusion of SCR into the final model might allow better selection of initial maintenance dose of the drug. A prospective study on larger sample size of pediatric patients is recommended for clinical validation of the final model.

Dosing of medications in morbidly obese patients in the intensive care unit setting

OBJECTIVE

To derive recommendations for the dosing of commonly used medications in the morbidly obese patient in the ICU.

DATA SOURCES

Articles were obtained through computerized searches involving MEDLINE. The bibliographies of retrieved publications and textbooks were reviewed for additional references.

STUDY SELECTION

All studies involving the pharmacokinetics or pharmacodynamics of medications in obese subjects or patients.

DATA EXTRACTION

The emphasis was on studies involving morbidly obese patients but, in the absence of such data, investigations involving lesser forms of obesity were extracted.

DATA SYNTHESIS

There is a paucity of data upon which to make recommendations for dosing commonly used medications in the morbidly obese patient in the ICU, although recommendations were provided based on the available information.

CONCLUSIONS

There is clearly a need for more investigations involving dosing regimens of medications in the morbidly obese population. Until such studies are available, the clinician must try to derive the best dosing regimens for medications based on the limited pharmacokinetic data available for some agents and clinical judgement.

Dosing of medications in morbidly obese patients in the intensive care unit setting

OBJECTIVE

To derive recommendations for the dosing of commonly used medications in the morbidly obese patient in the ICU.

DATA SOURCES

Articles were obtained through computerized searches involving MEDLINE. The bibliographies of retrieved publications and textbooks were reviewed for additional references.

STUDY SELECTION

All studies involving the pharmacokinetics or pharmacodynamics of medications in obese subjects or patients.

DATA EXTRACTION

The emphasis was on studies involving morbidly obese patients but, in the absence of such data, investigations involving lesser forms of obesity were extracted.

DATA SYNTHESIS

There is a paucity of data upon which to make recommendations for dosing commonly used medications in the morbidly obese patient in the ICU, although recommendations were provided based on the available information.

CONCLUSIONS

There is clearly a need for more investigations involving dosing regimens of medications in the morbidly obese population. Until such studies are available, the clinician must try to derive the best dosing regimens for medications based on the limited pharmacokinetic data available for some agents and clinical judgement.

Population pharmacokinetics of digoxin in pediatric patients

Digoxin pharmacokinetics were studied in a pediatric population with an age range of 6 days to 1 year using the population pharmacokinetic approach. Digoxin data were analyzed by mixed-effects modeling according to a one-compartment steady-state pharmacokinetic model using NONMEM software. The final model selected for the population prediction of digoxin clearance in pediatric patients was as follows: [equation: see text] Individual empirical Bayesian estimates were generated on the basis of the population estimates and were used to correlate the optimum dose of digoxin and patient age according to the following equation: [equation: see text] This equation and its derived nomogram may be used for the initial dosing of digoxin in children aged between 0 and 1 year. The use of this nomogram in routine monitoring requires further pharmacokinetic and clinical validation.

Population pharmacokinetics of digoxin in Egyptian pediatric patients: impact of one data point utilization

A population pharmacokinetic (PK) study was designed to estimate the PK parameters of digoxin among a selected group of Egyptian pediatric patients (n = 30) with mean age +/- SD and body weight +/- SD of 8.88 +/- 3.01 years and 23.9 +/- 5.8 kg, respectively. All patients had heart failure and were maintained on digoxin given orally. Nonlinear mixed effect modeling software version 5 (NONMEM Project Group, San Francisco, CA) and one-compartment modeling were used for fitting the data. A one-trough steady-state plasma concentration level of digoxin was used in the analysis. The population mean estimates for clearance (CL/f) and volume of distribution (V/f), in which f represents oral bioavailability, were 8.61 L/h and 450 L, respectively. Because of the limited number of samples per patient, regression analysis could not detect a correlation between patient covariates and estimated PK parameters. The analysis did not converge to obtain good parameter estimates. At least two samples per patient should be used to improve the PK estimation and allow better analysis of the relation between the potential covariates and estimated PK parameters.

