A closed-system, drug administering catheter assembly includes a transfer adapter, a stopcock, a medicament injector containing chemotherapy medicament, a medicament pressure reservoir, and a urethral balloon catheter comprising a drain lumen and a distal tip, all connected together in a closed-system. The medicament injector is configured to inject the chemotherapy medicament through the stopcock, the drain lumen, and into an environment of the distal tip within a patient's organ without leakage of the chemotherapy medicament from the patient into an environment of the patient. The medicament pressure reservoir is configured to store negative pressure that withdraws from the organ used chemotherapy medicament through the drain lumen and the stopcock and holds the used chemotherapy medicament in the medicament pressure reservoir without leakage of the used chemotherapy medicament into the environment of the patient.
