Hello there,welcome to Healthcaremagic. Inj Clexane is brand name of drug called Enoxaparin which belongs to a group of drugs called low molecular weight heparins.It prevents clotting of blood and one of its use is in prevention and treatment of Deep vein thrombosis. Prophylactic (preventive) dose of inj clexane is advised in a patient who is travelling through a flight if 1)The duration of flight is 4-6 hours 2)The patient falls under high risk category for getting deep vein thrombosis. 3)If he is not already taking Warfarin which is a drug which prevents blood clotting and is prescribed for treatment of deep vein thrombosis.To know that warfarin is in the required amount in the body ,a test known as INR (international normalised ratio) is done whose range should be maintained between 2-3 for deep vein thrombosis. Hence if you are already on warfarin with required INR you need not take clexane inj.But if You are not on warfarin then with a previous history of DVT you are at high risk for recurrence of DVT and You must take on dose of 40mg inj clexane subcutaneously just before the flight.(If you are having kidney issues then the drug should be used with caution as per advice of your doctor) Apart from that there are certain measures that You should take 1)Walk in between the journey 2)Move your legs frequently 3)Wear grade 2 elastic compression stockings (15-30 mm hg) 4)Avoid sleep medication. Hope that answers the question.Thank You.