Local Anesthetics Question And Answers

Local Anesthetics

 

Question 1. What Are Local Anesthetics? Classify Them. Describe Local Anesthetics In Dental Practice And Its Importance In Dental Practice.
Answer:

Local anesthetics are those drugs which upon topical application or local injection cause irreversible loss of all sensations in a restricted part of the body.

Classification Of Local Anesthetics

1. Based on Duration of Action

• Injectable:
  • Low potency and duration: Procaine and Chloroprocaine
  • Intermediate potency and duration: Lignocaine, prilocaine, mepivacaine, articaine
  • High potency and long duration: Tetracaine, bupivacaine, ropivacaine, and dibucaine.
• Surface Anesthetic:
  • Soluble: Cocaine, Lignocaine, tetracaine, benoxinate
  • Insoluble: Benzocaine, butylaminobenzoate, oxethazaine.

Read And Learn More: Pharmacology Question And Answers

2. Based On Chemical Structure

• Amides: Lignocaine, mepivacaine, bupivacaine and ropivacaine
• Esters:
  • Esters of benzoic acid: Butacaine, cocaine and tetracaine
  • Esters of para­aminobenzoic acid: Chloroprocaine, procaine, propoxycaine.
• Quinolones: Centbucridine.

3. Based on Biological Site and Mode of Action

Local Anesthetics In Dental Practice

• Local anesthetics are used by nerve block or field block techniques to carry out operative procedures in dentistry.
• An intradermal sensitivity test should be done before giving local anesthesia.
• The total amount of local anesthetic agent injected for dental anesthesia is generally much smaller as used for other purposes such as brachial plexus block, epidural anesthesia, etc.
• For children local anesthetic along with vasoconstrictor should be given in children to reduce systemic toxicity.
• The upper jaw is more vascular than the lower jaw, thus anesthesia in the upper jaw is short-lasting. 70 Mastering the BDS IInd Year (Last 25 Years Solved Questions) Pharmacology
• About 2% lignocaine with adrenaline is standard local anesthetic preparation used in dentistry. It provides good soft tissues and pulpal anesthesia and reduces postextraction bleeding.
• Complete pain relief is not obtained in patients with very sensitive teeth or inflammation.
• Topically lignocaine is applied on painful oral ulcers or before intraoral injection of local anesthetic in sensitive individuals.
• Bupivacaine with adrenaline can be used in long-lasting oral surgery or where postoperative pain control is required for a longer time, e.g. impacted third molar.
• A plain solution of local anesthetic is preferred when a short duration of soft tissue anesthesia without complete pulpal anesthesia is required or when a vasoconstrictor is contraindicated.

Question 2. Give Description Of Lignocaine. Describe Their Mechanism Of Action
Or
Describe The Mode Of Use Of Lignocaine As Local Anesthetic Agent By Giving Appropriate Examples.
Or
Write A Short Note On Lignocaine.
Or
Write A Short Note On Xylocaine.
Or
Explain Why Lignocaine Is Used As A Local Anesthetic Agent.
Answer:

Lignocaine is the most commonly used anesthetic. It is also called xylocaine or lidocaine.

Mechanism Of Action

Anesthesia Uses Of Lignocaine/Xylocaine

• It is used in surface anesthesia.
• It is used in nerve block, for example, it is used in tooth extraction by causing nerve block.
• It is given subcutaneously in field block and mainly it is used in dental procedures.
• It is used in epidural anesthesia.
• It is used in spinal anesthesia.
• It is used as an Antiarrhythmic agent.
• It is the drug of first choice in acute therapy for ventricular extrasystole and ventricular tachycardia.

Pharmacological Actions

1. Local Actions

• Lignocaine blocks sensory nerve endings, nerve trunk, neuromuscular junction, ganglionic synapses, and receptors.
• Lignocaine decreases the release of acetylcholine from motor nerve endings and leads to anesthesia of the skin as well as paralysis of voluntary muscles which are supplied by mixed nerves if it gets injected around it.
• So the order of nerve fibers that are affected is autonomic fibers – pain – touch – temperature, deep pressure, and motor fibers.

