Long acting local anesthetic is – a) Procaineb) Lignocainec) Bupivacained) Etidocaine

**Core Concept**
Local anesthetics can be classified based on their duration of action, which is influenced by their lipid solubility and protein binding properties. Long-acting local anesthetics have a higher lipid solubility, allowing them to penetrate nerve membranes more slowly and prolong their effect.

**Why the Correct Answer is Right**
Bupivacaine is a long-acting local anesthetic due to its high lipid solubility. This property enables it to bind to the nerve membrane for a longer period, effectively blocking sodium channels and preventing depolarization. Bupivacaine's unique pharmacokinetic profile makes it suitable for procedures requiring prolonged anesthesia, such as regional anesthesia and pain management.

**Why Each Wrong Option is Incorrect**
* **Option A:** Procaine is a short-acting local anesthetic with low lipid solubility, making it less effective for procedures requiring prolonged anesthesia.
* **Option B:** Lignocaine is a medium-acting local anesthetic with moderate lipid solubility. While it is more effective than procaine, it is not as long-acting as bupivacaine.
* **Option D:** Etidocaine is a long-acting local anesthetic, but it is less commonly used than bupivacaine due to its potential for central nervous system toxicity.

**Clinical Pearl / High-Yield Fact**
When selecting a local anesthetic, consider the duration of action required for the procedure. Long-acting local anesthetics like bupivacaine are ideal for procedures requiring prolonged anesthesia, while short-acting local anesthetics like procaine are better suited for minor procedures.

**Correct Answer: C. Bupivacaine**