Phosphodiesterase inhibitors: Types, Uses, Side Effects

Phosphodiesterase inhibitors

Phosphodiesterase Inhibitors are a class of drugs that inhibit phosphodiesterase (PDE) enzymes. Phosphodiesterase Inhibitors normally break down phosphate groups and lower cAMP or cGMP into target cells.

Phosphodiesterase inhibitors play an important role in regulating the levels of the second messengers cAMP and cGMP inside the cells.

PDE inhibitors are classified according to the enzymes for which they act as non-specific inhibitors of PDE5, PDE4 and PDE3.

Inhibitors of PDE3 have positive inotropic, vasodilatory and antiplatelet effects used in acute heart failure and peripheral vascular disease. PDE3 inhibitors are not recommended for long-term use because of their strong cardiostimulatory effect in patients with heart failure.

PDE4 inhibitors allow bronchial dilatation in severe COPD.

PDE5 inhibitors cause pulmonary vasodilation and slackening of the smooth muscle of the penis. They are used in pulmonary arterial hypertension and erectile dysfunction. Nitrates or alpha-blockers are highly contraindicated in patients taking PDE5 inhibitors because of the risk of life-threatening hypotension.


Phosphodiestrerase inhibitors are classified into PDE3 and PDE5 inhibitors

  • PDE3 inhibitors
    • Milrinone
    • Amrinone
    • Cilostazol
  • PDE5 inhibitors
    • Sildenafil
    • Tadalafil
    • Verdinafil
    • Udenafil

A. Phosphodiesterase Inhibitors Type 3 (PDE3 Inhibitors)


Some key highlights of this Phosphodiestrerase inhibitors class are

  • Milrinone is used for the treatment of congestive heart failure
  • Amrinone is Used in the treatment of congestive heart failure.
  • For the reduction of symptoms of intermittent claudication (pain in the legs that occurs with walking and disappears with rest).

1. Milrinone

It is a vasodilator used as a short-term treatment for treat life-threatening heart failure.  Milrinone belongs to a group of drugs called inotropes, which work by helping the heart pump more blood through the body.


Milrinone is used in the treatment of congestive heart failure.

Side Effects

Common side effects of milrinone include

  • Abnormal heart rhythm, and
  • Headache.
  • Dizziness or fainting.
  • Easy bruising or bleeding.
  • Tremors

Less common and more serious side effects include

  • feeling like you might pass out,
  • chest pain,
  • low potassium
  • bronchospasm (wheezing, chest tightness, trouble breathing)

Consult Your doctor if you have the above side effects.


  • Do not drive or operate heavy machinery until you know how milrinone affects you.
  • Get out of bed slowly to avoid dizziness or fainting.

 2. Amrinone

Amrinone (or inamrinone) is a type 3 pyridine phosphodiesterase inhibitor. Amrinone is a positive inotropic cardiotic with vasodilating properties.


Phosphodiesterase 3 inhibitor activity and how to stimulate the influx of calcium ions into the heart cell. Amrinone is an inhibitor of phosphodiesterase (PDE3), leading to an increase in cAMP and cGMP, resulting in increased calcium input, as caused by beta-agonists, resulting in an increased inotropic effect. The main route of excretion in humans is urine, both by inamrinone and by various metabolites (N-glycolyl, N-acetate, glucuronide and N-glucuronide). The chemical interaction with precipitates occurs with amrinone and dextrose or furosemide. Therefore, the mixture of drugs should be avoided.


It is used in the treatment of

  • congestive heart failure.

Side Effects

Common side effects of amrinone include

  • Upset stomach,
  • Lowered platelet counts, and
  • A sudden drop in blood pressure (hypotension).

3. Cilostazol

Cilostazol is an antiplatelet aggregate and a vasodilator. It works by preventing blood cells, called platelets, from clumping together and preventing the formation of harmful clots. It also dilates the blood vessels in the legs. Cilostazol helps the blood to move more easily and ensures the fluidity of blood in your body. Inhibition of platelet aggregation and vasodilation are important mechanisms of cilostazol, used to treat intermittent claudication in peripheral arterial disease. Cilostazol appears to have less cardiostimulant effects than milrinone.


Cilostazol is used to improve the symptoms of a certain blood flow problem in the legs

  • intermittent claudication
  • Cilostazol can decrease the muscle pain/cramps that occur during exercise/walking.

Side Effects

The most common adverse effects of cilostazol are:

  • abdominal pain,
  • abnormal stoolheadache,
  • diarrhea,
  • nausea,
  • upper respiratory tract infections,
  • fluid retention,
  • abnormal heartbeats.
  • dizziness and
  • runny nose.

B. Phosphodiesterase Inhibitors Type 5 (PDE5 Inhibitors)


  • These drugs are Used for the treatment of erectile dysfunction
  • They are also used for pulmonary hypertension.

1. Sildenafil

Sildenafil belongs to a group of drugs known as Phosphodiesterase Inhibitors type 5 (Phosphodiesterase 5 inhibitors) and  is used to treat male sexual function problems (impotence or erectile dysfunction-ED). In combination with sexual stimulation, sildenafil works by increasing blood flow to the penis to help a man get and keep an erection.


It is most commonly used for two primary conditions such as

  • Erectile dysfunctions
  • Pulmonary hypertension

Side Effects

The most common side effects include:

  • Nasal congestion
  • Headaches
  • Indigestion
  • Impaired vision
  • Photophobia, or sensitivity to light

Less commonly, some users have experienced cyanopsia, where everything appears to have a tinted blue tinge.

2. Tadalafil

It is in a class of drugs called Phosphodiesterase Inhibitors type-5 (PDE5) inhibitors that also includes sildenafil and vardenafil.


Tadalafil is an oral drug that is used for

  • Treating impotence (the inability to attain or maintain a penile erection) and
  • Benign prostatic hyperplasia (BPH).

Side Effects

The most common side effects of tadalafil are

  • headaches,
  • facial flushing
  • stomach upset,
  • blurred vision,
  • flu-like symptoms, and
  • nausea.
  • diarrhea,
  • abnormal ejaculation.
  • Tadalafil also may cause low blood pressure,
  • changes in color vision

3. Verdenfil

This drug also belongs to a group of drugs known as Phosphodiesterase Inhibitors type -5 (PDE5) inhibitors. Other agents of this group are sildenafil and udenafil. The mechanism of action is same as that of sildenafil.


It is used in the treatment of

  • Erectile dysfunction

Side Effects

Common side effects include

common side effects include:

  • Headache
  • stuffy or runny nose
  • dizziness
  • flushing
  • stomach upset

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