Tadalafil population pharmacokinetics in patients with erectile dysfunction

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 (AUC_0–24)/predicted AUC_0–24, with target AUC_0–24 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.

Pharmacokinetic and Bioequivalence Evaluation of 2 Tadalafil Tablets in Healthy Male Chinese Subjects Under Fasting and Fed Conditions

Tadalafil is an effective, reversible, and competitive phosphodiesterase 5 inhibitor mainly used to treat erectile dysfunction. This study investigated the bioequivalence of generic and marketed formulations of 10-mg tadalafil tablets under fasted and fed conditions. This open-label, randomized, single-dose, 2-period crossover study included 53 healthy Chinese men (aged 20-43 years). Plasma samples were collected from 0.5 hours before treatment to 72 hours after each dose and analyzed using ultra-high-performance liquid chromatography coupled with tandem mass spectrometry. Pharmacokinetic parameters were calculated using noncompartmental analysis. Safety assessments were performed throughout the study. For the fasted state, the 90% confidence intervals of the geometric mean ratios between the generic and marketed formulations were 86.1% to 99.1% for the maximum plasma concentration and 88.4% to 100.3% for the area under the plasma concentration-time curve from time 0 to infinity, and the corresponding values under the fed state were and 99.9% to 108.4% and 95.7% to 104.3%, respectively. All data were within the accepted bioequivalence range of 80% to 125%. After consuming high-fat, high-calorie meals in the fed condition, the time to the maximum plasma concentration was similar between the formulations, and area under the plasma concentration-time curve from time 0 to infinity and maximum plasma concentration were 10.2% and 6.55% higher, respectively, for the marketed formulation. Thus, food had no clinically relevant effect on tadalafil exposure following a single oral dose in healthy Chinese men. No serious adverse reactions were reported. These results indicated that the analyzed generic and marketed tadalafil tablets were bioequivalent with similar safety profiles.

Comparison of tadalafil pharmacokinetics after administration of a new orodispersible film versus a film-coated tablet

Background

An orodispersible film (ODF) of tadalafil may provide increased convenience for erectile dysfunction (ED) patients as compared to conventional tablet formulations. In this study, we aimed to compare the pharmacokinetic, safety, and tolerability profiles of a newly developed ODF formulation of tadalafil to those of a film-coated tablet (FCT) of tadalafil.

Materials and methods

This study was conducted in healthy male subjects using an open-label, randomized sequence, two-period, two-formulation, single-dose, crossover design. The subjects were randomly assigned to one of two sequences of the two formulations: both the test drug (ODF) and the reference drug (FCT) contained 20 mg of tadalafil. Blood samples were collected up to 72 h after administration. Plasma concentrations of tadalafil were analyzed using liquid chromatography-tandem mass spectrometry. Geometric mean ratios (GMRs) of the ODF to FCT formulations and their 90% CIs for the pharmacokinetic parameters were estimated. Safety and tolerability were assessed throughout the study.

Results

Forty healthy male subjects were enrolled, and 36 of these completed the study. The GMRs (90% CIs) of the maximum plasma concentration and the area under the plasma concentration-time curve from time zero to the time of the last quantifiable concentration for tadalafil were 0.927 (0.882-0.974) and 0.972 (0.918-1.029), respectively. Both ODF and FCT formulations were well tolerated, and no clinically significant changes from the baseline were observed after dosing.

Conclusion

The pharmacokinetics of the tadalafil ODF formulation did not differ significantly from those of the FCT formulation. Furthermore, the safety and tolerability profiles of the ODF formulation were comparable to those of the FCT formulation. Therefore, this tadalafil ODF formulation offers a convenient treatment option for patients with erectile dysfunction.

Plasma concentrations of tadalafil in children with pulmonary arterial hypertension

BACKGROUND

There is no report documenting the plasma concentrations of tadalafil in children. This study was performed to evaluate the variability in the pharmacokinetics of tadalafil in children with pulmonary arterial hypertension (PAH) treated routinely with the drug.

