This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anaesthesia
Why is the effect of local anaesthesia slow in infected tissues 
Select and explain. 
A. Less vascularity causing poor diffusion of drug, B. Rich in enzymes that metabolize the drug, C. Low extracellular pH that hinders diffusion of drug into cell, D. Rich in K+ that inhibits binding of the drug to the receptor
C: Low extracellular pH that hinders diffusion of drug into cell
Answer: C: Low extracellular pH that hinders diffusion of drug into cell 
Explanation: In case of infection there is acidic pH of tissue, and in that case local anaesthetics are mostly in ionized form. Ionized form of local anaesthetics is the one that binds to sodium channels, but non-ionized form is the one that is important for membrane penetration. That is the reason for delayed onset of local anaesthetics in site of infection.