© 2003 by the American Diabetes Association, Inc.
Sildenafil Citrate for Treatment of Erectile Dysfunction in Men With Type 1 DiabetesResults of a randomized controlled trial
1 Keogh Institute for Medical Research, Department of Endocrinology and Diabetes, Sir Charles Gairdner Hospital, Nedlands, Australia
OBJECTIVEIn the 510% of diabetic men with type 1 diabetes, erectile dysfunction (ED) may be a particularly common and unwanted complication. This is the first study focusing exclusively on the effects of sildenafil in men with type 1 diabetes and ED. RESEARCH DESIGN AND METHODSA total of 188 patients were entered into a double-blind, placebo-controlled, parallel-group, flexible-dose study and were randomized to receive sildenafil (25100 mg; n = 95) or placebo (n = 93) for 12 weeks. Efficacy was evaluated using questions three (Q3; achieving an erection) and four (Q4; maintaining an erection) from the International Index of Erectile Function (IIEF), a global efficacy question (GEQ; "Did treatment improve your erections?"), and a patient event log of sexual activity. RESULTSImprovements in mean scores from baseline to end-of-treatment for IIEF Q3 (35.7 vs. 19.9%) and Q4 (68.4 vs. 26.5%) were significant in patients receiving sildenafil compared with those receiving placebo (P = 0.0001). Moreover, the percent of improved erections (GEQ, 66.6 vs. 28.6%) and successful intercourse attempts (63 vs. 33%) was significantly increased with sildenafil compared with placebo. Improvements in sexual function were seen irrespective of the degree of ED severity. Adverse events were generally mild to moderate in severity, with headache (20 vs. 8%), flushing (18 vs. 3%), and dyspepsia (8 vs. 1%) reported more often in the sildenafil than in placebo-treated patients. CONCLUSIONSTreatment with sildenafil for ED was effective, resulting in an increased percentage of successful attempts at intercourse, and was well tolerated among men with type 1 diabetes.
Abbreviations: ED, erectile dysfunction EF, erectile function GEQ, Global Efficacy Question IIEF, International Index of Erectile Function
According to the World Health Organization, the number of adults with diabetes was 135 million in 1995, which corresponds to a worldwide prevalence of 4% (1). It is estimated that 510% of diagnosed cases are type 1 diabetes (2). A common complication of diabetes is erectile dysfunction (ED), with an estimated prevalence of 2085% (ranging from mild to complete ED) (3), which occurs at an earlier age than in nondiabetic men. In the Massachusetts Male Aging Study (4), men with treated diabetes had a 28% age-adjusted prevalence of complete ED (no erections), almost three times higher than the prevalence of complete ED observed in the entire sample of men (10%). Several studies have shown an increased risk of ED in men with diabetes; however, most information refers to the total male diabetic population, and few studies have presented data specifically for type 1 diabetes (58). Although the prevalence of ED in the total diabetic population increases with age, smoking, and poor metabolic control, one study reported that men with elevated BMI and type 1 diabetes showed a significantly higher risk of ED than men with elevated BMI and type 2 diabetes (7). The same study also showed that the age-adjusted prevalence of ED was higher in men with type 1 diabetes (51%) than with type 2 diabetes (37%). Although the etiology of ED in patients with diabetes is often complex and can be caused by several mechanisms, organic vasculogenic factors appear to be the most frequent cause of ED in men with diabetes (9), with some studies citing an incidence of up to 87% (10). Within vasculogenic ED, the most common etiology is arterial insufficiency, found more frequently in men with type 1 diabetes (73%) than with type 2 diabetes (61%) (11). Moreover, in men with type 1 diabetes, the severity of arterial insufficiency correlated with the presence of smoking, hypertension, and coronary artery disease, although only those with the latter disease showed a statistically significant reduction in penile blood flow compared with men who had type 2 diabetes (11). Treatment options for men with ED have advanced significantly during the past 1015 years, and a number of approaches have been used for men with diabetes (1214). However, efficacy and/or long-term satisfaction with most of these treatment options have been suboptimal. Sildenafil citrate (Viagra; Pfizer, New York) has in past studies demonstrated efficacy in men with diabetes (2,7,8,15,16); the aim of this study was to assess its efficacy exclusively in men with type 1 diabetes and ED.
