Pharmacokinetics of midazolam in anaesthetized cirrhotic patients

Analgesia, Sedation, and Anesthesia for Neonates With Cardiac Disease

Analgesia, sedation, and anesthesia are a continuum. Diagnostic and/or therapeutic procedures in newborns often require analgesia, sedation, and/or anesthesia. Newborns, in general, and, particularly, those with heart disease, have an increased risk of serious adverse events, including mortality under anesthesia. In this section, we discuss the assessment and management of pain and discomfort during interventions, review the doses and side effects of commonly used medications, and provide recommendations for their use in newborns with heart disease. For procedures requiring deeper levels of sedation and anesthesia, airway and hemodynamic support might be necessary. Although associations of long-term deleterious neurocognitive effects of anesthetic agents have received considerable attention in both scientific and lay press, causality is not established. Nonetheless, an early multimodal, multidisciplinary approach is beneficial for safe management before, during, and after interventional procedures and surgery to avoid problems of tolerance and delirium, which can contribute to long-term cognitive dysfunction.

Liver Cirrhosis Affects the Pharmacokinetics of the Six Substrates of the Basel Phenotyping Cocktail Differently

Background

Activities of hepatic cytochrome P450 enzymes (CYPs) are relevant for hepatic clearance of drugs and known to be decreased in patients with liver cirrhosis. Several studies have reported the effect of liver cirrhosis on CYP activity, but the results are partially conflicting and for some CYPs lacking.

Objective

In this study, we aimed to investigate the CYP activity in patients with liver cirrhosis with different Child stages (A-C) using the Basel phenotyping cocktail approach.

Methods

We assessed the pharmacokinetics of the six compounds and their CYP-specific metabolites of the Basel phenotyping cocktail (CYP1A2: caffeine, CYP2B6: efavirenz, CYP2C9: flurbiprofen, CYP2C19: omeprazole, CYP2D6: metoprolol, CYP3A: midazolam) in patients with liver cirrhosis (n = 16 Child A cirrhosis, n = 15 Child B cirrhosis, n = 5 Child C cirrhosis) and matched control subjects (n = 12).

Results

While liver cirrhosis only marginally affected the pharmacokinetics of the low to moderate extraction drugs efavirenz and flurbiprofen, the elimination rate of caffeine was reduced by 51% in patients with Child C cirrhosis. For the moderate to high extraction drugs omeprazole, metoprolol, and midazolam, liver cirrhosis decreased the elimination rate by 75%, 37%, and 60%, respectively, increased exposure, and decreased the apparent systemic clearance (clearance/bioavailability). In patients with Child C cirrhosis, the metabolic ratio (ratio of the area under the plasma concentration–time curve from 0 to 24 h of the metabolite to the parent compound), a marker for CYP activity, decreased by 66%, 47%, 92%, 73%, and 43% for paraxanthine/caffeine (CYP1A2), 8-hydroxyefavirenz/efavirenz (CYP2B6), 5-hydroxyomeprazole/omeprazole (CYP2C19), α-hydroxymetoprolol/metoprolol (CYP2D6), and 1′-hydroxymidazolam/midazolam (CYP3A), respectively. In comparison, the metabolic ratio 4-hydroxyflurbiprofen/flurbiprofen (CYP2C9) remained unchanged.

Conclusions

Liver cirrhosis affects the activity of CYP isoforms differently. This variability must be considered for dose adjustment of drugs in patients with liver cirrhosis.

Clinical Trial Registration

NCT03337945.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40262-022-01119-0.

Alterations of Cytochrome P450-Mediated Drug Metabolism during Liver Repair and Regeneration after Acetaminophen-Induced Liver Injury in Mice

