Effects of subchronic treatment with natural human interferons on antipyrine clearance and liver function in patients with chronic hepatitis

Brivaracetam disposition in mild to severe hepatic impairment

Brivaracetam is a high-affinity synaptic vesicle protein 2A (SV2A) ligand in clinical development for epilepsy. This open-label, single-dose study evaluated brivaracetam disposition in participants with different degrees of hepatic impairment versus matched healthy controls. Twenty-six participants (38-72 years; 19 males and 7 females) with hepatic impairment classified by Child-Pugh score (mild, n = 6; moderate, n = 7; severe, n = 7) or normal hepatic function (n = 6) received a single oral dose of 100 mg brivaracetam. The pharmacokinetics of brivaracetam and its three main metabolites (acid, hydroxy, hydroxyacid) were determined and correlated with impairment severity. Dynamic liver function tests correlated with hepatic impairment severity. The plasma half-life of brivaracetam was 9.8, 14.2, 16.4, and 17.4 hours and the area under the plasma concentration-time curve was 29.7, 44.6, 46.7, and 47.1 µg h/mL in healthy controls and participants with mild, moderate, and severe liver impairment, respectively. Production of the acid metabolite was increased and the hydroxylated metabolites were decreased in participants with hepatic impairment versus healthy controls. Exposure to brivaracetam increased by 50-60% in patients with hepatic impairment, irrespective of severity. The relative importance of biotransformation pathways was altered; cytochrome P450 (CYP)-dependent hydroxylation decreased; CYP-independent acid metabolite formation increased concomitantly.

Effects of pegylated interferon alfa-2b on the pharmacokinetic and pharmacodynamic properties of methadone: a prospective, nonrandomized, crossover study in patients coinfected with hepatitis C and HIV receiving methadone maintenance treatment

BACKGROUND

Hepatitis C virus (HCV) infection is common among methadone-maintained HIV-positive individuals. Pegylated interferon (pegIFN) used in combination with ribavirin is conventional treatment for HCV. However, pegIFN has been associated with adverse effects (AEs) that may simulate opioid withdrawal and be confused with insufficient methadone dosage.

OBJECTIVE

The aim of this study was to determine, using methadone pharmacokinetic properties, whether methadone dosage adjustments are needed on initiation of treatment with pegIFN alfa-2b for HCV in methadone-maintained HIV-positive patients.

METHODS

This prospective, nonrandomized, crossover study was conducted at the Albert Einstein College of Medicine and Montefiore Medical Center (Bronx, New York). Patients who were aged > or =18 years, coinfected with chronic HCV and HIV, and had been receiving methadone maintenance treatment (dosage, 40-200 mg/d PO) for at least 8 weeks prior to enrollment were eligible. We determined mean methadone C(max), T(max), Cn,in, AUC, and oral clearance (CL/F) values over a 24-hour period before (baseline) and after the administration of pegIFN alfa-2b 1.5 microg/kg SC (2 doses given 1 week apart). To determine differences in opiate withdrawal symptoms, one of the primary investigators administered the Subjective Opiate Withdrawal Scale (SOWS) and Objective Opiate Withdrawal Scale (OOWS) at baseline and 7, 14, and 21 days after the administration of the first dose. Study participants underwent weekly clinical evaluation for signs and symptoms of methadone withdrawal and for AEs of pegIFN.

RESULTS

Nine patients were included in the study (7 men, 2 women; 7 Hispanic, 2 black; mean [SD] age, 41 [8.3] years; mean [SD] weight, 75.0 [12.3] kg). We did not observe any significant changes from baseline in mean C(max), T(max), C(min), AUC, and CL/F values despite 80% power to detect a 30% change in either direction. Changes from baseline in SOWS and OOWS scores were not statistically significant. The only AEs reported were mild and consistent with those expected after pegIFN alfa-2b administration, such as inflammation at the injection site and mild, brief, flu-like symptoms.

CONCLUSION

Based on the results of this small, prospective, nonrandomized study, pegIFN alfa-2b did not appear to precipitate opioid withdrawal in this sample of methadone-maintained persons with HIV and chronic HCV coinfection; methadone dosage adjustments were unlikely to be needed.

