Drug disposition in neonates with patent ductus arteriosus

Predicting Volume of Distribution in Neonates: Performance of Physiologically Based Pharmacokinetic Modelling

The volume of distribution at steady state (Vss) in neonates is still often estimated through isometric scaling from adult values, disregarding developmental changes beyond body weight. This study aimed to compare the accuracy of two physiologically based pharmacokinetic (PBPK) Vss prediction methods in neonates (Poulin & Theil with Berezhkovskiy correction (P&T+) and Rodgers & Rowland (R&R)) with isometrical scaling. PBPK models were developed for 24 drugs using in-vitro and in-silico data. Simulations were done in Simcyp (V22) using predefined populations. Clinical data from 86 studies in neonates (including preterms) were used for comparison, and accuracy was assessed using (absolute) average fold errors ((A)AFEs). Isometric scaling resulted in underestimated Vss values in neonates (AFE: 0.61), and both PBPK methods reduced the magnitude of underprediction (AFE: 0.82-0.83). The P&T+ method demonstrated superior overall accuracy compared to isometric scaling (AAFE of 1.68 and 1.77, respectively), while the R&R method exhibited lower overall accuracy (AAFE: 2.03). Drug characteristics (LogP and ionization type) and inclusion of preterm neonates did not significantly impact the magnitude of error associated with isometric scaling or PBPK modeling. These results highlight both the limitations and the applicability of PBPK methods for the prediction of Vss in the absence of clinical data.

Gentamicin in Neonates with Hemodynamically Significant Patent Ductus Arteriosus

Background

Gentamicin has been shown to cause vasodilation in preclinical studies. Hemodynamically significant patent ductus arteriosus (hsPDA) is a commonly observed congenital heart disorder in preterm neonates. Concomitant gentamicin theoretically shall delay the closure/result in nonclosure of ductus arteriosus (DA). Similarly, hsPDA can alter the pharmacokinetics of gentamicin and so trough gentamicin concentrations. We carried out the present study to evaluate the association between gentamicin use and closure of hsPDA (treated with acetaminophen) as well as the effect of hsPDA on trough concentrations.

Methods

This study was a prospective, observational study that included 60 neonates diagnosed with hsPDA by echocardiography and 102 neonates without hsPDA. Demographic details, size of DA as per echocardiography at the end of treatment with acetaminophen, gentamicin-dosing regimen, and trough concentrations were collected. Standard definitions were adhered in classifying the gestational age, birth weights, and size of DA. The numerical values are reported in median (range).

Results

Neonates with hsPDA had significantly lower daily doses of gentamicin [4.5 (2.5-10), 7 (3.2-13) mg; P < 0.001] but longer duration of therapy [8 (3-14), 5 (3-7) days; P < 0.001] than those without hsPDA in very preterm neonates. No significant differences were observed in the trough concentrations of gentamicin between the groups. No association was observed between gentamicin use and closure of DA. However, those with successful closure of DA received gentamicin for a longer duration [6 (3-10), 4 (3-14) days; P < 0.05] that was independent of acetaminophen duration and had received higher cumulative doses of gentamicin.

Conclusion

In conclusion, we observed a significantly longer duration of gentamicin therapy in neonates with hsPDA compared to those without hsPDA. No significant differences were observed in the rates of closure of DA with concomitant gentamicin administration and gentamicin trough concentrations.

Preoperative sedation in children with congenital heart disease: 50% and 95% effective doses, hemodynamic effects, and safety of intranasal dexmedetomidine

STUDY OBJECTIVE

To determine the 50% and 95% effective doses (ED50 and ED95, respectively), hemodynamic effects, and safety of intranasal dexmedetomidine for preoperative sedation in pediatric patients with congenital heart disease (CHD) with a left-to-right shunt.

DESIGN

Double-blind sequential allocation trial.

SETTING

Pediatric preoperative waiting area.

PATIENTS

86 pediatric patients ASA physical status II-III scheduled for cardiac surgery, aged1-month to 6-years-old with left-to-right type CHD.

INTERVENTIONS

Children were divided into three groups according to age: infants (1 month-1 year), toddlers (1-3 years), and preschoolers (3-6 years). The first patient in all groups received intranasal dexmedetomidine (2 μg/kg), using the up-and-down Dixon method, and the and the next patient's dose was dependent on the previous patient's response.

MEASUREMENTS

Assessment using the Modified Observer's Assessment of Alertness/Sedation Scale and the Mask Acceptance Scale was performed before and every 5 min after treatment. Pulse oxygen saturation and heart rate were recorded at baseline, at 10-min intervals, and after admission to the operating room. Systolic pulmonary artery pressure was measured before anesthesia induction.