Acetaminophen (APAP)-induced liver injury (AILI) is the leading cause of acute liver failure in the United States, but its impact on metabolism, therapeutic efficacy, and adverse drug reactions (ADRs) of co- and/or subsequent administered drugs are not fully investigated. The current work explored this field with a focus on the AILI-mediated alterations of cytochrome P450-mediated drug metabolism. Various levels of liver injury were induced in mice by treatment with APAP at 0, 200, 400, and 600 mg/kg. Severity of liver damage was determined at 24, 48, 72, and 96 hours by plasma levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), microRNA miR122, and tissue staining. The expression and activities of CYP3A11, 1A2, 2B10, 2C29, and 2E1 were measured. Sedation efficacy and ADRs of midazolam, a CYP3A substrate, were monitored after APAP treatment. ALT, AST, and miR122 increased at 24 hours after APAP treatment with all APAP doses, whereas only groups treated with 200 and 400 mg/kg recovered back to normal levels at 72 and 96 hours. The expression and activity of the cytochromes P450 significantly decreased at 24 hours with all APAP doses but only recovered back to normal at 72 and 96 hours with 200 and 400, but not 600, mg/kg of APAP. The alterations of cytochrome P450 activities resulted in altered sedation efficacy and ADRs of midazolam, which were corrected by dose justification of midazolam. Overall, this work illustrated a low cytochrome P450 expression window after AILI, which can decrease drug metabolism and negatively impact drug efficacy and ADRs. SIGNIFICANCE STATEMENT: The data generated in the mouse model demonstrated that expression and activities of cytochrome P450 enzymes and correlated drug efficacy and ADRs are altered during the time course of liver repair and regeneration after liver is injured by treatment with APAP. Dose justifications based on predicted changes of cytochrome P450 activities can achieve desired therapeutic efficacy and avoid ADRs. The generated data provide fundamental knowledge for translational research to drug treatment for patients during liver recovery and regeneration who have experienced AILI.

Pharmacokinetic study of midazolam and α-hydroxymidazolam in guinea pig blood and hair roots after a single dose of midazolam

The appearance of midazolam (M) and its metabolites into the hair root following a single administration was examined by following the time course of M and α-hydroxymidazolam (αHM) in hair roots and blood from guinea pigs. The back hair of guinea pigs was shaved before drug administration and before each sampling, and hair roots (3-5 mm) were plucked at 5, 15, and 30 min, 1, 2, 4, 6, 10, 24, 48, 72, 96, 120, 144 h, and 7, 14, 21, and 28 days. The kinetic parameters of M and αHM in guinea pig blood and hair roots were determined for three doses (5, 10, and 25 mg/kg). Comparisons of drug time course between hair roots and blood indicated an association between drug concentrations in the hair root and the blood. M and αHM entered the hair root within 5 min after a single exposure. The detection windows were also longer for the hair root than for the blood. Consequently, the hair root can be a valuable specimen in acute poisonings or drug-facilitated crime (DFC) cases, if other matrices are unavailable, or if blood and urine results are negative. Hair shafts (with hair roots) were plucked at 28 days and segmented. The concentrations of M and αHM were lower in the hair shafts than in the hair roots. The concentrations of the metabolite αHM in hair shafts were barely detectable. The concentrations of M and αHM in the hair root showed a moderate correlation with dose. Comparison of drug levels in hair roots between the washed group and the unwashed group indicated a generally stable percentage between the washed and unwashed groups of 40-60 % during the entire time course. This indicates that drugs are likely to be immobilized in the hair root at the beginning of the incorporation process.

Midazolam: Safety of use in palliative care: A systematic critical review

PURPOSE

The undesired effects of midazolam can be life-threatening. This paper delineates the findings related to the pharmacokinetics, adverse effects and drug-drug interactions as well as associated therapeutic implications for safe midazolam use.

METHODS

A systematic review of literature was conducted.

RESULTS

The pharmacokinetics of midazolam depends on hepatic and renal functions, fat tissue mass, route and duration of administration, as well as potential drug-drug interactions. Palliative care patients constitute a high-risk group prone to side effects of drugs, due to polytherapy and multi-organ failure.

CONCLUSION

Midazolam is one of three most frequently administered drugs in palliative care. The indications for its use include anxiety, dyspnea, seizures, vomiting refractory to treatment, agitation, myoclonus, status epilepticus, restlessness, delirium, pruritus, hiccups, insomnia, analgosedation, palliative sedation and preventing or counteracting undesired effects of ketamine.

Safety and effectiveness of midazolam for cirrhotic patients undergoing endoscopic variceal ligation

BACKGROUND/AIMS

Endoscopic variceal ligation (EVL) is an established treatment for esophageal variceal bleeding. Midazolam (MDZ) is most commonly used for sedation during endoscopic procedures. However, adverse events (AEs) may occur more frequently in patients with cirrhosis due to altered MDZ metabolism.

MATERIALS AND METHODS

We retrospectively reviewed the records of 325 patients with cirrhosis who received EVL.

