Breast Cancer Resistance Protein Limits Fetal Transfer of Tadalafil in Mice.

Tadalafil, a phosphodiesterase 5 (PDE5) inhibitor, is a candidate therapeutic agent for fetal growth restriction and hypertensive disorders of pregnancy. In this study, we elucidated the fetal transfer of tadalafil in comparison with that of sildenafil, the first PDE5 inhibitor to be approved. We also examined the contributions of multidrug resistance protein 1 (MDR1) and breast cancer resistance protein (BCRP) to fetal transfer. Tadalafil or sildenafil was administered to wild-type, Mdr1a/b-double-knockout or Bcrp-knockout pregnant mice by continuous infusion from gestational day (GD) 14.5 to 17.5, and the fetal-to-maternal plasma concentration ratio of unbound drug (unbound F/M ratio) was evaluated at GD 17.5. The values of unbound F/M ratio of tadalafil and sildenafil in wild-type mice were 0.80 and 1.6, respectively. The unbound F/M ratio of tadalafil was increased to 1.1 and 1.7 in Mdr1a/b-knockout and Bcrp-knockout mice, respectively, while the corresponding values for sildenafil were equal to or less than that in wild-type mice, respectively. A transcellular transport study revealed that basal-to-apical transport of both tadalafil and sildenafil was significantly higher than transport in the opposite direction in MDCKII-BCRP cells. Our research reveals that tadalafil is a newly identified substrate of human and mouse BCRP, and it appears that the fetal transfer of tadalafil is, at least in part, attributed to the involvement of BCRP within the placental processes in mice. The transfer of sildenafil to the fetus was not significantly constrained by BCRP, even though sildenafil was indeed a substantial substrate for BCRP.

Intra-amniotic sildenafil administration in rabbits: Safety, pharmacokinetics, organ distribution and histologic evaluation.

BACKGROUND: The effectiveness of sildenafil in the management of pulmonary hypertension in congenital diaphragmatic hernia (CDH) has been reported but has not been systematically evaluated. Our studies have also demonstrated that intra-amniotic (IA) sildenafil administration improves pulmonary hypertension in CDH. METHODS: We evaluated the pharmacokinetics of sildenafil after IA administration in pregnant rabbits. Following maternal laparotomy, fetuses received IA injection of 0.8 mg of sildenafil. Maternal blood, amniotic fluid, and fetal tissues were collected at various time points. The concentrations of sildenafil and its major metabolite in samples were analyzed by liquid chromatography-mass spectrometry. To assess organ toxicity, 7 days after IA sildenafil administration, fetal organs were examined histologically. RESULTS: After IA dosing, sildenafil was absorbed quickly with an absorption half-life of 0.03-0.07 h into the fetal organs. All the organs showed a maximum concentration within 1 h and the disposition half-life ranged from 0.56 to 0.73 h. Most of the sildenafil was eliminated from both mothers and fetuses within 24 h after a single dose. There was no histological evidence of organ toxicity in the fetuses after a single dose of IA administration of sildenafil. CONCLUSION: IA sildenafil is rapidly absorbed into the fetus, distributes into the mother, and is eliminated by the mother without accumulation or fetal organ toxicity. This study confirms the feasibility and the safety of IA administration of sildenafil and enables future applications in the treatment of CDH fetuses.

Pharmacokinetics and pharmacodynamics of sildenafil in fetal lambs on extracorporeal support.

