Pharmacokinetics and pharmacodynamics of intravenous midazolam in patients with severe alcoholic cirrhosis

Pharmacokinetic and Pharmacodynamic Characteristics of??Medications Used for Moderate Sedation

The ability to deliver safe and effective moderate sedation is crucial to the ability to perform invasive procedures. Sedative drugs should have a quick onset of action, provide rapid and clear-headed recovery, and be easy to administer and monitor. A number of drugs have been demonstrated to provide effective sedation for outpatient procedures but since each agent has its own limitations, a thorough knowledge of the available drugs is required to choose the appropriate drug, dose and/or combination regimen for individual patients. Midazolam, propofol, ketamine and sevoflurane are the most frequently used agents, and all have a quick onset of action and rapid recovery. The primary drawback of midazolam is the potential for accumulation of the drug, which can result in prolonged sedation and a hangover effect. The anaesthetics propofol and sevoflurane have recently been used for sedation in procedures of short duration. Although effective, these agents require monitored anaesthesia care. Ketamine is an effective agent, particularly in children, but there is concern regarding emergence reactions. AQUAVAN injection (fospropofol disodium), a phosphorylated prodrug of propofol, is an investigational agent possessing a unique and distinct pharmacokinetic and pharmacodynamic profile. Compared with propofol emulsion, AQUAVAN is associated with a slightly longer time to peak effect and a more prolonged pharmacodynamic effect. Advances in the delivery of sedation, including the development of new sedative agents, have the potential to further improve the provision of moderate sedation for a variety of invasive procedures.

Comparative population pharmacokinetics of lorazepam and midazolam during long-term continuous infusion in critically ill patients

AIMS

It is well established that there is a wide intra- and interindividual variability in dose requirements for lorazepam and midazolam in intensive care patients. The objective of this study was to compare the population pharmacokinetics of lorazepam and midazolam after long-term continuous infusion in mechanically ventilated critically ill patients.

METHODS

Forty-nine critically ill patients randomly received either lorazepam (n = 28) or midazolam (n = 21) by continuous infusion for at least 24 h. Multiple blood samples were obtained for determination of the drug and metabolite concentrations by HPLC. Population pharmacokinetic models were developed using the Non-Linear Mixed Effect Modelling (NONMEM) program. The influence of selected covariates was investigated. The prospective performance of the models was evaluated on the basis of results in separate groups of patients for lorazepam (n = 31) and midazolam (n = 33).

RESULTS

The pharmacokinetics of lorazepam were best described by a two-compartment model. Alcohol abuse, positive end expiratory pressure (PEEP) and age were identified as significant covariates. Total body clearance for patients without alcohol abuse was 4.13 - (PEEP - 5) x 0.42 l h-1, and 0.74 l h-1 for patients with alcohol abuse. The volume of distribution was 0.74 l, the steady state volume of distribution was 56 - (age - 58) x 2.1 l and the intercompartmental clearance was 10 l h-1. The proportional residual error was 15% and the median absolute prediction error was 13.6% with a bias of 1.5%. The pharmacokinetics of midazolam were best described by a two-compartment model with alcohol abuse, APACHE score and age as significant covariates. Total body clearance for patients without alcohol abuse was 11.3 - (age - 57) x 0.14 l h-1, and 7.27 - (age -57) x 0.14 l h-1 for patients with alcohol abuse. The volume of distribution was 7.15 l, the steady state volume of distribution was 431 l, and the intercompartmental clearance was 40.8 - (APACHE score - 26) x 2.75 l h-1. The proportional residual error was 31% with an additive residual error of 32 ng ml-1. The median absolute prediction error was 12.9% with a bias of 1.2%. The prospective performance in the lorazepam evaluation group was better with the covariate adjusted model, but in the midazolam evaluation group it was not better than with the simple model. In all models a tendency to overestimate the lower plasma concentrations was observed.

CONCLUSIONS

The pharmacokinetics of both lorazepam and midazolam were well described by a two-compartment model. Inclusion of alcohol abuse and age as covariates improved both models. PEEP was identified as an additional covariate for lorazepam, and the APACHE score for midazolam. For both drugs there is a large interindividual variability in their pharmacokinetics when used for long-term sedation in critically ill patients. However, the intra-individual variability is much lower for lorazepam.

Pharmacology and pharmacokinetics of sedatives and analgesics

The agents used for sedation and analgesia during endoscopy have complex pharmacokinetic and pharmacodynamic properties. Knowledge of these characteristics is necessary for determining the proper agent and dose for specific patient needs. Short-acting agents, such as fentanyl, midazolam, and propofol, provide rapid sedation with a short duration of action that allows patients to return to normal functioning rapidly. When designing a dosing regimen with these agents, age and organ (liver, kidney) function of patients and concomitant medications that may interfere with metabolic and elimination pathways must be considered.

Nurse-administered propofol versus midazolam and meperidine for upper endoscopy in cirrhotic patients

OBJECTIVES

Upper GI endoscopy is often performed in patients with chronic liver disease to screen for esophageal and gastric varices. Propofol is currently under evaluation as an alternative to the combination of midazolam and meperidine for sedation during endoscopic procedures. The purpose of this study was to compare nurse-administered propofol to midazolam and meperidine for sedation in patients with chronic liver disease undergoing diagnostic upper GI endoscopy.

