Anesthesia · patient case question
Which local anaesthetic provides the LONGEST duration of action?
Patient case: An Extraction, a Block, and a Drooping Eyelid
Patient: 45-year-old female
Chief Complaint: Extraction of tooth #19.
Background: No medical history of note. No known drug allergies, though she reports her mother 'reacts to penicillin.'
Medications: None
Vital Signs: BP 120/76 mmHg · HR 74 bpm · RR 16 · T 98.4°F
Findings: An inferior alveolar nerve block is administered. Within minutes she is unable to close her right eye and the right corner of her mouth droops. Lip and tongue numbness on that side is profound.
Show answer and explanation
Correct answer: B. Bupivacaine
- A. Articaine 4% with epinephrine gives roughly 60–75 minutes, comparable to lidocaine, with better diffusion through bone.
- B. CORRECT. BUPIVACAINE 0.5% with 1:200,000 epinephrine is the longest-acting dental local anaesthetic, giving roughly 90–180 minutes of pulpal anaesthesia and 4–9 hours of soft-tissue anaesthesia. Its long duration comes from high lipid solubility and high protein binding (about 95%), which anchors it to the sodium channel. It is used for lengthy procedures and, importantly, for POST-OPERATIVE pain control after third molar surgery or periodontal surgery.
- C. Lidocaine 2% with 1:100,000 epinephrine gives roughly 60 minutes of pulpal anaesthesia — the standard workhorse.
- D. Mepivacaine 3% plain gives roughly 20–40 minutes and is useful where a vasoconstrictor is best avoided or a short procedure is planned.
Note: Bupivacaine's prolonged soft-tissue numbness is a real hazard in CHILDREN and in patients with cognitive impairment, who may bite the anaesthetized lip or tongue. Avoid it in those groups.