Antipyrine clearance in comparison to conventional liver function tests in hepatitis C virus patients

In this study, 15 healthy volunteers and 96 patients with hepatitis C virus, classified according to Child-Pugh into 36 Child-A, 31 Child-B and 29 Child-C, were examined. All subjects ingested 600 mg antipyrine in the form of hard gelatinous capsules after overnight fasting. One milliliter of saliva was collected at 4 and 24 h after ingestion of antipyrine and analyzed using high-performance liquid chromatography. Blood samples were collected from all subjects for examination, using conventional liver function tests. The pharmacokinetic variables for antipyrine were determined using the two concentration time points selected. A cut-off value of 0.34 ml/min/kg was used to distinguish between cirrhotic and non-cirrhotic patients. Alanine aminotransferase, aspartate aminotransferase and gamma-glutamyl transferase values were significantly higher with significantly lower antipyrine clearance in Child-A, B, and C patients than in normal volunteers. The total protein concentration was significantly lower in Child-B and C patients. Moreover, AST was significantly higher in Child-C patients and antipyrine clearance was lower in Child-B and C patients than in Child-A patients. Antipyrine clearance showed a significant negative correlation with Child-Pugh scores, total protein, the international normalization ratio of prothrombin time and globulin, and a positive correlation with albumin and albumin-to-globulin ratio. Unlike most of the conventional liver function tests, antipyrine clearance, which represents the intrinsic clearance capacity of the liver, measured using saliva, proved to be a sensitive marker of liver function. It was significantly impaired in the Child-Pugh group A patients with the least hepatic impairment. The international normalization ratio of prothrombin time was just as informative as antipyrine clearance in identifying minimal hepatic impairment.

Alfentanil-induced miosis as a surrogate measure of alfentanil pharmacokinetics in patients with mild and moderate liver cirrhosis

OBJECTIVES

(i) To evaluate the pupillary response to alfentanil as a surrogate measure of alfentanil pharmacokinetics in cirrhotic patients and to compare the data observed in cirrhotic patients with those found in healthy volunteers (historical control group); and (ii) to compare this test with other liver function tests in cirrhotic patients.

METHODS

Six patients with mild cirrhosis (Child-Pugh grade A) and six patients with moderate cirrhosis (Child-Pugh grade B) were studied after a single 15 microg/kg bolus of alfentanil. Alfentanil plasma concentrations were measured by liquid chromatography-tandem mass spectrometry, and pupillary responses were measured with a Pupilscan II pupillometer. Alfentanil pharmacokinetics (plasma concentration, area under the plasma concentration-time curve from time zero to infinity [AUC(infinity(p))] and from time zero to 2 hours [AUC(2(p))], apparent volume of distribution at steady state, clearance and terminal elimination half-life [t((1/2)(p))]) and miosis pseudo-kinetic parameters [AUC(infinity)((miosis)), AUC(2)((miosis)), t((1/2))((miosis))] were determined using a noncompartmental analysis method. In six patients (three Child-Pugh grade A and three Child-Pugh grade B), antipyrine (measure of liver intrinsic activity) and D-sorbitol (measure of liver blood flow) tests were performed.

RESULTS

A significant correlation was found between the alfentanil AUC(infinity(p)) and AUC(infinity)((miosis)) (r = 0.6, p < 0.05) in cirrhotic patients. This correlation was even more significant if AUC determinations were limited to the first 2 hours after alfentanil administration (r = 0.9, p < 0.01). Statistically significant differences in pharmacokinetics and miosis pseudo-kinetic parameters were observed between cirrhotic patients and healthy volunteers from our previous experiment (historical control group). The correlations were significant between alfentanil clearance and antipyrine clearance (n = 6, r = 0.9, p < 0.05), alfentanil clearance and steady-state hepatic blood clearance [CL(H(b))] measured by the D-sorbitol test (n = 6, r = 0.9, p < 0.05).

CONCLUSION

Alfentanil pharmacokinetic parameters were correlated with miosis pseudo-kinetic parameters in cirrhotic patients. There was a significant decrease in pharmacokinetics and miosis pseudo-kinetics in cirrhotic patients compared with volunteers from the historical control group. Alfentanil-induced miosis has the advantage of being noninvasive and can be limited to miosis measurements during the first 2 hours after alfentanil administration in cirrhotic patients. We thus propose to substitute the AUC(2(miosis)) for alfentanil pharmacokinetics in cirrhosis.

Important role of prodromal viral infections responsible for inhibition of xenobiotic metabolizing enzymes in the pathomechanism of idiopathic Reye's syndrome, Stevens-Johnson syndrome, autoimmune hepatitis, and hepatotoxicity of the therapeutic doses of acetaminophen used in genetically predisposed persons

