Quantifying hepatic function in the presence of liver disease with phenazone (antipyrine) and its metabolites

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.

Effect of antipyrine on the gastric emptying of liquid in rats

Antipyrine (At) and dipyrone (Dp) delay gastric emptying (GE) in rats. The objective of the present study was to assess the effects of intravenous (iv) and intracerebroventricular (icv) administration of At and Dp on the GE of liquid by rats. GE was assessed in male Wistar rats (5-10 in each group) 10 min after the icv or iv drug injection by measuring percent gastric retention (%GR) of a saline test meal labeled with phenol red 10 min after administration by gavage. The At iv group was significantly higher (64.4 +/- 2.6%) compared to control (33.4 +/- 1.5%) but did not differ from the Dp group (54.3 +/- 3.8%). After icv administration of At, %GR (34.2 +/- 2%) did not differ from control (32.6 +/- 1.9%), but was significantly higher after Dp (54.5 +/- 2.3%). Subdiaphragmatic vagotomy significantly reduced %GR in the At group (30.2 +/- 0.7%) compared to the sham group, but was significantly higher than in the controls (23.0 +/- 0.5%). In the animals treated with At iv, baclofen significantly reduced %GR (28.3 +/- 2.4%) compared to vehicle-treated animals (55.2 +/- 3.2%). The same occurred in the animals treated iv with vehicle and icv with baclofen. Although vagotomy and baclofen reduced %GR per se, the reduction was twice more marked in the animals treated with At. The results suggest that At administered iv, but not icv, delays GE of liquid in rats with the participation, at least in part, of the vagus nerve and that this phenomenon is blocked by the activation of GABA B receptors in the central nervous system.

Cytochrome P450 mediated-drug metabolism is reduced in children with sepsis-induced multiple organ failure

OBJECTIVE

Antipyrine metabolism is a "gold standard" measure of mixed cytochrome P450 (CYP) mediated drug metabolism in humans. Cytokines (e.g., interleukin-6) and nitric oxide reduce CYP 450 activity in vitro and in vivo. Because interleukin-6 and nitric oxide production increases in children with sepsis-induced multiple organ failure, we hypothesized impaired CYP 450 mediated drug metabolism in this population.

METHODS

Fifty-one consecutive children with sepsis and six critically ill children without sepsis were enrolled and given 18 mg/kg antipyrine per NG. Plasma antipyrine elimination rate, elimination half-life, and apparent oral clearance were measured and calculated. Plasma interleukin-6 and nitrite plus nitrate levels were measured and organs failing scored on days 1-3 of sepsis.

RESULTS

Children with sepsis had a twofold reduction in antipyrine clearance. Children with persistent failure of three or more organs had a fourfold reduction in antipyrine clearance. Antipyrine clearance was inversely correlated to circulating interleukin-6 and nitrite plus nitrate levels and to number of organ failures.

CONCLUSIONS

Interpretation CYP 450 mediated drug metabolism is decreased in children with sepsis, related in part to the degree of inflammation and organ failure. For drugs metabolized by CYP 450 enzymes there is an urgent need to reevaluate the use of standard drug dosage schedules in the sepsis population

Influence of albumin supplementation on tacrolimus and cyclosporine therapy early after liver transplantation

Liver transplant recipients administered gelatin (GEL) rather than human albumin solution (HAS) can become profoundly hypoalbuminemic in the early postoperative period and often have hepatic dysfunction at this time. The combined effect of these two abnormalities could be an increase in the unbound (active) concentration of low-extraction highly albumin-bound drugs, such as tacrolimus (TAC). This may increase the efficacy and/or toxicity of such drugs. We prospectively compared the clinical outcome of 69 de novo liver transplant recipients randomized primarily to TAC or cyclosporine (CYA) and secondarily to HAS or GEL therapy during the first 14 days after liver transplantation. Antipyrine clearance on the 7th postoperative day was used as a measure of liver metabolic function. Serum albumin levels were significantly lower in both GEL arms than HAS arms during the first 14 days (P <.001). Although antipyrine clearance was similar in all four trial arms, it was intermediate between that found in historic healthy controls and patients with cirrhosis (P <.0001). Serum creatinine concentrations were significantly greater in the TAC plus GEL arm than the other three arms (P <.001). The linearized treated acute rejection rate was significantly greater in the TAC plus HAS arm than the other three arms (relative risk, 2.02; 95% confidence interval, 1.07 to 3.78; P =.03). These data indicate that excess nephrotoxicity can occur with TAC in liver transplant recipients with impaired hepatic metabolism who are administered GEL. In addition, supplementary albumin may reduce the efficacy of TAC in liver transplant recipients at a time when the risk for rejection is greatest.

