Cimetidine does not reduce liver blood flow in cirrhosis

Cimetidine has been shown to reduce liver blood flow, as measured by indocyanine green clearance, in normal subjects. Concern over the potential deleterious effects of such reduction in cirrhosis led to the measurement of blood flow in 14 cirrhotics receiving oral or intravenous cimetidine. Liver blood flow was measured by the clearance of galactose at steady state during infusion of 40 mg per min. In six patients receiving 300 mg cimetidine by mouth each 6 hr for 4 days, basal flow (1,019 +/- 186 ml per min) was not significantly altered by cimetidine (1,087 +/- 156 ml per min). Intravenous infusion of cimetidine (300 mg) did not significantly alter flow in five patients between the basal (1,096 +/- 334 ml per min) and treatment periods (1,051 +/- 383 ml per min). Hepatic extraction of galactose in three patients (82 +/- 19%) was not significantly altered by cimetidine infusion (81 +/- 13%). The failure to reduce liver blood flow with cimetidine in this population may be due to their diminished proportion of portal venous flow, or alternatively suggests that histamine is not an important modulator of flow via H2 receptors. At a clinical level, the use of cimetidine in this population can continue without fear of further reduction in liver blood flow.     

Liver volume, portal vein flow, and clearance of indocyanine green and antipyrine in hyperthyroidism before and after antithyroid treatment.

BACKGROUND: The aim of the study was to examine liver volume, portal vein flow, and indocyanine green (ICG) and antipyrine clearance in hyperthyroidism before and after antithyroid drug treatment. METHODS: Liver volume and blood flow in the portal vein were investigated in nine fasting patients with hyperthyroidism by means of computed tomography scan and Doppler ultrasound, respectively. ICG clearance was estimated by bolus injection of ICG (0.5 mg/kg body weight) and antipyrine clearance with a one-sample technique. All patients were investigated before and after 3 months of antithyroid treatment, when euthyroidism had been achieved. The Wilcoxon matched-pairs test was used for statistical analysis. RESULTS: The median liver volume increased by 238 (155-289) ml (median, 95% confidence interval), corresponding to 19%, and the weight by 5.0 (0.0-8.0) kg (8%), and the antipyrine clearance decreased by 8 (3.1-34.4) ml/min (16%). These changes were all significant (P < 0.05). The relation between liver volume and body weight increased from 19.9 (16.5-23.7) ml/kg to 21.4 (17.1-21.9) ml/kg (P = 0.11). The liver blood flow as estimated by ICG clearance and Doppler ultrasound was not altered significantly after the treatment period (P = 0.07 and 0.77, respectively). CONCLUSIONS: The liver volume increased by 19% in nine hyperthyroid patients during treatment with antithyroids. Antipyrine clearance was reduced by 16%, whereas liver blood flow, as estimated by ICG clearance and Doppler ultrasound examination of portal vein flow, was not significantly altered. A differential regulation of liver volume and oxidative metabolic capacity in hyperthyroidism was seen.     

Renal sodium retention in cirrhosis: tubular site and relation to hepatic dysfunction

Renal sodium handling, assessed by the response to acute saline loading, was investigated in 14 well-compensated, nonascitic alcoholic cirrhotics and six normal controls. Urinary sodium excretion in cirrhotic patients (199 +/- 141 mumoles per min) was significantly lower than in controls (387 +/- 104 mumoles per min; p less than 0.01) at 3 hr postinfusion. In contrast to controls, renal plasma flow and glomerular filtration rate did not increase in the cirrhotics in response to acute saline loading. Proximal fractional reabsorption of sodium was estimated by clearance techniques in the presence of a hypotonic diuresis. Cirrhotic subjects with impaired functional liver cell mass as assessed by antipyrine clearance were unable to decrease proximal fractional reabsorption of sodium significantly in response to saline loading. Assessment in the cirrhotics included measurement of hepatic vein pressure gradient, indocyanine green extraction ratio, indocyanine green clearance, and antipyrine clearance as indices of portal pressure, intrahepatic shunting, hepatic blood flow and functional hepatocellular mass, respectively. Urinary sodium excretion in the cirrhotics correlated strongly with antipyrine clearance (r = 0.839, p less than 0.0001) and weakly with portal pressure (r = 0.562, p = 0.037). No correlation was seen with the other indices of hepatic blood flow and shunting. The findings of this study suggest that alcoholic cirrhosis is associated with a decline in hepatocellular function which results in either a decreased clearance of a salt-retaining hormone or decreased synthesis of a natriuretic hormone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hepatic metabolic function in patients receiving long-term methotrexate therapy: comparison with topically treated psoriatics, patient controls and cirrhotics