Pharmacology of inotropic agents in infants and children

Inotropic agents are drugs which increase the stroke work of the heart at a given pre-load and after-load. All of these agents work through a final common pathway involving the modulation of calcium interactions with various myocardial contractile proteins. The agents employed with pediatric patients include the cardial glycosides, catecholamine beta-agonists and the selective phosphodiesterase III inhibitors. Digoxin is the prototypic cardiac glycoside which has a long history of safe and effective use in infants and children. Its utility in improving right ventricular dysfunction in patients with cor pulmonale leading to biventricular dysfunction makes it ideally suited to the pediatric population. Monitoring digoxin pharmacokinetics in infants is confounded by the presence of an endogenous digoxin-like substance. Nevertheless, the drug is well suited for subacute and chronic myocardial support. In contrast, the catecholamines are the drugs of choice for acute intervention. Their pharmacokinetics permit rapid dosing titration. In infants and children the greatest experience has been accrued with dopamine, a mixed alpha- and beta-agonist but both epinephreine and norepinephrine are being used with increasing frequency as the need for drugs with increased potency and pressor activity becomes more common. The phosphodiesterase inhibitors amrinone and milrinone are the newest additions to our therapeutic armamentarium. In addition to their modest inotropic effects, amrinone and to a greater extent, milrinone offer significant pulmonary vasodilatation as part of their therapeutic package. These effects occur with little or any impact on myocardial oxygen consumpton while their lusitropic effects enhance relaxation in hypertrophied ventricular muscle. Of the two agents milrinone is probably preferred due to its greater therapeutic index and shorter elimination half-life. All of these agents remain important tools in the care of critically ill infants and children. The rational use of these drugs based upon their pharmacokinetic and pharmacodynamic properties is essential to achieve their optimal effects.

Effects of drugs on glucose measurements with handheld glucose meters and a portable glucose analyzer

Thirty drugs used primarily in critical care and hospital settings were tested in vitro to observe interference on glucose measurements with 6 hand-held glucose meters and a portable glucose analyzer. Paired differences of glucose measurements between drug-spiked samples and unspiked control samples were calculated to determine bias. A criterion of +/- 6 mg/dL was used as the cutoff for interference. Ascorbic acid interfered with the measurements on all glucose devices evaluated. Acetaminophen, dopamine, and mannitol interfered with glucose measurements on some devices. Dose-response relationships help assessment of drug interference in clinical use. High dosages of these drugs may be given to critically ill patients or self-administered by patients without medical supervision. Package inserts for the glucose devices may not provide adequate warning information. Hence, we recommend that clinicians choose glucose devices carefully and interpret results cautiously when glucose measurements are performed during or after drug interventions.

Hemodynamic support in fluid-refractory pediatric septic shock

OBJECTIVE

Assess outcome in children treated with inotrope, vasopressor, and/or vasodilator therapy for reversal of fluid-refractory and persistent septic shock.

DESIGN

Survey; case series.

SETTING

Three pediatric hospitals.

PATIENTS

Fifty consecutive patients with fluid-refractory septic shock with a pulmonary artery catheter within 6 hours of resuscitation.

INTERVENTIONS

Patients were categorized according to hemodynamic state and use of inotrope, vasopressor, and/or vasodilator therapy to maintain cardiac index (CI) >3.3 L/min/m2 and systemic vascular resistance >800 dyne-sec/cm/m to reverse shock.

OUTCOME MEASURES

Hemodynamic state, response to class of cardiovascular therapy, and mortality.

RESULTS

After fluid resuscitation, 58% of the children had a low CI and responded to inotropic therapy with or without a vasodilator (group I), 20% had a high CI and low systemic vascular resistance and responded to vasopressor therapy alone (group II), and 22% had both vascular and cardiac dysfunction and responded to combined vasopressor and inotropic therapy (group III). Shock persisted in 36% of the children. Of the children in group I, 50% needed the addition of a vasodilator, and in group II, 50% of children needed the addition of an inotrope for evolving myocardial dysfunction. Four children showed a complete change in hemodynamic state and responded to a switch from inotrope to vasopressor therapy or vice versa. The overall 28-day survival rate was 80% (group I, 72%; group II, 90%; group III, 91%).

CONCLUSIONS

Unlike adults, children with fluid-refractory shock are frequently hypodynamic and respond to inotrope and vasodilator therapy. Because hemodynamic states are heterogeneous and change with time, an incorrect cardiovascular therapeutic regimen should be suspected in any child with persistent shock. Outcome can be improved compared with historical literature.

