Heparin therapy should be given with caution to patients about undergo surgery, and those with impaired renal or hepatic function.
If oral anticoagulants are started, heparin should be continued in slightly decreasing doses for another 4-5 days until the oral drug has attained full prothrombin depressing activity.
Heparin should be used with caution in any patient with a history of allergy. Before a therapeutic dose is given to such a patient, a trial dose of 1,000 units may be advisable.