METHODS

Twenty outpatients who had known chronic liver disease (Child-Pugh class A or B) and were undergoing variceal screening were randomized to receive propofol or midazolam plus meperidine for sedation. Administration of sedation was performed by a registered nurse and supervised by the endoscopist. Outcome measures studied were induction and recovery times, efficacy and safety of sedation, patient satisfaction, and return to baseline function.

RESULTS

The mean dose of propofol and meperidine/midazolam administered was 203 mg (SD 43.7, range 150-280) and 71.3 mg (SD 17.7, range 50-100)/5.3 mg (SD 0.9, range 3.0-6.0), respectively. The mean time to achieve adequate sedation was 3.6 min (SD 1.2) for the propofol group in comparison to 7.3 min (SD 2.8) for the meperidine/midazolam group (p<0.05). Procedure times between the groups were similar: propofol, 3.9 min (SD 1.9); midazolam/meperidine, 2.7 min (SD 0.8) (p=0.11). The level of sedation achieved by the propofol group was greater (p=0.0001). Time to full recovery was faster in the propofol group: 34.9 min (SD 10.3) versus 51.6 min (SD 18.4) (p<0.05). The mean time to reach a maximal level of alertness on the Observer's Assessment of Alertness and Sedation Scale for the propofol group was 15 min (SD 3.6) versus 29 min (SD 10.5) (p=0.001). Although both groups recorded a high level of satisfaction, patients receiving propofol expressed greater overall mean satisfaction with the quality of their sedation at the time of discharge (p<0.05), and reported a return to baseline function sooner in the majority of cases. Propofol achieved comparable levels of efficacy and safety to meperidine/midazolam in our study group. Both were well tolerated with minimal complications.

CONCLUSIONS

Propofol sedation administered by registered nurses in the setting of adequate patient monitoring is efficacious and well tolerated in patients with liver disease who are undergoing variceal screening by upper endoscopy. Patients were more satisfied with the quality of sedation, and return to baseline function was usually sooner compared to results achieved with midazolam/meperidine. Propofol offers advantages over meperidine/midazolam in cirrhotic patients.

Human variability in CYP3A4 metabolism and CYP3A4-related uncertainty factors for risk assessment

CYP3A4 constitutes the major liver cytochrome P450 isoenzyme and is responsible for the oxidation of more than 50% of all known drugs. Human variability in kinetics for this pathway has been quantified using a database of 15 compounds metabolised extensively (>60%) by this CYP isoform in order to develop CYP3A4-related uncertainty factors for the risk assessment of environmental contaminants handled via this route. Data were analysed from published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and other subgroups using parameters relating primarily to chronic exposure [metabolic and total clearances, area under the plasma concentration-time curve (AUC)] and acute exposure (Cmax). Interindividual variability in kinetics was greater for the oral route (46%, 12 compounds) than for the intravenous route (32%, 14 compounds). The physiological and molecular basis for the difference between these two routes of exposure is discussed. In relation to the uncertainty factors used for risk assessment, the default kinetic factor of 3.16 would be adequate for adults, whereas a CYP3A4-related factor of 12 would be required to cover up to 99% of neonates, which have lower CYP3A4 activity.

Intestinal first pass metabolism of midazolam in liver cirrhosis --effect of grapefruit juice

AIMS

Grapefruit juice inhibits CYP3A4 in the intestinal wall leading to a reduced intestinal first pass metabolism and thereby an increased oral bioavailability of certain drugs. For example, it has been shown that the oral bioavailability of midazolam, a CYP3A4 substrate, increased by 52% in healthy subjects after ingestion of grapefruit juice. However, this interaction has not been studied in patients with impaired liver function. Accordingly, the effect of grapefruit juice on the AUC of midazolam and the metabolite alpha-hydroxymidazolam was studied in patients with cirrhosis of the liver.

METHODS

An open randomized two-way crossover study was performed. Ten patients (3 females, 7 males) with liver cirrhosis based on biopsy or clinical criteria participated. Six patients had a Child-Pugh score of A, one B and three C. Tap water (200 ml) or grapefruit juice were consumed 60 and 15 min before midazolam (15 mg) was administered orally. Plasma samples were analysed for midazolam and alpha-hydroxymidazolam.

RESULTS

Grapefruit juice increased the AUC of midazolam by 106% (16, 197%) (mean (95% confidence interval)) and the AUC of the metabolite alpha-hydroxymidazolam decreased to 25% (12, 37%) (P<0.05 for both). The ratio of the AUCs of the metabolite alpha-hydroxymidazolam to midazolam decreased from 0.77 (0.46, 1.07) to 0.11 (0.05, 0.19) (P<0.05). t(1/2) remained unaltered for both drug and metabolite. Midazolam C(max), t(max), and alpha-hydroxymidazolam t(max) increased, but these changes were not statistically significant, whereas C(max) of the metabolite decreased to 30% (14, 47%) (P<0.05).

