Non-invasive methods for the assessment of hepatic drug disposition

Assessment of hepatic drug metabolism by clearance techniques requires frequent blood sampling and has therefore received only limited application. Non-invasive methods enjoy better patient acceptance, but of necessity are indirect and therefore require extensive validation. The clinical usefulness of the aminopyrine breath test is now well established but it may yield abnormal results if the functioning liver cell mass is reduced irrespective of the aetiology of the disease. It is thus primarily an indicator for prognosis rather than diagnosis. It may also be influenced by drug interactions. In view of the different metabolic fate of glyceryl trinitrate this test compound may be used for the non-invasive detection of portal-systemic shunting, rather than for changes in the functional capacity of the liver. Thus, non-invasive tests of hepatic drug disposition can now be used to assess at least two different physiological derangements in patients with liver disease.