Cardiovascular/Nitrate

Nitrates

also: GTN · isosorbide mononitrate · ISMN

Overview

Venodilators for angina relief and acute heart failure / pulmonary oedema.

Mechanism

Donate nitric oxide → activate guanylate cyclase → ↑cGMP → vascular smooth muscle relaxation. Predominantly venodilation → ↓preload (↓venous return, ↓ventricular wall tension, ↓myocardial O₂ demand); coronary vasodilation.

Indications

Acute angina (sublingual GTN)
Angina prophylaxis (ISMN)
Acute pulmonary oedema / decompensated HF (IV GTN)

The agents

GTNshort-acting

sublingual/spray/IV

Onset seconds; for acute relief.

Isosorbide mononitratelong-acting

oral

Prophylaxis; needs a nitrate-free interval.

Adverse effects

Headacheclassic

Flushingcommon

Postural hypotensioncommon

Toleranceclassic

Requires a daily nitrate-free interval to prevent.

Cautions & contraindications

Concurrent PDE-5 inhibitor (sildenafil)all

Both raise cGMP → profound hypotension. Classic exam pairing.

Aortic stenosis / HOCMall

Preload-dependent — can collapse.

Hypotensionall

Interactions

Sildenafil/tadalafil/vardenafil → severe hypotension (avoid)

Monitoring & kinetics

BP, symptom relief

GTN has near-zero oral bioavailability (first-pass) → sublingual/transdermal/IV.

Source: BNF — Nitrates