MAIN RESULTS

The respective ED₅₀ (95% confidence interval [CI]) and ED₉₅ (95% CI) values for preoperative sedation using intranasally administered dexmedetomidine were 3.1 (2.8-3.3) and 3.5 (3.3-4.0) μg/kg for infants; 3.4 (3.2-3.6) and 3.9 (3.7-4.4) μg/kg for toddlers; and 2.4 (2.2-2.6) and 2.9 (2.6-3.3) μg/kg for preschoolers. ED₅₀ was lower for preschoolers than for toddlers (p < 0.001) and infants (p = 0.044). No obvious difference in ED50 was found between infants and toddlers. There was no significant difference in sedation onset time among the groups, and no adverse events were observed during sedation in all patients.

CONCLUSIONS

Intranasal dexmedetomidine can be safety used for preoperative sedation in children with CHD and is effective for sedation when dosed appropriately. Trial registrationclinicaltrials.gov (ChiCTR2100047472); registered 20 June 2021.

Physiologically based pharmacokinetic modelling of acetaminophen in preterm neonates-The impact of metabolising enzyme ontogeny and reduced cardiac output

In preterm neonates, physiologically based pharmacokinetic (PBPK) models are suited for studying the effects of maturational and non-maturational factors on the pharmacokinetics of drugs with complex age-dependent metabolic pathways like acetaminophen (APAP). The aim of this study was to determine the impact of drug metabolising enzymes ontogeny on the pharmacokinetics of APAP in preterm neonates and to study the effect of reduced cardiac output (CO) on its PK using PBPK modelling. A PBPK model for APAP was first developed and validated in adults and then scaled to paediatric age groups to account for the effect of enzyme ontogeny. In preterm neonates, CO was reduced by 10%, 20%, and 30% to determine how this might affect APAP PK in preterm neonates. In all age groups, the predicted concentration-time profiles of APAP were within 5th and 95th percentile of the clinically observed concentration-time profiles and the predicted Cmax and AUC were within 2-folds of the reported parameters in clinical studies. Sulfation accounted for most of APAP metabolism in children, with the highest contribution of 68% in preterm neonates. A reduction in CO by up to 30% did not significantly alter the clearance of APAP in preterm neonates. The model successfully incorporated the ontogeny of drug metabolising enzymes involved in APAP metabolism and adequately predicted the PK of APAP in preterm neonates. A reduction in hepatic perfusion as a result of up to 30% reduction in CO has no effect on the PK of APAP in preterm neonates.

Preterm Physiologically Based Pharmacokinetic Model. Part II: Applications of the Model to Predict Drug Pharmacokinetics in the Preterm Population

BACKGROUND

Preterm neonates are usually not part of a traditional drug development programme, however they are frequently administered medicines. Developing modelling and simulation tools, such as physiologically based pharmacokinetic (PBPK) models that incorporate developmental physiology and maturation of drug metabolism, can be used to predict drug exposure in this group of patients, and may help to optimize drug dose adjustment.

OBJECTIVE

The aim of this study was to assess and verify the predictability of a preterm PBPK model using compounds that undergo diverse renal and/or hepatic clearance based on the knowledge of their disposition in adults.

METHODS

A PBPK model was developed in the Simcyp Simulator V17 to predict the pharmacokinetics (PK) of drugs in preterm neonates. Drug parameters for alfentanil, midazolam, caffeine, ibuprofen, gentamicin and vancomycin were collated from the literature. Predicted PK parameters and profiles were compared against the observed data.

RESULTS

The preterm PBPK model predicted the PK changes of the six compounds using ontogeny functions for cytochrome P450 (CYP) 1A2, CYP2C9 and CYP3A4 after oral and intravenous administrations. For gentamicin and vancomycin, the maturation of renal function was able to predict the exposure of these two compounds after intravenous administration. All PK parameter predictions were within a twofold error criteria.

CONCLUSION

While the developed preterm model for the prediction of PK behaviour in preterm patients is not intended to replace clinical studies, it can potentially help with deciding on first-time dosing in this population and study design in the absence of clinical data.

