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.

Effects of itraconazole and rifampicin on the pharmacokinetics and safety of youkenafil, a novel phosphodiesterase type 5 inhibitor, in healthy Chinese subjects.

Youkenafil is a novel selective phosphodiesterase type 5 inhibitor to treat erectile dysfunction. In order to study the drug-drug interactions of youkenafil, in vitro experiments were conducted with human liver microsomes and recombinant isoenzymes to identify the effect of cytochrome P450 (CYP) enzymes on the metabolism of youkenafil. Then two clinical studies were performed to investigate the effects of itraconazole and rifampicin (potent CYP3A4/5 inhibitor and inducer, respectively) on the pharmacokinetics of youkenafil and its main metabolite, N-desethyl youkenafil (M1). Each study enrolled thirty healthy male subjects. In study 1, subjects were given a single dose of youkenafil (50 mg on Days 1 and 13) and multiple doses of itraconazole (200 mg once daily from Days 6 to 14). In study 2, subjects were given a single dose of youkenafil (100 mg on Days 1 and 20) and multiple doses of rifampicin (600 mg once daily from Days 6 to 20). The results showed that youkenafil was mainly metabolized through CYP3A4/5 in vitro. Itraconazole increased youkenafil AUC and Cmax by about 12- and 6-fold, respectively, and increased M1 AUC and Cmax by 5- and 1.3-fold, respectively. Conversely, rifampicin reduced youkenafil AUC and Cmax both by about 98%. It did not change the AUC of M1 significantly, but increased the Cmax by 30%. All treatments were well tolerated by subjects in both studies. Therefore, co-administration of youkenafil with potent inhibitors or inducers of CYP3A4/5 should be avoided or carefully monitored.

Physiologically based pharmacokinetic modeling of tadalafil to inform pediatric dose selection in children with pulmonary arterial hypertension.

Tadalafil, a phosphodiesterase 5 inhibitor, is being investigated as a treatment for pulmonary arterial hypertension (PAH) in children aged 6 months to less than 18 years. Tadalafil pharmacokinetic (PK) data in children less than 2 years old are unavailable, therefore a physiologically based pharmacokinetic (PBPK) model was developed to enable estimation of tadalafil doses in children less than 2 years old. The model was verified in adults and extended for use in children by modifying CYP3A-mediated intrinsic clearance to include CYP3A7. To account for co-dosing of the commonly prescribed moderate CYP3A4 inducer bosentan, predicted exposures were increased by a factor of 1.54 based on changes in exposure in adults with PAH. This factor was predictable using a bosentan PBPK model. The tadalafil model was verified in children aged greater than or equal to 2 years by comparing predicted and observed exposures. Tadalafil doses for children less than 2 years old were calculated as target area under the concentration curve from zero to 24 h (AUC0-24 )/predicted AUC0-24 , with target AUC0-24 of 10,000 ng*h/ml based on adult 40 mg single dose exposures determined in patients without bosentan background treatment. These doses were 2 mg, 3 mg, 4 mg, and 6 mg, respectively, for children aged birth to less than 1 month, 1 month to less than 6 months, 6 months to less than 1 year, and 1 to less than 2 years. Due to uncertainties in CYP maturation, a nonmechanistic steady-state volume scalar, and lack of PK data in children less than 2 years old, accumulation of tadalafil to steady-state in children less than 2 years was not verifiable. Safety of proposed doses is supported by postmarketing research and investigator-led trials.

Effects of phosphodiesterase V inhibition alone and in combination with BNP on cardiovascular and renal response to volume load in human preclinical diastolic dysfunction.