RESULTS

No significant differences were found in treatment outcome and procedure time among 151 patients in the MDZ group and 169 patients in the non-MDZ group. Desaturation (23.2% vs. 7.7%, p<0.01), bradycardia (22.5% vs. 17.2%, p=0.03), and hepatic encephalopathy (HE) (6.6% vs. 0.6%, p<0.01) were more common in the MDZ group than in the non-MDZ group. Logistic regression analyses revealed that an Eastern Cooperative Oncology Group (ECOG) score of ≥2 (p<0.01) and the use of MDZ (p<0.01) were associated with the development of overall AEs. An ECOG score of ≥2 (p=0.01), high serum creatinine level (p=0.02), and the use of MDZ (p<0.01) were significant risk factors for HE.

CONCLUSION

Extreme caution should be taken when sedating patients with cirrhosis receiving EVL due to the AEs associated with the use of MDZ.

Benzodiazepines and risk for hepatic encephalopathy in patients with cirrhosis and ascites

Background

There is limited evidence to support the belief that benzodiazepines increase cirrhosis patients' risk of hepatic encephalopathy (HE).

Objective

We aimed to examine the association between benzodiazepine use and HE development in cirrhosis patients.

Methods

We used data on 865 cirrhosis patients with ascites from three trials to study the effect of benzodiazepine use on development of first-time HE. For each patient, we classified periods of benzodiazepine use by the number of days since initiation. We used Cox regression to compare the risk of HE in current benzodiazepine users vs. non-users adjusting for confounders.

Results

Cirrhosis patients were not at increased risk of HE for the first two days of benzodiazepine use, but then faced a five-fold increased risk of HE during days 3 to 10 of benzodiazepine use. The risk of HE was not increased for those who had been using benzodiazepines for more than 28 days.

Conclusion

Cirrhosis patients who had begun using benzodiazepines between 3 and 10 days previously had a markedly increased risk of developing first-time HE. Cirrhosis patients who had been using benzodiazepines for just one or two days or continued use for more than 28 days did not have such an excess risk.

High-Fat Diet Feeding Alters Expression of Hepatic Drug-Metabolizing Enzymes in Mice

Medical conditions accompanying obesity often require drug therapy, but whether and how obesity alters the expression of drug-metabolizing enzymes and thus drug pharmacokinetics is poorly defined. Previous studies have shown that high-fat diet (HFD) feeding and subsequent obesity in mice lead to altered expression of transcriptional regulators for cytochrome P450 CYP2D6, including hepatocyte nuclear factor 4α (HNF4α, a transcriptional activator of CYP2D6) and small heterodimer partner (SHP, a transcriptional repressor of CYP2D6). The objective of this study was to examine whether diet-induced obesity alters CYP2D6 expression by modulating HNF4α and SHP expression. Male CYP2D6-humanized transgenic (Tg-CYP2D6) mice were fed with HFD or matching control diet for 18 weeks. Hepatic mRNA expression of CYP2D6 decreased to a small extent in the HFD group (by 31%), but the differences in CYP2D6 protein and activity levels in hepatic S9 fractions were found insignificant between the groups. Although hepatic SHP expression did not differ between the groups, HNF4α mRNA and protein levels decreased by ∼30% in the HFD group. Among major mouse endogenous cytochrome P450 genes, Cyp1a2 and Cyp2c37 showed significant decreases in the HFD group, whereas Cyp2e1 expression did not differ between groups. Cyp2b10 and Cyp3a11 expression was higher in the HFD group, with corresponding 2.9-fold increases in hepatic CYP3A activities in HFD-fed mice. Together, these results suggest that obesity has minimal effects on CYP2D6-mediated drug metabolism, although it modulates the expression of mouse endogenous P450s in a gene-specific manner.

A Prediction Model of Drug Exposure in Cirrhotic Patients According to Child-Pugh Classification

BACKGROUND AND OBJECTIVE

Prediction of drug clearance in liver cirrhosis patients is currently based on in vitro-in vivo extrapolation and physiologically-based pharmacokinetic models. No static model for this purpose has been described. The objectives of this study were to (1) derive a static model for predicting drug exposure in cirrhotic patients, and (2) to evaluate the model on a large set of published data.

METHODS

The impact of cirrhosis was characterized by the ratio of the total and unbound drug area under the concentration-time curve (AUC) in cirrhotic patients to the AUC measured in healthy subjects These ratios were predicted for Child-Pugh classes A, B, and C. The AUC ratios observed in published data were compared with AUC ratios predicted by the model.

