VIAGRA : IS IT A WONDER DRUG ?

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ABSTRACT

Male erectile dysfunction is common and frustrating after the age of forty years. Erectile dysfunction is a cause of misery, relationship difficulties, and significantly reduced quality of life. Sildenafil citrate (Viagra) has shown promising results in recently published clinical trials. Sildenafil is a potent and competitive inhibitor of cGMp specific phosphodiesterase-5, predominant isoenzyme in the human corpus cavernosum. It is effective in erectile dysfunction of diverse origin, however it requires a patent vascular system to be effective. It is not effective in patients with endocrinal impotence, loss of libido, premature ejaculation or infertility. Its main adverse effects are headache, flushing, dyspepsia, diarrhoea, nasal congestion, indigestion, visual disturbances, dizziness and rash. Ventricular tachycardia and acute myocardial infraction have been reported in patients of ischaemic heart disease after consumption of sildenafil. Six deaths have been reported in patients taking nitrates. In India it is likely to be prescribed by a primary care physician without complete evaluation of patient on complaint of impotence. Hence the ethical question of who should prescribe this drug should be addressed by medical fraternity and proper guidelines formulated to avoid misuse of sildenafil. Phosphodiesterase is distributed in nerve, central nervous system, and systemic vasculature, hence long-term effects of drug on these tissues has to be ascertained. It should be made mandatory to report all adverse drug reactions to ADR monitoring centres. It is a wonder for those who require it, but has potentially dangerous adverse effects and drug interactions and hence is and not a wonder pill for all kinds of impotence.

Section snippets

Chemical Structure

The chemical structure of the drug according to International Drug Nomenclature is 5-[2-Ethoxy-5-(4-methylpiperazin-1-sulphony1)phenyl]-1-methyl-3-propyl-6,7-dihydro-1H-pyrazolo [4,3-d]pyrimidin-7-one (Fig-1).

Anatomy And Physiology of Erectile Function

The penis has two corpora cavernosa, which is surrounded by a thick fibrous sheath, the tunica albuginea. The erectile tissue consists of multiple, interconnected lacunae lined by vascular epithelium. Multiple helicine arteries branch off from cavernosal artery and open directly into these lacunar spaces. Blood is drained off through subtunical venules, which are compressed against thick tunica albuginea during erection and helps in maintaining tumescence [3]. Erection is a vascular event under

Pharmacological Action

Sildenafil is a potent and competitive inhibitor of cGMP specific PDE5, predominant isoenzyme in the human corpus cavernosum and eye [8]. It decreases catabolism of cGMP, which enhances relaxation of the cavernosal smooth muscle, increases blood flow leading to increased intracavemosal pressure and penile rigidity (Fig-2). Sildenafil restores natural erectile response to various sexual stimuli but does not cause erection in the absence of stimuli. It is given in the dose of 50-100 mg orally. It

Therapeutic Effect

It is effective in erectile dysfunction of diverse origin, however it requires patent vascular system to be effective. Hence this is not effective in severe arterial or venous insufficiency. Boolell et al [8, 9] first reported its effectiveness in a double blind placebo controlled, four way cross over trial in erectile dysfunction of psychogenic origin in twelve patients. Goldstein et al [10] have demonstrated its effectiveness in men with erectile dysfunction of diverse causes e.g. organic,

Adverse Events

This drug is well tolerated. Its main adverse events are headache (16%), flushing 10%), dyspepsia (7%), diarrhoea (4.9%), nasal congestion (4%), indigestion (%), visual disturbances (3%), dizziness and rash (2%) [9, 10]. Patients reported seeing blue haze and transient increased brightness when taking doses over 200 mg. This may cause difficulty in distinguishing colour, hence pilots should be restrained from consuming this drug six hours before flying [16]. Ventricular tachycardia occurred in

Drug Interaction

Sildenafil enhances the muscle relaxant effect of nitric oxide, hence it potentiates blood pressure lowering effect of organic nitrates. 6 deaths have been reported by US FDA in patients taking nitrates, however no causal link has been established [11]. The manufacturing company has issued a warning that patients with ischemic heart disease taking nitrates should be prescribed sildenafil with caution. Drugs, which inhibit cytochrome P450 system, will increase the serum concentration of

Ethical Issue

It is likely to be prescribed by a primary care physician without complete evaluation of patient on complaint of impotence. Hence the ethical question of who should prescribe this drug should be addressed by medical fraternity by consensus and proper guidelines formulated to avoid misuse of sildenafil. In India drugs are commonly sold on prescription of varied forms of medical practitioners and even without prescription. Already there is news of availability of this drug under the counter and

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