Nitroglycerin (Glyceryl Trinitrate): veterinary dose and monograph

At a glance

Drug class

Cardiovascular

Also known as

GTN, Nitroglycerine, Nitro-Bid 2% ointment, Nitrocontin

Species with doses

Dogs, Cats and Ferrets

Routes

Topical

Last reviewed

1 October 2026

Indications

• Acute congestive heart failure / cardiogenic pulmonary oedema — preload reduction (adjunct)
• Acute decongestion in fulminant CHF (with furosemide/oxygen)
• Pulmonary hypertension / right-heart congestion (adjunct, IV)

Nitroglycerin (Glyceryl Trinitrate) dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Acute CHF / pulmonary oedema (2 % ointment): Papich 5e: 4–12 mg (up to 15 mg) topically — ¼–¾ inch of 2% ointment q6h (1 inch ≈ 15 mg). Plumb’s p.895: ¼ inch (small dogs) to 1 inch (large dogs) q8h for the first 24 h (DeFrancesco); ¼ inch per 5 kg q8h (Atkins); ¼–1 inch q6–12h (Macintire); 2.5–10 mg/24 h patch, 12 h on / 12 h off. Apply to hairless skin (pinna, groin, axilla) wearing gloves. Tolerance develops quickly; adjunct to furosemide and oxygen only.

Cats

• Acute CHF / pulmonary oedema: Papich 5e: 2–4 mg — ⅛–¼ inch of 2% ointment q4–6h. Plumb’s p.895: ⅛–¼ inch to the inner pinna q4–6h for the first 24 h with furosemide (Kittleson); ¼ inch q8h (DeFrancesco); hypertension adjunct ¼ inch q6–8h (Norsworthy). No feline efficacy studies — never delay diuretics or oxygen. Wear gloves.

Ferrets

• Heart failure (adjunct): Plumb’s p.895: ⅛ inch to the inside of the pinna q12h for the first 24 h (Hoeffer 2000); dilated cardiomyopathy ⅛ inch once or twice daily (Williams 2000). May cause hypotension.

Contraindications

Hypotension, hypovolaemia, and severe anaemia. Concurrent PDE5 inhibitors (sildenafil) — catastrophic hypotension. Raised intracranial pressure. Known nitrate hypersensitivity. Continuous uninterrupted use (tolerance). Handler skin contact (use gloves).

Species-specific warnings

Cats: Benefit is modest and unproven — use only as an adjunct to diuretics/oxygen, with gloves, and watch for hypotension.

Adverse effects

• Hypotension, reflex tachycardia
• Cutaneous flushing; weakness
• Tolerance with continuous use (needs nitrate-free interval)
• Headache/hypotension in HUMAN handlers (skin absorption)

Drug interactions

• PDE5 inhibitors (sildenafil): severe, potentially fatal hypotension — contraindicated
• Other vasodilators/antihypertensives/diuretics: additive hypotension
• Heparin: nitroglycerin infusion may reduce heparin effect

Pregnancy and lactation

Limited data; use only if clearly needed for acute decompensation.

Monitoring

• Blood pressure (titrate; avoid hypotension)
• Respiratory effort / resolution of pulmonary oedema (adjunct to furosemide/O2)
• Heart rate (reflex tachycardia)
• Rotate application sites and use a nitrate-free interval (tolerance); handler glove use

Toxicity and overdose

Overdose/over-application causes hypotension, reflex tachycardia, weakness/collapse and (theoretically, at very high doses) methaemoglobinaemia. Tolerance from continuous use blunts efficacy. Accidental human exposure (no gloves) causes headache and hypotension.

Management: No specific antidote. Remove the ointment (wipe off), position the patient, and give IV fluids/support for hypotension. Effects are short-lived as the drug is cleared. Treat significant methaemoglobinaemia (rare) with care (methylene blue — cat caution).

Clinical pearls

• A preload-reducing VENODILATOR for acute CHF/pulmonary oedema — the 2 % ointment on a hairless ear/groin is the classic small-animal delivery (wear gloves!)
• It is an ADJUNCT — furosemide and oxygen do the heavy lifting; the evidence for added benefit is modest, so never delay those
• NEVER combine with sildenafil/PDE5 inhibitors (fatal hypotension)
• Build in a nitrate-free interval to prevent tolerance, and rotate/clean application sites

Mechanism of action

Nitroglycerin is metabolised to nitric oxide in vascular smooth muscle, activating guanylate cyclase and raising cyclic GMP, which relaxes smooth muscle — predominantly VENOUS at usual doses (venodilation → reduced venous return/preload and pulmonary congestion), with arterial/coronary dilation at higher doses. Continuous exposure depletes the thiol cofactors needed for NO generation, producing the characteristic tolerance.

Formulations and products

• 2 % cutaneous ointment (Nitro-Bid type)
• IV infusion 5 mg/mL (dilute for CRI)
• Nitro-Bid 2 % ointment — 2 % cutaneous ointment, Topical ointment (human-label)
• Nitroglycerin IV / Nitrocontin — 5 mg/mL injection; SR tablets, Injection / tablet (human-label)

Storage

Ointment/injection: 15–30 °C, tightly closed (volatile), protect from light. Apply ointment with gloves/applicator; rotate/clean application sites.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other cardiovascular drugs

• Esmolol
• Hydralazine
• Metoprolol
• Mexiletine
• Norepinephrine (Noradrenaline)
• Phenylephrine
• Pimobendan
• Procainamide

Frequently asked questions