Nitroglycerin
**Nitroglycerin (NTG)** is a potent, rapid-acting **organic nitrate** primarily utilized as a **venodilator** in veterinary medicine. * **Primary Use**: Acute adjunctive management of **congestive heart failure (CHF)** and cardiogenic pulmonary edema. * **Clinical Pearl**: Due to the rapid development of **nitrate tolerance (tachyphylaxis)** within 48-72 hours of continuous use, it is typically reserved for acute, short-term hospital stabilization rather than chronic outpatient therapy. Intermittent dosing (e.g., 12 hours on, 12 hours off) is often employed to mitigate this tolerance. * **Administration**: Most commonly applied topically (as an ointment or transdermal patch) to hairless areas such as the inner pinna (ear flap), axilla, or groin. > **Note**: While highly effective in humans for angina and acute hypertension, its efficacy in small animals is sometimes debated due to variable transdermal absorption and rapid tolerance, but it remains a staple in emergency critical care for acute volume overload.
Mecanismo: Nitroglycerin acts as a prodrug that donates **nitric oxide (NO)** to vascular smooth muscle, initiating a cascade that leads to vasodilation. * **Nitroglycerin** → converted to **Nitric Oxide (NO)** in smooth muscle cells. * **NO** → activates the enzyme **soluble guanylyl cyclase (sGC)**. * **sGC** → increases intracellular levels of **cyclic GMP (cGMP)**. * **cGMP** → activates **protein kinase G (PKG)** → leads to dephosphorylation of myosin light chains. * **Result**: **Vascular smooth muscle relaxation**. > **Pharmacological Pearl**: At standard doses, NTG primarily dilates venous capacitance vessels. This significantly reduces **preload** (left ventricular end-diastolic pressure) and venous return to the heart, effectively relieving pulmonary congestion and decreasing myocardial oxygen demand. At higher doses, it may also provide some arteriolar dilation, thereby reducing afterload.
Dosificación por especie
- Adjunctive treatment of heart failure (severe pulmonary edema secondary to HCM) · ⅛th to ¼ inch of a 2% cream · Topical · every 4-6 hours · for the first 24 hours · Apply to a hairless area (e.g., inside the earflap) as long as furosemide is being administered concomitantly. Efficacy is suspect but safe. Wear gloves.
- To enhance resolution of pulmonary edema · ¼ to ½ inch · Topical · q6h · To reduce nitrate tolerance, alternate 12 hrs with and 12 hrs without nitroglycerin therapy.
- Adjunctive treatment of heart failure · 2.5-5 mg/24hr transdermal patch · Topical · 12 hours on, 12 hours off
- Adjunctive treatment of pulmonary edema · ¼ inch · Topical/Mucous membranes · every 8 hours · during the first 48 hours · Applied cutaneously or directly to mucous membranes.
- Cardiogenic pulmonary edema (headed for oxygen) · ¼ inch · Topical · q8h · for the first 24 hours · Apply on the inner ear pinnae, groin or axilla as needed. Wear gloves to apply.
- Adjunctive treatment of hypertension · ¼ inch · Topical · q6-8h · Applied to pinna.
- Adjunctive therapy for heart failure · ⅛th inch strip · Topical · q12h · for the first 24 hours of therapy · Applied to inside of pinna.
- Dilative cardiomyopathy · ⅛th of an inch · Topical · once to twice daily · Applied to shaved skin. Apply to ear pinna or skin of thigh. May cause hypotension.
Vías de administración
Contraindicaciones
- Severe anemia
- Hypersensitivity to nitrates
Efectos adversos
- Rashes or erythema at the application site
- Orthostatic hypotension
- Transient headaches (common in humans, suspected in animals)
- Lethargy or weakness secondary to hypotension
Interacciones farmacológicas
- Antihypertensive drugs · Use of nitroglycerin with other antihypertensive drugs may cause additive hypotensive effects.
- Phenothiazines · May increase hypotensive effects.
- Sildenafil (and other PDE inhibitors) · May profoundly increase risk for severe, potentially fatal hypotension.
Monitorización
- Clinical efficacy (resolution of pulmonary edema, improved breathing)
- Sites of application for signs of rash or erythema
- Blood pressure, particularly if hypotensive effects (lethargy, weakness) are seen
Sobredosis
If severe hypotension results after topical administration: * **Decontamination**: Immediately wash the site of application with soap and water to prevent any further absorption of the ointment. * **Supportive Care**: Intravenous fluids may be administered if necessary to support blood pressure. * **Contraindications**: **Epinephrine is contraindicated** as it is ineffective in this scenario and may further complicate the animal's cardiovascular condition.
La referencia de fármacos de VetSheet está destinada a veterinarios colegiados como apoyo a la decisión clínica, no sustituye el juicio profesional ni la ficha técnica vigente del fabricante.