Preclinical diastolic dysfunction (PDD) results in impaired cardiorenal response to volume load (VL) which may contribute to the progression to clinical heart failure with preserved ejection fraction (HFpEF). The objective was to evaluate if phosphodiesterase V inhibition (PDEVI) alone or combination PDEVI plus B-type natriuretic peptide (BNP) administration will correct the impaired cardiorenal response to VL in PDD. A randomized double-blinded placebo-controlled cross-over study was conducted in 20 subjects with PDD, defined as left ventricular ejection fraction (LVEF) >50% with moderate or severe diastolic dysfunction by Doppler echocardiography and without HF diagnosis or symptoms. Effects of PDEVI with oral tadalafil alone and tadalafil plus subcutaneous (SC) BNP, administered prior to acute volume loading, were assessed. Tadalafil alone did not result in improvement in cardiac response to VL, as measured by LVEF, LV end diastolic volume, left atrial volume (LAV), or right ventricular systolic pressure (RVSP). Tadalafil plus SC BNP resulted in improved cardiac response to VL, with increased LVEF (4.1 vs. 1.8%, p = 0.08) and heart rate (4.3 vs. 1.6 bpm, p = 0.08), and reductions in both LAV (-4.3 ± 10.4 vs. 2.8 ± 6.6 ml, p = 0.03) and RVSP (-4.0 ± 3.0 vs. 2.1 ± 6.0 mmHg, p < 0.01) versus tadalafil alone. Plasma and urinary cyclic guanosine monophosphate (cGMP) excretion levels were higher (11.3 ± 12.3 vs. 1.7 ± 3.8 pmol/ml, 1851.0 ± 1386.4 vs. 173.4 ± 517.9 pmol/min, p < 0.01) with tadalafil plus SC BNP versus tadalafil alone. There was no improvement in renal response as measured by GFR, renal plasma flow, sodium excretion, and urine flow with tadalafil plus SC BNP compared to tadalafil alone. In subjects with PDD, tadalafil alone resulted in no improvement in cardiac adaptation, while tadalafil and SC BNP resulted in enhanced cardiac adaptation to VL. TRIAL REGISTRATION: ClinicalTrials.gov NCT01544998.

A Phase I Study to Evaluate the Safety, Tolerability, and Pharmacokinetics of TPN171H, a Novel Phosphodiesterase Type 5 Inhibitor, in Healthy Subjects.

PURPOSE: TPN171H is a novel, potent and selective phosphodiesterase type 5 (PDE5) inhibitor for the treatment of pulmonary arterial hypertension (PAH). The objective of this study was to evaluate the safety, tolerability, and pharmacokinetics of TPN171H in healthy subjects after single and multiple dosing, in addition, to investigate the food effect on pharmacokinetics and safety of TPN171H. METHODS: The entire study was comprised of three parts: Part I (single ascending-dose study), Part II (food effect study), and Part III (multiple ascending-dose study). A total of 63 healthy subjects were enrolled in the study. TPN171H tablet or placebo was administered per protocol requirements. Blood samples were collected at the designated time points for pharmacokinetic analysis. Safety was assessed by clinical examinations and adverse events. RESULTS: In Part I, AUC and Cmax were proved to be linear within the 5-30 mg dose range. T1/2 of TPN171H was 8.02-10.88 h. In Part II, we figured out that TPN171H administration under fed condition could decrease Cmax, prolong Tmax, but had no effect on AUC. In Part III, the accumulation ratio at steady-state for AUC and Cmax indicated that TPN171H has a slight accumulation upon repeated dosing. Subjects were generally tolerable after TPN171H administration. Compared with other PDE5 inhibitors, TPN171H was found to have no impact on blood pressure and color discrimination. CONCLUSION: TPN171H was safe and generally tolerated in healthy subjects. Based on the half-life, food effect, and safety profile of TPN171H, we recommend a once-daily, post-meal administration of TPN171H in subsequent clinical studies in healthy subjects and patients with PAH.

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.

Dihydrotestosterone (DHT) rapidly increase after maximal aerobic exercise in healthy males: the lowering effect of phosphodiesterase's type 5 inhibitors on DHT response to exercise-related stress.

