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The physiological mechanism responsible for erection of the penis involves the release of nitric oxide (NO) in the corpus cavernosum during sexual stimulation. Nitric oxide then activates the enzyme guanylate cyclase, which results in increased levels of cyclic guanosine monophosphate (cGMP), producing smooth muscle relaxation in the corpus cavernosum and allowing inflow of blood.

Phosphodiesterase type 5 (PDE5) is the enzyme responsible for degradation of cGMP

Tadalafil, is an inhibitor of phosphodiesterase type 5 (PDE5). When sexual stimulation causes local release of NO, inhibition of PDE5 by Tadalafil causes increased levels of cGMP in the corpus cavernosum, resulting in smooth muscle relaxation and inflow of blood to the corpus cavernosum. Tadalafil at recommended doses has no effect in the absence of sexual stimulation.

Tadalafil is rapidly absorbed with the maximum plasma concentration occurring at 2 hours. The earliest significant time from dosing to erectogenic effect is 16 minutes with tadalafil 20 mg, and 30 minutes with the dose of 10 mg. Tadalafil has an extended terminal half-life of approximately 17.5 hours, with an effectiveness lasting up to 36h [1]


[edit] DOSAGE

  • Erectile Dysfunction:
    • For use as needed: Starting dose is 10 mg, 30 minutes prior to sexual activity. Increase to 20 mg or decrease to 5 mg based upon efficacy/tolerability.
    • For once daily use: 2.5 mg taken once daily, without regard to timing of sexual activity. May increase to 5 mg based upon efficacy and tolerability
  • Benign Prostatic Hyperplasia: 5 mg, taken at approximately the same time every day
  • Erectile Dysfunction and Benign Prostatic Hyperplasia: 5 mg, taken at approximately the same time every day.

Tadalafil may be taken without regard to food

The maximum dose frequency is once per day.


  • Tadalafil potentiate the hypotensive effects of nitrates and its administration in patients who use nitric oxide donors or nitrates in any form is therefore contraindicated.
  • History of known serious hypersensitivity reaction to Tadalafil
  • In men for whom sexual activity is inadvisable (e.g.Patients with severe cardiovascular disorders such as unstable angina or severe cardiac failure)
  • Patients who have loss of vision in one eye because of non-arteritic anterior ischaemic optic neuropathy (NAION)


  • Tadalafil has systemic vasodilatory properties and may augment the blood pressure lowering effect of anti-hypertensive medications.
  • Seek emergency treatment for prolonged erections greater than 4 hours and priapism
  • Caution is advised when Tadalafil is used as a treatment for Erectile dysfunction in men taking alpha blockers.



Pregnancy Category B (US). Tadalafil (Cialis) is not indicated for use in women.


Most common adverse reactions (≥2%) include: headache, dyspepsia, back pain, myalgia, nasal congestion, flushing, and pain in limb


Erectile Dysfunction (ED) - Causes, symptoms and treatment



  1. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2699638/
Benign Prostatic Hypertrophy
5α reductase inhibitors Dutasteride (Avodart)   Finasteride (Proscar)
Alpha 1 antagonists Alfuzosin (Uroxatral, Xatral)   Doxazosin (Cardura)   Prazosin   Silodosin (Silodyx, Rapaflo)   Tamsulosin (Omnic, Flomax, Secotex)   Terazosin (Hytrin)
Phytotherapy Pygeum africanum   Serenoa repens
PDE5 inhibitors Tadalafil (Cialis)
Combination products Dutasteride/Tamsulosin (Combodart, Jalyn, Duodart)
Other Mepartricin
Veterinary Osaterone (Ypozane)
Sexual dysfunction pharmacotherapies
PDE5 inhibitors Avanafil   Sildenafil   Tadalafil   Vardenafil
Prostaglandins (Erectile dysfunction) Alprostadil
Premature ejaculation Dapoxetine