Clinical pharmacokinetics of vasodilators. Part II

Stimulating cardiac beta 1-adrenoceptors with oxyfedrine causes dilatation of coronary vessels and positive inotropic effects on the myocardium. beta 1-adrenergic agonists increase coronary blood flow in nonstenotic and stenotic vessels. The main indication for the use of the phosphodiesterase inhibitors pamrinone, mirinone, enoximone and piroximone is acute treatment of severe congestive heart failure. Theophylline is indicated for the treatment of asthma, chronic obstructive pulmonary disease, apnea in preterm infants ans sleep apnea syndrome. Severe arterial occlusive disease associated with atherosclerosis can be beneficially affected by elcosanoids. These drugs must be administered parenterally and have a half-life of only a few minutes. Sublingual or buccal preparations of nitrates are the only prompt method (within 1 or 2 min) of terminating anginal pain, except for biting nifedipine capsules. The short half-life (about 2.5 min) of nitroglycerin (glyceryl trinitrate) makes long term therapy impossible. Tolerance is a problem encountered with longer-acting nitric oxide donors. Knowledge of the pharmacokinetic properties of vasodilating drugs can prevent a too sudden and severe blood pressure decrease in patients with chronic hypertension. In considering the administration of a second dose, or another drug, the time necessary for the initially administered drug to reach maximal efficacy should be taken into account. In hypertensive emergencies urapidil, sodium nitroprusside, nitroglycerin, hydralazine and phentolamine are the drugs of choice, with the addition of beta-blockers during catecholamine crisis or dissecting aortic aneurysm. Childhood hypertension is most often treated with angiotensin-converting enzyme (ACE) inhibitors or calcium antagonists, primarily nifedipine. Because of the teratogenic risk involved with ACE inhibitors, extreme caution must be exercised when prescribing for adolescent females. The propagation of health benefits to breast-fed infants, combined with more women delaying pregnancy until their fourth decade, has entailed an increase in the need for hypertension management during lactation. Low dose hydrochlorothiazide, propranolol, nifedipine and enalapril or captopril do not pose enough of a risk of preclude breastfeeding in this group. The most frequently used antihypertensive agents during pregnancy are methyldopa, labetalol and calcium channel antagonists. Methyldopa and beta-blockers are the drugs of choice for treating mild to moderate hypertension. Prazosin and hydralazine are used to treat moderate to severe hypertension and hydralazine, urapidil or labetalol are used to treat hypertensive emergencies. The use of overly aggressive antihypertensive therapy during pregnancy should be avoided so that adequate uteroplacental blood flow is maintained. Methyldopa is the only drug accepted for use during the first trimester of pregnancy.

Toxicokinetics in infants and children in relation to the ADI and TDI

Age-dependent developmental changes in toxicokinetics occur in both rats and humans, particularly in relation to renal function and hepatic xenobiotic metabolism. These processes are immature in humans at birth, especially in the pre-term neonate, but mature rapidly over the first months of life. In consequence the duration of immaturity primarily corresponds to the period of suckling. Similar developmental changes occur in the neonatal rat over the first weeks of life. Rat pups start to consume some of the adult diet in the third week of life, prior to weaning, so that there is a potential for consumption of the adult diet during the period of immaturity. There is an extensive database on the pharmacokinetics of therapeutic drugs in infants and children. The elimination/clearance of many drugs is higher in children than in adults and this difference would apply to other xenobiotics. In consequence, children frequently will have lower body burdens than adults for the same daily intake of a chemical when this is expressed on a body weight basis, as used to describe the ADI (Acceptable Daily Intake) or TDI (Tolerable Daily Intake) (e.g. mg/kg body weight/day). Therefore, an increased safety or uncertainty factor for post-suckling infants and children is not required in relation to age-related differences in toxicokinetics. Indeed, the higher clearance of many xenobiotics (toxicokinetics) by children compared with adults may compensate, at least in part, for increased organ sensitivity (toxicodynamics) during development.

