Dr. med. Dirk Manski

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Phosphodiesterase Inhibitors: Treatment of Erectile Dysfunction

Review Literature: (Hatzimouratidis and Hatzichristou, 2007).

Indications for Phosphodiesterase Inhibitors

Erectile Dysfunction

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

Nervous system:

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.

Alpha blocker:

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 ...).



Recent history of stroke (within 6 months).


Severe hepatic insufficiency.


Other contraindications of phosphodiesterase inhibitors:

PDE5-selective Phosphodiesterase Inhibitors

Index: 1–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


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. & Ara├║jo, 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