Phosphodiesterase type 5 inhibitors
The cyclic nucleotide phosphodiesterases constitute a group of enzymes that destroy the cyclic nucleotides cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Phosphodiesterases exist in different molecular forms and are unevenly distributed throughout the body. One of the forms of phosphodiesterase is termed PDE5, and inhibiting PDE5 increases the amount of cGMP available in the blood supply to the penis, thus increasing blood flow. The PDE5 inhibitors sildenafil (Viagra),vardenafil (Levitra) and tadalafil (Cialis) are prescription drugs which are taken orally.
A topical cream combining alprostadil with the permeation enhancer DDAIP has been approved in Canada under the brand name Vitaros as a first line treatment for erectile dysfunction.
Another treatment regimen is injection therapy. One of the following drugs is injected into the penis: papaverine, phentolamine, and prostaglandin E1.
The first option for the treatment of erectile dysfunction – once the condition has been established as a persistent problem, rather than a one-off or temporary one – is a group of drugs called PDE-5 (phosphodiesterase-5) inhibitors.
All except one of these pills are taken 30 to 60 minutes before sex – the best known being the blue-colored pill sildenafil (Viagra). Other options are vardenafil (Levitra), tadalafil (taken as a once-daily pill; Cialis), and avanafil (Stendra).
PDE-5 inhibitors must be prescribed by a doctor, who may check for heart conditions and use of other medications. For example, a cardiologist may need to advise on the best timing for the use of erectile dysfunction drugs in men who keep nitrate drugs for rare occasions of angina chest pain caused by coronary artery disease.
There is a list of potential adverse side-effects associated with PDE-5 inhibitors, including flushing, visual abnormalities, hearing loss, dyspepsia and headache.
Less commonly used drug options include prostaglandin E1, which is applied locally, into the penis (either injected into it or inserted down the opening into the urethra, as with the suppository alprostadil, brand named Muse). Most men prefer a pill, however, so these locally acting drugs tend to be reserved for men who cannot take oral treatment.
The treatment for ED depends on what is causing it.
Your health care provider may ask you to change certain habits, stop smoking, or using drugs or alcohol. He or she may suggest treatment for emotional problems, relationship conflicts, depression, or performance anxiety. Or you may be asked to change the way you take other medicines. (Never stop or change any drug without first talking to your health care provider.)
If a blood test shows low testosterone levels (low T), testosterone replacement therapy (TRT) may help. However, adding TRT will not help your erection problems if you have normal testosterone levels.
Dietary supplements (often called “herbal remedies”) for ED are popular but may not be safe or even work. Unlike prescription drugs, they do not have to be proven to work to be sold. Check with your health care provider before you take any supplements or drugs to treat your ED.
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