CONCLUSIONS

A marked interaction between oral midazolam and grapefruit juice was found and the data are consistent with a reduced first-pass metabolism of midazolam. This is likely to occur at the intestinal wall inhibition of CYP3A4 activity by grapefruit juice. These results indicate that patients with liver cirrhosis are more dependent on the intestine for metabolism of CYP3A4 substrates than subjects with normal liver function.

Impairment of psychomotor responses after conscious sedation in cirrhotic patients undergoing therapeutic upper GI endoscopy

OBJECTIVES

The aim of this study was to determine whether the number connection test (NCT) times of a group of cirrhotic patients without clinically overt hepatic encephalopathy and a group of healthy patients without liver disease who were undergoing endoscopy were prolonged after sedation with short acting i.v. benzodiazepines.

METHODS

All patients were administered the NCT in a standard fashion for 30 min before sedation for an upper GI endoscopy and then 2 h after sedation postprocedure. Two NCTs were carried out before and 2 h after sedation, and the mean of the tests pre- and postsedation calculated. Based on the upper limit of the 95% CI of the presedation NCT of patients without liver disease as the cut-off level for hepatic encephalopathy, the proportion of cirrhotic patients with subclinical encephalopathy before and after sedation were also determined.

RESULTS

A total of 61 consecutive cirrhotic patients who underwent therapeutic upper GI endoscopy completed the study. The mean presedation NCT time was 43.5 s (95% CI = 39.0-48.1 s) and the mean postsedation NCT time 60.0 s (95% CI = 50.7-69.3 s). The difference between the mean pre- and postsedation NCT times was 16.4 s (95% CI = 9.8-23.1 s; p < 0.001). A total of 38 consecutive patients without clinical or biochemical evidence of liver disease who presented for upper GI endoscopy completed the NCT as described for the group of cirrhotic patients. The mean (+/- SD) baseline NCT time was 34.7+/-7.9 s (95% CI = 32.1-37.2 s), whereas the mean postsedation NCT time was 33.7+/-8.5 s (95% CI = 30.9-36.5 s). This difference was not statistically significant (p = 0.177). Using the upper limit of the 95% CI of the mean (37.4 s) of the presedation time in the patients without liver disease as the cut-off between normal and encephalopathy, the number of cirrhotic patients with abnormal presedation NCT times was 33 patients (54.1%), and this number rose to 46 patients (75.4%) after sedation with midazolam. This increase in proportion of cirrhotic patients with prolonged NCT time was statistically significant (p < 0.001).

When midazolam fails

Significant distress is experienced by patients, families, and caregivers when a symptom or disorder, such as an agitated delirium, becomes an intractable, or a catastrophic event, such as irreversible stridor. When palliative sedation is indicated for these patients, midazolam is usually the preferred drug. In some cases, however, midazolam fails to provide adequate sedation. Two cases are presented to illustrate this phenomenon and explore the possible mechanisms underlying this lack of response. These mechanisms appear to be multifaceted. The heterogeneity of the GABA(A) receptor complex and the alterations that this complex can undergo functionally can explain, to some degree, the diversity of the physiological and pharmacological outcomes. Other factors responsible for the diversity in response may include concomitant medications, age, concurrent disease, overall health status, alcohol use, liver disease, renal disease, smoking and hormonal status. Evidence-based guidelines on alternative treatment options should midazolam fail are required. In the interim, a lower threshold for adding an alternative drug, such as phenobarbital, or substituting midazolam with another drug, such as propofol, should be considered in these circumstances.

Correlation between midazolam and lignocaine pharmacokinetics and MEGX formation in healthy volunteers

AIMS

The objectives of the present investigation were: (a) to determine the correlation between lignocaine and midazolam pharmacokinetics following intravenous administration in healthy volunteers, (b) to determine the effects of treatment with an inhibitor of CYP3A4 (erythromycin) on this correlation and (c) to assess the precision of the MEGX-test as a sole predictor of lignocaine and midazolam pharmacokinetics.

METHODS

The study was conducted in four male and four female healthy volunteers, aged between 21 and 26 years, who received 1 mg kg-1 lignocaine HCl i.v. on days 1, 3, 5, 9 and 10 of the investigation. On days 5 and 10 they also received midazolam, 0.075 mg kg-1 i.v. and from days 6-10 they took erythromycin 500 mg orally, four times daily. Following administration of lignocaine and midazolam, frequent venous blood samples were obtained for determination of the concentrations of lignocaine, MEGX and midazolam.

RESULTS

In the absence of erythromycin a statistically significant linear correlation was observed between the clearance of lignocaine and midazolam (CL(midazolam)= 0.41 x CL(lignocaine)+ 1.2; r(2) = 0.857; P < 0.001). Erythromycin cotreatment resulted in a loss of the correlation between the two clearances (r(2) = 0.39; P = 0.1). Erythromycin caused a statistically significant reduction in midazolam clearance from the original value of 3.8 to 2.5 (95% CI for the difference -2.27, -0.35) ml kg-1 min-1. Interestingly there was no significant change in the clearance of lignocaine (6.4 vs 5.8 (95% CI for the difference -2.74, -1.51) ml kg-1 min-1). Furthermore no correlation at all was observed between the MEGX-test and lignocaine or midazolam clearances. Considering the data on day 1, 3 and 5 the intra-individual coefficient of variation in the MEGX-test was 45.3% at 15 min and 23.5% at 30 min, respectively.

