Can they be dispensed/transferred into smaller containers? Or is that not viable for a reason? (e.g. practical quantity required is full 4oz, or it is not practical to change container to another?)

(one of the hoots is that security screeners just go by what is printed on a label, so if something is labelled 100ml that is fine! Even if it is a jumbo deodorant container, etc. Nobody is saying security rules are sensible - especially as you could have 5(Etc) x 100ml bottles, but not a 500ml bottle)

Anyway, if it can't be transferred to a smaller container, I would:

(1) Carry a medical note to that effect (Stating hat this is the smallest size available for the medicine, and that it is required to carry it on the person, not just that you need the product, but this is the size you must carry - as nothing smaller exists). But I would check all airport and country requirments in advance of travel - and what their policies and requirments are for required medicines above 100ml and supporting documents.

(2) Be urgently contacting the manufacturer, and asking them to make 100ml sizes for travellers.

Do they already make 100ml sizes for metric markets? Or does someone need about 4oz exactly?