Tadalafil population pharmacokinetics in patients with erectile dysfunction.

OBJECTIVE: The purpose of this study was to characterize pharmacokinetics of tadalafil (Cialis) and potential sources of variability in patients with erectile dysfunction (ED). METHODS: Population models were developed to describe tadalafil pharmacokinetics in 227 patients with mild to severe ED in a phase III trial. Parallel groups of patients received 2, 5, or 10 mg tadalafil or placebo orally, as needed, for 12 weeks. RESULTS: Tadalafil pharmacokinetics in patients with ED were linear with respect to dose and duration of treatment, and a one-compartment model adequately described the data. The absorption rate was rapid (1.86 h(-1)), and the typical population estimates of the apparent oral clearance (CL/F) and apparent volume of distribution were 1.6 l/h and 63.8 l, respectively. Disposition parameters showed a moderate degree of interindividual variability (39-45%). The value of CL/F decreased slightly with increasing serum gamma-glutamyl transferase (GGT) concentration, the only statistically significant covariate detected. Systemic exposure to tadalafil was not influenced by age, weight, smoking status, alcohol consumption, liver enzyme status, ED severity, cardiovascular condition, or diabetes mellitus. CONCLUSION: Pharmacokinetics in the efficacy/safety trial population are essentially similar to pharmacokinetics in healthy subjects, and no patient-specific factor warranting clinical consideration of dose regimen adjustment was identified in these analyses.

Effects of gender, age, diabetes mellitus and renal and hepatic impairment on tadalafil pharmacokinetics.

AIMS: To evaluate the effects of gender, age, diabetes mellitus, renal and hepatic impairment on tadalafil pharmacokinetics and tolerability. METHODS: Six single-dose (5, 10 or 20 mg orally) clinical pharmacology studies were conducted in the UK, Belgium, Poland and Germany in healthy male and female subjects, elderly subjects and subjects with diabetes mellitus, renal impairment, end-stage renal failure (ESRF) or hepatic impairment. The gender study also incorporated administration of 10 mg tadalafil daily for 10 days. RESULTS: Systemic exposure in the elderly was 25% greater than in young subjects (mean AUC ratio 1.25; 90% confidence interval 0.972, 1.61). The AUC was 19% lower in subjects with diabetes mellitus than in healthy age/gender-matched controls. Pharmacokinetics in female subjects were essentially similar to those in males. Exposure in subjects with mild or moderate renal insufficiency was approximately twice that in healthy subjects. The mean AUC for the major metabolite (total methylcatechol glucuronide) in the presence of ESRF was three times the mean for healthy subjects. Haemodialysis contributed negligibly to elimination of tadalafil or the metabolite. Hepatic impairment had negligible effects on exposure. The most common adverse events in these six studies were headache, back pain and myalgia. A 10-mg dose was not well tolerated by subjects with moderate renal dysfunction in this study. CONCLUSIONS: No clinically significant effect of gender, age, diabetes mellitus or hepatic impairment on tadalafil pharmacokinetics was observed. Renal insufficiency resulted in increased systemic exposure. Tadalafil was not associated with any serious clinically significant adverse events or study discontinuations due to adverse events.

Model-based drug development: the road to quantitative pharmacology.

High development costs and low success rates in bringing new medicines to the market demand more efficient and effective approaches. Identified by the FDA as a valuable prognostic tool for fulfilling such a demand, model-based drug development is a mathematical and statistical approach that constructs, validates, and utilizes disease models, drug exposure-response models, and pharmacometric models to facilitate drug development. Quantitative pharmacology is a discipline that learns and confirms the key characteristics of new molecular entities in a quantitative manner, with goal of providing explicit, reproducible, and predictive evidence for optimizing drug development plans and enabling critical decision making. Model-based drug development serves as an integral part of quantitative pharmacology. This work reviews the general concept, basic elements, and evolving role of model-based drug development in quantitative pharmacology. Two case studies are presented to illustrate how the model-based drug development approach can facilitate knowledge management and decision making during drug development. The case studies also highlight the organizational learning that comes through implementation of quantitative pharmacology as a discipline. Finally, the prospects of quantitative pharmacology as an emerging discipline are discussed. Advances in this discipline will require continued collaboration between academia, industry and regulatory agencies.

