Sildenafil (Viagra) is the first effective oral therapy used in the treatment of erectile dysfunction. It is produced by Pfizer (Pfizer US Pharmaceutical Group, New York, NY) and was approved by the FDA in 1998. It is considered to be the first-line therapy for the treatment of erectile dysfunction in men who have no contraindications to its use. Unlike the therapies that were available before the FDA approved Viagra, simply taking the “little blue pill” does not produce an erection. To understand this, it is first important to review the processes involved in the normal erection. When aroused or stimulated, the brain sends out messages that result in an increase in the release of nitric oxide from the nerves in the pelvis. This nitric oxide then stimulates the production of a chemical called cGMP, which in turn tells the cavernosal smooth muscle and the cavernosal arteries to relax and dilate, thus increasing blood flow to the penis. cGMP is broken down by the enzyme (chemical that causes reactions to occur) phosphodiesterase type 5. Viagra stops phosphodiesterase type 5; thus, there will be more cGMP around to stimulate the cavernosal smooth muscle and arteries, thereby allowing more blood to flow into the penis. Critical to the success of Viagra is the need for arousal (sexual stimulation) so that the brain will stimulate the release of nitric oxide.
What is the success rate for Viagra?
The success rate for Viagra varies from 48% to 81% and varies with the cause of the erectile dysfunction.
Read more: Cialis vs Viagra – Viagra (sildenafil) and Cialis (tadalafil) difference and comparison.
Success of Viagra by Cause of Erectile Dysfunction
| Etiology | Success rate | Source(s) and studies |
| General population | 70% | N Engl J Med 1998;338:1397-1404 Urology 1999;S3:800-805 |
| Hypertension | 70% | N Engl J Med 1998;338:1397-1404 |
| Spinal cord injury | 57-93% | Eur Urol 2000;38:134-193 Neurology 1998;51:1629-1633 |
| Spina bifida (myelomeningocele) | 80% | J Urol 2000;164(3, part 2):958-961 |
| Multiple sclerosis | 90% | Urol Clin N Am 2001;32:289-308 |
| Psychogenic: depression and antidepressent treatment related | 73-89% | Int J Impot Res 1998;10:53, 254a |
| Bilateral nerve-sparing radical prostatectomy | 32-80% | Int J Impot Res 2001;13(Suppl 5):568 |
| Radiation for prostate cancer | 70-80% | Urology 2001;57:769-773 J Clin Oncol 1999;17:3444-3449 |
| Diabetes mellitus | 50-65% | JAMA 1999;281:421-426 |
Spinal Cord Injury
Patients whose erectile dysfunction is caused by spinal cord injury or spina bifida (a congenital condition affecting the spinal cord, also called myelomeningocele) frequently respond to 25 to 50 mg of Viagra. Men with complete spinal cord injuries tend to require higher doses than those with incomplete lesions.
Diabetes Mellitus
The effectiveness of Viagra in men with diabetes mellitus-related erectile dysfunction does not appear to be affected by the patient’s age, duration of the erectile dysfunction, or duration of the diabetes mellitus. In addition, the glycosylated hemoglobin (hemoglobin A1C, a chemical in the blood that allows blood sugar control to be monitored) levels and the prevalence of peripheral neuropathy do not affect the patient’s response to Viagra.
Dialysis
Viagra is successful in restoring erectile function in 60% of men with erectile dysfunction who are on hemodialysis and continuous ambulatory peritoneal dialysis, and was well tolerated.
Penile Prosthesis
Viagra has been shown to increase sexual satisfaction in men with inflatable penile prostheses. By inducing dilation and engorgement of the residual corporeal erectile tissue as well as the glans (tip) of the penis, Viagra can complement the erection obtained from the penile prosthesis.
External-Beam Radiation Therapy
The response rates of Viagra after radiation therapy exceed 70%. Men who note some erectile function, albeit inadequate, after external-beam radiation therapy have up to a 90% response rate with Viagra, whereas those who do not note any erections at all after external-beam radiation therapy have a 52% response rate with Viagra. Most men require the 100 mg dose.
After Radical Prostatectomy
Satisfaction rates with Viagra for postradical prostatectomy erectile dysfunction range from 15% to 80%. Preoperative erectile function, the nerve-sparing nature of the surgery, and the timing of Viagra administration affect response rates. As would be expected, the best success rates are in men who experienced adequate erectile function before surgery and who underwent a bilateral nerve-sparing radical prostatectomy. The worst success rates are in those with erectile dysfunction before surgery and in those who had a non-nerve-sparing radical prostatectomy. The success rates of Viagra for men who have had a bilateral nerve-sparing radical prostatectomy are around 70%; for those who have had a unilateral nerve-sparing radical prostatectomy, they are about 50%; and for those who have had a non-nerve-sparing radical prostatectomy, the success rates are about 15%. Studies have shown that erectile dysfunction may improve in men after radical prostatectomy during the first year or two after surgery. Lack of erections, both sexually aroused and nocturnal, after radical prostatectomy has been associated with penile fibrosis and loss of penile length over the long term. Exciting studies evaluating the benefit of consistent use of Viagra or injection therapy to promote penile blood flow after radical prostatectomy are being evaluated. It is the hope that enhancing tissue oxygenation will minimize scarring and may lead to earlier recovery of erectile function or improved response to therapy.
