Phosphodiesterase type 5 inhibitors are the drugs that are widely used to block the degradation of cGMP (Cyclic guanosine monophosphate) in the smooth muscle cells lining the blood vessels supplying the main erectile tissues of the penis. Phosphodiesterase type 5 inhibitors are expected to cause relaxation of smooth muscles and maintain healthy penile function. PDE5 inhibitors are the most recommended drugs to treat erectile dysfunction and several other men’s sexual problems- Sildenafil, Tadalafil and Vardenafil are mostly recommended. Due to the high degree of effectiveness and its record, PDE5 inhibitors are said to be the drugs of choice for the treatment and management of erectile function.
There are many types of PDE enzymes that function to degrade cGMP. These enzymes are widely distributed throughout the body and perform an activity in different tissues. Phosphodiesterase type 5 enzymes are found in the smooth muscle of corpus cavernosum, skeletal muscle, cerebellar and pancreatic tissues, vascular and visceral smooth muscle, platelets, kidneys, and lungs. Phosphodiesterase type 5 inhibitors cause vasodilation in the penis region and block the breakdown of cGMP and results in the prolonged action of the mediators of vasodilators such as nitric oxide. Penile erection is dependent on the release of nitric oxide which stimulates the production of cGMP. Penile erection is a process which is initiated by the relaxation of smooth muscles in the corpus cavernosum which is the main erectile tissue. At the time of sexual stimulation, nitric oxide is released from the nerve ending in the corpus cavernosum. This increases the synthesis of cGMP in the corpus cavernosum and triggers smooth muscle relaxation. This further increases the blood flow into the penis region and results in an erection.
Drugs that belongs to phosphodiesterase type 5 inhibitors are usually recommended to treat three men’s health problem, erectile dysfunction, pulmonary arterial hypertension and benign prostatic hyperplasia. Erectile dysfunction is one of the most common sexual problems in men and it is a condition in which men are incapable of attaining or maintaining penile erection sufficient enough to have a satisfactory sexual intercourse. Erectile function involves various different factors and problems in any factor can lead to impaired erectile function. Pulmonary arterial hypertension refers to the high blood pressure in the arteries going to the lungs. When the pulmonary arterial pressure exceeds 25 mm Hg then, it is a sign of pulmonary arterial hypertension. Benign prostatic hyperplasia is a common problem among men by the age of 50 and it is a condition in which the rapid increase of the prostatic stromal cells results in an enlarged prostate gland.
Common PDE5 inhibitors
Viagra is the marketed brand name of Sildenafil and along with erectile dysfunction, it is also used to treat pulmonary arterial hypertension and raynaud's phenomenon. The oral dose of sildenafil has an expected onset of action in 30 minutes and the estimated maximum effect at one hour. The serum half life of this drug is four hours. Also, this drug is a lipophilic molecule and taking a dose of this drug close to the consumption of fatty meal reduces the efficacy of sildenafil.
Tadalafil is marketed under a brand name of Cialis and Adcirca. Cialis is a marketed pill to treat erectile dysfunction and benign prostatic hyperplasia and Adcirca is a marketed pill to treat pulmonary arterial hypertension. Tadalafil has been shown to have an onset of action as early as 16 minutes. Also, taking the dose of this drug close to the consumption of fatty meals has no effect on the efficacy of Tadalafil.
Vardenafil is marketed under the names of Levitra, Staxyn, and Vivanza and it is one of the recommended drugs to treat erectile dysfunction. Vardenafil should be taken thirty minutes to one hour before the sexual intercourse. Also, it is recommended to consume this drug one to two hours before having a meal or one to two hours after having a meal as it can affect the efficiency of this drug. The duration and the effect of this drug remain for 5 - 7 hours.
It should be noted that the consumption of these drugs should be done only after consulting a doctor as these drugs are known to interact with several medicines such as nitrates. The doctor will guide you about all the related information and about all the medications and health conditions under which one should avoid taking these drugs.