The effects of age and chronic liver disease on the elimination of temazepam

The Activity of Members of the UDP-Glucuronosyltransferase Subfamilies UGT1A and UGT2B is Impaired in Patients with Liver Cirrhosis

BACKGROUND AND OBJECTIVE

The impact of liver cirrhosis on the activity of UDP-glucuronosyltransferases (UGTs) is currently not well characterized. We investigated the glucuronidation capacity and glucuronide accumulation in patients with liver cirrhosis.

METHODS

We administered the Basel phenotyping cocktail (caffeine, efavirenz, flurbiprofen, omeprazole, metoprolol, midazolam) to patients with liver cirrhosis (n = 16 Child A, n = 15 Child B, n = 5 Child C) and n = 12 control subjects and obtained pharmacokinetic profiles of substrates and primary metabolites and their glucuronides.

RESULTS

Caffeine and its metabolite paraxanthine were only slightly glucuronidated. The metabolic ratio (AUCglucuronide/AUCparent, MR) was not affected for caffeine but decreased by 60% for paraxanthine glucuronide formation in Child C patients. Efavirenz was not glucuronidated whereas 8-hydroxyefavirenz was efficiently glucuronidated. The MR of 8-hydroxyefavirenz-glucuronide formation increased three-fold in Child C patients and was negatively correlated with the glomerular filtration rate. Flurbiprofen and omeprazole were not glucuronidated. 4-Hydroxyflurbiprofen and 5-hydroxyomeprazole were both glucuronidated but the corresponding MRs for glucuronide formation were not affected by liver cirrhosis. Metoprolol, but not α-hydroxymetoprolol, was glucuronidated, and the MR for metoprolol-glucuronide formation dropped by 60% in Child C patients. Both midazolam and its metabolite 1'-hydroxymidazolam underwent glucuronidation, and the corresponding MRs for glucuronide formation dropped by approximately 80% in Child C patients. No relevant glucuronide accumulation occurred in patients with liver cirrhosis.

CONCLUSIONS

Detailed analysis revealed that liver cirrhosis may affect the activity of UGTs of the UGT1A and UGT2B subfamilies according to liver function. Clinically significant glucuronide accumulation did not occur in the population investigated.

CLINICAL TRIAL REGISTRATION

NCT03337945.

Hepatic impairment as a risk factor of adverse drug reactions

There are a lot of clinical variants of hepatic impairment ranging from asymptomatic increase in transaminases to acute liver failure and fulminant hepatitis. Hepatic impairment is a polietiologic syndrome. According to the epidemiological study conducted in the United States (19982008), the main causes of hepatic impairment were paracetamol overdose (46%), idiopathic liver dysfunction (14%), other drugs (excluding paracetamol, 11%), viral hepatitis B (7%), other infectious and non-infectious diseases with liver damage (except for viral hepatitis) 7%, autoimmune hepatitis (5%), ischemic hepatitis (syn. hypoxic hepatitis, liver infarction) 4%, viral hepatitis A (3%) and Wilson's disease (2%). Hepatic impairment have a direct impact on the pharmacokinetics and pharmacodynamics of drugs decreasing clearance, elimination and excretion of drugs. Also Transjugular intrahepatic porto-systemic shunts, which are often used to treat portal hypertension in patients with liver cirrhosis, can significantly reduce the presystemic elimination of drugs, thereby increasing their absorption. Moreover, in patients with liver cirrhosis, concomitant renal dysfunction also requires an adjustment of the dose of drugs. Correction of pharmacotherapy in accordance to pharmacokinetic and pharmacodynamic changes of drugs ingested by patients with impaired liver function will improve the quality of medical care and reduce the risks of adverse drug reactions.

Prescribing in Chronic Severe Hepatic Impairment

Therapeutic Reviews aim to provide essential independent information for health professionals about drugs used in palliative and hospice care. Additional content is available via www.palliativedrugs.com. The series editors welcome feedback on the articles.

Metabolic profile of oxazepam and related benzodiazepines: clinical and forensic aspects

Anxiolytic drugs, namely benzodiazepines, are the most commonly used psychoactive substances since anxiety disorders are prevalent mental disorders particularly in the Western world. Oxazepam is a short-acting benzodiazepine and one of the most frequently prescribed anxiolytic drugs. It is also the active metabolite of a wide range of other benzodiazepines, such as diazepam, ketazolam, temazepam, chlordiazepoxide, demoxazepam, halazepam, medazepam, prazepam, pinazepam, and chlorazepate. Therefore, relevant clinical and forensic outocomes may arise, namely those related to interference in driving performance. It is clinically available as a racemic formulation, with S-enantiomer being more active than R-enantiomer. In humans, it is mainly polimorphically metabolized by glucuronide conjugation at the 3-carbon hydroxyl group, yielding stable diastereomeric glucuronides (R- and S-oxazepam glucuronide). Relevant metabolic and stereoselective interspecies differences have been reported. In this work, the pharmacokinetics of oxazepam with particular focus on metabolic pathways is fully reviewed. Moreover, the metabolic profile of other prescribed benzodiazepines that produce oxazepam as a metabolite is also discussed. It is aimed that knowing the metabolism of oxazepam and related benzodiazepines may lead to the development of new analytical strategies for its early detection and help in further toxicological and clinical interpretations.

