Which of the following drugs is hydrolyzed by a plasma esterase that is abnormally low in activity in about 1 in every 2500 humans ?
## **Core Concept**
The question tests knowledge of pharmacogenetics, specifically regarding the metabolism of certain drugs by plasma esterases. One such esterase, known as pseudocholinesterase or butyrylcholinesterase, exhibits genetic variability that affects its activity.
## **Why the Correct Answer is Right**
The correct answer, **Succinylcholine (C)**, is a depolarizing muscle relaxant that is metabolized by pseudocholinesterase, a plasma esterase. Individuals with abnormally low activity of this enzyme, due to genetic variations, are at risk of prolonged apnea because succinylcholine is not broken down efficiently. This condition affects about 1 in every 2500 humans.
## **Why Each Wrong Option is Incorrect**
- **Option A:** Aspirin is primarily metabolized in the liver and does not have a significant association with plasma esterase deficiency related to its metabolism.
- **Option B:** Procaine is metabolized by plasma esterases, but the specific condition described (affecting 1 in 2500 humans) is more closely associated with succinylcholine.
- **Option D:** Mivacurium is a non-depolarizing muscle relaxant that is also metabolized by pseudocholinesterase, but the clinical significance and prevalence of the condition described fit more precisely with succinylcholine.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that patients with pseudocholinesterase deficiency are at risk of prolonged apnea when administered succinylcholine or mivacurium. This deficiency can be identified through family history or by measuring pseudocholinesterase activity.
## **Correct Answer: C. Succinylcholine**