Alcohol biomarker screening in medical and surgical settings.

This article highlights the proceedings of a symposium presented at the 28th Annual Meeting of the Research Society on Alcoholism in Santa Barbara, CA, on June 28, 2005, organized and chaired by Peter Miller. The presentations included (1) Screening for Alcohol Use Disorders in Surgical and Trauma Patients, presented by Claudia Spies; (2) Are Serum Levels of %CDT and GGT Related to Severity of Liver Biopsy Inflammation, Fibrosis, and Steatohepatitis in Patients with Hepatitis C? by Martin Javors; (3) Biochemical Alcohol Screening in the Treatment of Hypertension, presented by Peter Miller; and (4) The Cost-Effectiveness of a New Biomarker, CDT, in a Primary Care Sample, by Michael Fleming. Presentations were discussed by Raymond Anton.

Review article: the pharmacokinetics of rabeprazole in health and disease.

Rabeprazole, a newly developed proton pump inhibitor, has been shown to be effective for the treatment of gastric and duodenal ulcers and for gastro-oesophageal reflux disease. It is a rapid and potent inhibitor of gastric H+,K(+)-ATPase, the gastric acid (proton) pump. The maximum plasma concentration (Cmax) and the area under the plasma concentration time curve (AUC) are linearly related to dose, while the time to maximum plasma concentration (tmax) and elimination half-life (t1/2) are dose-independent. Rabeprazole is extensively metabolized in the liver via the cytochrome P450 enzyme system, and its metabolites are excreted primarily in the urine. Rabeprazole does not accumulate with repeated dosing. Its bioavailability is not influenced by the coingestion of either food or antacids. The pharmacokinetic profile of rabeprazole is substantially altered in the elderly and patients with stable compensated chronic cirrhosis; however, these alterations are not associated with clinically significant abnormalities in laboratory parameters or serious adverse events. The influence of severe decompensated liver disease on the pharmacokinetics of rabeprazole has not been assessed. The pharmacokinetic profile of rabeprazole is not significantly altered by renal dysfunction requiring maintenance haemodialysis. These findings suggest that dosage adjustment is not required in these special patient populations. Caution should be exercised, however, in patients with severe liver disease.

Rabeprazole: pharmacokinetics in patients with stable, compensated cirrhosis.

This single-center, open-label study was undertaken to compare the tolerability and pharmacokinetic profiles of rabeprazole, a new proton-pump inhibitor (PPI), in healthy volunteers and in subjects with chronic cirrhosis. Thirteen healthy men and 10 men with stable, compensated cirrhosis documented by biopsy or liver/spleen scan received a single 20-mg rabeprazole dose. Blood samples were drawn before and up to 24 hours after drug administration for the determination of plasma rabeprazole concentrations using high-performance liquid chromatography. Adverse events, vital signs, electrocardiograms, physical findings, and clinical laboratory test results were monitored before and during treatment to determine how rabeprazole was tolerated. Chronic liver disease substantially altered the pharmacokinetic profile of rabeprazole. The maximum rabeprazole concentration (+/- SD) in subjects with cirrhosis (635+/-199 ng/mL) was approximately 50% higher than that in the healthy volunteers (401+/-246 ng/mL), and both area under the curve and elimination half-life were increased by approximately 100%. Oral clearance in subjects with cirrhosis was 38% of that in the healthy volunteers. Rabeprazole was well tolerated by both groups. Three subjects reported a total of 5 clinical adverse events that were judged as definitely or possibly related to rabeprazole treatment. Some minor changes in laboratory values were judged to be clinically insignificant. In patients with mild-to-moderate liver dysfunction, clearance of this PPI, as with other members of the class, was markedly reduced and plasma levels were increased. Although caution is always warranted in patients with severe liver disease, drug accumulation is unlikely with rabeprazole 20 mg once daily, and dose adjustment does not appear to be indicated in patients with mild-to-moderate liver dysfunction.

Thiamine-transfer by human placenta: normal transport and effects of ethanol.

