PDE5 Inhibitors for Treatment of Erectile Dysfunction
Introduction Three selective phosphodiesterase type-5 (PDE5) inhibitors are licensed for the treatment of erectile dysfunction – sildenafil, tadalafil and vardenafil. They are all included in the joint formulary. These medications have proven efficacy and safety; the major difference between them is that sildenafil and vardenafil are relatively short-acting drugs, with a half-life of approximately 4 hours, whereas tadalafil has a longer half-life of 17.5 hours. In addition, sildenafil absorption may be delayed when taken with food while tadalafil is unaffected. Choice of Agent
Sildenafil should be considered first line in patients who meet the NHS criteria for
Patients should be exposed to a minimum of 4 (preferably 8) doses up to the
highest tolerated dose of sildenafil before switching to an alternative PDE5 inhibitor.
Patients should be followed up, within 6 weeks of commencing therapy to assess
Patients who do not respond to several doses of sildenafil up to the maximum
dose can be switched to a trial of tadalafil and assessed according to response.
Patients who do not respond to either sildenafil or tadalafil at the maximum dose
should be referred to an appropriate specialist.
Prescribing on the NHS: Drug treatments for erectile dysfunction may only be prescribed on the NHS under certain circumstances. PDE5 inhibitors should not be prescribed on the NHS except to treat erectile dysfunction in men who: i. Have diabetes, multiple sclerosis, Parkinson’s disease, poliomyelitis, prostate
cancer, severe pelvic injury, single gene neurological disease, spina bifida or spinal cord injury.
ii. Are receiving dialysis for renal failure. iii. Have had radical pelvis surgery, prostatectomy (including transurethral resection
iv. Were receiving Caverject, Erecnos, MUSE, Viagra or Viridal for erectile
dysfunction at NHS expense on 14 September 1998.
v. Are suffering severe distress as a result of impotence. In this case, the patient
must be assessed by a specialist; in Brighton & Hove, this is provided by the ED clinic based at the Hove Polyclinic.
The following criteria should be considered when assessing distress: i. Significant disruption to normal social and occupational activities. ii. A marked effect on mood, behaviour, social and environmental awareness. iii. A marked effect on interpersonal relationships. Quantities for “as required” use are normally limited to 4 per month.
Guidance Issue date: May 13 Review Date: May 2017
Drug interactions Organic nitrates (e.g., GTN, isosorbide mononitrate, isosorbide dinitrate), other nitrate preparations used to treat angina such as nicorandil and recreational drugs such as amyl nitrate (poppers) are absolute contraindications with PDE5 inhibitors. Combined use could result in unpredictable falls in blood pressure and, potentially, catastrophic hypotension. In the case of sildenafil and vardenafil, the risk of interaction remains high for 24 hours after the dose is taken. With tadalafil, the risk remains high for 48 hours after dosing. Alpha blockers may interact with PDE5 inhibitors to cause orthostatic hypotension, particularly notable if tadalafil is co-administered with doxazosin – this combination is not recommended by the manufacturers of tadalafil. Ritonavir inhibits metabolism of PDE5Is; this effect is particularly marked with sildenafil and the combination is not advised. Non-responders to PDE5 inhibitors Approximately 25% of patients do not respond to PDE5 inhibitors. Patients should be exposed to a minimum of 4 (preferably 8) of the highest tolerated dose of at least two drugs (taken sequentially, not concurrently) with adequate sexual stimulation. Patients should be followed up, ideally within 6 weeks of commencing therapy. Apparent failure may be due to suboptimal counselling at the initial consultation, which should aim to ensure that the patient understands how to take the tablets properly and to return to the doctor if they are dissatisfied. Cost of drug therapy and reluctance of the partner are frequent reasons for unsatisfactory response. References Lilly, UKSPC for Cialis (2006) Bayer, UKSPC for Levitra (2006) Pfizer, UKSPC for Viagra (2006) British Society for Sexual Medicine Guidelines on the Management of Erectile Dysfunction
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