Neoplasms of the lung.

SIR,-I wish to comment on the excellent paper on the failure of aspirin to prevent postoperative deep-vein thrombosis in patients undergoing total hip replacement (22 April, p 1031). Without faulting the conclusion of Mr J D Stamatakis and his colleagues that aspirin in a dose of 600 mg twice daily is an ineffective prophylaxis against this complication, I think that there are other considerations to be borne in mind. Aspirin inhibits haemostasis through two mechanisms. The most widely known mechanism is inhibition of platelet aggregation,' and for this purpose 600 mg twice daily is apparently adequate. However, and this is less well known but probably as important, aspirin interferes with the hepatic synthesis of vitamin-K-dependent clotting proteins,2 and does so in a manner quantitatively related to the plasma level attained and not necessarily to the dose administered to any given individual.3 It therefore seems evident that optimum results will not be achieved by administration of a standard dose but are more likely to be attained by attention to the plasma level of aspirin in each individual.