Standard biochemical liver function tests and the clearances of antipyrine and indocyanine green have been compared in psoriatic patients taking methotrexate, psoriatic patients on topical treatment, patient controls and patients with hepatic cirrhosis. The methotrexate-treated patients showed significant elevations in alkaline phosphatase (p less than 0.025) and gamma glutamyl transpeptidase activities (p less than 0.05) compared to topically treated psoriatics and patient controls. The clearance of antipyrine was reduced in the methotrexate treated group but not significantly (p less than 0.1 greater than 0.05). In contradistinction, the weight-adjusted clearance of indocyanine green was significantly impaired in the methotrexate group in comparison with the topically treated psoriatics (p less than 0.01). The clearance of both antipyrine and indocyanine green were markedly lowered in the cirrhotics (p less than 0.001 against all other groups). These data suggest that the serial measurement of alkaline phosphatase and indocyanine green clearance may provide a non-invasive indicator of the development and progression of methotrexate-related liver injury.     

Liver blood flow and enzyme induction in man

An increased liver blood flow in rats and monkeys found following induction of the liver microsomal enzyme system by antipyrine and phenobarbitone, formed the basis of the present study in 7 volunteers. The total body clearance of antipyrine, gamma GT, and the urinary excretion of d-glucaric acid and 6-beta-hydroxycortisol were measured. Liver blood flow was estimated after an overnight fast under basal conditions using the 133Xenon inhalation technique. In addition, liver volume was determined by 7 independent investigations using a 99mTechnetium-sulfur-colloid scan of the liver. Afterwards, each volunteer received 1,000 mg antipyrine daily for 14 days and all measurements were repeated. After antipyrine administration the antipyrine half-life decreased significantly from 12.5 to 7.7 hours with an increase of the antipyrine clearance from 34.1 to 50.8 ml/min. In addition, glucaric acid, gamma-GT and 6-beta-hydroxycortisol were significantly increased. Liver blood flow increased from 36.8 ml/min/100 g to 50.9 ml/min/100 g liver (p less than 0.02). The liver volume showed a tendency to increase but was significantly higher in only three of the seven volunteers investigated. The mean liver volumes of 1483 g before and 1585 g after antipyrine administration were not significantly different. In contrast, total liver blood flow increased significantly from 590 ml/min before to 809 ml/min after enzyme induction (p less than 0.02).     

Effects of anesthetic agents and abdominal surgery on liver blood flow

The cause of postoperative liver dysfunction is often unclear, but a decrease in liver blood flow during anesthesia and/or major surgery may be important. Plasma half-life and clearance of indocyanine green were therefore measured in 42 patients before, during and after anesthesia and abdominal surgery. In 13 patients, liver blood flow was also estimated from indocyanine green extraction using hepatic vein catheterization. The major finding was an early decrease in estimated liver blood flow after induction of anesthesia, but not later during or after surgery. Mean indocyanine green half-life increased by 26% (p less than 0.005), mean indocyanine green plasma clearance decreased by 19% (p less than 0.01) and mean estimated hepatic blood flow decreased by 36% (p less than 0.005) during the first 30 min of anesthesia. These changes were greater in males and in patients older than 55 yr, but changes were similar with each of three anesthetic groups. Half-life, but not indocyanine green clearance, was also significantly prolonged by mid-operation in the older (greater than 55 yr) patients and in those undergoing lower abdominal surgery. We suggest that this period of reduced liver blood flow during anesthesia is caused by the effects of neuromuscular blocking agents and may contribute to postoperative liver damage.     

