Viagra Uses | Dosage | Side Effects | How it Works, How Long it Lasts | Warnings
The public’s interest in Viagra (sildenafil) is not solely
due to media hype and the drug’s association with sex: there is a huge demand
for treatment. Since its March release in the United States, it has become the
fastest selling drug in history. 1 Prescriptions are being filled in the United
States and around the world via the internet and on the street, which in Europe
precedes its licencing for prescription by doctors.
Given the prevalence of erectile dysfunction in men aged
50-70, and the unacceptability, ineffectiveness, or unavailability of existing
treatments such as implants, intracavernosal injection, intraurethral pellets,
hoover devices, and sex therapy, the level of demand was predictable. 2 A
tablet treatment must have seemed too good to be true for most patients.
Because of the specificity of Viagra action, a
localised effect after oral administration is possible. The final common
pathway for sexual arousal and stimulation leading to erection is the
production of cyclic guanosine monophosphate (GMP) in cavernosal tissues, which
relaxes smooth muscle and allows blood to fill the corpora. Sildenafil is a
potent and specific inhibitor of the isoenzyme responsible for the breakdown of
cyclic GMP in the corpus cavernosum, cyclic GMP specific phosphodiesterase type
5. As a result, its effect is dependent on sexual arousal or stimulation,
resulting in a more “natural” erectile response.
Viagra treatment has been studied in 21 randomised,
double blind, placebo controlled trials and ten open label extension studies
(continued non-blind treatment after trials),3 but only three randomised
controlled trials and one open label study have received peer review.
Sildenafil improves rigidity and the number of erections in men with erectile
dysfunction, according to objective and subjective measures. 4 Two large
studies found a significant and significant improvement over placebo in
erection quality, proportion of successful sexual intercourse attempts, and
overall satisfaction with treatment. 5 Orgasmic function, satisfaction with
intercourse, and overall sexual satisfaction all improved, but sexual drive
remained unchanged.. Placebo effects were typically minor. An open label
extension study showed effectiveness over 32 weeks, with only 3% of men withdrawing
due to insufficient response, but no further details are currently available. 5
Effects of Viagra
Pooled safety data from 18 of the 21 studies, totaling over
3700 men aged 18-87 years (equivalent to 1631 years of exposure), revealed no
evidence of serious adverse effects attributable to sildenafil. 3 The most
common side effects are headaches, flushing, dyspepsia, nasal congestion, and
transient colour discrimination impairment. Up to 30% of participants
experienced a side effect, but the authors described these as transient, and
only 2% of participants in the published randomised controlled trials
discontinued treatment as a result. 5 There were no significant changes in
pulse, blood pressure, electrocardiographic findings, or laboratory test
results (unspecified), and no cases of priapism.. The US Food and Drug
Administration reported 69 deaths in people taking sildenafil from March to
July 1998, a period in which 3.6 million prescriptions were dispensed, but
determined that no regulatory action was required. 6 The only significant drug
interaction described thus far is the potentially dangerous potentiation of
nitrates’ hypotensive effect. 3 This contraindication is significant not only
because erectile dysfunction is commonly associated with cardiovascular
disease, but also because amyl nitrates (“poppers”) are commonly
abused drugs, particularly among homosexuals. 7
The studies used a long list of exclusion criteria,
including a history of alcohol or substance abuse, poorly controlled diabetes,
and a stroke or myocardial infarction within six months. As a result, the
samples are not representative of all those who will seek treatment, and we
cannot apply the effectiveness and safety findings to these populations.
Nonetheless, there is significantly more data on this treatment than on
previous treatment options. 8
The research evidence does not extend to female use, where
it may increase genital arousal. Women are already being prescribed sildenafil
by some doctors in the United States, and a trial is currently underway.
Viagra has also been used to improve sexual performance in men who do not
have sexual dysfunction, sometimes in combination with stimulants. This amounts
to inappropriate use or misuse, for which no safety or dependency information
is currently available. Researchers must continue to investigate the efficacy
and safety of long-term use in patients who were excluded from previous
studies. There are also intriguing questions about who the drug does not work
for, who would benefit from potentially curative treatments like surgery or
therapy, and what impact successful treatment has on quality of life as well as
mental and physical health.
In the United Kingdom, the immediate challenge posed by
sildenafil is the need for rational decision making regarding availability on
the NHS or from medical insurers. The challenge for clinicians, primarily
general practitioners, is to be adequately informed, which will necessitate the
immediate availability of information and education, which is typically lacking
in the field of sexual health. Although Viagra appears to be a simple
solution to a common problem, it should not be prescribed without first
assessing the patient’s physical and mental health, as well as his sexual and
general relationships, and then treating underlying causes such as diabetes,
cardiovascular disease, or switching to antihypertensive, antipsychotic, or
antidepressant drug treatment. Cigarette smoking and alcohol consumption can
have a significant negative impact on erections.. Patients may be experiencing
severe relationship or personal problems that necessitate counselling or
therapy. Before deciding on a treatment option, the patient and, if possible,
his partner should discuss it.
For many men and their partners, erectile dysfunction causes
misery, relationship problems, and a significantly lower quality of life.
Regardless of whether sildenafil is available on the NHS, the effectiveness of
this treatment and the high prevalence of this distressing disorder make it
unavoidable that many men will use it. The medical profession must respond with
acceptable assessment standards, followed by regular monitoring of ongoing
effectiveness, appropriateness, and, most importantly, safety.
