Local Anesthetics Practice Questions

Q: What is the common strength of Xylocaine used in dentistry?

2%. **Explanation:** **Lignocaine (Xylocaine)** is the most widely used local anesthetic in dentistry due to its rapid onset, moderate duration of action, and excellent safety profile. 1. **Why 2% is Correct:** The standard concentration for dental procedures is **2% Lignocaine**. This concentration provides an ideal balance between efficacy and safety. It is typically combined with **Adrenaline (1:80,000 or 1:200,000)** to prolong the duration of anesthesia, provide local hemostasis, and reduce systemic toxicity by slowing absorption. 2. **Why other options are incorrect:** * **5%:** This concentration is generally used for **topical/surface anesthesia** (e.g., Lignocaine ointment) or in specific spinal anesthesia formulations, but it is too toxic for routine dental infiltration or nerve blocks. * **8% & 10%:** These high concentrations are exclusively used as **topical sprays** for mucous membranes (e.g., suppressing the gag reflex during endoscopy or intubation). Injecting such high concentrations into vascular dental tissues would lead to a high risk of Systemic Local Anesthetic Toxicity (LAST). **High-Yield Clinical Pearls for NEET-PG:** * **Maximum Dose:** The maximum dose of plain Lignocaine is **4.5 mg/kg**, while with Adrenaline, it increases to **7 mg/kg**. * **Mechanism:** It works by blocking voltage-gated **sodium (Na+) channels** on the inner surface of the nerve membrane. * **Order of Blockade:** Small myelinated fibers (Autonomic > Pain > Temperature) are blocked before large unmyelinated fibers (Touch > Pressure > Motor). * **Metabolism:** Lignocaine is an **Amide** local anesthetic and is metabolized in the **liver** (unlike Esters, which are metabolized by plasma pseudocholinesterase).

Q: Which of the following local anesthetics is known to cause malignant hyperthermia?

Lignocaine. **Explanation:** **Malignant Hyperthermia (MH)** is a life-threatening hypermetabolic crisis triggered in genetically susceptible individuals (mutations in the **RYR1 receptor**) primarily by volatile inhalational anesthetics (e.g., Halothane) and the depolarizing muscle relaxant Succinylcholine. **Why Lignocaine is the Correct Answer:** Historically, **Amide-type** local anesthetics, specifically **Lignocaine**, were considered potential triggers for MH based on early animal studies suggesting they could increase calcium release from the sarcoplasmic reticulum. While modern clinical evidence suggests that local anesthetics are generally safe in MH-susceptible patients, for the purpose of standard examinations like NEET-PG, Lignocaine remains the classic "textbook" answer associated with this risk among the options provided. **Analysis of Incorrect Options:** * **B. Prilocaine:** Primarily associated with **Methemoglobinemia** due to its metabolite, o-toluidine. It is not a recognized trigger for MH. * **C. Bupivacaine:** Known for its high **cardiotoxicity** (due to slow dissociation from sodium channels). It is the drug of choice for spinal anesthesia but not linked to MH. * **D. Dibucaine:** An amide anesthetic used to test for **pseudocholinesterase deficiency** (Dibucaine Number). It does not trigger MH. **Clinical Pearls for NEET-PG:** * **Safe Alternatives:** Ester-type local anesthetics (e.g., Procaine) were traditionally considered safer, though currently, all LAs are deemed safe in practice. * **Treatment of Choice:** **Dantrolene** (a hydantoin derivative) which acts by inhibiting the Ryanodine receptor. * **Early Sign:** The earliest sign of MH is an **increase in End-Tidal CO2 (ETCO2)**, followed by tachycardia and muscle rigidity. Hyperthermia is often a late sign.

Q: Which of the following conditions is a contraindication to the use of a local anesthetic agent?

