Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
1
Is any of this happening now?
Call 911
Call emergency services now for:
Trouble breathing
Collapse, seizure, or inability to wake
Severe confusion or loss of coordination
Repeated vomiting with marked weakness
Very little or no urine
Chest pain, fainting, or signs of shock
An intentional ingestion requires urgent emergency assessment and compassionate mental health support.
And for anyone, someone who:
you believe has taken an overdose or swallowed something poisonous
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has chest pain, tightness or pressure lasting more than a few minutes
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
Someone who is unconscious, or cannot be woken
Someone who is bleeding heavily and it will not stop with firm pressure
Someone who has had a seizure that will not stop, or does not wake up afterwards
Someone who has lips or skin that look pale, blue, grey or blotchy
2
Is any of this happening?
Be seen today
Contact a poison centre immediately if anyone has swallowed a Merthiolate product, even if there are no symptoms.
Also seek immediate advice after an injection, a large spill onto broken skin, an eye exposure that remains painful after rinsing, or an exposure involving an unknown amount or product.
3
Does any of this apply?
Book an appointment
A mild rash that appears later is usually appropriate for routine medical review unless it is widespread, blistering, or accompanied by facial swelling or breathing difficulty.
The article also says
For a small skin exposure without symptoms, wash the area and contact a poison centre if the ingredients or concentration are uncertain.
Every sign above is quoted from the sofidex article on Merthiolate poisoning. If you are not sure, err upward — it is always reasonable to be checked.