Pharmacokinetics and pharmacodynamics of nifedipine in children with bronchopulmonary dysplasia and pulmonary hypertension

Bronchopulmonary Dysplasia-Associated Pulmonary Hypertension: Basing Care on Physiology

Bronchopulmonary dysplasia (BPD) is the heterogeneous chronic lung developmental disease of prematurity, which is often accompanied by multisystem comorbidities. Pulmonary vascular disease and pulmonary hypertension (PH) contribute significantly to the pathogenesis and pathophysiology of BPD and dramatically influence the outcomes of preterm infants with BPD. When caring for those patients, clinicians should consider the multitude of phenotypic presentations that fall under the "BPD-PH umbrella," reflecting the need for matching therapies to specific physiologies to improve short- and long-term outcomes. Individualized management based on the patient's prenatal and postnatal risk factors, clinical course, and cardiopulmonary phenotype needs to be identified and prioritized to provide optimal care for infants with BPD-PH.

Virtual Clinical Trials Guided Design of an Age-Appropriate Formulation and Dosing Strategy of Nifedipine for Paediatric Use

The rapid onset of action of nifedipine causes a precipitous reduction in blood pressure leading to adverse effects associated with reflex sympathetic nervous system (SNS) activation, including tachycardia and worsening myocardial and cerebrovascular ischemia. As a result, short acting nifedipine preparations are not recommended. However, importantly, there are no modified release preparations of nifedipine authorised for paediatric use, and hence a paucity of clinical studies reporting pharmacokinetics data in paediatrics. Pharmacokinetic parameters may differ significantly between children and adults due to anatomical and physiological differences, often resulting in sub therapeutic and/or toxic plasma concentrations of medication. However, in the field of paediatric pharmacokinetics, the use of pharmacokinetic modelling, particularly physiological-based pharmacokinetics (PBPK), has revolutionised the ability to extrapolate drug pharmacokinetics across age groups, allowing for pragmatic determination of paediatric plasma concentrations to support drug licensing and clinical dosing. In order to pragmatically assess the translation of resultant dissolution profiles to the paediatric populations, virtual clinical trials simulations were conducted. In the context of formulation development, the use of PBPK modelling allowed the determination of optimised formulations that achieved plasma concentrations within the target therapeutic window throughout the dosing strategy. A 5 mg sustained release mini-tablet was successfully developed with the duration of release extending over 24 h and an informed optimised dosing strategy of 450 µg/kg twice daily. The resulting formulation provides flexible dosing opportunities, improves patient adherence by reducing frequent administration burden and enhances patient safety profiles by maintaining efficacious levels of consistent drug plasma levels over a sustained period of time.

The evolution of disease: chronic lung disease of infancy and pulmonary hypertension

PURPOSE OF REVIEW

Bronchopulmonary dysplasia (BPD) or chronic lung disease of infancy BPD was originally described 50 years ago, in 1967 by Northway et al. This article possesses two fundamental objectives to provide: a brief historical perspective on BPD; and an update relative to current notions of epidemiology, pathophysiology, evaluation, and clinical management of BPD complicated by vascular disease. The review highlights areas of consensus and ongoing uncertainty.

RECENT FINDINGS

The clinical cause and presentation of infants with BPD has evolved over the past several decades. Considerable improvements in neonatal care, including surfactant replacement therapies, antenatal steroids, nutritional support, ventilator management, and attention to the potential of oxygen toxicity, underlie the evolution of BPD. Most children with BPD improve over time. However, in the presence of vascular disease, the morbidity and mortality associated with BPD increases considerably. Though recent recommendations include procuring an echocardiogram to screen for pulmonary hypertension in infants with established BPD, there is less agreement surrounding the additional diagnostic and putative treatment modalities for infants with BPD and pulmonary hypertension. The indications, rationale, potential benefits, and risks of vasodilator therapy in BPD are discussed.

SUMMARY

The pediatric community has 50 years of experience with BPD. Past experience should be used to inform present and future diagnostic and treatment strategies. This review seeks to arm the clinician with evidence that motivates a physiology-based approach to the management of infants with BPD and pulmonary hypertension.