BACKGROUND: Maternal transplacental administration of sildenafil is being considered for a variety of fetal conditions. Clinical translation also requires evaluation of fetal safety in a higher species, such as the fetal lamb. Experiments with the pregnant ewe are curtailed by minimal transplacental transfer as well as limited access to the fetus. The EXTra-uterine Environment for Neonatal Development (EXTEND) model renders the isolated fetal lamb readily accessible and allows for direct fetal administration of sildenafil. METHODS: Five fetal lambs were placed on extracorporeal support in the EXTEND device and received continuous intravenous (IV) sildenafil (0.3-0.5-0.7 mg/kg/24hr) for a duration of one to seven days. Plasma sildenafil concentrations were sampled at regular intervals to establish the pharmacokinetic profile using population pharmacokinetic modeling. Serial Doppler ultrasound examination, continuous non-invasive hemodynamic monitoring and blood gas analysis were done to evaluate the pharmacodynamic effects and fetal response. FINDINGS: The target concentration range (47-500 ng/mL) was attained with all doses. Sildenafil induced an immediate and temporary reduction of pulmonary vascular resistance, mean arterial pressure and circuit flow, without change in fetal lactate levels and acid-base status. The duration of the systemic effects increased with the dose. INTERPRETATION: Immediate temporary pulmonary vascular and systemic hemodynamic changes induced by sildenafil were biochemically well tolerated by fetal lambs on extracorporeal support, with the 0.5 mg/kg/24 h dose balancing rapid attainment of target concentrations with short-lived systemic effects. RESEARCH IN CONTEXT: None. SEARCH STRATEGY BEFORE UNDERTAKING THE STUDY: A literature review was conducted searching online databases (Medline, Embase and Cochrane), using search terms: fetal OR prenatal OR antenatal AND sildenafil, without time-limit and excluding human studies. Where relevant, investigators were contacted in order to avoid duplication of work. EVIDENCE BEFORE THIS STUDY: Prenatal therapy with sildenafil, a phosphodiesterase-5 inhibitor with vasodilatory and anti-remodeling effects on vascular smooth muscle cells, has been considered for a variety of fetal conditions. One multicenter clinical trial investigating the benefit of sildenafil in severe intrauterine growth restriction (the STRIDER-trial) was halted early due to excess mortality in the sildenafil-exposed arm at one treatment site. Such findings demonstrate the importance of extensive preclinical safety assessment in relevant animal models. Transplacentally administered sildenafil leads to decreased pulmonary arterial muscularization, preventing or reducing the occurrence of pulmonary hypertension in rat and rabbit fetuses with diaphragmatic hernia (DH). Validation of these results in a higher and relevant animal model, e.g. fetal lambs, is the next step to advance clinical translation. We recently demonstrated that, in contrast to humans, transplacental transfer of sildenafil in sheep is minimal, precluding the in vivo study of fetal effects at target concentrations using the conventional pregnant ewe model. ADDED VALUE OF THIS STUDY: We therefore used the extracorporeal support model for fetal lambs, referred to as the EXTra-uterine Environment for Neonatal Development (EXTEND) system, bypassing placental and maternal metabolism, to investigate at what dose the target concentrations are reached, and what the fetal hemodynamic impact and response are. Fetal hemodynamic and metabolic tolerance to sildenafil are a crucial missing element on the road to clinical translation. This is therefore the first study investigating the pharmacokinetics, hemodynamic and biochemical effects of clinical-range concentrations of sildenafil in fetal lambs, free from placental and maternal interference. IMPLICATIONS OF ALL THE AVAILABLE EVIDENCE: We demonstrated self-limiting pulmonary vasodilation, a decrease of both systemic arterial pressures and circuit flows, induced by clinical range concentrations of sildenafil, without the development of fetal acidosis. This paves the way for further investigation of prenatal sildenafil in fetal lambs on extracorporeal support. A dose of 0.5 mg/kg/24 h offered the best trade-off between rapid achievement of target concentrations and shortest duration of systemic effects. This is also the first study using the EXTEND as a model for pharmacotherapy during pregnancy.

Method development and validation of sildenafil, N-desmethylsildenafil and N1,N4-desmethylsildenafil by LC-MS/MS and its application.

This study aimed to develop an LC-MS/MS method for determining sildenafil and its metabolites N-desmethylsildenafil and N1,N4-desmethylsildenafil in human plasma and applying it to a pharmacokinetic study of sildenafil in healthy volunteers. Sildenafil-d8 was used as the internal standard. Plasma samples were pretreated via protein precipitation with acetonitrile. The extractives were then separated on an ACQUITY UPLC BEH C18 (50-mm × 2.1-mm, 1.7-µm) column using gradient elution. The aqueous and organic mobile phases were ammonium formate 2 mM supplemented with 0.1% formic acid in water and acetonitrile, respectively, and the flow rate was 0.3 mL/min. An electrospray ionization source was applied, and multiple reaction monitoring was operated in the positive mode with selective channels at m/z 475.30 â†’ 100.10, 461.20 â†’ 283.30, 483.30 â†’ 108.10, and 449.00 â†’ 283.00 for sildenafil, sildenafil-d8, N-desmethylsildenafil, and N1,N4-desmethylsildenafil, respectively. The linear calibration curves of sildenafil and its metabolites spanned 1.0-1000 ng/mL. The lower limit of quantification was 1.0 ng/mL. The extractive recovery of analytes from the biological matrix was more than 90% and the matrix effect complied with relevant provisions. The intra- and inter-day precisions of sildenafil and its metabolite were <10%. The intra- and inter-day accuracy of sildenafil, N-desmethylsildenafil, and N1,N4-desmethylsildenafil was more than 99%. The method is highly sensitive and selective, and it was successfully applied to the bioequivalence studies of 100-mg sildenafil citrate tablets in 40 healthy Chinese volunteers.