Upper respiratory tract febrile illnesses caused by various viruses, mycoplasma, chlamydia infections, and/or inflammatory diseases are usually observed a few days to a few (several) weeks before the onset of Reye's syndrome, Stevens-Johnson syndrome, autoimmune hepatitis (hepatotropic virus infections), or hepatotoxicity associated with therapeutic administration of acetaminophen in persons with varying degrees of deficits of important enzymatic activity. Activation of systemic host defense mechanisms by inflammatory component(s) results in depression of various induced and constitutive isoforms of cytochrome P-450 mixed-function oxidase system superfamily enzymes in the liver and most other tissues of the body. Because several cytochrome P-450 enzymes activities important for biotransformation of many endogenous and egzogenous substances show considerable variability between individuals, in some genetically predisposed persons, even the administration of therapeutic doses of a drug may result in serious clinical mishaps, if an important concomitant risk factor (eg, acute viral infection) is involved. Several inflammatory cytokines, such as interleukins, transforming growth factor beta1, human hepatocyte growth factor, and lymphotoxin, downregulate gene expression of major cytochrome P-450 enzymes with the specific effects on mRNA levels, protein expression, and enzyme activity observed with a given cytokine varying for each P-450 studied, thus eventually leading to metabolite-mediated adverse drug reactions and immunometallic diseases which sometimes result in tissue injury beyond the site(s) where metabolic bioactivation takes place. On the other hand, it must be emphasized that inhibition of metabolism of several drugs, as well as influence on the concentration and/or ratio of various cytokines in inflamed tissues, may exert beneficial effects in patients with different diseases, thus opening new therapeutic possibilities. Clinically relevant interactions may be exemplified by the effects of some fluoroquinolone antibiotics, such as pefloxacin and ciprofloxacin, which probably have a steroid-sparing effect in some patients with frequently relapsing nephrotic syndrome, and an increased bioavailability of several drugs following concomitant intake with freshly pressed grapefruit juice, eventually caused by inhibition of their metabolism, mediated mainly by CYP3A and specifically inhibited by naturally occurring flavonoids.

Alteration of drug biotransformation and elimination during infection and inflammation

During infection or inflammation, the expression of cytochrome P450 and its dependent biotransformation pathways are modified. This results in a change in the capacity of the liver to handle drugs and in alterations in the production and elimination of endogenous substances throughout the body. The majority of the CYP isoforms are modified at pre-translational steps in protein synthesis, and, in most cases, cytokines are involved as mediators of the response. Recent information suggests that inflammatory responses that are localized to the CNS cause a loss of CYP within the brain. This is accompanied by a parallel down-regulation of CYP in peripheral organs that is mediated by a signaling pathway between the brain and periphery. This review covers the loss that occurs in the major mammalian CYP families in response to infection/inflammation and the mediator pathways that are key to this response.

Hepatic drug metabolism and immunostimulation

When host defence mechanisms are stimulated there is a concomitant decrease in cytochrome P450 based drug biotransformation and elimination. This has resulted in a number of clinically important unwanted drug responses in patients with infections or inflammatory responses. The loss in cytochrome P450 is predominantly an effect at the level of the gene expression and the majority of enzyme forms examined to date are involved. Although the effect occurs predominantly in the liver it has been recently shown that inflammatory responses in the brain also cause a loss of the same enzyme forms in that organ. The loss of cytochrome P450 in the brain in response to localised inflammation is accompanied by a similar loss in the liver. The decrease of cytochrome P450 and its dependent drug biotransformation is of concern whenever drugs are used in patients with infections or disease states with an inflammatory component.

Assessment of antipyrine kinetics from saliva or plasma: influence of age

The purpose of this study was to investigate whether antipyrine estimation in saliva provides valid information on plasma antipyrine clearance (APCl) and can be useful as an index of changes in drug metabolism with age. Antipyrine kinetics was studied in 93 elderly (mean age 82 years) and 23 young (mean age 29 years) volunteers. Plasma antipyrine half-life (APt1/2) increased and plasma APCl declined with age. No significant difference between plasma- and saliva-derived parameters was found in either young or old subjects. However, the saliva/plasma ACCl ratio tended to increase with age. A highly significant correlation between saliva and plasma APCl or APt1/2 was found in young subjects. Values were less closely related in the elderly and the slope of the saliva/plasma APCl relationship was significantly different in both groups of subjects. Residual variance was higher in the regressions corresponding to the elderly. The findings in the study indicate that the relationship between saliva and plasma kinetics in young subjects becomes less reproducible with age.

Antipyrine clearance in surgical patients maintained on hypocaloric peripheral parenteral nutrition

BACKGROUND

Antipyrine clearance (CLAP) constitutes a sensitive indicator of hepatic microsomal enzyme activity providing specific information on hepatic function. The purpose of this study was to evaluate the influence of hypocaloric peripheral parenteral nutrition on CLAP in patients receiving nutrition support after elective surgery.

METHODS

CLAP was measured in 15 patients before elective gastrointestinal surgery and 6 days after the surgery. Antipyrine (1 g) was administered orally, and CLAP was determined by the one-sample method. Subjects received a postoperative 786 kcal/d regimen providing 66 g of amino acid per day and 133 g of glucose per day for 5 days. Nutritional status was evaluated by anthropometric parameters. A control group of 15 patients received no postoperative hypocaloric peripheral parenteral nutrition but received conventional fluid therapy.

