Species differences in the CYP3A-catalyzed metabolism of TPN729, a novel PDE5 inhibitor.

TPN729 is a novel phosphodiesterase 5 (PDE5) inhibitor used to treat erectile dysfunction in men. Our previous study shows that the plasma exposure of metabolite M3 (N-dealkylation of TPN729) in humans is much higher than that of TPN729. In this study, we compared its metabolism and pharmacokinetics in different species and explored the contribution of its main metabolite M3 to pharmacological effect. We conducted a combinatory approach of ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry-based metabolite identification, and examined pharmacokinetic profiles in monkeys, dogs, and rats following TPN729 administration. A remarkable species difference was observed in the relative abundance of major metabolite M3: i.e., the plasma exposure of M3 was 7.6-fold higher than that of TPN729 in humans, and 3.5-, 1.2-, 1.1-fold in monkeys, dogs, and rats, respectively. We incubated liver S9 and liver microsomes with TPN729 and CYP3A inhibitors, and demonstrated that CYP3A was responsible for TPN729 metabolism and M3 formation in humans. The inhibitory activity of M3 on PDE5 was 0.78-fold that of TPN729 (The IC50 values of TPN729 and M3 for PDE5A were 6.17 ± 0.48 and 7.94 ± 0.07 nM, respectively.). The plasma protein binding rates of TPN729 and M3 in humans were 92.7% and 98.7%, respectively. It was astonishing that the catalyzing capability of CYP3A4 in M3 formation exhibited seven-fold disparity between different species. M3 was an active metabolite, and its pharmacological contribution was equal to that of TPN729 in humans. These findings provide new insights into the limitation and selection of animal model for predicting the clinical pharmacokinetics of drug candidates metabolized by CYP3A4.

Simultaneous LC-MS analysis of plasma concentrations of sildenafil, tadalafil, bosentan, ambrisentan, and macitentan in patients with pulmonary arterial hypertension.

Phosphodiesterase-5 (PDE-5) inhibitors and endothelin receptor antagonists (ERAs) are standard therapies for pulmonary arterial hypertension (PAH). The inter-individual variability of these pharmacokinetics is reported remarkably large, and therapeutic drug monitoring (TDM) can be useful to improve the likelihood of the desired therapeutic and safety outcomes. This study aimed to develop a LC-MS method to determine the concentrations of five PAH drugs (PDE-5 inhibitors: sildenafil and tadalafil, ERAs: bosentan, macitentan, and ambrisentan) from plasma samples using a simple process followed by a single mass spectrometric run, and to validate this approach through pharmacokinetic analyses in patients. A solid extraction method was used for sample preparation of the drugs from human plasma. The total run time for a single injection was within 10 min. The calibration curves for all drugs were linear, and the lower limits of quantitation were 1 (sildenafil), 2 (tadalafil), 5 (ambrisentan), and 10 ng/mL (bosentan, macitentan). The accuracy and precision values suggested that the assay had high accuracy and reliability. To prove the utility of this method, the plasma concentrations of the five PAH drugs were determined after their oral administration to nine PAH patients.

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.

Antenatal sildenafil treatment improves neonatal pulmonary hemodynamics and gas exchange in lambs with diaphragmatic hernia.

