Nitro paste is a topical medication formulated with nitroglycerin, also known as glyceryl trinitrate, which is a compound historically associated with treating chest pain. This ointment is classified as a nitrate, a class of drugs that acts as a potent vasodilator.
While nitroglycerin is widely recognized for its effects on the coronary arteries to improve blood flow to the heart, the paste form is utilized in dermatology and wound care for its localized action on the skin and underlying tissue. The application of this paste to the skin allows the drug to be absorbed and exert its influence on the smaller blood vessels near the surface. This unique ability to influence local circulation is the foundation of its therapeutic use outside of traditional cardiac care. The goal of this topical application is to enhance the delivery of oxygen and nutrients to compromised tissue, especially in wounds where poor circulation is preventing recovery.
The Mechanism of Nitric Oxide in Healing
The therapeutic effect begins once nitroglycerin is absorbed into the skin, where it acts as a prodrug, converting into an active molecule. Enzymes within the cells metabolize the nitroglycerin, releasing Nitric Oxide (NO) gas directly into the local environment. This release of NO is the primary biological mechanism driving the wound-healing process.
Nitric Oxide is a powerful signaling molecule that quickly influences surrounding blood vessels, leading to local vasodilation (the widening of the vessels). This widening increases the diameter of the small arteries and arterioles, resulting in a measurable increase in blood flow to the wound bed. Enhanced blood flow supplies the injury site with higher concentrations of oxygen, growth factors, and immune cells necessary to fight infection and support tissue repair.
Beyond its immediate impact on blood flow, NO also stimulates angiogenesis, the formation of new blood vessels. It encourages the migration and proliferation of endothelial cells, which are the building blocks of capillaries, helping to rebuild the compromised vascular network within the healing tissue. This process is particularly important in chronic wounds where the local blood supply is often severely restricted.
Nitric Oxide also modulates the cellular activities essential for tissue repair. It promotes the function of fibroblasts, the cells responsible for synthesizing collagen, which provides structural integrity to the new tissue. Furthermore, NO supports re-epithelialization by encouraging the migration of keratinocytes, the cells that form the skin’s outer layer, to cover the wound surface.
Clinical Applications for Difficult Wounds
Nitro paste is often considered for chronic or ischemic wounds where poor local blood supply prevents healing. The topical application is particularly beneficial because it delivers the vasodilatory effect directly to the impaired area without significantly affecting the entire circulatory system to the same degree as an oral medication.
One common application is in the management of chronic venous ulcers, which occur when faulty veins lead to blood pooling and high pressure in the lower legs, damaging the skin. While the underlying cause is venous insufficiency, the resulting tissue damage benefits from the localized increase in arterial blood flow and oxygenation provided by the paste. Similarly, certain types of diabetic ulcers, especially those where small blood vessel damage (microangiopathy) restricts circulation, can show improved healing rates due to the enhanced perfusion.
Wounds associated with peripheral artery disease, where plaque buildup narrows the arteries supplying the limbs, also represent a group of ischemic injuries that may benefit from this therapy. By locally dilating the remaining functional vessels, the paste helps maximize the delivery of necessary healing components to the starved tissue. The improvement in circulation can also help reduce the severe pain often associated with these ischemic wounds.
The paste formulation also has a long-standing application in treating anal fissures, which are small tears in the lining of the anus. These fissures frequently become chronic because the local blood vessels spasm, creating localized ischemia that prevents the tear from healing. The topical nitroglycerin relaxes the smooth muscle surrounding the area, reducing the spasm and increasing blood flow directly to the fissure, thereby promoting tissue repair.
Practical Application and Safety Profile
Nitroglycerin paste requires precise dosing and careful application. The dose is typically measured by the length of the ointment squeezed onto a special dosing paper or ruler supplied with the medication, rather than by weight or volume.
The ointment is generally applied to clean, intact skin near the wound site, but not directly into the open wound bed. It is spread thinly over a designated area on the chest, back, or extremities, and the application site is often rotated daily to prevent skin irritation. After application, the site is typically covered with the dosing paper or a transparent dressing.
Because nitroglycerin is absorbed through the skin and enters the bloodstream, systemic side effects are possible even with topical use. The most common adverse effect is a severe headache, which results from the widening of blood vessels in the head. Other systemic concerns include dizziness and hypotension. Monitoring blood pressure is a standard precaution, particularly when therapy is initiated.
As a nitrate, a serious contraindication exists for patients taking phosphodiesterase type 5 (PDE5) inhibitors, such as Sildenafil. The combination of the two drug classes creates a synergistic effect that leads to a profound and potentially life-threatening drop in blood pressure. Patients must inform their healthcare provider about all medications they are taking before starting treatment with nitroglycerin paste.