Tadalafil pharmacokinetics in healthy subjects.

AIMS: To characterize tadalafil plasma pharmacokinetics in healthy subjects following single and multiple doses. METHODS: Noncompartmental parameters were calculated for healthy subjects receiving a single 2.5-20-mg tadalafil dose in 13 clinical pharmacology studies. An integrated statistical analysis of results in 237 subjects provided global averages and an assessment of effects of body mass index (BMI), age, gender and smoking status. Diurnal variation, food effects and proportionality of exposure to dose were analysed in three studies. Multiple-dose pharmacokinetics were evaluated in a separate study in which parallel groups of 15 subjects received 10 or 20 mg tadalafil once daily for 10 days. RESULTS: Tadalafil was absorbed rapidly with mean Cmax (378 microg l-1 for 20 mg) observed at 2 h; thereafter, concentrations declined nearly monoexponentially with a mean (5th, 95th percentiles) t1/2 of 17.5 (11.5, 29.6) hours. Mean oral clearance (CL/F) was 2.48 (1.35, 4.35) l h-1 and apparent volume of distribution (Vz/F) was 62.6 (39.5, 92.1) l. No clinically meaningful effect of BMI, age, gender or smoking was identified. Exposure was not substantially affected by time of dosing. Food had negligible effects on bioavailability as assessed by 90% confidence intervals for Cmax and AUC mean ratios. Parameters were proportional to dose, indicating that doubling the dose doubled exposure. Steady state was attained by day 5 following once-daily administration, and accumulation (1.6-fold) was consistent with the t1/2. CONCLUSIONS: Tadalafil pharmacokinetics are linear with respect to dose and time, and are not affected by food. Systemic clearance is low relative to other phosphodiesterase 5 inhibitors.

Effect of tadalafil on cytochrome P450 3A4-mediated clearance: studies in vitro and in vivo.

OBJECTIVES: Tadalafil was examined in vitro and in vivo for its ability to affect human cytochrome P450 (CYP) 3A-mediated metabolism. METHODS: Reversible and mechanism-based inhibition of CYP3A by tadalafil was examined in human liver microsomes. The ability of tadalafil to influence CYP3A activity was also examined in primary cultures of human hepatocytes. The effect of tadalafil on the pharmacokinetics of CYP3A probe substrates was evaluated in human volunteers before and after coadministration with either a single dose or multiple doses of tadalafil (10 or 20 mg). RESULTS: Negligible competitive inhibition of CYP3A was observed in vitro. Mechanism-based inhibition of CYP3A was detected, albeit with a low potency. In human hepatocytes, exposure to 1 micromol/L or greater of tadalafil resulted in increased CYP3A protein expression; however, as with a combined effect of induction and inhibition, a corresponding increase in CYP3A activity did not occur. The clinical pharmacokinetics of midazolam and lovastatin, probe substrates of CYP3A, were unaffected by up to 14 days of tadalafil administration (90% confidence intervals for the ratio of least squares means for the pharmacokinetic parameters of tadalafil were contained within the no-effect boundaries of 0.7 to 1.43). CONCLUSIONS: In vitro results suggested that tadalafil would have little effect on the pharmacokinetics of drugs metabolized by CYP3A. Clinical studies demonstrated that the pharmacokinetics of 2 different CYP3A substrates, midazolam and lovastatin, were virtually unchanged after tadalafil coadministration. Thus therapeutic concentrations of tadalafil do not produce clinically significant changes in the clearance of drugs metabolized by CYP3A.

Population dose-response model for tadalafil in the treatment of male erectile dysfunction.