Study design This was a double-blind, randomized, placebo-controlled, multicenter, parallel-group, flexible-dose study that included 188 patients with type 1 diabetes and ED. Following a 4-week run-in period, during which baseline data on sexual function were collected, patients were randomized to sildenafil (50 mg) or matching placebo and entered a 12-week double-blind treatment period with follow-up visits after 2, 4, 8, and 12 weeks of treatment. Dosage adjustments to 100 or 25 mg sildenafil or matching placebo were made according to efficacy and tolerability.
Inclusion criteria
Major exclusion criteria
Randomization and blinding
Study drug
Study evaluations
Secondary efficacy assessment
Stratification of efficacy results
Statistical evaluation
Ethics
The baseline characteristics of men with ED randomized to placebo or sildenafil were largely similar with respect to age, race, ED etiology, duration of ED and diabetes, metabolic control, concomitant illnesses, and previous ED treatment received (Table 1). There were twice as many patients with HbA1c levels 8% (n = 125) than with levels <8% (n = 63). Patient disposition during the course of the study is shown in Fig. 1.
Efficacy After 12 weeks, there were marked improvements in the ability to achieve and maintain an erection, with the mean scores for IIEF Q3 (Fig. 2A) and Q4 (Fig. 2B) significantly higher (33 and 48%, respectively) in the sildenafil group (3.61 ± 0.48 and 3.25 ± 0.52; P 0.001) compared with the placebo group (2.71 ± 0.47 and 2.19 ± 0.5). Patients with mild/moderate ED achieved higher final scores for Q3 and Q4 (4.48 and 4.05) than patients with severe ED (2.39 and 2.41) but also started with approximately three times higher baseline scores. The percent of successful intercourse attempts (Fig. 2C) was significantly higher in the sildenafil group (P < 0.051), with twice as many patients answering in the affirmative compared with the placebo group, irrespective of ED severity; however, patients with severe ED had fewer overall successful attempts compared with men who had mild/moderate ED. Positive responses to the GEQ ("Has treatment improved your erections?") were higher in the sildenafil group, with 66% of patients with mild/moderate ED responding in the affirmative compared with 29% of patients taking placebo. Patients with severe ED (sildenafil, n = 33; placebo, n = 41) reported a lower percent of improved erections (sildenafil, 30%; placebo, 10%).
After 12 weeks of sildenafil treatment, the EF domain showed on average a 6-point increase in the mean score over placebo, irrespective of the ED severity (Fig. 2D). As observed for the other efficacy parameters, men with mild/moderate ED achieved a higher overall score compared with men with severe ED (Fig. 2D).
Stratification of efficacy by metabolic control, smoking status, and presence of cardiovascular complications.
Adverse events
Men with diabetes have an approximate threefold higher risk for ED than men without diabetes (4). In the present study, sildenafil (50100 mg) was an effective oral therapy for men with type 1 diabetes; >66% of patients reported improved erections (compared with 29% in the placebo group), and the number of successful intercourse attempts with sildenafil (63%) was significantly higher compared with placebo (33%). These data are in agreement with an earlier study, where sildenafil was shown to be an effective and well-tolerated treatment in a group of 268 men with ED and concomitant diabetes (type 1 and 2) (2). In this patient group, efficacy of sildenafil was independent of age, duration of ED, and duration of diabetes, and erections were improved in 56% of patients receiving sildenafil compared with 10% of patients taking placebo. Similarly, a recent study in 219 patients exclusively with type 2 diabetes demonstrated that sildenafil was well tolerated and effective in improving ED in this patient group (65% of patients reported improved erections compared with 11% in the placebo group), even in cases with poor glycemic control and chronic complications (16). Thus, the current study demonstrated similar efficacy, although the improvement in the placebo group was larger. It is well documented that in comparison with other disease-specific populations, the efficacy of sildenafil is lower in men with diabetes. For example, Goldstein et al. (19) reported improved erections in 7788% of men with broad spectrum ED receiving sildenafil. Similarly, men with spinal cord injury (20) or depression (21) demonstrated high response rates to sildenafil (78 and 69%, respectively). The reason for poorer efficacy in the diabetic population is thought to be the multifactorial nature of the disease. Poor vascular blood supply to the penile arteries as a result of macrovascular disease and atherosclerotic lesions (22), reduced production of nitric oxide and cyclic guanosine monophosphate in the corpus cavernosum as a result of advanced glycosylation product accumulation (23), and impaired neurogenic and endothelium-dependent relaxation of penile arteries (24) all contribute to diabetes-associated ED. Moreover, concomitant medications frequently used in diabetic patients, such as antihypertensive agents (ß-blockers, calcium channel antagonists) (25) and lipid-lowering drugs (fibrates, statins) can contribute to a reduced efficacy of sildenafil (26). Patients with type 1 diabetes are often relatively young and may thus benefit from a well-tolerated treatment regimen. The drop-out rate with sildenafil treatment is low compared with that for other treatments for ED, such as intracavernosal injections, which have a high attrition rate, pain with injection, or nodule formation (27), and penile implants, which may require implant removal because of infection (28). However, because sildenafil does not resolve ED in all patients with diabetes, each patient should be given information on other treatment options that have shown efficacy for this population.
