ANTI ANGINAL DRUGS
Among the three types of angina the classic stable angina which accounts 90% of the incidents and is treatable and reversible.On the other hand the other two types the unsable type,and varient type which are accounting 10% to very rare and are medical emergencies as mostly they are irriversible and can lead to heart attack
The tretments are based on the strategy that the stable angina is always due to the demand of oxygen exceeds the supply.Hence the reatments should be either 1)Increasing the oxygen supply or 2)Decreasing the oxygen demand by the heart muscles
Oxygen Demand
One must know the fundamental of this strategy.We know our heart is hardly working without rest upto our death.Every time it is contracting and relaxing with an average speed of 70 per minute.Every contractions and relaxes are composed of the following events:-
1.Preload - the diastolic filling pressure.When the blood enters into the chambers the chamber has to expand to accomodate the filling blood.For this its muscles has to relax against an external pressure and need oxygen.
2.Afterload-the systolic ejection pressure against the peripheral or outside vascular resistance pressure,and need oxygen
3.Heart rate-To keep the heart contractions and relaxations at a constant rate per fixed time need oxygen
4.Wall tension
All the above cosequences need oxygen.
Classes of Anti-Anginal Drugs
1.Nitrates
2.Calcium channel blockers
3.Beta adrenergic blockers
4.Aspirin
Nitrates
Nirates are acting on heart smooth muscles and relax them as follows:
Nitrates releases nitric oxide which increases in the blood an hormone like substance cyclic Guanosine Mono Phosphate (cGMP) which inturn dephosphorylate the myosin content of the heart and vascular muscles and relax them.
Because of this the veins get dilated and relaxed,the venous pressure is diminished and hence there is a reduction in preload pressure.As a result preload and cardiac output are reduced.
On higher doses nitrates dilates arterioles also followed by reduced peripheral resistance and B.P
Examples of Nitrates
1.Glyceryl trinitrate for sublingual and intra dermal administration on emergencies as the onset of action is immediate and lost immediately
2.Isosorbide Dinitrate-for oral administration and the effect is not immediate but last for longer time
3.Amyl nitrate - same as above
1.Glyceryl trinitrate which should be taken sub lingually to prevent the first pass metabolism by liver if taken orally as the drug will be 90% deactivated by liver.Also this can be taken by skin patches
this medicine is useful for acute anginal attacks and the onset of action is in seconds to minutes.
As a prophylactic we can use the oral and transdermal forms
Because of tolerance please keep up nitrate free periods for long time use.
Toxicity Side effects mainly due to its vasodilating effects such as
1.Postural hypotention
2.Dizziness
3.Reflux tachycardia
4.Headaches
Calcium Channel Blockers
1.Nifedipine
2.Verapamil
3.Diltiazem
The mechanism of action is blocking the calcium channels of the vascular muscles and thereby preventing the entry of calcium ions and thus relaxing the muscles.
These are the drugs of choice for treating the variant types of angina known as Prinzmetal's syndrome.
Out of the above three verapamil is more cardiac dependant.
It is he powerfull inhibitor of the conduction at AV node.
Nifedipine is acting mostly on arterioles and therefore it much reduces the B.P.It has no effect on AV coduction system.
Diltiazem is having moderate action on arterioles and AV conduction system
They can be taken I.V.;Oral and Sublingual.
Toxicity
1. headache
2.Dizziness
3.Nausea
4.Vomiting
5.Constipation
More serious Toxicities
1.Congestive Heart Failure
2.AV node conduction block.
Beta-Adrenergic Blockers
Examples 1.Propranolo
2.Atenolol
3.Metoprolol
4.Carvedilol
5.Labetelol
6.Esmolol
7.Pindolol
8.Timolol
They are useful in stable anginas by reducing frequencies and severity of the attacks by reducing heart rate,contractility and BP
They have no much use in variant and unstable anginas
Contraindications
Beta blockers are contra indicated in Asthma,Diabetes,and Peripheral vascular diseases such as leg pains.
Calcium channel blockers are alternative for these patients
Selection Any medicine in this group can be used but atenolol, timolol,and metoprolol are more preferable as they are cardio selective.
They can be used in combination also as per the requirements
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