Nitrates
High-yield Verified · Oct 2026Prototype: nitroglycerin
Nitrates are a class of medications used for acute angina attack.
Medical view → mechanisms, drug comparisons and Step 1 pharmacology
Organic nitrates — the first-line rescue and prevention drugs for anginal chest pain.
How it works in the body
The system involved, what goes wrong, and how the drug and body interact.
01 Angina — supply cannot meet demand
Angina is chest pain caused by the heart muscle not getting enough oxygen. It appears when demand (a fast, forceful heart pumping against high pressure) outstrips supply (blood delivered through narrowed coronary arteries). Physical effort can tip that balance and trigger an attack.
Nitrates relieve angina mainly by attacking the demand side — and, in coronary spasm, the supply side too. They are the fastest tool for an acute attack and a mainstay for prevention.
02 How nitrates intervene — nitric oxide and venodilation
Nitrates are converted in the vessel wall into nitric oxide (NO), the body’s own vasodilator signal. NO raises cGMP in vascular smooth muscle, relaxing it. The most important effect is on veins: dilating the venous system pools blood in the periphery, so less blood returns to the heart (↓ preload). A heart with less to pump does less work and needs less oxygen.
At higher doses nitrates also relax arteries (↓ afterload) and dilate the coronary arteries — especially valuable in vasospastic (Prinzmetal) angina. The net result is a rapid drop in the heart’s oxygen demand and, often, a real increase in supply.
03 The deadly interaction — and why tolerance develops
Because nitrates work through the cGMP pathway, they are catastrophic when combined with PDE5 inhibitors (sildenafil/Viagra, tadalafil/Cialis, vardenafil). PDE5 inhibitors block the breakdown of cGMP; stack them with a nitrate and cGMP soars, causing profound, potentially fatal hypotension. This combination is an absolute contraindication — always ask about erectile-dysfunction and pulmonary-hypertension drugs before giving a nitrate.
A second quirk is tolerance: give nitrates continuously and the vessels stop responding within about 24 hours. To keep them working, therapy is dosed with a daily nitrate-free interval (typically 10–12 hours overnight) — which is why the transdermal patch is removed at night.
Drug names
Indications
- Acute angina attack (sublingual nitroglycerin — rescue)
- Chronic angina prevention (long-acting isosorbide, transdermal patch)
- Acute coronary syndromes, acute heart failure, hypertensive emergency (IV nitroglycerin)
Mechanism of action
Metabolized to nitric oxide, which activates guanylate cyclase and raises cGMP in vascular smooth muscle, causing relaxation. Predominant venodilation reduces preload (and cardiac oxygen demand); higher doses add arterial and coronary vasodilation.
Therapeutic effects — what you'll see working
For an acute attack, success is prompt relief of chest pain — but relief that requires more than the standard sublingual protocol is an emergency. For chronic use, success is fewer, less severe episodes, preserved only if a nitrate-free interval prevents tolerance.
- Rapid chest-pain relief
- Sublingual nitroglycerin bypasses first-pass metabolism and acts within 1–3 minutes, dropping preload fast enough to abort an acute anginal attack.
- ↓ Preload / cardiac workload
- Venodilation reduces venous return, so the heart pumps a smaller volume against less wall tension — cutting myocardial oxygen demand. Lower left ventricular filling pressure is also why IV nitroglycerin is used in acute heart failure.
- Coronary vasodilation
- Dilating the coronary arteries increases oxygen supply, which is the primary benefit in vasospastic (Prinzmetal) angina.
Adverse effects
Most of the common side effects are vasodilation showing up somewhere other than the coronary arteries — the head (headache), the arterioles (flushing), and the whole circulation (hypotension).
Interactions
Contraindications
Most contraindications are situations where an abrupt fall in blood pressure or preload is dangerous — above all, co-administration with a PDE5 inhibitor or an sGC stimulator such as riociguat; the labels also list severe anemia and allergy to nitrates.
When to hold
Assess before giving — these findings mean hold the dose and act.
Nursing considerations
The RN-specific layer — each action paired with the reason it matters.
Common questions
What are Nitrates used for?
How do Nitrates work?
What are the serious side effects of Nitrates?
When should a nurse hold Nitrates, and what safety checks apply?