CONCLUSIONS

It is concluded that there is a significant correlation between lignocaine and midazolam clearances but this correlation is lost after CYP3A4 inhibition by erythromycin. The MEGX-test is of no value in assessing intra- and inter-individual variability in midazolam clearance.

Sedation for endoscopy

A review of the recent literature reveals an increasing published opinion in favour of unsedated endoscopy. However, recent studies show that the majority of US patients are unwilling or unable to tolerate this. In order for there to be a shift towards unsedated endoscopy, physicians will have to change patients' expectations. The indications for diagnostic and therapeutic endoscopic procedures continue to expand, involving increasingly complex techniques that require a high degree of patient cooperation. There is still a need to refine the sedative regimen for these cases.

Effects of liver disease on pharmacokinetics. An update

Liver disease can modify the kinetics of drugs biotransformed by the liver. This review updates recent developments in this field, with particular emphasis on cytochrome P450 (CYP). CYP is a rapidly expanding area in clinical pharmacology. The information currently available on specific isoforms involved in drug metabolism has increased tremendously over the latest years, but knowledge remains incomplete. Studies on the effects of liver disease on specific isoenzymes of CYP have shown that some isoforms are more susceptible than others to liver disease. A detailed knowledge of the particular isoenzyme involved in the metabolism of a drug and the impact of liver disease on that enzyme can provide a rational basis for dosage adjustment in patients with hepatic impairment. The capacity of the liver to metabolise drugs depends on hepatic blood flow and liver enzyme activity, both of which can be affected by liver disease. In addition, liver failure can influence the binding of a drug to plasma proteins. These changes can occur alone or in combination; when they coexist their effect on drug kinetics is synergistic, not simply additive. The kinetics of drugs with a low hepatic extraction are sensitive to hepatic failure rather than to liver blood flow changes, but drugs having a significant first-pass effect are sensitive to alterations in hepatic blood flow. The drugs examined in this review are: cardiovascular agents (angiotensin converting enzyme inhibitors, angiotensin II receptor antagonists, calcium antagonists, ketanserin, antiarrhythmics and hypolipidaemics), diuretics (torasemide), psychoactive and anticonvulsant agents (benzodiazepines, flumazenil, antidepressants and tiagabine), antiemetics (metoclopramide and serotonin antagonists), antiulcers (acid pump inhibitors), anti-infectives and antiretroviral agents (grepafloxacin, ornidazole, pefloxacin, stavudine and zidovudine), immunosuppressants (cyclosporin and tacrolimus), naltrexone, tolcapone and toremifene. According to the available data, the kinetics of many drugs are altered by liver disease to an extent that requires dosage adjustment; the problem is to quantify the required changes. Obviously, this requires the evaluation of the degree of hepatic impairment. At present there is no satisfactory test that gives a quantitative measure of liver function and its impairment. A critical evaluation of these methods is provided. Guidelines providing a rational basis for dosage adjustment are illustrated. Finally, it is important to consider that liver disease not only affects pharmacokinetics but also pharmacodynamics. This review also examines drugs with altered pharmacodynamics.

Low-dose midazolam sedation: an option for patients undergoing serial hepatic venous pressure measurements

The hepatic venous pressure gradient (HVPG) is becoming increasingly used clinically. It is useful in the differential diagnosis of portal hypertension and provides a prognostic index in cirrhotic patients. Performance of serial measurements has been shown to be useful in guiding pharmacological therapy of portal hypertension and variceal hemorrhage. The technique is safe to perform; however, many patients are anxious and reluctant to undergo serial measurements. The effects of sedatives on portal pressure measurements have not yet been defined. The objective of this study was to evaluate the effects of midazolam on the HVPG. Twenty patients with compensated cirrhosis were included in this prospective, double-blind study. The HVPG was determined by subtracting the free hepatic venous pressure (FHVP) from the wedged hepatic venous pressure (WHVP). Patients were randomized to receive either placebo, 0.02 mg/kg midazolam, or 0.03 mg/kg midazolam, administered intravenously over 3 minutes. Immediately after drug administration and every 3 minutes thereafter, for a total of 30 or 40 minutes, measurements were repeated. Three hours later, patients were asked to state whether the sedative affected their state of comfort/relaxation. The effects of both doses of midazolam on HVPG did not differ significantly from those of placebo. Furthermore, neither dose of midazolam induced significant changes in HVPG as compared with baseline values. However, higher-dose midazolam (0.03 mg/kg) was associated with significant reductions in FHVP from baseline and a tendency for a reduction in WHVP. Both doses significantly increased patient comfort and relaxation during the test. Midazolam, used at a dose of 0.02 mg/kg, is effective in increasing patient comfort and relaxation during hepatic venous pressure measurements, without significantly affecting pressures (HVPG, WHVP, or FHVP). It is therefore an acceptable option for patients undergoing serial hepatic venous pressure measurements.

