A High doses of
aspirin (4 g daily or more) can increase prothrombin times. It also
damages the stomach wall, which increases the risks of bleeding. Low-dose
aspirin (75 to 325 mg daily) increases the risk of bleeding when given with
warfarin by about 1.5- to 2.5-fold, although, in most studies the absolute risks have been small. Increased
warfarin effects have been seen when the salicylates methyl salicylate or trolamine salicylate, were used on the skin.
It is usual to avoid normal analgesic and anti-inflammatory doses of
aspirin while taking any anticoagulant. Patients should be told that many non-prescription analgesic, antipyretic, cold and
influenza preparations may contain substantial amounts of
aspirin. Warn them that it may be listed as acetylsalicylic acid. Paracetamol (acetaminophen) is a safer analgesic substitute. Low-dose
aspirin appears to interact to a lesser extent, and where problems are seen it still appears that the benefits of use sometimes outweigh the risks. Any interaction with topical salicylates seems likely to be rare.