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From the Department of Urology, Harran University Faculty of Medicine, Sanliurfa, Turkey.
| Correspondence to: Dr Murat Savas, Urology Department, Medicine School of Harran University, 63100 Sanliurfa, Turkey (e-mail: mrtsvs{at}yahoo.com). |
| Received for publication November 18, 2008; accepted for publication February 2, 2009. |
Erectile dysfunction (ED) is prevalent among men, and several factors can
contribute to the failure of ED treatment based on phosphodiesterase-5 (PDE-5)
inhibitors. The aim of this study was to investigate the impact of penile size
in treatment of ED with PDE-5 inhibitor (tadalafil; 20 mg). We prospectively
scrutinized and enrolled in the present study 42 consecutive patients with ED.
All measurements of penile length in fully stretched states and the erectile
function domain of the International Index of Erectile Function (IIEF-EF)
scores were recorded by the same physician (M.S.). Patients were divided into
3 groups according to stretched penile length: small (<25th percentile),
normal (25th to 75th percentiles), and large (>75th percentile). Mean
IIEF-EF scores were recorded before and after treatment period. Patients
received tadalafil (20 mg), taken on demand, a minimum of 6 times. The mean
stretched penile length was 13.44 ± 2.4 cm (range, 9.50–18.00
cm). Overall mean IIEF-EF domain scores were 11.90 ± 4.78 and 18.67
± 6.70 for before and after the treatment period, respectively.
Although PDE-5 inhibitor treatment significantly improved all domains of the
IIEF-EF scores (P < .05), no statistically significant difference
was found among the 3 groups according to mean IIEF-EF domain scores before
and after treatment (P > .05). We conclude that penile size is not
a factor in treatment of ED patients with a PDE-5 inhibitor.
Key words: Penis, IIEF
A preoccupation with penile size is a common condition in the male population. Penile length, circumference, and/or geometry may also contribute to, or be a consequence of, medical treatment of ED (Rany, 2005). In our clinical observations, a proportion of ED patients who have a preoccupation with penile size treatment with PDE-5 inhibitors are affected negatively. On the basis of our clinical observations, we investigated whether penile size (stretched penile length) is a factor in the treatment outcome of ED patients with PDE-5 inhibitors. To our knowledge, none of the studies reported to date have investigated the potential effect of penile length on PDE-5 inhibitor therapy in men with ED. The aim of this study was to investigate the influence of penile length in treatment of ED with PDE-5 inhibitors.
Materials and Methods
The study was approved by an institutional review committee, and each participant gave written, informed consent. A total of 42 men were enrolled in the study (mean age, 52.05 ± 8.90 years; range, 37–75 years). Criteria for inclusion of all patients were: a minimum 3-month history of mild to severe ED, a stable monogamous relationship with a female partner, and at least 1 attempt of sexual intercourse over the preceding 4 weeks. All patients were evaluated with a detailed sexual history, physical examination, blood chemistry and endocrine assay, and color Doppler ultrasonography (CDU) during pharmacologically induced and sexually stimulated erection. Patients with angina during intercourse, unstable angina or any other evidence of recently diagnosed coronary artery disease, poorly controlled blood pressure or orthostatic hypotension, congestive heart failure, arrhythmia, significant renal or hepatic dysfunction, and anemia were excluded. Also ineligible were patients who failed to achieve an erection after radical prostatectomy or pelvic surgery; those who had penile implants; those who had clinically noteworthy penile deformities, such as conditions that may predispose to changes in penile length due to fibrosis radiation, trauma, injection therapy, and Peyronie disease; those with a history of stroke or spinal cord trauma within 6 months of study onset; and those who were receiving nitrates, antiandrogens, or cancer chemotherapy.
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Patients were divided into 3 groups according to penile stretched length (Mondaini et al, 2002) as follows: group I, small penile length, stretched penile length below the 25th percentile; group II, normal penile length, stretched penile length between the 25th and 75th percentiles; and group III, large penile length, stretched penile length above the 75th percentile (Figure).
Erectile function was evaluated by the erectile function domain of the International Index of Erectile Function (IIEF-EF) a validated 15-item, self-administered questionnaire. Although objective measurements of erectile function were not performed in this study, the IIEF-EF questionnaire is established as a reliable tool in assessing erectile function. Erectile function is specifically addressed by 6 questions that form the so-called erectile function domain of the questionnaire. Each question is scored 0 to 5. ED is defined as any value less than 26 points. The IIEF-EF questionnaire was administered to patients before and again after receiving tadalafil (20 mg, taken on demand, minimum 6 doses). The mean IIEF-EF score was recorded before starting treatment and after treatment (Cappelleri et al, 1999).
All statistical analyses were conducted using SPSS software (SPSS for
Windows, version 11.5; SPSS Inc, Chicago, Illinois). Continuous variables were
expressed as mean ± SD. Normality of distribution was evaluated with
the Kolmogorov-Smirnov test. The correlation between penile length, age, BMI,
and IIEF-EF domain scores before and after treatment of patients was
determined by Pearson analysis. Multiple linear-regression analysis was
performed to identify the independent predictors of final IIEF-EF scores. The
1-way analysis of variance was used for a simultaneous statistical test
between groups. Paired-samples t test was used to compare mean
IIEF-EF scores before and after treatment. A 
2 test was used
for comparison among demographic characteristics and risk factors for ED. All
statistical tests were 2 sided. A P value less than .05 was
considered significant.