Effect of hepatic insufficiency on pharmacokinetics and drug dosing

The liver plays a central role in the pharmacokinetics of many drugs. Liver dysfunction may not only reduce the plasma clearance of a number of drugs eliminated by biotransformation and/or biliary excretion, but it can also affect plasma protein binding which in turn could influence the processes of distribution and elimination. In addition, reduced liver blood flow in patients with chronic liver disease will decrease the systemic clearance of flow limited (high extraction) drugs and portal-systemic shunting may substantially reduce their presystemic elimination (first-pass effect) following oral administration. When selecting a drug and its dosage regimen for a patient with liver disease additional considerations such as altered pharmacodynamics and impaired renal excretion (hepatorenal syndrome) of drugs and metabolites should also be taken into account. Consequently, dosage reduction is necessary for many drugs administered to patients with chronic liver disease such as liver cirrhosis.

In vitro and in vivo drug interactions involving human CYP3A

Cytochrome P4503A (CYP3A) is importantly involved in the metabolism of many chemically diverse drugs administered to humans. Moreover, its localization in high amounts both in the small intestinal epithelium and liver makes it a major contributor to presystemic elimination following oral drug administration. Drug interactions involving enzyme inhibition or induction are common following the coadministration of two or more CYP3A substrates. Studies using in vitro preparations are useful in identifying such potential interactions and possibly permitting extrapolation of in vitro findings to the likely in vivo situation. Even if accurate quantitative predictions cannot be made, several classes of drugs can be expected to result in a drug interaction based on clinical experience. In many instances, the extent of such drug interactions is sufficiently pronounced to contraindicate the therapeutic use of the involved drugs.

Pharmacokinetics of drugs used in critically ill adults

Critically ill patients exhibit a range of organ dysfunctions and often require treatment with a variety of drugs including sedatives, analgesics, neuromuscular blockers, antimicrobials, inotropes and gastric acid suppressants. Understanding how organ dysfunction can alter the pharmacokinetics of drugs is a vital aspect of therapy in this patient group. Many drugs will need to be given intravenously because of gastrointestinal failure. For those occasions on which the oral route is possible, bioavailability may be altered by hypomotility, changes in gastrointestinal pH and enteral feeding. Hepatic and renal dysfunction are the primary determinants of drug clearance, and hence of steady-state drug concentrations, and of efficacy and toxicity in the individual patient. Oxidative metabolism is the main clearance mechanism for many drugs and there is increasing recognition of the importance of decreased activity of the hepatic cytochrome P450 system in critically ill patients. Renal failure is equally important with both filtration and secretion clearance mechanisms being required for the removal of parent drugs and their active metabolites. Changes in the steady-state volume of distribution are often secondary to renal failure and may lower the effective drug concentrations in the body. Failure of the central nervous system, muscle, the endothelial system and endocrine system may also affect the pharmacokinetics of specific drugs. Time-dependency of alterations in pharmacokinetic parameters is well documented for some drugs. Understanding the underlying pathophysiology in the critically ill and applying pharmacokinetic principles in selection of drug and dose regimen is, therefore, crucial to optimising the pharmacodynamic response and outcome.

Drug administration in chronic liver disease

Cirrhosis encompasses a range of pathophysiological changes that may alter drug disposition. Drugs that are dependent primarily on the liver for their systemic clearance are more likely to be subject to reduced elimination and subsequent accumulation. Drug accumulation may lead to excessive plasma drug concentrations and adverse effects, if the adverse effects of the drug are concentration-dependent. The effects of hepatic insufficiency on the pharmacokinetics of drugs are not consistent or predictable. Furthermore, the influence of hepatic disease on the disposition of various drugs can vary, even though those drugs may share the same apparent metabolic pathway. Problems in forecasting drug kinetic behaviour are further enhanced by the additional impairment of kidney function (frequently encountered in patients with advanced liver disease) and by the unpredictability of the glomerular filtration rate using customary methods in patients with cirrhosis. Accordingly, dosages are generally adapted empirically, with the help of serum drug concentrations, when applicable. However, drugs eliminated predominantly by hepatic metabolism are not among those most commonly inducing adverse drug reactions or causing severe complications in patients with cirrhosis. Electrolyte disturbances and the hepatorenal syndrome produced by furosemide (frusemide)-the disposition of which is not substantially modified in liver disease-appear to be the most frequent adverse drug reactions in patients with liver disease. Furthermore, clinically significant alterations in the action of medications at concentrations generally considered to be in the normal therapeutic range are not uncommon. Tissue responsiveness to the pharmacological action of some drugs may be modified, as evidenced by the increased susceptibility of the brain in patients with cirrhosis to the action of many psychoactive agents. Another example is the greater susceptibility of such patients to the nephrotoxic potential of aminogly-cosides, which should not be used in this patient group. Drugs may also interfere with adaptive physiological processes induced by liver disease. ACE inhibitors and nonsteroidal anti-inflammatory drugs counteract the enhanced activity of the renin-angiotensin system in advanced liver disease, thereby generating a high risk of excessive hypotension or acute renal failure, respectively. These drugs are best avoided in patients with cirrhosis. Finally, there may be pharmacological effects that overlap with some pathophysiological modifications related to the process of liver disease, such as increased portal pressure produced by some calcium antagonists, or hypoprothrombinaemia related to the inhibition of synthesis of vitamin K-dependent clotting factors by some beta-lactam antibacterials (especially moxalactam and cefamandole). Accordingly, the use of these drugs should be avoided in advanced liver disease. It is noteworthy that reduced drug metabolism in patients with liver disease does not seem to have a significant impact on the frequency of hepatotoxicity. Special caution should be exercised, however, in patients with alcoholic liver disease because excessive alcohol intake may potentiate the hepatotoxic effect of paracetamol (acetaminophen).

