Pharmacokinetics of drugs for pediatric pulmonary hypertension

Treatment of pulmonary arterial hypertension in children

Pulmonary arterial hypertension (PAH) is a devastating illness causing already significant morbidity in childhood. Currently approved treatment options for children comprise the endothelin receptor antagonist bosentan, as well as the phosphodiesterase-5 inhibitor sildenafil. But PAH treatment has advanced significantly over the past decade, and new classes of targeted drug therapies, such as stimulators of the soluble guanylate cyclase (riociguat) or prostacyclin receptor agonists (selexipag), are currently evaluated regarding their efficacy and safety in children, in order to limit off-label use. Due to the different etiologies in children, such as PAH-CHD, there is no evidence that initial combination therapy in children is superior to a mono-therapy with respect to survival. Special attention should also be paid to the pharmacology of PAH drugs in children, which might be impacted by ontogeny or drug-drug-interactions. Therapeutic drug monitoring may be useful in pediatric patients. There is a clear need for more controlled studies of PAH medications, alone or in combination therapy in the pediatric age group. Data from clinical trials as well as from patient registries should be pooled to optimize drug development and evaluation, trial design, and evidence-based pharmacotherapy in pediatric patients with PAH. In this review, the current treatment options of pediatric PAH are summarized, and an overview of new treatment concepts, which are already evaluated in adults, is presented.

Bosentan Alters Endo- and Exogenous Bile Salt Disposition in Sandwich-Cultured Human Hepatocytes

Bosentan, a well-known cholestatic agent, was not identified as cholestatic at concentrations up to 200 µM based on the drug-induced cholestasis (DIC) index value, determined in a sandwich-cultured human hepatocyte (SCHH)-based DIC assay. To obtain further quantitative insights into the effects of bosentan on cellular bile salt handling by human hepatocytes, the present study determined the effect of 2.5-25 µM bosentan on endogenous bile salt levels and on the disposition of 10 µM chenodeoxycholic acid (CDCA) added to the medium in SCHHs. Bosentan reduced intracellular as well as extracellular concentrations of both endogenous glycochenodeoxycholic acid (GCDCA) and glycocholic acid in a concentration-dependent manner. When exposed to 10 µM CDCA, bosentan caused a shift from canalicular efflux to sinusoidal efflux of GCDCA. CDCA levels were not affected. Our mechanistic model confirmed the inhibitory effect of bosentan on canalicular GCDCA clearance. Moreover, our results in SCHHs also indicated reduced GCDCA formation. We confirmed the direct inhibitory effect of bosentan on CDCA conjugation with glycine in incubations with liver S9 fraction. SIGNIFICANCE STATEMENT: Bosentan was evaluated at therapeutically relevant concentrations (2.5-25 µM) in sandwich-cultured human hepatocytes. It altered bile salt disposition and inhibited canalicular secretion of glycochenodeoxycholic acid (GCDCA). Within 24 hours, bosentan caused a shift from canalicular to sinusoidal efflux of GCDCA. These results also indicated reduced GCDCA formation. This study confirmed a direct effect of bosentan on chenodeoxycholic acid conjugation with glycine in liver S9 fraction.

Oral drugs used to treat persistent pulmonary hypertension of the newborn

Introduction:Persistent Pulmonary Hypertension of the Newborn (PPHN) is a life-threatening neonatal condition, mostly treated with inhaled nitric oxide (iNO), intravenous prostaglandins, oral bosentan, sildenafil and tadalafil. However, the utility of non-oral agents is limited in PPHN for their side effects and inconvenient deliveries. Therefore, oral agents such as bosentan, sildenafil and tadalafil are becoming appealing for their satisfactory efficacy, easy mode of administration and acceptable side effects. Areas covered: We conducted a comprehensive search on Pubmed, Scopus, Web of Sciences concerning the use of bosentan, sildenafil and tadalafil to treat PPHN and summarized their efficacy, safety and pharmacokinetics. Expert opinion: Current randomized controlled trials (RCTs) have demonstrated the favorable responses and tolerable side effects of bosentan and sildenafil. Nevertheless, those RCTs are small and only one study has described the pharmacokinetics of sildenafil in neonates. Accordingly, bosentan, sildenafil and tadalafil remain off-label in clinical use. More well-designed RCTs with large samples and long-term follow-up and pharmacometrics studies are needed to demonstrate the efficacy, safety and pharmacokinetics of bosentan, sildenafil and tadalafil in PPHN.

A retrospective study on children with pulmonary arterial hypertension: A single-center experience

Objective:

The aim of this study was to evaluate children with pulmonary arterial hypertension (PAH) regarding epidemiological characteristics, clinical status with respect to the WHO functional class (WHO-FC), prognostic factors, and efficacy of medical treatment.

Methods:

A retrospective evaluation of 41 patients with PAH was made in the Pediatric Cardiology Unit, Gazi University Medical Faculty, between February 2006 and October 2015.

Results:

Of the 41 patients included in this study, 51.2% were female. The median age was 60 months at first evaluation. The median follow-up was 60 months. At the start of the treatment, 43.9% patients were receiving combined drug therapy, and this rate increased to 60.9% by the last evaluation. The median time of adding a new medication to the therapy was 20 months. The 1- and 5-year survival rates were 94% and 86%, respectively. At the time of diagnosis, only pro-brain natriuretic peptide (proBNP) levels were associated with mortality (p=0.004), but at the last evaluation, 6-min walking test, proBNP and uric acid levels, and WHO-FC were also associated with survival (p=0.02, p=0.001, p=0.002, and p=0.05, respectively).

Conclusion:

With current treatment choices in experienced centers, positive results are obtained with respect to the functional status and survival rates of patients with PAH. At the time of diagnosis, only proBNP had a prognostic value, whereas at the last evaluation, WHO-FC, 6-min walking test, proBNP, and uric acid were reported prognostic factors. For preventing rapid progression, determination of factors that have an effect on prognosis, in particular, is extremely important.

Oxidative stress assessment in intestine of newborn rats submitted to hypoxia and reoxygenation with tadalafil

Purpose:

To evaluate the functional and structural response of tadalafil effects in the intestinal mucosa, using an experimental model of hypoxia and reoxygenation injury in rats.

Methods:

The animals were divided into 4 groups: CTL, H/R, H/R+Td and M+Td. The newborn rats allocated in groups H/R, H/R+Td and M+Td were submitted twice a day, to a gas chamber with CO₂ at 100% for 10 minutes and afterward reoxygenation with O₂ at 98% for 10 minutes, in the three first days of life. Tadalafil dose was given to newborn of group H/R+Td and to the pregnant rat of group M+Td. Histological analysis was made with hematoxylin-eosin technique and oxidative stress through nitrite and nitrate levels and lipid peroxidation.

Results:

The histological analysis showed a reduction of mucosa alterations in the groups that received tadalafil. In the oxidative stress evaluation, occurred an increase of NO levels and less lipidic peroxidation in the ileum segments that received tadalafil.

Conclusion:

Tadalafil provides tissue protection when administered independently to both, pregnant or newborns.