An Integrative Approach for Improved Assessment of Cardiovascular Safety Data.

Cardiovascular adverse effects in drug development are a major source of compound attrition. Characterization of blood pressure (BP), heart rate (HR), stroke volume (SV), and QT-interval prolongation are therefore necessary in early discovery. It is, however, common practice to analyze these effects independently of each other. High-resolution time courses are collected via telemetric techniques, but only low-resolution data are analyzed and reported. This ignores codependencies among responses (HR, BP, SV, and QT-interval) and separation of system (turnover properties) and drug-specific properties (potencies, efficacies). An analysis of drug exposure-time and high-resolution response-time data of HR and mean arterial blood pressure was performed after acute oral dosing of ivabradine, sildenafil, dofetilide, and pimobendan in Han-Wistar rats. All data were modeled jointly, including different compounds and exposure and response time courses, using a nonlinear mixed-effects approach. Estimated fractional turnover rates [h-1, relative standard error (%RSE) within parentheses] were 9.45 (15), 30.7 (7.8), 3.8 (13), and 0.115 (1.7) for QT, HR, total peripheral resistance, and SV, respectively. Potencies (nM, %RSE within parentheses) were IC 50 = 475 (11), IC 50 = 4.01 (5.4), EC 50 = 50.6 (93), and IC 50 = 47.8 (16), and efficacies (%RSE within parentheses) were I max = 0.944 (1.7), Imax = 1.00 (1.3), E max = 0.195 (9.9), and Imax = 0.745 (4.6) for ivabradine, sildenafil, dofetilide, and pimobendan. Hill parameters were estimated with good precision and below unity, indicating a shallow concentration-response relationship. An equilibrium concentration-biomarker response relationship was predicted and displayed graphically. This analysis demonstrates the utility of a model-based approach integrating data from different studies and compounds for refined preclinical safety margin assessment. SIGNIFICANCE STATEMENT: A model-based approach was proposed utilizing biomarker data on heart rate, blood pressure, and QT-interval. A pharmacodynamic model was developed to improve assessment of high-resolution telemetric cardiovascular safety data driven by different drugs (ivabradine, sildenafil, dofetilide, and pimobondan), wherein system- (turnover rates) and drug-specific parameters (e.g., potencies and efficacies) were sought. The model-predicted equilibrium concentration-biomarker response relationships and was used for safety assessment (predictions of 20% effective concentration, for example) of heart rate, blood pressure, and QT-interval.

Studies on metal-organic framework (MOF) nanomedicine preparations of sildenafil for the future treatment of pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is an incurable disease, although symptoms are treated with a range of dilator drugs. Despite their clinical benefits, these drugs are limited by systemic side-effects. It is, therefore, increasingly recognised that using controlled drug-release nanoformulation, with future modifications for targeted drug delivery, may overcome these limitations. This study presents the first evaluation of a promising nanoformulation (highly porous iron-based metal-organic framework (MOF); nanoMIL-89) as a carrier for the PAH-drug sildenafil, which we have previously shown to be relatively non-toxic in vitro and well-tolerated in vivo. In this study, nanoMIL-89 was prepared and charged with a payload of sildenafil (generating Sil@nanoMIL-89). Sildenafil release was measured by Enzyme-Linked Immunosorbent Assay (ELISA), and its effect on cell viability and dilator function in mouse aorta were assessed. Results showed that Sil@nanoMIL-89 released sildenafil over 6 h, followed by a more sustained release over 72 h. Sil@nanoMIL-89 showed no significant toxicity in human blood outgrowth endothelial cells for concentrations up to100µg/ml; however, it reduced the viability of the human pulmonary artery smooth muscle cells (HPASMCs) at concentrations > 3 µg/ml without inducing cellular cytotoxicity. Finally, Sil@nanoMIL-89 induced vasodilation of mouse aorta after a lag phase of 2-4 h. To our knowledge, this study represents the first demonstration of a novel nanoformulation displaying delayed drug release corresponding to vasodilator activity. Further pharmacological assessment of our nanoformulation, including in PAH models, is required and constitutes the subject of ongoing investigations.

Physical-chemical Stability of Compounded Sildenafil 100-mg Rapid-dissolving Tablets.