Simultaneous measurement of effective hepatic blood flow and systemic circulation

BACKGROUND/AIMS: Because the disappearance rate of indocyanine green depends not only on hepatocyte function but also hepatic blood flow, the disappearance rate of indocyanine green is considered to be affected by the systemic circulation. Although the disappearance rate of indocyanine green is slower in cirrhotic patients, a hyperdynamic state is reported to be present. Purpose of this study was to evaluate hepatic function and systemic circulation simultaneously with reference to the hyperdynamic state of cirrhotic liver. METHODOLOGY: Forty-six patients were selected randomly for this study. Simultaneous measurement of effective hepatic blood flow and systemic circulation using an indocyanine green clearance meter was performed. We calculated the effective hepatic blood flow using the early disappearance rate of indocyanine green movement, cardiac output, and circulating time simultaneously with indocyanine green clearance meter. RESULTS: Hepatic function and hyperdynamic circulation could be evaluated quantitatively. The indocyanine green disappearance rate was dependent on cardiac index in normal subjects, whereas the indocyanine green disappearance rate was lower in cirrhotic patients, although the cardiac index was relatively high. CONCLUSIONS: Hepatic function and systemic circulation could be evaluated simultaneously with this indocyanine green clearance meter. Hyperdynamic circulation was suggested to compensate the impaired hepatic function of cirrhotic liver. Simultaneous measurement of hepatic function and systemic circulation may be essential to studying liver function.     

The effect of cimetidine on hepatic drug elimination in cirrhosis

Both cimetidine therapy and cirrhosis individually interfere with normal elimination of various drugs. Cimetidine is often prescribed in patients with cirrhosis but there is incomplete data on its effect on drug elimination in cirrhotics. The purpose of this study was to address this issue. Eight stable cirrhotics were studied prior to and following 7 days of cimetidine administration, (300 mg orally q.i.d.). Chlordiazepoxide (Librium), which is eliminated by the liver after demethylation, and indocyanine green, which is removed by the liver without biotransformation, were used as probes. Consistent with the concept that cimetidine interferes with drug metabolism by inhibiting microsomal oxidation, chlordiazepoxide clearance in the cirrhotics was inhibited by cimetidine (p less than 0.05), but indocyanine green clearance was unaffected. As shown by us previously (Roberts, R. K. et al., Gastroenterology 1978; 75:479-485), untreated cirrhotics had substantially lower chlordiazepoxide clearance than did controls. The inhibitory effect of cimetidine on chlordiazepoxide clearance was less in cirrhotics than in controls (p less than 0.05). In all subjects, there was excellent correlation between initial clearance and magnitude of depression in clearance after cimetidine, i.e., the larger the initial clearance, the larger the change (r = 0.97, p less than 0.0001). Forty-eight hours after stopping cimetidine, chlordiazepoxide clearance returned to baseline in cirrhotics and controls. Our data demonstrate that cimetidine and cirrhosis may act additively to impair drug metabolism. This effect of cimetidine on chlordiazepoxide clearance is smaller in cirrhotics than in controls, but, because of impaired initial drug elimination in cirrhosis, it may result in adverse clinical effects.     

Quantitative liver functions in Turner syndrome with and without hormone replacement therapy

BACKGROUND: Studies have documented elevated levels of liver enzymes in many females with Turner syndrome (TS). Histology has shown a range of changes. Treatment with female hormone replacement therapy (HRT) reduces liver enzymes. AIM: To study quantitative liver functions in TS in detail with and without HRT. DESIGN: Randomized crossover study with active treatment (HRT in TS and P-pill in controls) or no treatment. SUBJECTS: Women with TS (n = 8, age 29.7 +/- 5.6 (mean +/- s.d.) years), verified by karyotype, and age-matched controls (C; n = 8, age 27.3 +/- 4.9 years). METHODS: We determined liver enzymes in blood, used the galactose elimination capacity to assess hepatocyte cytosol activity, plasma clearance of indocyanine green to assess excretory function, antipyrine clearance to estimate microsomal activity, and the functional hepatic nitrogen clearance (FHNC) to assess mitochondrial-cytosolic metabolic capacity for conversion of amino-nitrogen. RESULTS: Liver enzymes were elevated in untreated TS and reduced by HRT. The hepatic capacities for conversion of galactose, indocyanine green, and antipyrine were normal and did not change by HRT. The FHNC was marginally reduced (untreated TS vs C: 19.4 +/- 5.4 vs 25.2 +/- 7.3 L/h, P = 0.1). FHNC changed slightly with HRT in TS (19.4 +/- 5.4 vs 24.4 +/- 10.2 L/h, P = 0.2). CONCLUSIONS: The elevations of liver enzymes in untreated TS are readily suppressed by HRT. Quantitative liver functions in TS are comparable to controls and are not affected by HRT.     

