Urokinase (Abbokinase, Kinlytic)

Urokinase is a real, FDA-approved human-enzyme thrombolytic, first approved in 1978 — pulled from the US market in 1999 after inspectors found its manufacturer had not adequately screened the human kidney cells used to make it for viral and bacterial contamination, reapproved in 2002 with a narrower label, and, as of this review, off the US market again with a funded, multi-year effort under way to bring it back.

A human enzyme, historically grown in human kidney cells

Urokinase is a serine protease that the human kidney naturally produces and that converts plasminogen directly into plasmin, the enzyme that dissolves fibrin clots — a different, more direct mechanism than streptokinase's indirect plasminogen-complex approach, and one that does not provoke the antibody and allergic-reaction risk of a foreign bacterial protein. Commercial urokinase was historically extracted and purified from cultured human neonatal kidney (HNK) cells, a manufacturing approach that made viral and bacterial screening of the source cell cultures a critical safety step — one that would later become the center of the drug's biggest regulatory crisis.

1978 approval, broad indications

The FDA first approved urokinase, marketed by Abbott Laboratories as Abbokinase, in January 1978. Its original label was broad by later standards, covering lysis of acute massive pulmonary emboli, thrombi obstructing coronary arteries, occlusive thromboemboli in peripheral arteries and vascular grafts, and clearance of blocked intravenous catheters. For roughly two decades it served as a widely used thrombolytic alongside streptokinase, before both were substantially displaced in cardiology by the tPA-class drugs and by the rise of catheter-based angioplasty for coronary artery thrombi specifically.

1999: pulled from the market over unscreened, contaminated cell cultures

In October and November 1998, FDA inspectors found that Abbott's manufacturing process for the human neonatal kidney cells used to produce urokinase fell short of current Good Manufacturing Practice requirements: HNK cells used in 1997 and 1998 production campaigns had not been tested for hepatitis C virus, one cell lot tested positive for hepatitis B surface antigen, another tested positive for mycoplasma, and reovirus was detected in three lots of in-process product. The FDA issued a formal drug warning to physicians on 25 January 1999, and Abbott suspended shipments of Abbokinase; a brief resumption was followed by a full stop in March 1999, taking urokinase off the US market entirely for the first time since its 1978 approval. This was a manufacturing and quality-control failure, not a finding that the drug molecule itself was unsafe or ineffective — but it removed urokinase from clinical use for years while Abbott rebuilt its production process to meet current standards.

Current status: reapproved in 2002, off the market again, now the subject of a funded 2028 comeback plan

The FDA approved Abbott's supplemental application to reintroduce Abbokinase on 14 October 2002 — nearly four years after the shutdown — but with a narrower label than before, limited to pulmonary embolism, reflecting both the tightened manufacturing controls and the fact that catheter-based angioplasty had by then become the preferred treatment for coronary artery thrombi. The product was later rebranded Kinlytic under subsequent owners (including ImaRx Therapeutics), and its regulatory assets eventually passed to Microbix Biosystems, a Canadian biologics company. Kinlytic has not been commercially available in the US in recent years. In 2025, Microbix and manufacturing partner Sequel Pharma announced a funded agreement to modernize urokinase production — including eliminating animal-derived components from the cell-culture process — and return Kinlytic to the US market, initially for catheter clearance, with a market return publicly targeted for 2028. As of this review, urokinase remains unavailable to US patients. It carries no wellness, cosmetic, or self-administered use of any kind.