Pharmacokinetics and pharmacodynamics of midazolam given via continuous intravenous infusion in intensive care units

Critically ill patients often benefit from sedation to optimize their care and their ventilatory support. Ideally, incremental doses of a drug are administered to produce the desired level of sedation without toxicity or overdose. Because metabolism and elimination of drugs are often altered in critically ill patients, knowledge of the pharmacokinetics of sedative hypnotics is essential to ensure their appropriate selection and administration. Furthermore, the administration of sedatives via continuous infusion minimizes fluctuations in drug concentrations and permits more consistent control of the patient's agitation and anxiety. Physician preference and the patient's individual requirements and underlying diseases are the primary determinants for the selection of a given sedative. Benzodiazepines are the most commonly used sedatives in critical care. Midazolam is readily distinguished from other benzodiazepines because of its rapid onset and short duration of action, low incidence of thrombophlebitis and pain on injection, and minimal cardiovascular and respiratory effects. The physiochemical properties of midazolam allow for enhanced water solubility, which limits physicochemical incompatibilities. These properties make midazolam a valuable sedative that can be given via continuous intravenous infusion in the intensive care unit.

Sedation during Artificial Ventilation by Continuous Intravenous Infusion of Midazolam: Effects of Hepatocellular or Renal Damage

To evaluate the effects of hepatocellular or renal damage on therapeutic doses of midazolam and emergence time after withdrawal of the drug, 87 patients under continuous sedation with midazolam on artificial ventilation were prospectively studied. They needed continuous sedation for 12 hours or more. They included 55 patients with normal hepatocellular and renal functions (C group), 21 patients with hepatocellular damage (II group), and 11 patients with hepatocellular and renal damage (HR group). Midazolam was initiated with an intravenous dose of 0.1 mg/kg followed by 0.05 mg/kg/hr. Dosage was regulated to maintain a state in which patients responded to verbal command and had bucking responses to endotracheal suctioning. The three groups were compared with respect to midazolam dosage, emergence time, aspartate aminotransferase (AST), alanine aminotransferase (ALT), blood urea nitrogen (BUN), and creatinine (Cr) levels and urine volume. The mean doses of midazolam in the C, H, and HR groups were 0.083 ± 0.038 mg/kg/hr, (mean ± standard deviation) 0.073 ± 0.037 mg/kg/hr, and 0.088 ± 0.048 mg/kg/hr, respectively, showing no differences among these groups. Emergence time was significantly longer in the H group (333 ± 263 min; p < 0.005) and the HR group (305 ± 225 min; p < 0.025) than in the C group (171 ± 106 min). No effect of midazolam administration was seen on AST, ALT, BUN, Cr, and urine volume in all groups. In conclusion, presence of hepatocellular or renal damage did not alter required dosage of midazolam. Hepatocellular damage prolonged emergence time, but renal damage had no more additive effect. There was no evidence of hepatocellular and renal damages during treatment.

What changes drug metabolism in critically ill patients--III? Effect of pre-existing disease on the metabolism of midazolam

Liver samples were obtained at hepatectomy from patients with end stage alcoholic liver disease (n = 5), primary biliary cirrhosis (n = 5) and chronic rejection needing retransplantation (n = 5). Normal liver material was also obtained from five organ donors. From these samples microsomes were made containing cytochrome P450 3A. The amount of this enzyme was measured by Western immunoblotting and its function assessed by measuring the rate of production of two metabolites of midazolam, 1-hydroxy midazolam and 4-hydroxy midazolam. There was a wide range in all groups for both the expression and function of this enzyme. Liver tissue affected by cirrhotic disease showed greater preservation of enzyme function than that affected by hepatocellular disease. There was a good correlation between the expression of the enzyme and production of the 1-hydroxy metabolite, but a poor correlation between production of the 4-hydroxy metabolite and expression. This poor correlation may reflect the failure to measure the specific enzyme responsible for producing 4-hydroxy midazolam.

