If you have serious risk factors or must sleep during the flight, pharmaceutical prophylaxis may be advisable.
A 9/03 Angiology study is very positive for pinokinase. Pinokinase contains ingredients that reduce edema, a suspected cause of clots, and dissolve fibrin, a component of clots.
You could ask your doctor for a prescription for a low molecular weight heparin, which is effective reaches maximum effectiveness quickly, in about four hours, and does not need to be repeated for 24 hours. Your prescription may come as two syringes with no instructions. It needs to be injected in the stomach fat, not in a muscle. You can find instructions at lovenox.com. For Innohep, go to Innohep
Starting warfarin just before a flight is a very bad idea. Warfarin must be accompanied by heparin (or other anticoagulant) in the first few days. Otherwise a hypercoagulable state may occur, putting you at greater risk of clots. (See article on PE by Dr. Sat Sharma at http://www.emedicine.com/med/topic1958.htm, where drugs are listed by name in a section titled Medication.) The new low-dose warfarin regimen apparently can be started without simultaneous heparin, but you would first need go through the blood testing regimen to know your correct dosage. (See N Engl J Med. 2003 Apr 10; 348(15): pp 1425-34)
Aspirin and clopidogrel, Plavix, are effective for arterial clotting, aggregation of platelets. They are not effective for venous clotting, knitting together of proteins. Plavix may be desirable for those who cannot tolerate aspirin and who have had a stroke, myocardial infarction, or peripheral arterial disease.