Drugs Used in Chronic Ischemic Heart Disease -DSA Flashcards Preview

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1

Approach to treating angina pectoris

1 - increase coronary blood flow
2 - reduce myocardial oxygen demand

2

Determinants of myocardial oxygen demand

Heart rage
contractility
preload
afterload

3

Drug classes used in chronic IHD

Nitrates - nitrovasodilators
CCB
Beta blockers
Ranolazine

4

Nitrovasodilators

Nitroglycerin
Isosorbide dinitrate
Isosorbide mononitrate - active metabolite of dinitrate

5

Nitrovasodilator pharmacokinetics

Significant first-pass metabolism - high nitrate reductase activity in the liver (Nitrate reeducates activity in saturable)
Bioavailability with oral route is low - other routes avoid first pass metabolism
partially denigrated metabolites have activity and longer half-lives
Isosorbide mononitrate is poor substrate of nitrate reductase - high bioavailability

6

Nitrovasodilator pharmacodynamics - MOA

– Unknown enzymatic reaction releases NO (or other active metabolite – nitrosothiol?)
• The role of mitochondrial aldehyde dehydrogenase 2 (ADH2)

– Thiol compounds are needed to release NO from nitrates

– Vascular smooth muscle relaxation by NO

– Sensitivity of vasculature to nitrate-induced vasodilation:
Veins > Large arteries > Small arteries and arterioles

– No “coronary steal” phenomenon

– Inhibit platelet aggregation

7

Beneficial action of nitrovasodilators in angina

decreased myocardial oxygen demand

Relaxation of vascular smooth muscle - dilation of veins (major effect) and dilation of arteries

8

Dilation of veins with nitrovasodilators for treatment of angina

major effect

increased venous capacitance

reduced ventricular preload

9

Dilations of arteries with nitrovasodilators for treatment of angina

higher concentrations of nitrates are needed compared to venous dilation

reduced arterial pressure and after load

may dilate large epicardial coronary arteries

No significant increase in coronary blood flow into the ischemic area in atherosclerotic angina

10

Nitrate effects in angina of effort

decreased preload

decreased oxygen demand

11

Nitrate effects on vasospastic angina

relaxation of coronary artery vascular smooth muscle

Relieving coronary artery spasm

12

Clinical use of nitrovasodilators

short-acting formulations used to relieve angina attack

Long-acting preparations may be used to prevent attacks

13

Development of nitrate tolerance

• Depletion of thiol compounds

• Increased generation of oxygen radicals

• Reflex activation of sympathetic nervous system (tachycardia, decreased
coronary blood supply)

• Retention of salt and water

14

Adverse effects of nitrates

• Headache (meningeal vasodilation)

• Orthostatic hypotension

• Increased sympathetic discharge
– Tachycardia
– Increased cardiac contractility

• Increased renal Na+ and H2O reabsorption

15

Nitrate drug interactions

ED treatment:

– Sildenafil, vardenafil, tadalafil
• Inhibit cGMP-phosphodiesterase-5, increases cGMP
• Minimal effects on hemodynamics when administered alone in men
with coronary artery disease
– Combination with nitrates causes severe increase in cGMP and a dramatic drop in BP

– Acute myocardial infarction cases have been reported

16

Non-cardioactive calcium channel blockers (dihydropyridines)

Amlodipine - long acting (t1/2 30-50 h)
Nifedipine - short acting (t1/2 4 h)
Nicardipine - short acting (t1/2 2-4 h)

17

Cardioactive calcium channel blockers (non-dihydropyridines)

Diltiazem
Verapamil

18

Calcium channel blockers MOA

• Ca2+ mediates smooth muscle contraction; enters cells via voltage-dependent
calcium channels

• CCBs block Ca2+ entry to relax vascular smooth muscle

19

Anti-Anginal mechanisms of CCBs - decreased myocardial oxygen demand

– Dilation of peripheral arterioles
• Decreased PVR and afterload, decreased blood pressure
• Arterioles more affected than veins (less orthostatic hypotension)
• Dihydropyridines are more potent vasodilators

– Decreased cardiac contractility and heart rate (observed with cardioactive CCBs)

20

Anti-antinal mechanisms of CCB - increased blood supply

Dilation of coronary arteries relieves local spasms (this mechanism may operate in vasospastic (Prinzmetal) angina and NOT in atherosclerotic angina)

21

Major adverse effects of CCB

Cardiac depression, cardiac arrest, acute heart failure (cardioactive CCBs)

Bradyarrhythmias, AV block (cardioactive CCBs)

Short acting dihydropyridine CCBs - vasodilation triggers reflex sympathetic activation

Nifedipine - immediate release: increases risk of MI in patient with HTN, slow release and long acting dihydropyridines better tolerated

22

Minor adverse effects of CCB

Flushing, HA, anorexia, dizziness
Peripheral edema
Constipation

23

Beta blockers indicated in angina

Propranolol
Nadolol
Metoprolol
Atenolol

24

Beta blocker MOA in angina

decreased myocardial oxygen demand

– Decrease in HR leads to improved myocardial perfusion and reduced
oxygen demand at rest and during exercise

– Decrease in contractility

– Decrease in blood pressure leads to reduced afterload

25

Adverse effects of beta-blockers

– Reduced cardiac output
– Bronchoconstriction
– Impaired liver glucose mobilization
– Produce an unfavorable blood lipoprotein profile (increase VLDL and
decrease HDL)
– Sedation, depression
– Withdrawal syndrome associated with sympathetic hyperresponsiveness

26

Contraindications of beta-blockers

– Asthma
– Peripheral vascular disease
– Raynaud’s syndrome
– Type 1 diabetics on insulin
– Bradyarrhythmias and AV conduction abnormalities
– Severe depression of cardiac function

27

Effects of nitrates alone on heart rate, arterial pressure, end-diastolic volume, contractility, and ejection time in angina pectoris

Heart Rate: Reflex increase (not desirable)
Arterial pressure: Decrease
End-diastolic Volume: Decrease
Contractility: Reflex increase (not desirable)
Ejection time: Decrease

28

Effects of Beta Blockers or CCBs on heart rate, arterial pressure, end-diastolic volume, contractility, and ejection time in angina pectoris

Heart Rate: Decrease
Arterial pressure: Decrease
End-diastolic Volume: Increase (not desirable)
Contractility: Decrease
Ejection time: Increase (not desirable)

29

Effects of nitrates with beta blockers or CCBs on heart rate, arterial pressure, end-diastolic volume, contractility, and ejection time in angina pectoris

Heart Rate: Decrease
Arterial pressure: Decrease
End-diastolic Volume: none or decrease
Contractility: None
Ejection time: None

30

Ranolazine MOA

– Inhibits late Na+ current in cardiomyocytes
– Ischemic myocardium is often partially depolarized
– Na+ channel in cardiomyocytes is voltage-gated
– Late Na+ current is enhanced in ischemic myocardium and brings about Ca2+ overload and repolarization abnormalities
– Ranolazine normalizes repolarization of cardiac myocytes and reduces
mechanical dysfunction