Assessment of portosystemic shunting from superior mesenteric vein by duodenal administration of iodoamphetamine I123

A semi-mechanistic model to predict the effects of liver cirrhosis on drug clearance

BACKGROUND AND OBJECTIVE

Liver cirrhosis is characterized by a decrease in functional hepatocytes, lowered circulating levels of plasma proteins and alterations in blood flow due to the development of portacaval shunts. Depending on the interplay between these parameters and the characteristics of an administered drug, varying degrees of impaired systemic clearance and first-pass metabolism are anticipated. The Simcyp Population-based ADME Simulator has already been used successfully to incorporate genetic, physiological and demographic attributes of certain subgroups within healthy populations into in vitro-in vivo extrapolation (IVIVE) of xenobiotic clearance. The objective of this study was to extend population models to predict systemic and oral drug clearance in relation to the severity of liver cirrhosis.

METHODS

Information on demographics, changes in hepatic blood flow, cytochrome P450 enzymes, liver size, plasma protein binding and renal function was incorporated into three separate population libraries. The latter corresponded to Child-Pugh scores A (mild), B (moderate) and C (severe) liver cirrhosis. These libraries, together with mechanistic IVIVE within the Simcyp Simulator, were used to predict the clearance of intravenous and oral midazolam, oral caffeine, intravenous and oral theophylline, intravenous and oral metoprolol, oral nifedipine, oral quinidine, oral diclofenac, oral sildenafil, and intravenous and oral omeprazole. The simulated patients matched the clinical studies as closely as possible with regard to demographics and Child-Pugh scores. Predicted clearance values in both healthy control and liver cirrhosis populations were compared with observed values, as were the fold increases in clearance values between these populations.

RESULTS

There was good agreement (lack of statistically significant difference, two-tailed paired t-test) between observed and predicted clearance ratios, with the exception of those for two studies of intravenous omeprazole. Predicted clearance ratios were within 0.8- to 1.25-fold of observed ratios in 65% of cases (range 0.34- to 2.5-fold).

CONCLUSION

The various drugs that were studied showed different changes in clearance in relation to disease severity, and a 'one size fits all' solution does not exist without considering the multiple sources of the changes. Predictions of the effects of liver cirrhosis on drug clearance are of potential value in the design of clinical studies during drug development and, clinically, in the assessment of likely dosage adjustment.

Binding cells of 125I-iodoamphetamine in rat liver

We recently reported that transrectal or intestinal portal scintigraphy with 123I-iodoamphetamine (IMP) could be a useful method for the non-invasive and quantitative evaluation of the portosystemic shunt in portal hypertension, but what cells in the liver trap IMP has not been clarified. This study was aimed at elucidating whether IMP was extracted by parenchymal cells, sinusoidal endothelial cells, Kupffer cells or fat storing cells. Each type of liver cell was isolated from rats and cultured. The cells were incubated with 125I-IMP and the radioactivity of the lysate was determined. Nonspecific binding was assessed in the presence of an excess of unlabeled IMP, and specific binding was determined by subtracting the nonspecific from total binding. Specific binding observed in parenchymal cells, endothelial cells and Kupffer cells was 70.2 +/- 0.4, 4.2 +/- 1.4 and 2.3 +/- 0.8 pmol/well, respectively, but no specific binding was observed in fat storing cells. The binding in parenchymal cells was much higher than that in endothelial cells or Kupffer cells (p < 0.005). In addition, the binding to parenchymal cells reached equilibrium within 20 min and was not saturable over the concentration range tested (0.5-10 microM). These findings indicate that IMP is mostly extracted by parenchymal cells in the liver.

Effect of propranolol on portosystemic collateral circulation estimated by per-rectal portal scintigraphy with technetium-99m pertechnetate

BACKGROUND/AIMS

Propranolol is widely used in the prevention of variceal bleeding. However, in certain patients with cirrhosis, the portal hypotensive effect of propranolol cannot be obtained. An explanation for portal unresponsiveness to propranolol could be an increase in portocollateral vascular resistance mediated by this drug.

METHODS

In 33 patients with cirrhosis the effect of chronic administration of propranolol on portocollateral blood flow from the inferior mesenteric vein was examined by means of per-rectal portal Tc-99m pertechnetate scintigraphy.

RESULTS

Propranolol significantly reduced the shunt index by 15.3 +/- 4.2%. This reduction was observed only in patients with cirrhosis classified as Child-Pugh A and B groups, but not group C. Differences between groups in portosystemic shunt index changes after propranolol were significant (F = 3.4, p < 0.05).

CONCLUSIONS

The data presented suggest that propranolol changes the distribution of blood between the portal and systemic circulation, which is probably due to the increase in vascular resistance of portocollateral vessels. The magnitude of the vascular response to propranolol depends on the severity of liver disease.

Evaluation of portal circulation through the superior mesenteric vein with an enteric capsule of [123I]iodoamphetamine

We report a method by which the contribution of the superior mesenteric vein to the portal blood flow can be evaluated noninvasively. An enteric-coated capsule containing [123I]iodoamphetamine is given by mouth 3h before the examination. The data obtained are treated by computer to calculate the portal shunt index (SI) through the superior mesenteric vein. The SI was higher for more severe liver disorders, Increasing in the order of chronic persistent hepatitis, chronic aggressive hepatitis, and cirrhosis. The SI was higher in cirrhotic patients than in chronic hepatitis patients or healthy volunteers (both, P < 0.0001). The SI was higher in cirrhotic patients with esophageal varices than in such patients without varices (P < 0.05). The SI was higher in cirrhotic patients with ascites than in such patients without ascites (P < 0.001). The SI was higher in cirrhotic patients with encephalopathy than in those without encephalopathy (P < 0.01). Correlation was significant between the SI and classical indicators of functional reserve. This method is clinically useful.