Nitrates

Nitrates are a class of medications that increase the release of nitric oxide (NO) in vascular smooth muscle cells, leading to smooth muscle relaxation and subsequent vasodilation. Veins are affected more than arteries, and most therapeutic effects of nitrates result from venous pooling and subsequently decreased preload. Rapid- and short-acting nitrates are primarily used in the symptomatic treatment of acute angina pectoris and hypertensive urgency. Side effects may include headache (nitrate-induced headache), gastroesophageal reflux, and hypotension with syncope. Prior intake of PDE-5 inhibitors significantly increases the risk of hypotension.

• Organic nitrates (nitroglycerin, isosorbide dinitrate, and isosorbide mononitrate) require activation by mitochondrial aldehyde reductase, therefore, the onset of action is not immediate.
• Sodium nitroprusside is activated non-enzymatically; therefore the onset of action is immediate
• Oral nitrates undergo extensive first-pass metabolism in the liver.

References:^[1][2]

The authors cannot be held responsible for the contents provided being exhaustive, correct, or up to date. The contents have been meticulously researched by our editors. Especially updates regarding warnings and recommendations must be considered. Unless otherwise noted, the recommendations provided apply to adults.

• Exogenous supply of nitric oxide (NO) through nitrate → activation of guanylyl cyclase → ↑ cyclic guanosine monophosphate (cGMP) → activation of protein kinase G
  • Increases SERCA activity → ↓ intracellular calcium → ↓ recruitment of contractile units → vasodilation
  • Increases myosin light chain phosphatase activity → ↓ phosphorylated myosin → smooth muscle relaxation → vasodilation
    • Peripheral vasodilation
      • Decreased preload through venous dilation (venous pooling); → reduces myocardial wall tension → improved myocardial perfusion
      • Decreased afterload → reduces contraction effort → ↓ myocardial oxygen demand
      • Greater vasodilatory effect on veins than arteries (except for sodium nitroprusside)
    • Coronary dilation → improved myocardial perfusion
      • In patients with atherosclerotic CAD, arterioles are already dilated to maximize cardiac blood flow (due to flow-limiting stenosis) → difficult to dilate coronary vessels further → limited effect of nitrates
• Anginal pain relief: ↓ preload through venous pooling → ↓ heart size → ↓ oxygen demand → ↓ pain

References:^[1]

• Circulatory dysregulation: hypotension, reflex sympathetic activity → reflex tachycardia → nitrate syncope
  • Beta blockers can be applied to counter this mechanism
• Nitrate-induced headache (due to the dilation of the cerebral arteries)
• Flushing
• Gastroesophageal reflux (due to the relaxation of the lower esophageal sphincter)
• Development of tolerance
  • Prevention: intermittent therapy with nitrate-free intervals of at least 8 hours
• Cyanide toxicity after sodium nitroprusside infusion (see cyanide poisoning)
• Methemoglobinemia
• “Monday disease”
  • Industrial workers who are exposed to nitrates during the work week develop a tolerance over the course of the week.
  • No exposure during weekends leads to loss of tolerance.
  • Reexposure on Monday causes dizziness, tachycardia, and headache.

We list the most important adverse effects. The selection is not exhaustive.

• Angina pectoris
  • Short-acting nitrates such as sublingual nitroglycerin, isosorbide dinitrate, or nitroglycerin spray for treatment of acute attacks
  • Long-acting nitrates such as isosorbide mononitrate can be taken regularly (2–3 times daily) for anginal prophylaxis: unlike some other nitrates, isosorbide mononitrate does not undergo first-pass metabolism by the liver and thus has ∼100% bioavailability.
• Hypertensive crisis: short-term reduction of blood pressure
• Acute coronary syndrome
• Hypertensive pulmonary edema
• Chronic heart failure

References:^[1][2]

• Hypotension
  • Risk of life-threatening hypotension if taken within 24 hours of a PDE-5 inhibitor (e.g., patients with angina pectoris)
• Stenosis of the left ventricular ejection tract; (e.g., aortic stenosis, hypertrophic cardiomyopathy)
• Myocardial infarction with right ventricular failure
• Increased intracranial pressure

References:^[3]

We list the most important contraindications. The selection is not exhaustive.