RESULTS

Among 171 drugs examined, 83 published AUC ratios for 45 drugs in cirrhotic patients were available for analysis. The mean ± standard deviation relative prediction error for the total and unbound AUC ratios was 0.22 ± 0.58 and 0.24 ± 0.56, respectively. There were four outliers among the 83 predicted values. Simulations showed that the prediction error was negligible provided that the hepatic extraction coefficient was less than 0.8.

CONCLUSIONS

For mild and moderate cirrhosis (classes A and B), the predicted unbound AUC ratio is typically approximately 2 and 3.5, respectively, for most drugs. In the absence of data in cirrhotic patients, the drug dose might be empirically reduced by these factors. In severe cirrhosis (class C), our model may help clinicians to adjust their prescriptions.

CYP3A activity in severe liver cirrhosis correlates with Child-Pugh and model for end-stage liver disease (MELD) scores

AIMS

Impaired liver function often necessitates drug dose adjustment to avoid excessive drug accumulation and adverse events, but a marker for the extent of the required adjustment is lacking. The aim of this study was to investigate whether Child-Pugh (CP) and model for end-stage liver disease (MELD) scores correlate with drug clearance.

METHODS

Midazolam was used as a CYP3A probe and its pharmacokinetics were analyzed in 24 patients with mild to severe liver cirrhosis (n = 4, 10 and 10 with CP class A, B and C, respectively) and six patients without liver disease.

RESULTS

Both scores correlated well with unbound midazolam clearance (CLu ), unbound midazolam fraction and half-life (all P < 0.01), whereas the unbound steady-state volume of distribution was not significantly changed. In patients with severe liver cirrhosis unbound midazolam clearance was only 14% of controls (CP C: CLu = 843 ± 346 l  h(-1), MELD ≥ 15: CLu = 805 ± 474 l  h(-1), controls: CLu = 5815 ± 2649 l  h(-1), P < 0.01).

CONCLUSION

The correlation with unbound midazolam clearance suggests that either score predicts the metabolic capacity of CYP3A, the most relevant drug metabolizing enzyme subfamily in humans.

Pharmacokinetic of antiepileptic drugs in patients with hepatic or renal impairment

Many factors influence choice of antiepileptic drugs (AEDs), including efficacy of the drug for the indication (epilepsy, neuropathic pain, affective disorder, migraine), tolerability, and toxicity. The first-generation AEDs and some newer AEDs are predominately eliminated by hepatic metabolism. Other recent AEDs are eliminated by renal excretion of unchanged drug or a combination of hepatic metabolism and renal excretion. The effect of renal and hepatic disease on the dosing will depend on the fraction of the AED eliminated by hepatic and/or renal excretion, the metabolic isozymes involved, as well as the extent of protein binding, if therapeutic drug monitoring is used. For drugs that are eliminated by renal excretion, methods of estimating creatinine clearance can be used to determine dose adjustments. For drugs eliminated by hepatic metabolism, there are no specific markers of liver function that can be used to provide guidance in dosage adjustments. Based on studies with probe drugs, the hepatic metabolic enzymes are differentially affected depending on the cause and severity of hepatic disease, which can aid in predicting dose adjustment when clinical data are not available. Several AEDs are also associated with laboratory markers of mild hepatic dysfunction and, rarely, more severe hepatic injury. In contrast, the risk of renal injury from AEDs is generally low. In general, co-morbid hepatic or renal diseases influence the decision for the selection of an AED. For some patients dosing changes to their existing AEDs may be appropriate. For others, a change to another AED may be a better option.

Randomized controlled trial for endoscopy with propofol versus midazolam on psychometric tests and critical flicker frequency in people with cirrhosis

BACKGROUND AND AIM

People with cirrhosis are at increased risk of development of complications related to sedation. The aim of the present study was to compare the effects of sedation for upper gastrointestinal endoscopy (UGIE) with propofol and midazolam on psychometric tests and critical flicker frequency (CFF) in people with cirrhosis.

METHODS

A total of 127 people with cirrhosis were randomized into three groups: propofol group (n = 40), midazolam group (n = 42) and no sedation (n = 45). All patients underwent CFF test and combination of psychometry (number connection test-A and B [NCT-A,B]; digit symbol test [DST], line tracing test [LTT] and serial dotting test [SDT]) at baseline and at 2 h post-endoscopy. CFF was done at 30 min and repeated every 30 min for 2 h.