The efficacy and safety of sildenafil have been assessed from more than 11,000 patient-years of observation in controlled clinical trials, many of which focused on and/or included men with diabetes (29). The safety profile of sildenafil in this study of men with ED and type 1 diabetes is in agreement with previous reports in which the most common adverse events associated with use of sildenafil in flexible-dose studies were headache (20%), flushing (18%), dyspepsia (8%), and visual disturbances (2%), all consistent with the known pharmacological effects of the drug (30). These effects were generally transient and mild to moderate in nature, and the rate of discontinuations because of these events was similar for patients receiving placebo (2.2%) or sildenafil (1.1%). All clinical studies conducted so far have shown that the incidence of adverse events and the rate of discontinuations attributed to them are similar in patients with diabetes compared with patients without diabetes ( Adverse effects on metabolic control are an important consideration when treating patients with diabetes. There is no indication from clinical trial data that sildenafil adversely affects blood glucose levels in patients with diabetes; furthermore, in a previously published study in 21 men with type 1 or 2 diabetes, no clinically significant changes in laboratory test results were observed, suggesting that sildenafil did not impair metabolic control (15). In summary, ED is known to occur with greater frequency in patients with type 1 diabetes than in the general population (32). It is thus encouraging that treatment with sildenafil was able to improve erections and was well tolerated in men with ED and concomitant diabetes in this study, irrespective of ED severity, level of metabolic control, smoking status, or the presence of cardiovascular complications. Therefore, unless there is a contraindication to the use of sildenafil, it would be reasonable for sildenafil to be considered the initial therapeutic choice for patients with ED and concomitant type 1 diabetes.
This study was sponsored by Pfizer Inc., New York, New York. Clinical Investigators Mauricio N. Jadzinsky, Buenos Aires, Argentina Isacc Sinay, Buenos Aires, Argentina Richard Gilbert, Heidelberg, Australia Bronwyn Stuckey, Nedlands, Australia Fadlo Fraige, Sao Paulo, Brazil Liam J. Murphy, Winnipeg, Canada Ehud Ur, Halifax, Canada Andre Belanger, Laval, Canada Man Chi Wai, Hong Kong Riccardo Giorgino, Cesare, Italy Guido Pozza, Milano, Italy Francesco Montorsi, Milano, Italy Domenico Fedele, Padova, Italy Renzo Cordera, Genova, Italy Andrea Corsi, Genova, Italy Julia Alvarez, Spain Soledad Ruiz de Arana, Spain Pilar Manzano, Madrid, Spain Chaicham Deerochanawong, Bangkok, Thailand Kadri Anafarta, Ankara, Turkey Ali Ergen, Ankara, Turkey Adil Esen, Izmir, Turkey Halim Hattat, Istanbul, Turkey Ates Kadioglu, Istanbul, Turkey
Address correspondence and reprint requests to Dr. Bronwyn Stuckey, Keogh Institute for Medical Research, Sir Charles Gairdner Hospital, Nedlands, WA 6009, Australia. E-mail: bstuckey{at}cyllene.uwa.edu.au. Received for publication 28 May 2002 and accepted in revised form 3 November 2002. B.G.A.S. has previously received research grants from Pfizer; L.J.M. has received honoraria from Merck Pfizer, GlaxoSmithKline, Abbott, and Bristol Myers Squibb; and A.K. has received honoraria and research grants from Pfizer. A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances.
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