Sildenafil Concentrations Research Articles

The Physicochemical Compatibility of Sildenafil Injection with Parenteral Medications Used in Neonatal Intensive Care Settings.

Sildenafil is used to treat pulmonary hypertension in neonatal intensive care unit (NICU) settings. As multiple intravenous (IV) medications are co-administered in NICU settings, we sought to investigate the physicochemical compatibility of sildenafil with a range of IV drugs. Sildenafil 600 mcg/mL or 60 mcg/mL was mixed 1:1 with the secondary drug solution to simulate Y-site co-administration procedures. Physical compatibility was evaluated by visual observation against a black and white background and under polarized light for two hours for changes in colour, precipitation, haze and evolution of gas. Chemical compatibility was determined from sildenafil concentrations, using a validated, stability-indicating high-performance liquid chromatography assay. Sildenafil 600 mcg/mL was physicochemically compatible with 29 of the 45 drugs tested at 'high-end' clinical concentrations and physically incompatible with 16 drugs and six '2-in-1' parenteral nutrition solutions. Sildenafil 600 mcg/mL was compatible with lower, clinically relevant concentrations of calcium gluconate, heparin and hydrocortisone. Aciclovir, amoxicillin, ampicillin, ibuprofen lysine, indometacin, phenobarbitone and rifampicin were incompatible with sildenafil 600 mcg/mL, however these IV medications were compatible with sildenafil 60 mcg/mL. Sildenafil 600 mcg/mL and 60 mcg/mL were incompatible with amphotericin, flucloxacillin, furosemide, ibuprofen, meropenem and sodium bicarbonate. Sildenafil compatibility with commonly used syringe filters was also investigated. Sildenafil solution was compatible with nylon syringe filters, however, absorption/adsorption loss occurred with polyethersulfone and cellulose ester filters.

Application of terahertz Time-Domain spectroscopy and chemometrics-based whale optimization algorithm in PDE5 inhibitor detection

Combating the illicit use of PDE5 inhibitor drugs is a focal point in forensic science research. In order to achieve rapid identification of such drugs, this study applies terahertz time-domain spectroscopy combined with chemometrics to establish a fast and accurate detection method for PDE5 inhibitors. The optimal detection method is determined by comparing the spectral performance of three optical parameters, namely absorption coefficient, refractive index, and dielectric constant. Linear discriminant models based on different spectral parameters, whale optimization algorithm optimized extreme learning machine models, and whale optimization algorithm optimized random forest models are established. The effectiveness and performance of principal component analysis and competitive adaptive reweighted sampling algorithm for spectral feature data selection are also investigated. The PDE5 inhibitor identification model based on the competitive adaptive reweighted sampling - whale optimization algorithm - random forest (CARS-WOA-RF) model achieves an accuracy of 98.61%, and the identification model for two concentrations of Sildenafil achieves 100% accuracy. The results demonstrate that terahertz time-domain spectroscopy combined with chemometrics can effectively detect various common types of PDE5 inhibitor drugs and different concentrations.

Oral Bioavailability and Pharmacokinetics of Sildenafil Orally Disintegrating Tablets under Various Gastric pH Levels Following Administration of Omeprazole in Rats.

Sildenafil citrate, an oral drug used to treat erectile dysfunction, has low water solubility and oral bioavailability. The solubility is greatly influenced by the pH, changing from 37.25 mg/mL to 0.22 mg/mL with a change in pH from 1.2 to 8.0. This indicates that the absorption may decrease in patients who use drugs, such as proton pump inhibitors (PPIs), for gastroesophageal reflux disease. To improve the absorption of sildenafil citrate at various gastric pH levels, a sildenafil citrate orally disintegrating tablet (ODT), which has a rapid disintegration feature, was produced by a 3D printing technique. Our study investigated the pharmacokinetic parameters of the sildenafil citrate ODT in rats after oral administration and compared the absorption of the sildenafil citrate ODT and sildenafil citrate commercial tablet (RLD), with and without PPI treatment. The LC/MS/MS analysis of the plasma sildenafil concentration revealed that the area under curve from time 0 to infinity (AUC0-∞) of sildenafil in the sildenafil citrate ODT group was significantly higher than in the sildenafil citrate RLD group whether it was in combination with the PPI or not (274.8% and 144%, respectively; p < 0.05). The relative systemic bioavailability of sildenafil citrate RLD significantly decreased with the PPI, but that of sildenafil citrate ODT was not affected by the PPI. These results indicate that the relative systemic bioavailability of sildenafil citrate ODT was increased when it was prepared using the 3D printing technique and the absorption of this formulation was not affected by the PPI.

