Vetdrugs 2.0Nitroglycerin, also called glyceryl trinitrate, is an organic nitrate vasodilator used as a short-term adjunct in selected heart-failure patients. Veterinary use commonly involves topical preparations intended to reduce cardiac filling pressures. Its clinical role is predominantly venodilatory, and controlled evidence of improved veterinary outcomes is limited.
Group
Nitrate vasodilator
Mechanism of Action
Bioactivation of nitroglycerin generates nitric-oxide-related signaling that stimulates soluble guanylyl cyclase in vascular smooth muscle. Increased cyclic GMP promotes relaxation, especially of venous capacitance vessels. Greater venous capacity reduces blood return to the heart and lowers filling pressures and preload. At sufficient exposure, arterial dilation can also reduce vascular resistance.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Preload reduction | 4–12 mg/animal | TOPICAL | As needed | Maximum 15 mg/dose; Up to 15 mg has been used. Reported guidance also describes 1/4-3/4 inch of 2% ointment every 6 hours; 1 inch is approximately 15 mg. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Preload reduction | 2–4 mg/animal | TOPICAL | Every 4–6 h | Approximately 1/8-1/4 inch of ointment is also described; the length-to-mass conversion is approximate. |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Laminitis adjunct | Reference only | TOPICAL | Apply 2% ointment to the skin above the hoof; a numeric amount is not established and efficacy is questionable. |
Indications
- Short-term adjunctive reduction of elevated filling pressures in selected dogs or cats with congestive heart failure or cardiogenic pulmonary edema, with limited controlled clinical efficacy evidence.
Contraindications
- Hypotension
Interactions
- Other vasodilators can compound blood-pressure reduction.
Adverse effects
- Hypotension; methemoglobinemia is uncommon.
Toxicity
For excessive topical hypotension, remove ointment to stop further absorption and support circulation. Historical guidance cautions against epinephrine as a reflex treatment.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Nitroglycerin ointment 2% | Other | 20 mg / g | TOPICAL |
Monitoring and Administration
Monitor blood pressure. Wear gloves, apply to hairless skin inaccessible to licking and allow a nitrate-free interval of at least 8 hours during intermittent chronic use.
Protect from heat and light; keep tablets in a tightly closed glass container.
Additional canine 2% ointment protocols: 1/4-1 inch every 6-12 hours for heart-failure support; 1/4-2 inches every 8 hours during the first 48 hours for pulmonary edema; 1/4 inch per 5 kg three times daily for the first day. Length-based alternatives are product-dependent and do not override separately stated mass-dose caps.
Feline alternatives include 1/4-1/2 inch topically every 6 hours, or 1/4 inch every 6-8 hours for hypertension. Ferrets have received a 1/8-inch strip on hairless skin every 12 hours for the first day, or once to twice daily for dilated cardiomyopathy. Monitor hypotension; pulmonary-edema benefit, especially in cats, is uncertain.
Transdermal device protocols use a 2.5-10 mg/24-hour patch in dogs or 2.5-5 mg/24-hour patch in cats, worn for 12 hours and removed for 12 hours. Patch delivery is a rate; its labeled content is not an amount to administer all at once.