OBJECTIVES: Infants with congenital diaphragmatic hernia (CDH) are predisposed to pulmonary hypertension after birth, owing to lung hypoplasia that impairs fetal pulmonary vascular development. Antenatal sildenafil treatment attenuates abnormal pulmonary vascular and alveolar development in rabbit and rodent CDH models, but whether this translates to functional improvements after birth remains unknown. We aimed to evaluate the effect of antenatal sildenafil on neonatal pulmonary hemodynamics and lung function in lambs with diaphragmatic hernia (DH). METHODS: DH was surgically induced at approximately 80 days' gestation in 16 lamb fetuses (term in lambs is approximately 147 days). From 105 days' gestation, ewes received either sildenafil (0.21 mg/kg/h intravenously) or saline infusion until delivery (n = 8 fetuses in each group). At approximately 138 days' gestation, all lambs were instrumented and then delivered via Cesarean section. The lambs were ventilated for 120 min with continuous recording of physiological (pulmonary and carotid artery blood flow and pressure; cerebral oxygenation) and ventilatory parameters, and regular assessment of arterial blood gas tensions. Only lambs that survived until delivery and with a confirmed diaphragmatic defect at postmortem examination were included in the analysis; these comprised six DH-sildenafil lambs and six DH-saline control lambs. RESULTS: Lung-to-body-weight ratio (0.016 ± 0.001 vs 0.013 ± 0.001; P = 0.06) and dynamic lung compliance (0.8 ± 0.2 vs 0.7 ± 0.2 mL/cmH2 O; P = 0.72) were similar in DH-sildenafil lambs and controls. Pulmonary vascular resistance decreased following lung aeration to a greater degree in DH-sildenafil lambs, and was 4-fold lower by 120 min after cord clamping than in controls (0.6 ± 0.1 vs 2.2 ± 0.6 mmHg/(mL/min); P = 0.002). Pulmonary arterial pressure was also lower (46 ± 2 vs 59 ± 2 mmHg; P = 0.048) and pulmonary blood flow higher (25 ± 3 vs 8 ± 2 mL/min/kg; P = 0.02) in DH-sildenafil than in DH-saline lambs at 120 min. Throughout the 120-min ventilation period, the partial pressure of arterial carbon dioxide tended to be lower in DH-sildenafil lambs than in controls (63 ± 8 vs 87 ± 8 mmHg; P = 0.057), and there was no significant difference in partial pressure of arterial oxygen between the two groups. CONCLUSIONS: Sustained maternal antenatal sildenafil infusion reduced pulmonary arterial pressure and increased pulmonary blood flow in DH lambs for the first 120 min after birth. These findings of improved pulmonary vascular function are consistent with improved pulmonary vascular structure seen in two previous animal models. The data support the rationale for a clinical trial investigating the effect of antenatal sildenafil in reducing the risk of neonatal pulmonary hypertension in infants with CDH. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Investigation of Interactive Activity of Electro-Acupuncture on Pharmacokinetics of Sildenafil and Their Synergistic Effect on Penile Blood Flow in Rats.

Erectile dysfunction (ED) is a disorder found in males throughout the world, which negatively affects relationships with partners with advancing age. Hence, in this study, we tested a combined novel treatment of electro-acupuncture (EA) and sildenafil citrate against ED. In addition to EA therapy, the sildenafil citrate, a phosphodiesterase 5 inhibitor, is a widely recognized drug that has achieved considerable success in the treatment of ED. However, the combined effect of both the EA and sildenafil has not yet been investigated. Hence, we aimed to examine the effect of EA on the pharmacokinetics and pharmacodynamics of sildenafil in rat plasma. The pharmacokinetic parameters were determined using ultra performance liquid chromatography (UPLC) after EA and sildenafil administration (10 mg/Kg). Following this, the pharmacodynamics was studied via blood flow pattern using developing Doppler images of the lower body and penis. The pharmacokinetic studies demonstrated that sildenafil significantly increases by administration of low-frequency EA. Further, the pharmacodynamic studies using Doppler imaging revealed an elevated blood flow in rat penis compared with lower body during combined treatment of sildenafil and low-frequency EA. These data indicate a synergistic therapeutic effect of EA and sildenafil for the treatment of ED.

[Dosage forms of sildenafil in the management of erectile dysfunction].

The experience in the management of erectile dysfunction shows that taking even the most effective medications in tablet form may be inconvenient due to the need for natural settings for intimacy. The phosphodiesterase type 5 inhibitor sildenafil, presented in the orally disintegrating film formulation (Dynamic Forward), differs from all forms of the drug for the treatment of erectile dysfunction available in the Russian pharmaceutical market. The drug in the form of a film makes it possible to realize a pathogenetic approach to treating ED without changing the patients habitual way of life.

Plasma Drug Concentrations in Patients with Pulmonary Arterial Hypertension on Combination Treatment.

