A Randomized, Open-Label, 3-Way Crossover Study to Demonstrate Bioequivalence of Sildenafil Powder for Oral Suspension With Tablets Used Commercially and in Clinical Studies for the Treatment of Pulmonary Arterial Hypertension

The Complexity of Bariatric Patient's Pharmacotherapy: Sildenafil Biopharmaceutics and Pharmacokinetics before vs. after Gastric Sleeve/Bypass

Postbariatric altered gastrointestinal (GI) anatomy/physiology may significantly harm oral drug absorption and overall bioavailability. In this work, sildenafil, the first phosphodiesterase-5 (PDE5) inhibitor, was investigated for impaired postbariatric solubility/dissolution and absorption; this research question is of particular relevance since erectile dysfunction (ED) is associated with higher body mass index (BMI). Sildenafil solubility was determined both in vitro and ex vivo, using pre- vs. postsurgery gastric contents aspirated from patients. Dissolution tests were done in conditions mimicking the stomach before surgery, after sleeve gastrectomy (post-SG, pH 5), and after one anastomosis gastric bypass (post-OAGB, pH 7). Finally, these data were included in physiologically based pharmacokinetic (PBPK) modelling (GastroPlus®) to simulate sildenafil PK before vs. after surgery. pH-dependent solubility was demonstrated with low solubility (0.3 mg/mL) at pH 7 vs. high solubility at pH 1-5, which was also confirmed ex vivo with much lower solubility values in postbariatric gastric samples. Hampered dissolution of all sildenafil doses was obtained under post-OAGB conditions compared with complete (100%) dissolution under both presurgery and post-SG conditions. PBPK simulations revealed delayed sildenafil absorption in postbariatric patients (increased tmax) and reduced Cmax, especially in post-OAGB patients, relative to a presurgery state. Hence, the effect of bariatric surgery on sildenafil PK is unpredictable and may depend on the specific bariatric procedure. This mechanistically based analysis suggests a potentially undesirable delayed onset of action of sildenafil following gastric bypass surgery.

Population pharmacokinetics of riociguat in a pediatric population (aged ≥ 6 years) with pulmonary arterial hypertension

BACKGROUND

The PATENT-CHILD study investigated riociguat in children aged ≥ 6 to <18 years with pulmonary arterial hypertension (PAH) treated with tablets or an oral pediatric suspension based on bodyweight-adjusted dosing of up to 2.5 mg three times daily. PATENT-CHILD demonstrated an acceptable riociguat safety profile and individual plasma concentrations in pediatric patients were consistent with those in adult patients.

METHODS

Using the data set from PATENT-CHILD and building on existing population pharmacokinetic (PK) models for riociguat and its major metabolite (M1) in adults with PAH, a coupled riociguat-M1 PK model was developed. The final model developed incorporated a one-compartment model for riociguat, coupled to a one-compartment model for M1, allowing for presystemic formation of M1. It included allometric scaling exponents for bodyweight.

RESULTS

Apparent clearance of riociguat was similar in children and adult patients with PAH (median [interquartile range] 2.20 [1.75-3.44] and 2.08 L/h [1.55-2.97]). Factors contributing to lower PK exposure were lower riociguat maintenance dose in PATENT-CHILD, and a higher riociguat clearance in some adolescent patients, compared with adult patients. No effects of formulation, sex, or age on riociguat PK were observed. An exploratory PK/pharmacodynamics analysis found the increase in 6-min walking distance in pediatric patients treated with riociguat was not related to riociguat PK.

CONCLUSIONS

Body size is the main determinant of PK in growing children, and the model supports clinical data that, for children weighing < 50 kg, a bodyweight-adjusted dose of riociguat should be used to achieve a similar exposure to that observed in adults with PAH.

Model-Informed drug development of gastroretentive release systems for sildenafil citrate

Gastroretentive drug delivery systems (GRDDS) are modified-release dosage forms designed to prolong their residence time in the upper gastrointestinal tract, where some drugs are preferentially absorbed, and increase the drug bioavailability. This work aimed the development of a novel GRDDS containing 60 mg of sildenafil citrate, and the evaluation of the feasibility of the proposed formulation for use in the treatment of pulmonary arterial hypertension (PAH), for once a day administration, by using in silico pharmacokinetic (PK) modeling and simulations using GastroPlus^TM. The Model-Informed Drug Development (MIDD) approach was used in formulation design and pharmacokinetic exposure prospecting. A 2² factorial design with a central point was used for optimization of the formulation, which was produced by direct compression and characterized by some tests, including buoyancy test, assay, impurities, and in vitro dissolution. A compartmental PK model was built using the GatroPlus^TM software for virtual bioequivalence of the proposed formulations in comparison with the defined target release profile provided by an immediate release (IR) tablet formulation containing 20 mg of sildenafil administered three times a day (TID). The results of the factorial design showed a direct correlation between the dissolution rate and the amount of hydroxypropyl methyl cellulose (HPMC) in the formulations. By comparing the PK parameters predicted by the virtual bioequivalence, the formulations F1, F2, F3 and F5 failed on bioequivalence. The F4 showed bioequivalence to the reference and was considered the viable formulation to substitute the IR. Thus, GRDDS could be a promising alternative for controlling the release of drugs with a pH-dependent solubility and narrow absorption window, specifically in the gastric environment, and an interesting way to reduce dose frequency and increase the drug bioavailability. The MIDD approach increases the level of information about the pharmaceutical product and guide the drug development for more assertive ways.

A randomized, open-label 3-way crossover study to investigate the relative bioavailability and bioequivalence of crushed sildenafil 20 mg tablets mixed with apple sauce, extemporaneously prepared suspension (EP), and intact sildenafil 20 mg tablets in healthy volunteers under fasting conditions

The relative bioavailability and bioequivalence of 20-mg doses of a pediatric formulation of sildenafil extemporaneous preparation suspension (EP; 10 mg/mL), the sildenafil 20-mg intact tablet and the crushed sildenafil 20-mg tablet mixed with apple sauce were assessed in a single-dose, randomized, open-label, 3-way crossover study with 18 healthy adult volunteers. Blood samples were collected at predefined times and analyzed for sildenafil plasma concentrations. Natural log-transformed sildenafil pharmacokinetic parameters (Cmax , AUClast , and AUCinf ) were used to estimate relative bioavailability and construct 90% confidence intervals (CI) using a mixed-effects model. Bioequivalence was concluded among the three formulations with one exception, in which the EP suspension showed a 15% decrease in Cmax with a lower 90% CI of 76% compared with the intact tablet. The 15% decrease in sildenafil Cmax is not considered to be clinically relevant. Therefore, the EP suspension is considered to be an appropriate pediatric formulation. All 3 formulations were well tolerated in healthy adult volunteers.