Chronic Stable Angina Flashcards
Does NTG dilate venous or arterial? Preload or afterload?
- Both
- Venous dilation is more pronounced because relaxation of arterial smooth muscle requires higher NTG levels
- Reduces preload (venous dilation)
How does reducing preload decrease myocardial O2 demand?
Filling pressures in ventricles are reduced
What is an example of a relative CI to BB in SIHD (stable ischemic heart disease)?
- COPD or asthma with non-selective BB
2. Worsen bronchoconstriction by blocking B2 receptors in the lungs
Are cardioselective beta blockers always selective?
- Dose of when it is lost in any patient cannot be predicted
- Metoprolol 50-100mg could cause wheezing
What is the mechanism of aspirin?
- Inhibit cyclooxygenase
- Blocks formation of prostaglandins from arachidonic acid
- Inhibits thromboxane and prostacyclin
- Thromboxane A2, a potent vasoconstrictor, activates platelets
- Prostacyclin counter balances thromboxane A2
What is BB withdrawal syndrome? How to avoid?
- Rebound phenomenon
- BB leads to heighten B receptor sensitivity (upregulation)
- An overshoot in HR
- Increased myocardial O2 demand
- Gradual taper schedule (1-2 weeks)
How was nitrate tolerance first discovered?
- Workers exposed to NTG during production of explosives
- Developed severe HA and dizziness after initial exposure
- Side effects would diminish after days
- If workers were not exposed for several days symptoms would return
How long is needed for a nitrate-free interval? What time of day is best?
- 10-12 hours day
2. Nitrate-free at night; angina most likely during day
Will the use of long acting nitrates alter SL NTG?
No evidence that this occurs
What are the mechanisms for nitrate tolerance?
- Depletion of sulfhydryl groups which are needed for conversion of nitrate to NO
- Chronic nitrate produces a state of oxidative stress; this leads to dysfunction of aldehyde dehydrogenase (in mitochondria) the enzyme responsible for nitrate to NO
How often is isosorbide dinitrate dosed? Schedule?
- BID-TID
- 7 AM, Noon, 5 PM (BID less definite)
- If dosed with a traditional TID dosing, there would be a danger that the nitrate free period would be too short
Which long acting nitrate does not undergo first-pass metabolism?
- Isosorbide mononitrate
2. Bioavailability ~100%
What is first pass metabolism?
- Concentration of drug is greatly reduced before systemic circulation
- Drug enters hepatic portal system and is metabolized
What is the half life of isosorbide mononitrate?
5 hours
What are the differences in dosing schedules for isosorbide mononitrate IR vs ER?
- IR is BID, second dose ~7 hours after first. Asymetrical
2. ER is daily, helps avoid asymmetric IR dosing.