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.

Hippuric Acid Test Using 13C-Labelling and NMR Spectroscopy

This article describes a 13C-labelling and nuclear magnetic resonance approach for hippuric acid test which is potentially useful for evaluating liver reserve. In this approach, urine samples collected after ingestion of 13C-labelled benzoic acid were directly analysed by 13C nuclear magnetic resonance spectroscopy, and the excreted 13C-labelled hippuric acid formed from the administered benzoic acid was quantitated. The amount of labelled hippuric acid excreted in a specified time can be a useful index of liver reserve. In this study, the feasibility of the nuclear magnetic resonance approach has been investigated in several healthy subjects. This approach is simple and convenient compared with conventional analytical procedures, because no chromatographic separation is required. The approach could give new insights into the liver reserve, because the benzoic acid conversion to hippuric acid intimately relates to the hepatic energy metabolism. This measurement can be conducted at a wide range of dosages without interference from endogenous hippuric acid.

Potential use of pharmacological markers to quantitatively assess liver function during liver transplantation surgery

Early functioning of the transplanted liver is of crucial importance to the recipient. This function may be assessed by measuring the disposition of substances that are mainly eliminated via the liver. None of the agents currently used is ideal for this purpose. Measurement of mono-ethyleneglycinexylidide (MEGX) formation from lignocaine is useful and has been widely used in liver transplantation to assess liver graft function. MEGX formation can be affected by the use of drugs that influence liver perfusion or interfere with the CYP450 enzyme system. Indocyanine green clearance is a convenient method but both blood flow and hepatocellular function affect the test results. Tests of caffeine clearance, galactose elimination capacity and antipyrine clearance all require time-consuming, technically cumbersome and expensive serial blood sampling. The aminopyrine breath test is non-invasive, but gastric emptying and the patient's physical state affect results. The potential hazard of exposure to radioactive compounds limits the wide clinical use of both aminopyrine and erythromycin breath tests. Monitoring the rate of recovery from neuromuscular blockade induced by vecuronium and rocuronium can provide valuable information on liver function.

Single-dose pharmacokinetics of quetiapine in subjects with renal or hepatic impairment

1. The atypical antipsychotic quetiapine ('Seroquel') provides equivalent efficacy to the typical antipsychotics chlorpromazine and haloperidol in the short-term treatment of schizophrenia. Moreover, the incidence of extrapyramidal symptoms associated with quetiapine treatment is equivalent to that observed with placebo treatment, which may lead to increased patient compliance with quetiapine compared with typical antipsychotics. 2. This report presents the results from two small studies aimed at determining the pharmacokinetics of quetiapine in nonpsychotic subjects with renal or hepatic impairment. Equal numbers of impaired subjects and healthy control subjects were administered a single, 25 mg dose of quetiapine, and plasma concentrations were determined up to 48 hr after dosing. 3. No clinically significant differences were found when the pharmacokinetic parameters for subjects with renal or hepatic impairment were compared with those for healthy control subjects. The results indicate that dosage adjustment of quetiapine may be unnecessary in psychotic patients with decreased renal function. 4. In subjects with hepatic impairment related to alcoholic cirrhosis, the results suggest that no change is needed in the recommended quetiapine starting dose (25 mg). However, because of a noted inter-subject variability in the clearance of quetiapine in the cirrhotic group, it is recommended that dose escalation be performed with caution in patients with hepatic impairment. 5. The single dose of quetiapine 25 mg generally was well tolerated in nonpsychotic subjects in good health or with either renal or hepatic impairments. Quetiapine also had no effect on the endogenous creatinine clearance of renally impaired or healthy control subjects.