METHODS

Plasma samples were taken twice (post- and predose) after repetitive oral administration, and the pharmacokinetic parameters (CL/F and V/F) in individual patients were estimated by the Bayesian method using the nonlinear mixed effects model. We also determined the unbound concentration of tadalafil using ultrafiltration.

RESULTS

Tadalafil was administered to 23 children aged between 0.25 and 17.4 years, with a mean age of 3.58 years. The mean (±SD) daily dose of tadalafil was 0.97 ± 0.41 mg/kg. Sixteen of the 23 children received bosentan concomitantly. The mean CL/F and V/F values of tadalafil were 0.149 L·h-1·kg-1 and 1.87 L/kg, respectively, which were higher than those reported in adults. No effects of age, bosentan, or the estimated glomerular filtration rate were observed on the CL/F value, indicating that other residual factors might account for the interindividual variability among children with PAH. The unbound tadalafil concentrations of the postdose samples ranged from 5.9 to 146 (46.9 ± 37.1) nmol/L, higher than the reported IC50 value of this phosphodiesterase-5 drug for humans (2-4 nmol/L, corresponding to 0.8-1.6 ng/mL).

CONCLUSIONS

We demonstrated variability in the total and unbound plasma concentrations of tadalafil in children. However, all children received the empirical doses of the drug; a mean dose of 0.97 mg·kg-1·d-1 showed sufficient unbound concentrations needed for half-maximal inhibition of human phosphodiesterase-5 in vitro. These observations may provide information for the proper use of tadalafil to treat children with PAH.

Management of benign prostatic hyperplasia: role of phosphodiesterase-5 inhibitors

Several studies have highlighted a strong association between benign prostatic hyperplasia/lower urinary tract symptoms (BPH/LUTS) and erectile dysfunction (ED), particularly in elderly men. Many epidemiological trials, such as in vitro and in vivo studies, have reported the emerging role of metabolic syndrome, including abdominal obesity, impaired glucose metabolism, hypertriglyceridemia, low high-density lipoprotein cholesterol, and hypertension, in the development and progression of urinary and sexual symptoms. Moreover, many authors have focused their studies on the identification of all the shared pathogenetic mechanisms of LUTS/BPH and ED, including alteration of cyclic guanosine monophosphate and RhoA-ROCK pathways or vascular and neurogenic dysfunction. All these are potential targets for proposed phosphodiesterase type 5 inhibitors (PDE5-Is). Therefore, several trials have recently been designed to evaluate the role of PDE5-Is alone or in combination with conventional treatment for BPH, such as α-adrenergic blockers, in men affected by LUTS/BPH, with or without ED. Different PDE5-Is are in clinical use worldwide and currently six of them are licensed for the oral treatment of ED. All these compounds differ in pharmacokinetic factors, with influence on drug action, and subsequently in the overall safety and efficacy profile.

Phosphodiesterase type 5 (PDE5) inhibitors in erectile dysfunction: the proper drug for the proper patient

INTRODUCTION

Erectile dysfunction (ED) is a very common multidimensional disorder affecting men worldwide. Physical illness, reaction to life stresses, or an unhappy couple relationship influence clinical outcome. Phosphodiesterase type 5 (PDE5) inhibitors are recognized as efficacious and well tolerated, and are the first-line treatment for ED. Sildenafil, tadalafil, and vardenafil are the most widely used and studied PDE5 inhibitors. Data acquired during a routine diagnostic workup for ED should be taken into account when choosing the best PDE5 inhibitor for the individual patient, creating an individualized treatment plan, and going beyond "experience-based" subjective opinion and unfounded ideas and prejudice regarding currently available drugs.

AIM

As the process of matching a given patient's profile to any selected PDE5 inhibitor often relies more on physician's personal convictions than on solid evidence, the aim of this review is to identify the main clinical, demographic, and relational factors influencing the choice of the PDE5 inhibitor to be used for the treatment of ED.

METHODS

A systematic literature search and current treatment guidelines were evaluated in a systematic manner.

MAIN OUTCOME MEASURES

The main clinical, cultural, and demographical factors to be considered for the treatment of ED have been identified.

RESULTS

Main factors influencing the choice of the treatment for ED have been described. A short list of items that may help in choosing the right PDE5 inhibitor for the treatment of different patients in daily clinical practice has been prepared.

