Category
New applications
Recent data have indicated a potential association between epidemiological, physiologic, pathophysiologic, and treatment aspects of ED and lower urinary tract symptoms (LUTS) secondary to BPH. The 17.5 hour half-life of tadalafil makes it the most suitable PDE5 inhibitor for once-daily dosing in a trial of LUTS secondary to BPH. McVary and associates reported a multicentered, randomized, double-blind, placebo controlled study of 281 men with LUTS secondary to BPH who were randomly assigned to once-daily tadalafil 5 mg for 6 weeks, followed by dose escalation to 20 mg for 6 weeks, or 12 weeks of placebo. They reported modest decreases in International Prostate Symptom Score (IPSS), with a mean change from baseline to 6 weeks of −2.8 with tadalafil 5 mg versus −1.2 with placebo (p < 0.003), and to 12 weeks of −3.8 with tadalafil 5/20 mg versus −1.7 with placebo (p < 0.001).
Once-daily dosing
The latest innovation in the treatment of ED has arrived in the form of a simpler, once-daily dosing schedule for tadalafil, unlinking the temporal association of the medication and the sexual encounter. The unnatural process of taking a medication just prior to sex is a negative aspect of ED treatment for many patients. The 17.5 hour half-life of tadalafil lends itself to daily dosing because steady-state plasma concentrations are attained within five days of initiating daily dosing. Additionally, at steady-state concentration, the daily exposure is 1.6-fold greater than the same dose taken intermittently. Therefore, after 5 days of once-daily dosing, the plasma concentration of tadalafil (Cialis) achieved with a 2.5 mg and 5 mg dose is 4 mg and 8 mg, respectively. The FDA announced approval for once-daily dosing of tadalafil in January 2008 after a thorough review of the studies outlined below.
ED after prostate cancer treatment
All of the available prostate cancer treatments, including radical prostatectomy, external beam radiation therapy, brachytherapy, cryotherapy, androgen-deprivation therapy, and even active surveillance alone, can result in ED. ED after prostate cancer treatment includes both organic and psychogenic causes, as significant anxiety and depression may result from a diagnosis of prostate cancer, leading to psychogenic ED.
The most important risk for organic ED after prostate cancer treatment of any type is damage to the cavernosal nerves. Walsh first described the technique for sparing the bilateral neurovascular bundles to better preserve erectile function, and a bilateral nerve sparing radical prostatectomy (BNSRP) is the surgical standard for prostate cancer today. Approximately 155,000 prostatectomies were performed in the United States in 2005 according to hospital discharge data. Potency in men after open BNSRP has a wide reported range of 10% to 97% in the literature. Of 1288 men who underwent radical prostatectomy as part of the Prostate Cancer Outcomes Study, only 28% had erections sufficient for intercourse at 5 years.
ED secondary to diabetes mellitus
ED is a common problem afflicting over a third of all men with diabetes mellitus type 2, and diabetes is independently responsible for a 3- to 4-fold increase in the risk of ED according to a survey of 1460 diabetic men. ED is strongly related to the severity of diabetes, with a higher incidence in patients with a long history of diabetes, patients using insulin, and patients with microvascular complications of diabetes. Diabetic men with ED also have significantly worse disease-specific health-related quality of life.
Difficult-to-treat ED
In the two trials mentioned in the previous section, the patient population was largely a primary care population of relatively healthy men with ED of varying severities and etiologies. To the contrary, a multicentered, randomized, double-blind, placebo controlled trial evaluated how tadalafil 20 mg improved ED in men presenting to tertiary care centers with more severe, organic ED and with more comorbid medical conditions than previous studies.
The general ED population
The most frequently referenced study supporting the efficacy of tadalafil is an integrated analysis of 5 randomized, double-blind, placebo controlled, multicentered phase III trials from 1112 men at 74 centers worldwide. The average age was 59, and the etiology of ED was 61% organic, 9% psychogenic, and 31% mixed. The ED severity at baseline was mild in 41%, moderate in 23%, and severe in 36%. Subjects were randomized to placebo or tadalafil at doses from 2.5 mg to 20 mg and instructed to self-administer a dose before initiating intercourse up to once daily. IIEF-EF, SEP, and GAQ scores were assessed at baseline and at 12 weeks.
Background on outcome measures
Although the effectiveness of PDE5 inhibitors on such intermediate objective outcomes as penile rigidity through penile plethysmography with the RigiScan device (Dacomed Corporation, Minneapolis, MN, USA) has been studied, measuring the therapeutic effectiveness of tadalafil (Cialis Professional) is more accurately defined through an integration of the patient’s reported treatment response and tolerability with the reported satisfaction of both the patient and his partner. Despite their intrinsically subjective nature, validated questionnaires are the preferred major outcome measure of treatment effectiveness of tadalafil and other PDE5 inhibitors.
The International Index of Erectile Function (IIEF) was developed by Rosen and colleagues in 1997 as a multidimensional, 15-item, self-administered questionnaire with the goal of assessing five domains of male sexual function including erectile function, orgasmic function, sexual desire, intercourse satisfaction, and overall satisfaction. The erectile function domain of the IIEF (IIEF-EF) contains 6 questions which the patient answers on a scale from 1 (never or almost never) to 5 (almost always or always), providing a total score of 6 to 30 points. The questions concern erectile frequency, firmness, penetration ability, maintenance frequency, maintenance ability, and erection confidence. Based on a controlled study of 1151 men taking sildenafil professional in order to establish cutoff scores for the IIEF-EF, a score of 26 or greater is defined as normal function, mild ED is a score from 22 to 25, mild to moderate ED 17 to 21, moderate ED 11 to 16, and severe ED 6 to 10.