PURPOSE: Few data exist on dihydrotestosterone (DHT) adaptation to exercise-related stress. The aim of the study was to investigate on serum DHT and other androgens' responses to acute aerobic exercises, and to verify if a long-acting phosphodiesterase's type 5 inhibitors could influence these responses, as previously observed for salivary testosterone. METHODS: In a double-blind cross over study, 12 healthy trained male volunteers were submitted to both an acute sub-maximal and maximal exercise tests on cycle ergometer, after randomly receiving a two days placebo or tadalafil administration (20 mg, Cialis®, Ely-Lilly, Indianapolis, IN, USA). Blood sample collections were performed at different time points before and after exercise. Serum DHT, total testosterone (TT), dehydroepiandrosterone sulfate (DHEAS) and luteinizing hormone (LH), were assayed. RESULTS: Serum DHT increase in placebo treatment immediately post maximal aerobic exercise and return to basal values at 60 min of recovery whereas tadalafil administration significantly reduced the DHT increase after exercise. The values of areas under curves showed the increase of TT after acute sub-maximal and maximal exercise and of DHEAS only after acute maximal aerobic exercise independently from treatment. CONCLUSIONS: In addition to testosterone, also DHT plays an exercise-related adaptive role during high intensity aerobic exercise, but its rapid useful effects during exercise have to be determined. We hypothesized that the increased androgens secretion during exercise could be mainly related to steroidogenic enzymes modifications in peripheral tissues (i.e., muscles). Moreover, the blunting effect of tadalafil on DHT increase support a possible role of peripheral nitric oxide/GMPc related pathways in influencing physical-stress related DHT metabolism.

Natural phosphodiesterase 5 (PDE5) inhibitors: a computational approach.

In 1998, sildenafil was marketed as the first FDA-approved oral drug for the treatment of erectile dysfunction (ED). During the last two decades, the commercialization of other synthetic phosphodiesterase 5 (PDE5) inhibitors has been paralleled by the rise of remedies based on natural molecules from different chemical classes (flavonoids, polyphenols and alkaloids in general). In this work, a set of in silico tools were applied to study a panel of 30 natural compounds claimed to be effective against ED in the scientific literature or in folk medicine. First, pharmacokinetic properties were analysed to exclude the compounds lacking in specific drug-like features. Estimated binding energy for PDE5 and selectivity towards other PDE isoforms were then considered to highlight some promising molecules. Finally, a detailed structural investigation of the interaction pattern with PDE in comparison with sildenafil was conducted for the best performing compound of the set.

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.

Discovery of Evodiamine Derivatives as Highly Selective PDE5 Inhibitors Targeting a Unique Allosteric Pocket.

Clinical use of phosphodiesterase-5 (PDE5) inhibitors is limited by several side effects due to weak isoform selectivity. Herein, a unique allosteric pocket of PDE5 is identified by molecular modeling and structural biology, which enables the discovery of highly selective PDE5 inhibitors from natural product evodiamine (EVO). The crystal structure of PDE5 with bound EVO derivative (S)-7e revealed that binding of (S)-7e to the novel allosteric pocket induced dramatic conformation changes in the H-loop with a maximum 24 Å movement of their Cα atoms. This movement directly blocks the binding of substrate/inhibitors to the PDE5 active site, which is different from all traditional PDE5 inhibitors such as sildenafil, tadalafil, and vardenafil. These derivatives showed >570-fold selectivity over PDE6C and PDE11A and achieved potent efficacy for the effective treatment of pulmonary hypertension in vivo.

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.

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.

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.

The first-generation phosphodiesterase 5 inhibitors and their pharmacokinetic issue.

