Effect of tadalafil on erectile dysfunction in male patients with diabetes mellitus

Background/Aim. During the first 10 years over 50% of diabetes patients develop erectile dysfunction (ED). It is more severe and resistant to therapy than in male patients with normal glucoregulation. The purpose of this pilot study was to estimate the tadalafil (Cialis) efficacy and safety in male patients with diabetes mellitus (DM), together with moderate to severe ED. Methods. The study included 30 male patients with diagnozed type 1 or type 2 DM together with ED. ED was estimated through the International Index of Erectile Function (IIEF-6), Sexual Encounter Profile (SEP) questionnaire and prostaglandin test, at the beginning of the research and three months after the 20 mg tadalafil therapy initiation, once a week (on Fridays). Glycosylated haemoglobin in blood (HbA1c) values were also monitored. According to the ED severity (IIEF values at the beginning of the therapy) the patients were divided into 2 groups. The previous experience with sildenafil citrate (Viagra) and prostaglandin E1 intracavernous therapy was recorded. Results. Tadalafil significantly improved ED (p < 0.001) for 7.40 points of the IIEF score, i.e. for 58% and 60% towards SEP2 and SEP3 questionnaire, respectively. Compared to the previous ED therapy subjectively better tadalafil experience was recorded. Each group experienced a significant improvement in IIEF score (p < 0.001), more significantly in the group 2 (8.26±1.49 points) compared with the medium improvement in the group 1 (6.27±1.35 points). After three months HbA1c values decreased for 2.26±1.62 (p < 0.001). Conclusion. Tadalafil is an effective tool for treating ED in diabetes patients. In some situations tadalafil application could replace prostaglandin test. The sexual sphere motivation leads to the improvement of glucoregulation in DM patients.


Introduction
One of the most perfidious diabetes mellitus (DM) complications is autonomic neuropathy.The most dangerous autonomic neuropathy complications are 'mute infarction' and a sudden death.However, the first symptoms to occur are most commonly on the part of the urinary tract.In male patients this is erectile dysfunction (ED), and in female patients reduced vagina lubrication and the absence of orgasm.Due to common retrograde ejaculation (RE) complications of ED male population is more exposed, which significantly affects the quality of life and leads to sterility.That suggests to the importance of an adequately taken anamnesis and the application of sexology questionnaire in the prevention of severe complications.
Diabetes patients are exposed to 4.1 times greater risk of developing ED than non-diabetics of the same age, whereas the risk in hyperlipoproteinemia patients is only 1.7 times greater, and in hypertonic patients the risk is 1.6 times greater versus healthy population 1 .During the first 10 years from the onset of the disease more than 50% of diabetes patients develop ED 1 .ED in DM male patients is more severe and resistant to treatment than in male population with normal glycoregulation 2 .DM duration, therapy type and its adequate application, age, dyslipidemia, hypertension and risk factors, firstly nicotine, to a great extent define the ED severity.
Both ED and DM strike more than 150 million people worldwide, and according to the estimations by the year 2025 the number will doubled 3−5 .
The initial event for the normal erectile function is sexual stimulation.As an answer to the sexual stimulation in potent men nitrogen oxide (NO) is set off.NO actives guanylin cyclase enzyme that further activates guanosine 3 phosphate (GTP) and creates cyclic 3'5' guanosine monophosphate (cGMP).cGMP leads to relaxed smooth artery muscles, arterioles and sinusoidal corpus cavernous.Distended sinusoids comprise venulas on tunica albuginea and in this way the blood stays trapped in the penis corpus cavernous.Combination of the enhanced blood flow into the penis along with the labored discharge increases the intracavernous pressure that quickly moves up to the systolic blood pressure.With these pressure values the penis attains satisfactory hardness for penetrating the vagina.The main phosphodiesterasis (PDE) that unbinds cGMP of the smooth penis blood vessel muscles is PDE5.PDE5 inhibitors (tadalafil, sildenafil citrate, vardenafil, etc.) block cGMP degradation thus enhancing NO effect.Although these drugs are effective in men with different etiology and ED degree, their effect depends on the quality of pudendal bloodstream and endothelial cells and pudendal nerves to free NO during the sexual stimulation 6−8 .In patients with DM hyperglycemia it aggravates NO discharge from these structures 9−11 .Accordingly, the combination of vascular insufficiency, autonomic neuropathy and endothelial dysfunction leads to more severe ED in men with DM, and these patients have a weaker response to PDE5 inhibitors than the patients of the same age and without DM 2 .
Numerous researches 12−15 show that PDE5 oral inhibitors are effective and well tolerated in male patients with DM and ED.Tadalafil is potent, reversible and selective PDE5 inhibitor.It is used as an oral pharmacotherapy in ED, psychogenic, organic or mixed etiology 16 .The aim of this pilot study was to determine the tadalafil efficacy and safety in male patients with DM together with moderate to severe ED.

