**Core Concept:**
Local anaesthetics work by blocking the voltage-gated sodium channels in neurons, inhibiting the propagation of pain signals. Infected tissues have an increased inflammatory response, which can alter the pharmacokinetics and pharmacodynamics of local anaesthetics due to changes in tissue composition and increased vascularity.

**Why the Correct Answer is Right:**
Infected tissues exhibit increased vascularity and inflammation, which can lead to changes in the pharmacokinetics and pharmacodynamics of local anaesthetics. This results in a slower onset of action and reduced duration of local anaesthesia in infected tissues compared to healthy tissues.

**Why Each Wrong Option is Incorrect:**
A. **Not relevant**: This option is irrelevant to the question as it does not address the impact of infected tissues on the action of local anaesthetics.
B. **Incorrect rationale**: This option wrongly suggests that local anaesthetics are less effective in infected tissues due to increased vascularity, which is not the primary reason for the slower effect.
C. **Incorrect rationale**: This option incorrectly claims that local anaesthetics penetrate deeper in infected tissues, which is not the main cause for the slow effect.
D. **Incorrect rationale**: This option incorrectly states that inflammatory cells may cause a faster onset of action, which contradicts the actual reason for the slower effect in infected tissues.

**Clinical Pearl / High-Yield Fact:**
Understanding the pharmacokinetics and pharmacodynamics of local anaesthetics in infected tissues is crucial for safe and effective regional anaesthesia. When administering local anaesthesia in infected areas, it is essential to consider the altered pharmacokinetics and pharmacodynamics, allowing for appropriate dosing and technique adjustments to ensure adequate and safe anaesthesia.

**Correct Answer:**
D. **Incorrect rationale**: This option correctly highlights that the pharmacokinetics of local anaesthetics can be altered in infected tissues due to changes in tissue composition and increased vascularity. This alteration leads to a slower onset of action and reduced duration of local anaesthesia in infected tissues compared to healthy tissues.

**Explanation:**
In healthy tissues, local anaesthetics can penetrate deeper and reach the site of action more easily, resulting in a faster onset and prolonged duration of action. In contrast, in infected tissues, the pharmacokinetics and pharmacodynamics of local anaesthetics are altered due to changes in tissue composition and increased vascularity. This leads to a slower onset of action and reduced duration of local anaesthesia in infected tissues compared to healthy tissues.