Pharmacokinetics of drugs used in critically ill adults

Critically ill patients exhibit a range of organ dysfunctions and often require treatment with a variety of drugs including sedatives, analgesics, neuromuscular blockers, antimicrobials, inotropes and gastric acid suppressants. Understanding how organ dysfunction can alter the pharmacokinetics of drugs is a vital aspect of therapy in this patient group. Many drugs will need to be given intravenously because of gastrointestinal failure. For those occasions on which the oral route is possible, bioavailability may be altered by hypomotility, changes in gastrointestinal pH and enteral feeding. Hepatic and renal dysfunction are the primary determinants of drug clearance, and hence of steady-state drug concentrations, and of efficacy and toxicity in the individual patient. Oxidative metabolism is the main clearance mechanism for many drugs and there is increasing recognition of the importance of decreased activity of the hepatic cytochrome P450 system in critically ill patients. Renal failure is equally important with both filtration and secretion clearance mechanisms being required for the removal of parent drugs and their active metabolites. Changes in the steady-state volume of distribution are often secondary to renal failure and may lower the effective drug concentrations in the body. Failure of the central nervous system, muscle, the endothelial system and endocrine system may also affect the pharmacokinetics of specific drugs. Time-dependency of alterations in pharmacokinetic parameters is well documented for some drugs. Understanding the underlying pathophysiology in the critically ill and applying pharmacokinetic principles in selection of drug and dose regimen is, therefore, crucial to optimising the pharmacodynamic response and outcome.

Pharmacology of pediatric resuscitation

The resuscitation of children from cardiac arrest and shock remains a challenging goal. The pharmacologic principles underlying current recommendations for intervention in pediatric cardiac arrest have been reviewed. Current research efforts, points of controversy, and accepted practices that may not be most efficacious have been described. Epinephrine remains the most effective resuscitation adjunct. High-dose epinephrine is tolerated better in children than in adults, but its efficacy has not received full analysis. The preponderance of data continues to point toward the ineffectiveness and possible deleterious effects of overzealous sodium bicarbonate use. Calcium chloride is useful in the treatment of ionized hypocalcemia but may harm cells that have experienced asphyxial damage. Atropine is an effective agent for alleviating bradycardia induced by increased vagal tone, but because most bradycardia in children is caused by hypoxia, improved oxygenation is the intervention of choice. Adenosine is an effective and generally well-tolerated agent for the treatment of supraventricular tachycardia. Lidocaine is the drug of choice for ventricular dysrhythmias, and bretylium, still relatively unexplored, is in reserve. Many pediatricians use dopamine for shock in the postresuscitative period, but epinephrine is superior. Most animal research on cardiac arrest is based on models with ventricular fibrillation that probably are not reflective of cardiac arrest situations most often seen in pediatrics.

Inotropes in the hypoplastic left heart syndrome: effects in an animal model

BACKGROUND

Despite substantial changes in the surgical treatment of children born with the hypoplastic left heart syndrome, overall mortality remains high. Although further improvements in outcomes appear to depend on more effective perioperative care, few experimental data exist to guide appropriate pharmacologic therapy in these infants. Because different inotropic agents may have different effects on the ratio of pulmonary to systemic flow (Qp/Qs), we hypothesize that they may not be equally effective at increasing oxygen delivery.

METHODS

In neonatal piglets (n = 6; 3.5 to 6.5 kg), we placed an innominate artery-to-pulmonary artery shunt, created an atrial septal defect, and then occluded right ventricular outflow. We examined the effects of a number of commonly used inotropic agents, administering high and low concentrations of dopamine (5 and 15 micrograms.kg-1 .min-1), dobutamine (5 and 15 micrograms.kg-1.min-1), and epinephrine (0.05 and 0.1 microgram /min).

RESULTS

Dobutamine at 15 micrograms.kg-1.min-1 increased the Qp/Qs ratio from 1.03 +/- 0.6 at baseline to 2.52 +/- 0.55 (p < 0.05) and decreased oxygen delivery from 50 +/- 4.3 to 36 +/- 1.7 mL/min (p < 0.1). The arterial-venous oxygen difference increased as oxygen delivery went down, going from 44% +/- 1% to 48% +/- 2% (p < 0.1). Epinephrine at 0.1 microgram.kg-1.min-1 decreased the Qp/Qs ratio from 1.23 +/- 0.21 to 0.82 +/- 0.08 (p < 0.05) and increased oxygen delivery from 40 +/- 9.7 to 56 +/- 1.7 mL/min (p < 0.05). Systemic venous oxygen saturation increased from 36% +/- 4.8% to 50% +/- 8.6% (p < 0.05). Although dopamine decreased the Qp/Qs ratio and increased oxygen delivery, these changes were not statistically significant.

CONCLUSIONS

Dopamine, dobutamine, and epinephrine all increased cardiac output but had substantially different effects on the Qp/Qs ratio and on oxygen delivery, possibly due to differential effects on systemic and pulmonary vascular resistances. This suggests that inotropic agents may not be equally beneficial in the clinical setting. Systemic venous oxygen saturation and the arteriovenous oxygen difference may help determine if a given inotrope improves oxygen delivery.