Surgery in patients with portal hypertension: a preoperative checklist and strategies for attenuating risk

Patients with liver disease and portal hypertension are at increased risk of complications from surgery. Recent advances have allowed better optimization of patients with cirrhosis before surgery and a reduction in postoperative complications. Despite this progress, the estimation of surgical risk in a patient with cirrhosis is challenging. The MELD score has shown promise in predicting postoperative mortality compared with the Child-Turcotte-Pugh score. This article addresses current concepts in the perioperative evaluation of patients with liver disease and portal tension, including a preoperative liver assessment (POLA) checklist that may be useful towards mitigating perioperative complications.

Pharmacologically active drug metabolites: impact on drug discovery and pharmacotherapy

Metabolism represents the most prevalent mechanism for drug clearance. Many drugs are converted to metabolites that can retain the intrinsic affinity of the parent drug for the pharmacological target. Drug metabolism redox reactions such as heteroatom dealkylations, hydroxylations, heteroatom oxygenations, reductions, and dehydrogenations can yield active metabolites, and in rare cases even conjugation reactions can yield an active metabolite. To understand the contribution of an active metabolite to efficacy relative to the contribution of the parent drug, the target affinity, functional activity, plasma protein binding, membrane permeability, and pharmacokinetics of the active metabolite and parent drug must be known. Underlying pharmacokinetic principles and clearance concepts are used to describe the dispositional behavior of metabolites in vivo. A method to rapidly identify active metabolites in drug research is described. Finally, over 100 examples of drugs with active metabolites are discussed with regard to the importance of the metabolite(s) in efficacy and safety.

Preoperative risk assessment for patients with liver disease

Patients with underlying liver disease often present for non-liver-related surgery and are at risk for postoperative decompensation. Several predictive models exist to determine the risk of morbidity and mortality after surgery in such patients, but the risk depends on the severity of liver disease and also the type and urgency of the surgery. Clinicians should be cognizant of the various risk assessment tools and incorporate them into their practice when encountering patients with liver disease undergoing surgery.

Drug-Induced Liver Disease and Drug Use Considerations in Liver Disease

Chronic liver disease encompasses a large number of hepatic disorders. One of the most important etiologies of liver disease is drug-induced liver disease, which is the leading cause of liver failure in patients referred for liver transplantation in the United States. Drug-induced liver disease can present in all forms of acute and chronic liver disease with highly variable clinical presentations. There is no effective treatment for most drug-induced liver disease and the recognition and prevention of drug-induced liver disease remain the most important management strategy. Drug dosing in patients with liver disease represents an even more challenging task to clinicians, as there is only scant information on biomarkers that can be used to predict the pharmacokinetic changes of drugs in patients with underlying liver disease. Several factors contribute to alterations in drugs metabolism and clearance in cirrhotic patients, including the severity of the liver disease and the metabolic pathways of each individual drug. Only general guidelines on dosage adjustment in patients with hepatic impairment are available. When drugs with extensive hepatic metabolism are required in patients with preexisting liver disease, benefit of therapeutic effect must be evaluated against the risk of toxicity, and the drugs must be initiated with extreme caution with appropriate dosage reduction.

Pharmacokinetics and dosage adjustment in patients with hepatic dysfunction

The liver plays a central role in the pharmacokinetics of the majority of drugs. Liver dysfunction may not only reduce the blood/plasma clearance of drugs eliminated by hepatic metabolism or biliary excretion, it can also affect plasma protein binding, which in turn could influence the processes of distribution and elimination. Portal-systemic shunting, which is common in advanced liver cirrhosis, may substantially decrease the presystemic elimination (i.e., first-pass effect) of high extraction drugs following their oral administration, thus leading to a significant increase in the extent of absorption. Chronic liver diseases are associated with variable and non-uniform reductions in drug-metabolizing activities. For example, the activity of the various CYP450 enzymes seems to be differentially affected in patients with cirrhosis. Glucuronidation is often considered to be affected to a lesser extent than CYP450-mediated reactions in mild to moderate cirrhosis but can also be substantially impaired in patients with advanced cirrhosis. Patients with advanced cirrhosis often have impaired renal function and dose adjustment may, therefore, also be necessary for drugs eliminated by renal exctretion. In addition, patients with liver cirrhosis are more sensitive to the central adverse effects of opioid analgesics and the renal adverse effects of NSAIDs. In contrast, a decreased therapeutic effect has been noted in cirrhotic patients with beta-adrenoceptor antagonists and certain diuretics. Unfortunately, there is no simple endogenous marker to predict hepatic function with respect to the elimination capacity of specific drugs. Several quantitative liver tests that measure the elimination of marker substrates such as galactose, sorbitol, antipyrine, caffeine, erythromycin, and midazolam, have been developed and evaluated, but no single test has gained widespread clinical use to adjust dosage regimens for drugs in patients with hepatic dysfunction. The semi-quantitative Child-Pugh score is frequently used to assess the severity of liver function impairment, but only offers the clinician rough guidance for dosage adjustment because it lacks the sensitivity to quantitate the specific ability of the liver to metabolize individual drugs. The recommendations of the Food and Drug Administration (FDA) and the European Medicines Evaluation Agency (EMEA) to study the effect of liver disease on the pharmacokinetics of drugs under development is clearly aimed at generating, if possible, specific dosage recommendations for patients with hepatic dysfunction. However, the limitations of the Child-Pugh score are acknowledged, and further research is needed to develop more sensitive liver function tests to guide drug dosage adjustment in patients with hepatic dysfunction.