PURPOSE: To determine the population dose-response relationship for tadalafil during on-demand (as-needed) administration for treatment of erectile dysfunction (ED). METHODS: A total of 212 male patients with mild, moderate, or severe ED participated in a multicenter, randomized, double-blind, placebo-controlled, parallel-group study. Patients were randomized to receive placebo or 2, 5, 10, or 25 mg tadalafil, taken on demand over an 8-week period. Efficacy was assessed on the basis of questions 2 and 3 of the Sexual Encounter Profile (SEP) and questions 3 and 4 of the International Index of Erectile Function (IIEF) questionaires. These scores were modeled using logistic regression. A fifth patient response, the IIEF EF (erectile function) domain score, was modeled as a continuous variable. RESULTS: The dose-response relationship for each efficacy variable was best described with an Emax model, in which maximum effect increased with ED severity at baseline. Response scores increased substantially between 10 and 25 mg tadalafil doses, and the dose-response parameter estimates suggested possibly higher responses at even higher doses. CONCLUSIONS: Population dose-response modeling of all five oucome measures indicated that efficacy in all ED severity groups in the studied population generally increased across the 2 to 25 mg tadalafil dose range. Estimates of maximal improvement (Emax) in the IIEF EF domain score were 7.5, 11.4, and 16.3 points for patients with mild, moderate, and severe ED, respectively. Corresponding tadalafil doses to attain half-maximal improvement (ED50 estimates) were 4.7 mg, 7.1 mg, and 10.1 mg.

Efficacy and safety of LY315920Na/S-5920, a selective inhibitor of 14-kDa group IIA secretory phospholipase A2, in patients with suspected sepsis and organ failure.

OBJECTIVE: Concentrations of group IIA secretory phospholipase A, an inflammatory response mediator, are increased in the plasma of patients with sepsis and septic shock, and the extent of elevation is correlated with mortality. LY315920Na/S-5920 is a selective inhibitor of group IIA secretory phospholipase A that has been shown to inhibit serum group IIA secretory phospholipase A enzyme activity in patients with severe sepsis. The primary objectives of this study were to determine whether there was a dose-response relationship between two doses of LY315920Na/S-5920 compared with placebo in the reduction of 28-day all-cause mortality in patients with severe sepsis and to determine whether LY315920Na/S-5920 had an acceptable safety profile.(2) (2) (2) DESIGN: Multicenter, double-blind, placebo-controlled trial of two doses of LY315920Na/S-5920 in a parallel design. PATIENTS: A total of 586 patients with severe sepsis at 72 institutions in the United States. INTERVENTIONS Patients enrolled within 72 hrs from onset of first sepsis-induced organ failure were randomized (1:1:1) to low-dose LY315920Na/S-5920 (target plasma concentration of 200 ng/mL, n = 196), high-dose LY315920Na/S-5920 (800 ng/mL, n = 194), or placebo (n = 196). Study medication was administered as a constant-rate intravenous infusion for 168 hrs. MEASUREMENTS AND MAIN RESULTS: The study was stopped prematurely because it was unlikely that a statistically significant difference in mortality between LY315920Na/S-5920 and placebo would be found. There was no effect of LY315920Na/S-5920 on the primary end point of 28-day all-cause mortality across the entire study population. The 28-day all-cause mortality was distributed as follows: placebo group, 33.2% (65/196 patients); low-dose LY315920Na/S-5920, 37.2% (73/196); and high-dose LY315920Na/S-5920, 36.1% (70/194); p = .525. However, in a prospectively planned analysis, there was a favorable overall dose-response effect on 28-day all-cause mortality in patients administered LY315920Na/S-5920 within 18 hrs of onset of the first sepsis-induced organ failure. Among these patients, 28-day all-cause mortality was distributed as follows: placebo group, 43.5% (20/46 patients); low-dose LY315920Na/S-5920, 31.4% (16/51); and high-dose LY315920Na/S-5920, 20.8% (10/48); p = .018. CONCLUSIONS: Administration of LY315920Na/S-5920 had an acceptable safety profile in patients with severe sepsis. There was no overall survival benefit associated with the use of LY315920Na/S-5920 in this study. However, prospectively planned secondary analyses suggested that treatment with LY315920Na/S-5920 was associated with an improvement in survival in patients treated within 18 hrs of the first sepsis-induced organ failure.