Comparison of bolus and infusion methods for estimating hepatic blood flow in patients with liver disease using indocyanine green

A non-invasive method of estimating liver blood flow by a two-compartment pharmacokinetic model of the plasma clearance of indocyanine green has been previously described in normal animals and patients without liver disease. This non-invasive technique has been compared with the conventional method of measuring liver blood flow by hepatic vein catheterisation in 25 patients with liver disease. There was good correlation between the values for indocyanine green clearance, with the infusion method tending to produce slightly higher results. However, there was poor agreement in the measurement of liver blood flow, as the non-invasive technique over-estimated the hepatic extraction ratio and thus underestimated liver blood flow. Therefore, in patients with liver disease the non-invasive method cannot be relied upon or replace hepatic vein catheterisation for the measurement of liver blood flow.     

Hemodynamic and liver function predictors of serum hyaluronan in alcoholic liver disease.

To define hepatic predictors of serum hyaluronan in patients with chronic liver disease, 62 patients with alcoholic liver disease were evaluated. In group 1, 30 patients had concurrent assessment of serum hyaluronan, liver function tests, Pugh grade and hemodynamic indices. A second, overlapping group of 42 patients (group 2) also had antipyrine clearance measured but without hemodynamic assessment. All but six patients had elevated serum hyaluronan levels. In both groups, serum hyaluronan levels differed between Pugh grades and, in each group, was significantly greater in Pugh grade C compared with those in Pugh grade A (p less than 0.05, Kruskal-Wallis test). When analyzed by correlation, serum hyaluronan was significantly associated with several indices in group 1, but on multivariate linear regression only three statistically independent predictors of serum hyaluronan were identified: serum albumin (p = 0.008), indocyanine green clearance (p = 0.024) and indocyanine green extraction (p = 0.036). The overall R2 for these correlates was 65%. In the second group, antipyrine clearance was not significantly associated with serum hyaluronan (r = 0.29, p = 0.06), but other associations were similar to the first group. On multivariate analysis, only serum albumin predicted serum hyaluronan (p less than 0.001; R2 = 43%). In conclusion, indices of hepatocyte synthetic function, sinusoidal blood flow and degree of intrahepatic shunting are independent predictors of serum hyaluronan in alcoholic liver disease. These data show the unique nature of serum hyaluronan and suggest its potential application to the assessment of acute hemodynamic changes in patients with liver disease.     

Antipyrine, oxazepam, and indocyanine green clearance in patients with chronic pancreatitis and healthy subjects.