Hypersensitivity to the drug. **Explanation:** **Correct Answer: D. Hypersensitivity to the drug** The only absolute contraindication among the choices is a known **hypersensitivity (allergy)** to the specific local anesthetic (LA) or its chemical class. Allergic reactions are more common with **Esters** (due to the metabolite para-aminobenzoic acid - PABA) than with **Amides**. Anaphylaxis, though rare, can be life-threatening, making hypersensitivity a definitive contraindication. **Analysis of Incorrect Options:** * **A. Parkinson’s Disease:** This is not a contraindication. While clinicians must be cautious with drug interactions (e.g., avoiding epinephrine in patients on COMT inhibitors to prevent hypertensive crises), LAs themselves do not worsen the pathology of Parkinson’s. * **B. Liver Damage:** This is a **relative contraindication/precaution**, not an absolute one. Amide LAs (like Lidocaine and Bupivacaine) are metabolized in the liver. In patients with hepatic failure, the half-life is prolonged, increasing the risk of **Systemic Toxicity (LAST)**. Dosage must be reduced, but the drugs are not strictly forbidden. * **C. Pregnancy (3rd Trimester):** LAs are frequently used for labor analgesia (Epidurals). While pregnancy increases sensitivity to LAs (requiring a dose reduction of ~30% due to engorged epidural veins and hormonal changes), it is not a contraindication. **High-Yield Clinical Pearls for NEET-PG:** * **Classification Trick:** Amides have two "i"s in their name (L**i**doca**i**ne, Bup**i**vaca**i**ne, Pr**i**loca**i**ne), while Esters have only one (Procaine, Benzocaine). * **Maximum Doses:** Lidocaine (4 mg/kg plain; 7 mg/kg with Adrenaline); Bupivacaine (2 mg/kg). * **Drug of Choice for LAST:** Intravenous **20% Lipid Emulsion** is the antidote for Local Anesthetic Systemic Toxicity. * **Prilocaine Side Effect:** Can cause **Methemoglobinemia** (treated with Methylene Blue).

Q: Eutectic lignocaine-prilocaine has which of the following unique properties?

By surface application, it can anaesthetize unbroken skin.. **Explanation:** **Eutectic Mixture of Local Anesthetics (EMLA)** is a 1:1 oil-in-water emulsion containing 2.5% Lignocaine and 2.5% Prilocaine. **1. Why Option B is Correct:** The term "eutectic" refers to a mixture of two substances that has a **lower melting point** than either of its individual components. While Lignocaine and Prilocaine are solids at room temperature, their mixture becomes a liquid. This unique property allows for a high concentration of the drug to penetrate the **stratum corneum** (the skin's primary barrier). Consequently, EMLA can provide effective topical anesthesia to **intact, unbroken skin**, a feat standard local anesthetics cannot achieve. **2. Why Other Options are Incorrect:** * **Option A:** EMLA provides **sensory blockade** (analgesia), not isolated motor blockade. It is used to numb the skin for procedures like venipuncture or skin grafting. * **Option C:** It **is absorbed** systemically through the skin. Prolonged application or use on large surface areas (especially in infants) can lead to systemic toxicity or methemoglobinemia. * **Option D:** EMLA actually has **biphasic vascular effects**. It typically causes initial vasoconstriction followed by **vasodilation**. It does not possess strong vasoconstrictive properties like cocaine or adrenaline. **High-Yield Clinical Pearls for NEET-PG:** * **Application Time:** Requires **60 minutes** of contact under an occlusive dressing for peak effect (depth of 3-5 mm). * **Contraindication:** Avoid in patients with **Methemoglobinemia** or infants <12 months receiving methemoglobin-inducing drugs (due to the Prilocaine component). * **Usage:** Ideal for pediatric venipuncture, lumbar punctures, and split-thickness skin grafts. * **Warning:** Do not apply to mucous membranes or broken skin, as rapid absorption can lead to **LAST** (Local Anesthetic Systemic Toxicity).

Q: Which of the following local anesthetics is most cardiotoxic?

