(HEL). Sildenafil (Viagra®) has been on the market for the treatment of erectile dysfunction for five years. Last year, Tadalafil (Cialis®) and Vardenafil (Levitra®) launched two other drugs in this class of drugs. Prof. Dr. Hartmut Porst, a urologist from Hamburg, has used all three phosphodiesterase-5 (PDE-5) inhibitors in his practice and now compares them directly in a currently ongoing, open, company-independent and practical comparative study.

DAZ:
What is your experience with the three phosphodiesterase inhibitors sildenafil, tadalafil , nd vardenafil?

Porst:
Since its introduction five years ago, my practice has treated more than 8,000 patients with erectile dysfunction with Viagra®. In addition, my practice was the Europe-wide responsible testing center for the two other new PDE-5 inhibitors, Vardenafil (Levitra®) and Tadalafil (Cialis®), with nearly 10% of all test patients treated worldwide with these agents being treated by my practice.

In addition, we are currently conducting a fully independent study in which patients will need to try all three medicines in turn, then fill out questionnaires on efficacy and benefits and drawbacks of the drugs and then tell them which substance they would prefer at the end of the study want to have prescribed permanently.

Currently more than 1000 patients are integrated in this study. Based on this wealth of experience, it can be said without any restrictions that all three drugs are highly effective, very safe and undoubtedly an indispensable asset in the treatment of impotence disorders.

DAZ:
How do these phosphodiesterase inhibitors work?

Porst:
Since all three substances act at the same target site, in particular inhibit the abundant enzyme in the erectile tissue Phosphodiesterase 5, all cause the same thing: they prevent the breakdown of cGMP, without an erection can not be achieved. It is important to note that all erectile dysfunction – mental and psychological – ultimately results in the same result: too little cGMP is produced in the penis, and as a result, the erection remains off. Inhibiting the degradation of this erectile, as is done for example by the PDE-5 inhibitors, there is an increase in itself primarily insufficiently formed cGMP in the erectile tissue, and the erection can still occur. In principle, all three drugs are therefore equally effective, but it may well occur in daily use,

DAZ:
The mechanism of action is always the same. How are the three phosphodiesterase inhibitors different?

Porst:
The main difference of the three substances lies in their pharmacokinetics, that is, in the onset of action and the duration of action. With Levitra® and Viagra®, the fastest erection is achieved, usually within 30 to 40 minutes, whereas with Cialis®, in many patients the best erection is often only achieved after 2 to 3 hours. Cialis® is still effective after 1 to 2 days in the majority of patients, which is why this substance has been nicknamed the “weekend pill”. This long duration of action allows couples to make their sexual activities more spontaneous, not as much on the clock as Viagra® and Levitra®, as these are only effective for 4 to 10 hours in many patients.

As a rule of thumb, at the maximum dose of each PDE-5 inhibitor, the clinical duration is 2.5 to 3 times the half-life (t½), that of Viagra® is about 4 hours, Levitra® is between 4 and 5 hours, and at Cialis® is 17.5 hours.

DAZ:
Are there any other differences?

Porst:
In addition, the substances differ in terms of their interactions with food intake: While the effectiveness and the onset of action of Cialis® by food intake of any kind remains unaffected, it comes with Viagra® and Levitra® after a long dinner quite a delay of the onset of an hour and more, partly also to a reduction of the effectiveness.

DAZ:
Can you recommend suitable substances for specific patient groups?

Porst:
Since all three medicines always work in the same place, there is by definition no special patient group that seems to be the most suitable for one of the three drugs.

However, due to one’s own experience in practice, it can happen that one or the other of the patients has one of the three medications, which is why I generally recommend that patients should try all three medications in succession. Then they and, of course, their partner can best decide which PDE-5 inhibitor is most suitable for them, both in terms of erection quality, onset and duration, and side effects.

DAZ:
What side effects do users have to expect?

Porst:
If all the data from the clinical trials are summarized, more common side effects are headache (about 14 to 15%), flushing (4 to 14%), heartburn (4 to 10%), nasal congestion (3 to 9%), and all three in Cialis® back and muscle pain in about 5% and in Viagra® color vision problems in about 5 to 6% of users.

The side effects mentioned are usually only mild to moderate and resulted in only 2 to 3% of all patients treated to an early termination of therapy. It is quite possible that the patient may experience severe headache or heartburn in response to a PDE-5 inhibitor, while he may not have this with any other drug in this class. For this reason too, it seems reasonable that the patients all three

Try PDE-5 inhibitors in succession. More serious side effects on the cardiovascular system were more common in the placebo studies than under the particular PDE-5 inhibitor. The PDE-5 inhibitors may well have protective properties on the cardiovascular system.

DAZ:
Which patients should not take phosphodiesterase inhibitors?

Porst:
Viagra®, Cialis® and Levitra® are absolutely contraindicated in all patients who regularly need nitrate- or molsidomine-containing medications for coronary heart disease or other cardiac damage, as the concomitant administration of these PDE-5 inhibitors leads to a life-threatening circulatory decline can.

Precautions are also imperative in patients who need because of hypertension or benign prostate enlargement of the simultaneous medication of a so-called alpha-blocker, as it may also lead to higher blood pressure drops. For this reason, a time interval of at least six hours between the administration of the alpha-blocker and the PDE-5 inhibitor should be respected.

In patients with a recent myocardial infarction or stroke (<6 months), PDE-5 inhibitors are also considered unindicated and should be used only after careful examination by the appropriate cardiologist. Sildenafil and vardenafil are also contraindicated in patients with more severe ocular disease (eg retinitis pigmentosa).

DAZ:
Dear Prof. dr. Porst, we thank you for this interview!

Sildenafil (Viagra) has been on the market for the treatment of erectile dysfunction for five years. Last year, two more drugs of this class were introduced with tadalafil (Cialis) and vardenafil (Levitra). Prof. Dr. Hartmut Porst, urologist from Hamburg, has used all three phosphodiesterase-5 (PDE-5) inhibitors in his practice and compared them in a currently ongoing, open, company-independent comparative study.