Vasodilator · Nitrate · Antihypertensive

Nitroglycerin

Also called NTG

Reviewed by Alex G, BSN, RN, CEN, CCRN, CMC, NREMT-P · From the Reference tab of the app

Indications

• ACS chest pain not relieved by sublingual nitroglycerin and beta-blockers
• Heart failure and pulmonary congestion complicating acute MI
• Hypertensive pulmonary edema or acute heart failure without MI (off-label)
• Perioperative hypertension
• Controlled hypotension during surgery
• Uterine relaxation for retained placenta (off-label)
• Ointment for vasopressor extravasation (off-label)

Dosing

Infusion start: 5–10 mcg/min. Flash pulmonary edema with SBP 160 or more (SCAPE): high dose, starting at 100 mcg/min with NIV (CAEP 2025). Titration: 5–10 mcg/min every 3–5 minutes; larger steps above 20. SCAPE: toward 200 within minutes, then wean as BP and breathing settle.

On the quick cards

• Nitrates (nitroglycerin, isosorbide)NCLEX Drug Classes: Angina relief and prevention

Mechanism of action

Nitroglycerin is a prodrug: in vascular smooth muscle, mitochondrial aldehyde dehydrogenase 2 (ALDH2) and other enzymes denitrate it to release nitric oxide. NO binds the heme of soluble guanylyl cyclase and raises cGMP, which activates protein kinase G to lower cytosolic calcium and activate myosin light-chain phosphatase, relaxing the muscle. Veins respond at lower concentrations than arteries, so low doses mainly cut preload and higher doses also dilate arterioles and coronaries; continuous exposure blunts this pathway (tolerance).

Pharmacology

• Cardiovascular: venodilation lowers preload, LVEDP and wedge pressure, cutting oxygen demand; higher doses lower SVR and BP
• Cardiovascular: dilates epicardial coronaries and collaterals and relieves spasm; reflex tachycardia, or paradoxical bradycardia with hypotension
• Respiratory: lowers PA pressure but blunts hypoxic pulmonary vasoconstriction, so PaO₂ can fall
• CNS: cerebral and meningeal vasodilation causes headache and can raise ICP
• Other: relaxes esophageal, biliary and uterine smooth muscle

Pharmacokinetics

Chemistry

• Glyceryl trinitrate: a nitrate ester of glycerol, not a true nitro compound; MW 227
• Small, uncharged (no ionizable group) and lipid soluble, so it crosses mucosa and skin
• Volatile and explosive when pure; tablets lose potency outside the capped original glass bottle
• Premixed 0.1, 0.2 or 0.4 mg/mL in D5W in glass bottles (pH 3–5); 5 mg/mL vials hold 30% alcohol and 30% propylene glycol and need dilution
• Migrates into PVC: only 20–60% reached patients through PVC sets in studies; with non-PVC tubing, doses learned on PVC run high

Adverse effects and cautions

In the one-pagers

• Heart FailureDecompensated HF and shock: Warm-wet: Most common: IV loop diuretic; vasodilator (nitroglycerin, nitroprusside) if BP allows
• Physiological Adaptation: Conditions at a GlanceCardiac and blood pressure: Right ventricular (inferior) MI: Low BP, distended neck veins, clear lungs after nitroglycerin: Stop nitrates, legs up, fluid bolus as ordered: At once
• Mental Health: Meds and CommunicationStimulant toxicity: Cocaine chest pain gets aspirin, benzodiazepines and nitroglycerin, with phentolamine or a calcium-channel blocker for persistent hypertension. The 2014 AHA/ACC NSTE-ACS guideline advises against β-blockers in patients with signs of acute intoxication, yet a meta-analysis of 1,794 patients found no more MI or death with them (Pham 2018), so practice varies.

In the algorithms

• New Hypotension
• New Hypoxemia
• STEMI

Sources

1. FDA label: Nitroglycerin in 5% Dextrose (2016)
2. FDA label: Nitrostat (2023)
3. Chen 2002 (ALDH2, PNAS)

For education and exam preparation only. Follow your institution’s protocols. Typical adult values for study. Follow the order, the label and your institution's protocols.