Pharmacokinetics and dosage adjustment in patients with hepatic dysfunction

The liver plays a central role in the pharmacokinetics of the majority of drugs. Liver dysfunction may not only reduce the blood/plasma clearance of drugs eliminated by hepatic metabolism or biliary excretion, it can also affect plasma protein binding, which in turn could influence the processes of distribution and elimination. Portal-systemic shunting, which is common in advanced liver cirrhosis, may substantially decrease the presystemic elimination (i.e., first-pass effect) of high extraction drugs following their oral administration, thus leading to a significant increase in the extent of absorption. Chronic liver diseases are associated with variable and non-uniform reductions in drug-metabolizing activities. For example, the activity of the various CYP450 enzymes seems to be differentially affected in patients with cirrhosis. Glucuronidation is often considered to be affected to a lesser extent than CYP450-mediated reactions in mild to moderate cirrhosis but can also be substantially impaired in patients with advanced cirrhosis. Patients with advanced cirrhosis often have impaired renal function and dose adjustment may, therefore, also be necessary for drugs eliminated by renal exctretion. In addition, patients with liver cirrhosis are more sensitive to the central adverse effects of opioid analgesics and the renal adverse effects of NSAIDs. In contrast, a decreased therapeutic effect has been noted in cirrhotic patients with beta-adrenoceptor antagonists and certain diuretics. Unfortunately, there is no simple endogenous marker to predict hepatic function with respect to the elimination capacity of specific drugs. Several quantitative liver tests that measure the elimination of marker substrates such as galactose, sorbitol, antipyrine, caffeine, erythromycin, and midazolam, have been developed and evaluated, but no single test has gained widespread clinical use to adjust dosage regimens for drugs in patients with hepatic dysfunction. The semi-quantitative Child-Pugh score is frequently used to assess the severity of liver function impairment, but only offers the clinician rough guidance for dosage adjustment because it lacks the sensitivity to quantitate the specific ability of the liver to metabolize individual drugs. The recommendations of the Food and Drug Administration (FDA) and the European Medicines Evaluation Agency (EMEA) to study the effect of liver disease on the pharmacokinetics of drugs under development is clearly aimed at generating, if possible, specific dosage recommendations for patients with hepatic dysfunction. However, the limitations of the Child-Pugh score are acknowledged, and further research is needed to develop more sensitive liver function tests to guide drug dosage adjustment in patients with hepatic dysfunction.

Palliation and liver failure: palliative medications dosage guidelines

Palliation of symptoms is important in a variety of conditions, both malignant and nonmalignant. These symptoms may be present in patients with chronic or acute liver failure. However, to date there is a notable lack of reliable information on the use of medications that are commonly required in the palliative care of these patients. To facilitate care, a literature review was conducted with extensive searches of MEDLINE and Micromedex as well as reviews of the major textbooks of pharmacology, palliative care, gastroenterology and hepatology. A table is presented that includes medications organized in groupings of functional importance in palliative medicine such as opioids, antiarrhythmics, antidepressants, aperients, and other medications as selected for use at a Sydney palliative care unit. Data have been collected on the pharmacologic half-life in normal liver function and in cirrhosis. The latter, where suitable data could be obtained, were divided into three subgroups, using the Child-Pugh criteria. The further development of this information may help limit difficulties in choice of medication and reduce potential complications and improve palliation.

Mechanisms of Pharmacokinetic and Pharmacodynamic Drug Interactions Associated with Ritonavir-Enhanced Tipranavir

Tipranavir is a nonpeptidic protease inhibitor that has activity against human immunodeficiency virus strains resistant to multiple protease inhibitors. Tipranavir 500 mg is coadministered with ritonavir 200 mg. Tipranavir is metabolized by cytochrome P450 (CYP) 3A and, when combined with ritonavir in vitro, causes inhibition of CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A in addition to induction of glucuronidase and the drug transporter P-glycoprotein. As a result, drug-drug interactions between tipranavir-ritonavir and other coadministered drugs are a concern. In addition to interactions with other antiretrovirals, tipranavir-ritonavir interactions with antifungals, antimycobacterials, oral contraceptives, statins, and antidiarrheals have been specifically evaluated. For other drugs such as antiarrhythmics, antihistamines, ergot derivatives, selective serotonin receptor agonists (or triptans), gastrointestinal motility agents, erectile dysfunction agents, and calcium channel blockers, interactions can be predicted based on studies with other ritonavir-boosted protease inhibitors and what is known about tipranavir-ritonavir CYP and P-glycoprotein utilization. The highly complex nature of drug interactions dictates that cautious prescribing should occur with narrow-therapeutic-index drugs that have not been specifically studied. Thus, the known interaction potential of tipranavir-ritonavir is reported, and in vitro and in vivo data are provided to assist clinicians in predicting interactions not yet studied. As more clinical interaction data are generated, better insight will be gained into the specific mechanisms of interactions with tipranavir-ritonavir.

