Sildenafil is a medication recognized for its therapeutic application in managing pulmonary hypertension. This condition involves elevated blood pressure within the arteries supplying the lungs, which can significantly impact heart function. Sildenafil helps address this by influencing blood vessel relaxation in the lungs. Its role has expanded, becoming a widely accepted treatment option for individuals with pulmonary hypertension.
What is Pulmonary Hypertension?
Pulmonary hypertension (PH) describes a condition where blood pressure in the arteries leading to the lungs becomes abnormally high. These pulmonary arteries carry deoxygenated blood from the heart to the lungs. Normal pulmonary artery pressure ranges from 11-20 mmHg at rest; exceeding this indicates pulmonary hypertension.
This elevated pressure forces the heart, specifically the right ventricle, to work harder to pump blood into the lungs. Over time, this increased workload can cause the right ventricle to enlarge and weaken, potentially leading to right-sided heart failure. The narrowing and stiffening of these pulmonary arteries restrict blood flow, further exacerbating the pressure within the lungs.
How Sildenafil Addresses Pulmonary Hypertension
Sildenafil is classified as a phosphodiesterase-5 (PDE5) inhibitor, meaning it blocks the action of an enzyme called phosphodiesterase type 5. This enzyme is found in high concentrations within the pulmonary arteries and is responsible for breaking down a substance known as cyclic guanosine monophosphate (cGMP).
Normally, nitric oxide (NO) released by the lining of blood vessels stimulates the production of cGMP, which then signals the smooth muscle cells in the arteries to relax and widen. By inhibiting PDE5, sildenafil prevents the breakdown of cGMP, leading to increased levels of cGMP within these cells. The elevated cGMP levels promote prolonged relaxation and widening of the pulmonary arteries. This vasodilation reduces the pressure within the lungs, making it easier for the heart to pump blood through them.
Who Can Use Sildenafil for Pulmonary Hypertension?
Sildenafil is specifically approved for the treatment of pulmonary arterial hypertension (PAH), which is categorized as WHO Group 1 pulmonary hypertension. This medication is prescribed by healthcare professionals following a thorough diagnosis and assessment of a patient’s condition.
Sildenafil is effective for adults with WHO functional class II-III PAH, including those with idiopathic PAH or PAH associated with connective tissue diseases. While sildenafil (Revatio) is used for PAH, sildenafil sold under the brand name Viagra is primarily for erectile dysfunction and is not used for PAH treatment. It can be used by both men and women with PAH, and studies have not indicated gender-specific differences in side effects or effects on sexual function in women.
Administering Sildenafil and Managing Side Effects
Sildenafil for pulmonary hypertension is available in tablet and oral suspension forms. The recommended dosage for adults is 20 mg taken three times a day, with doses spaced approximately four to six hours apart. While some patients have received doses up to 80 mg three times a day, studies have not shown greater efficacy with higher doses than 20 mg. An injectable form of sildenafil is also available, usually administered in hospitals, in single-use 10 mg (12.5 mL) doses three times a day for patients temporarily unable to take oral medication. The medication can be taken with or without food.
Patients may experience common side effects such as headaches, flushing, indigestion, nasal congestion, and dizziness. Other reported side effects include heartburn, diarrhea, nosebleeds, difficulty sleeping, numbness or tingling in the extremities, muscle aches, changes in color vision, and light sensitivity. Many of these effects are often mild and may resolve on their own, but if they are severe or persistent, a healthcare provider should be consulted.
More serious potential side effects require immediate medical attention. These include a sudden, severe loss of vision or blurred vision, sudden decrease or loss of hearing, ringing in the ears, fainting, chest pain, or worsening shortness of breath. A painful erection lasting longer than four hours, known as priapism, also necessitates immediate medical care to prevent permanent damage.
Sildenafil should not be taken with nitrates or nitric oxide donors, as this combination can lead to a dangerous drop in blood pressure. Caution is also advised when consuming alcohol or taking other blood pressure-lowering medications due to the potential for hypotension. Patients should inform their healthcare team about all medications they are taking, as sildenafil is metabolized by the liver enzyme CYP3A4 and can interact with various drugs, including certain antivirals, antifungals, and other blood pressure medications.