2. Systemic actions

• Nervous System
  • In peripheral nerves, the autonomic fibers get blocked before somatic fibers. Pain sensation disappears.
  • On CNS most of local anesthetics cross the blood-brain barrier and lead to stimulation of CNS and depression. At initial doses, there is the presence of excitement, tremors, twitching, restlessness, and convulsion. Large doses cause respiratory depression, coma, and death.
• Cardiovascular System
  • Heart: Local anesthetics block Na+ channels and reduce abnormal pacemaker activity along with contractility, conductivity, excitability, heart rate, and cardiac output and enhance effective refractory period.
  • In its higher concentration, IV administration of local anesthetics can precipitate cardiac arrhythmias.
  • Bupivacaine is most cardiotoxic as compared to other local anesthetics and can lead to cardiovascular collapse and death.
  • Lignocaine reduces automaticity and is indicated in ventricular arrhythmias.
  • Blood vessels: Local anesthetic drugs cause hypotension. This is because of sympathetic blockage or direct relaxation of arteriolar smooth muscles during high dosages.

Local Anesthetics Adverse Effects

The following are the adverse effects of local anesthetics:

• CNS effects: Lightheadedness, dizziness, auditory and visual disturbances, mental confusion, disorientation, shivering, twitching, involuntary movements, convulsion, respiratory arrest, coma, and death.
• Cardiovascular toxicity of local anesthesia is manifested as bradycardia, hypotension, cardiac arrhythmias, and vascular collapse.
• Injection of local anesthesia may be painful, but local tissue toxicity of local anesthesia is low. However, wound healing may be sometimes delayed. The addition of vasoconstrictors enhances the local tissue damage; rarely localized mucosal sloughing and necrosis result.
• Hypersensitivity reactions like rashes, angioedema, dermatitis, contact sensitivity, asthma, and rarely anaphylaxis occur.
• Mucosal irritation and methemoglobinemia can also be seen.

Question 3. Classify Local Anesthetics. Describe Different Methods For Giving Local Anesthesia.
Answer:

Local anesthetics are those drugs which upon topical application or local injection cause irreversible loss of all sensations in a restricted part of the body.

Different Methods Of Giving Local Anesthesia

Following are the different methods of giving local anesthesia:

• Surface anesthesia: It is produced by topical application of local anesthetic to mucous membranes and skin. It is produced by Lignocaine, prilocaine, and benzocaine. It is topically applied in the mouth for stomatitis.
• Infiltration anesthesia: Local anesthesia is infiltrated subcutaneously in the area of operation. Local anesthetic can also be infiltrated into the skin, subcutaneous tissue, and deep structures too. Here the nerve endings are anesthetized by their direct exposure to drugs. The onset of action is immediate.
  2% procaine and 2% Lignocaine are commonly used. This anesthesia is used in incision, excision, and other minor operations.
• Conduction block: The local anesthesia is injected near the nerve trunk so that area distal to the injection is anesthetized. It is of two types:
• Field block: Local anesthesia is given subcutaneously such that all nerves coming to a particular area are blocked, For Example. dental procedure.
• Nerve block: Local anesthetic is injected around a particular nerve or plexus. It is used for tooth extraction.
• Spinal anesthesia: Local anesthesia is injected in the subarachnoid space between L2-3 or L3-4. This anesthesia is used for the operation of the lower limb, obstructive procedures, and cesarean section.
• Epidural anesthesia: It is produced when local anesthesia is injected into the epidural space where it acts on spinal nerve roots. This technique is difficult as compared to spinal anesthesia Lignocaine and bupivacaine are commonly used in epidural anesthesia.
• Intravenous regional anesthesia or Bier’s block: In this technique, a local anesthetic agent is injected in the vein of the upper limb in which blood flow become occluded by the tourniquet. Local anesthetics used are lignocaine and prilocaine.