Bupivacaine. **Explanation:** **Bupivacaine** is the most cardiotoxic local anesthetic among the commonly used clinical agents. Its high lipid solubility and high affinity for voltage-gated sodium channels in the myocardium lead to a "slow-in, slow-out" phenomenon. Unlike Lignocaine, Bupivacaine dissociates very slowly from cardiac sodium channels during diastole, leading to a cumulative blockade. This results in severe ventricular arrhythmias (like Torsades de Pointes), negative inotropy, and refractory cardiac arrest that is notoriously difficult to resuscitate. **Analysis of Incorrect Options:** * **A. Dibucaine:** While it is a potent amide anesthetic, it is primarily used for its "Dibucaine Number" to identify atypical pseudocholinesterase. It is not the most cardiotoxic in clinical practice. * **C. Lignocaine:** It is the prototype amide anesthetic with a "fast-in, fast-out" profile. It is actually used as an anti-arrhythmic (Class Ib) and has a much higher safety margin regarding cardiac toxicity compared to Bupivacaine. * **D. Chloroprocaine:** An ester-linked anesthetic with a very short half-life due to rapid metabolism by plasma cholinesterases. It has the lowest potential for systemic toxicity. **High-Yield Clinical Pearls for NEET-PG:** * **CC/CNS Ratio:** Bupivacaine has a low ratio (approx. 3.0), meaning the dose required to cause cardiovascular collapse (CC) is close to the dose that causes CNS seizures, leaving a narrow safety margin. * **Antidote:** Intravenous **Lipid Emulsion (20% Intralipid)** is the specific treatment for Local Anesthetic Systemic Toxicity (LAST). * **S-Enantiomers:** Levobupivacaine and Ropivacaine were developed as safer alternatives to Bupivacaine, as they exhibit significantly less cardiotoxicity. * **Pregnancy:** Bupivacaine cardiotoxicity is enhanced in pregnancy due to progesterone-induced sensitivity.

Question 1

What is the common strength of Xylocaine used in dentistry?

Accepted Answer

2%

Answer

5%

Answer

8%

Answer

10%

Question 2

What is the drug of choice for ventricular arrhythmias induced by bupivacaine?

Accepted Answer

Bretylium tosylate

Answer

Lidocaine

Answer

Nifedipine

Answer

Verapamil

Question 3

In which of the following conditions is local anesthesia generally ineffective?

Accepted Answer

Localized infection

Answer

Edema

Answer

Hematoma

Answer

Anemia

Question 4

Which of the following statements is TRUE regarding dental local anesthetics containing 2% lignocaine with adrenaline 1:80,000?

Accepted Answer

Dental local anesthetics containing 2% lignocaine with adrenaline 1:80,000 may cause tachycardia.

Answer

Dental local anesthetics containing 2% lignocaine with adrenaline 1:80,000 are contraindicated in patients with heart disease in any dosage.

Answer

Dental local anesthetics containing 2% lignocaine with adrenaline 1:80,000 can produce allergic reactions, in which lignocaine is usually responsible.

Answer

Dental local anesthetics containing 2% lignocaine with adrenaline 1:80,000 or even prilocaine with felypressin should not be used in the pregnant patient because of the oxytocic effects of adrenaline or felypressin.

Question 5

Which of the following concentrations of lignocaine can be used?

Accepted Answer

2%, 4%, 5%, 1%

Answer

2%, 5%, 1%

Answer

2%, 4%, 5%, 10%

Answer

2%, 4%, 10%, 1%

Question 6

Which of the following local anesthetics is known to cause malignant hyperthermia?

Accepted Answer

Lignocaine

Answer

Prilocaine

Answer

Bupivacaine

Answer

Dibucaine

Question 7

Which of the following conditions is a contraindication to the use of a local anesthetic agent?

Accepted Answer

Hypersensitivity to the drug

Answer

Parkinson's disease

Answer

Liver damage

Answer

Pregnancy (3rd trimester)

Question 8

Which local anesthetic agent has the highest local tissue irritancy?

Accepted Answer

Bupivacaine

Answer

Procaine

Answer

Chloroprocaine

Answer

Lidocaine

Question 9

Eutectic lignocaine-prilocaine has which of the following unique properties?

Accepted Answer

By surface application, it can anaesthetize unbroken skin.

Answer

It causes motor blockade without sensory block.

Answer

It is not absorbed after surface application.

Answer

It has strong vasoconstrictor action.

Question 10

Which of the following local anesthetics is most cardiotoxic?

Accepted Answer

Bupivacaine

Answer

Dibucaine

Answer

Lignocaine

Answer

Chloroprocaine

Local Anesthetics — MCQs

Local Anesthetics — MCQs

On this page

Practice by Chapter

Want unlimited practice?