The purpose of the study is to compare the safety and effectiveness of alfimeprase to a placebo in restoring function of occluded central catheters.

Primary Outcomes: The ability to withdraw at least 3 ml of blood and infuse more at least 5 mL of sterile saline through the occluded catheter lumen at 15 minutes after receiving initial instillation of study drug.

Secondary Outcomes:

The ability to withdraw at least 3 mL of blood and infuse at least 5 mL of sterile saline through the occluded catheter lumen at 30 minutes following a single instillation of study drug and at 30 minutes following a second instillation of study drug if patency is not restored within 30 minutes of the first instillation.

Safety:

• Adverse events
• Major bleeding events
• Change in laboratory values.

Inclusion Criteria:

• Must give written informed consent
• Unable to withdraw 3 mL of blood from a central venous access device
• Hemodynamically stable
• Available for follow-up assessments

Exclusion Criteria:

• Inability to infuse at least 2 mL of saline through the catheter
• Catheter placed less than 48 hours prior to detection of occlusion
• Catheter used for hemodialysis of pheresis
• Less than 18 years of age
• Evidence of mechanical or nonthrombotic occlusion
• Receipt of any thrombolytic agent within 24 hours of randomization
• In the opinion of the investigator, subject is at "high risk" for bleeding events of embolic complications, or has a condition for which bleeding constitutes a significant hazard
• Increased risk for drug extravasation
• Pregnant, lactating, or actively menstruating women and women of child-bearing potential who are not using adequate contraceptive precautions (e.g. intrauterine device, oral contraceptives, barrier methods, or other contraception deemed adequate by the investigator)
• Known right-to-left cardiac shunt, patent foramen ovale, or atrial/ventricular septal defect
• Participation in any other study of an investigational device, medication, biologic, or other agent within 30 days before enrollment and until the 30-day follow up visit
• Any other subject feature that in the opinion of the investigator should preclude study participation