RESULTS

In the propofol group there was no deterioration in psychometry (NCT-A [55.6 ± 18.7 vs 56.4 ± 19.0 s], NCT-B [98.2 ± 35.1 vs 97.8 ± 34.6 s], DST [26.7 ± 5.7 vs 26.3 ± 5.3], LTT [112.9 ± 35.7 vs 113.7 ± 36.6 s], SDT [94.6 ± 34.1 vs 95.2 ± 34.5 s]). Significant deterioration from baseline (39.8 ± 2.9 Hz) was seen in CFF at 30 min (38.8 ± 2.3 Hz) and 1 h (39.2 ± 2.4 Hz), P = 0.01 but no difference thereafter. In the midazolam group, significant deterioration was observed on psychometry (NCT-A [56.0 ± 18.5 vs 60.4 ± 19.8 s], NCT-B [99.9 ± 29.1 vs 105.9.6 ± 30.3 s], DST [26.1 ± 4.7 vs 25.2 ± 4.3], LTT [129.1 ± 34.5 vs 132.9 ± 35.4 s], SDT [95.6 ± 34.2]). No deterioration was observed in psychometry and CFF in people with cirrhosis without sedation.

CONCLUSIONS

Propofol sedation for UGIE was associated with earlier recovery compared with midazolam, which causes deterioration of psychometric tests and CFF for a longer time in comparison with propofol.

Determining the time course of CYP3A inhibition by potent reversible and irreversible CYP3A inhibitors using A limited sampling strategy

We established a new limited sampling strategy to assess CYP3A activity and evaluated the time course of reversible (voriconazole) and irreversible (ritonavir) CYP3A inhibition. In this randomized trial, two groups, each with eight healthy participants, received CYP3A inhibitors voriconazole or ritonavir orally for 9 days, with 3 mg midazolam (MDZ) administered before the inhibitor treatment, on days 1, 2, 3, 5, 8, and 9 during inhibitor treatment, and on days 10, 11, and 12 (3 days) after discontinuation. Plasma MDZ area under the curve (AUC) between 2 and 4 h after oral administration in the form of a solution strongly correlated with MDZ clearance. Using this parameter, maximum inhibition of voriconazole and ritonavir was calculated to have occurred only 48 h after starting of the inhibitor (percentage of baseline MDZ clearance, voriconazole: 10.6%; ritonavir: 8.4%). Recovery of CYP3A activity occurred with a half-life of 24 h after voriconazole, whereas ritonavir inhibition was still strong 3 days after discontinuation. These findings underscore the substantial and gradual alterations in dose requirements in the first days of and after such combination therapies.

Drug dosing considerations for the critically ill patient with liver disease

Hepatic dysfunction in the critically ill patient presents a unique challenge to clinicians when designing pharmacotherapeutic treatment plans. Overall, the literature regarding drug dosing in critically ill patients with hepatic dysfunction is incomplete and current tools available to bedside clinicians have limitations. Despite these challenges, rational drug regimens can be implemented by critical care nurses who consider the potential impact of hepatic dysfunction on drug pharmacokinetics. This information can be applied clinically and careful monitoring plans can be implemented to assess a drug for efficacy and safety. This article reviews the pharmacokinetic changes that can occur in hepatic failure, identifies practical ways to quantify the severity of dysfunction, and discusses general drug dosing strategies in this patient population.

Endoscopic sedation of patients with chronic liver disease

Endoscopic procedures are often necessary in patients with chronic liver disease. The preprocedure evaluation of such patients should include an assessment of hepatic synthetic function and identification of neuropsychiatric findings suggestive of hepatic encephalopathy. It may be possible, in some cases, to perform diagnostic esophagogastroduodenoscopy without administration of sedation; this is desirable to eliminate the risks of sedation, especially encephalopathy. Nonetheless, most patients undergoing upper and lower endoscopy require sedation. Currently, the use of propofol is preferred to benzodiazepines and opioids for endoscopic sedation of patients with advanced liver disease due to its short biologic half-life and low risk of provoking hepatic encephalopathy. In appropriately selected patients, gastroenterologist-directed propofol administration seems safe.

