Serial antipyrine clearance studies detect altered hepatic metabolic function during spontaneous and interferon-induced changes in chronic hepatitis B disease activity

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.

The C-caffeine breath test distinguishes significant fibrosis in chronic hepatitis B and reflects response to lamivudine therapy

BACKGROUND

The 13C-caffeine breath test is a non-invasive, quantitative test of liver function.

AIM

To determine the utility of the 13C-caffeine breath test in chronic hepatitis B virus and its ability to monitor response to lamivudine.

METHODS

Forty-eight chronic hepatitis B virus patients and 24 controls underwent the 13C-caffeine breath test. In 28 patients commenced on lamivudine, 13C-caffeine breath tests were performed at 1 week (n = 12) and after 1 year of therapy.

RESULTS

Patients with Metavir F0-1 fibrosis (2.30 +/- 1.02 Delta per thousand per 100 mg caffeine) had a 13C-caffeine breath test similar to controls (2.31 +/- 0.85, P = 0.96). However, patients with F2-3 fibrosis (1.59 +/- 0.78, P = 0.047) and cirrhotic patients (0.99 +/- 0.33, P = 0.001) had a decreased 13C-caffeine breath test. Fibrosis correlated best with the 13C-caffeine breath test (r(s) = -0.62, P < 0.001). The 13C-caffeine breath test independently predicted significant (F > or = 2) and advanced (F > or = 3) fibrosis and yielded the greatest area under the receiver operating characteristic curve (0.91 +/- 0.04) for predicting advanced fibrosis. The 13C-caffeine breath test was unaltered by 1 week of lamivudine but improved by 61% (P < 0.001) in responders to long-term lamivudine, whereas in those with viraemia and elevated alanine aminotransferase, values remained stable or deteriorated.

CONCLUSION

The 13C-caffeine breath test distinguishes chronic hepatitis B virus-related fibrosis and detects improvement in liver function in response to long-term lamivudine.

Changes in antipyrine clearance and platelet count, but not conventional liver tests, correlate with fibrotic change in chronic hepatitis C: value for predicting fibrotic progression

OBJECTIVE

We tested whether fibrotic progression in chronic hepatitis C could be predicted by liver tests, antipyrine clearance, or platelet count.

METHODS

In 58 patients (6 untreated, 52 interferon-treated), a second liver biopsy was taken median 4.5 yr after first histologic diagnosis. We used receiver operating characteristic curves to determine whether changes in conventional liver tests, antipyrine clearance, or platelet count were predictive of altered hepatic fibrosis score.

RESULTS

Apart from a weak association with change in ALT, conventional liver tests (albumin, bilirubin, prothrombin time) failed to correlate with changes (Delta) in hepatic fibrosis, but there were significant correlations between deltaantipyrine clearance or deltaplatelet count and deltafibrosis score (p < 0.01). As indicated by areas under the receiver operating characteristic curves, the diagnostic accuracy of deltaantipyrine clearance for fibrotic progression was 68%; for Deltaplatelet count it was 80%. With defined cut-off values (-0.05 ml/min/kg for deltaantipyrine clearance; -41 x 10(9)/L for deltaplatelet count), the negative predictive values for fibrotic progression were 85% with antipyrine clearance and 89% with platelet count. Corresponding positive predictive values were 48% and 91%, respectively.

CONCLUSIONS

Changes in antipyrine clearance and platelet count are more sensitive than conventional tests for indicating fibrotic change in chronic hepatitis C. Both could be used to reliably identify those who do not have fibrotic progression, and platelet count also has a high positive predictive value for disease progression.

How reversible is hepatic functional impairment in autoimmune hepatitis?

BACKGROUND AND AIMS

We quantifed the short-term effects of immunosuppressive therapy on hepatic metabolic function in autoimmune hepatitis to establish how long it takes to achieve maximum functional improvement.

METHODS

We studied 14 newly diagnosed patients with autoimmune hepatitis (12 type 1, two type 2) by antipyrine clearance and conventional liver tests, then repeated studies at 3-6 month intervals during the first 18 months of immunosuppressive therapy.

RESULTS

Low values for antipyrine clearance were found in 13 of 14 cases; serum albumin concentration was low in four, bilirubin raised in eight and prothrombin time prolonged in four. Following immunosuppressive treatment for 3 months, antipyrine clearance improved by 98% (standard error of the mean 24%), which was proportionally greater than for serum albumin, bilirubin or prothrombin time. Antipyrine clearance and serum albumin continued to improve after 6-12 months of immunosuppressive treatment in several cases, whereas there were no further improvements in alanine aminotransferase (ALT), bilirubin and prothrombin time.