The relationship between trough drug concentrations and ductal closure in preterm infants treated with three-dose-oral ibuprofen

The aim of the present study was to characterize the pharmacokinetic profile of oral ibuprofen on consecutive 3 d by trough serum levels, and if possible to define a cut-off level for ductal closure in preterm infants. The study enrolled 20 preterm infants with gestational age ≤30 weeks, birth weight <1250 g and hemodynamically significant patent ductus arteriosus (hsPDA). Patients received oral ibuprofen at an initial dose of 10 mg/kg, followed by 5 mg/kg at 24 and 48 h. Patients were compared for serum ibuprofen levels in addition to their demographic and clinical data in case of their response to the treatment. hsPDA closed in 16 (80%) of the patients. Although mean ibuprofen levels on consecutive 3 d showed a plateau in general, ibuprofen serum levels on the first treatment day were statistically low in patients with unclosed hsPDA (p = 0.003). The optimal cut-off value for serum ibuprofen level on the first treatment day was measured as 5.5 mg/l with 100% sensitivity and 93% specificity. Serum ibuprofen level on the first treatment day seems to be an important factor for a successful ductal closure. Target concentration approach by the evaluation of trough level may be applicable to real-time dosing strategy.

Pharmacology in the very young: anaesthetic implications

Anaesthesia dosing in infants (0-2 years) should be based on pharmacokinetic-pharmacodynamic considerations and adverse effects profiles. Disease processes and treatments in this group are distinct from those in adults. Absorption, distribution and clearance change dramatically during this period because of maturation of anatomical and physiological processes as well as behavioural changes. Pharmacogenomic expression also matures in this period. Population-based and physiological-based pharmacokinetic modelling has improved the understanding of maturation and subsequent dose approximation. Postmenstrual, rather than postnatal, age is a reasonable measure for maturation. There remains a need for clinically applicable tools to assess pharmacodynamics which can provide response feedback; this has been achieved for neuromuscular monitoring, but not yet fully for depth of anaesthesia, sedation or pain. Morbidity and mortality associated with paediatric anaesthesia have historically been highest in this age group and continue to be so. Some of this morbidity was attributable to a poor understanding of developmental pharmacology; this facet continues to plague the specialty.

My child is unique; the pharmacokinetics are universal

The pharmacokinetic (PK) parameters that are important for dosing (e.g., clearance and volume) are well known. They are used in universal mathematical formulae that describe the time course of drug concentration. Additional formulae can be used to describe major covariate effects in children, such as size and maturation. PK parameters describing the time-concentration profile of a drug after administration are those for a typical individual in a population. These parameters are associated with variability. Further, any one individual may not be typical of the population studied. While size and maturation are two important considerations in children and assist with dosing estimation, there are also a number of additional PK covariates (e.g., organ function, disease, drug interactions, pharmacogenetics), and identifying these sources of variability allows us to individualize drug dose. Pharmacology is not simply an application of PK, and determinants of drug dose also require an understanding of the variability associated with pharmacodynamic response and a balancing of beneficial effects against unwanted effects. Each child is unique in this respect.

Gentamicin dosing for pediatric patients with congenital heart disease

Pediatric patients with congenital heart disease can have physiologies that alter the pharmacokinetics of certain medications, such as aminoglycosides. Currently, no literature describes the appropriate dosing of aminoglycoside antibiotics for infants and children with congenital heart disease. Patients were identified through the pharmacy and laboratory computer systems. Patients were included in the study if they were younger than 18 years, received gentamicin on the acute-care (nonintensive care) cardiology floor at the authors' institution, had structural congenital heart disease, and had a peak and trough level obtained at about the third dose or later. Cohort achievement of therapeutic peak and trough concentrations based on standard dosing guidelines was evaluated. The inclusion criteria were met by 48 patients (31 boys). Eight patients (17%) had baseline cyanosis. Cardiac surgery was performed for 23 patients (48%) during the same admission at which aminoglycoside therapy was initiated. A total of 27 patients (56%) received at least one other nephrotoxic medication at the time of aminoglycoside therapy. Six patients had undetectable serum trough levels. A therapeutic peak concentration was not achieved by 16.7% of the cohort, and 7.1% of the cohort did not achieve a therapeutic trough concentration. Pediatric patients with congenital heart disease may require alterations in gentamicin dosing. Close pharmacokinetic monitoring of aminoglycoside therapy for these patients is warranted to ensure attainment of goal concentrations.

Therapeutic drug monitoring of aminoglycosides in neonates

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

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.

Efecto de la administración concomitante de indometacina o ibuprofeno en la farmacocinética de amikacina en neonatos prematuros

OBJECTIVE

To evaluate whether the concomitant administration of ibuprofen or indomethacin plus amikacin may alter the latter drug s pharmacokinetic parameters, and hence amikacin plasma levels.