Methods
This pilot study was conducted in the Institute of Endocrinology, Diabetes and Metabolism Diseases, Clinical Center of Serbia in cooperation with the Institute of Urology (urodyname researches), Institute of Physical Medicine (electromyography researches) and Institute of Cardiovascular Diseases.The study involved 30 male patients over 18 years of age, clinically diagnozed with type 1 or type 2 DM together with ED during the minimum period of 6 months.
The first examination included anamnesis, laboratory tests with the glycaemia profile assessment and glycosylated haemoglobin in blood (HbA1c), EKG, sexology questionnaire with 6 standardized questions − International Index of Erectile Function (IIEF-6 score), physical examination and the lower extremities polyneuropathy electromyography tests.In all patients the ED severity was estimated through IIEF score, Sexual Encounter Profile (SEP) questionnaire, and in 20 patients also through the prostaglandin test (10−20 µg Prostaglandin E1 intracavernous) and the artificial erection 1−3 response was graduated.IIEF is a 15-questionquestionnaire divided into 5 sections related to erectile function (6 questions), orgasm (2 questions), sexual desire (2 questions), pleasure gained from sexual intercourse (3 questions), and general sexual satisfaction (2 questions).
The study used IIEF-6 score relating to the erection frequency, the erection hardness, penetrating ability, preserving frequency and the ability to maintain erection and the certainty of achieving erection, with the score of 1 to 30 points.
SEP questionnaire assumed 2 questions to which patients answered with YES/NO.SEP Q2: Were you able to place your penis into the partner's vagina?SEP question 3: Did your erection last long enough for having a successful sexual intercourse?
Patients were asked to compare tadalafil with the previous ED therapy (if applied) and to say if the erection achieved with the help of tadalafil feels as natural or as artificially caused.
Patients agreed not to apply another ED therapy during the study.They all gave their assent to the research and they were all very motivated.
All the patients who had been using nitrates as well as those who recently suffered a severe cardiovascular event, stroke or the spinal cord injury were excluded from the study.Patients with HbA1c values > 13% were also excluded.The study included male patients with microvascular complications, including retinopathy.
According to the ED severity (IIEF score values at the beginning of the study) patients were divided into 2 groups.
Differences in the IIEF score values and the number of a YES responds of the SEP questionnaire at the beginning of the research and at the end of the study were taken as a leading parameter in evaluating the treatment efficacy.
The therapy side-effects were also monitored.

The drug study
The 20 mg tadalafil (Cialis) was used in this study.The patients were given instructions to take the drug with water once a week, on Fridays, and no more than 1 pill.They were also explained that their sexual activity should not necessarily be of a limited duration.

Statistic analysis
The results were presented as individual or medium values with standard deviation.The obtained data were processed through the SPSS 13.0 software package.Chi-square test, Independent sample t-test, 2 sample paired t-test with the Bonferini's correction were used.
All the patients were on an antidiabetic therapy (Table 2).Twenty-seven (90%) patients tried sildenafil (Viagra), whereas 3 (10%) patients experienced intra-cavernous therapy (prostaglandin E1, standard dosage) of limited duration.Twenty five patients stated that compared with the previous therapy they had had a more favorable experience with tadalafil (Cialis), whereas 2 patients hadn't noticed any difference.These favorable experiences were firstly explained by the erection duration (and on the following day), and 5 out of 8 patients with reduced ejaculate said that there had been a real improvement in the amount of ejaculate.
Tadalafil improved erectile function in all the patients.The medium improvement in the IIEF score was 7.40 points (41.67%).A significant improvement has also been recorded in SEP 2, i.e.SEP 3 question, for 58% and 60% respectively.It also come to a significant glucoregulation improvement (Table 3).According to the values of the basic IIEF score the patients were subsequently divided into groups.Of all the patients, 36.7% diabetes patients had the severe ED (Table 4).
The group 1 included 11 patients who according to the IIEF score had the most severe ED (Table 5).Six (54.5%) of the patients were diagnozed with type 1 DM, and 5 (45.5%) with type 2 DM.Only 1 (9%) patient didn't have RE and all the others had been previously using sildenafil citrate (Viagra).
In the group 1 tadalafil improved the erectile function in all the patients.Medium improvement of the IIEF score was 6.27±1.35points compared with the basic values.HbA1c values were also significantly reduced for 2.03±1.50%(Table 6).
Erectile function and glucoregulation improvement tendency in the patients with severe ED treated with tadalafil.
The goup 2 included 19 patients with moderate ED according to the IIEF score (Table 7).Eight patients (42.1%) were diagnozed with type 1 DM, and 11 (57.9%) with type 2 DM.Ten patients (52.6%) had already developed RE and apart from 2 patients all others had been using sildenafil citrate.
Ten patients had RE lasting for at least 6 months.In all the patients tadalafil led to the IIEF score improvement of 8.26±1.49points of the erectile function.A significant HbA1c values reduction was also detected (Table 8).
There hasn't been any statistically important age and BMI difference between groups 1 and 2 and the HbA1c values.A statistically significant difference was detected in the number of the IIEF score points that had improved after the 3-month-use of tadalafil in each group (p < 0.01) 9).
According to expectations and considering the fact that their ED was of less severe form, the increase was more significant in the group 2.
There were no cases of myocardial infraction or myocardial ischemia, as well as no significant changes in laboratory values, EKG parameters or internist examinations.