BACKGROUND: Combination therapy with the phosphodiesterase type 5 inhibitors (PDE-5i) sildenafil or tadalafil and the endothelin receptor antagonists (ERA) bosentan, ambrisentan, or macitentan may cause mutual pharmacokinetic interactions in patients with pulmonary arterial hypertension (PAH). OBJECTIVE: The objective of this study was to analyze plasma drug concentrations in PAH patients receiving different combination treatments. METHODS: PAH patients receiving a stable combination treatment with ERA and PDE-5i with targeted dosage for at least 1 month were routinely assessed, including clinical parameters and plasma drug concentrations. Concentrations were normalized considering dose and time from last medication intake and presented as multiples of the expected mean (MoM) of the respective monotherapies. RESULTS: A total of 125 PAH patients (84 female, 41 male, 57% idiopathic/heritable) were included. Sildenafil and tadalafil concentrations were lowest in combination with bosentan (MoM 0.44 ± 0.42, 95% confidence interval [CI] 0.30-0.57, and MoM 0.89 ± 0.53, 95% CI 0.50-1.28, respectively) compared to the combination with ambrisentan (MoM 1.3 ± 0.97, 95% CI 0.86-1.73, and MoM 1.67 ± 0.63, 95% CI 1.40-1.94, respectively) and macitentan (MoM 1.16 ± 0.87, 95% CI 0.86-1.46, and MoM 1.59 ± 0.99, 95% CI 0.80-2.38, respectively). The combination of sildenafil and bosentan led to more than twice the expected bosentan concentrations in 53.8%. Patients switching from sildenafil-bosentan to macitentan showed a significant increase in sildenafil concentrations (p < 0.001). CONCLUSIONS: Only the combination with macitentan or ambrisentan led to targeted mean PDE-5i plasma concentrations and should therefore be preferred to combination with bosentan. Sildenafil-bosentan showed the strongest interaction, with low sildenafil and high bosentan concentrations. The study was not powered to analyze whether lower PDE-5i concentrations cause unsatisfying clinical response. However, plasma concentrations within a targeted range are desirable and may become of increasing importance.

A single dose, randomized, open-label, cross-over bioequivalence study of sildenafil citrate tablets in healthy Chinese volunteers
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OBJECTIVE: The present study was designed to evaluate the bioequivalence of a newly developed sildenafil citrate tablet 50 mg (Jinge®, Test) and a marketed counterpart (Viagra®, 100 mg, Reference) in healthy adult male Chinese volunteers. METHODS: This single-dose, randomized, open-label, four-period, and two-treatment self-crossover study included two parts: fasting and postprandial studies. In each part of the study, the subjects were randomly assigned to receive test or reference products (100 mg sildenafil) in a 1 : 1 ratio, and then received the alternative products, following a 1-week washout period. Plasma sildenafil concentrations were analyzed by liquid chromatography-tandem mass spectrometry. Tolerability was assessed during the entire study period. RESULTS: 32 healthy volunteers (aged 19 - 30) were enrolled in the study; 31 volunteers completed the fasting study, while 32 volunteers completed the postprandial study. The test formulation was bioequivalent to the marketed formulation as the 90% CIs for the ratio of geometric means of Cmax (fasting: 98.79 - 119.61%; fed: 94.47 - 119.65%), AUClast (fasting: 98.70 - 109.71%; fed: 96.39 - 112.89%), and AUC∞ (fasting: 98.45 - 108.87%; fed: 96.36 - 112.74%) were within equivalence limits (80 - 125%) under both fasting and postprandial conditions. When sildenafil was given with high-fat meals, mean Cmax was reduced by 23%, and median tmax ranged from 0.75 to 1.50 hours (p ≤ 0.05). However, both AUClast and AUC∞ were comparable between fasting and postprandial conditions. No serious adverse events were found among the subjects. CONCLUSIONS: This study confirmed that test and reference sildenafil citrate tablets were bioequivalent under fasting and postprandial conditions.
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Treatment with rilpivirine does not alter plasma concentrations of the CYP3A substrates tadalafil and midazolam in humans.

OBJECTIVES: Antiretroviral combination therapy of patients infected with HIV has greatly increased their life expectancy. Hence, the treatment of HIV-related long-term complications and age-related comorbidities has become more important. Reported incidence rates of erectile dysfunction (ED) and pulmonary arterial hypertension (PAH) are increasing in HIV-positive patients, potentially requiring treatment with phosphodiesterase 5 inhibitors such as sildenafil or tadalafil. In vitro, the NNRTI rilpivirine is both a pregnane X receptor agonist and cytochrome P450 (CYP) 3A inhibitor. Clinical data concerning the potential effects of rilpivirine coadministration on the pharmacokinetics of the CYP3A substrate tadalafil are lacking. METHODS: We enrolled 20 healthy volunteers in an open-label, two-part, one-arm Phase I clinical trial to investigate acute and chronic effects of multiple doses of 25 mg of oral rilpivirine on single-dose and steady-state pharmacokinetics of multiple oral 20 mg doses of tadalafil. CYP3A activity was measured simultaneously with the oral midazolam microdose test. RESULTS: We did not observe a change of tadalafil single-dose and steady-state exposure or of CYP3A activity measured at initiation, during maintenance and upon discontinuation of rilpivirine treatment after single-dose and chronic administration of rilpivirine. CONCLUSIONS: Tadalafil can be combined with rilpivirine without dose adjustment or drug monitoring in HIV patients with ED or PAH. Rilpivirine at daily therapeutic doses of 25 mg does not induce or inhibit CYP3A-dependent drug metabolism.