BACKGROUND: Erectile dysfunction (ED) is a relatively frequent disease that negatively impacts the overall quality of life, well-being, and relationships. Although the use of phosphodiesterase 5 inhibitors (PDE5is) has revolutionized the treatment of ED, a high percentage of ED patients discontinue PDE5i treatment. OBJECTIVES: (i) To analyze the reasons for patient dissatisfaction leading to PDE5i discontinuation; (ii) analyze the pharmacokinetics of new formulations focusing on the time needed to reach an effective plasma concentration of PDE5is (Tonset ) following drug intake; and (iii) summarize the physicochemical properties of sildenafil to understand which excipients may increase the absorption rate. MATERIAL AND METHODS: An online PubMed literature search was conducted to identify English language publications from inception to January 2019. RESULTS: The main reasons for patient dissatisfaction when using PDE5is on demand are the relatively long Tonset after taking vardenafil and sildenafil, including formulations such as film-coated tablets, fine granules, orally disintegrating tablets (ODTs), and oral thin films (ODFs). The relatively long Tonset , further worsened when accompanied by eating, highlights the following: (i) the need for planning intercourse, determining partner-related issues; (ii) issues when having sex before the maximum effect of the drug; and (iii) lower drug-related placebo effects. Some data suggest that sildenafil is a 'difficult' molecule, but Tonset can be improved following absorption by buccal mucosa using appropriate excipients. CONCLUSIONS: We conclude that several ODT and ODF formulations can improve the 'discretion' issue because they are taken without water, but they have similar pharmacokinetics to corresponding film-coated tablet formulations. One ODF formulation of sildenafil was characterized by a shorter Tonset and could potentially increase patient satisfaction following treatment. However, more clinical studies are needed to confirm the findings. Surfactants and ascorbic acid appear to be crucial excipients for achieving a high absorption rate, but more studies are needed.

Pharmacokinetics and safety of tadalafil in a paediatric population with pulmonary arterial hypertension: A multiple ascending-dose study.

AIMS: To evaluate the pharmacokinetics and safety of once-daily (QD) tadalafil in paediatric patients with pulmonary arterial hypertension (PAH) to establish an appropriate dose range for further research. METHODS: This was an open-label, multicentre, international, multiple-ascending-dose study. Patients aged ≥2 years were enrolled into 1 of 3 cohorts based on body weight: heavy-weight (≥40 kg), middle-weight (25 to <40 kg), and light-weight (<25 kg). Each patient received tadalafil QD for 10 weeks: 5 weeks at a low dose, then 5 weeks at a high dose. The doses for each cohort were intended to produce plasma tadalafil concentrations within the range produced by 5-10 mg (for the low dose) or 20-40 mg (for the high dose) of tadalafil in adults with PAH. Area under the plasma concentration-time curve during 1 dosing interval (AUCτ ), maximum concentration, and apparent clearance were assessed throughout the trial, as were safety and tolerability. RESULTS: The study enrolled 19 patients aged 2-17 years, weighing 9.9-76.0 kg. Tadalafil's median (range) steady-state AUCτ at the high dose was 7243 (3131-13 088) ng•h/mL across all patients. Concentrations were higher in no bosentan-treated patients than in bosentan-treated patients, but both populations were within the range of respective adult patients taking 20-40 mg QD. Tadalafil had an acceptable safety profile consistent with the known safety profile of tadalafil in adults. CONCLUSIONS: Tadalafil 40 mg QD for patients ≥40 kg, and 20 mg QD for patients <40 kg and aged ≥2 years, are suitable for further research in paediatric patients with PAH.

Intranasal Tadalafil nanoemulsions: formulation, characterization and pharmacodynamic evaluation.

