Tadalafil is an effective drug for Erectile Dysfunction (ED). It is a selective and reversible inhibitor of cGMP-specific PDE 5. When sexual stimulation leads to local release of NO, PDE-5 is inhibited by Tadalafil, which increases the level of cGMP in the penile cavernous body, resulting in relaxation of smooth muscle and erection. Compared with other ED drugs such as sildenafil and vardenafil, they are not affected by alcohol or high fat diet, and the dosage does not need to be adjusted by age. In addition, Tadalafil also has a long acting time, up to 36 hours, high safety, more easily accepted by patients. Tadalafil is becoming the preferred drug in the treatment of ED because it can enhance patients'sexual self-confidence and have a harmonious sexual life, and has a good effect on ED patients with medical diseases.
Keywords: erectile dysfunction; Tadalafil; mechanism; therapeutic effect.
Erectile Dysfunction (ED) refers to the inability to achieve and/or maintain sufficient erectile status to achieve a satisfactory sexual life . ED is a common and frequently-occurring disease in andrology. In the epidemiological survey of ED, WespesE  found that about 5% to 20% of men complain of moderate to severe ED, which is related to age. Therefore, with the intensification of the aging process in the world, the prevalence of ED is likely to continue to increase . Some medical diseases, such as cardiovascular disease, heart disease and diabetes, can increase the incidence of ED, and people with ED are often precursors of cardiovascular disease. At present, the first-line drugs for the safe treatment of ED are phosphodiesterase type 5 inhibitors (PDE5i), including sildenafil, valtanafil and Tadalafil. The advent of PDE5Is has brought the gospel to ED patients and is a real change in the treatment of ED. Compared with other PDE5 inhibitors, Tadalafil has a higher selectivity for PDEI5s and a longer half-life (17.5h). After oral administration for 16 minutes, Tadalafil can rapidly reach the blood concentration and prolong the action time. Tadalafil can last for 36 hours, and has good tolerance, less abnormal color perception. Tadalafil can also reduce the times of taking drugs and increase patient compliance. Sex. This article reviews the mechanism, efficacy and safety of Tadalafil in the treatment of ED.
1, Mechanism of action of Tadalafil.
ED is essentially a disease with impaired vascular endothelium and dysfunction. Endothelin (ET) is the strongest vasoconstrictor and the most durable vasoconstrictor in vivo. ET has three isomers, namely ET-1, ET-2 and ET-3. It has been found that ET-1 is mainly produced by vascular endothelial cells, which can constrict blood vessels, promote the proliferation of vascular smooth muscle and cell adhesion, and mediate the contraction of various smooth muscle including penile cavernous body and urethral cavernous body. ET-1 is one of the most powerful indicators of vascular endothelial function. Domestic Hu Dayi  studies have confirmed that vascular endothelial function not only plays a key role in the pathogenesis and progress of cardiovascular diseases, but also has an important impact on sexual activity. When the endothelial function was impaired, the level of NO in the penis decreased and cGMP production decreased. Cavernous smooth muscle cells of the penis can not fully relax, blood flow in the penile vessels is reduced, and ED symptoms appear. PDE5Is can improve vascular endothelial function, repair damaged endothelial cells and maintain the stability of vascular endothelial environment, thus achieving the goal of treating ED. Tadalafil (Tadalafil) is a potent, selective and reversible inhibitor of cGMP-specific phosphodiesterase 5 (PDE5) with beta-carbaline group. Its unique piperazine diketone ring is further improved on the basis of sildenafil isohydantoin ring. The molecular structure of Tadalafil contains a double-ring heterocyclic nitrogen-containing system similar to that of cGMP, which enables Tadalafil to competently bind to the PDE 5 catalyst site 5 inhibitor. It can inhibit the hydrolysis of cGMP, increase the concentration of cGMP in the smooth muscle cells of the corpus cavernosum, enhance the relaxation of smooth muscle and increase blood flow, so as to achieve the effect of treating erectile dysfunction.
2, Efficacy of Tadalafil in the treatment of ED.
Tadalafil was approved in the US in 2003 and entered the Chinese market in 2005. Compared to sildenafil and fdenafil, Tadalafil is not affected by high-fat meal after oral intake. The main circulating metabolite is methyl catechol glucuronide, which is 13,000 times less active than Tadalafil. Therefore, the metabolite has no clinical activity. Mainly excreted from feces (about 61% of the dose), a small part from urine (about 36% of the dose), and studies also show that long-term use of Tadalafil will not appear in the penile tissue accumulation of PDE5 . Oral Tadalafil has different effects on ED patients with internal diseases.
2.1, Tadalafil for the treatment of ED patients with cardiovascular disease.
In cardiovascular diseases, arteriography showed that atherosclerosis could significantly affect the internal pudendal artery, more than 50% of the internal pudendal artery and cavernous artery lumen stenosis . And data show that the incidence of ED in heart disease patients can reach 44%. Studies have shown that the effective rate of Tadalafil 20mg oral therapy for ED patients with hypertension is 82.1%, and that of ED patients with hyperlipidemia is 85.6% . Smoking can increase hypertension and atherosclerosis, reduce NO concentration in the penile cavernous body, and cause ED, while oral Tadalafil in the treatment of ED, smoking has no effect on it .
2.2, Tadalafil in treatment of ED patients with diabetes mellitus.