Conditions treated
SL nitroglycerin 0.4 mg every 5 min, up to 3 doses, venodilates to drop preload and oxygen demand and relieve ischemic pain (IV is more effective for ongoing symptoms). Three hard stops: SBP < 90 mm Hg, suspected right-ventricular (inferior) infarction — an RV infarct is preload-dependent, and nitrates can collapse the pressure — and a PDE5 inhibitor within 48 h.
Isosorbide dinitrate plus hydralazine increases survival in advanced DCM, and hydralazine or nitrates are among the pregnancy-safe PPCM options. Nitroglycerin is on the HCM avoid list, and nitroprusside is contraindicated in pregnancy (cyanide toxicity).
The acute rescue and the exam favorite: venodilation pools blood in the veins — preload falls, wall stress falls, oxygen demand falls (higher doses also dilate coronaries toward ischemic areas). Sublingual NTG is the therapy of choice for acute episodes (onset 1–3 minutes); long-acting forms prevent episodes but need a 10–12 hour nitrate-free interval daily to avoid tolerance. Absolute contraindication with PDE-5 inhibitors (sildenafil, vardenafil, tadalafil) — combined vasodilation can cause severe hypotension.
Hydralazine + isosorbide dinitrate: the vasodilator combination with proven benefit in African American patients with NYHA III–IV HFrEF on guideline therapy.
Intraoperative hypertension — "Short-acting vasodilators such as nitroprusside and nitroglycerin" are among the options when tumour handling releases catecholamines.
See also
Slow heart rate & lower BP by blocking β-adrenergic receptors. Watch for bradycardia.
Lower BP by blocking angiotensin conversion. Classic dry cough & angioedema risk.
Lower LDL cholesterol via HMG-CoA reductase inhibition. Monitor for myopathy.
Injectable antibodies that protect the liver’s LDL receptors, cutting LDL cholesterol by about half and lowering cardiovascular events. Given subcutaneously every 2–4 weeks.
PPAR-α agonists that mainly lower triglycerides — used with diet for severe hypertriglyceridemia — with muscle, gallbladder, liver and kidney risks, highest for gemfibrozil combined with a statin.
Non-absorbed resins that trap bile acids in the gut, forcing the liver to use cholesterol and pull LDL from the blood. Constipation, drug binding and rising triglycerides are the issues to manage.
Sources
- Nitroglycerin — formulations, mechanism, sublingual use — StatPearls (NCBI)
- Nitrates — vasodilation, tolerance, nitrate-free interval — StatPearls (NCBI)
- CIALIS (tadalafil) — nitrate contraindication and 48-hour interval (FDA label) — FDA / DailyMed
- NITROSTAT (nitroglycerin sublingual) — prescribing information — DailyMed (NLM)
- Antianginal – nitrates (Ch. 6.8) and sildenafil (6.13) — Open RN — Nursing Pharmacology
- NITRO-DUR (nitroglycerin transdermal) — prescribing information — DailyMed (NLM)
- NITRO-BID (nitroglycerin ointment) — prescribing information — DailyMed (NLM)
- NITROLINGUAL Pumpspray — prescribing information — DailyMed (NLM)
- Isosorbide dinitrate tablets — prescribing information — DailyMed (NLM)
- Isosorbide mononitrate extended-release tablets — prescribing information — DailyMed (NLM)
- Nitroglycerin in 5% Dextrose Injection — prescribing information (IV) — DailyMed (NLM)
- VIAGRA (sildenafil) — nitrate contraindication — DailyMed (NLM)
- Vardenafil tablets — nitrate contraindication — DailyMed (NLM)
- REVATIO (sildenafil, pulmonary hypertension) — nitrate contraindication — DailyMed (NLM)
- Drugs@FDA — IMDUR (NDA 020225) marketing status — U.S. FDA
- Drugs@FDA — ISORDIL (NDA 012093) marketing status — U.S. FDA
- Biochemistry, Cyclic GMP — PDE5 inhibitors and nitrates — StatPearls (NCBI)
- Administration of Medications Via Other Routes — transdermal patches — Open RN — Nursing Skills
Reviewed by Hae Suk Lee, RN
Educational summary for nursing students. Always verify against current prescribing information and your institution's protocols before administering. Not medical advice.