Pulmonary Vascular Disease in Bronchopulmonary Dysplasia

Pulmonary vascular disease and pulmonary hypertension (PH) contributes significantly to the pathogenesis, pathophysiology, and clinical course of infants with bronchopulmonary dysplasia (BPD). This article briefly reviews the impact of premature birth on the developing lung circulation, mechanisms that contribute to the development of PH in premature newborns, and the diagnostic evaluation and management of severe PH in infants with BPD.

Pediatric Pulmonary Hypertension: Guidelines From the American Heart Association and American Thoracic Society

Pulmonary hypertension is associated with diverse cardiac, pulmonary, and systemic diseases in neonates, infants, and older children and contributes to significant morbidity and mortality. However, current approaches to caring for pediatric patients with pulmonary hypertension have been limited by the lack of consensus guidelines from experts in the field. In a joint effort from the American Heart Association and American Thoracic Society, a panel of experienced clinicians and clinician-scientists was assembled to review the current literature and to make recommendations on the diagnosis, evaluation, and treatment of pediatric pulmonary hypertension. This publication presents the results of extensive literature reviews, discussions, and formal scoring of recommendations for the care of children with pulmonary hypertension.

Anaesthetic management of the child with co-existing pulmonary disease

Children with co-existing pulmonary disease have a wide range of clinical manifestations with significant implications for anaesthetists. Although there are a number of pulmonary diseases in children, this review focuses on two of the most common pulmonary disorders, asthma and bronchopulmonary dysplasia (BPD). These diseases share the physiology of bronchoconstriction and variably decreased flow in the airways, but also have unique physiological consequences. The anaesthetist can make a difference in outcomes with proper preoperative evaluation and appropriate preparation for surgery in the context of a team approach to perioperative care with implementation of a stepwise approach to disease management. An understanding of the importance of minimizing the risk for bronchoconstriction and having the tools at hand to treat it when necessary is paramount in the care of these patients. Unique challenges exist in the management of pulmonary hypertension in BPD patients. This review covers medical treatment, intraoperative management, and postoperative care for both patient populations.

Upregulation of vascular calcium channels in neonatal piglets with hypoxia-induced pulmonary hypertension

Inhibition of voltage-gated, L-type Ca(2+) (Ca(L)) channels by clinical calcium channel blockers provides symptomatic improvement to some pediatric patients with pulmonary arterial hypertension (PAH). The present study investigated whether abnormalities of vascular Ca(L) channels contribute to the pathogenesis of neonatal PAH using a newborn piglet model of hypoxia-induced PAH. Neonatal piglets exposed to chronic hypoxia (CH) developed PAH by 21 days, which was evident as a 2.1-fold increase in pulmonary vascular resistance in vivo compared with piglets raised in normoxia (N). Transpulmonary pressures (DeltaPtp) in the corresponding isolated perfused lungs were 20.5 +/- 2.1 mmHg (CH) and 11.6 +/- 0.8 mmHg (N). Nifedipine reduced the elevated DeltaPtp in isolated lungs of CH piglets by 6.4 +/- 1.3 mmHg but only reduced DeltaPtp in lungs of N piglets by 1.9 +/- 0.2 mmHg. Small pulmonary arteries from CH piglets also demonstrated accentuated Ca(2+)-dependent contraction, and Ca(2+) channel current was 3.94-fold higher in the resident vascular muscle cells. Finally, although the level of mRNA encoding the pore-forming alpha(1C)-subunit of the Ca(L) channel was similar between small pulmonary arteries from N and CH piglets, a profound and persistent upregulation of the vascular alpha(1C) protein was detected by 10 days in CH piglets at a time when pulmonary vascular resistance was only mildly elevated. Thus chronic hypoxia in the neonate is associated with the anomalous upregulation of Ca(L) channels in small pulmonary arteries in vivo and the resulting abnormal Ca(2+)-dependent resistance may contribute to the pathogenesis of PAH.

