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A, Dihydropyridine (Lipophilic): These are the most potent calcium channel blockers
- Nifedipine
- Amlodipine
- Nimodipine
- Nitrendipine
- Felodipine
B, Phenylalkylamine (Hydrophilic )
- Verapamil
C, Benzothiazepine
- Diltiazem
Mechanism of Action:
1, Smooth Muscle:
- CCB work by blocking Voltage-gated Calcium channels in blood vessels
- This leads to decreases intracellular Ca+ influx resulting in muscle contraction also decreased.
- Decreased vascular smooth muscle contraction resulting in increased arterial vascular diameter.
- CCB markedly dilate arterial smooth muscle but have a mild effect venous smooth muscle.
- If vasodilation then decrease peripheral vascular resistance..
- CCB are effective against large vessels stiffness which occurs usually in elder patients where there is increased Sytolic BP
2, Heart:
- CCB blocks Voltage-gated Calcium channels which results in decrease cardiac contractlity.
- Decreases in cardiac contractility leads to decreases in cardiac output.
- The 0 phase depolarization in SA and AV nodes is largely Ca+ mediated.
- Verapamil and diltiazem slows sinus rate and AV conduction due to delayed membrane depolarization. This leads to depression of pacemaker and conduction activity i.e. positive chronotropic and dromotropic action.
- Nifedipine doesn't cause delayed membrane depolarization hence it do not decrease SA and AV conduction that is no negative chronotropic and dromotropic action.
-Dihydropyridine are more selective for smooth vascular muscle and negligible -ve inotropic action.
-Diltiazem causes less depression of contractility than verapamil.
CO= Cardiac Output
PVR= Peripheral Vascular Resistance
Hence,
BP= CO x PVR
If there is Decreased CO and Decreased PVR= Decrease BP.
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