Preoperative evaluation of patients with liver disease

Patients with end-stage liver disease often undergo surgery for indications other than liver transplantation. These patients have an increased risk of morbidity and mortality that is related to their underlying liver disease. Assessments of surgical risk provide a basis for discussion of risks and benefits, treatment decision making, and for optimal management of patients for whom surgery is planned. The most useful indicators of surgical risk are indices that predict advanced disease, such as the Child-Turcotte-Pugh score, or those that predict prognosis, such as the Model for End-stage Liver Disease score. Careful preoperative risk assessment, patient selection, and management of various manifestations of advanced disease might decrease morbidity and mortality from nontransplant surgery in patients with liver disease.

Dose adjustment in patients with liver disease

Unfortunately, there is no endogenous marker for hepatic clearance that can be used as a guide for drug dosing. In order to predict the kinetic behaviour of drugs in cirrhotic patients, agents can be grouped according to their extent of hepatic extraction. For drugs with a high hepatic extraction (low bioavailability in healthy subjects), bioavailability increases and hepatic clearance decreases in cirrhotic patients. If such drugs are administered orally to cirrhotic patients, their initial dose has to be reduced according to hepatic extraction. Furthermore, their maintenance dose has to be adapted irrespective of the route of administration, if possible, according to kinetic studies in cirrhotic patients. For drugs with a low hepatic extraction, bioavailability is not affected by liver disease, but hepatic clearance may be affected. For such drugs, only the maintenance dose has to be reduced, according to the estimated decrease in hepatic drug metabolism. For drugs with an intermediate hepatic extraction, initial oral doses should be chosen in the low range of normal in cirrhotic patients and maintenance doses should be reduced as for high extraction drugs. In cholestatic patients, the clearance of drugs with predominant biliary elimination may be impaired. Guidelines for dose reduction in cholestasis exist for many antineoplastic drugs, but are mostly lacking for other drugs with biliary elimination. Dose adaptation of such drugs in cholestatic patients is, therefore, difficult and has to be performed according to pharmacological effect and/or toxicity. Importantly, the dose of drugs with predominant renal elimination may also have to be adapted in patients with liver disease. Cirrhotic patients often have impaired renal function, despite a normal serum creatinine level. In cirrhotic patients, creatinine clearance should, therefore, be measured or estimated to gain a guideline for the dosing of drugs with predominant renal elimination. Since the creatinine clearance tends to overestimate glomerular filtration in cirrhotic patients, the dose of a given drug may still be too high after adaptation to creatinine clearance. Therefore, the clinical monitoring of pharmacological effects and toxicity of such drugs is important. Besides the mentioned kinetic changes, the dynamics of some drugs is also altered in cirrhotic patients. Examples include opiates, benzodiazepines, NSAIDs and diuretics. Such drugs may exhibit unusual adverse effects that clinicians should be aware of for their safe use. However, it is important to realise that the recommendations for dose adaptation remain general and cannot replace accurate clinical monitoring of patients with liver disease treated with critical drugs.

Interactions between recreational drugs and antiretroviral agents

OBJECTIVE

To summarize existing data regarding potential interactions between recreational drugs and drugs commonly used in the management of HIV-positive patients.

DATA SOURCES

Information was obtained via a MEDLINE search (1966-August 2002) using the MeSH headings human immunodeficiency virus, drug interactions, cytochrome P450, medication names commonly prescribed for the management of HIV and related opportunistic infections, and names of commonly used recreational drugs. Abstracts of national and international conferences, review articles, textbooks, and references of all articles were also reviewed.

STUDY SELECTION AND DATA EXTRACTION

Literature on pharmacokinetic interactions was considered for inclusion. Pertinent information was selected and summarized for discussion. In the absence of specific data, prediction of potential clinically significant interactions was based on pharmacokinetic and pharmacodynamic properties.

RESULTS

All protease inhibitors (PIs) and nonnucleoside reverse transcriptase inhibitors are substrates and potent inhibitors or inducers of the cytochrome P450 system. Many classes of recreational drugs, including benzodiazepines, amphetamines, and opioids, are also metabolized by the liver and can potentially interact with antiretrovirals. Controlled interaction studies are often not available, but clinically significant interactions have been observed in a number of case reports. Overdoses secondary to interactions between the "rave" drugs methylenedioxymethamphetamine (MDMA) or gamma-hydroxybutyrate (GHB) and PIs have been reported. PIs, particularly ritonavir, may also inhibit metabolism of amphetamines, ketamine, lysergic acid diethylmide (LSD), and phencyclidine (PCP). Case series and pharmacokinetic studies suggest that nevirapine and efavirenz induce methadone metabolism, which may lead to symptoms of opiate withdrawal. A similar interaction may exist between methadone and the PIs ritonavir and nelfinavir, although the data are less consistent. Opiate metabolism can be inhibited or induced by concomitant PIs, and patients should be monitored for signs of toxicity and/or loss of analgesia. PIs should not be coadministered with midazolam and triazolam, since prolonged sedation may occur.

