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Local Anesthesia

all the local anesthetics are Basic Drugs

 local anesthetics cross the membrane in non ionized for and block the Na channels in ionized form

 local anesthetics are of 2 types Ester and Amide but the name of both type of local anesthetics end with CAINE

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mechanism of action of local anesthesia

 

Ester                                      Amide 

cocaine                                    lignocaine

procaine                                        bupivacaine

chlorprocaine                            prilocaine 

tetracaine                                 Etidocaine    

benzocaine                                ropivacaine

                                                 Dibucaine

So What is the significance of amide and ester and why should we always keep in mind which is ester and which is amide??

ans-  we should always remember which group is ester and which group is amide because if a person is allergic to one drug of any category then they may be allergic to all the drugs of the category , hence we will have to shift our category of drugs to avoide an allergic reaction

 

*a small trick to find out the group of the local anesthetic  , if the name contains an i like lignocaine , prilocaine etc. ( see in the table above ) they belong to the goup of amide , and one more thing to note is that Caine always contains an I so if we go into details it could be said that ester has 1 i and that in the suffix Caine and amides have 2 i,

 

 The special properties of some of these Local anesthetics which can be asked during MCQs –

1.     Cocaine is the only local anesthetic which can cause vasoconstriction, and all other local anesthetics cause vasodilation leading to hypotension but cocaine is the only one which can cause hypertensio.( Cocaine has a co which we can take as constriction so we can say constriction causing caine)

2.     Lignocaine is the most commonly used local anesthetic

3.     Chlorprocaine is the shortest acting local anesthetic

4.     Prilocaine can cause methemoglobinemia 

m Methemoglobinemia, or methaemoglobinaemia, is a condition of elevated methemoglobin in the blood. Symptoms may include headache, dizziness, shortness of breath, nausea, poor muscle coordination, and blue-colored skin (cyanosis)

5.     All local anesthetics if they enter heart can cause arrythmias

6.     Bupivacaine is the most cardiotoxic of all the local anesthetics

Special use of Local anesthtics is infiltration anesthesia

Normally when we give a local anesthesia at a place with the help of subcutaneous route it does not mean that the drug will stay their as their maybe blood vessels at the place which will lead the drug away from the site of application

Now this has 2 main implications

1.     The local anesthetics are short acting due to the reason that the drug is transported away from the site of application leading to short anesthetic affects

2.     And secondly the blood can transport these anesthetics to heart( arrythmia ) and brain(seizures)  leading to systemic adverse effects of local anesthetics

Now to stop the drug from dispersing into the blood stream we use vasoconstrictors to constrict the vessels and hinder the movement of the drugs and for this we use Adrenalin

Local anesthetics are provided along with adrenalin to decrease the 2 shortcomings of the local anesthetics

·       To make local anesthetics fast acting we use NaHCO3

·       To make a drug long acting we use Adrenaline

But adrenalin should not be given to the areas where end arteries are present end arteries are present at tip of nose , ear pinna , fingers and penis

 

 
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