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

BackgroundThe 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. MethodsWe 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. ResultsAfter 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. ConclusionIA 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.

PBPK-based dose finding for sildenafil in pregnant women for antenatal treatment of congenital diaphragmatic hernia.

Sildenafil is a potent vasodilator and phosphodiesterase type five inhibitor, commercially known as Revatio® and approved for the treatment of pulmonary arterial hypertension. Maternal administration of sildenafil during pregnancy is being evaluated for antenatal treatment of several conditions, including the prevention of pulmonary hypertension in fetuses with congenital diaphragmatic hernia. However, determination of a safe and effective maternal dose to achieve adequate fetal exposure to sildenafil remains challenging, as pregnancy almost always is an exclusion criterion in clinical studies. Physiologically-based pharmacokinetic (PBPK) modelling offers an attractive approach for dose finding in this specific population. The aim of this study is to exploit physiologically-based pharmacokinetic modelling to predict the required maternal dose to achieve therapeutic fetal exposure for the treatment congenital diaphragmatic hernia. A full-PBPK model was developed for sildenafil and N-desmethyl-sildenafil using the Simcyp simulator V21 platform, and verified in adult reference individuals, as well as in pregnant women, taking into account maternal and fetal physiology, along with factors known to determine hepatic disposition of sildenafil. Clinical pharmacokinetic data in mother and fetus were previously obtained in the RIDSTRESS study and were used for model verification purposes. Subsequent simulations were performed relying either on measured values for fetal fraction unbound (fu = 0.108) or on values predicted by the simulator (fu = 0.044). Adequate doses were predicted according to the efficacy target of 15ng/mL (or 38ng/mL) and safety target of 166ng/mL (or 409ng/mL), assuming measured (or predicted) fu values, respectively. Considering simulated median profiles for average steady state sildenafil concentrations, dosing regimens of 130mg/day or 150mg/day (administered as t.i.d.), were within the therapeutic window, assuming either measured or predicted fu values, respectively. For safety reasons, dosing should be initiated at 130mg/day, under therapeutic drug monitoring. Additional experimental measurements should be performed to confirm accurate fetal (and maternal) values for fu. Additional characterization of pharmacodynamics in this specific population is required and may lead to further optimization of the dosing regimen.

Sildenafil affects the human Kir2.1 and Kir2.2 channels at clinically relevant concentrations: Inhibition potentiated by low Ba2.

Sildenafil (Viagra), the first approved and widely used oral drug for the treatment of erectile dysfunction, was occasionally associated with life-threatening ventricular arrhythmias in patients. Since inward rectifier potassium current (I K1) may considerably contribute to this arrhythmogenesis, we investigated the effect of sildenafil on the human Kir2.1 and Kir2.2, the prevailing subunits forming the ventricular I K1 channels. Experiments were performed by the whole-cell patch clamp technique at 37°C using Chinese hamster ovary cells transiently expressing the human Kir2.1 and Kir2.2 channels. Changes of both the inward and outward current components (at -110 and -50mV, respectively) were tested to be able to consider the physiological relevance of the sildenafil effect (changes at -110 and -50mV did not significantly differ, results at -50mV are listed below). A significant Kir2.1 inhibition was observed at all applied sildenafil concentrations (16.1% ± 3.7%, 20.0% ± 2.6%, and 15.0% ± 3.0% at 0.1, 1, and 10μM, respectively). The inhibitory effect of 0.1μM sildenafil was potentiated by the presence of a low concentration of Ba2+ (0.1μM) which induced only a slight Kir2.1 inhibition by 5.95% ± 0.75% alone (the combined effect was 35.5% ± 3.4%). The subtherapeutic and therapeutic sildenafil concentrations (0.1 and 1μM) caused a dual effect on Kir2.2 channels whereas a significant Kir2.2 activation was observed at the supratherapeutic sildenafil concentration (10μM: 34.1% ± 5.6%). All effects were fully reversible. This is the first study demonstrating that sildenafil at clinically relevant concentrations inhibits both the inward and outward current components of the main human ventricular I K1 subunit Kir2.1. This inhibitory effect was significantly potentiated by a low concentration of environmental contaminant Ba2+ in agreement with recently reported data on rat ventricular I K1 which additionally showed a significant repolarization delay. Considering the similar subunit composition of the human and rat ventricular I K1 channels, the observed effects might contribute to sildenafil-associated arrhythmogenesis in clinical practice.