CONCLUSIONS

Interactions between agents commonly prescribed for patients with HIV and recreational drugs can occur, and may be associated with serious clinical consequences. Clinicians should encourage open dialog with their patients on this topic, to avoid compromising antiretroviral efficacy and increasing the risk of drug toxicity.

Alcohol exposure and paracetamol-induced hepatotoxicity

Most instances of hepatotoxicity due to paracetamol in the United Kingdom and Australia are the result of large overdoses of the drug taken with suicidal or parasuicidal intent. In contrast, serious hepatotoxicity at recommended or near-recommended doses for therapeutic purposes has been reported, mainly from the United States and in association with chronic alcohol use, leading to the widely held belief that chronic alcoholics are predisposed to paracetamol-related toxicity at relatively low doses. Yet the effects of alcohol on paracetamol metabolism are complex. Studies performed in both experimental animals and humans indicate that chronic alcohol use leads to a short-term, two- to threefold increase in hepatic content of cytochrome P4502E1, the major isoform responsible for the generation of the toxic metabolite from paracetamol, although increased oxidative metabolism of paracetamol at recommended doses has not been demonstrated clinically. A reduced hepatic content of glutathione, required to detoxify the reactive metabolite, has been documented in chronic alcoholics, due probably to associated fasting and malnutrition, providing a metabolic basis for any possible predisposition of this group to hepatotoxicity at relatively low paracetamol doses. Simultaneous alcohol and paracetamol ingestion reduces oxidative metabolism of paracetamol in both rodents and humans, predominantly as a consequence of depletion in cytosol of free NADPH. The possibilities that chronic alcohol use may predispose to paracetamol-related hepatotoxicity and that alcohol taken with paracetamol may protect against it, based on these metabolic observations, are examined in this review.

The use of psychotropics in the medically ill

Underlying medical illness may present a challenge when prescribing psychotropic medications. Disease-related changes in pharmacokinetics and pharmacodynamics, as well as vulnerability to side effects, polypharmacy, and potential drug interactions are all important considerations. Successful treatment of psychiatric disorders may have a beneficial impact on medical morbidity and mortality, as well as quality of life. This article reviews the relevant considerations when using psychotropic medications in six major medical populations (cardiac, cerebral vascular, pulmonary, liver, renal, and seizure disorders).

Pharmacokinetics of opioids in liver disease

The liver is the major site of biotransformation for most opioids. Thus, the disposition of these drugs may be affected in patients with liver insufficiency. The major metabolic pathway for most opioids is oxidation. The exceptions are morphine and buprenorphine, which primarily undergo glucuronidation, and remifentanil, which is cleared by ester hydrolysis. Oxidation of opioids is reduced in patients with hepatic cirrhosis, resulting in decreased drug clearance [for pethidine (meperidine), dextropropoxyphene, pentazocine, tramadol and alfentanil] and/or increased oral bioavailability caused by a reduced first-pass metabolism (for pethidine, dextropropoxyphene, pentazocine and dihydrocodeine). Although glucuronidation is thought to be less affected in liver cirrhosis, and clearance of morphine was found to be decreased and oral bioavailability increased. The consequence of reduced drug metabolism is the risk of accumulation in the body, especially with repeated administration. Lower doses or longer administration intervals should be used to remedy this risk. Special risks are known for pethidine, with the potential for the accumulation of norpethidine, a metabolite that can cause seizures, and for dextropropoxyphene, for which several cases of hepatotoxicity have been reported. On the other hand, the analgesic activity of codeine and tilidine depends on transformation into the active metabolites, morphine and nortilidine, respectively. If metabolism is decreased in patients with chronic liver disease, the analgesic action of these drugs may be compromised. Finally, the disposition of a few opioids, such as fentanyl, sufentanil and remifentanil, appears to be unaffected in liver disease.

Comparative effects of oxygen supplementation on theophylline and acetaminophen clearance in human cirrhosis

BACKGROUND & AIMS

Sinusoidal capillarization in cirrhosis may impair the transfer of oxygen into hepatocytes; this may contribute to impaired oxidative drug metabolism. The aim of this study was to test this hypothesis by comparing the effects of oxygen supplementation in cirrhotic patients on the clearance of theophylline, which is dependent on hepatic oxidative metabolism, with its effect on the clearance of acetaminophen, which is reliant on hepatic conjugation reactions.

METHODS

Ten cirrhotic patients awaiting liver transplant and 5 control subjects were studied. Oral acetaminophen (1000 mg) and intravenous theophylline (3 mg/kg) were administered simultaneously on two separate occasions, 7 days apart. Subjects were randomized to breathe either room air or oxygen via face mask at 12 L/min for 9 hours of blood sampling.

