Drugs for Chronic IHD

Question 1

Why are Arterial Vasodilators not useful in the treatment of Classic (Atherosclerotic) Angina?

Answer 1

Arterial Vasodilators will induce the “Coronary Steal” Phenomenon whereby blood flow won’t increase to the arteries affected by Atherosclerosis, but it will to the other unaffected arteries

Question 2

Why do Nitrates have a high first-pass metabolism?

Answer 2

There is high Nitrate Reductase activity in the Liver

Question 3

How is the Bioavailability of Nitrates via the Oral route?

Answer 3

Nitrates have low bioavailability via the Oral route due to high Nitrate Reductase Activity in the Liver

Question 4

Why does Isosorbide Mononitrate have a greater bioavailability then other Nitrates?

Answer 4

Isosorbide Mononitrate has a greater bioavailability than other nitrates as it is a poor substrate of Nitrate Reductase

Question 5

What Enzymes/Compounds are required for the release of NO from Nitrates?

Answer 5

Mitochondrial ADH2

Thiols

Question 6

What blood vessels does NO preferentially function to Vasodilators?

Answer 6

NO fxns to Vasodilate:

Veins > Large Arteries > Small Arteries and Arterioles

Question 7

What is the major mechanism of action of Nitrates in the treatment of Classic (Atherosclerotic) Angina?

Answer 7

Nitrates -> NO which functions to Vasodilate Veins.

Vasodilate veins leads to increased Venous Capacitance and Decreased Preload -> Decreased Work required of Heart -> Decreased demand of O2

Question 8

Why is using higher doses of Nitrates to try and induce Arterial/Arteriolar vasodilation not very. Useful in treating Atherosclerotic Angina?

Answer 8

Much higher concentrations of Nitrates are needed in order to induce Arterial Vasodilation, and it would then primarily only affect large pericardial coronary arteries.

While Arterial Vasodilation will decrease Afterload of the Heart (thus decreasing Myocardial work and O2 demand), it will also not correct the ischemia in Classic (Atherosclerotic) Angina as it will lead to Coronary Steal

Question 9

What is the major mechanism of action of Nitrates in the treatment of Variant (Prinzmetal) Angina?

Answer 9

Nitrates -> NO -> Vascular Smooth Muscle Relaxation -> Coronary Artery Vasodilation -> Coronary Vasospasm Relief

Question 10

How might an individual gain tolerance to Nitrates?

Answer 10

Methods of Nitrate Tolerance:

• Depletion of Thiol Compounds
• Increased Generation of ROS (H2O2 and Peroxynitrite)
• Reflex Activation of Sympathetic NS
• Retention of Salt and Water

Question 11

What is the difference between Nitrates used to relieve an Angina attack, versus Nitrates used to prevent Angina attacks?

Answer 11

Short-Acting Nitrate formulations are used to treat Angina attacks when they occur. This includes Nitroglycerin and Isosorbide Dinitrate. They are administered in sublingual sprays.

Long-Acting Nitrate formulations are used to prevent Angina Attacks. This includes Nitroglycerin (Oral, Ointment, Patch), Isosorbide Dinitrate (Oral), and Isosorbide Mononitrate (oral).

Question 12

What are some of the adverse effects of Nitrates?

Answer 12

• Orthostatic Hypotension
• Increased Sympathetic Outflow (tachycardia, increased cardiac contractility)
• Increased Renal Salt and Water reabsorption
• Headache (due to meningeal vasodilation; Nitrates are contraindicated if Intracranial Pressure is elevated)

Question 13

What is the importance of the drug interaction between Nitrates and the PDE-5 Inhibitors used in treating ED?

Answer 13

PDE-5 Inhibitors function to inhibit cGMP-PDE-5, which leads to a decrease in the breakdown of cGMP to GMP.

Nitrates function to generate NO which leads to increased activation of Guanylyl Cyclase. GC then functions to convert GTP into cGMP.

Together these drugs can cause a massive increase in cGMP leading to severe drops in BP. MI have been reported due to this.

Question 14

What are the 2 classes of Ca2+ Channel Blockers (CCB’s) used in treating Chronic IHD?

Answer 14

The 2 Classes of CCB’s used in treating Chronic IHD are:

Cardiactive

Non-Cardioactive (Dihydropyridines)

Question 15

What is the mechanism of CCB’s action in treating IHD?

Answer 15

Calcium entry into cells is inhibited by CCB’s, leading to a lack of Myosin-LC Phosphorylation, and a decrease in Smooth Muscle contraction. This can function to Dilate Peripheral Arterioles -> decrease PVR and Afterload -> decreased myocardial O2 demand.

Cardioactive CCB’s can also function to decrease Heart contractility and Heart Rate by inhibiting Phosphorylation of Myosin-LC’s in the Heart

Question 16

Are Cardioactive CCB’s or Non-Cardioactive (Dihydropyridines) more potent arteriolar Vasodilators?

Answer 16

Dihydropyridines are more potent Arteriolar Vasodilators than Cardioactive CCB’s

Question 17

By what mechanism may CCB’s be used to treat Variant (Prinzmetal) Angina?

Answer 17

CCB’s may be used to cause Arteriolar Vasodilation -> Dilation of Coronary Arteries -> Relief of local Vasospasms-> increased blood supply

Question 18

What type of Ca2+ channels are effected by CCB’s?

Answer 18

L-Type Voltage-Gated Ca2+ Channels

Question 19

What does cGMP function to activate in cells? What are the effects of that enzyme?

Answer 19

CGMP functions to activate Protein Kinase G

Protein Kinase G functions to:

• Cause Myosin-LC Dephosphorylation -> SM Relaxation
• Open K+ Channels -> Cell Hyperpolarization and Decreased Ca2+ entry

Question 20

What are the 3 Non-Cardiogenic (Dihydropyridine) CCB’s?

Answer 20

Amlodipine (Long-Acting, t1/2 = 30-50hrs)
Nifedipine (Short-Acting, t1/2 = 4hrs)
Nicardipine (Short-Acting, t1/2 = 2-4hrs)

Question 21

What are the 2 Cardioactive CCB’s we discussed?

Answer 21

Diltiazem

Verapamil