Local Anaesthetics

The mechanism of action of local anesthetics involves:

• Blocking potassium channels
• Blocking sodium channels
• Enhancing GABA activity
• Inhibiting acetylcholinesterase

Answer explanation

Local anesthetics work by blocking voltage-gated sodium channels, preventing nerve impulse transmission and producing anesthesia.

Which of the following is an amino ester type local anesthetic?

• Lidocaine
• Procaine
• Mepivacaine
• Etidocaine

Answer explanation

Procaine is an amino ester local anesthetic, while lidocaine, mepivacaine, and etidocaine are amino amides.

The basic structure of local anesthetics consists of:

• Hydrophobic portion only
• Hydrophilic portion only
• Hydrophobic portion, intermediate chain, and hydrophilic portion
• Only intermediate chain

Answer explanation

Local anesthetics have three structural components: hydrophobic aromatic ring, intermediate chain (ester/amide), and hydrophilic tertiary amine.

Ester-type local anesthetics are metabolized by:

• Proteases

• Esterases

• Amidases

• Hydrolases

Answer explanation

Ester-type local anesthetics are rapidly hydrolyzed by plasma cholinesterases (pseudocholinesterases).

Which characteristic is NOT desired in an ideal local anesthetic?

• Reversible blockade
• Rapid onset
• High systemic toxicity
• Chemical stability

Answer explanation

High systemic toxicity is undesirable; ideal local anesthetics should have minimal systemic effects and wide margin of safety.

Lidocaine belongs to which chemical class?

• Benzoic acid derivatives
• Amino benzoic acid derivatives
• Anilide derivatives
• Miscellaneous

Answer explanation

Lidocaine is an anilide derivative (amino amide) with the characteristic acetanilide structure.

The resting potential of a nerve cell membrane is approximately:

• +70 mV
• -70 mV
• +35 mV
• -35 mV

Answer explanation

The resting membrane potential of nerve cells is approximately -70 mV due to the sodium-potassium pump maintaining ionic gradients.

Which type of local anesthetics generally have longer duration of action?

• Esters
• Amides
• Both have equal duration
• Duration depends only on dose

Answer explanation

Amide local anesthetics have longer duration because they are metabolized slowly by liver enzymes compared to rapid ester hydrolysis.

Cocaine is derived from which natural source?

• Coca leaves
• Opium poppy
• Willow bark
• Foxglove plant

Answer explanation

Cocaine is naturally found in coca leaves (Erythroxylum coca) and was the first local anesthetic discovered.

The hydrophilic portion of local anesthetics is usually:

• An aromatic ring
• An ester or amide linkage
• A tertiary amine
• An alkyl chain

Answer explanation

The hydrophilic portion is typically a tertiary amine that can be protonated at physiological pH to interact with sodium channels.