Plasma concentrations of midazolam during continuous subcutaneous administration in palliative care

We have investigated the steady-state plasma concentrations of midazolam during continuous subcutaneous administration in palliative care. Using a sensitive gas chromatography with electron capture detector assay, plasma concentrations of midazolam were measured in 11 patients (median age 68 years; range 47-82 years; six females) receiving the drug by continuous subcutaneous infusion (median rate 20 mg/day; range 10-60 mg/day). While not significant, the infusion rate tended to decrease with increasing age of the patient (Spearman's p = -0.51; p = 0.11). The steady-state plasma concentration range was 10-147 ng/ml, with a median of 30 ng/ml. Infusion rates and plasma concentrations of midazolam were correlated (Spearman's p = 0.71; p < 0.05). No other significant relationships were found between plasma concentrations and the variables of age, sex and liver function.

Review article: premedication and intravenous sedation for upper gastrointestinal endoscopy

Upper gastrointestinal endoscopy can be performed without intravenous sedation but the evidence suggests that, in the United Kingdom and United States, most patients and endoscopists prefer that some form of premedication is given. Intravenous diazepam or midazolam are used by the majority of endoscopists. In the UK, the ratio of diazepam to midazolam users is approximately 2:1, while in the USA more endoscopists are now using midazolam. Midazolam is approximately twice as potent as diazepam but, when allowance is made for this, there is probably little or no difference in the propensity of the two drugs to produce respiratory depression. The antegrade amnesic effect of midazolam is significantly superior to that of diazepam. A benzodiazepine/narcotic combination can achieve a smoother and more rapid induction with less gagging and choking, but the incidence of adverse outcomes--particularly respiratory depression--is increased significantly. Over 50% of the deaths that are associated with upper gastrointestinal endoscopy are due to cardiopulmonary problems. Hypoxia is very common if measured using non-invasive monitoring equipment, such as a pulse oximeter. Methods of preventing oxygen desaturation and thus, by inference, most cardiac arrhythmias associated with endoscopy are discussed, as is the role of flumazenil, the new benzodiazepine antagonist.

Midazolam versus diazepam for combined esophogastroduodenoscopy and colonoscopy

This study compares the effects of two different benzodiazepines used for conscious sedation during combined upper gastrointestinal endoscopy (EGD) and colonoscopy. Subjects were assessed for their degree of analgesia and amnesia for the procedure, prior experience with endoscopy, and willingness to undergo another similar procedure should such be necessary. The patients were randomized single blind to receive either midazolam or diazepam for their preprocedure sedation. The amount of preprocedure sedation utilized was determined by titration of the dose to achieve slurring of speech. Prior to receiving either agent, the subjects were shown a standard card containing pictures of 10 common objects, were asked to name and remember them, and were told they would be "quizzed" (at 30 min and 24 hr) after being sedated for their recollection as to the objects pictured on the card. Each subject filled out a questionnaire addressing their perceived discomfort during the endoscopic procedure and their memory of the procedure 24 hr after the procedure. Sixty-three percent of the midazolam-sedated subjects reported total amnesia for their colonoscopy vs 20% of diazepam-sedated patients (P less than 0.001). Fifty-three percent of midazolam-sedated patients reported total amnesia of their upper gastrointestinal endoscopy vs only 23% of diazepam-sedated subjects (P less than 0.05). The midazolam-sedated subjects reported experiencing less pain with both upper gastrointestinal endoscopy (P less than 0.05) and colonoscopy (P less than 0.001) than did the diazepam-sedated group. Most importantly, the midazolam group was more willing to undergo another similar endoscopic procedure should they be asked to do so by their physician (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics of the newer benzodiazepines

The assay methods used to determine the concentrations of the newer benzodiazepines include electron-capture gas-liquid chromatography, high performance liquid chromatography with ultraviolet detection, gas chromatography-mass spectrometry, radioassay and radioreceptor assay. The method used frequently is the highly sensitive and specific electron-capture gas-liquid chromatography. Other methods are associated with limitations. The triazolo- and imidazolebenzodiazepines differ structurally from the 'classical' benzodiazepines such as diazepam, and offer distinct differences in pharmacological activity and in time-course of effect. Alprazolam and triazolam, both 1,4-triazolobenzodiazepines, have high affinities for the benzodiazepine receptor as do midazolam and loprazolam, which are 1,4-imidazolebenzodiazepines. Absorption is characteristically rapid, with peak alprazolam and triazolam concentrations occurring within 1 hour after oral administration. Sublingual administration results in peak alprazolam and triazolam concentrations that are higher and occur earlier than with the oral route. The volume of distribution of alprazolam and triazolam is approximately 1L. Alprazolam is 70% bound to plasma proteins and the extent of binding is independent of concentration. Similarly, triazolam is approximately 85% bound to plasma proteins, variability in binding being explained by variations in alpha 1-acid glycoprotein concentration. The 1,4-triazolo ring prevents the oxidative metabolism of the classical benzodiazepines which results in formation of active metabolites with long elimination half-lives. Alprazolam is extensively metabolised: 29 metabolites have been identified in the urine, and its major metabolite, alpha-hydroxyalprazolam, has pharmacological activity. alpha-Hydroxyalprazolam and 4-hydroxyalprazolam are detectable in plasma in amounts which account for less than 10% of the administered dose. Mean alprazolam elimination half-life in healthy adult subjects ranges from 9.5 to 12 hours; liver disease prolongs alprazolam elimination, but renal insufficiency does not. Triazolam also undergoes oxidation and subsequent glucuronidation. alpha-Hydroxytriazolam is the major metabolite, in addition to which 4-hydroxyalprazolam and alpha-4-hydroxytriazolam have been identified in plasma and urine. The elimination half-life of triazolam ranges between 1.8 and 5.9 hours, while that of the conjugated metabolites is short, approximately 3.8 hours. Accumulation of triazolam or its metabolites after multiple doses does not occur. Liver disease prolongs triazolam elimination from the body, but renal disease does not.(ABSTRACT TRUNCATED AT 400 WORDS)

