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ED and its associated conditions.(9) From its mode
of action it becomes clear why the use of nitrate medication is absolutely
contraindicated with sildenafil. The build up of exogenous NO with nitrate
medication together with the indirect internal build up of NO via
sildenafil may lead to a profound hypotensive event.(2) A relative
contraindication to the use of sildenafil (and, it may be argued, for any
treatment for ED) is the patient's cardiovascular risk. It has been
demonstrated that if a patient can, for example, walk 1 km in 15 minutes
on the flat and climb two flights of stairs in 10 seconds without chest
discomfort, pain or undue breathlessness, the risk for ischaemia during
sexual activity is low, provided that the patient is with the usual sexual
partner in a familiar setting, and without the added stress of a heavy
meal and/or alcohol.(10)
Sildenafil is generally well tolerated. Adverse events such as headache, flushing, dyspepsia, and
nasal congestion occurred in 4-16% of patients (compared to placebo: 1-4%). Only a small proportion
of these patients ceased medication as a result of these side effects which are usually mild
and transient.(9)
Tadalafil (Cialis) was launched in Australia in March 2003, and vardenafil (Levitra) in May 2003.
They have similar efficacy, safety and tolerability to sildenafil. Vardenafil has a half life of 4-5
hours.(15) Pharmacokinetic differences between tadalafil and sildenafil are shown in Table 3.
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Table 3. Comparison of
Sildenafil and Tadalafil
| Onset |
Duration |
Dose |
Special comments |
Sildenafil
60 minutes |
3-4 hours |
50 mg |
25 mg in the elderly. 100 mg in
some patients. Absorption retarded by heavy meals. Efficiency
reduced by alcohol. Partially inhibits PDE6 causing transient
blue-green difficulty in 3% of patients |
Tadalafil
30 minutes |
36 hours |
10-20 mg |
10 mg dose in renal impairment.
Not affected by meals or alcohol. Do not give nitrate within 4-5
days of dose. |
Apomorphine
An alternative first line medication to PDE5 inhibitors is apomorphine, soon to be available in
Australia. Taken sublingually, it acts centrally via the paraventricular nucleus of the hypothalamus,
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