Sildenafil citrate is a phosphodiesterase-5 inhibitor that is approved by the U.S. Food and Drug Administration for the treatment of erectile dysfunction. Rapid-dissolving tablets are relatively novel dosage forms that can be prepared by extemporaneous compounding and potentially provide unique advantages for medications like sildenafil. However, such preparations may present newer stability considerations previously unreported. Therefore, the purpose of this study was to assess the physical and chemical stability of sildenafil 100-mg rapid-dissolving tablets prepared by a commonly practiced molding method, using two different proprietary rapid-dissolving tablet bases (Medi-RDT or RDTPlus) immediately after preparation and over six months of storage at ambient room temperature. To prepare the rapid-dissolving tablets, the powder ingredients were homogeneously mixed, filled, and compressed into a 96-cavity metal mold. The formulation was then heated at 110°C for 10 minutes in the mold, released from the mold, and cooled at room temperature for 15 minutes. The prepared tablets were packaged in amber-colored blister packs with cold-adhesive backing seals and stored at ambient room temperature. At predetermined time points, rapid-dissolving tablets of each formulation were retrieved to perform stability analyses. These analyses included weight variation, breaking force, disintegration, friability, and potency via high-performance liquid chromatography following the United States Pharmacopoeia methods and visual inspection. At time 0 (immediately after preparation), the results of the tests for rapid-dissolving tablets made with Medi-RDT base v. RDT-Plus base were as follows: average tablet weight (649.7 mg v. 753.6 mg); breaking force (24.01 N v. 32.34 N); friability (8.52% v. 7.55%); disintegration time (34 seconds v. 35 seconds); and potency (98.61% v. 101.41%), respectively. Over the six-month storage period, both formulations of rapid-dissolving tablets had no significant changes in visual appearance, tablet weight, breaking force, or disintegration time. High-performance liquid chromatographic-based tablet assays for both formulations were consistently above 95% label claim at each time point, with no chromatographic evidence of degradation. Thus, the studied formulations of compounded sildenafil 100-mg rapid-dissolving tablets prepared using both Medi-RDT or RDT-Plus were found to be physically and chemically stable over six months of storage at ambient room temperature.

Physiologically-Based Pharmacokinetic Modeling Characterizes the CYP3A-Mediated Drug-Drug Interaction Between Fluconazole and Sildenafil in Infants.

Physiologically-based pharmacokinetic (PBPK) modeling can potentially predict pediatric drug-drug interactions (DDIs) when clinical DDI data are limited. In infants for whom treatment of pulmonary hypertension and prevention or treatment of invasive candidiasis are indicated, sildenafil with fluconazole may be given concurrently. To account for developmental changes in cytochrome P450 (CYP) 3A, we determined and incorporated fluconazole inhibition constants (KI ) for CYP3A4, CYP3A5, and CYP3A7 into a PBPK model developed for sildenafil and its active metabolite, N-desmethylsildenafil. Pharmacokinetic (PK) data in preterm infants receiving sildenafil with and without fluconazole were used for model development and evaluation. The simulated PK parameters were comparable to observed values. Following fluconazole co-administration, differences in the fold change for simulated steady-state area under the plasma concentration vs. time curve from 0 to 24 hours (AUCss,0-24 ) were observed between virtual adults and infants (2.11-fold vs. 2.82-fold change). When given in combination with treatment doses of fluconazole (12 mg/kg i.v. daily), reducing the sildenafil dose by ~ 60% resulted in a geometric mean ratio of 1.01 for simulated AUCss,0-24 relative to virtual infants receiving sildenafil alone. This study highlights the feasibility of PBPK modeling to predict DDIs in infants and the need to include CYP3A7 parameters.

A UPLC-MS/MS method for simultaneous quantification of sildenafil and N-desmethyl sildenafil applied in pharmacokinetic and bioequivalence studies in a Chinese population.

OBJECTIVE: To evaluate the pharmacokinetic parameters and bioequivalence of two sildenafil tablets (20 mg) in healthy Chinese subjects. MATERIALS AND METHODS: A random, crossover, self-control design was used. 20 healthy subjects including males and females were randomized into two groups. A single oral dose of the trial or reference preparation was given to the two groups of subjects after an overnight fast of 10 hours. Blood samples were taken at scheduled time points. Plasma concentrations of sildenafil and N-desmethyl sildenafil were measured by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). ANOVA was used to check the difference of the mean values of the pharmacokinetic parameters between the two preparations. Bioequivalence was determined by two one-sided t-tests and 90% confidence intervals. RESULTS: The quantitative range of sildenafil and N-desmethyl sildenafil was 2.000 - 200.0 ng/mL and 0.800 - 80.00 ng/mL, respectively. Plasma samples were stable, and there was no mutual interference between the analyte and internal standard. With the 90% confidence limit, the trial preparations AUC0→t and Cmax fall within 80.00 - 125.00% of the reference preparation's AUC0→t and Cmax. The tmax of sildenafil and N-desmethyl sildenafil was ~ 0.9 hours and 1 hour, and the T1/2 was 2.4 hours and 3.7 hours, respectively. The relative bioavailability of sildenafil and N-desmethyl sildenafil was 99.28 ± 3.30% and 99.20 ± 3.39%. No significant difference was found in every factor between the trial preparation and the reference preparation. CONCLUSION: The UPLC-MS/MS method was successfully established to evaluate the pharmacokinetic parameters of sildenafil in healthy Chinese subjects. The trial preparation was bioequivalent to the reference preparation.