Question 4. Explain Why Lignocaine Is Given With Adrenaline?
Or
Write A Short Note On Adrenaline With Lignocaine For Local Anesthesia.
Or
Explain The Pharmacological Basis Of Use Of Adrenaline With Lignocaine.
Or
Discuss The Mode Of Action And Advantages Of Why Adrenaline Preferred With Lignocaine For Local Anesthesia?
Or
Write The Basis Of Combination Of Adrenaline With Xylocaine.
Answer:

Adrenaline is added to lignocaine because of the following reasons:

1. Infiltration block: The duration of action of lignocaine is proportional to the time of contact with the nerve. When lignocaine is infiltrated around the injury site (by subcutaneous route), some of it may enter the subcutaneous blood vessels. It has two implications, i.e.

• Lignocaine goes away from the nerves of the injury site. Thus, its action quickly diminishes.
• The lignocaine which has entered the blood vessel may go to the heart and brain causing systemic toxicity, i.e. cardiotoxicity and neurotoxicity.

The addition of adrenaline cause vasoconstriction and thus lignocaine is not able to enter the blood vessels resulting in:

• Prolongation of the duration of action
• Less systemic toxicity
• Adrenaline provides blood flow for sur- gery.

2. Spinal anesthesia: Adrenaline is added to lignocaine for spinal anesthesia to increase the duration and intensity of the block. It acts by:

• Decreasing the spinal blood flow may reduce the clearance of lignocaine from CSF
• Acting on the α2A; receptors, it may reduce the tiring of neurons and inhibit the release of pain mediators like substance P or neurokinin-1.

Question 5. Explain Why Lignocaine Is Preferred Over Procaine As Local Anesthetic Agent.
Answer:

Amide-linked local anesthetics like lignocaine is referred to over ester-linked local anesthetics like procaine because:

• Lignocaine is longer-acting whereas ester procaine has a short duration of action.
• There is less risk of allergic reactions with lignocaine as compared to procaine. Procaine metabolized to p-aminobenzoic acid (PABA) derivatives which may be responsible for allergic reactions.
• Lignocaine provides more intense and longer-lasting anesthesia as compared to procaine.
• Lignocaine is used for surface anesthesia, nerve block, epidural and spinal anesthesia while procaine is poorly absorbed from mucous membranes and cannot be used topically.

Question 6. Write A Note On Local Anesthetic Drugs, Name, Uses In Dentistry, and Toxicity.
Answer:

Toxicity Of Local Anesthetics

• CNS effects: Lightheadedness, dizziness, auditory and visual disturbances, mental confusion, disorientation, shivering final convulsion and respiratory arrest, coma, and death
• Cardiovascular toxicity: Bradycardia, hypotension, cardiac arrhythmia, and vascular collapse.
• Hypersensitivity reactions, i.e. rashes, angioedema, dermatitis, asthma, and rarely anaphylaxis.

Question 7. Local Anesthetics Precautions To Be Observed For Their Use In Patients With Concurrent Diseases.
Answer:

Precautions For Their Use In Patients With Concurrent Disease

• Local anesthetics are very rarely used in hypersensitive patients because hypersensitivity reactions are very common in this type of patient.
• It is not used in patients with cardiac diseases and high blood pressure because it produces tachycardia and a fall in blood pressure.
• It is not used in asthmatics because it causes vasoconstriction.
• It is not used in patients with hyperthyroidism.
• It is very cautiously used in patients with diabetes mellitus.

Question 8. Classify Local Anesthetic. Describe Why Adrenaline Is Combined With Local Anesthetic?
Or
Explain Why Adrenaline Is Given In Combination With Local Anesthetics.
Answer:

Adrenaline is added to local anesthetic because of the following reasons:

1. Infiltration block: The duration of action of local anesthetic is proportional to the time of contact with the nerve. When local anesthetics are infiltrated around the injury site (by subcutaneous route), some of it may enter the subcutaneous blood vessels. It has two implications i.e.