This study aims at improving the bioavailability of a poorly soluble phosphodiesterase-5 inhibitor; tadalafil (TD) via developing intranasal (IN) nanoemulsions (NEs). Optimum NE ingredients were selected based on solubility studies, emulsification tests, and phase diagram construction. Both o/w and w/o NEs were selected based on their drug loading capacity. Optimum formulations were subjected to physicochemical characterization and were assessed for nasal toxicity through biochemical analysis of tumor necrosis factor-α (TNF-α) and caspase-3 in rat nasal tissues. Pharmacodynamic study was performed via biochemical analysis of cyclic guanosine monophosphate (cGMP) in rat penis 2-h post-treatment and compared with oral suspension of Cialis® tablets. Optimum o/w and w/o NEs were successfully prepared using different ratios of Capmul-MCM-EP, Labrasol:Transcutol-HP (1:1) and water. Optimized formulations exhibited more than 4000-fold increase in TD solubility compared with its aqueous solubility. Both formulations were optically isotropic with the majority of globules in the nanometric-size range. Nasal toxicity study revealed no significant difference in values of TNF-α and caspase-3 between the NE-treated groups and the control group. Both TD-NEs succeeded to achieve a significant enhancement in cGMP levels. Our findings suggested that IN administration of the developed TD-NEs could provide a safe and effective alternative to TD oral delivery.

Tadalafil nanocomposites as a dry powder formulation for inhalation, a new strategy for pulmonary arterial hypertension treatment.

Tadalafil (a phosphodiesterase-5 inhibitor) is a choice for treatment of pulmonary arterial hypertension (PAH) that is known as an increase in mean pulmonary arterial pressure ≥25 mmHg at rest and ≥30 mmHg during exercise with reduced cardiac output. The aim of this study was to prepare inhalable tadalafil nanocomposites as a dry powder formulation by spray drying technique for increasing bioavailability and treatment efficacy, as well as decreasing systemic side effects. The D-optimal design was used for optimization of formulation parameters. Microparticle size, morphology, crystallinity, density, solubility, redispersion (%), and in-vitro inhalation performance of tadalafil nanocomposites were investigated as physicochemical characteristics. Pharmacokinetic parameters were also evaluated in plasma and lung tissue of Wistar rats after intratracheal insufflation and compared with a control group receiving an oral tadalafil marketed product (dose = 10 mg/kg). The suggested optimum formulation contained stable amorphous particles with almost rounded shape and corrugated surface that were completely redispersed in the lung simulated medium with the mass median geometric diameter of 3.2 µm, density of 1.4 g/cm3, fine particle fraction based on emitted dose (%) of 57.2 ±â€¯6.5%, and 13.7-fold enhancement in dissolution rate. In-vivo studies showed that the ratio of AUC0-24h lung/AUC0-24h plasma, achieved in the treated group after intratracheal insufflation, was significantly higher than the control group that means high local drug concentration and more efficacy. Besides, plasma data analysis indicated high value of MRT (2.3-fold) and tmax (3.7-fold) after intratracheal insufflation of tadalafil nanocomposites in comparison with the conventional oral route, indicating longer retention of tadalafil molecules in the lungs and their slower entry to the systemic blood circulation. In conclusion, it seems that inhalable tadalafil nanocomposites can be introduced as an alternative to oral tadalafil in the treatment of PAH.

Pharmacokinetics-Driven Optimization of 4(3 H)-Pyrimidinones as Phosphodiesterase Type 5 Inhibitors Leading to TPN171, a Clinical Candidate for the Treatment of Pulmonary Arterial Hypertension.

Phosphodiesterase type 5 (PDE5) inhibitors are first-line therapy for pulmonary arterial hypertension (PAH) and erectile dysfunction. As a continuing work to improve the terminal half-lives and oral bioavailabilities of our previously reported 4(3 H)-pyrimidones, a pharmacokinetics-driven optimization focusing on the terminal substituent is described. Two major congeneric series of 4(3 H)-pyrimidones, the aminosulfonylphenylpyrimidones and acylaminophenylpyrimidones, were designed, synthesized, and pharmacologically assessed in vitro and in vivo. Among them, compound 15 (TPN171) with subnanomolar potency for PDE5 and good selectivity over PDE6 was finally recognized as a potential drug candidate, and its pharmacokinetic profiles in rats and dogs are significantly improved compared to the starting compound (3). Moreover, TPN171 was proven to exert a longer lasting effect than sildenafil in animal models, providing a foundation for a once-daily oral administration for its clinical use. TPN171 is currently being investigated in a phase II clinical trial for the treatment of PAH.