The most frequent and severe side effect of urokinase therapy is haemorrhage. The haemostatic status of the patient may be more profoundly altered with urokinase therapy than with heparin or coumarin-derivative anticoagulant therapy.
Severe spontaneous bleeding, including fatalities resulting from cerebral haemorrhage, has occurred during urokinase therapy. Less severe spontaneous bleeding has occurred approximately twice as frequently as that occurring during heparin therapy. Patients with pre-existing haemostatic defects have the greatest risk of spontaneous bleeding.
In contrast to streptokinase, urokinase is reportedly non-antigenic. However, mild allergic reactions including bronchospasm and rash have been reported rarely. In addition, very rare cases of fatal anaphylaxis have been reported.
Fever and chills, including shaking chills (rigors), have been reported occasionally in patients receiving urokinase. Symptomatic treatment is usually sufficient to alleviate discomfort caused by urokinase-induced fever; however, acetylsalicylic acid should not be used.
Other infusion reactions reported with urokinase therapy include dyspnoea, cyanosis, hypoxemia, acidosis, back pain, and nausea and/or vomiting; these effects reactions generally occurred within one hour of beginning urokinase infusion.