Sildenafil Inhibits the Growth and Epithelial-to-mesenchymal Transition of Cervical Cancer via the TGF-β1/Smad2/3 Pathway.

The study aims to explore new potential treatments for cervical cancer. Cervical cancer is the second most common cancer in women, causing >250,000 deaths worldwide. Patients with cervical cancer are mainly treated with platinum compounds, which often cause severe toxic reactions. Furthermore, the long-term use of platinum compounds can reduce the sensitivity of cancer cells to chemotherapy and increase the drug resistance of cervical cancer. Therefore, exploring new treatment options is meaningful for cervical cancer. The present study was to investigate the effect of sildenafil on the growth and epithelial-tomesenchymal transition (EMT) of cervical cancer. HeLa and SiHa cells were treated with sildenafil for different durations. Cell viability, clonogenicity, wound healing, and Transwell assays were performed. The levels of transforming growth factor-β1 (TGF-β1), transforming growth factor-β type I receptor (TβRI), phosphorylated (p-) Smad2 and p-Smad3 in cervical cancer samples were measured. TGF-β1, Smad2 or Smad3 were overexpressed in HeLa cells, and we measured the expression of EMT marker proteins and the changes in cell viability, colony formation, etc. Finally, HeLa cells were used to establish a nude mouse xenograft model with sildenafil treatment. The survival rate of mice and the tumor size were recorded. High concentrations of sildenafil (1.0-2.0 μM) reduced cell viability, the number of HeLa and SiHa colonies, and the invasion/migration ability of HeLa and SiHa cells in a dose- and time-dependent manner. The expression of TGF-β1, TβRI, p-Smad2 and p-Smad3 was significantly enhanced in cervical cancer samples and cervical cancer cell lines. Sildenafil inhibited the expression of TGF-β1-induced EMT marker proteins (Snail, vimentin, Twist, E-cadherin and N-cadherin) and p-Smad2/3 in HeLa cells. Overexpression of TGF-β1, Smad2, and Smad3 reversed the effect of sildenafil on EMT, viability, colony formation, migration, and invasion ability of HeLa cells. In the in vivo study, sildenafil significantly increased mouse survival rates and suppressed xenograft growth. Sildenafil inhibits the proliferation, invasion ability, and EMT of human cervical cancer cells by regulating the TGF-β1/Smad2/3 pathway.

A Systematic Review of Sildenafil Mortality Through the Years.

Sildenafil is a medication used for the treatment of erectile dysfunction. It was approved by the U.S. Food and Drug Administration (FDA) in 1998. Several articles have raised concerns regarding the use of sildenafil and the occurrence of serious adverse events, such as myocardial ischemia, stroke, and even death. Our aim is to systematically review the existing literature on mortality associated with sildenafil use. The method used for this systematic review was completed by searching three databases: PubMed, Scopus, and Web of Science. Articles were screened and assessed for eligibility. This review uses the articles found to address the concerns associated with sildenafil and mortality. A total of 19 reports were used in our systematic review, in which there were 10 case reports, two case series, three systematic reviews, one narrative review, one retrospective study, one article in the British Medical Journal, and one commentary article. One FDA article in particular included case reports and reports to the FDA on the use of sildenafil eight months after its introduction to the market in 1998, with 522 deaths reported. Another retrospective study examined the use of sildenafil on infants below the age of 1 who did not have congenital heart disease but did suffer from severe pulmonary hypertension. The study found a mortality rate of 29%, which increased with sildenafil dosage. A case series examined six deaths related to non-prescription use of sildenafil. All these cases were subjected to autopsies and related to sexual activity. The study suggests that phosphodiesterase 5 inhibitors induced the deaths, and the concentration of sildenafil in the femoral blood was found to be between 0.032and0.087 μg. To conclude, the literature available on this topic is deemed insufficient to provide enough data to establish a direct link of causality between sildenafil and mortality. Although some studies paint sildenafil as the culprit behind these deaths, further studies and research are needed to explain the unexpected deaths following sildenafil use.

Screening and Determination of Synthetic PDE-5 Inhibitors in Adulterated Sexual Enhancement Supplements.

