Rare side effects These may affect up to 1 in every 1000 people treated with Arixtra. • allergic reaction • internal bleeding in the brain or abdomen • anxiety or confusion • headache • fainting or dizziness, low blood pressure • drowsiness or tiredness • flushing • coughing • leg pain or stomach pain • diarrhoea or constipation • indigestion • wound infection • increase in bilirubin (a substance produced by the liver) in the blood • reduction in potassium in your blood