• Local anesthetic goes away from the nerves of the injury site. Thus, its action quickly diminishes.
• The local anesthetic which has entered the blood vessel may go to the heart and brain causing systemic toxicity i.e. cardiotoxicity and neurotoxicity.

The addition of adrenaline cause vasoconstriction and thus local anesthetic is not able to enter the blood vessels resulting in:

• Prolongation of the duration of action
• Less systemic toxicity
• Adrenaline provides a bloodless field for surgery.

2. Spinal anesthesia: Adrenaline is added to local anesthetic for spinal anesthesia to increase the duration and intensity of the block. It acts by:

• Decreasing the spinal blood flow, it may reduce the clearance of local anesthetic from CSF
• Acting on the α2A; receptors, it may reduce the tiring of neurons and inhibit the release of pain mediators like substance P or neurokinin-1.

Question 9. Write Notes On Local Anesthetics.
Or
Write Short Note On Local Anesthetic Drugs.
Or
Write Short Note On Local Anesthetics.
Or
Describe Briefl Local Anesthetic Agents.
Or
Classify Local Anesthetic Agents.
Answer:

Local anesthetics are those drugs which upon topical application or local injection cause irreversible loss of all sensations in a restricted part of the body.

Classification Of Local Anesthetics

1. Based On Duration Of Action

• Injectable:
  • Low potency and duration: Procaine and Chloroprocaine
  • Intermediate potency and duration: Lignocaine, prilocaine, mepivacaine, articaine
  • High potency and long duration: Tetracaine, bupivacaine, ropivacaine, and dibucaine.
• Surface Anesthetic:
  • Soluble: Cocaine, Lignocaine, tetracaine, benoxinate
  • Insoluble: Benzocaine, butylaminobenzoate, oxethazaine.

2. Based On Chemical Structure

• Amides: Lignocaine, mepivacaine, bupivacaine and ropivacaine
• Esters:
  • Esters of benzoic acid: Butacaine, cocaine and tetracaine
  • Esters of para­aminobenzoic acid: Chloroprocaine, procaine, propoxycaine.
  • Quinolones: Centbucridine.

3. Based On Biological Site And Mode Of Action

Mechanism Of Action Of Local Anesthetics

Local Anesthetics In Dental Practice

• Local anesthetics are used by nerve block or field block techniques to carry out operative procedures in dentistry.
• An intradermal sensitivity test should be done before giving local anesthesia.
• The total amount of local anesthetic agent injected for dental anesthesia is generally much smaller as used for other purposes such as brachial plexus block, epidural anesthesia, etc.
• For children local anesthetic along with vasoconstrictor should be given in children to reduce systemic toxicity.
• The upper jaw is more vascular than the lower jaw, thus anesthesia in the upper jaw is short-lasting.
• About 2% Lignocaine with adrenaline is standard local anesthetic preparation used in dentistry. It provides good soft tissues and pulpal anesthesia and reduces postextraction bleeding.
• Complete pain relief is not obtained in patients with very sensitive teeth or inflammation.
• Topically lignocaine is applied on painful oral ulcers or before intraoral injection of local anesthetic in sensitive individuals.
• Bupivacaine with adrenaline can be used in long-lasting oral surgery or where postoperative pain control is required for a longer time, For Example. impacted the third molar.
• A plain solution of local anesthetic is preferred when a short duration of soft tissue anesthesia without complete pulpal anesthesia is required or when a vasoconstrictor is contraindicated.

Therapeutic Uses Of Local Anesthetics

• Surface local anesthetics are useful before injecting a local anesthetic, in subgingival and periodontal scaling, etc.
• Local anesthetics should be infiltrated for draining the abscess, gingivectomy, excision of small swelling, and suturing of cut wounds, before commencement of root canal treatment.
• Local anesthetics in field block are used in minor dental procedures, in the anterior abdominal wall.
• Local anesthetics are used for nerve blocks in the oral cavity.
• They are used in spinal anesthesia for surgical procedures below the level of the umbilicus.
• Local anesthetics are used in epidural anesthesia in cases of obstetric analgesia.