Ambrisentan and Tadalafil Up-front Combination Therapy in Scleroderma-associated Pulmonary Arterial Hypertension.

BACKGROUND: Scleroderma-associated pulmonary arterial hypertension (SSc-PAH) is a rare disease characterized by a very dismal response to therapy and poor survival. We assessed the effects of up-front combination PAH therapy in patients with SSc-PAH. METHODS: In this prospective, multicenter, open-label trial, 24 treatment-naive patients with SSc-PAH received ambrisentan 10 mg and tadalafil 40 mg daily for 36 weeks. Functional, hemodynamic, and imaging (cardiac magnetic resonance imaging and echocardiography) assessments at baseline and 36 weeks included changes in right ventricular (RV) mass and pulmonary vascular resistance as co-primary endpoints and stroke volume/pulmonary pulse pressure ratio, tricuspid annular plane systolic excursion, 6-minute walk distance, and N-terminal pro-brain natriuretic peptide as secondary endpoints. RESULTS: At 36 weeks, we found that treatment had resulted in significant reductions in median (interquartile range [IQR]) RV mass (28.0 g [IQR, 20.6-32.9] vs. 32.5 g [IQR, 23.2-41.4]; P < 0.05) and median pulmonary vascular resistance (3.1 Wood units [IQR, 2.0-5.7] vs. 6.9 Wood units [IQR, 4.0-12.9]; P < 0.0001) and in improvements in median stroke volume/pulmonary pulse pressure ratio (2.6 ml/mm Hg [IQR, 1.8-3.5] vs. 1.4 ml/mm Hg [IQR 8.9-2.4]; P < 0.0001) and mean ( ± SD) tricuspid annular plane systolic excursion (2.2 ± 0.12 cm vs. 1.65 ± 0.11 cm; P < 0.0001), 6-minute walk distance (395 ± 99 m vs. 343 ± 131 m; P = 0.001), and serum N-terminal pro-brain natriuretic peptide (647 ± 1,127 pg/ml vs. 1,578 ± 2,647 pg/ml; P < 0.05). CONCLUSIONS: Up-front combination therapy with ambrisentan and tadalafil significantly improved hemodynamics, RV structure and function, and functional status in treatment-naive patients with SSc-PAH and may represent a very effective therapy for this patient population. In addition, we identified novel hemodynamic and imaging biomarkers that could have potential value in future clinical trials. Clinical trial registered with www.clinicaltrials.gov (NCT01042158).

Reverse-phase high-performance liquid chromatography for the simultaneous determination of sildenafil and N-desmethyl sildenafil in plasma of children.

Sildenafil is a selective inhibitor of cGMP-specific type 5 phosphodiesterase used for the treatment of pulmonary arterial hypertension (PAH) in the adults. In pediatrics, PAH treatment options include the off-label use of sildenafil. Sildenafil is metabolized in the liver by cytocrome P450 into its active metabolite, N-desmethyl sildenafil. The determination of plasma levels of sildenafil and N-desmethyl sildenafil could be useful for therapy optimization and pharmacokinetic studies. We have developed and validated a method for the quantification of sildenafil and its metabolite in plasma of children by rapid extraction, using high-performance liquid chromatography with ultraviolet detection. The calibration range was fitted at least square model (r2 ≥ 0.999), with an accuracy and an intra- and inter-day relative standard deviation <15% for both analytes. The mean recovery was 102.5% for sildenafil and 101.8% for N-desmethyl sildenafil. This simple method could be successfully used in children with PAH under treatment with sildenafil.

Preclinical pharmacokinetics of TPN729MA, a novel PDE5 inhibitor, and prediction of its human pharmacokinetics using a PBPK model.

