Q: Name at least one drug overdose which may give negative or very low an-ion gap (AG)?

AG = Na+ - (Cl- + CO2)


Answer: Lithium toxicity

Lithium is basically read as a charged ion which may give very low or even negative an-ion gap.

Overdose of cough syrup containing dextromethorphan bromide may do the same as bromide may get measured as chloride.

Other 2 conditions known to do that are: hypo-proteinemia and multiple myeloma.