How long should i take PrEP HIV?

Good day I’m asking for a friend (I already have HIV so PrEP is not something I need.) Say if my friend go on a months holiday to somewhere he is highly likely to engage in risky sex. Is it viable to use PrEP just for this trip? How long before the first sexual encounter does he need to take PrEP and how long does he need to stay on it after the last sexual encounter? for example in Bangkok PrEP is available from red cross at a cost below a dollar a day. Would this be a good option (together with condoms) for a short trip of say a few weeks to a month?

Response from Dr. Young

While PrEP is typically recommended as a daily medication, for those who have periods of no risk (ie, sexual or injection drug activity), it’s reasonable to consider limiting the treatment time.

I conservatively recommend that people with possible HIV exposures be taking PrEP for at least 1 week prior to the exposure and for a month afterwards.