Transport of "physiologic" concentrations of thiamine by the normal, term human placenta was studied by using the perfused cotyledon technique. Thiamine, 50 nmol/L, crossed from the maternal to fetal compartment at a rate somewhat below that of antipyrine, a freely diffusible marker drug. The transport was saturable and inhibited by structural analogues of thiamine, implying participation of carriers. Thiamine accumulated in the fetal compartment against a concentration gradient, suggesting active transport. Consistent with this, transfer of thiamine from the fetal to maternal compartment was significantly lower than in the opposite direction. The vitamin was concentrated in the placenta when compared with maternal and fetal levels. There was no evidence of phosphorylation of thiamine during its transfer. Exposure of the placenta to ethanol, 400 mg/dl, for up to 4 hours did not alter maternal-to-fetal transfer of the vitamin.

Effects of liver disease on the disposition of ciramadol in humans.

To determine the effects of liver disease on the disposition of ciramadol, an analgesic that undergoes ether glucuronidation, we studied its plasma pharmacokinetics in 10 patients with stable cirrhosis, 8 with acute viral hepatitis, and 16 age-matched healthy controls. Renal excretion of the glucuronides was also determined. In healthy controls given a single intravenous dose of the drug the t 1/2 was 3.4 +/- 0.3 hrs and the systemic clearance was 668 +/- 109 ml/min of which renal clearance was 320 +/- 73 ml/min and non-renal clearance 349 +/- 74 ml/min. The corresponding values after an oral dose were similar. Renal clearance was related directly to the estimated creatinine clearance. Moreover, the renal clearance of ciramadol exceeded creatinine clearance, suggesting that the drug was excreted not only by glomerular filtration but also by tubular secretion. The systemic clearance of intravenous ciramadol was diminished by 40% in cirrhosis, P less than 0.05, due to a reduction in renal clearance, while non-renal clearance remained normal. Renal clearance of the inactive glucuronides, on the other hand, was not affected. In patients with acute viral hepatitis, systemic clearance was unchanged, but renal clearance of ciramadol tended to increase during the acute phase of the disease and to return toward normal after recovery. Renal excretion of the inactive glucuronides was decreased by 48% (P less than .05). These findings suggest that the non-renal ether glucuronidation of ciramadol remains intact in patients with stable cirrhosis or acute viral hepatitis. However, the renal clearance of the drug may be impaired in cirrhosis, but tends to be enhanced in acute hepatitis.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of vitamin deficiencies in alcoholism.

Chronic alcoholic patients are frequently deficient in one or more vitamins. The deficiencies commonly involve folate, vitamin B6, thiamine, and vitamin A. Although inadequate dietary intake is a major cause of the vitamin deficiency, other possible mechanisms may also be involved. Alcoholism can affect the absorption, storage, metabolism, and activation of many of these vitamins. Possible factors which cause alterations in the absorption, storage, and metabolism of these vitamins are discussed. Suggestions for management of vitamin deficiencies in chronic alcoholics are also discussed.

Hepatic oxidative drug metabolism and the microsomal milieu in a rat model of congenital hyperbilirubinemia.

The aims of this study were to evaluate the hypothesis that impaired glucuronidation of bilirubin and possibly of drug oxidation in the liver of homozygous (jj) Gunn rats may be due to an altered microsomal milieu. Accordingly, we investigated and compared in vivo and in vitro demethylation of aminopyrine, hepatic cytochrome P-450 levels, microsomal lipid composition, and microsomal membrane fluidity in icteric, homozygous (jj) Gunn rats and in their anicteric heterozygous (jJ) littermates. In both males and females, [14C]aminopyrine demethylation in vivo, using the 14CO2 breath test, was unimpaired in the icteric animals. Likewise, cytochrome P-450 levels in the icteric and nonicteric groups were similar, and aminopyrine kinetics in vitro in the females were comparable in icteric and nonicteric littermates. The main lipid classes were also similar in the homozygous and heterozygous female Gunn rats, whereas only minor changes were seen in the phospholipid fatty acyl composition with a small, but significant, increase in the unsaturated index in the icteric group. Despite this, there was no apparent effect on hepatic microsomal membrane fluidity as measured by the order parameter of I[12,3] and the rotational correlation time of I[1,14] in either female or male sets of homozygous and heterozygous Gunn rats. Our data, therefore, do not support an alteration of composition or fluidity of the microsomal milieu as a mechanism of impaired bilirubin glucuronidation and possibly of oxidation in these animals. They also absolve long-term unconjugated hyperbilirubinemia as a mechanism of hepatic microsomal dysfunction. Our study, therefore, indirectly suggests that abnormal glucuronidation of bilirubin and some other aglycones in homozygous Gunn rats is due to genetic abnormalities involving the enzyme(s) itself.

