The local anaesthetic with the longest duration of action is
**Core Concept**
The question is testing the knowledge of local anesthetics and their duration of action. Local anesthetics are a class of drugs that block the transmission of nerve impulses, leading to numbness or insensitivity to pain in a specific region of the body.
**Why the Correct Answer is Right**
The correct answer is **Bupivacaine**. Bupivacaine is a long-acting local anesthetic that works by inhibiting the sodium channels in nerve fibers, which prevents the generation and conduction of action potentials. It has a duration of action of approximately 6-12 hours, making it suitable for procedures that require prolonged anesthesia, such as joint injections or epidural anesthesia.
**Why Each Wrong Option is Incorrect**
* **Option A:** Lidocaine is a short- to intermediate-acting local anesthetic with a duration of action of approximately 1-3 hours. It is commonly used for minor surgical procedures and peripheral nerve blocks.
* **Option C:** Procaine is a short-acting local anesthetic with a duration of action of approximately 1-2 hours. It is often used for minor surgical procedures and topical anesthesia.
**Clinical Pearl / High-Yield Fact**
It's essential to note that the duration of action of local anesthetics can be influenced by factors such as the concentration of the solution, the site of administration, and the presence of vasoconstrictors. Bupivacaine is often used in combination with epinephrine to prolong its duration of action and reduce systemic toxicity.
**Correct Answer: B. Bupivacaine**