What is the recommended dosage and length of time to take antibiotic as a prophylactic against food poisoning? rifaximin for example can be taken for 3 days to treat travelers diarrhea, do you have to take the full cycle when using as prophylactic?

Especially in a foreign country the best preventative is careful avoiding of eating certain foods& drinking bottled water. It's not customary to take antibiotics preventatively to prevent food poisoning but having antibiotics on hand to take if it occurs is wise. With a single dose of rafampin, half of it is gone after 2 hours & 75% gone in 4 hours,etc as a guideline. I hope this helps.