BACKGROUND: Hepatic drug metabolism was examined in patients with chronic pancreatitis and healthy controls by using a cocktail design with three different model compounds: antipyrine to express phase-I oxidation, oxazepam to express phase-II conjugation, and indocyanine green (ICG), a high-clearance compound. METHODS: Eight patients with chronic pancreatitis and seven healthy controls participated. Patients were diagnosed by the presence of typical morphologic changes of the pancreas on imaging and had a moderately but significantly reduced exocrine function and no or only slight impairment of the glucose tolerance. No one had a history or clinical signs of liver disease. Clearance of the three model compounds was estimated after the administration of 1 g antipyrine and 15 mg oxazepam orally and a bolus of indocyanine green, 0.5 mg/kg body weight, intravenously. RESULTS: The antipyrine clearance and ICG clearance were significantly decreased in the patients compared with the controls (mean, 27.2 ml/min; 95% confidence interval (CI), 19.4-35; versus 46.2 ml/min; 34.7-58.7, and 501 ml/min; 4014601, versus 771 mU/min; 677-865 (P < 0.05), respectively). The oxazepam clearance did not differ significantly between the two groups (181 ml/min (145-217) versus 178 ml/min (152-204)). The model drug clearance ratios between the patient and control clearances showed decreased values for antipyrine and ICG compared with the oxazepam data (0.59 and 0.65 versus 1.02, respectively). Patients and controls were characterized by a body weight of 58.2 kg (53.1-63.3) and 83.4 kg (72.7-94.1), respectively, and a body mass index (BMI) of 19.6 kg/m2 (17.9-21.3) versus 25.9 kg/m2 (23.4-28.4) (P < 0.05 for both). CONCLUSIONS: Patients with chronic pancreatitis characterized by a moderately reduced exocrine function and absence of diabetes mellitus and overt liver disease had a decreased antipyrine oxidation and ICG clearance, whereas no difference was seen in oxazepam conjugation when compared with healthy volunteers. In chronic pancreatitis the hepatic phase-I oxidation is reduced compared with the phase-II conjugation, as shown by the model drug clearance ratios. The clearance of ICG was also affected, pointing at a reduced hepatic plasma flow, provided that the hepatic extraction fraction is normal for these patients.     

Effect of Triglycyl-Lysin-Vasopressin on Quantitative Liver Function Tests in Patients with Cirrhosis

The effects of vasopressin and of its analogues on liver function, and their possible mechanisms of action, are poorly understood. This study was designed to assess the effect of triglycyl-lysin-vasopressin on liver function, evaluated by two quantitative tests independent of liver blood flow, i.e., indocyanine green intrinsic hepatic clearance and galactose elimination capacity. Indocyanine green intrinsic hepatic clearance and galactose elimination capacity were determined before and after administration of 2 mg triglycyl-lysin-vasopressin to (respectively) 10 and 12 patients with cirrhosis. Eighteen additional patients with cirrhosis were studied before and after infusion of placebo. No significant variation in either test was observed in placebo-treated patients. A significant decrease in indocyanine green intrinsic hepatic clearance, averaging 22%, was observed in patients receiving the drug (p = 0.04). Conversely, galactose elimination capacity remained unchanged after the drug. These results are compatible with the hypothesis that the drug produced a preferential decrease in perfusion in functioning areas of the liver, with relative maintenance of blood flow in non-functioning areas.     

H2-receptor antagonists and hepatic drug disposition

The effect of four H2-receptor antagonists (cimetidine, burimamide, oxmetidine, and ranitidine) on antipyrine elimination was studied in the isolated perfused rat liver. The first three drugs are substituted imidazoles, whereas ranitidine contains a furanyl nucleus. Isolated livers were perfused using a 100-ml, recycling, constant flow circuit for 4 hr. Antipyrine elimination was studied with or without an H2-receptor antagonist present. In all experiments, antipyrine concentrations declined monoexponentially. In control experiments (no other drug present), antipyrine clearance was 32.5 +/- 0.9 ml per hr. This was greatly reduced in the presence of cimetidine (clearance = 10.1 +/- 0.8 and 5.8 +/- 1.5 ml per hr after 1 and 5 mg doses, p less than 0.01) and burimamide (4.5 +/- 0.6 and 3.0 +/- 1.7 ml per hr, p less than 0.001). By contrast, neither oxmetidine nor ranitidine significantly altered antipyrine pharmacokinetics. These results indicate that the inhibitory effect on hepatic mixed-function oxidases is rapid in onset, independent of H2-receptor antagonist activity, and is not an inevitable consequence of the presence of an imidazole nucleus.     