METHOD

Retrospective cohort study performed by reviewing the medical records of premature children with persistent ductus arteriosus receiving amikacin and ibuprofen, or amikacin and indomethacin. They were divided up into three groups: group 1: treatment with amikacin went before indomethacin or ibuprofen; group 2: simultaneously treated with amikacin and indomethacin; group 3: simultaneously treated with amikacin and ibuprofen. Pharmacokinetic parameters, distribution volume, and amikacin clearance were measured using the PKS program (a non-linear regression method). Half life was determined from previous parameters.

RESULTS

Twenty-eight patients were included. No statistically significant differences were found among pharmacokinetic parameters corresponding to each study group.

CONCLUSIONS

Further studies are needed with a greater number of patients and currently recommended doses to assess the influence of indomethacin and ibuprofen in the pharmacokinetics of amikacin in premature children with persistent ductus arteriosus.

Vancomycin

This review describes the use of vancomycin in neonates over the last three decades. Given the relation of late-onset neonatal septicaemia to outcome and the increase in coagulase-negative staphylococcal infection as causative organism, vancomycin remains an important antibacterial in the neonatal intensive care unit. The pharmacokinetic behaviour of vancomycin in neonates can be adequately described by a one- or two-compartment model and is mainly determined by postconceptional age and renal function. In neonates, a patent ductus arteriosus as well as treatment with indomethacin or extracorporeal membrane oxygenation (ECMO) leads to an increase in volume of distribution and a decrease in clearance. Microbiological studies in vitro have shown that an increase in vancomycin concentrations above the minimum inhibitory concentration does not result in more effective killing. The microbiological and clinical efficacy of vancomycin in neonates has only been studied explicitly in a restricted number of patients. There are no definitive data relating serum concentrations to effect in this patient group. Vancomycin-related nephrotoxicity and ototoxicity in neonates is rare, and no clear relation to serum concentrations has been demonstrated. Based on the pharmacokinetic profile of vancomycin in neonates, several administration regimens have been constructed. Recent guidelines have suggested that dosage can be independent of gestational age or postconceptional age in neonates without renal failure. In patients with renal failure, therapy can be adequately tailored by using a regimen based on serum creatinine. The usefulness of routine monitoring of peak serum concentrations is doubtful based on the current literature. Recent research demonstrates a shift towards taking only routine trough serum concentrations in order to optimise efficacy. Patients with renal failure and other special subpopulations, such as patients exposed to ECMO or indomethacin, need to be monitored more closely.

Pharmacokinetics of oral ibuprofen in premature infants

Patent ductus arteriosus (PDA) is a frequent complication in premature infants. So far, intravenous indomethacin is the standard mode of medical therapy in such patients but carries a risk of frequently occurring side effects. Ibuprofen, another nonsteroidal anti-inflammatory drug, has also been shown to be efficacious in closing ductus with lesser adverse effects after parenteral administration. However, limited data are available on the pharmacokinetics of intravenous ibuprofen in this population. Nonavailability of parenteral preparation and lack of information regarding pharmacokinetic disposition of ibuprofen in this subgroup of the population led the authors to conduct this pharmacokinetic study with oral ibuprofen. Twenty premature infants with a gestational age of 30.45 +/- 0.33 weeks and a birth weight of 1262.5 +/- 55.4 g (values given as mean +/- SEM) admitted to the neonatal unit were enrolled in this study. Ibuprofen was administered in a single oral dose of 10 mg/kg between 4 and 72 hours postnatally, and blood samples were collected through an indwelling vascular catheter at time 0 and 1, 2, 4, 8, 12, and 24 hours. Ibuprofen plasma concentrations were assayed by high-performance liquid chromatography. There was a large interindividual variability observed for plasma concentrations, elimination half-life (t1/2) (15.72 +/- 3.76 h), and area under the plasma concentration-time curve (AUC0-infinity) (402.60 +/- 79.67 micrograms.h/mL) in these babies. Variables such as gestational age, birth weight, and sex did not affect ibuprofen pharmacokinetics significantly (p > 0.05). Moreover, no correlation could be found between elimination half-life and gestational age (r = 0.02). Ibuprofen pharmacokinetics showed a wide variability in premature infants. The results of the present study warrant revising the oral dosage schedule to achieve comparable plasma concentrations of ibuprofen associated with successful closure of ductus, as reported in earlier studies.

