**Question:** Which of the following properties of the drug will enable it to be used in low concentration?

A. High solubility
B. High lipophilicity
C. High protein binding
D. High stability

**Core Concept:** The ability of a drug to be used in low concentration is determined by its solubility, lipophilicity, and protein binding. These factors influence how effectively a drug can diffuse across biological membranes and interact with its target molecules.

**Why the Correct Answer is Right:** The correct answer, B (High lipophilicity), contributes to a drug's ability to be used in low concentration. High lipophilicity allows a drug to easily diffuse across lipid membranes, including cell membranes, which is crucial for effective drug action. This property enhances the drug's ability to interact with its target molecules, such as enzymes or receptors, thereby minimizing the required concentration for therapeutic effect.

**Why Each Wrong Option is Incorrect:**

A. High solubility (option A): While solubility is an essential property for drug administration (determining the ease of dissolving the drug in water or other solvents), it does not directly correlate with the drug's ability to be used at low concentrations. High solubility may help with administration but not necessarily with minimizing the required drug concentration at the site of action.

C. High protein binding (option C): High protein binding typically reduces the fraction of a drug available for interaction with its target molecules (e.g., receptors, enzymes). This results in an increased drug concentration being required at the site of action, making it less desirable for minimizing the drug concentration needed.

D. High stability (option D): Stability refers to a drug's resistance to degradation or breakdown. Although stable drugs can maintain therapeutic concentrations over time, it does not directly impact the drug's ability to be used at low concentrations.

**Clinical Pearl:** Optimal drug concentrations should be maintained at the site of action to ensure therapeutic efficacy and minimize side effects. In this context, high lipophilicity is crucial for a drug to be used at low concentrations, whereas high solubility, protein binding, and stability do not directly correlate with this property.