Viagra is a safe and effective oral treatment for men with erectile dysfunction of physical, psychological or mixed cause. However, it is important that patients should be aware of the low probability (less than 50%) that intercourse will be possible after the first dose - particularly in severe or advanced cases. The majority of men who stop Viagra because of apparent lack of effect will in fact respond and achieve intercourse if they continue to try, progress from 50 mg to 100 mg, or take the pill without food on an empty stomach (3 hours after eating).
Reliable safety data gathered in the 4 years since Viagra was launched confirm that side effects such as Priapism(prolonged erection), red eyes, painful eyes, syncope(fainting), tachycardia (rapid heart rate), and nausea do occur, but are rare. HIV medications (protease inhibitors) have been shown to raise Viagra blood levels. Certain patient groups are more susceptible to a decrease of their blood pressure, including those with aortic stenosis, hypertrophic obstructive cardiomyopathy, and multiple system atrophy. Finally, Viagra remains contraindicated in patients taking nitrates.
No new safety concerns have emerged in the past year, reinforcing that Viagra is very safe. Indeed, we now know that many patients with cardiovascular disease (CVD) and ED benefit from it.
The following can be prescribed Viagra safely without the need for extensive Cardiovascular investigation:
- men who are a symptomatic and have fewer than three risk factors for coronary artery disease
- those with controlled hypertension
- those with mild stable angina
- patients who have undergone successful coronary revascularisation (bypass or stent placement)
- men with a history of uncomplicated heart attack that happened greater than 6-8 weeks ago
- those with mild valvular disease of the heart
- patients with mild left ventricular disease and congestive heart failure (NYHA Class I)
Alternative oral therapies for Erectile Dysfunction (availability may vary geographicall, especially by countryy) are Cialis (Tadalafil), Levitra (Vardenafil), Uprima (apomorphine), and phentolamine. Both Uprima and phentolamine have very low or no efficacies and therefore for present purposes will not be addressed.
Uprima is approved for the treatment of Erectile Dysfunction in Europe and initial sales have not been impressive (less than 20% of ED market). Refill rates are dismal supporting lack of efficacy.
Phentolamine's application to the FDA was withdrawn and the drug is not available.
The only chemicals that work and remain interesting are the drugs that work like Viagra, (PDE5 inhibitors), Levitra and Cialis.
Levitra is currently under development. Placebo-controlled phase III trials have shown doses of 5 mg, 10 mg, and 20 mg to improve erectile response and intercourse, with side-effects similar to those seen with Viagra. Cialis is also under development and has similar efficacy and side-effects to Viagra. Cialis is approved and available for the treatment of ED in Europe and Australia. However, unlike Viagra, no food interaction has been observed for Cialis which means that the medication can be taken with food. In addition because the drug stays in the blood stream for 36 t0 48 hours, the window of opportunity for intercourse is wide, at 30 minutes to 36 hours. This represents a distinct advantage from the patient's perspective as it diminishes the need for planning. Sex can be more spontaneous and natural.
Although Viagra, Levitra and Cialis differ in their biochemical potency and selectivity, and in onset and duration of action, it is important not to extrapolate those findings inappropriately to the clinical setting. For example, greater biochemical potency does not necessarily translate into enhanced clinical efficacy. The same is true of selectivity.
The only clinically significant differences between Vigra, Levitra and Cialis are in duration and maximum concentration. Cialis's half-life of 17.5 h makes it a "slow drug", (not slow in onset) and explains why it does not interact with food. In general a medication for ED is effective for a period that equals two times the half life.
In short, there appears to be little biochemical or clinical differences between the three agents except for the lack of food interaction and the duration of activity for Cialis. All three medications are contraindicated in patients who take nitrates.
A recent survey looking at what patients with ED really want from their treatment found that efficacy and a favorable side-effect profile were the highest priorities.3 Fast onset was desirable, but there were major differences in what was considered fast. Duration was important only in terms of lasting long enough to complete intercourse. Few men (or their partners) felt that multiple erections, or the ability to achieve them over time, were critical as long as one dose was enough for a successful encounter. The majority of men already taking Viagra said it worked for them and had relatively consistent effects. Onset of action ranged from 15-75 min, and its duration was 6-8 h. Side-effects such as headache, flushing, and blue vision were well recognized and tolerated. Most complaints were about high cost or lack of insurance coverage.
An underlying desire was reported by most couples for initiation of sex to be normal (spontaneous and natural). Few patients fully understood the duration of activity that Viagra can provide, and its advantages. Cialis may indeed fulfill the desire that couples and patients with ED have for the initiation of sex to be normal (spontaneous and natural).
Although Viagra, Levitra and Cialis are safe and effective they do, like all medications, have disadvantages. They essentially enhance partial (sexual) erections, rather than initiating them. At best, the response rate among men with advanced ED (for example following radical prostatectomy) is 40%. Correct administration is critical, and if Viagra does not work when taken correctly, no other oral Viagra like drug (PDE5 inhibitor) will either.
In conclusion, the potencies of Viagra, Levitra and Cialis are broadly similar, but each has unique pharmacological properties related to its molecular structure. Viagra is an exemplary PDE-5 inhibitor that, after 4 years of widespread clinical use, is acknowledged to be effective and particularly well tolerated. The new medications are expected to be similar to Viagra in their efficacy and contraindications, but careful clinical evaluation will be necessary to ensure their safety. The only new attributes of clinical significance will be the lack of food interaction and the long duration of action of Cialis. This may translate into greater efficacy of the first dose as well as a return to more spontaneous (normal) initiation of sexual activity.
Levitra has been approved and is on the US market. Placebo-controlled phase III trials have shown doses of 5 mg, 10 mg, and 20 mg to improve erectile response and intercourse, with side-effects similar to those seen with Viagra.
- McCullough AR, et al. J Urol 2001. In press.
- DeBusk R, et al. Am J Cardiol 2000; 86: 175-81.
- Data from Six Degrees Survey, October 2001.