CONCLUSIONS

In the short term, immunosuppressive therapy for autoimmune hepatitis markedly improves hepatic metabolic function, which is particularly striking for the sensitive metabolic test antipyrine clearance, but may also be seen with serum albumin. However, it may take up to 12 months to achieve maximal functional recovery. Management guidelines on autoimmune hepatitis should be extended to emphasize that changes in hepatic metabolic function, as well as ALT and gamma-globulin levels, be taken into consideration in the definition of remission.

Impairment of metabolic function in chronic hepatitis C is related to factors associated with resistance to therapy

OBJECTIVE

Liver disease causes a loss of hepatic function, and remission is associated with improved functional hepatic mass. The object of the present study was to investigate whether liver metabolic function assessed by antipyrine clearance is related to other disease characteristics influencing response to therapy in chronic hepatitis C.

METHODS

Patients (n = 96) received three different treatment regimens: one group received interferon alfa-2b for 48 wk; in a second group with maintained positive hepatitis C virus (HCV) RNA after 12 wk, interferon was combined for 36 wk with oral ribavirin; and patients who were relapsers or nonresponders to a previous therapy with interferon alone received interferon alfa-2b plus ribavirin for 48 wk.

RESULTS

Twenty-five patients (26%) showed sustained normalization of ALT levels and negative HCV RNA 6 months after therapy. The response was more likely to be sustained in patients with a genotype other than 1 (52.0% vs 15.5% in patients with genotype 1, p < 0.001), and the percentage of sustained responders was higher among patients who demonstrated negativity of HCV RNA at the end of 4 wk of treatment (64% vs 13% without negativity, p < 0.001). Sustained response was associated with significantly lower baseline serum ferritin (-46%, p < 0.01) and duration of infection (-33%, p < 0.01). Baseline antipyrine clearance was higher in sustained responders than in nonresponders (+19%, p < 0.05) and lower in genotype 1 patients than in those with a genotype other than 1 (-24%, p < 0.05). Antipyrine clearance increased by 12% at the end of the 48-wk course of treatment among sustained responders (+34% vs nonresponders, p < 0.001) and still remained elevated at the end of the follow-up (+35% vs nonresponders, p < 0.001).

CONCLUSION

In summary, the present study shows that liver oxidative metabolism is related to antiviral response rates and suggests that much of the effect is explained by viral genotype.

The effect of folic acid on the drug metabolizing liver function in man with viral hepatitis

The investigations were carried out on 31 patients (16 men and 15 women, at the age of 20-50) with viral hepatitis. The all patients were divided at two groups. The first group (12 man) received usual treatment (diet, corsil), the second group (19 man) received in addition to the base treatment folic acid (5 mg per day, 10 days). It was found, that at patients with viral hepatitis was decreased the activity of monooxygenase system of liver. So, period of semielimination (T1/2) of antipyrine (AP) was greater in 1,4 time, area under the pharmacokinetic curve - 1,5 time and clearance was below by 39% than in volunteers (29 man). On day of treatment only by corsil, the rate of elimination of AP and clearance were increased by 34 and 31% (p < 0.05) respectively, T1/2 was decreased by 23% (p < 0.05) and area under the pharmacokinetic curve - 17 %. On 10 day of treatment by corsil with folic acid (5 mg per day), the rate of elimination of AP and clearance was increased by 43% (p < 0.05), area under the pharmacokinetic curve and T 1/2 were decreased by 30 and 33% (p < 0.05) respectively. The positive effect of folic acid in treatment of hepatitis at restoration period may be cause participating its derivatives in de novo nucleotide synthesis.

Antipyrine clearance in chronic and neoplastic liver diseases: a study of 518 patients

Antipyrine metabolism is widely used as an index of the drug-metabolizing reserve of the liver. It is well known that metabolism of this drug is impaired in subjects with acute hepatitis or cirrhosis, but conflicting data have been reported regarding patients with chronic postinfectious hepatitis or liver cancer. We studied conventional liver-function parameters and antipyrine metabolism (antipyrine per o.s. 18 mg/kg) in 518 subjects. One hundred and one patients had liver metastases (various primaries). Based on the number and size of lesions, the hepatic involvement was considered minimal in 47 and massive in 54 (groups B1 and B2, respectively). One hundred and two had chronic active hepatitis (CAH); 51 patients with histological evidence of fibrosis/early cirrhosis and 51 patients were without histological evidence of fibrosis/early cirrhosis. Ninety-two had histologically confirmed cirrhosis (group D), and the remaining 120 had cirrhosis and hepatocellular carcinoma (group E). The control group was composed of 103 subjects with healthy livers (group A). Antipyrine clearance (AP Cl) in CAH patients with fibrosis (0.246 +/- 0.98 mL/min per kg) was similar to that observed in patients with cirrhosis (0.223 +/- 0.148 mL/min per kg), and both values were significantly lower than that found in CAH patients without fibrosis (0.406 +/- 0.159 mL/min per kg, P < 0.01). Antipyrine clearance in patients with liver metastases (0.426 +/- 0.174 mL/min per kg) was similar to that of the healthy group (0.489 +/- 0.210 mL/min per kg). Cirrhotics and cirrhotics with hepatocellular carcinoma (HCC) presented similar degrees of impairment. Antipyrine clearance was positively correlated with serum albumin (r2 = 0.10, P = 0.01) and prothrombin time (r2 = 0.129, P < 0.01) in all groups, except those with liver metastases. In patients with CAH, the presence of fibrosis/cirrhosis is associated with impaired antipyrine metabolism. The lack of impairment in groups with liver metastases suggests that the functional hepatic reserve is maintained even in the presence of massive neoplastic invasion.