Pulmonary artery hypertension in formerly premature infants with bronchopulmonary dysplasia: clinical features and outcomes in the surfactant era

BACKGROUND

Although abnormal pulmonary vascular structure and function in preterm infants with bronchopulmonary dysplasia may predispose infants to pulmonary artery hypertension, little is known about the characteristics and outcomes of bronchopulmonary dysplasia-associated pulmonary artery hypertension in the surfactant era.

METHODS

We studied 42 premature infants (< 32 weeks of gestation) with bronchopulmonary dysplasia who were diagnosed as having pulmonary artery hypertension > or = 2 months after birth, between 1998 and 2006, at a median age of 4.8 months. Pulmonary artery hypertension was graded through echocardiography for all patients; 13 patients also underwent cardiac catheterization.

RESULTS

Eighteen (43%) of 42 patients had severe pulmonary artery hypertension (systemic or suprasystemic right ventricular pressure). Among 13 patients who underwent catheterization, the mean pulmonary artery pressure was 43 +/- 8 mmHg and the pulmonary vascular resistance index was 9.9 +/- 2.8 Wood units. In 12 patients, pulmonary artery pressure and pulmonary vascular resistance improved with 100% oxygen and 80 ppm inhaled nitric oxide but remained elevated. The pulmonary vascular resistance index decreased to 7.9 +/- 3.8 Wood units in 100% oxygen and to 6.4 +/- 3.1 Wood units with the addition of nitric oxide. Sixteen patients (38%) died during the follow-up period. Estimated survival rates were 64% +/- 8% at 6 months and 53% +/- 11% at 2 years after diagnosis of pulmonary artery hypertension. In multivariate analyses, severe pulmonary artery hypertension and small birth weight for gestational age were associated with worse survival rates. Among 26 survivors (median follow-up period: 9.8 months), pulmonary artery hypertension was improved, relative to its most severe level, in 24 patients (89%).

CONCLUSION

Premature infants with bronchopulmonary dysplasia and severe pulmonary artery hypertension are at high risk of death, particularly during the first 6 months after diagnosis of pulmonary artery hypertension.

Pulmonary Vascular Effects of Inhaled Nitric Oxide and Oxygen Tension in Bronchopulmonary Dysplasia

Pulmonary hypertension contributes significantly to morbidity and mortality in bronchopulmonary dysplasia (BPD), but little is known about the relative contribution of arterial tone, structural remodeling, and vessel density to pulmonary hypertension, especially in older patients. To determine the role of high pulmonary vascular tone in pulmonary hypertension, we studied the acute effects of oxygen tension, inhaled nitric oxide (iNO), and calcium channel blockers (CCB) in 10 patients with BPD who underwent cardiac catheterization for evaluation of pulmonary hypertension. During normoxic conditions, mean pulmonary arterial pressure (PAP) and pulmonary to systemic vascular resistance ratio (PVR/SVR) were 34 +/- 3 mm Hg and 0.42 +/- 0.07, respectively. In response to hypoxia, PAP and PVR/SVR increased by 50 +/- 8% and 82 +/- 14%, respectively (p < 0.01). Hyperoxia decreased PVR/SVR by 28 +/- 9% (p = 0.05). The addition of iNO treatment (20-40 ppm) to hyperoxia decreased PAP and PVR/SVR by 29 +/- 5% (p < 0.01) and 45 +/- 6% (p < 0.05) from baseline values, respectively, achieving near normal values. CCB did not alter PAP or PVR/SVR from baseline values. We conclude that hyperoxia plus iNO causes marked pulmonary vasodilatation in older patients with BPD, suggesting that heightened pulmonary vascular tone contributes to pulmonary vascular disease in BPD.

