Antidotes

Current · V5 (2025) → Q.i Historical · V4 (2023) → Y13 1 exam appearance

2024B Q20

Exam question

Explain the mechanism of action by which the following drugs exert their clinical and pharmacological effect when used to treat drug toxicity or overdose, including the time taken to exert this clinical effect: (a) N-acetylcysteine (25% of marks). (b) Digoxin FAb (25% of marks). (c) Naloxone (25% of marks). (d) Lipid emulsion (i.e. Intralipid) (25% of marks).

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Field	N-ACETYL CYSTEINE (NAC) Antidotes · Antidotes · Level 3	DIGOXIN ANTIBODIES Antidotes · Antidotes · Level 3	NALOXONE Antidotes · Antidotes · Level 3	Intralipid 20% Antidotes · Antidotes · Level 3
Mechanism of action	- Metabolized to cysteine → Regeneration of sulphydril groups and glutathione - acting as an alternate substrate for conjugation - reduces disulfide bonds in mucoproteins	Binds excess digoxin or digitoxin molecules circulating in the blood - Fab fragment-digoxin complex excreted by kidney - Net shifts the equilibrium away from binding of digoxin to receptors	Reversal of MoP receptor effects such as sedation, hypotension, respiratory depression, and the dysphoric effects of partial agonists Will precipitate acute withdrawal symptoms in opiate addicts	- unclear - may involve establishment of concentration gradient away from primary site of action of LA
Main Action	antioxidant and glutathione inducer	Binds Digoxin Molecules	competitive antagonist at mu-, delta-, kappa-, and sigma-opioid receptors	- Energy substrate - Reverse local anaesthetic cardiotoxicity
Onset Peak Duration	Duration: short	Onset: 0-60min Peak: 30-360min	Onset: 1-3 mins Peak effect: 15 mins Duration: 30 mins > Less than the effect site time of most opioids → requirement for repeat dosing or infusion.	(For LA tox) onset: minutes peak: 15-30mins

Past papers

Exam appearances

1 appearance

Exam	Exact exam wording	Candidate success
2024B Q20	Explain the mechanism of action by which the following drugs exert their clinical and pharmacological effect when used to treat drug toxicity or overdose, including the time taken to exert this clinical effect: (a) N-acetylcysteine (25% of marks). (b) Digoxin FAb (25% of marks). (c) Naloxone (25% of marks). (d) Lipid emulsion (i.e. Intralipid) (25% of marks).	65%