Contribution of itraconazole metabolites to inhibition of CYP3A4 in vivo

Itraconazole (ITZ) is metabolized in vitro to three inhibitory metabolites: hydroxy-itraconazole (OH-ITZ), keto-itraconazole (keto-ITZ), and N-desalkyl-itraconazole (ND-ITZ). The goal of this study was to determine the contribution of these metabolites to drug-drug interactions caused by ITZ. Six healthy volunteers received 100 mg ITZ orally for 7 days, and pharmacokinetic analysis was conducted at days 1 and 7 of the study. The extent of CYP3A4 inhibition by ITZ and its metabolites was predicted using this data. ITZ, OH-ITZ, keto-ITZ, and ND-ITZ were detected in plasma samples of all volunteers. A 3.9-fold decrease in the hepatic intrinsic clearance of a CYP3A4 substrate was predicted using the average unbound steady-state concentrations (C(ss,ave,u)) and liver microsomal inhibition constants for ITZ, OH-ITZ, keto-ITZ, and ND-ITZ. Accounting for circulating metabolites of ITZ significantly improved the in vitro to in vivo extrapolation of CYP3A4 inhibition compared to a consideration of ITZ exposure alone.

An overview of psychiatric issues in liver disease for the consultation-liaison psychiatrist

Liver disease is a common cause of morbidity and mortality in the United States and elsewhere. Arising from infectious, hereditary, or toxin-induced sources, the detection of liver disease often requires a high index of suspicion. Clinical presentations are highly variable and are often accompanied by neuropsychiatric symptoms. This fact, along with an increased incidence of liver disease among patients with primary psychiatric disorders and the presence of varied drug use, complicates the tasks of providing care to patients with liver disease. To assist the consultation-liaison psychiatrist, the authors present the first of a two-part series focused on psychiatric issues in liver disease.

Criteria for immediate postoperative extubation in adult recipients following living-related liver transplantation with total intravenous anesthesia

STUDY OBJECTIVE

To evaluate whether our criteria for immediate postoperative extubation predicts successful extubation in living-related liver transplantation of the right lobe, and to test the effects of our standardized anesthetic technique on the success of immediate postoperative extubation.

DESIGN

Open-label, descriptive study.

SETTING

University hospital.

PATIENTS

6 ASA physical status III and IV patients with end-stage liver disease undergoing living-related liver transplantation of the right lobe.

INTERVENTIONS

Patients received a standardized anesthetic technique with propofol, remifentanil, and cisatracurium. They were extubated when they met our criteria for immediate postoperative extubation: good donor liver function, <10 U packed red blood cells administered, hemodynamic stability, and alveolar-arterial oxygen gradient <200 mmHg.

MEASUREMENTS AND MAIN RESULTS

At the end of surgery, four of the six patients fulfilled our criteria for immediate postoperative extubation. They were uneventfully extubated rapidly after surgery and soon arrived in the intensive care unit. Their postoperative stay in the operating room was only 36 minutes (range: 30 to 42 min). No patient required reintubation in the operating room or the intensive care unit. They had no recorded hemodynamic or respiratory problems postoperatively.

CONCLUSIONS

Immediate extubation of selected living-related liver transplant recipients can be a safe procedure. Anesthetic management to immediate extubation seems appropriate and the derived guidelines appear acceptable.

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.

Prediction of pharmacokinetics prior to in vivo studies. 1. Mechanism-based prediction of volume of distribution

In drug discovery and nonclinical development the volume of distribution at steady state (V(ss)) of each novel drug candidate is commonly determined under in vivo conditions. Therefore, it is of interest to predict V(ss) without conducting in vivo studies. The traditional description of V(ss) corresponds to the sum of the products of each tissue:plasma partition coefficient (P(t:p)) and the respective tissue volume in addition to the plasma volume. Because data on volumes of tissues and plasma are available in the literature for mammals, the other input parameters needed to estimate V(ss) are the P(t:p)'s, which can potentially be predicted with established tissue composition-based equations. In vitro data on drug lipophilicity and plasma protein binding are the input parameters used in these equations. Such a mechanism-based approach would be particularly useful to provide first-cut estimates of V(ss) prior to any in vivo studies and to explore potential unexpected deviations between sets of predicted and in vivo V(ss) data, when the in vivo data become available during the drug development process. The objective of the present study was to use tissue composition-based equations to predict rat and human V(ss) prior to in vivo studies for 123 structurally unrelated compounds (acids, bases, and neutrals). The predicted data were compared with in vivo data obtained from the literature or at Roche. Overall, the average ratio of predicted-to-experimental rat and human V(ss) values was 1.06 (SD = 0.817, r = 0.78, n = 147). In fact, 80% of all predicted values were within a factor of two of the corresponding experimental values. The drugs can therefore be separated into two groups. The first group contains 98 drugs for which the predicted V(ss) were within a factor of two of those experimentally determined (average ratio of 1.01, SD = 0.39, r = 0.93, n = 118), and the second group includes 25 other drugs for which the predicted and experimental V(ss) differ by a factor larger than two (average ratio of 1.32, SD = 1.74, r = 0.42, n = 29). Thus, additional relevant distribution processes were neglected in predicting V(ss) of drugs of the second group. This was true especially in the case of some cationic-amphiphilic bases. The present study is the first attempt to develop and validate a mechanistic distribution model for predicting rat and human V(ss) of drugs prior to in vivo studies.