RESULTS

Theophylline and acetaminophen clearances were significantly reduced by a mean of 54% and 50%, respectively, in cirrhotic patients compared with controls. Oxygen supplementation improved plasma theophylline clearance in cirrhotic patients by a mean of 34% (P = 0. 001), whereas acetaminophen clearance remained unchanged.

CONCLUSIONS

These findings indicate that, in cirrhosis, impaired hepatocyte oxygenation contributes to reduced oxidative drug metabolism and that oxidative drug metabolism can be improved by oxygen supplementation.

Effects of liver disease on the disposition of the opioid antagonist nalmefene

OBJECTIVES

The pharmacokinetics of nalmefene and its glucuronide metabolite were investigated in 12 patients with liver disease (four patients with mild, five patients with moderate, and three patients with severe liver disease) and 12 age-, weight-, and gender-matched control subjects.

METHODS

Subjects received a single intravenous bolus 2.0 mg dose of nalmefene. Multiple blood and urine samples were collected for 48 hours. Within 1 week of nalmefene administration, antipyrine and galactose clearances were determined as general markers of hepatic metabolism and effective liver plasma flow, respectively. Plasma concentrations of nalmefene were determined by radioimmunoassay.

RESULTS

The antipyrine and galactose clearance values were 56% and 33% lower, respectively, in the patients with liver disease compared with the normal healthy control subjects. The systemic clearance of nalmefene was reduced by 32% (0.61 +/- 0.21 versus 0.90 +/- 0.27 L/hr/kg [mean +/- SD]) and the terminal elimination half-life was increased by 31% (10.5 +/- 1.9 versus 8.0 +/- 2.2 hours) in the patients with liver disease. This was primarily the result of a 31% reduction (0.181 +/- 0.067 versus 0.263 +/- 0.072 L/hr/kg) in nalmefene glucuronide formation clearance. There were no significant differences in nalmefene volumes of distribution or protein binding. There was a significant inverse relationship between nalmefene clearance and Pugh score (r = -0.57; p = 0.004), indicating decreasing nalmefene clearance with increasing severity of liver disease.

CONCLUSIONS

The clearance of nalmefene was significantly reduced in the presence of liver disease. However, because nalmefene will be primarily used in the acute care setting for reversal of opioid-induced effects, it is not likely that these alterations will necessitate a dosage modification.

Effects of phenobarbital on aniline metabolism in primary liver cell culture of rats with ethionine-induced liver disorder

In experiment 1, the amount of aniline (AN) metabolites in the primary cell culture medium of the liver cells obtained from ethionine (ET)-treated rats was compared with that of the control (normal) rats. Although the metabolites detected in both groups were p-aminophenol (p-AP), N-acetyl-p-AP (AAP), acetoanilide (AAN), AAP-glucuronide (AAPG), phenylhydroxylamine sulfate (PHAS) and p-AP-glucuronide (p-APG), the amount of AAP was lower and that of p-APG was markedly higher in the ET-treated rats than in the control rats. In experiment 2, phenobarbital (PB) was orally administered to the ET-treated and control rats at a dose of 100 mg/kg. The time course changes in AN metabolites in the primary cell culture medium of liver cells obtained at 2 or 48 hr after PB treatment were compared with those without PB treatment. In the ET-treated rats, the amount of PHAS was slightly higher at 2 hr after PB treatment, and that of AAP was lower and that of p-APG was higher at 48 hr after PB treatment as compared with those without PB treatment. In the control rats, the amounts of AAP, AAN, p-AP and p-APG at 2 hr after PB treatment remained lower than those without PB treatment, and that of AAP was markedly lower and that of p-APG was higher at 48 hr after PB treatment as compared with those without PB treatment. These findings indicated greater detoxication in the primary liver cell culture in the ET-treated rats than in the control rats. Furthermore, detoxication was greater in the primary cell culture of liver cell obtained from the ET-treated rats after PB treatment than from those without PB treatment, because the production of acetylates (AAP) decreased and p-APG increased (induction of conjugated enzyme) in the PB treatment group.

Cholestasis as a liver protective factor in paracetamol acute overdose

1. The effect of paracetamol overdoses on its disposition was investigated in cholestatic rats. 2. Paracetamol plasma concentration and hepatic accumulation decrease about 70-80% in cholestatic rats. 3. Cholestatic rats intoxicated with paracetamol showed less hepatic damage as concluded from biochemical and histological findings. These data are correlated with liver and plasmatic paracetamol. 4. These results indicate a decrease in paracetamol toxicity related to stagnant bile.

Effects of liver disease on the pharmacokinetics of intravenous and oral chlordesmethyldiazepam

We studied the pharmacokinetics of a single 0.5-mg i.v. dose of chlordesmethyldiazepam in 8 patients with liver disease and in 12 age-matched healthy controls. The kinetics were also studied of a single 1-mg oral dose in the patients with liver disease. After i.v. administration the kinetics of total chlordesmethyldiazepam in patients with liver disease differed from those in controls: elimination half-life was almost twice that in controls (395 and 204 h), as a consequence of a marked reduction in total clearance (0.13 and 0.25 ng.ml-1.h-1), whereas the apparent volume of distribution was similar in patients and controls (4.7 and 3.9 l/kg-1). The free fraction of the drug in patients was higher (5.5%) than in controls (2.9%). Correction for differences in protein binding revealed clearance in the patients was one-fifth (1.8 and 10.5 ng ml-1.kg-1) and volume of distribution one-half (65.0 and 118.4 l.kg-1) that in controls. The systemic availability of oral chlordesmethyldiazepam was high (110%) in spite of a relatively slow absorption rate. These results indicate a need for caution in the administration of chlordesmethyldiazepam to patients with liver disease.