Viagra has been shown to be quite effective in reversing antidepressant-induced sexual dysfunction and antipsychotic-induced sexual dysfunction.
If you tried Viagra and it didn’t work for you, it is important that you re-evaluate how you used the medication. Remember the effects of diet and stomach emptying on the absorption of the medication. Also, if you only tried a few pills, you may not have given it a sufficient trial. Studies have shown that it may take up to eight trials with the medication (including the need to increase the dose if several attempts at a lower dose are not effective and are not producing significant side effects) before you get a good response. In a similar manner, if you are anxious, concerned, worried, or stressed when you are trying the medication, Viagra will not be as effective. It is important for both you and your partner to be as relaxed as possible and to minimize the pressure and anxiety related to concern about whether it will work so that it has the best chance of working. Some people advocate taking the pill and participating only in foreplay on several occasions, just to get both you and your partner to relax, and then giving it a complete trial.
It is okay to have a glass of wine, a beer, or a mixed drink when using Viagra – it should not interfere with the Viagra. Remember, however, that too much alcohol may have a negative effect on erectile function and thus one should limit one’s alcohol intake. Viagra may also affect other phosphodiesterases in the body, such as phosphodiesterase type 6 in the eye, which may account for some of its side effects.
Who is a candidate for Viagra?
Most men can take Viagra; however, there are contraindications to the use of Viagra, and if these are not adhered to, serious life-threatening problems may arise.
Contraindications to the use of Viagra include:
- Use of products containing organic nitrates such as sublingual nitroglycerin, amyl nitrates, nitroglycerin patch, and long-acting nitrates, such as Imdur. Nitrates, which are a form of nitric acid that causes opening of the blood vessels to the heart (e.g., nitroglycerin), and nitrites should not be used for angina for at least 24 hours after Viagra is taken. The reason for this is that when combined, nitrates and Viagra may significantly lower blood pressure.
- Unstable angina requiring frequent use of short-acting or sublingual nitroglycerin (medication taken for the relief of angina).
The FDA and Pfizer Corporation both recommend certain precautions regarding conditions that could be affected or exacerbated by using Viagra. These conditions include:
- Congestive heart failure (inability of the heart to adequately pump blood, leading to swelling and fluid in the lungs) with a borderline low blood volume.
- Recent heart attack (myocardial infarction).
- High blood pressure requiring three or more medications to control.
- Retinitis pigmentosa, a congenital eye condition that causes blindness.
- Severe arrhythmias (irregular heart beat).
- A condition that may leave men prone to priapism, such as sickle cell disease and trait, leukemia, and multiple myeloma. There has been a case report of priapism associated with Viagra use in a male with sickle cell trait.
If you are unsure of your cardiac status, have a strong family history of cardiovascular disease, or do not exercise regularly, then you should consider further cardiac evaluation before you use Viagra. A cardiac stress test can help determine whether you have any significant cardiac risks associated with the use of Viagra.
How does one use Viagra?
Use of Viagra is on demand, meaning that each time you want to have intercourse, you need to take a pill. Viagra cannot be taken any more frequently than once in a 24-hour period. The pill should be taken 1/2 hour to 1 1/2 hours before anticipated intercourse; however you can realistically take it up to 3 to 5 hours before anticipated intercourse. Remember, the pill facilitates your body’s response, and thus it requires sexual stimulation/foreplay for it to work. A high-fat meal around the time of Viagra use can slow the drug’s absorption and, as a result, delay its time of onset – in other words, it might not be affecting you when you need it to, so it is important to be careful what you eat. In addition, men with diabetes who have delayed gastric emptying (food does not move through their stomach quickly) may need to take the pill a few hours before anticipated intercourse. The half-life of Viagra is 3 to 5 hours, which means that if you have any Viagra-related side effects, they may last up to 3 to 5 hours, although most reported side effects have lasted less time and are generally mild to moderate in severity. Very few patients have discontinued taking Viagra because of side effects. Viagra is widely distributed throughout the tissues in the body, but unlike MUSE, there are insignificant quantities of Viagra in the ejaculate. There are three different doses of Viagra: 25, 50, and 100 mg. Typically, the starting dose is 50 mg; however, in men over 65 years of age, those with liver disease, those with impaired renal function, or those using medications that increase the concentration of Viagra in the blood, the recommended starting dose is 25 mg. If there is no response or an inadequate response to 50 mg, then the physician will often prescribe a dose of 100 mg, which is the level that about 75% of men using Viagra prefer. Medications that increase Viagra levels include erythromycin (E-mycin), clarithromycin (Biaxin), ketoconazole (Nizoral), itraconazole (Sporanox), and cimetidine Tagamet). Men taking protease inhibitors, such as indinavir (Crixivan), nelfinavir (Viracept), ritonavir (Norvir), and saquinavir (Fortovase), should start at a dose of 25 mg because the protease inhibitors (generally prescribed for HIV/AIDS), increase the blood levels of Viagra. In fact, the peak plasma level in this situation is higher than in men who take a 100-mg dose of Viagra. Men taking ritonavir, the most potent of these protease inhibitors, are recommended to take Viagra no more than once every 48 hours. Rifampin (Rifadin), a medication used to treat tuberculosis, may lead to lower concentrations of Viagra in the blood.