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.

Sedation and analgesia in paediatric intensive care units: a guide to drug selection and use

The indications for sedation in the paediatric intensive care unit (PICU) patient are varied ranging from short term use for various procedures to prolonged administration to provide comfort during mechanical ventilation. When faced with the decision to institute sedation, the healthcare provider must make three decisions: the agent to be used, the route of delivery, and the mode of administration (intermittent versus continuous). There are several agents that have been used to provide sedation in the PICU patient including the inhalational anaesthetic agents, benzodiazepines, opioids, ketamine, propofol, chloral hydrate, phenothiazines, and the barbiturates. This review describes the various agents for sedation and discusses their advantages and disadvantages as they pertain to the PICU. Consequences of and treatment strategies for long term problems with prolonged sedation including tolerance, physical dependency, and withdrawal are reviewed.

Clinical pharmacology of midazolam in infants and children

Midazolam is a parenteral benzodiazepine with sedative, amnesic, anxiolytic, muscle relaxant and anticonvulsant properties. The drug exerts its clinical effect by binding to a receptor complex which facilitates the action of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Midazolam has a faster onset and shorter duration of action than other benzodiazepines such as diazepam and lorazepam. The most serious adverse events associated with midazolam in children include hypoventilation, decreased oxygen saturation, apnoea and hypotension. It is water soluble in the commercially prepared formulation but becomes lipid soluble at physiological pH and can then cross the blood brain barrier. It is metabolised in the liver by the cytochrome P450 system, and its chief metabolite is 1-hydroxymethyl midazolam. The latter is conjugated to the glucuronide form, and it has only minimal biological activity. Midazolam is excreted primarily by the kidney. Its half-life in children over 12 months is reported to be 0.8 to 1.8 hours, with a clearance of 4.7 to 19.7 ml/min/kg. Doses given to children must be calculated on a mg/kg basis. For children 6 months to 5 years of age the initial dose is 0.05 to 0.1 mg/kg. A total dose up to 0.6 mg/kg titrated slowly may be necessary to achieve the desired endpoint. For children 6 to 12 years of age the initial dose is 0.025 to 0.05 mg/kg with a total dose up to 0.4 mg/kg to achieve the desired end-point.

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.

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.

Sedation and Analgesia for Children in the Pediatric Intensive Care Unit

Several situations arise in the Pediatric Intensive Care Unit (PICU) patient which may require the pharmacologic control of pain and anxiety. The author discusses the various pharmacologic agents available for sedation and analgesia including the inhalational anesthetic agents, nitrous oxide, benzodiasepines, opioids, ketamine, propofol, and the barbiturates. While intravenous administration is generally chosen for the PICU patient, certain situations may arise which preclude this route. The available information concerning alternative routes of delivery for the various agents including subcutaneous and transmucosal administration is presented. The role of various regional anesthetic techniques to control pain in the PICU patient are reviewed.