Recent advances in diagnosis and management of pulmonary hypertension in chronic lung disease

Pulmonary hypertension with elevated pulmonary vascular resistance is a common cardiovascular complication associated with increased morbidity and mortality in preterm infants with chronic lung disease. Injury to the developing pulmonary circulation results in structural and functional abnormalities of the pulmonary vasculature. Animal studies have demonstrated that disruption of angiogenesis may contribute to the failure of normal alveolarisation in chronic lung disease. Levels of vascular endothelial growth factor in bronchoalveolar lavage fluid are lower in infants with chronic lung disease compared to preterm controls. Supplemental oxygen is commonly used to prevent and treat pulmonary hypertension, although optimal arterial oxygen saturation levels remain uncertain. Other vasodilators such as inhaled nitric oxide appear promising, but as yet have not been evaluated in the form of randomised controlled trials. Further studies are required to investigate the long-term effectiveness of pulmonary vasodilator therapy.

The pulmonary circulation in bronchopulmonary dysplasia

Abnormalities of the pulmonary circulation are increasingly being recognized as a major contributor to the high morbidity and mortality of bronchopulmonary dysplasia. Historically, studies have focused on the importance of pulmonary hypertension to the pathophysiology of BPD, with the assumption that pulmonary vascular abnormalities are a secondary consequence of primary injury to the airspace. Recent studies suggest, however, that abnormalities of the pulmonary vasculature, including altered growth and structure, may directly contribute to the abnormal alveolarization that characterizes the condition. In this article, we briefly outline mechanisms of pulmonary vascular injury in infants at risk of BPD. We then focus on the recognition and management of pulmonary hypertension in these infants. Finally, we review how disordered pulmonary vascular growth may contribute to the pathogenesis of BPD and emphasize the importance of the reciprocal development of the airspace and the pulmonary circulation.

Enteral suspension of nifedipine for neonates. Part 1. Formulation of nifedipine suspension for hospital use

OBJECTIVE

To formulate an oral suspension of nifedipine for paediatric use and to assess its content uniformity as well as the microbiological and physical stabilities of the hypromellose solution that was used in the formulation.

METHOD

Six concentrations (0.5-3.0%) of hypromellose colloids and water as a blank were compounded with nifedipine, both as a powder and as crushed tablets, to a concentration of 1 mg/mL. Four different screening tests were used to find the most homogenous and dose-accurate combination. First, nifedipine suspensions were stored in vials for one month and visual homogenity of the redispersed suspensions was observed. Second, the homogenity of the suspensions was studied by measuring the nifedipine concentration from upper, middle and lower parts of the redispersed suspension. Next, the nifedipine concentration was measured from the suspensions immediately, 1 min and 2 min after shaking to ensure dose accuracy during the administration period. Finally, suspensions were packaged into oral disposable syringes and nifedipine concentrations were determined after one month of storage. Content uniformity of the packaged single-dose syringe suspensions was studied according to a method established by the European Pharmacopoeia. Microbiological stability, density, pH, osmolality, viscosity and surface tension of the hypromellose solution were studied over a 12-month storage period.

RESULTS

From the results of the screening tests of hypromellose solution, 1.0% hypromellose was chosen as the vehicle for nifedipine enteral suspensions, made from both crushed tablets and nifedipine powder. Nifedipine suspensions made from hypromellose 1.0% were easiest to redisperse as a homogenous solution, and it also appeared best on visual inspection. The content uniformity of the suspension complied with the test recommended by the European Pharmacopoeia. The 1.0% hypromellose solution was found to be microbiologically stable for 6 months and physically stable for 12 months.

