Viagra, Levitra or Cialis – Which works best?
EUROPEAN JOURNAL OF MEDICAL RESEARCH 435
Abstract: Since introduction of the PDE-5 inhibitor sildenafil 4 years ago, there has been a fundamental change in the treatment of erectile dysfunction (ED).Intracavernosal or intraurethral injections of vasoactive substances or penile implants as mechanical aids now play hardly any part in it.
The development of the PDE-5 inhibitors vardenafil and tadalafil prompts the question of whether and how these three substances differ in terms of their efficacy and adverse effects. Sildenafil has proven to be a very effective medicinal product. Studies with a follow-up period of up to 6 years have been conducted. The success rate of sildenafil varies in the group of ED patients with an organic underlying disease from 43% in patients who have undergone radical prostatectomy to 85% in patients with a neurological underlying disease, and amounts to an average 82% (range 43-85%, 100mg).
In an evaluation of spontaneous reports of deaths associated with sildenafil, the FDA concluded that
there was no deducible evidence of an increase in the mortality rate among sildenafil users compared to the general population. In fact, fewer deaths associated in time with the ingestion of sildenafil were reported than might have been expected purely statistically on the basis of the normal mortality rate for men in this age group.
According to the initial studies conducted, vardenafil and tadalafil demonstrate efficacy data approximately comparable to those of sildenafil. As yet, insufficient data are available to evaluate the adverse effects of vardenafil and tadalafil, particularly their long-term use and use in high-risk groups. Sildenafil has already been used by over 20 million men in over 110 countries and is one of the beststudiedpharmacological substances available. This adventage in terms of knowledge and safety data makes sildenafil a safe and reliable treatment for patients
with erectile dysfunction.
1. INTRODUCTION
According to epidemiological surveys, one in five men experiences impaired erection. Although these erection disorders have been used to be attributed mainly to psychogenic causes, they are now known to be mainly organic in origin, at least in the 50-plus age group.
Sexual dysfunction used to be, and still is in many societies, a taboo subject, and the scientific study of it was not pursued as vigorously as that of other medical conditions. This situation only changed with the market introduction of the first effective drug for the treatment of erectile dysfunction, sildenafil (viagra).
Since an effective oral drug treatment for erectile dysfunction has been available, treatments involving
intracavernosal or intraurethral injections of vasoactive substances or penile implants as mechanical aids now play hardly any part. Sildenafil and the substances vardenafil(livitra) and tadalafil (cialis), which were developed later, are known as PDE- 5 inhibitors. Sildenafil and vardenafil differ only minimally in terms of their structure, while tadalafil differs markedly from sildenafil and vardenafil in terms of its molecular structure, which is also reflected in pharmacokinetic differences.
The development of the PDE-5 inhibitors vardenafil and tadalafil now prompts the question of whether and how these three substances differ in terms of efficacy and adverse effects from sildenafil.Since few full publications about tadalafil and vardenafil have been published, abstracts and poster publications will also be considered in the followig review.
Because patients ask for efficacy and side-effects of the new substances being informed by marketing reports in newspapers it is time to write this review
now, based on the informations available for the public.
2. ERECTILE DYSFUNCTION
October 29, 2002
Eur J Med Res (2002) 7: 435-446 © I. Holzapfel Publishers 2002
ERECTILE DYSFUNCTION:
COMPARISON OF EFFICACY AND SIDE EFFECTS OF THE PDE-5 INHIBITORS
SILDENAFIL, VARDENAFIL AND TADALAFIL
REVIEW OF THE LITERATURE
U. Gresser1, C. H. Gleiter2
1Praxisklinik Sauerlach, Internal Medicine, Germany,
2Department of Clinical Pharmacology, University of Tübingen, Germany
2.1. PHYSIOLOGY OF ERECTIONS
The physiological process of erection is based on the interplay of neural, neurochemical and endocrinological mechanisms (Sachs 2000). The smooth muscle tone of corpus cavernosum and vascular system is controlled by complex biochemical processes, regulated by the peripheral and central nervous system.
This takes place via neuroanatomical connections that constitute part of the innervation of the lower
urogenital tract (Moreland et al. 2001).
In the healthy man, sexual stimulation triggers a release of the neurotransmitter nitric oxide (NO)
from non-adrenergic, non-cholinergic (NANC) neurones that innervate the corpus cavernosum of the penis. NO effects intracellular activation of guanylate cyclase, which regulates the conversion
of 5-GTP to 3`,5`-cGMP. cGMP mediates intracellular signal transduction, which leads via protein
activation mechanisms to a reduction in the intracellular Ca++ concentration and so to relaxation
of the smooth muscles in the penis, producing vasodilation and erection (Moreland et al. 2001).
2.2. DEFINITION AND CLASSIFICATION OF ERECTILEDYSFUNCTION
2.2. DEFINITION AND CLASSIFICATION OF ERECTILEDYSFUNCTION
According to the internationally recognised definition of the National Institute of Health (NIH) in 1993, Erectile Dysfunction (ED) is defined as the persistent inability of a man to achieve and/or maintain an erection sufficient for a satisfactory sexual performance (NIH Consensus Statement of
Impotence 1993). ED can be classified according to its aetiology or severity. From an aetiological viewpoint, a distinction is made between an organic and psychogenic form, with the organic form being further differentiated according to vascular, neurogenic, anatomical and endocrinological
causes. With the psychogenic form, a distinction is made between generalised and situation-dependent ED (Lizza and Rosen 1999). Besides a purely organic or purely psychological origin, mixed
forms combining both causes frequently exist, and certain classes of drugs (e.g. beta-blockers, SSRI’s, diuretics, etc) are also regarded as triggers of ED (Meinhardt et al. 1997). Erection disorders are subdivided into mild, moderate, or severe ED, according to the severity of the symptoms.
To Be Continued......
To Be Continued......
