**Study Overview:** This study examines how safe and effective DEFENCATH® is in preventing infections in adults who receive their nutrients directly into their bloodstream, a method called Total Parenteral Nutrition (TPN), using a tube called a Central Venous Catheter (CVC). The study compares DEFENCATH® to heparin, a blood-thinning medicine. **Key Points:** - The study may require participants to lock their catheter with a special solution for at least 4 hours, every week for several months. - Participants must agree to training sessions and maintain a daily diary about their catheter care. - Participants must be stable for at least four weeks before joining and able to follow all study procedures. **Eligibility:** Participants must be adults (18+), living in the US, and need TPN for more than 6 months, at least 3 days a week. They must have a permanent CVC or PICC line (a kind of tube) and be stable without recent infections or antibiotics. People with certain health issues, allergies to study medications, or those who are pregnant or breastfeeding cannot participate.