Intravenous administration of diazepam in patients with chronic liver disease

An intensive drug monitoring study suggesting possible clinical irrelevance of impaired drug disposition in liver disease

1 Liver disease can alter the disposition and clinical effects of drugs. However, even though altered drug disposition occurs, there is no clinical evidence relating it to an increased susceptibility to adverse drug reactions (ADRs). 2 An intensive prospective drug monitoring study of 2,582 hospitalized patients was conducted. The adverse drug reactions probability scale (APS) was used to assess ADRs. Only non-mild, definite or probable ADRs (APS greater than or equal to 5) were included. Severity of liver dysfunction was assessed by a composite clinical and laboratory index (CCLI). 3 The frequency of ADRs was higher in 402 patients with cirrhosis (27.4%) than in 661 with renal dysfunction (22.8%) and in 249 with other parenchymatous liver diseases (13.7%) or in 1,270 patients with neither liver diseases nor renal dysfunction (10.9%) (chi 2 3 = 85.53, P less than 0.001). The frequency of ADRs in cirrhotics was highly correlated with the severity of the liver dysfunction measured by CCLI (r = 0.82, P less than 0.001). 4 Drugs predominantly eliminated by liver metabolism were not among those most commonly inducing ADRs or those causing severe reactions in cirrhotics. Thus, frusemide caused the most common and the most severe ADRs, whereas reactions induced by sedatives were uncommon. Drug-induced hepatic encephalopathy was more common in cirrhotics receiving diuretics (13.3%) than in those receiving sedatives (1.8%) (chi 2 y.c. = 5.29, P less than 0.025). Patients with alcoholic liver disease had more drug-induced hepatic encephalopathy (7.7%) than those with non-alcoholic liver disease (1.2%) (chi 2 y.c. = 11.86, P less than 0.001). 5 These results indicate that susceptibility to ADRs is increased only in severe cirrhosis and that the most common and severe ADRs seem more likely related to enhanced pharmacodynamic action than to impaired drug disposition.

Intravenous benzodiazepines as anaesthetic agents: pharmacokinetics and clinical consequences

Despite extensive and numerous pharmacokinetic studies on benzodiazepines, the published pharmacokinetic data do not adequately explain the clinical differences found between different benzodiazepine derivatives after intravenous administration. Especially, correlations between initial drug responses and distributional changes of the benzodiazepines are limited. However, during the elimination phase some relationships exist between the kinetic and dynamic phenomena. Age, sex, diseases and concomitantly given drugs cause clinically important alterations in the pharmacokinetics of benzodiazepines. Generally these anxiolytics and sedatives should be considered as adjuvants to general anaesthesia, but not primarily as routine induction agents. The major reasons for this limitation are a high variability in drug response, a relatively slow onset of action and long-lasting residual effects. However, benzodiazepines have many important advantages (see Table 5) when used as intravenous inducing agents of general anaesthesia.

Use of benzodiazepines during pregnancy, labour and lactation, with particular reference to pharmacokinetic considerations

Knowledge of the pharmacokinetic properties of the benzodiazepines is playing an increasingly important role in their use during pregnancy, labour and lactation. All of the benzodiazepine derivatives are lipophilic, undissociated agents which readily penetrate membranes. Thus, they exhibit rapid placental transfer with significant fetal uptake of the drug. In the first trimester of pregnancy there is seldom a clear indication for the use of benzodiazepines. In late pregnancy and at parturition there may be more clear indications for their use. During delivery, the lowest effective dose should be used, since after high doses the so-called 'floppy infant syndrome' may occur, and the slow elimination of these agents by the newborn should be considered. Oxazepam, lorazepam, nitrazepam and, especially, flunitrazepam, appear to penetrate the human placenta more slowly than diazepam, but the clinical significance of this phenomenon remains uncertain. All of these derivatives appear in human milk, but only high clinical doses might be expected to exert a possible effect on the nursing newborn.

Drugs as indicators of hepatic function

It is well recognized that liver disease may influence the disposition of many drugs. Conversely, it has been suggested that knowledge of the disposition of a model drug might provide an index of certain aspects of hepatic function. This review discusses the physiology of drug disposition and indicates how recent progress in understanding the determinants of drug disposition has provided useful indices of individual aspects of hepatic function. Topics which are discussed are the interpretation of pharmacokinetic parameters as indices of hepatic function, including half-life clearance, and intrinsic clearance. Utilizing the "intact hepatocyte hypothesis" as an operational model, an approach is described that uses the pharmacokinetic disposition of high and low intrinsic clearance drugs following p.o. and i.v. administration to provide quantitative estimates of hepatic function, flow to functioning hepatocytes, and the extent of portasystemic shunting through the liver. Thus, the theoretical basis for quantitation of certain aspects of hepatic function are available. It remains to be determined whether these indices will provide clinically useful measures to follow the natural history of hepatic disease.

Diurnal variations in plasma diazepam concentrations associated with reciprocal changes in free fraction

1 The characteristics and mechanism of fluctuations in diazepam and N-desmethyldiazepam concentrations and diazepam free fraction were studied in six volunteers, who received diazepam (10 mg, i.v. over 20 min) and in five chronic diazepam users. 2 Within a day total diazepam and N-desmethyldiazepam concentrations varied significantly (P less than 0.001) and were lower than predicted between 23.00 and 08.00 h and higher by 09.00 h. In contrast, diazepam free fraction also varied significantly (P less than 0.001) and was highest between 23.00 and 08.00 h and lower by 09.00 h. Coincident increases in total diazepam concentrations (P less than 0.005) and decreases in diazepam free fraction were associated with food intake (P less than 0.05). 3 The coincident diurnal variations in diazepam and N-desmethyldiazepam concentrations and the negative correlation between total diazepam concentration and diazepam free fraction (r = 0.73, P less than 0.001) suggest that the mechanism of the fluctuations is intravascular and tissue redistribution rather than effect on drug biotransformation. 4 These variations may introduce large between and within investigator experimental differences in the determination of kinetic parameters. Free drug concentration varies over the day, and within day variations in clinical effect may be observed.

Drug prescribing in hepatobiliary disease

Liver disease in man is associated with a variety of pathophysiological processes which may influence the disposition of drugs in several ways. Interpretation of the observed pharmacokinetic changes in liver disease requires an understanding of the relationship between systemic drug clearance (Cls), volume of distribution (Vd) and the elimination half-life [t1/2(beta)], i.e. t1/2(beta) = 0.693 . Vd/Cls. Half-life will be a measure of the fluctuation in drug level one may expect with continued administration of a drug while clearance will determine the dose required to achieve a particular steady state level. Liver disease may affect clearance and volume of distribution and so produce changes in half-life; in addition, alterations in plasma binding of drugs may occur and so influence free (unbound) drug levels. It is also possible that the end organ response, particularly in the case of sedative drugs, may be affected by liver disease. Other factors such as age, nutrition, smoking, and concomitant drug therapy may also influence drug elimination in patients with liver disease. At the present time, caution should be exercised in prescribing drugs to patients with liver disease and the dose should be titrated to the clinical response. The development of liver 'function' tests using model or marker drugs may offer some help to the prescriber in the future and enable a less empirical approach.

Some clinical features of liver cell failure: an appraisal of their causes

The mechanisms underlying the cause of the major clinical features of liver cell failure are reviewed. These include jaundice, fluid retention, hepatic encephalopathy, bleeding tendency, etc.