Week 2 Nitrates Flashcards
(15 cards)
What is the primary mechanism of action of nitrates?
They release nitric oxide (NO), which activates guanylyl cyclase → ↑ cGMP → smooth muscle relaxation → venodilation > arteriodilation.
How do nitrates reduce myocardial oxygen demand?
By decreasing preload (venodilation) and, at higher doses, afterload (arterial dilation), thereby reducing wall stress and O2 consumption.
What is the clinical significance of nitrate-induced epicardial artery dilation?
It improves coronary blood flow and may relieve vasospasm in variant (Prinzmetal’s) angina.
How do nitrates enhance collateral coronary circulation?
By dilating large coronary arteries, they increase perfusion to ischemic zones.
What is the onset, peak, and duration of sublingual nitroglycerin?
Onset: 1–3 min, Peak: 4–8 min, Duration: 30–60 min.
What nitrate formulation is preferred in hypertensive emergencies and acute MI (excluding RV infarct)?
IV nitroglycerin.
What are the main adverse effects of nitrates?
Headache, hypotension, reflex tachycardia, flushing, and (at high doses) methemoglobinemia.
What is nitrate tolerance and how is it prevented?
Tolerance is reduced drug effect with continuous use. Prevent it with a daily nitrate-free interval (8–10 hours).
What drug interaction with nitrates is potentially fatal and why?
PDE5 inhibitors (e.g., sildenafil) → synergistic ↑ cGMP → profound hypotension.
Why are nitrates contraindicated in right-sided MI?
Right ventricular infarcted hearts rely on preload to maintain output. Nitrates reduce preload → severe hypotension.
Which nitrate is used for chronic stable angina prophylaxis due to longer duration?
Isosorbide mononitrate.
What is the mechanism behind nitrate-induced methemoglobinemia?
Nitrates oxidize Fe²⁺ to Fe³⁺ in hemoglobin → impaired O2 transport → functional anemia.
What is the role of sodium nitroprusside, and what is a key toxicity risk?
Used IV for hypertensive crises; prolonged use may cause cyanide toxicity.
Why are nitrates contraindicated in hypertrophic cardiomyopathy or severe aortic stenosis?
↓ preload and afterload can worsen obstruction and cause critical hypotension.
What differentiates isosorbide dinitrate from mononitrate?
Mononitrate is the active metabolite of dinitrate, with better bioavailability and longer half-life.