Localization of uridine 5'-diphosphate-glucuronosyltransferase in human liver injury

BACKGROUND/AIMS

Pharmacokinetic studies in patients with cirrhosis have shown a decreased clearance of drugs metabolized by cytochrome P450, whereas drugs metabolized by glucuronidation frequently have a normal elimination. The mechanism for the apparent preservation of glucuronidation has not been elucidated. The aim of this study was to examine the expression of uridine 5'-diphosphate-glucuronosyltransferase (UGT) in human liver injuries.

METHODS

UGT was measured by immunohistochemistry using a UGT polyclonal antibody, which was then compared with a representative isoform of cytochrome P450. Normal liver biopsy specimens (n = 8) and a spectrum of liver injury biopsy specimens (n = 47) were examined.

RESULTS

Compared with normal liver, increased staining for UGT in remaining hepatocytes was seen in liver damaged by chronic alcohol abuse, but the most intense immunoreactivity was observed in remaining and regenerative hepatocytes in specimens with cirrhosis. Primary biliary cirrhosis showed diffusely increased immunoreactivity. Other nonmalignant groups showed an increased staining relative to chronicity of liver disease. In contrast, in all liver injuries, cytochrome P450 staining was reduced as compared with controls.

CONCLUSIONS

Chronic liver damage results in increased UGT in remaining viable hepatocytes. Mechanisms may operate in liver injury to preserve expression of UGT in functional hepatocytes, and this may explain the preservation of glucuronidation in cirrhosis.

Oxygen supplementation restores theophylline clearance to normal in cirrhotic rats

BACKGROUND/AIMS

Capillarization associated with hepatic fibrosis may present a functional barrier to oxygen diffusion into the hepatocyte, and restriction on cellular oxygen supply may represent the rate-limiting constraint on hepatic oxidative drug metabolism. The aim of this study was to test this hypothesis by examining the effect of oxygen supplementation on plasma theophylline clearance in 10 control and 10 cirrhotic rats.

METHODS

Theophylline (3 mg/kg) was administered intravenously on two separate occasions, 24 hours apart, during which time the rats breathed either room air or oxygen (95%) from 1 hour before dosing until the end of plasma sampling with a randomized order of gas exposure.

RESULTS

Theophylline clearance was significantly reduced by a mean of 37% (n = 10; P = 0.003) in cirrhotic rats compared with controls. Oxygen supplementation significantly improved plasma theophylline clearance in cirrhotic rats by a mean of 40% (n = 10; P = 0.007), whereas clearance remained unchanged in healthy rats. Clearance in oxygen-supplemented cirrhotic rats was not significantly different from that in controls (P > 0.05).

CONCLUSIONS

These novel findings indicate an important role for hepatic oxygenation in improving drug disposition in cirrhosis, which may have potentially important clinical implications for the management of this disease.

Release of latent glucuronosyltransferase activity contributes to the sparing of glucuronidation in experimental liver injuries

In patients with parenchymal liver disease, glucuronidation of drugs is generally preserved but oxidation is impaired. This study explores the effects of liver injuries induced in rats by the administration of acute carbon tetrachloride, chronic bile duct ligation and chronic choline deficiency for 30 weeks on the glucuronidation of p-nitrophenol and 1-naphthol, both before and after solubilization of the microsomes and compares this to three measures of oxidation. Cytochrome P450 content was reduced to 17% of control values after acute carbon tetrachloride and to 35% of control values after bile duct ligation. Cytochrome C reductase fell to 58 and 32% of control and aniline hydroxylase to 46 and 13%, respectively, after acute carbon tetrachloride and bile duct ligation. P-nitrophenol glucuronidation by native microsomes was 206 and 73% of controls in the respective models, while 1-naphthol glucuronidation was 167 and 66% of control. Latent uridine diphosphate-glucuronosyltransferase (UDP-GT) activity, that is, differences between solubilized and native activity, was decreased by each liver injury. Chronic choline deficiency had little effect on the oxidation and native glucuronidation activity, although latent glucuronidation activity was lower. These studies suggest a preservation of glucuronidation compared to oxidation at the microsomal level in these experimental liver injuries. The data also support the hypothesis that a release of latent UDP-GT activity may contribute to this phenomenon.