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.

[Pharmacokinetic features of sildenafil spray in healthy men depending on food intake].

AIM: In order to evaluate the bioequivalence and benefits of a new dosage form of the type 5 phosphodiesterase inhibitor, sildenafil, two open-label studies in healthy male volunteers were carried out. MATERIALS AND METHODS: An open, randomized, crossover study to compare the pharmacokinetics after a single dose of sildenafil at a dosage of 50 mg on an empty stomach in a new spray form (test drug) and in a traditional tablet form (comparison drug) on 44 volunteers (18 to 43 years old) was done. To assess the effect of food intake on pharmacokinetics, an open, non-randomized study was conducted on 6 healthy male volunteers (from 23 to 35 years old) who received sildenafil (50 mg) after a meal in timely fashion: 1) spray, under the tongue, without drinking, 2) spray , in the mouth, drinking water and 3) the tablet form, drinking water. For pharmacokinetic analysis, blood was analyzed for 24 hours. Plasma concentration of sildenafil was determined by high performance liquid chromatography with tandem mass spectrometric detection (HPLC/TM/SD). The main parameters were the rate (maximum concentration; Cmax) and the degree of absorption (area under the pharmacokinetic curve "concentration-time" during the observation period; AUC0-t) after a single dose of drugs. In addition, the pharmacokinetic profiles of the bioavailability of sildenafil and its active metabolite, N-desmethyl sildenafil, as well as the safety of the different dosage forms, were evaluated. RESULTS: When comparing taking drugs on an empty stomach, the 90% confidence intervals (CI) of the ratios of the mean Cmax and AUC0-t values of sildenafil were 82-106% and 82-101%, respectively. An earlier achievement of the maximum concentration of sildenafil was detected when taking the test drug compared with the standard form (51 and 62 minutes, respectively, Z-value=-2.25, p-value=0.0244). In addition, it was shown that when taking Viagra after a meal, the determination of sildenafil in plasma was delayed (after 30 minutes) compared to the tested drugs (after 10 minutes), however, significant differences in Tmax between the dosage forms were not seen. In two studies, most adverse events were mild to moderate and resolved uneventfully. DISCUSSION: The bioavailability of the new dosage form, the sildenafil spray, is equivalent to the traditional form, however, it has an advantage in terms of onset of action. For example, when taking a spray, an earlier achievement of the maximum concentration of sildenafil and an earlier detection of sildenafil in plasma are shown compared to the traditional tablet form. CONCLUSIONS: Our results suggest that the new dosage form of sildenafil is a reliable alternative therapeutic option for the treatment of erectile dysfunction.

The Pharmacokinetics of Sildenafil May Be Affected by Intestinal Absorption Rate in Children Admitted to the Intensive Care Unit.

This study was performed for a better understanding of the pharmacokinetics of sildenafil (SIL) and N-desmethyl sildenafil (DMS) in 13 children treated in the intensive care unit (ICU). Blood samples were taken periodically after the first oral administration of SIL (0.5 mg/kg). Plasma concentrations were analyzed by tandem LC/MS. Of the 13 patients, apparent peaks in the plasma concentration of SIL were observed in four patients, with the other nine patients showing reduced or delayed drug absorption of SIL. The maximum plasma concentrations of SIL after administration varied in range from 7.8 to 101.0 ng/mL. The parent drug-to-metabolite (SIL/DMS) ratios of the nine patients with reduced or delayed drug absorption of SIL were relatively lower than those in the four patients with rapid absorption of the drug. These observations suggested that the inter-individual variability of intestinal absorption and/or first-pass extraction of SIL was involved in the pharmacokinetic variability of the drug. Next, we evaluated the impact of changes in the gastrointestinal absorption rate on the pharmacokinetics of the drug. That is, SIL (2.5 mg/body) was administered at two different rates in the duodenum of rats. When SIL was administered for 10 min, the Cmax and bioavailability were 3.46 ± 1.65 µg/mL and 23.2 ± 11.1%, respectively. When SIL was administered for 60 min, the Cmax and bioavailability were 0.990 ± 0.352 µg/mL and 9.91 ± 3.79%, respectively. These findings suggest that the drug absorption rate was at least partly responsible for the pharmacokinetic variability of SIL in the ICU children.