CONCLUSIONS

The simple algorithms prepared should be a useful tool to be used in daily practice, which may help in choosing the right treatment for each subject affected by ED.

Tadalafil once daily in the management of erectile dysfunction: patient and partner perspectives

Erectile dysfunction (ED) is a prevalent condition that affects men and their partners. Significant improvements in the sexual lives of these couples have been achieved with the introduction of phosphodiesterase 5 (PDE5) inhibitors. A PDE5 inhibitor is now widely recognized as the first-line therapy for the majority of men with ED. Currently, three PDE5 inhibitors - sildenafil, tadalafil and vardenafil - are approved to be taken as needed in anticipation of sexual activity, but only one of these, tadalafil, has been approved to be taken once daily. The primary aims of this review are to summarize the patients' and partners' viewpoints of ED management with PDE5 inhibitors, and to determine whether once-daily tadalafil can contribute to improving some psychological aspects of ED (such as sexual self-confidence, spontaneity and time concerns) compared with on-demand tadalafil or other PDE5 inhibitors taken by patients with ED.

Managing Erectile Dysfunction in Patients With Cardiovascular Diseases: The Efficacy and Safety of Phosphodiesterase-5 Inhibitors

Patients with cardiovascular disease have a high prevalence of erectile dysfunction. Recent evidence demonstrated that erectile dysfunction is an early indication of coronary artery disease. Phosphodiesterase-5 (PDE-5) inhibitors are effective in managing erectile dysfunction due to cardiovascular disease. However, when used together with nitrates or other vasodilators such as alpha-antagonists, they may cause hypotension. Clinical studies demonstrated that in patients with stable coronary artery disease, heart failure, and hypertension controlled by medications who were not receiving nitrates, PDE-5 inhibitors were well tolerated. Therefore, it is important for clinicians to carefully evaluate each patient before initiating PDE-5 inhibitors. PDE-5 inhibitors are absolutely contraindicated with concurrent nitrate use. No PDE-5 inhibitors should be administered within 12 hours after the last nitrate dose. If a patient develops chest pain while taking PDE-5 inhibitors, nitrates should be administered only after the PDE-5 inhibitors have been washed out of the system, based on the half-life of individual agents (washed-out period for sildenafil ∽20 hours; vardenafil ∽ 24 hours; tadalafil ∽88 hours [or 3-4 days]). If symptomatic hypotension occurs, patients should be put in a Trendelenburg position. Fluid resuscitation therapy and alpha-agonists should be used to support blood pressure, if necessary. PDE-5 inhibitors have not been studied in patients with severe and unstable cardiac conditions.

The use of phosphodiesterase 5 inhibitors with concomitant medications

The phosphodiesterase-5 inhibitors (PDE5i) sildenafil, vardenafil, and tadalafil are considered first-line therapy for the treatment of patients with erectile dysfunction (ED). In addition to the classical pro-erectile-effect, clinical findings have suggested that they can also influence vascular tone in pulmonary, coronary and other vascular tissues, as well as improving symptoms associated with benign prostatic hyperplasia. Therefore, considering the hypothetical widespread application of PDE5i, the potential for drug-drug interactions emerges as a relevant factor in determining the safety profile of PDE5i. Review of relevant literature was conducted using data sources from MEDLINE (1998, to June 2007). The use of nitrates remains the only contraindication for all 3 PDE5i. Vardenafil is also not recommended in patients taking type 1A (such as quinidine, or procainamide) or type 3 antiarrhythmics (such as sotalol, or amiodarone) while no other major limitations have been reported for tadalafil and sildenafil. In contrast to previously reported labeling, recent studies have suggested only a precaution, but not contraindication with the concomitant use of alpha-blockers agents. In addition, precaution is also suggested in the presence of potent CYP3A inhibitors, such as azole antifungals, antiretroviral protease inhibitors, or macrolid antibiotics. This is because sildenafil, vardenafil, and tadalafil are metabolized mainly via the CYP3A4 pathway. On the other hand, statins and testosterone seem to have synergic effects with PDE5i on sexual activity.