Two years versus six months of interferon therapy for chronic hepatitis C

Short-term (end-of-treatment) responses (ETR) to interferon (IFN) therapy for chronic hepatitis C are encouraging; however, the relapse rate is high, and long-term response is obtained in only 12-25% of patients. The Australian Hepatitis C Study Group conducted a trial of 230 patients that compared the standard 3 MU three times a week six-month course of IFN-alpha2b with 5 MU three times a week for six months (5 MU group) or 3 MU three times a week for two years (two-year group). ETR (normalization of serum aminotransferase level until the end of treatment) rates based on an intent-to-treat analysis were 64% for the 5 MU group and 58% for the combined 3 MU groups. After six months of treatment, the overall relapse rate was 71%, and the long-term response (LTR; continued normal aminotransferase until six month follow up) rate did not differ significantly between the 3 MU (17% of all treated, 27% ETR) and 5 MU groups (20% of all treated, 31% ETR). In contrast, among the 46 patients who exhibited an ETR in the two-year group, 27 (59%) had a LTR to IFN, resulting in an overall LTR rate of 33% for all patients treated for up to two years (P < 0.001 compared with 3 MU group). Among these 46 subjects, 11 did not complete the full two-year course, including eight who withdrew due to adverse effects. Nine of these 11 patients had received at least 12 months of therapy. All 18 LTR subjects tested (irrespective of treatment group) were serum HCV-RNA negative at the 12-month follow-up evaluation. Improvement in hepatic inflammation was significantly greater among those treated for two years compared with six months, but there was no reduction in fibrosis score in any group. Among the entire study group, treatment duration, liver histology, and liver function (assessed by antipyrine clearance test) were the only independent predictors of ETR, although HCV genotype was closely related to histological severity (eg, cirrhosis was present in 60% of type 1 and 18% of type 3). Viral load and duration of infection were additional predictors of LTR; however, there were insufficient data to determine whether prolonging treatment beyond six months overcomes the negative impact of these predictors. Continuing IFN therapy for at least 12 months decreases the relapse rate by 50% and thereby improves the LTR rate compared with a six-month treatment course. However, our experience of 24 months of treatment indicates that initial IFN treatment courses of this duration are not well tolerated by approximately 20% (8/46) of patients and are unlikely to improve the results obtained with 12-18 months of treatment.

Clinical significance of the trimethadione tolerance test in chronic hepatitis: a useful indicator of hepatic drug metabolizing capacity

Trimethadione (TMO) was chosen as an indicator of quantitative hepatic microsomal function, and its pharmacokinetics were studied in 52 patients with chronic hepatitis. Findings in these patients were compared with those for 26 healthy subjects and 13 patients with renal failure. Patients with chronic hepatitis, but not those with renal failure, showed significant reduction in clearance (CL) and prolongation of half-life (t1/2), and the extent of abnormalities was found to reflect the severity of histologic changes in liver tissue. The serum dimethadione (DMO)/TMO ratio 4 h after the administration of TMO altered in parallel with the CL and t1/2 of TMO, and abnormalities in this simple ratio were also related to the histologic severity of changes in the liver tissue. A low DMO/TMO ratio (< 0.4) was associated with advanced histologic changes (chronic active hepatitis with bridging or chronic active hepatitis with cirrhosis), whereas a high DMO/TMO ratio (> 0.4) was associated with mild histologic changes (chronic persistent hepatitis or chronic active hepatitis) (sensitivity, 0.81; specificity, 0.86). These results indicate that the DMO/TMO ratio, which can be obtained from a single blood sampling, reflects the histologic severity of changes in tissue liver, and that the TMO tolerance test is a useful indicator of quantitative liver function.

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.