RESULTS

Mean CLAP was increased by 61% (0.66 +/- 0.06 mL/min.kg-1 body wt vs 0.41 +/- 0.05 mL/min.kg-1 body wt in the preoperative period; p < .001), and antipyrine half-life was reduced by 42% (10.9 +/- 1.0 hours vs 18.9 +/- 2.0 hours; p < .001) after 5 days of hypocaloric peripheral parenteral nutrition. No significant modification was shown among control patients in CLAP (0.54 +/- 0.07 mL/min.kg-1 body wt vs 0.46 +/- 0.05 mL/min.kg-1 body wt in the preoperative period) or in antipyrine half-life (14.0 +/- 1.4 hours vs 16.5 +/- 1.8 hours). No significant correlation was observed between CLAP changes and those for the nutritional status of the patients.

CONCLUSIONS

The results of our study indicate that oxidative drug-metabolizing capacity is increased in surgical patients maintained on hypocaloric peripheral parenteral nutrition. Clinicians should be conscious of the potential of this effect for altering the efficacy or toxicity of many therapeutic agents.

Elimination of antipyrine and its metabolites in interferon treated hepatitis C

1. To study the effect of interferon on hepatic drug metabolism in chronic hepatitis C, we examined nine patients before and at the end of 6 months of interferon treatment. 2. Routine liver function was determined together with the salivary clearance of antipyrine and the 48 h urinary excretion of the main metabolites of antipyrine: 4-hydroxyantipyrine, 3-hydroxymethylantipyrine and norantipyrine before and after 6 months of interferon treatment. 3. Liver pathology, routine liver function, and antipyrine metabolism remained unchanged after patients were treated for 6 months with interferon for a histologically advanced but clinically compensated chronic hepatitis C.

Clinical toxicity of the interferons

Since their initial description in 1957, the interferons (IFNs) have been increasingly used to treat a wide array of diseases. Acute adverse effects, i.e. 'flu-like' syndromes, hypo- or hypertension, tachycardia, headache, myalgias and gastrointestinal disorders, occur within the first hour or day after starting treatment. They are seldom treatment-limiting and are easily manageable. Sub-acute and chronic effects develop after several days, usually within 2 and 4 weeks of therapy. The most typical is neurological toxicity, including fatigue/asthenia, and behavioural and cognitive changes. Such symptoms may seriously impair quality of life and result in treatment discontinuation. Seizures have seldom been described. Other infrequent central nervous system adverse effects include vertigo, cramp and oculomotor nerve paralysis. Distal paraesthesias and peripheral neuropathy have been reported. IFN-associated autoimmunity is quite rare but a matter of concern. Biological or clinical manifestations usually require several months to become apparent. Autoantibodies have been shown to develop in most patients but have been inconsistently associated with clinical symptoms of systemic lupus erythematosus, rheumatoid-like arthritis and thyroiditis. Both hypo- and hyperthyroidism have been described but are usually reversible. Other infrequent autoimmune reactions include diabetes, pemphigus and worsening of multiple sclerosis. Although several patients present with a pre-existing autoimmune disorder, no predisposing factor has been clearly established. While hypotension and tachycardia are the most frequent acute cardiovascular complications, a few additional cases of cardiac arrhythmias and myocardial ischaemia have been reported after a short course or several weeks of treatment. These latter complications do not appear to be dose-dependent or age-related. Isolated cases of congestive heart failure have also been described. Mild proteinuria has been observed in 15 to 25% of patients, but acute renal toxicity is uncommon. A transient rise in serum aminotransferase levels is frequently noted during the first stage of therapy, especially in patients receiving the highest dosages. Direct hepatotoxicity is extremely rare. Autoimmune hepatitis, which is ill-diagnosed as chronic viral hepatitis, and de novo induction of autoimmune hepatitis, account for the majority of liver diseases. Haematotoxicity is relatively common but mild to moderate, and develops gradually during the first weeks of treatment. Neutropenia is the most common haematological toxicity, but is usually not dose-limiting and resolves rapidly upon drug discontinuation. Myelosuppression, autoimmune and immune allergic haemolytic anaemias and thrombocytopenias have seldom been described. Cutaneous adverse effects comprised nonspecific erythema and hair loss and, less frequently, vasculitis, local ulcerations at the site of injection and exacerbation of psoriasis.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of long-term treatment with naltrexone on hepatic enzyme activity

The influence of naltrexone on liver function in heroin addicts was studied, with respect to the metabolizing function by using the antipyrine clearance and to cellular damage by monitoring plasma levels of hepatic enzymes. The clearance of antipyrine was not affected by naltrexone treatment, and, during the study period, the use and withdrawal of benzodiazepines and alcohol did not change this parameter; moreover, there was no relationship between changes in plasma hepatic enzymes and antipyrine half-life. Mean plasma levels of hepatic enzymes did not show significant modification in the course of treatment with naltrexone.