Local Anaesthetics

Local anaesthetic agents are classified into two main groups based on their chemical structure. Which of the following is a characteristic feature that distinguishes ester local anaesthetics from amide local anaesthetics?

Which local anaesthetic agent is contraindicated in patients with a history of methemoglobinemia or in those at high risk for methemoglobinemia (e.g., neonates, patients on sulfonamides)?

A 42-year-old man undergoes dental extraction under local anaesthesia. The dentist administers 2% lidocaine with 1:100,000 epinephrine for inferior alveolar nerve block. Within 5 minutes of injection, the patient develops tremor, anxiety, tachycardia (HR 110/min), and mild confusion. Blood pressure is 145/92 mmHg. The patient has no prior history of cardiac disease. What is the most likely cause of this acute presentation?

A 38-year-old woman undergoes suturing of a laceration on her forearm under local infiltration anaesthesia. The surgeon uses 0.5% bupivacaine without epinephrine, injecting a total of 80 mL over 10 minutes. After 20 minutes, the patient complains of dizziness, develops slurred speech, and then has a brief generalized tonic-clonic seizure lasting 30 seconds. Vital signs: BP 110/70 mmHg, HR 92/min, RR 16/min, O₂ saturation 98% on room air. The seizure self-terminates. What is the most appropriate immediate next step in management?