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Phosphodiesterase Inhibitors: Treatment of Erectile Dysfunction
- PDE5 inhibitors (1/4): basic pharmacology, side effects, contraindications
- PDE5 inhibitors (2/4): Sildenafil
- PDE5 inhibitors (3/4): Tadalafil
- PDE5 inhibitors (4/4): Vardenafil
Review Literature: (Hatzimouratidis and Hatzichristou, 2007).
Indications for Phosphodiesterase Inhibitors
PDE5 inhibitors are used for the medical treatment of erectile dysfunction.
Phosphodiesterase Inhibitors and Benign Prostatic Hyperplasia
Smooth muscle of the prostate and urinary bladder also express type 4 and type 5 phosphodiesterase. The release of NO relaxes the muscle cells and plays an important role during micturition. Randomized studies have shown that treatment with tadalafil relieves BPH symptoms (Laydner et al, 2011) (Oelke et al, 2012).
PDE5 Inhibitors: Mode of Action
The phosphodiesterase type 5 plays a crucial role in the inactivation of the signal transduction for the penile erection. Inhibition of the phosphodiesterase type 5 causes a preponderance of the erectile signal transduction and thus an improvement in erection. The mode of action requires thus for an erection a sufficient sexual stimulation, some innervation of the penis and an anatomical intact erectile tissue.
All phosphodiesterase inhibitors for the treatment of erectile dysfunction inhibit potent and highly specific the type 5 phosphodiesterase. The strong treatment effect and the favorable side effect profile make PDE5 inhibitors the first choice treatment option of erectile dysfunction.
Side Effects of Phosphodiesterase Inhibitors
Headaches (very often). Dizziness (often).
Visual impairment like blurring or disturbed color vision (often). Eye pain.
Cardiovascular system:Palpitations, flushing (often). Rarely clinically significant cardiac arrhythmia, angina pectoris or cardiac death (the causality of phosphodiesterase inhibitors in cardiac death is difficult to assess).
Other side effects of phosphodiesterase inhibitors:
Stuffy nose (often). Heartburn or dyspepsia (occasionally). Rarely prolonged erection (priapism). Very rarely severe allergic skin reactions.
Drug Interactions with Phosphodiesterase Inhibitors
Phosphodiesterase inhibitors potentiate the blood pressure lowering effects of nitrates. Co-administration of nitrates and phosphodiesterase inhibitors is contraindicated.
Increased orthostatic hypotension with simultaneous administration of alpha-blocker and phosphodiesterase inhibitors may occur.
Inhibitors of cytochrome P450:
Ritonavir, saquinavir, erythromycin, ketoconazole and itraconazole: enhance phosphodiesterase activity and increase side effects.
Contraindications of Phosphodiesterase Inhibitors
No concomitant therapy with nitrates or potent inhibitors of cytochrome P450 (ritonavir, ketoconazole ...).
- Severe heart failure (from NYHA II) or unstable coronary heart disease
- Uncontrolled hypotension
- Caution in aortic stenosis and hypertrophic obstructive cardiomyopathy
Recent history of stroke (within 6 months).
Severe hepatic insufficiency.
- Non-arteritic anterior ischemic optic neuropathy
- Retinitis pigmentosa
Other contraindications of phosphodiesterase inhibitors:
- Galactose intolerance
- Women or children
- Caution in patients with multiple system atrophy.
- Beware of a predisposition for priapism in sickle cell anemia
PDE5-selective Phosphodiesterase Inhibitors
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- Hatzimouratidis und Hatzichristou 2007 HATZIMOURATIDIS, Konstantinos ; HATZICHRISTOU, Dimitrios:
- Phosphodiesterase type 5 inhibitors: the day after.
In: Eur Urol
51 (2007), Jan, Nr. 1, S. 75–88; discussion 89
- Laydner, H. K.; Oliveira, P.; Oliveira, C. R. A.; Makarawo, T. P.; Andrade, W. S.; Tannus, M. & Araújo, J. L. R.
- Phosphodiesterase 5 inhibitors for lower urinary tract symptoms secondary to benign prostatic hyperplasia: a systematic review. BJU Int, 2011, 107, 1104-1109.
- Oelke, M.; Giuliano, F.; Mirone, V.; Xu, L.; Cox, D. & Viktrup, L.
- Monotherapy with tadalafil or tamsulosin similarly improved lower urinary tract symptoms suggestive of benign prostatic hyperplasia in an international, randomised, parallel, placebo-controlled clinical trial. Eur Urol, 2012, 61, 917-925.
Deutsche Version: Phosphodiesterase Hemmer