Pain management and sedation in the pediatric intensive care unit

Several situations arise in the PICU patient that require the administration of drugs for sedation and analgesia. A "cookbook" approach is impossible because of the diversity of patient and clinical scenarios. When amnesia is required, these authors prefer a continuous infusion of a benzodiazepine such as midazolam or lorazepam. Although the majority of clinical experience has been with midazolam, lorazepam either by bolus dose or continuous infusion offers a cost-effective alternative. When analgesia is required, the addition of a continuous infusion of narcotic or the use of a PCA device in the older patient should prove effective. Although fentanyl is frequently chosen, morphine is an effective and cost-effective alternative for patients with stable cardiovascular function. The synthetic narcotics are recommended for neonates, especially following cardiac surgical procedures and those at risk for pulmonary vasospasm. Narcotics may also be used for the treatment of agitation in those situations that do not necessarily require analgesia. Our clinical experience suggests that narcotics may be more effective for sedation than benzodiazepines in children less than 1 year of age. When the above agents fail to be effective or are associated with cardiovascular depression, alternatives may include ketamine or pentobarbital. Ketamine may be useful for the unstable patient or those with a bronchospastic component to their disease process. We have found pentobarbital to be effective when the combination of benzodiazepines and narcotics fails to provide the desired level of sedation. Aside from these techniques, regional anesthesia may offer a more effective means of controlling pain in the PICU patient. These techniques may be effective when parenteral narcotics are inadequate or lead to undesired effects. Although most commonly used for postoperative analgesia, their use in patients with pain from other causes (e.g., multiple trauma) may be indicated, especially when parenteral narcotics may interfere with respiratory function or the ongoing assessment of the patient's mental status.

Clinical pharmacokinetics in patients with liver disease

From considerations of hepatic physiology and pathology coupled with pharmacokinetic principles, it appears that altered drug elimination in liver disease may result from the following mechanisms: reduction in absolute cell mass, in cellular enzyme content and/or activity, in portal vein perfusion due to extrahepatic/intrahepatic shunting, or of portal perfusion of hepatocyte mass due to decreased portal flow or sinusoidal perfusion; increase in arterial perfusion relative to portal perfusion; preferential perfusion of the sinusoidal midzone and terminal zones by arterioles; potential for direct mixing of arterial blood within the space of Disse; reduced exchange across the endothelial lining; and impaired diffusion within the space of Disse. In general, oxidative drug metabolism is impaired in liver disease and the degree of impairment of oxidisation differs between drugs but correlates best with the degree of sinusoidal capillarisation, i.e. the degree of access of the drug from the sinusoid to the hepatocyte. Drug conjugation appears to be relatively unaffected by liver disease, whereas elimination by biliary excretion correlates best with the degree of intrahepatic shunting and not with sinusoidal capillarisation. As the latter should impair hepatocyte access of all compounds similarly, a potentially important mechanism could be impaired access of oxygen to hepatocytes as oxidative metabolism is much more sensitive to oxygen supply than are conjugation or biliary excretion. This suggests a potentially important therapeutic role for agents which increase the hepatic oxygen supply. Useful adjunctive strategies may also derive from the oxygen limitation hypothesis. Anaemia should be targeted as a critically important variable, as should oxygen-carrying capacity, i.e. modification of the smoking habit. Additionally, enzyme inducers such as barbiturates may be used if overriding hypoxic constraints are removed by oxygen supplementation. Agents likely to seriously compromise arterial perfusion of the hepatic vascular bed should be avoided, e.g. those causing postural hypotension or vasospasm. Vasodilators can be used to actively promote arterial perfusion. While the effect of liver disease on drug handling is highly variable and difficult to predict, there are well recognised principles for modifying dosage. These include halving the dose of drugs given systemically (or of low clearance drugs given orally) and a 50 to 90% reduction in the dose of drugs with a high hepatic clearance given orally. Changes in the pharmacodynamic effects of drugs (either alone or in addition to pharmacokinetic changes) can also be profound, and awareness of this possibility should be increased.

Effect of upper abdominal surgery and cirrhosis upon the pharmacokinetics of methohexital

The pharmacokinetic profile of methohexital was studied in cirrhotic patients (n = 8), patients undergoing upper abdominal surgery (n = 8) and orthopaedic patients under general anaesthesia (n = 8). The total plasma clearance of methohexital was unchanged in cirrhotics: 54 +/- 22 l.h-1 (mean +/- s.d.) as well as in patients undergoing upper abdominal surgery: 60 +/- 14 l.h-1 in comparison to orthopaedic surgery: 70 +/- 24 l.h-1. The central volume and total volume of distribution and the distribution and elimination half-lives were similar between the three groups. Despite its hepatic dependent elimination, methohexital elimination kinetics were unchanged in patients undergoing upper abdominal surgery and in cirrhosis. Owing to the high hepatic extraction ratio of methohexital, its elimination should be influenced by the hepatic blood flow. The unchanged elimination kinetics presently observed in patients with cirrhosis or those undergoing upper abdominal surgery suggest that the hepatic blood flow is less diminished than expected in these patients.