Simultaneous determination and determination of sildenafil and its active metabolite in human plasma using LC-MS/MS method.

A sensitive and selective high-performance liquid chromatography-tandam mass spectrometry (LC-MS/MS) method was developed and validated for the simultaneous quantification of sildenafil and its metabolite N-desmethyl sildenafil in human plasma. Sildenafil-d8 was used as an internal standard. The analytes were extracted by precipitation extraction and chromatographed on a C18 column using mobile phase A of water (containing 0.1% formic acid) and mobile phase B of acetonitrile (containing 0.1% formic acid) with gradient elution. Quantification was done using multiple reaction monitoring mode to monitor the precursor-to-product ion transitions of m/z 475.4 → m/z 283.3 for sildenafil, m/z 461.4 → m/z 283.2 for N-desmethyl sildenafil and m/z 483.3 → m/z 108.1 for IS in positive ionization mode. The calibration curve was established over the range of 2.00-1,000 ng/ml and the correlation coefficient was >0.99. The intra-day and inter-day relative standard deviations were <6.5% for sildenafil and 6.3% for N-desmethyl sildenafil respectively. Accuracy determinaed at four concentrations was 86.50-105.67% for sildenafil and 96.83-114.40% for N-desmethyl sildenafil. This method was successfully applied to a pharmacokinetic description of sildenafil and the effect of food intake on the pharmacokinetics of sildenafil was also demonstrated in healthy Chinese volunteers.

Bioequivalence and Bioavailability of an Orodispersible Tablet of Sildenafil Citrate in Healthy Chinese Male Subjects.

Sildenafil citrate is approved to treat erectile dysfunction. An orally disintegrating tablet (ODT) of sildenafil citrate that does not require swallowing or administration with fluids has been developed. The bioequivalence and bioavailability of sildenafil citrate ODT (50 mg) without and with water were compared with conventional sildenafil citrate tablets (50 mg) in an open-label, randomized crossover study. Healthy Chinese male subjects (n = 36) were allocated to 1 of 6 sildenafil citrate treatment sequences under fasted conditions, and plasma samples for determination of sildenafil concentrations were collected predose through 14 hours postdose. Bioequivalence was demonstrated for sildenafil citrate ODT administered without water relative to the sildenafil citrate tablet administered with water; 90%CIs for the ratios of adjusted geometric means for sildenafil AUClast , Cmax , and AUCinf (ratio, 101.41%; 90%CI, 95.49%-107.70%; ratio, 93.55%; 90%CI, 84.15%-104.00%; and ratio, 101.03%; 90%CI, 94.80%-107.66%; respectively) were wholly contained within the bioequivalence acceptance range of 80% to 125%, indicating bioequivalence criteria were met. Relative bioavailability of sildenafil citrate ODT administered with water to the sildenafil citrate tablet (50 mg) administered with water was 97.10%, 91.43%, and 97.09% with respect to sildenafil AUClast , Cmax , and AUCinf , respectively (90%CI, 91.43%-03.12%, 82.25%-101.65%, and 90.90%-103.71%, respectively). Both sildenafil citrate formulations were generally well tolerated in healthy Chinese men. Sildenafil citrate ODT administered without or with water was bioequivalent to or met bioequivalence criteria compared with conventional sildenafil citrate tablets administered with water under fasted conditions in healthy Chinese men, thus offering a convenient alternative method of oral administration.

Enhanced nanoparticle accumulation by tumor-acidity-activatable release of sildenafil to induce vasodilation.

Inefficient nanoparticle accumulation in solid tumors hinders the clinical translation of cancer nanomedicines. Herein, we proposed that sildenafil, a vasodilator ampholyte, could be used to promote nanoparticle accumulation by inducing vasodilation after its tumor acidity-triggered release from the nanocarriers. To confirm this, sildenafil was first encapsulated in a cisplatin-incorporated polymeric micelle. The dense PEG shell of the micelle reduced its endocytosis by cancer cells, which in return resulted in accumulative extracellular release of protonated sildenafil in the acidic tumor microenvironment. The released sildenafil was found to be more effective in enlarging the tumor blood vessels than could be achieved without sildenafil. As a result, we demonstrated considerable improvement in the intratumoral accumulation of the sildenafil-cisplatin co-loaded nanoparticle and its enhanced cancer therapeutic efficacy over the control group. Given the generality of a dense PEG shell and a hydrophobic part in most clinically developed nanomedicines, this work implies the great potential of sildenafil as a simple and universal adjuvant to selectively promote the intratumoral accumulation of nanomedicines, thus improving their clinical translation.