Sedation for dermatologic surgery

This review focuses on some of the most common classes of parenteral and inhalational sedating agents used during cutaneous surgery. Emphasis also is placed on potential adverse effects and their treatments.

The pharmacokinetics of midazolam following orthotopic liver transplantation

Seven patients with chronic liver disease received a 10 mg intravenous bolus dose of midazolam immediately following orthotopic liver transplantation. Plasma samples were analysed for midazolam and alpha-hydroxymidazolam by gas chromatography with electron capture detection. Data from three patients could not be evaluated. In the remaining four patients the pharmacokinetics of midazolam were essentially normal but the plasma concentrations of alpha-hydroxy-midazolam were higher than those found in healthy subjects. All patients required further sedation between 0.5 and 5 h later indicating that the duration of action of midazolam was not prolonged. These results suggest that following liver transplantation, patients have considerable drug metabolising capacity either in the liver or at extrahepatic sites.

Premedication for upper gastrointestinal endoscopy

Premedication is not essential to endoscopy but patient tolerance is clearly improved and, thus, ease of examination. Although comparable results can be achieved through nonpharmacologic means, the time and effort involved precludes their widespread use. Despite near universal utilization of premedication in endoscopy, the associated risk is difficult to determine from the available literature. The reported data reveal nominal risk yet must be viewed as minimums. The ideal drug with predictable clinical effects, minimal postprocedure impairment, little respiratory compromise, and proven antagonist is not yet available. Although midazolam seems to represent an advance, recent emphasis on respiratory depression is particularly troublesome. Studies evaluating various agents have suffered from lack of quantitation of such parameters as patient tolerance, ease of examination, and postprocedure impairment. Development of proven standards for these parameters would have to occur before a definitive double-blind randomized trial could be undertaken. Suggested means of assessing these parameters are listed in Table I. Improvement in major morbidity would be difficult in light of its low incidence. As the search for the ideal drug continues, endoscopists must continue to use drugs whose full effects are incompletely understood. The ability to increase patient comfort must be balanced with the small, but ever present, risk of morbidity and mortality.

Diazepam versus midazolam (versed) in outpatient colonoscopy: a double-blind randomized study

Midazolam is a new parenteral benzodiazepine premedication for endoscopy. Consecutive patients were randomized to receive either intravenous midazolam or diazepam as premedication for outpatient total colonoscopy by one endoscopist. Fifty-five patients received diazepam (0.15 mg/kg) and 50 received midazolam (0.07 mg/kg). Both patient and endoscopist were blind to the study drug used. The two groups were similar with respect to age, sex, and indication for colonoscopy. Patients were rated by the endoscopist for degree of cooperation, sedation, and pain during examination. There was significantly more oversedation in the midazolam group than in the diazepam group (p less than 0.05). Immediate procedure recall was less in midazolam patients (p less than 0.005), but on repeat interview the next day there was no difference between the two groups concerning recall of the endoscopy. There was no significant difference between the two groups in the incidence of arm pain. We conclude that in a clinical setting, midazolam does not appear to offer any significant advantage over diazepam, except for cost. Midazolam carries an increased risk of oversedation when it is administered on a milligram per kilogram basis and should instead be titrated individually.

Mechanism of the excessive sedative response of cirrhotics to benzodiazepines: model experiments with triazolam

Mechanisms responsible for disproportional sedation resulting from triazolam administration to patients with cirrhosis were investigated. Ordinary sedative doses (0.25 mg) were given p.o. to 8 cirrhotics and 18 controls. Plasma concentrations of unbound drug were assessed by capillary gas chromatography and equilibrium dialysis. Median apparent oral clearances of unbound triazolam were 14.8 ml per min per kg in cirrhotics and 23.9 ml per min per kg in controls (p less than 0.01). Clearances were significantly correlated with severity of liver disease as assessed by the aminopyrine breath test (Rs = 0.77, n = 17, p less than 0.001). At a time when plasma concentrations of unbound triazolam were the same in both groups, i.e., 2.25 hr after dosing, flicker sensitivity at 5 Hz which was used as an index of CNS performance was impaired by a factor of 3.2 in cirrhotics and 1.4 in controls (p less than 0.01 for group difference). Performance was also significantly lower in cirrhotics with the digit symbol substitution test (p less than 0.05). It is concluded that, in patients with cirrhosis, disproportional sedation after benzodiazepine administration may be due not only to impaired drug elimination, but also to hypersensitivity of the brain.