PDE5 Inhibitors (PDE5i)
What are PDE5i?
The oral medications Viagra™ (sildenafil), Cialis™ (tadalafil) and Levitra™ (vardenafil) belong to a group of medicines called phosphodiesterase type 5 inhibitors (PDE5i). These medications are a treatment for erectile dysfunction. They work through the nitric oxide and cyclic GMP metabolic pathways to enhance penile blood flow. These medications do not increase libido though they may be less effective in the presence of low testosterone. These medications work best in the presence of sexual stimulation.
PDE5 inhibitors were developed for the treatment of older men with penile blood flow problems resulting in erectile dysfunction. These days younger men without blood flow problems are taking PDE5 inhibitors where the sexual problem may be related to performance anxiety or lack of confidence. These medications are also very effective in this situation but should be considered a short term solution and prescribed in association with counselling.
How are they taken?
The PDE5 inhibitors should be taken about 1-2 hours before planned sexual activity. Sexual stimulation is required to activate the relaxation of the penile blood sinusoids (internal blood containing spaces) allowing blood to engorge the penis. These medications may be less effective or take longer to work if taken during a heavy meal or in association with alcohol intake, so on the first few attempts, take the medication before a meal or at least 2 hours afterwards. Taking the medication at least on 5 different occasions is required before the effectiveness can be ascertained.
The different types of PDE5i
Viagra and Levitra are usually effective after one hour and have a window of opportunity between 4-6 hours. Cialis may take up to 2 hours to become effective but the window of opportunity may last up to 36 hours or even longer. The usual on demand dose of Viagra is 50mg or 100mg, Levitra is 10mg or 20mg and Cialis also 10mg or 20mg.
As all three medications come in different strengths, your doctor will advise the appropriate dose. Viagra is now off patent and a number of generic variations are available on the market, these usually carry the name Sildenafil.
Cialis also comes in the form of a low dose daily medication in a dose of 5mg a day. This tablet is indicated for men who have difficulty planning sexual activity with on demand medication. By taking a tablet each day at the same time, sexual activity can be undertaken at any time without planning. It is also used in sexual rehabilitation after radical prostatectomy where the taking of daily medication encourages preservation of erectile tissue whilst waiting for healing of the damaged erection nerves and as a treatment where erectile dysfunction and lower urinary tract symptoms present together.
Side effects of PDE5i
All the PDE5 inhibitors have similar side effects, the commonest being facial flushing, blocked nose and headache. Another side effect is gastric reflux (heart burn). Viagra™ has a side effect affecting colour vision and a rare effect on vision called NAION. Cialis has a side effect of low back pain and muscular pain in the legs. Often the side effects are mild and may lessen over time. These medications have mostly been proven to be safe when taken in the long term.
PDE5 inhibitors should not be taken by any man who is not fit enough to engage in sexual activity, particularly by men who have unstable cardiovascular disease. Any man taking nitrate medication which is a treatment for heart pain known as angina, is not allowed to take these medications. The recreational drug amyl nitrate poppers is a nitrate medication and is thus also not allowed to be taken together with PDE5 inhibitors.
Please note that PDE5 inhibitors are not licensed for use in women.
Illegal products
Many men purchase these types of medications over the internet. These are called counterfeit medications. These medications are unsafe and may contain unknown and poisonous substances and there are documented cases of fatalities from consuming counterfeit internet sourced medications. It is strongly advised that prescribed medications should only be purchased from an Australian pharmacy.
The intention of this handout is for educational purpose only and not to be used as a guide for self-management. Consult with your specialist or GP.
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