Toxicity Of Local Anesthetics

• CNS effects: Lightheadedness, dizziness, auditory and visual disturbances, mental confusion, disorientation, shivering final convulsion, and respiratory arrest.
• Cardiovascular toxicity: Bradycardia, hypotension, cardiac arrhythmia, and vascular collapse.
• Hypersensitivity reactions, i.e. rashes, angioedema, dermatitis, asthma, and rarely anaphylaxis.

Question 10. Explain Why Procaine Is Not Used For Surface Anesthesia.
Answer:

Since the tissue penetrability of procaine is poor that’s why it is not used for surface anesthesia.

Question 11. Write Short Note On The Adverse Effects Of Local Anesthetics.
Answer:

The following are the adverse effects of local anesthetics:

• CNS effects: Lightheadedness, dizziness, auditory and visual disturbances, mental confusion, disorientation, shivering, twitching, involuntary movements, convulsion, respiratory arrest, and death.
• Cardiovascular toxicity of local anesthesia is manifested as bradycardia, hypotension, cardiac arrhythmias, and vascular collapse.
• Injection of local anesthesia may be painful, but local tissue toxicity of local anesthesia is low. However, wound healing may be sometimes delayed. The addition of vasoconstrictors enhances the local tissue damage; rarely localized mucosal sloughing and necrosis result.
• Hypersensitivity reactions like rashes, angioedema, dermatitis, contact sensitivity, asthma, and rarely anaphylaxis occur.
• Mucosal irritation and methemoglobinemia can also be seen.

Question 12. Describe Add A Note On Its Combination With Vasoconstrictors.
Answer:

Note On Lignocaine Combined With Vasoconstrictors

A very commonly combined vasoconstrictor with lignocaine is adrenaline.

Following Are The Advantages Of the Combination Of Lignocaine With Adrenaline

• It prolongs the duration of action of local anesthetics by decreasing their rate of removal from the site into the systemic circulation.
• It increases the intensity of nerve block.
• Adrenaline provides a bloodless field for surgery.
• It reduces systemic toxicity.

Following Are The Disadvantages And Contraindications Of the Combination Of Lignocaine With Adrenaline

• Due to the intense vasospasm as well as ischemia in tissues along with end arteries may lead to gangrene of any parts i.e. toes, fingers, penis, the tip of the nose, etc. So in these sites, vasoconstrictors are contraindicated.
• Absorption of adrenaline may lead to systemic toxicity which causes tachycardia, palpitation, increase in blood pressure, and precipitation of angina or cardiac arrhythmias. So this combination is to be avoided in patients with hypertension, congestive cardiac failure, arrhythmia, ischemic heart disease, etc.
• The combination can result in delayed wound healing by decreasing blood flow to the affected area.

Question 13. Advantages Of Xylocaine, As A Local Anesthetic Preparation.
Answer:

The following are the advantages of xylocaine as a local anesthetic agent:

• Xylocaine provides more intense and long-lasting anesthesia.
• Xylocaine is excellent for both surface application as well as injection.
• Xylocaine produces less risk of allergic reactions as compared to other local anesthetic agents.
• In peripheral nerves, the autonomic fibers get blocked before somatic fibers and pain sensation disappears.
• Xylocaine is used by nerve block or field block techniques to carry out operative procedures in dentistry.
• A plain solution of local anesthetic is preferred when a short duration of soft tissue anesthesia without complete pulpal anesthesia is required or when a vasoconstrictor is contraindicated.
• About 2% Xylocaine with adrenaline is standard local anesthetic preparation used in dentistry. It provides good soft tissue and pulpal anesthesia and reduces postextraction bleeding.