Poor control of blood sugar in diabetic patients will lead to atherosclerosis, especially macrovascular atherosclerosis and capillary disease. These factors lead to ischemia and hypoxia of the cavernous body, decrease of oxygen saturation, decrease of smooth muscle of the cavernous body, increase of fibrosis and increase of elastin and collagen in the albumin. Causing irreversible damage to smooth muscle function of cavernous body and loss of venous closure function increases the risk of ED. Therefore, ED is a common complication of diabetes mellitus (DM). Studies have shown that the incidence of ED in diabetic patients is 3 to 6 times higher than that in the general population, and the symptoms of ED patients with diabetes mellitus are more serious than those of ED patients with diabetes mellitus. Yu Siming et al.  studied 90 ED patients with type 2 diabetes mellitus. It was found that the erectile function improved significantly 14 days after taking Tadalafil 20 mg orally. The cure rate was as high as 51.11% and the effective rate was 75.56%. It further proved that Tadalafil had a good therapeutic effect on ED patients with diabetes mellitus.
2.3, Tadalafil in the treatment of prostate cancer or spinal cord injury combined with ED.
Chronic prostatitis is a common disease in andrology. Studies have shown that ED is more common in male prostatitis patients in China. Even though surgical techniques have been improved in recent years and bilateral nerve-sparing surgery has been used to treat prostate cancer or spinal cord injury, the incidence of ED after surgery is still high. A study by Montorsi  et al. found that oral administration of 20 mg Tadalafil improved erectile function in 62% of patients with prostate cancer or spinal cord injury complicated with ED, and IIEF-5 score increased by 5.9 points, with less adverse reactions and self-mitigation.
2.4, Tadalafil treatment of male masturbation failure patients.
It is a challenging task for male clinicians to successfully extract sperm for clinical diagnosis and treatment in a specific hospital environment for male patients who fail to obtain sperm through masturbation. In response to this situation, Tang Wenhao  and others gave Tadalafil to 60 male sperm extraction failure patients. After research, it was found that Tadalafil could freely and autonomously choose the time of taking medicine because it did not need to take medicine immediately before sperm extraction, which helped to reduce patients'anxiety, shyness and embarrassment about sperm extraction, and was more conducive to extracting sperm. High sperm extraction rate.
3, Tadalafil effective assessment
The International Erectile Function Index Score (IIEF-5) is a commonly used evaluation system for ED research, which covers five aspects of male sexual function. The IIEF-5 score < 7 was divided into severe ED, 8~11 moderate ED and 12~21 mild ED. The higher the IEF-5 score, the better the erectile function. The increase of IIEF-5 score by more than 4 points can be regarded as clinical efficacy. Erectile dysfunction function inventoryoftreatment satisfaction (EDITS) is a tool to evaluate the satisfaction of ED treatment. The higher the score, the better the therapeutic effect. Simplified Psychological and Interpersonal Relations Scales (SF-PAIRS) is an effective index for evaluating psychological factors. It mainly includes three sub-items: Sexual Self-confidence Index, Sexual Natural Index and Sexual Time Concern Index. The higher the scores of the former two, the higher their sexual self-confidence and sexual naturalness, the lower the scores of the latter. It shows that the less time it takes to worry about sex. At the same time, the adverse reactions of patients were recorded and tracked. The PAIRS scale includes psychological and interpersonal factors which were not included in the previous ED evaluation scale. It can systematically and scientifically reflect the role of psychosocial factors in patients with ED. Because IIEF-5 mainly evaluates patients'sexual function and pays less attention to other important factors considered by patients and their partners, PAIRS has a better complement to IIEF-5 .
4, Effectiveness and security of Tadalafil.
Many studies have confirmed that Tadalafil has a good therapeutic effect on ED patients. The flushing and headache in the face during the treatment are mild and self-alleviating. In the course of research on taking Tadalafil on time and on demand, it was found that taking 5 mg Tadalafil orally daily at low doses had better therapeutic effect on ED patients. Compared with taking Tadalafil orally on demand, it could eliminate the embarrassment and worry of taking medicine before sexual intercourse, thus increasing the self-confidence of men and avoiding psychological disorders of both spouses, especially severe ED. The patient has an obvious effect on . Because Tadalafil has a good protective effect on endothelial progenitor cells (EPCs) in the corpus cavernosum of the penis, and can treat ED patients fundamentally. Cui Hongqing  and other research found that taking 5 mg Tadalafil daily, while continuing to repair vascular endothelial function, if 50 mg sildenafil before sexual life, can ensure that the penis can quickly and fully erect, complete satisfactory sexual intercourse, enhance self-confidence and achieve the goal of cure. Another study found that the main reason women prefer Tadalafil is that they feel more relaxed, less stress, and can quickly reach blood concentration, maintain for a long time, and have good tolerance. Clinical studies have shown that Tadalafil can enhance the hypotensive effect of nitrate drugs, which is considered to be the result of the combined action of nitrate drugs and Tadalafil on NO/cGMP pathway. Therefore, taking any form of nitrate drugs is prohibited.
ED is a common and frequently-occurring disease in andrology. The treatment of ED should not only consider erectile stiffness, but also consider patients'psychological factors, safety factors, partner preferences and so on. Tadalafil is a long-acting (half-life is 17.5h) selective inhibitor with long duration and good tolerance. It can effectively improve erection. Tadalafil is suitable for patients with diabetes, cardiovascular and cerebrovascular diseases, prostatic diseases and ED. It has good clinical safety. Considering psychological factors, Tadalafil can make both men and women take Tadalafil. Sexual life is more relaxed, time pressure is less, sexual experience is more natural. So that patients and their partners can get maximum satisfaction from physiology and psychology and improve their quality of life. Therefore, Tadalafil is worth promoting in the treatment of ED patients. However, there are no 2.5 mg and 5 mg Tadalafil on the market in China, only 10 mg and 20 mg. In addition, more and more clinical studies show that Tadalafil has good clinical value, which requires further research and development.
NEXT：Avanafil CAS 330784-47-9