Cytochrome P450 3A: ontogeny and drug disposition

The maturation of organ systems during fetal life and childhood exerts a profound effect on drug disposition. The maturation of drug-metabolising enzymes is probably the predominant factor accounting for age-associated changes in non-renal drug clearance. The group of drug-metabolising enzymes most studied are the cytochrome P450 (CYP) superfamily. The CYP3A subfamily is the most abundant group of CYP enzymes in the liver and consists of at least 3 isoforms: CYP3A4, 3A5 and 3A7. Many drugs are mainly metabolised by the CYP3A subfamily. Therefore, maturational changes in CYP3A ontogeny may impact on the clinical pharmacokinetics of these drugs. CYP3A4 is the most abundantly expressed CYP and accounts for approximately 30 to 40% of the total CYPcontent in human adult liver and small intestine. CYP3A5 is 83% homologous to CYP3A4, is expressed at a much lower level than CYP3A4 in the liver, but is the main CYP3A isoform in the kidney. CYP3A7 is the major CYP isoform detected in human embryonic, fetal and newborn liver, but is also detected in adult liver, although at a much lower level than CYP3A4. Substrate specificity for the individual isoforms has not been fully elucidated. Because of large interindividual differences in CYP3A4 and 3A5 expression and activity, genetic polymorphisms have been suggested. However, although some gene mutations have been identified, the impact of these mutations on the pharmacokinetics of CYP3A substrates has to be established. Ontogeny of CYP3A activity has been studied in vitro and in vivo. CYP3A7 activity is high during embryonic and fetal life and decreases rapidly during the first week of life. Conversely, CYP3A4 is very low before birth but increases rapidly thereafter, reaching 50% of adult levels between 6 and 12 months of age. During infancy, CYP3A4 activity appears to be slightly higher than that of adults. Large interindividual variations in CYP3A5 expression and activity were observed during all stages of development, but no apparent developmental pattern of CYP3A5 activity has been identified to date. Profound changes occur in the activity of CYP3A isoforms during all stages of development. These changes have, in many instances, proven to be of clinical significance when treatment involves drugs that are substrates, inhibitors or inducers of CYP3A. Investigators and clinicians should consider the impact of ontogeny on CYP3A in both pharmacokinetic study design and data interpretation, as well as when prescribing drugs to children.

In vivo age-related changes in hepatic drug-oxidizing capacity in humans

Very few studies have been carried out looking at how the effects of drugs and their toxicity in humans change during their lifespan (developing and ageing). The purpose of this study is to review the literature on the changes in probe-drug metabolism, classified by cytochrome P450 (P450 or CYP) at five stages in life: neonates < 4 weeks, infants < 12 months, children < 19 years, young/mature adults 20-64 years, and elderly adults > 65 years. The main probe drugs include caffeine and theophylline, whose metabolism is catalysed by CYP1A2, tolbutamide, phenytoin and ibuprofen, catalysed by CYP2C9, amitriptyline and nortriptyline, catalysed by CYP2C19, acetaminophen, catalysed by CYP2E1 and lidocaine, midazolam and terfenadine, catalysed by 3A3/4. From the published in vivo studies two different patterns of drug metabolism can be identified: (i) activity is low immediately after birth, increases, then peaks at the young/mature adult level and, finally, decreases in old age (drugs catalysed by CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A3/4) and (ii) activity increases rapidly after birth to reach a level equivalent to that in the young/mature adult, then gradually decreases and finally decreasing faster in old age (drugs catalysed by CYP2E1). Further study of the changes in P450 with age is warranted to help prevent adverse reactions and to guide us in tailoring therapy better for the individual patient.

Pulmonary artery pressure changes in the very low birthweight infant developing chronic lung disease

Pulmonary artery pressure may be estimated non-invasively in the premature newborn infant because of its negative correlation with the time to peak velocity:right ventricular ejection time (TPV:RVET) ratio calculated from the pulmonary artery Doppler waveform. We studied 54 very low birthweight infants on days 1, 2, 3, 7, 14, 21, and 28 after birth. Thirty four infants developed chronic lung disease (CLD). Twenty did not and acted as controls. After correcting the TPV:RVET ratio for heart rate (TPV:RVET(c)), during the first 14 days the TPV:RVET(c) ratio rose progressively in both groups suggesting a fall in pulmonary artery pressure. This occurred at a significantly slower rate in the CLD group. From days 14 to 28 there was a significant fall in the ratio in the CLD group only, suggesting an increase in pulmonary artery pressure. Using CLD as the end point, a TPV:RVET(c) ratio < 0.54 on day 7 had a predictive value of 78% (sensitivity 73%, specificity 65%). This rose to a predictive value of 97% (sensitivity 88%, specificity 95%) on day 28. The non-invasive assessment of pulmonary artery pressure may be useful in the early clinical management of the very low birthweight infant at risk of developing CLD.