Antipyrine,Oxazepam, and Indocyanine Green Clearance in Patients with Chronic Pancreatitis and Healthy Subjects

Background: Hepatic drug metabolism was examined in patients with chronic pancreatitis and healthy controls by using a cocktail design with three different model compounds: antipyrine to express phase-I oxidation, oxazepam to express phase-II conjugation, and indocyanine green (ICG), a high-clearance compound. Methods: Eight patients with chronic pancreatitis and seven healthy controls participated. Patients were diagnosed by the presence of typical morphologic changes of the pancreas on imaging and had a moderately but significantly reduced exocrine function and no or only slight impairment of the glucose tolerance. No one had a history or clinical signs of liver disease. Clearance of the three model compounds was estimated after the administration of 1 g antipyrine and 15 mg oxazepam orally and a bolus of indocyanine green, 0.5 mg/kg body weight, intravenously. Results: The antipyrine clearance and ICG clearance were significantly decreased in the patients compared with the controls (mean, 27.2 ml/min; 95% confidence interval (CI), 19.4-35; versus 46.2 ml/min; 34.7-58.7, and 501 ml/min; 401-601, versus 771 ml/min; 677-865 (P &lt; 0.05), respectively). The oxazepam clearance did not differ significantly between the two groups (181 ml/min (145-217) versus 178 ml/min (152-204)). The model drug clearance ratios between the patient and control clearances showed decreased values for antipyrine and ICG compared with the oxazepam data (0.59 and 0.65 versus 1.02, respectively). Patients and controls were characterized by a body weight of 58.2 kg (53.1-63.3) and 83.4 kg (72.7-94.1), respectively, and a body mass index (BMI) of 19.6 kg/m² (17.9-21.3) versus 25.9 kg/m² (23.4-28.4) (P &lt; 0.05 for both). Conclusions: Patients with chronic pancreatitis characterized by a moderately reduced exocrine function and absence of diabetes mellitus and overt liver disease had a decreased antipyrine oxidation and ICG clearance, whereas no difference was seen in oxazepam conjugation when compared with healthy volunteers. In chronic pancreatitis the hepatic phase-I oxidation is reduced compared with the phase-II conjugation, as shown by the model drug clearance ratios. The clearance of ICG was also affected, pointing at a reduced hepatic plasma flow, provided that the hepatic extraction fraction is normal for these patients.     

Steady-state extrarenal sorbitol clearance as a measure of hepatic plasma flow

Hepatic plasma flow was assessed with sorbitol (hepatic extraction = 0.96) at steady state. After infusion of 50 mg/min for 3 h, total and renal sorbitol clearances were calculated, and the extrarenal clearance was obtained by taking the difference between the two. In normal volunteers, the mean (+/- SD) extrarenal sorbitol clearance was 10.6 +/- 2.1 ml/min.kg. In patients with various liver diseases, it was correlated more closely to the fractional clearance of indocyanine green (r = 0.83, n = 57) than the galactose elimination capacity (r = 0.66, n = 55). Hepatic vein catheterization showed that the hepatic extraction of sorbitol was always much higher than the extraction of indocyanine green; there was no evidence for extrahepatic, extrarenal sorbitol elimination. On the basis of these findings, sorbitol is kinetically superior to indocyanine green and, although the noninvasively determined extrarenal sorbitol clearance at steady state may not be equal to total hepatic plasma flow, it may at least be regarded as a measure of parenchymal liver plasma flow.     

Cimetidine and omeprazole have different effects on hepatic extraction of lidocaine in rats

The effect of two antisecretory drugs, omeprazole and cimetidine, on the hepatic extraction of indocyanine green and lidocaine was studied in the isolated perfused rat liver. Both indocyanine green and lidocaine are removed by the liver with high extraction efficiency in a flow-dependent manner. The elimination of lidocaine, but not indocyanine green, involves metabolism by the mixed-function oxidase in the liver. A selective effect on the hepatic extraction of lidocaine, but not indocyanine green, may therefore indicate an inhibition of hepatic mixed-function oxidase. To test this hypothesis, a nonrecycling system at a fixed perfusion flow rate was used to measure the extraction of lidocaine. Under control conditions, the extraction rate of lidocaine was 83% +/- 8%. In the presence of omeprazole at concentrations of 0.9, 2.0, and 4.5 micrograms/mL, the extraction rates were 81% +/- 9%, 82% +/- 7%, and 75% +/- 7%, respectively. These changes were not significantly different than control rates. In contrast, the increasing concentrations of cimetidine caused significant decreases in the hepatic extraction of lidocaine to values of 78% +/- 8%, 63% +/- 14%, and 48% +/- 14% at concentrations of 0.25, 0.50 and 1.25 micrograms/mL, respectively. The hepatic extraction of indocyanine green, 39% +/- 6%, was not affected by the administration of either omeprazole or cimetidine. Thus, in the rat, omeprazole seems to be a less potent inhibitor of cytochrome P-450 than cimetidine.     