Rapid ethanol elimination in patients with type I glycogen storage disease is an adaptive change resulting from recurrent hypoglycemia.

Patients with deficient activity of hepatic glucose-6-phosphatase (glycogen storage disease type I [GSD-I]) have fasting-induced hypoglycemia, lactic acidemia, hyperuricemia, hyperlipidemia, and a markedly increased capacity for ethanol elimination. The mechanism(s) responsible for the rapid ethanol elimination is not known but has been thought to be directly related to the enzyme defect. We postulated however, that the increased elimination of ethanol was an adaptive phenomenon that would revert toward normal with correction of other blood abnormalities by long-term maintenance of normal blood glucose concentration. Six patients were observed before treatment (group A), and four of the six were observed again 3 to 6 months after dietary treatment had normalized all blood abnormalities (group B). Patients received 16 ml/m2 absolute ethanol as a 5% solution in 0.9% sodium chloride over a 20-minute period. The rate of ethanol elimination was significantly greater (P less than 0.03) in group A than in group B (55.1 +/- 11.1 vs. 37.5 +/- 8.6 mg/dl/hr). Changes in lactate level after ethanol were also significant between the two groups (P less than 0.005). Group A showed a decrease from 9.4 +/- 0.5 to 6.4 +/- 0.4 mEq/L, whereas group B showed an increase in lactate level from 2.7 +/- 0.2 to 4.4 +/- 0.64 mEq/L. Ethanol induced no significant change in blood glucose concentration in group A, whereas there was a significant increase (P less than 0.03) in group B from 93 +/- 6 to 123 +/- 9 mg/dl.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Alcohol interactions with benzodiazepines and cocaine.

A rational management of alcoholic patients requires an understanding of alcohol interactions with other drugs. In this discussion, the influence of alcohol on benzodiazepine and cocaine metabolism is examined. The effect of alcohol may be indirect by producing liver disease and secondary impairment of drug metabolism, or direct following acute or chronic alcohol administration. The acute administration of alcohol suppresses the oxidative metabolism of chlordiazepoxide and diazepam and their principal metabolites. This finding may account partly for the enhanced psychomotor impairment following combined benzodiazepine-alcohol ingestion. The conjugation of lorazepam is also decreased, but for unclear reasons that of oxazepam remains normal. Data are insufficient to establish the effect of chronic alcohol administration on benzodiazepine disposition, especially in man. On the other hand, with respect to cocaine, chronic alcohol exposure causes induction of hepatic microsomal enzyme activity and enhances the production of metabolites that prove injurious to the liver, thereby augmenting the hepatotoxic effect of alcohol.

Inhibition of caffeine elimination by short-term ethanol administration.

Short-term ethanol ingestion has been shown to inhibit the metabolism of a number of drugs metabolized by cytochrome P-450 in both man and laboratory animals. However, the effects of short-term ethanol administration on the metabolism of cytochrome P-448-dependent drugs in man is unknown. Caffeine is a commonly used drug that is metabolized predominantly by a component of the hepatic microsomal mixed-function oxidase complex, known as cytochrome P-448. Therefore the elimination of caffeine given orally was studied in normal volunteers after receiving either orange juice or 0.8 gm/kg ethanol as a 25% solution in orange juice. Short-term administration of ethanol resulted in a significant decrease in the plasma clearance of caffeine from 96.6 +/- 13.4 ml/min to 60.7 +/- 10.5 (mean +/- S.E., p less than 0.05). There was also a corresponding significant increase in the elimination half-life of caffeine from 4.03 +/- 0.52 hr to 6.04 + 0.73 (mean + S.E., p less than 0.01). To determine whether the decrease in caffeine elimination was due to an inhibition of caffeine metabolism by ethanol or to an effect on caffeine absorption, caffeine disposition was studied in four healthy, mongrel dogs after intravenous administration. Each animal served as its own control. Caffeine clearance decreased significantly from a baseline value of 19.6 +/- 1.5 ml/min to 8.0 +/- 1.5 (mean +/- S.E., p less than 0.05) after administration of 3.0 gm/kg ethanol given orally 1 hr before intravenous caffeine injection. These results imply that short-term administration of ethanol inhibits the metabolism of caffeine, a predominantly cytochrome P-448-dependent substrate, in both man and dogs.