How do phosphodiesterase-5 enzyme inhibitors work?
Phosphodiesterase-5 enzyme inhibitors are medications used to treat erectile dysfunction, enlarged prostate (benign prostate hyperplasia), and pulmonary arterial hypertension (PAH), a condition of high blood pressure in the arteries that carry deoxygenated blood from the heart to the lungs.
Phosphodiesterase-5 enzyme inhibitors work in the following ways:
- Relax the smooth muscles in the penis and increase blood flow into the corpus cavernosum, the erectile tissue in the penis.
- Improve blood flow in the prostate and relieve urinary symptoms associated with an enlarged prostate.
- Relax the smooth muscles around the pulmonary arteries, which results in arterial dilation and reduced pulmonary blood pressure.
Normally, sexual stimulation causes nitrous oxide to be released into the corpus cavernosum, which increases the concentration of a signaling molecule known as cyclic guanosine monophosphate (cGMP). An increase in cGMP levels leads to relaxation of vascular smooth muscles, dilation of blood vessels, and improved blood flow.
The phosphodiesterase-5 enzyme regulates cGMP levels by degrading them. Phosphodiesterase-5 enzyme inhibitors prevent PDE-5 from degrading cGMP, increase its concentration in the tissue, and enhance the muscle relaxation effects of nitrous oxide.
How are phosphodiesterase-5 enzyme inhibitors used?
Phosphodiesterase-5 enzyme inhibitors are administered orally as tablets or suspensions, or as intravenous injections for the treatment of the following conditions:
- Erectile dysfunction
- Benign prostatic hyperplasia with or without erectile dysfunction
- Pulmonary arterial hypertension, to improve exercise ability and slow down the progression of disease in patients with:
- Duchenne muscular dystrophy (an inherited muscle degeneration disorder)
What are side effects of phosphodiesterase-5 enzyme inhibitors?
Side effects of phosphodiesterase-5 enzyme inhibitors may include the following:
- Rhinitis (inflammation of the nasal passage)
- Epistaxis (nasal bleeding)
- Nasal congestion
- Sinus congestion
- Sinusitis (inflammation of the sinuses)
- Nasopharyngitis (nose and throat inflammation)
- Bronchitis (inflammation of the bronchial passage)
- Upper respiratory tract infection
- Oropharyngeal pain (oral and throat pain)
- Exertional dyspnea (shortness of breath)
- Dyspepsia (indigestion)
- Gastroesophageal reflux disease (GERD)
- Stomach discomfort
- Myalgia (muscle pain)
- Arthralgia (joint pain)
- Flulike syndrome
- Back pain
- Amnesia (memory loss)
- Erythema (redness of the skin)
- Skin rash
- Pruritus (itching)
- Anaphylaxis (severe allergic reaction)
- Peripheral edema
- Hypotension (low blood pressure)
- Postural hypotension (sudden drop in blood pressure when standing up from sitting or lying down)
- Increased creatine phosphokinase (CPK) levels in the blood
- Hypertension (high blood pressure)
- Angina pectoris (chest pain)
- Myocardial infarction (heart attack)
- Deep vein thrombosis (blood clot in the vein)
- Priapism (prolonged erection)
- Genitourinary tract infection
- Pollakiuria (frequent urination)
- Hematuria (blood in urine)
- Nephrolithiasis (kidney stone)
- Balanitis (inflammation in the head of the penis)
- Hyperglycemia/hypoglycemia (Increase/decrease in blood glucose levels)
- Blood vessel block in people with sickle cell anemia
- Change in color vision
- Conjunctival hyperemia (dilation and redness of blood vessels in the conjunctiva, the membrane on the whites of the eyes, and the inner surface of eyelids)
- Visual field defect
- Retinal vein/artery occlusion (block)
- Non-arteritic anterior ischemic optic neuropathy (NAION), a condition that causes loss of blood flow and damage to the optic nerve
- Hearing loss
Information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.