## **Core Concept**
Abnormal plasma cholinesterase, also known as pseudocholinesterase or butyrylcholinesterase, is an enzyme responsible for hydrolyzing certain choline esters, including the muscle relaxant succinylcholine. Variants of this enzyme can lead to prolonged apnea in patients administered succinylcholine.

## **Why the Correct Answer is Right**
The correct answer, **D. Succinylcholine**, is right because abnormal or atypical plasma cholinesterase has reduced activity towards succinylcholine. Succinylcholine is a depolarizing muscle relaxant commonly used in anesthesia to facilitate endotracheal intubation and to provide muscle relaxation during surgery. Normally, it is rapidly metabolized by plasma cholinesterase. However, in individuals with atypical or deficient cholinesterase, succinylcholine is metabolized much more slowly, leading to prolonged paralysis and apnea.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while certain local anesthetics are metabolized by plasma cholinesterase, they are not primarily associated with prolonged apnea due to abnormal cholinesterase activity.
- **Option B:** This option is incorrect as it does not directly relate to the action or metabolism of drugs by plasma cholinesterase in a way that would cause apnea.
- **Option C:** This option is incorrect because, although mivacurium is a muscle relaxant that is metabolized by plasma cholinesterase, the question specifically asks about abnormal plasma choline esterase producing apnea, and succinylcholine is much more commonly associated with this clinical scenario.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that patients with abnormal plasma cholinesterase activity are at risk of prolonged apnea if administered succinylcholine. This condition can be diagnosed using a dibucaine test or genetic testing. Clinicians should be cautious and consider alternative muscle relaxants in patients with a known family history of prolonged apnea after succinylcholine administration.

## **Correct Answer:** . Succinylcholine