The Effect of Liver and Kidney Disease on the Pharmacokinetics of Clozapine and Sildenafil: A Physiologically Based Pharmacokinetic Modeling.

BACKGROUND AND OBJECTIVES: Physiologically based pharmacokinetic (PBPK) modeling permits clinical scientists to reduce practical constraints for clinical trials on patients with special diseases. In this study, simulations were carried out to validate the pharmacokinetic parameters of clozapine and sildenafil using Simcyp® simulator in young male adults and compare the effect of renal or hepatic impairment on the pharmacokinetic parameters of clozapine and sildenafil. Also, the effect of age on pharmacokinetic parameters of both drugs was investigated in healthy population and in patients with renal and hepatic impairment. METHODS: A full PBPK model was built in the simulator for clozapine and sildenafil based on physicochemical properties and observed clinical results. The model used was Advanced, Dissolution, Absorption and Metabolism (ADAM) for both drugs. RESULTS: The PBPK model adequately predicted the pharmacokinetic parameters of clozapine and sildenafil for the healthy adult population. In the simulation results, the bioavailability of both drugs was remarkably raised in both renal and hepatic impairment in young and elderly populations. CONCLUSION: PBPK modeling could be helpful in the investigation and comparison of the pharmacokinetics in populations with specific disease conditions.

Pharmacokinetics of single dose sildenafil orally administered in canine models of chronic embolic pulmonary hypertension.

Information regarding the pharmacokinetics of oral sildenafil in dogs with pulmonary hypertension is limited. In this study, we examined the pharmacokinetics of oral sildenafil in a canine model of chronic embolic pulmonary hypertension (CEPH). The CEPH model was developed by repeatedly injecting microspheres into the pulmonary arteries. The pharmacokinetics of oral sildenafil at 1, 2 and 4 mg/kg was evaluated using four dogs with pulmonary hypertension in the fasted state. The plasma concentrations of sildenafil were determined using high-performance liquid chromatography, and pharmacokinetic parameters were calculated using a noncompartmental analysis. Sildenafil was well tolerated in this study. Proportional increments in the maximum plasma concentration and area under the curve extrapolated to infinity at drug doses of 1, 2 and 4 mg/kg were detected using a power model analysis. No significant differences were observed among the three doses in the time to maximum plasma concentration. The mean residence time and elimination half-life were slightly but significantly higher at a dose of 4 mg/kg than at a dose of 1 mg/kg.

Pharmacokinetic modeling of intravenous sildenafil in newborns with congenital diaphragmatic hernia.

PURPOSE: We developed a pharmacokinetic model of intravenous sildenafil in newborns with congenital diaphragmatic hernia (CDH) to achieve a target plasma concentration of over 50 µg/l. METHODS: Twenty-three CDH newborns with pulmonary hypertension (64 blood samples) received intravenous sildenafil. Patients received a loading dose of 0.35 mg/kg (IQR 0.16 mg/kg) for 3 h, followed by a continuous infusion of 1.5 mg/kg/day (IQR 0.1 mg/kg/day). For model development, non-linear mixed modeling was used. Inter-individual variability (IIV) and inter-occasion variability were tested. Demographic and laboratory parameters were evaluated as covariates. Normalized prediction distribution errors (NPDE) and visual predictive check (VPC) were used for model validation. RESULTS: A two-compartment disposition model of sildenafil and a one-compartment disposition model of desmethyl sildenafil (DMS) was observed with IIV in sildenafil and DMS clearance and volume of distribution of sildenafil. NPDE and VPC revealed adequate predictability. Only postnatal age increased sildenafil clearance. This was partly compensated by a higher DMS concentration, which also has a therapeutic effect. In this small group of patients, sildenafil was tolerated well. CONCLUSIONS: This model for sildenafil in CDH patients shows that concentration-targeted sildenafil dosing of 0.4 mg/kg in 3 h, followed by 1.6 mg/kg/day continuous infusion achieves appropriate sildenafil plasma levels.

The Effect of Food on the Pharmacokinetics of Sildenafil after Single Administration of a Sublingual Testosterone and Oral Sildenafil Combination Tablet in Healthy Female Subjects.

