What is the most appropriate pre-biopsy treatment?
Well done, correct.
Vitamin K deficiency due to disruption of enterohepatic recirculation by the biliary obstruction is the likely cause of the significantly prolonged PT. IV vitamin K is best as there is likely to be difficulty with absorption. Note that this will take at least 6 hours to correct the PT and therefore should be given the day before to allow re-checking of the coagulation. FFP may be necessary if vitamin K does not work.