Here's the solution, courtesy of playstationtrophies.org:
This trophy can only be earned while Claire is still on Rockfort Island. Rodrigo, your jailer who released you is injured and needs his meds; you'll need to find and deliver his meds to him to earn this trophy.
The Hemostatic Medicine is located in the Military Training Facility. Once you enter the facility there are two Biohazard shutters on the right side of the room. The further set of shutters leads to a room where you get ambushed by Alfred. Chase him into the next room and you'll have two possible exits. One of them starts a cutscene where Alfred locks you in the room, the other doorway leads to a save room, the medicine is on the couch in the save room.
Once you have the meds you can go back and deliver them to Rodrigo at any time; when you deliver the meds you'll also hand over your lighter and he'll give you a lock pick. Giving Rodrigo the meds is required to earn the A-Rank in the game. To save time, the best time to give him the meds is when you head back to the Prison Facility with a Blue Crest.