Presribing in liver disease Flashcards
extraction ratio
the percentage of the drug removed from the perfusing blood during its passage through the organ
ie the ratio of hepatic clearance of a drug to the hepatic blood flow
>0.7 = high 0.3-0.7 = intermediate <0.3 = low
the higher the extraction rate, the higher the first pass metabolism, and a low bioavailability
therefore in cirrhotic patients, dose monitoring and reduction is vital
prescribing high extraction drugs
oral: reduce initial dose and maintenance dose
IV: normal initial dose, reduced maintenance dose according to hepatic blood flow
reduced dose = normal dose x bioavailability/100
ie an extraction ratio of 0.8 would mean a bioavailability of 0.2
prescribing in low extraction ratio
low albumin binding: reduce maintenance dose, or increase dosing interval
general guidelines
use drugs that are not metabolised by the liver
avoid hepatotoxic drugs
avoid sedatives, diuretics or drugs that cause constipation, as this can lead to encephalopathy
avoid drugs that alter haemostasis
avoid drugs that cause Na retention as this can exacerbate ascites/fluid retention