Galactose clearance measurements and liver blood flow

Galactose clearance, measured during low galactose infusion and calculated as infusion rate divided by peripheral galactose concentration (systemic clearance), has been proposed as a measure of liver blood flow. This requires nearly complete hepatic extraction as well as negligible extrahepatic elimination. The purpose of the study was to examine if these assumptions are fulfilled in subjects with no liver disease, and to compare the galactose clearance measurement with an independent measurement of liver blood flow. Liver blood flow was measured in 6 subjects by means of a constant indocyanine green infusion, indocyanine green concentration measurements in a peripheral artery and a hepatic vein, and calculation according to Fick's principle. The mean (+/- SEM) blood flow rate was 1.2 +/- 0.1 L/min. Galactose was given at a constant infusion rate of 142 +/- 10 mumol/min, and steady-state concentrations were measured in the peripheral artery (A) and the hepatic vein (V). The hepatic extraction fraction [(A - V)/A] was 0.91 +/- 0.03. The hepatic galactose elimination rate [(A - V) X flow] was 101 +/- 12 mumol/min; this is about two-thirds of the total elimination rate (viz., infusion rate). Urinary excretion was negligible. This indicates an extrahepatic galactose elimination of approximately 41 mumol/min. Systemic galactose clearance, calculated as mentioned above, was 1.5 +/- 0.1 L blood/min. It was significantly higher than the liver blood flow in each subject (paired t-test, each p less than 0.02), on average 133% of the flow. Thus the systemic galactose clearance value overestimates liver blood flow, probably due to a small, but in this context quantitatively important, extrahepatic galactose elimination.     

Cimetidine impairs clearance of antipyrine and desmethyldiazepam in the elderly

Sixteen young (21-40 years) and nine elderly (65-78 years) volunteers received single intravenous doses of antipyrine on two occasions: once in the control state, and again while receiving therapeutic doses of cimetidine (300 mg every six hours). In the control state, antipyrine half-life was longer in elderly than in young subjects (16.4 vs 11.0 hours), and metabolic clearance lower (0.48 vs 0.72 ml/min/kg). However, coadministration of cimetidine prolonged antipyrine half-life to a similar extent in elderly and in young groups (150 and 153 per cent of control) and reduced metabolic clearance to a similar extent in both (79 vs 69 per cent of control) groups. Three young and six elderly volunteers received a single 15 mg oral dose of clorazepate, a precursor of desmethyldiazepam, with and without cimetidine. As in the case of antipyrine, cimetidine prolonged desmethyldiazepam half-life similarly in young and elderly groups (175 vs 164 per cent of control) and similarly reduced metabolic clearance (51 vs 65 per cent of control). The elderly population may already have an impaired capacity to oxidize drugs. This capacity is further impaired by coadministration of cimetidine.     

Increased sulfobromophthalein clearance in a patient receiving phenobarbital and other anticonvulsant drugs.

A marked increase in bromosulfophthalein, dibromosulfophthalein, and indocyanine green fractional clearance was found in a patient who had received phenobarbital for 30 years and other anticonvulsant agents for 6 years. This was related to a marked increase in hepatic blood flow, while hepatic extraction remained normal. These changes were associated with signs of hepatic microsomal enzyme induction (in particular a 2-fold increase in liver bilirubin UDP-glucuronyltransferase activity and hypertrophy of the smooth endoplasmic reticulum in the hepatocytes). Drug administration (especially phenobarbital) should be considered as a possible cause of increased bromosulfophthalein clearance in man.