Results
The mean age of the 42 patients was 52.05 ± 8.90 years (range, 37–75 years). Demographic characteristics and risk factors for ED are shown in Table 1 and are presented separately for groups I, II, and III. Overall, the mean stretched penile length was 13.44 ± 2.40 cm (range, 9.50–18.00 cm). For group I patients (n = 7 [17%]), stretched penile length was 10.07 ± 0.34 cm (range, 9.50–10.50 cm); for group II patients (n = 24 [57%]), stretched penile length was 13.01 ± 1.34 cm (range, 11.00–15.00 cm); for group III patients (n = 11 [26%]), stretched penile length was 16.50 ± 0.84 cm (range, 15.50–18.00 cm). Overall mean IIEF-EF domain scores for before treatment and after treatment were 11.90 ± 4.78 and 18.67 ± 6.70, respectively. Tadalafil treatment significantly improved all domains of the IIEF-EF from baseline (P < .05). IIEF-EF scores before and after treatment among groups I, II, and III are shown in Table 2. For erectile function scores, a significant correlation was not found between penile length and tadalafil treatment (P > .05). A statistically significant negative correlation between age and IIEF-EF scores after treatment was found (Table 3). It was found that posttreatment IIEF-EF score was dependent on independent domains, such as pretreatment IIEF-EF score, penile length, and age, with a rate of 34 (R2 = 0.337; P = .01). The baseline IIEF-EF score in multivariate regression analysis was reported as the unique independent domain on posttreatment IIEF-EF score; however, penile length and patient age were not found to be factors on final IIEF-EF scores (Table 4). CDU values according to the vascular status of patients with ED are shown in Table 5.
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Discussion
Erection is a hemodynamic phenomenon resulting from a complex interaction between cerebrospinal pathways, smooth muscle, and endothelium. ED can be defined as the inability to obtain penile rigidity (Erdogru et al, 2001). The Food and Drug Administration approved 3 drugs of the PDE-5 category for clinical use in the treatment of ED. Sildenafil was the first drug in this class, followed by the agents tadalafil and vardenafil. These drugs are potent and selective inhibitors of cyclic guanosine monophosphate (cGMP)–specific PDE-5. They prevent the breakdown of cGMP and prolong and improve smooth muscle relaxation. PDE-5 is the isoform of the enzyme highly expressed in cavernosal tissue. Hence, vasodilatation is greater in this tissue (Thethi et al, 2005). Tadalafil is a potent, reversible, and selective inhibitor of PDE-5 developed as an oral therapy for mild to severe ED of psychogenic, organic, or mixed etiology (Padma-Nathan et al, 2001). Several factors can contribute to the failure of treatment of ED with PDE-5 inhibitors. Penile length, circumference, and/or geometry may also contribute to, or be a consequence of, medical treatment of ED. The present study investigated whether penile length was a factor in the efficacy of treatment of ED with PDE-5 inhibitors.
The importance of penile mechanical, geometrical, and hemodynamic
properties for erectile function, demonstrated by the work of Udelson et al
(1998), is generally accepted.
It is suggested that the reason for inadequate penile rigidity despite normal
hemodynamic properties could be related to improper mechanical tissue
properties or penile geometry
(Hatzimouratidies, 1998;
Erdogru et al, 2001). Two
penile geometric properties are critical: the penile aspect ratio, defined as
the diameter to length ratio of the pendulous penis, and the magnitude of the
flaccid penile diameter (Goldstein and
Udelson, 1998). Clinically measured values of axial buckling
forces in patients undergoing dynamic pharmacocavernosometry strongly
correlated to theoretic-based, analytic-derived magnitudes of axial penile
rigidity based on pressure, tissue, and geometric determinants. In this study,
we did not measure the penile aspect ratio, but we suggested that stretched
penile length may be used as an indicator for penile geometry. Chen et al
(1992) suggested that a
comparison of the increase of penile erectile parameters after prostaglandin
E1 (PGE1) injection between the good- and poor-response groups of
patients with ED revealed a significantly greater increase in the diameter of
corpus cavernosum in the good-response patients. In that study, penile Doppler
ultrasonography was performed to check the diameter of each corpus cavernosum,
as well as the diameter and peak flow velocity of each cavernous artery before
and after intracavernous injection with PGE1. After PGE1
injection, a significant increase of erectile parameters (penile length,
diameter of corpus cavernosum, and total erectile volume) was found in each
group of patients. To our knowledge, none of the studies reported to date have
investigated the potential penile size or geometry effect of PDE-5 inhibitor
therapy on ED. The aim of the present study was to investigate the impact of
stretched penile length in the treatment of ED with a PDE-5 inhibitor
(tadalafil). Despite tadalafil treatment significantly improving all domains
of the IIEF-EF (P 
.05), no statistically significant difference
was found among the 3 patient groups before and after treatment with tadalafil
(P > .05 for each). No correlation was found between stretched
penile length and BMI of the patients (P > .05). A negative
correlation was found between patient age and IIEF-EF domain scores after the
treatment period (P < .05).
The present study is significant in being the first evaluation for penile length effects in treatment of ED with a PDE-5 inhibitor. The issue of the importance of penile length is thought provoking. However, the data provided in this paper should be viewed in the perspective of related clinical studies.
We conclude that penile size (stretched penile length) is not a factor in treatment of ED with PDE-5 inhibitors. These findings might serve to guide further studies investigating factors that contribute to the failure of ED treatment with PDE-5 inhibitors.
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