This paper reports an important investigation and quantification of adulteration of sexual enhancement supplements with prescription medicines available in United Arab Emirates (UAE): tadalafil, sildenafil and vardenafil. A total of 158 sexual enhancement supplements were collected and analyzed in the current study. The samples were screened using REVERSE-phase liquid chromatography tandem high-resolution mass spectrometry/mass spectrometry (RP-HPLC-MS/MS). Of all sexual enhancements, 12.7% (95% CI: 7.4–18) contained undeclared sildenafil, 3.8% (95% CI: 0.78–6.81) contained undeclared tadalafil and 1.9% (95% CI: 0.25–4.05) contained undeclared vardenafil. Of all sexual enhancement supplements, 13.9% (95% CI: 8.5–19.4) contained significant concentrations of sildenafil, tadalafil or vardenafil. While the study found relatively low levels of undeclared pharmaceutical ingredients in the sexual enhancement dietary supplements available on the UAE market, it is likely that patients with ED tend to consume multiple such supplements daily, thereby exposing themselves to highly elevated cumulative levels.

Utilization of UiO-66-NH2@cellulose hybrid aerogel for solid-phase extraction of sildenafil in health products

研究建立了一种基于UiO-66-NH2@纤维素复合气凝胶的高灵敏度固相萃取新方法,与高效液相色谱法联用用于保健品中西地那非的检测。先将纤维素进行醛基和酰肼基的功能化,然后将两种功能化的纤维素通过交联并负载UiO-66-NH2形成复合气凝胶。将此复合气凝胶作为固相萃取的吸附剂使用时,易于收集且不需要外加磁场或者抽真空的辅助作用,操作简单。研究对制备所得的UiO-66-NH2@纤维素复合气凝胶进行了X-射线粉末衍射、扫描电镜、红外光谱和N2吸附等表征,结果显示UiO-66-NH2成功负载于气凝胶的孔道中,纤维素气凝胶掺杂了UiO-66-NH2之后其孔道结构变得规整,并且比表面积增大。研究优化了复合气凝胶中UiO-66-NH2的负载量对萃取的影响,高比例的负载量有利于西地那非的富集,并且最高的负载率为50%。研究优化了影响西地那非富集效率的实验条件,包括溶液pH、萃取时间、洗脱剂类型、洗脱时间、洗脱体积和离子强度。采用安捷伦Zorbax Eclipse Plus C18色谱柱(150 mm×4.6 mm, 5 μm)进行分离,以含0.1 mol/L三乙胺的磷酸盐水溶液(pH=6.50)-乙腈(30∶70, v/v)为流动相进行洗脱,检测波长为292 nm。在最佳的萃取条件下(pH为9.0,萃取时间为60 min,洗脱剂为乙腈,洗脱液体积为3×2 mL,洗脱时间为40 min),该分析方法的线性范围为10~2000 ng/mL (相关系数R2=0.9949),检出限(LOD, S/N=3)为2.85 ng/mL,富集因子为59.17。将该方法用于保健品中西地那非的萃取,所得回收率为74.93%~89.12%,相对标准偏差为2.8%~5.3%,表明了方法的回收率和精密度良好,说明了该方法具有应用于保健品中西地那非日常检测的潜力。

Population pharmacokinetic analysis of sildenafil in term and preterm infants with pulmonary arterial hypertension.

Sildenafil is widely used off-label in pediatric patients with pulmonary arterial hypertension (PAH). This study was conducted to characterize the pharmacokinetics (PK) of sildenafil in term and preterm neonates with PAH, by developing a population PK model, and to suggest appropriate doses to achieve clinically effective concentrations. A population PK modelling analysis was performed using sildenafil and its metabolite N-desmethyl sildenafil (DMS) concentration data from 19 neonates with PAH, whose gestational ages ranged 24–41 weeks. They received sildenafil orally at a dose of 0.5–0.75 mg/kg, four times a day. To investigate the appropriate sildenafil dose, simulations were conducted according to body weight which was significant covariate for sildenafil clearance. A one-compartment model with first-order absorption adequately described the PKs of sildenafil and DMS. Sildenafil clearance was expected to increase rapidly with increasing body weight. In the simulation, sildenafil doses > 1 mg/kg was required to achieve and maintain target concentrations of sildenafil and to expect timely clinical effects in term and preterm infants. These results could be utilized for the safer and more effective use of sildenafil in term and preterm infants.

Influence of methylxanthines isolated from Bancha green tea on the pharmacokinetics of sildenafil in rats.

