Apomorphine acts on central dopamine receptors and enhances signals in supraspinal neuronal pathways, which are involved in the regulation of penile erection, and can hereby improve an otherwise subnormal erectile response. In the management of erectile dysfunction, apomorphine is approved and clinically used by sublingual administration. In the recommended dose-range, this route of administration of apomorphine avoids first pass hepatic metabolism and ensures rapid therapeutic concentrations, with a low frequency of side effects. With the sublingual preparation, the recommended starting dose of apomorphine should be 2 mg, which can be clinically effective in producing satisfactory erections with minimal side effects. If necessary, the apomorphine dose can be increased to 3 mg. At 3 mg of apomorphine (irrespective of severity of ED), a roughly 20–30% increase in attempts resulting in satisfactory erections, ie erections firm enough for intercourse, compared to placebo have been reported.1,2 At this dose, common adverse effects include headache and nausea (3–7%). Adverse effects have also been reported to decline by ‘optimizing’ the dosage, ie by starting at a lower dose of apomorphine (2 mg), or by repeated use of the compound. A dose of 4 mg of apomorphine did not further improve erectile responses but increased the occurrence of headache and nausea (6–14%). 1,2 Use of higher doses than recommended increases the risk of more adverse events such as transient hypotension
When combining apomorphine with peripherally vasoactive drugs on an experimental or clinical trial basis, circulatory side effects must be taken into careful consideration. The main aim of such combinations would be to obtain better efficacy and to diminish side effects by reducing the dose or preferably by increasing the selectivity for the target structure of the respective agent. By oral route (ingestion), instead of sublingual administration, first-pass hepatic metabolism of apomorphine is extensive and bioavailabilty of the drug is low.
References
Heaton JP . Characterising the benefit of apomorphine SL (Uprima®) as an optimised treatment for representative populations with erectile dysfunction. Int J Impot Res 2001 13: Suppl 3 S35–S39
Heaton JP . Key issues from the clnical trials of apomorphine SL. World J Urol 2001 19: 25–31
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Hedlund, P. Editorial Comment. Int J Impot Res 14, 59–60 (2002). https://doi.org/10.1038/sj.ijir.3900818
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DOI: https://doi.org/10.1038/sj.ijir.3900818