**Question:** Cis atracurium is preferred over atracurium due to an advantage of aEUR'

A. improved pharmacokinetics
B. increased potency
C. reduced incidence of dyskinesias
D. enhanced neuromuscular recovery

**Core Concept:**

Atracurium and its enantiomer, cis atracurium, are non-depolarizing neuromuscular blocking agents used in clinical practice for inducing muscle relaxation during general anesthesia. They belong to the class of drugs known as steroid-based neuromuscular blocking agents, also known as steroid neuromuscular junction blockers or steroid relaxants. Both atracurium and cis atracurium act by competitively blocking the neuromuscular transmission at the nicotinic acetylcholine receptors on motor endplates, leading to muscle relaxation and immobilization.

**Why the Correct Answer is Right:**

Cis atracurium is preferred over atracurium due to the advantage of a reduced incidence of dyskinesias. Dyskinesias are abnormal involuntary muscle contractions, usually seen as twitching or jerking movements, which can occur in response to neuromuscular blocking agents. The primary reason for this preference is the higher proportion of the enantiomer R(-)-cis atracurium, which is less likely to cause dyskinesias compared to its enantiomer S(+) atracurium.

**Why Each Wrong Option is Incorrect:**

A. Improved pharmacokinetics: Both atracurium and cis atracurium have similar pharmacokinetic properties, including half-life, clearance, and volume of distribution. The choice between these two drugs should be based on other factors, not pharmacokinetics.

B. Increased potency: Potency refers to the drug's ability to block neuromuscular transmission. Atracurium and cis atracurium have similar potency and efficacy. Both are equipotent, meaning they have the same affinity for the neuromuscular receptors.

D. Enhanced neuromuscular recovery: While both atracurium and cis atracurium have similar recovery rates, the primary reason for preferring cis atracurium is not based on this factor. The choice between these two drugs should be based on their ability to reduce the risk of dyskinesias, not on their recovery properties.

**Clinical Pearl:**

The preference for cis atracurium over atracurium should be based on its reduced risk of causing dyskinesias, which can negatively impact patient comfort, clinical outcomes, and the efficiency of the surgical procedure. Understanding the pharmacology of these drugs, including their enantiomers, is crucial for selecting the appropriate neuromuscular blocking agent for a specific clinical scenario.