Bayer said it has started patient enrollment in a second pivotal Phase III clinical trial of its blood clot dissolving enzyme, alfimeprase, along with US partner Nuvelo.

Alfimeprase is being developed for the treatment of central venous catheter occlusion (CO), the blockage of intravenous devices used to deliver medications or withdraw blood from patients.

COs are a common problem that can block the administration of therapies to patients. It is estimated that up to 25 % of catheters become occluded, and that nearly two thirds of all those blockages are caused by the formation of a blood clot.

The companies estimate that the market alfimeprase in this indication could be valued in the hundreds of millions of dollars, although the real pay-off with the drug could come if it shows efficacy in treating stroke, deep vein thrombosis and heart attack. Bayer licensed rights to alfimeprase from Nuvelo last month in a $385 million deal that included $50 million in upfront payments.

The new alfimeprase trial, known as SONOMA-3 (Speedy Opening of Non-functional and Occluded catheters with Mini-dose Alfimeprase-3), is the second of two multinational studies in the drug's Phase III programme for CO. This open-label trial will evaluate the safety and efficacy of 3mg of alfimeprase in 800 patients.

Interim results from the first trial of alfimeprase showed that the drug could restore function to occluded catheters in 15 minutes or less.

If approved for CO, alfimeprase will compete with Genentech’s thrombolytic product Cathflo Activase (alteplase), which was approved for clearing catheter blockages in 2001 and became the first pharmacological alternative to removing and replacing the device.