AIM: TPN729MA is a novel selective PDE5 inhibitor currently under clinical development in China for the treatment of erectile dysfunction. In this study we characterized its preclinical pharmacokinetics (PK) and predict its human PK using a physiologically based pharmacokinetic (PBPK) model. METHODS: The preclinical PK of TPN729MA was studied in rats and dogs. Human clearance (CL) values for TPN729MA were predicted from various allometric methods and from intrinsic CL determined in human liver microsomes. Human PK and plasma concentration versus time profiles of TPN729MA were predicted by using a PBPK model in GastroPlus. Considering the uncertainties in the prediction, a preliminary human study was conducted in 3 healthy male volunteers with an oral dose of 25 mg. RESULTS: After a single intravenous administration of TPN729MA at a dose of 1 mg/kg in rats and 3 mg/kg in dogs, the plasma CL was 69.7 mL·min(-1)·kg(-1) in rats and 26.3 mL·min(-1)·kg(-1) in dogs, and the steady-state volumes of distribution (V(ss)) were 7.35 L/kg in rats and 6.48 L/kg in dogs. The oral bioavailability of TPN729MA was 10% in rats and above 34% in dogs. Profiles of predicted plasma concentration versus time were similar to those observed in humans at 25 mg, and the predicted T(max), C(max) and AUC values were within 2-fold of the observed values. CONCLUSION: TPN729MA demonstrates good preclinical PK. This compound is a valuable candidate for further clinical development. This study shows the benefits of using a PBPK model to predict PK in humans.

Investigation of mutual pharmacokinetic interactions between macitentan, a novel endothelin receptor antagonist, and sildenafil in healthy subjects.

AIM: To study the mutual pharmacokinetic interactions between macitentan, an endothelin receptor antagonist, and sildenafil in healthy male subjects. METHODS: In this open-label, randomized, three way crossover study, 12 healthy male subjects received the following oral treatments: A) a loading dose of 30 mg macitentan on day 1 followed by 10 mg once daily for 3 days, B) sildenafil 20 mg three times a day for 3 days and a single 20 mg dose on day 4 and C) both treatments A and B concomitantly. Plasma concentration-time profiles of macitentan and its active metabolite ACT-132577 (treatments A and C) and sildenafil and its N-desmethyl metabolite (treatments B and C) were determined on day 4 and analyzed non-compartmentally. RESULTS: The pharmacokinetics of macitentan were not affected by sildenafil. In the presence of sildenafil Cmax and AUCτ of the metabolite ACT-132577 decreased with geometric mean ratios (90% confidence interval (CI)) of 0.82 (0.76, 0.89) and 0.85 (90% CI 0.80, 0.91), respectively. In the presence of macitentan, plasma concentrations of sildenafil were higher than during treatment with sildenafil alone, resulting in increased Cmax and AUCτ values. The respective geometric mean ratios were 1.26 (90% CI 1.07, 1.48) and 1.15 (90% CI 0.94, 1.41). The pharmacokinetics of N-desmethylsildenafil were not affected by macitentan. All treatments were well tolerated. CONCLUSION: A minor, not clinically relevant, pharmacokinetic interaction was observed between macitentan and sildenafil. Based on these results, no dose adjustment of either compound appears necessary during concomitant treatment with macitentan and sildenafil.

Pharmacokinetics of a new orally soluble film formulation of sildenafil administered without water.

OBJECTIVE: To compare the pharmacokinetic profiles and to assess bioequivalence of a newly developed orally soluble film formulation of sildenafil, taken without water, with those of a conventional formulation of sildenafil. METHODS: This study was conducted in a population of healthy subjects as an open-label, randomized sequence, two-period, two-formulation, single-dose, crossover design. The subjects were randomly assigned to 1 of 2 sequences of the two formulations: an orally soluble film (OSF) of 50 mg sildenafil as the test drug and a film-coated tablet (FCT) of 50 mg sildenafil as the reference drug. Blood samples were collected at intervals from 0 to 24 hours after administration. Plasma concentrations of sildenafil and its active metabolite N-desmethyl sildenafil were analyzed using a liquid chromatography/tandem mass spectrometry method. RESULTS: 48 healthy male subjects completed the study. The geometric mean (CV%) for Cmax in the OSF and FCT formulations were 267.21 (4.68%) ng/mL and 285.97 (5.32%) ng/mL, respectively. The geometric mean for AUClast in the OSF and FCT formulations were 664.48 (4.40%) ng x h/mL and 647.96 (4.63%) ng x h/mL, respectively. The geometric mean for AUCinf in the OSF and FCT formulations were 685.65 (4.37%) ng x h/mL and 666.28 (4.60%) ng x h/ mL, respectively. The 90% confidence intervals of the ratios of the geometric means of the Cmax, AUClast, and AUCinf were 0.844 - 1.030, 0.961 - 1.091, and 0.965 - 1.093, respectively. CONCLUSIONS: The OSF sildenafil formulation exhibited no significant differences in its pharmacokinetics compared with those of the FCT formulation. Therefore this convenient OSF sildenafil formulation, which can be taken without the need for water or chewing, offers physicians a novel and attractive treatment option for men with erectile dysfunction. *These authors contributed equally to this work.