INTRODUCTION: Female sexual interest/arousal disorder (FSIAD) affects many women worldwide, but pharmacological treatment options are scarce. A new medicine being developed for FSIAD is an on-demand, dual-route, dual-release drug combination product containing 0.5 mg testosterone (T) and 50 mg sildenafil (S), referred to here as T+S. AIM: The aim of this study was to compare the effect of a fed and a fasted state on the pharmacokinetics of sildenafil following administration of T+S. METHODS: Eighteen healthy women were administered T+S under fed and fasted conditions during 2 separate overnight visits in this randomized, open-label, balanced, 2-period, 2-treatment, 2-sequence crossover study. MAIN OUTCOME MEASURES: The pharmacokinetics of sildenafil and its active metabolite N-desmethyl sildenafil were determined over a 24-hour period. Total testosterone was assessed only at a limited number of time points for quality purposes, as sublingual uptake is not expected to be affected by food intake. RESULTS: The observed geometric mean ratios (GMRs) and 90% confidence intervals of sildenafil were not all contained within the prespecified bounds (0.80, 1.25). The GMR (90% CI) for plasma AUC0-last was 1.2753 (0.9706-1.6755); for AUC0-14h, it was 1.7521 (1.0819-2.8374); and for Cmax, it was 1.5591 (0.8634-2.8153). Only lower limits of the CIs fell within the bounds. For N-desmethyl sildenafil, the GMR (90% CI) for AUC0-last was 0.8437 (0.6738-1.0564); for AUC0-10h, it was 1.0847 (0.7648-1.5383); and for Cmax, it was 1.0083 (0.6638-1.5318). Only the GMRs were contained within bounds. No differences were observed between plasma testosterone Cmax and Tmax under fed and fasted conditions, which is in line with expectations for a sublingual administration. CLINICAL IMPLICATIONS: The T+S combination tablet ruptures too late when taken in a fasted state and should therefore not be taken on an empty stomach. STRENGTHS & LIMITATIONS: This is a well-controlled study that provides important insights into the performance characteristics of the delayed-release coating of the combination tablet. The higher variability of the pharmacokinetic parameters in the fasted state was caused by severely delayed rupture in one-third of the women. A reason for this is proposed but the present data do not explain this phenomenon. CONCLUSION: The pharmacokinetics of sildenafil from this modified-release tablet are more robust under fed conditions as compared to the artificial fasted condition where no food is consumed 10 hours prior to and 4 hours after dosing. The dosing situation under the tested fasting condition does not represent the expected common use of this product. Patients should, however, be instructed not to take the tablet on an empty stomach. Bloemers J, Gerritsen J, van Rooij K, et al. The Effect of Food on the Pharmacokinetics of Sildenafil After Single Administration of a Sublingual Testosterone and Oral Sildenafil Combination Tablet in Healthy Female Subjects. J Sex Med 2019; 19:1433-1443.

Population pharmacokinetics of sildenafil in extremely premature infants.

AIMS: To characterize the population pharmacokinetics (PK) of sildenafil and its active metabolite, N-desmethyl sildenafil (DMS), in premature infants. METHODS: We performed a multicentre, open-label trial to characterize the PK of sildenafil in infants ≤28 weeks gestation and < 365 postnatal days (cohort 1) or < 32 weeks gestation and 3-42 postnatal days (cohort 2). In cohort 1, we obtained PK samples from infants receiving sildenafil as ordered per the local standard of care (intravenous [IV] or enteral). In cohort 2, we administered a single IV dose of sildenafil and performed PK sampling. We performed a population PK analysis and dose-exposure simulations using the software NONMEM®. RESULTS: We enrolled 34 infants (cohort 1 n = 25; cohort 2 n = 9) and collected 109 plasma PK samples. Sildenafil was given enterally (0.42-2.09 mg/kg) in 24 infants in cohort 1 and via IV (0.125 or 0.25 mg/kg) in all infants in cohort 2. A 2-compartment PK model for sildenafil and 1-compartment model for DMS, with presystemic conversion of sildenafil to DMS, characterized the data well. Coadministration of fluconazole (n = 4), a CYP3A inhibitor, resulted in an estimated 59% decrease in sildenafil clearance. IV doses of 0.125, 0.5 and 1 mg/kg every 8 hours (in the absence of fluconazole) resulted in steady-state maximum sildenafil concentrations that were generally within the range of those reported to inhibit phosphodiesterase type 5 activity in vitro. CONCLUSIONS: We successfully characterized the PK of sildenafil and DMS in premature infants and applied the model to inform dosing for a follow-up, phase II study.