Gentamicin pharmacokinetics in preterm infants with a patent and a closed ductus arteriosus

BACKGROUND AND AIM

A patent ductus arteriosus (PDA) may influence renal and hepatic blood flow and hence pharmacokinetics of drugs in neonates compared to neonates with a closed ductus arteriosus (CDA). A 10-percent difference of gentamicin pharmacokinetic parameters between PDA and CDA has been reported; but its implications are unclear. The relevance of this difference relative to the variability within the neonatal population was investigated.

METHODS

Twenty-four neonates (12 with a PDA and 12 with a CDA) treated with gentamicin were retrospectively included. Before closing treatment of the PDA, serum levels were drawn and analysed for regular therapeutic drug monitoring of gentamicin. Data were analysed using the standard two-stage approach (STS) and an iterative 2-stage Bayesian population analysis approach (It2B).

RESULTS

Both types of analysis showed no significant differences between both populations for gentamicin total body clearance per kg bodyweight (CL/kg). Volume of distribution per kg bodyweight (Vd/kg) tended to be larger and elimination rate (Kel) tended to be smaller in neonates with PDA. Multiple regression analysis showed for both populations highly significant correlations between total body clearance and body weight (p < 0.0001) or gestational age (p < 0.0001), and between volume of distribution and body weight (p < 0.0001) or gestational age (p < 0.0001).

CONCLUSION

Although neonates with a PDA may have small differences in gentamicin pharmacokinetics compared to neonates with a CDA, this is not relevant for clinical practice taking the variability within that population into account.

Common errors of drug administration in infants: causes and avoidance

Drug administration errors are common in infants. Although the infant population has a high exposure to drugs, there are few data concerning pharmacokinetics or pharmacodynamics, or the influence of paediatric diseases on these processes. Children remain therapeutic orphans. Formulations are often suitable only for adults; in addition, the lack of maturation of drug elimination processes, alteration of body composition and influence of size render the calculation of drug doses complex in infants. The commonest drug administration error in infants is one of dose, and the commonest hospital site for this error is the intensive care unit. Drug errors are a consequence of system error, and preventive strategies are possible through system analysis. The goal of a zero drug error rate should be aggressively sought, with systems in place that aim to eliminate the effects of inevitable human error. This involves review of the entire system from drug manufacture to drug administration. The nuclear industry, telecommunications and air traffic control services all practise error reduction policies with zero error as a clear goal, not by finding fault in the individual, but by identifying faults in the system and building into that system mechanisms for picking up faults before they occur. Such policies could be adapted to medicine using interventions both specific (the production of formulations which are for children only and clearly labelled, regular audit by pharmacists, legible prescriptions, standardised dose tables) and general (paediatric drug trials, education programmes, nonpunitive error reporting) to reduce the number of errors made in giving medication to infants.

Gentamicin pharmacokinetics in neonates with patent ductus arteriosus

OBJECTIVES

To determine the effect of patent ductus arteriosus on the pharmacokinetics of gentamicin in neonates and to examine whether any particular pharmacokinetic parameter is of value as a marker of patent ductus arteriosus.

DESIGN

Cohort study of neonates treated with gentamicin, according to a standard dosing protocol.

SETTING

A 24-bed, Level III, neonatal intensive care unit.

PATIENTS

Neonates treated with gentamicin at the time of admission to the neonatal intensive care unit, using a standard protocol, and who were < 36 wks of gestational age.

INTERVENTIONS

All patients received a gentamicin loading dose, and had gentamicin concentrations measured at 2 and 12 hrs after this dose, in order to determine pharmacokinetic parameters and calculate the optimum maintenance dose. Those neonates subsequently diagnosed to have patent ductus arteriosus, based on clinical suspicion and echocardiographic confirmation, were compared with those neonates without clinically suspected patent ductus arteriosus. Gentamicin pharmacokinetic parameters were calculated using a one-compartment model.

MEASUREMENTS AND MAIN RESULTS

A total of 322 courses of gentamicin were administered (patent ductus arteriosus, n = 106; control, n = 216). Gentamicin clearance was decreased in the patent ductus arteriosus group vs. the control group (40.02 vs. 44.73 mL/kg/hr; p < .0108). Volume of distribution was greater for patent ductus arteriosus patients (0.61 L/kg) than for controls (0.54 L/kg) (p < .0002). Also, volume of distribution was a useful marker for presence of patent ductus arteriosus, with a 92% specificity for patent ductus arteriosus.

CONCLUSIONS

Gentamicin dosing should be altered in neonates with patent ductus arteriosus to reflect the impact of higher volume of distribution and lower clearance. When the gentamicin volume of distribution exceeds 0.7 L/kg, it may be of predictive value for the presence of patent ductus arteriosus.