Pharmacokinetics and bioequivalence of sildenafil granules and sildenafil tablets in Korean healthy volunteers.

BACKGROUND: A sildenafil tablet formulation as a PDE-5 inhibitor is widely used for the treatment of erectile dysfunction. Recently, a fine granular formulation of sildenafil was developed by a domestic Korean pharmaceutical company. OBJECTIVES: This study was performed to compare the bioavailability of sildenafil fine granules with that of sildenafil tablets for assessing bioequivalence in 40 healthy male volunteers. METHODS: This was an open-label, randomized sequence, single-dose, two-period, and two-treatment crossover study. Half of the volunteers received a single dose of sildenafil fine granule 50 mg and then sildenafil tablet 50 mg after a 7-day washout period. The remaining half of volunteers received the tablet first and the the granule with the same washout period. 10- mL blood samples were serially sampled to measure the concentrations of sildenafil and the N-desmethyl metabolite. Tolerability was assessed during the study. RESULTS: The pharmacokinetic parameters of sildenafil were similar between granular and tablet formulations. The 90% CI of geometric mean ratios (sildenafil granule/tablet) for the pharmacokinetic parameters of sildenafil were within 0.8 – 1.25, as a bioequivalent acceptable range; 1.111 (90% CI, 1.002 - 1.231) for maximum plasma concentration (Cmax) and 1.092 (1.019 - 1.117) for area under the concentration- time curve from time zero to time of last measurable concentration (AUClast). Also, the 90% CI of geometric mean ratios for Cmax and AUClast of the metabolite were within 0.8 - 1.25. Both formulations were well tolerated by volunteers. CONCLUSION: This study confirmed that sildenafil granules and sildenafil tablet are bioequivalent with regards to pharmacokinetics of sildenafil and N-desmethyl sildenafil.

High inter-individual variability of vardenafil pharmacokinetics in patients with pulmonary hypertension.

PURPOSE: To evaluate the pharmacokinetic parameters of a single oral dose of vardenafil in patients with pulmonary hypertension (PH). METHODS: Sixteen patients with PH received vardenafil in single oral doses (20, 10 or 5 mg), and repeated blood sampling for up to 9 h was performed. Vardenafil plasma concentration was determined using liquid chromatography tandem mass spectrometry. Pharmacokinetic parameters were calculated using model-independent analysis. RESULTS: The plasma vardenafil concentration increased rapidly and exhibited a median time to maximum plasma concentration (t(max)) of 1 h and a mean elimination half-life (t(1/2)) of 3.4 h. The geometric mean and standard deviation of (1) the peak plasma concentration (C(max)) was 21.4 ± 1.7 µg/L, (2) the normalized C(max) (C(max, norm)) 79.1 ± 1.6 g/L, (3) the area under the time-concentration curve (AUC) 71.5 ± 1.6 µg · h/L and (4) the normalized AUC (AUC(norm)) 261.6 ± 1.7 g · h/L. Patients co-medicated with bosentan reached t(max) later and had a 90% reduction of C(max), C(max, norm), AUC and AUC(norm). CONCLUSION: The pharmacokinetic profile of vardenafil overall revealed considerable inter-individual variability in patients with PH. Co-medication with bosentan resulted in a pharmacokinetic drug interaction, leading to significantly decreased plasma concentrations of vardenafil. Therapeutic drug monitoring for individual dose optimization may be warranted.

Detection and validated quantification of the phosphodiesterase type 5 inhibitors sildenafil, vardenafil, tadalafil, and 2 of their metabolites in human blood plasma by LC-MS/MS--application to forensic and therapeutic drug monitoring cases.