Efficacy of steroid withdrawal and low-dose interferon treatment in chronic active hepatitis B. Results of a randomized multicenter trial. Swiss Association for the Study of the Liver

Fifty-six patients with biopsy-proven, chronic active hepatitis B were included in a multi-center, randomized trial comparing steroid withdrawal followed by 1.5 MU recombinant interferon alpha 2b (Intron) with placebo withdrawal followed by either 1.5 or 5 MU interferon. The patients were equally distributed between the treatment groups with respect to biochemical and histologic activity as well as with respect to DNA levels and quantitative liver function tests. One patient was lost to follow up. After 1 year of treatment, 10/18, 13/19 and 11/18 patients had lost hepatitis B virus DNA in the three groups, respectively (non-significant). Transaminase levels were normal in 27/34 of the responders but in only 4/21 of the non-responders (p < 0.0001). Both galactose elimination capacity and aminopyrine breath test improved significantly in responders, but either did not change (aminopyrine breath test) or deteriorated in non-responders (galactose elimination capacity). Biopsy score improved in both groups but this reached statistical significance only in responders. This effect was due to improvements in both inflammatory and fibrotic activity. Side effects included almost universally a flu-like syndrome, granulocytopenia (1), depression (3) and thyroid dysfunction (2). Two deaths occurred, one due to hepatocellular cancer, and the other to hepatorenal syndrome after spontaneous bacterial peritonitis. A severe cytolytic episode was observed in three patients in the steroid withdrawal group. We conclude that in patients with marked histologic activity, lower doses of interferon may be as effective as the standard dose of 5 MU.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Identification of patients with impaired hepatic drug metabolism using a limited sampling procedure for estimation of phenazone (antipyrine) pharmacokinetic parameters

Phenazone (antipyrine) 1g was given by short intravenous infusion to 62 study participants (10 healthy drug-free volunteers and 52 patients with chronic liver disease). A Bayesian approach was developed to determine the individual pharmacokinetic parameters of phenazone. Statistical characteristics of the population pharmacokinetic parameters were first evaluated for 30 patients. When combined with 1 plasma drug concentration from members of the second group, these led to a Bayesian estimation of individual pharmacokinetic parameters for the remaining 32 individuals. Total clearance computed by Bayesian estimation was compared with maximal likelihood estimation of this parameter, the classical procedure. No statistically significant differences were found. Performance of the developed methodology was evaluated by computing bias and precision. The mean error was 0.0477 L/h. The precision of the prediction of this parameter (0.155 L/h) remained lower than the interindividual standard deviation (0.765 L/h). This procedure enables the estimation of individual pharmacokinetic parameters for phenazone. In this study, numerous laboratory tests were performed. A highly significant correlation (p < 0.001) was found between phenazone clearance and the prothrombin time, albumin, gamma-globulin, factor V, antithrombin III, fibrinogen and total bilirubin. Discriminant analysis determined that protein, alkaline phosphatase, creatininaemia and gamma-globulin had more significant discriminating power and gave better prognostic results than those seen with the Child-Pugh test.

Prediction of response to interferon in patients with chronic active hepatitis C, and evidence that this improves hepatic metabolic function

We sought to ascertain whether response to alpha interferon treatment could be predicted among patients with chronic active hepatitis C, and whether antipyrine clearance estimations would determine changes in liver function with this disease. The patients came from a randomized controlled trial, with patients who were initially untreated eventually being offered interferon treatment. Among 28 patients treated with interferon 18 (64%) responded with normalization of serum aminotransferase levels. Responders were less likely to have acquired hepatitis C by blood transfusion and more likely to have acquired it by intravenous drug abuse (P less than 0.05). All 13 patients with less severe chronic active hepatitis responded to interferon but only 5 of 15 patients with progressive fibrosis or cirrhosis responded (P less than 0.01). During 8-39 (median 19) months of observation of 16 untreated patients, there was a significant fall in antipyrine clearance (Cl-Ap) but no change in serum albumin. Among interferon-treated patients, Cl-Ap improved in 9 of 16 compared with 1 of 14 controls observed for the same time period (P less than 0.02). It is concluded that Cl-Ap is a sensitive test for detecting changes in liver function during chronic hepatitis. Without treatment, deterioration is evident at 18 months in 50% of patients with chronic active hepatitis C. Conversely, normalization of serum aminotransferase levels by interferon is associated with improvement of Cl-Ap.(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.

Evaluation of patients with portal hypertension

In order to select the most suitable management of portal hypertension, a full evaluation of the patient is desirable. The aspects studied should include the possible causes of portal hypertension and the disease and function of the liver, as well as the psychosocial aspects of this condition. The usual reason to investigate the presence and causes of portal hypertension is the detection of gastroesophageal varices. The estimated probability of bleeding from the varices and the cause of the varices should be investigated. If cirrhosis is detected, then its cause or mechanism should be clarified and the activity of the process estimated in semiquantitative terms. If therapy is available, it should be initiated. The evaluation of liver function is based on quantitative measurements of hepatocellular metabolic function (such as the galactose elimination capacity or antipyrine clearance), liver volume (weight), liver blood flow, and systemic hemodynamics (cardiac output index).