Factors and conditions affecting the glucuronidation of oxazepam

The aim of the present work was to investigate the impact of disease states and environmental and host factors on the glucuronidation of oxazepam. Glucuronidation represents quantitatively one of the most important metabolic conjugation pathways (phase II) in man for the inactivation and detoxication of xenobiotics and endogenous compounds and the liver is the major site for it to take place. Far less attention has been paid to the conjugation reactions in previous clinical research in this field compared to the immense interest in the oxidative biotransformation pathways (phase I). This fact is mainly due to the latter giving rise to active or reactive metabolites with a toxicological potential. The metabolism of oxazepam expresses exclusively the capacity for glucuronide formation. It was a prerequisite to establish the bioavailability of oxazepam prior to succeeding studies on the oral disposition of the drug. A preparation for intravenous administration was created. Clearance was chosen as measurement of the capacity to glucuronidate oxazepam. Severe decompensated liver disease was associated with a significant decrease in oxazepam clearance, that became even more obvious when corrected for by a diminished binding to plasma proteins. This increase in free fraction of oxazepam was substantial and could mainly be accounted for by low plasma albumin values. The results are in part a settlement with earlier studies on glucuronidation in liver disease and they may undoubtedly be ascribed to the severe degree of liver disease. For the first time it was shown that hypothyroidism led to a decline in the clearance and metabolism of oxazepam and paracetamol that is mainly biotransformed by glucuronidation. It was concluded that the enzymes responsible for glucuronidation in hypothyroidism are under the influence of thyroid hormones as is the case with oxidative enzymes. Further studies focused on the effect of host and environmental factors on glucuronidation. A commercially available very low calorie product for the treatment of obesity resulted in a decrease in oxazepam clearance and a lack of co-factors as a consequence of the low calorie intake was explanatorily proposed. Beta-adrenoceptor antagonists are often prescribed together with other drugs and close knowledge on interactions is mandatory but insufficient in regard of drugs being glucuronidated. Despite the mutual metabolic pathway labetalol exerted no dispositional alterations concerning oxazepam. It was moreover suggested that very elderly subjects between the age of 80 to 94 years had a reduced clearance of oxazepam.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Glucuronidation of 7-hydroxy-4-methylcoumarin by microsomes from normal and diseased human livers

Glucuronidation of 7-hydroxy-4-methylcoumarin (7-H-4-MC) by microsomal UDP-glucuronosyltransferases from 12 human liver biopsy samples was studied. Glucuronidation rates were highest for livers with mild cholestasis while those for livers with mild fatty changes were similar to normal livers. The lowest rates were exhibited by livers showing primary or metastatic carcinoma on histological examination. Thus, glucuronidation of not only bile acids but also of other substrates such as 7-H-4-MC may be elevated in cholestasis. These results are also consistent with other studies stating that glucuronidation might be spared in certain mild hepatic diseases.

Drug glucuronidation in humans

Glucuronidation is a major metabolic pathway for a large number of drugs in humans. Conjugation of drugs and other chemicals with glucuronic acid is catalyzed by the multigene UDP-glucuronosyltransferase family. It is believed that a number (unspecified at present) of glucuronosyltransferase isozymes, which probably differ in terms of substrate specificity and regulation, contribute to drug glucuronidation. Factors known to influence the pharmacokinetics of glucuronidated drugs in man, presumably via an effect on specific glucuronosyltransferases, include age (especially the neonatal period), cigarette smoking, diet, certain disease states, coadministered drugs, ethnicity, genetics and hormonal effects.

Psychopharmacology in patients with hepatic and gastrointestinal disease

Psychotropic drugs often need to be prescribed to patients who also have pre-existing gastrointestinal (GI) and/or hepatic disease. This paper addresses the effect of GI and hepatic disease on the pharmacokinetics of psychotropic drugs, the effect of psychotropic drugs on pre-existing GI and hepatic diseases, the adverse GI and hepatic effects of psychotropic medications, the effects of GI medications on mental status, and the potential drug interactions between commonly prescribed GI medications and psychotropic drugs. Drug selection and dosage modification based on these considerations should allow safe and effective psychotropic treatment for patients with pre-existing GI and/or hepatic disease.

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.

Hepatic extraction of morphine is impaired in cirrhosis

Using hepatic vein catheterization this study has provided the first direct measurement of morphine hepatic extraction in 8 controls and 8 cirrhotics. The extraction ratio was 0.52 in the control group and was reduced by 25% in the cirrhotics. This reduction is due to impaired enzyme capacity rather than reduced blood flow. The effect of cirrhosis is less than that reported in similar studies of high clearance oxidized drugs and this lends support to the concept that glucuronidation may be relatively spared in cirrhosis. A discrepancy between the systemic clearance and the hepatic clearance provides indirect support for extra-hepatic metabolism of morphine.

Pharmacokinetics of a new sublingual formulation of temazepam

The pharmacokinetics of a new 10 mg sublingual tablet formulation of temazepam and those of a currently marketed 10 mg oral capsule formulation were evaluated in a group of ten healthy volunteers. No significant differences were observed between the two formulations with respect to any of the pharmacokinetic parameters assessed. Lethargy and somnolence were reported on both capsule and tablet by several subjects at a time which corresponded with the maximum concentration of drug in plasma. The data indicate that the sublingual tablet and orally administered capsule have a similar pharmacokinetic and pharmacodynamic profile.