How PDE5is work?

How PDE5 inhibitors work and how their efficacy is measured

In order for a man to attain an erection, he needs to be sexually aroused. Once he is stimulated, nitric oxide (NO) diffuses into the smooth muscle cells, activating guanylate cyclase to change guanosine triphosphate (GTP) into cyclic guanosine monophosphate (cGMP). The cGMP causes a decrease in intracellular calcium inducing smooth muscle relaxation, allowing more blood to flow into the vessels of the penis, making the penis rigid and erect.

Phosphodiesterase type 5 inhibitors (PDE5is) are responsible for reducing cGMP in the penis. This reduction causes the smooth muscle surrounding the blood vessels to contract, resulting in blood being forced out of the penis and the erection becoming flaccid.

PDE5 inhibitors block the action of PDE5, preventing it from breaking down cGMP. This results in an improved blood flow to the penis, enabling it to gain and maintain an erection.

PDE5 inhibitors block the action of PDE5, preventing it from breaking down cGMP. This results in an improved blood flow to the penis, enabling it to gain and maintain an erection.

Click here to view a PowerPoint presentation explaining how PDE5 inhibitors work

The self reporting takes three main forms:

SEP (Sexual Encounter Profile)

  • SEP1 – Were you able to achieve at least some erection (some enlargement of the penis?)
  • SEP2 – Were you able to insert your penis into your partner’s vagina?
  • SEP3 – Did your erection last long enough for you to have successful intercourse?
  • SEP4 – Were you satisfied with the hardness of your erection?
  • SEP5 – Were you satisfied overall with this sexual experience?

IIEF (International Index of Erectile Function)

The IIEF is a 15-question questionnaire which is completed by the patient after a minimum of 4 weeks following enrolment in a study. The IIEF asks questions related to various aspects of the patient’s sexual function:

  • Erectile function Q1-Q5, Q15
  • Intercourse frequency Q6
  • Satisfaction with intercourse Q7-Q8
  • Orgasm and ejaculation Q9-Q10
  • Sexual desire Q11-Q14

GAQ (Global Assessment Questions)

  • Has the treatment you have been receiving over the last 4 weeks improved your erections?

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