Sildenafil is used to treat erectile dysfunction and pulmonary arterial hypertension and is metabolized in the liver mainly by CYP3A4, thus co-administration with drugs or herbal extracts that affect CYP3A4 activity may lead to drug-drug or drug-herb interactions, respectively. The aim of the present study was to evaluate the influence of single and multiple oral doses of methylxanthine fraction, isolated from Bancha green tea leaves on the pharmacokinetics of sildenafil in rats. Rats were given sildenafil alone as well as simultaneously with methylxanthines or ketoconazole. The plasma concentrations of sildenafil were measured with high-performance liquid chromatography method with ultraviolet detection. The pharmacokinetic parameters of sildenafil were calculated by non-compartmental analysis. Concomitant use of sildenafil with a single oral dose of methylxanthines resulted in a decrease in Cmax (p > 0.05), AUC0-t (p < 0.05) and AUC0-inf (p < 0.05), while the administration of sildenafil after methylxanthines pretreatment resulted in an increase in Cmax (p < 0.0001), AUC0-t (p < 0.0001) and AUC0-inf (p < 0.001) compared to the sildenafil group. After co-administration of sildenafil and ketoconazole, a significant increase in Cmax, AUC0-t and AUC0-inf was observedin both of the experiments. Drug-herb interactions were observed when sildenafil was co-administered with Bancha methylxanthines in rats. Further in vivo studies about the potential drug interactions between sildenafil and methylxanthines, especially caffeine, are needed to clarify mechanisms underlying the observed changes in sildenafil pharmacokinetics.

Pharmacokinetics and pharmacodynamics of sildenafil in fetal lambs on extracorporeal support

BackgroundMaternal 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. MethodsFive 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. FindingsThe 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. InterpretationImmediate 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 contextNone. Search strategy before undertaking the studyA 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 studyPrenatal 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 studyWe 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 evidenceWe 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.

Transplacental Transfer and Fetal Pharmacodynamics of Sildenafil in the Pregnant Sheep Model

Background: Sildenafil is a phosphodiesterase-5 inhibitor considered for antenatal use for a variety of indications. We sought to assess sildenafil pharmacokinetics in the pregnant ewe and fetus and evaluate its physiological fetal effects. Methods: Twelve fetal lambs (127–133 days GA, term 145) were chronically catheterized in utero. Ewes received different doses of sildenafil, either via subcutaneous injection (1.6, 2.0 mg/kg/day) or intravenous (IV) infusion (3, 5, 7, 10, and 12 mg/kg/day). Maternal and fetal sildenafil concentrations and metabolic status (blood gas analysis) were measured at given intervals. The fetal heart rate, pulmonary blood flow, systemic and aortic pressure, and maternal uterine artery pressure were continuously monitored. Results: The transplacental sildenafil transfer was 2.9% (range: 1.4–7.8%), preventing attainment of fetal target concentrations without toxic maternal levels. IV sildenafil infusion induced an immediate, temporary, dose-dependent reduction of pulmonary vascular resistance (38–78%) and increased both pulmonary blood flow (32–132%) and heart rate (13–49%), with limited nonlinear dose-dependent effects on systemic and pulmonary pressures. Fetal and maternal blood gases and maternal uterine artery pressures were unaffected by sildenafil infusion. Conclusion: In sheep, transplacental transfer of sildenafil is extremely low. Though, minimal fetal sildenafil concentrations induce an acute transient pulmonary vasodilation, well-tolerated by the fetus and ewe.

Changes in the Pharmacokinetics and Pharmacodynamics of Sildenafil in Cigarette and Cannabis Smokers.

Sildenafil citrate, a widely-used oral therapy for erectile dysfunction, is a cytochrome P3A4 (CYP3A4) enzyme substrate. Studies have reported that this substrate has an inhibitory effect on CYP3A4 enzymes in long-term cigarette and cannabis smokers, which predominantly mediate the hepatic elimination of sildenafil. Cigarette and/or cannabis smoking could therefore alter the exposure of sildenafil. The aim of this study was to examine the effect of smoking cigarettes and/or cannabis on the pharmacokinetics, pharmacodynamics, safety and tolerability of sildenafil. Thirty-six healthy human subjects were equally divided into three groups: non-smokers, cigarette smokers and cannabis smokers. Each group was administered a single dose of sildenafil (50 mg tablets). The primary outcome measures included the maximum concentration of sildenafil in plasma (Cmax), the elimination half-life (t1/2) and the area under the plasma concentration time curve from zero to time (AUC0–t). The pharmacodynamics were assessed by the International Index of Erectile Function (IIEF-5). The exposure of sildenafil (AUC0–t) showed a statistically significant increase in cigarette smokers (1156 ± 542 ng·h/mL) of 61% (p < 0.05) while in cannabis smokers (967 ± 262 ng·h/mL), a non-significant increase in AUC0–t of 35% (p > 0.05) was observed relative to non-smokers (717 ± 311 ng·h/mL). Moreover, the Cmax of sildenafil increased by 63% (p < 0.05) and 22% (p > 0.05) in cigarette smokers and cannabis smokers, respectively. Cigarette smoking increases the exposure of sildenafil to a statistically significant level with no effect on its pharmacodynamics, safety and tolerability.

