Local anaesthetics: infected tissue: practice question

A Anaesthesia question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Anaesthesia · Local anaesthetics: infected tissue

Sample item

Why is a local anaesthetic often ineffective when infiltrated into an abscess?

AThe drug precipitates in pusBBacterial enzymes destroy the drugCBlood flow is reduced so less drug entersDThe acidic environment increases the ionised fraction that cannot cross the membrane

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. The acidic environment increases the ionised fraction that cannot cross the membrane

In infected tissue the pH falls, so more of the weak base is in the ionised form and less crosses the membrane to the intracellular binding site. Greater vascularity also increases systemic uptake.

Option by option

A. The drug precipitates in pus
Precipitation in pus is not the main reason.
B. Bacterial enzymes destroy the drug
Bacterial inactivation is not the mechanism.
C. Blood flow is reduced so less drug enters
Blood flow is typically raised in inflammation.
D. The acidic environment increases the ionised fraction that cannot cross the membrane (correct)
Correct. Low pH favours ionisation.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is D, The acidic environment increases the ionised fraction that cannot cross the membrane. In infected tissue the pH falls, so more of the weak base is in the ionised form and less crosses the membrane to the intracellular binding site.

Why is "The drug precipitates in pus" not the answer?

Precipitation in pus is not the main reason.

Why is "Bacterial enzymes destroy the drug" not the answer?

Bacterial inactivation is not the mechanism.

Why is "Blood flow is reduced so less drug enters" not the answer?

Blood flow is typically raised in inflammation.

What concept does this question test?

It tests Local anaesthetics: infected tissue in Anaesthesia. Greater vascularity also increases systemic uptake.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Local anaesthetics: infected tissue?

Make a table of each agent, its key advantage and its main side effect. Then use the flashcards and the other Anaesthesia questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.