Thrombolytic agents, commonly called "clot-busting" drugs, are frequently used in the treatment patients with blood clots in the lungs but a new study says clot-busting drug are no more effective than traditional blood thinners for the majority of the patients who get them. Thrombolytic agents also appear to increase the risk of death in patients with normal blood pressure.

The study utilized data from patients enrolled in the Registro Informatizado de la Enfermedad Trombo Embólica (RIETE registry), a computerized registry of patients who have blood clots, including pulmonary blood clots. The researchers reviewed the health information of 15,944 registry-enrolled patients with confirmed symptomatic acute pulmonary embolism to determine if thrombolytic therapy caused an effect on patient mortality during the first three months after diagnosis.

They found that while patients with low blood pressure who were treated with thrombolytic agents had a non-statistically significant reduction in death compared to patients treated with anticoagulants, patients who had normal blood pressure and were treated with thrombolytic drugs had a statistically significant increased risk of death compared to those who received standard anticoagulants.

"The results of our study do not support the use of thrombolytic, or clot-busting, agents in most patients with acute symptomatic pulmonary embolism," said study author David Jiménez, MD, senior consultant for the respiratory department at the Ramón y Cajal Hospital and Alcalá de Henares University in Madrid.  "We also found that, compared to standard anticoagulation drugs, thrombolytic therapy demonstrated a trend toward increased survival in patients who presented with low blood pressure, while it significantly worsened survival in those without low blood pressure.

"The primary finding of the study was expected, as there are no large randomized clinical trials that demonstrate the benefit of thrombolytic therapy on patient survival. However, it was surprising to note that thrombolytic therapy was associated with worsened survival in pulmonary embolism patients with stable blood pressure.   "Unless further information that suggests otherwise becomes available, the guidelines for treatment of patients with pulmonary embolism should not recommend thrombolytic therapy for patients who have normal blood pressure."

Dr. Jiménez said randomized clinical trials should assess the clinical benefit of thrombolysis in selected patients with pulmonary embolism and normal blood pressure.

"Investigators also should conduct prospective studies to assess if cardiac biomarkers and/or imaging testing might identify those patients with low blood pressure who are at highest risk of death and who might benefit from thrombolytic therapy," he said.

  The study will be presented at the American Thoracic Society 2011 International Conference in Denver.