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

To evaluate the pharmacokinetic parameters and bioequivalence of two sildenafil tablets (20 mg) in healthy Chinese subjects. 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. 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. 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.

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.

Accumulation of human pharmaceuticals and activity of biotransformation enzymes in fish from two areas of the lower Rio de la Plata Basin

The accumulation of four human pharmaceuticals active compounds (HPhAC) in the muscle of four fish species of the Rio de la Plata Basin were assessed regarding the compound logP and pKa, and fish trophic levels. For Prochilodus lineatus, accumulation was compared to hepatic biotransformation enzymes and fish from two sampling areas with different urbanization degree. Species were the detritivore Prochilodus lineatus, the omnivores Megaleporinus obtusidens and Pimelodus maculatus, and the piscivorous Salminus brasiliensis. Sampling areas were the Inner Rio de la Plata Estuary (RLP), in front of the Buenos Aires Metropolitan Area, and at the Lower Uruguay River (URU), a relatively unpopulated area. Carbamazepine, atenolol, enalapril, and sildenafil concentrations in fish muscle were analyzed by HPLC-MS. EROD, BROD, and GST activities were measured in P. lineatus liver. Average (maximum) concentrations and detection frequency were: Atenolol 24.4 (69.4) μg kg−1, 60%; carbamazepine 5.5 (45.8) μg kg−1, 19%; enalapril 7.0 (56.9) μg kg−1, 28%; sildenafil 17.1 (71.6) μg kg−1, 56%. Enalapril and sildenafil detection in fish was first-time reported. Atenolol and carbamazepine concentrations were positively correlated. No correlation was observed between HPhAC accumulation and logP or pKa. A potential biomagnification trend was observed for atenolol, showing higher accumulation in S. brasiliensis. HPhACs accumulation was higher for P. lineatus collected at URU, but GST and BROD were significantly higher for individuals sampled at RLP and were positively correlated. A significant negative correlation was observed for enalapril and BROD. The study contributes to the knowledge of the accumulation of HPhACs in fish.

Фармакокинетические особенности силденафила в форме спрея для здоровых мужчин в зависимости от приема пищи

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.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.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.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.Our results suggest that the new dosage form of sildenafil is a reliable alternative therapeutic option for the treatment of erectile dysfunction.

Sildenafil Potentiates the Therapeutic Efficacy of Docetaxel in Advanced Prostate Cancer by Stimulating NO-cGMP Signaling.

Docetaxel plays an indispensable role in the management of advanced prostate cancer. However, more than half of patients do not respond to docetaxel, and those good responders frequently experience significant cumulative toxicity, which limits its dose duration and intensity. Hence, a second agent that could increase the initial efficacy of docetaxel and maintain tolerability at biologically effective doses may improve outcomes for patients. We determined phosphodiesterase 5 (PDE5) expression levels in human and genetically engineered mouse (GEM) prostate tissues and tumor-derived cell lines. Furthermore, we investigated the therapeutic benefits and underlying mechanism of PDE5 inhibitor sildenafil in combination with docetaxel using in vitro, Pten conditional knockout (cKO), derived tumoroid and xenograft prostate cancer models. PDE5 expression was higher in both human and mouse prostate tumors and cancer cell lines compared with normal tissues/cells. In GEM prostate-derived cell lines, PDE5 expression increased from normal prostate (wild-type) epithelial cells to androgen-dependent and castrated prostate-derived cell lines. The addition of physiologically achievable concentrations of sildenafil enhanced docetaxel-induced prostate cancer cell growth inhibition and apoptosis in vitro, reduced murine 3D tumoroid growth, and in vivo tumorigenicity as compared with docetaxel alone. Furthermore, sildenafil enhanced docetaxel-induced NO and cGMP levels thereby augmenting antitumor activity. Our results demonstrate that sildenafil's addition could sensitize docetaxel chemotherapy in prostate cancer cells at much lesser concentration than needed for inducing cell death. Thus, the combinatorial treatment of sildenafil and docetaxel may improve anticancer efficacy and reduce chemotherapy-induced side-effects among patients with advanced prostate cancer.