Discussion
PDE5 inhibitors, which include tadalafil, by cGMP blockade degradation enhance the NO effect and in this way provide successful erection.
What separates tadalafil from the rest of PDE5 inhibitors is the ability of acquiring the active drug concentration 2 hours after the intake, with the 17.5 h half-life and the effect lasting up to 36 h.Drug absorption is not affected by food or alcohol intake.As with other drugs from this group there is the possibility of developing hypertension and when combined with nitrates the risk of undesirable cardiovascular events 17 .
Tadalafil improved the erectile function of both diabetes groups even more significantly in the group with the less severe ED.Medium improvement of 6.27±1.35points of the IIEF score was achieved in the group 1, and 8.26±1.49 in the group 2 (p < 0.01).
After the 3-month-follow-up HbA1c values were significantly lower.Judging from our experience with diabetes patients we can say that the more attention they are given the better discipline they show and the satisfactory glucoregulation is achieved, which is obvious from the HbA1c values that improved for 2.03% after 3 months bearing the statistical significance (p < 0.01).Normoglycaemia in diabetes patients affects the improvement of the endothelial function, enhanced NO bioavailability, and therefore a better reaction to the PDE5 inhibitor treatment.If diabetes patients understand that the erectile function and diabetes control are connected, they are then more motivated to improve the disease control.It is necessary to continue examining good diabetes control effect on the erectile function and, due to the fact that the male population is seriously exposed to the disease with the better patient motivation purpose.In the Fonseca et al. 15 study the patients were divided according to their HbA1c values, into the patients with good glucoregulation (HbA1c <7%), bad (HbA1c 7.0−9.5%)and distinctly bad (HbA1c >9.5%) glucoregulation, which showed that the IIEF score was lower in the group with the bad glucoregulation that only points to the ED development glucoregulation significance.In our study the drug efficacy was certainly affected by a tendency to improve glucoregulation.Considering the ED development etiology, organic factors (the existence of neurogenic and vasculogenic components), but the psychogenic upgrade as well, compared to diabetes type as well as the oral, combined or insulin therapy application no significant difference in ED patients was detected.
Tadalafil improved erectile function in our patients and, compared to the previously used preparations proved more effective primarily regarding erection duration.A new moment is a subjective detection of the patients with scarce  ejaculate, which is a tendency to increase ejaculate amount that has not yet been recorded.In addition, the authors found interesting a statement given by 27 patients who had previously been using sildenafil citrate, that while using tadalafil most of them (20−74%) had a subjective sensation of a natural erection.The patients who had experienced intracavernous ED therapy experienced erection as artificial, whereas all 3 patients with that experience characterized tadalafil application as having a more natural erection sensation.
Regarding side-effects, our study is not different from the Fonseca et al. 15 study.In no case the therapy was discontinued, and the stated changes (headaches, nausea) were of a transitive nature, and backache was attributed to the increased physical activity and previously known polyneuropathic discomforts.

Conclusion
Tadalafil proved to be an effective tool for treating ED in diabetes patients.According to the expectations, the drug efficacy was better in the patients with less severe ED.Compared with the previously applied PDE5 inhibitors tadalafil also proved to be more effective.Considering the prostaglandin test procedure complexity, we are of the opinion that the application of this drug could in some cases replace the prostaglandin test (difficulties in the intracavernous injection application, the patients' fear, side-effects, etc.).Tadafil sideeffects are very mild, almost negligible and no one has discontinued the therapy.Sexuality is an inalienable part of a good quality life, and in this case the sexual sphere motivation proved to have a good effect on achieving satisfactory glucoregulation in DM patients.