INTRODUCTION: Phosphodiesterase type 5 inhibitors such as sildenafil, vardenafil, and tadalafil are a class of drugs used primarily in the treatment of erectile dysfunction. Sildenafil and tadalafil are also approved for the treatment of pulmonary hypertension. The aim of this study was to develop and validate a procedure for the detection and quantification of these 3 drugs and some of their metabolites in human blood plasma. METHODS: After liquid-liquid extraction of 0.5 mL of blood plasma using diethyl ether-ethyl acetate (1:1), the analytes sildenafil, norsildenafil, vardenafil, norvardenafil, and tadalafil were separated using a Shimadzu Prominence High-Performance Liquid Chromatography System (C18 separation column, gradient elution, and a total flow of 0.5 mL/min). They were detected using an AB Sciex 3200 Q-Trap LC-MS-MS System (electrospray ionization and multiple reaction monitoring mode). The method was fully validated according to international guidelines. RESULTS: The assay was found to be selective for the tested compounds. It was linear from 5 to 1000 ng/mL for sildenafil, from 2 to 700 ng/mL for norsildenafil, from 0.5 to 350 ng/mL for vardenafil, from 0.5 to 200 ng/mL for norvardenafil, and from 5 to 1000 ng/mL for tadalafil. The recoveries were generally more than 50%. Matrix effects were not observed. Accuracy, repeatability, and intermediate precision were within the required limits (<15% or <20% near the limit of quantification). No instability was observed after repeated freezing and thawing or in processed samples. CONCLUSIONS: A liquid chromatography-tandem mass spectrometry assay for the determination of sildenafil, norsildenafil, vardenafil, norvardenafil, and tadalafil in human blood plasma was developed and validated. It has proven to be selective, linear, accurate, and precise for all studied drugs. The method has also proven to be applicable for forensic cases and for therapeutic drug monitoring.

Safety, tolerability and pharmacokinetics of an intravenous bolus of sildenafil in patients with pulmonary arterial hypertension.

AIMS: To assess pharmacokinetics and pharmacodynamics of a 10 mg intravenous sildenafil bolus in pulmonary arterial hypertension (PAH) patients stabilized on 20 mg sildenafil orally three times daily. METHODS: Pharmacokinetic parameters were calculated using noncompartmental analysis. RESULTS: After an acute increase, plasma concentrations stabilized within the range reported previously for a 20 mg oral tablet. At 0.5 h, mean ± SD changes from baseline were -8.4 ± 11.7 mmHg (systolic pressure), -2.6 ± 7.3 mmHg (diastolic pressure) and -3.5 ± 10.4 beats min(-1) (heart rate). There was no symptomatic hypotension. CONCLUSIONS: Although further research is warranted, a 10 mg sildenafil intravenous bolus appears to provide similar exposure, tolerability and safety to the 20 mg tablet.

Association between sexual activity-related death and non-prescription use of phosphodiesterase type 5 inhibitors.

In recent years, there has been an increase in the use of phosphodiesterase type 5 inhibitors (PDE5i) that are purchased from abroad without a doctor's diagnosis via the Internet or other means. We report six cases in which nonprescription use of PDE5i may have led to death. Among the four deceased individuals who were believed to have experienced sudden cardiac death, three (cases 1-3) had a history of cardiovascular disease, which is a contraindication, and the remaining case (case 4) involved combined use of multiple PDE5i. Sildenafil (0.063 µg/mL, 0.087 µg/mL) was detected in two of the four cases of sudden cardiac death. Tadalafil (0.096 µg/mL) was detected in one of the remaining two cases, and tadalafil (0.197 µg/mL) and vardenafil (0.011 µg/mL) were detected in the other case. Sildenafil (0.032 µg/mL), tadalafil (0.062 µg/mL), and ethanol were detected in a traffic accident case with a history of contraindications. In a case of asphyxiation by vomit aspiration, autopsy showed 90% stenosis in the anterior descending branch of the coronary artery, and sildenafil (0.063 µg/mL) was detected. To the best of our knowledge, this is the first report of postmortem blood levels of tadalafil and vardenafil likely contributing to the cause of death. Despite all the warnings about the dangers of using PDE5 inhibitors, cases of PDE5i contributing to death are still identified during autopsies. Therefore, raising public awareness of the risks of the risks associated with the imported drug use by individuals is necessary.