What are the side effects of Viagra?
Table below presents the more common side effects of Viagra. Headache, flushing, and nasal congestion are vasodilatory effects and reflect dilation (increased opening) of blood vessels in the head, face, skin of the chest and nasal mucosa, respectively. Dyspepsia (indigestion) may occur as a result of dilation of the gastroesophageal sphincter. The gastroesophageal sphincter lies at the junction between the stomach and the esophagus, the tube that food passes through to enter into the stomach after you swallow. With relaxation of the sphincter, there may be reflux (backflow) of acidic stomach contents into the esophagus, causing a sour taste. Abnormal vision that can occur with Viagra use is typically a change in color vision (abnormal blue/green discrimination) related to the inhibitoryeffect of Viagra on phosphodiesterase type 6 in the eye. Other visual disturbances that have been reported include double vision, temporary visual loss, ocular redness, and burning. The visual side effects are transient, no long-standing changes in the eye or in vision have been reported, and ophthalmologic evaluation of the effects of Viagra on the eye has demonstrated no long-term adverse effects. Viagra also does not increase intraocular pressure.
Use of Viagra produces a non-dose-related reduction in blood pressure. Systolic and diastolic pressures are decreased by 8 to 10 mmHg and 5 to 6 mmHg, respectively, during therapeutic use. In most cases, this does not cause any significant side effects; however, in men who are taking many medications to control hypertension, this mild change may be significant.
Since Viagra’s FDA approval, certain rare side effects have been reported. Although none of these side effects are necessarily caused by Viagra, it’s still important that patients and doctors stay aware of them. They include the following:
- Heart attacks and death. In some cases, these are clearly related to the combined use of nitroglycerin-containing products and Viagra. Some such events have occurred in men with known cardiovascular disease, but others have not had previously identified cardiovascular disease. Therefore, men with cardiovascular disease should discuss the risks of Viagra use with your primary care provider or cardiologist, if you have one, prior to taking the Viagra. If you are unsure as to the status of your cardiovascular health, you should discuss further evaluation, such as a stress test, with your primary care provider.
- Stroke.
- Onset of irregular fast heart beat (atrial fibrillation).
- Priapism in an individual who crushed the Viagra, dissolved it in fluid, and injected it into his penis.
There have been other rare reported cases of priapism with oral use of Viagra. The drug has not been shown to affect the sperm motility (the sperms’ ability to move, an important consideration for conception) or the shape of the sperm. It also does not appear to have any effect on the lungs and breathing in individuals with chronic obstructive pulmonary disease.
There have been reports of tachyphylaxis to Viagra. Tachyphylaxis is the decreased response to a drug after a few doses, such that the medication initially works but after using it for a short period of time, the same dose is not effective. It is unclear whether Or not the reported phenomena were truly cases of tachyphylaxis, as opposed to progression of the erectile dysfunction or the effects of dietary indiscretions and improper use of the medication. Isolated case reports of hemorrhoidal bleeding and a skin reaction that were temporarily related to use of Viagra have also been reported.
Side Effects Associated with Viagra
| Side Effects: | Viagra (n = 734) | Placebo (n = 725) |
| Headache | 15.3* | 3.9 |
| Flushing | 10.5 | 0.7 |
| Dyspepsia | 6.5 | 1.7 |
| Nasal congestion | 4.2 | 1.5 |
| Respiratory tract infection | 4.2 | 5.4 |
| Urinary tract infection | 3.1 | 1.5 |
| Flu syndrome | 33 | 2.9 |
| Altered vision | 2.7 | 0.4 |
| Diarrhea | 2.6 | 1.0 |
| Dizziness | 2.2 | 1.2 |
| Rash | 2.2 | 1.4 |
| Back pain | 2.2 | 1.7 |
| Arthralgia | 2.0 | 1.5 |
*No. of patients reporting an adverse event (%)
What is yohimbine?
Yohimbine is an oral medication that acts primarily in the brain (centrally). How it exerts an effect on erectile function is not well understood, and study results are conflicting in regard to its effectiveness. Currently, because not enough information is available to demonstrate a clear-cut superiority of yohimbine over placebo, it is not recommended as a first-line therapy for erectile dysfunction. Side effects of yohimbine occur in 10% to 30% of individuals; they are usually mild and include agitation, anxiety, headache, mild increase in blood pressure, increased urinary output, and upset stomach.