Antipyrine, oxazepam, and indocyanine green clearance in patients with chronic pancreatitis and healthy subjects

BACKGROUND

Hepatic drug metabolism was examined in patients with chronic pancreatitis and healthy controls by using a cocktail design with three different model compounds: antipyrine to express phase-I oxidation, oxazepam to express phase-II conjugation, and indocyanine green (ICG), a high-clearance compound.

METHODS

Eight patients with chronic pancreatitis and seven healthy controls participated. Patients were diagnosed by the presence of typical morphologic changes of the pancreas on imaging and had a moderately but significantly reduced exocrine function and no or only slight impairment of the glucose tolerance. No one had a history or clinical signs of liver disease. Clearance of the three model compounds was estimated after the administration of 1 g antipyrine and 15 mg oxazepam orally and a bolus of indocyanine green, 0.5 mg/kg body weight, intravenously.

RESULTS

The antipyrine clearance and ICG clearance were significantly decreased in the patients compared with the controls (mean, 27.2 ml/min; 95% confidence interval (CI), 19.4-35; versus 46.2 ml/min; 34.7-58.7, and 501 ml/min; 4014601, versus 771 mU/min; 677-865 (P < 0.05), respectively). The oxazepam clearance did not differ significantly between the two groups (181 ml/min (145-217) versus 178 ml/min (152-204)). The model drug clearance ratios between the patient and control clearances showed decreased values for antipyrine and ICG compared with the oxazepam data (0.59 and 0.65 versus 1.02, respectively). Patients and controls were characterized by a body weight of 58.2 kg (53.1-63.3) and 83.4 kg (72.7-94.1), respectively, and a body mass index (BMI) of 19.6 kg/m2 (17.9-21.3) versus 25.9 kg/m2 (23.4-28.4) (P < 0.05 for both).

CONCLUSIONS

Patients with chronic pancreatitis characterized by a moderately reduced exocrine function and absence of diabetes mellitus and overt liver disease had a decreased antipyrine oxidation and ICG clearance, whereas no difference was seen in oxazepam conjugation when compared with healthy volunteers. In chronic pancreatitis the hepatic phase-I oxidation is reduced compared with the phase-II conjugation, as shown by the model drug clearance ratios. The clearance of ICG was also affected, pointing at a reduced hepatic plasma flow, provided that the hepatic extraction fraction is normal for these patients.

Pharmacokinetics of antipyrine, warfarin and paracetamol in the brushtail possum

The plasma pharmacokinetics of antipyrine, warfarin and paracetamol have been studied in the Australian brushtail possum (Trichosurus vulpecula). The plasma elimination half-lives (t1/2) were 1.2 h for antipyrine, 11.9 h for warfarin and 5.2-12.9 h for paracetamol. Our data indicate that the clearance of these three xenobiotics in the possum is similar to that reported in eutherian mammals. There was no dose-dependent increase in paracetamol plasma t1/2 over the dose range 100-1000 mg kg(-1), indicating a lack of capacity saturation. This observation may in part explain the unusual resistance of the possum to the hepatotoxic effect of high doses of paracetamol.

Evaluation of liver function by co-administration methodology using 13C-labelled benzoic acid and hippuric acid coupled with nuclear magnetic resonance spectroscopy

The amount of hippuric acid synthesized and excreted in the urine after benzoic acid loading (hippuric acid test) is a useful index of liver function. However, the hippuric acid test gives erroneous results in the event of failure of renal excretory function. A new stable isotope co-administration methodology using nuclear magnetic resonance (NMR) spectroscopy has been developed to overcome this defect. [7-(13)C]Benzoic acid and [glycine carbonyl-13C]hippuric acid ([gly-13C]hippuric acid), each 0.4-0.6 mmol kg(-1) were simultaneously administered intravenously as probes to normal or liver-injured rats and the urine was analysed by 100 MHz 13C NMR spectroscopy. Consequently, urinary excretion of [7-(13)C]hippuric acid formed from [7-(13)C]benzoic acid and [gly-13C]hippuric acid was successfully traced with very simple and convenient procedures. The urinary excretion of [7-(13)C]hippuric acid indicated the combined functions of hippuric acid synthesis and renal excretion, whereas that of [gly-13C]hippuric acid was indicative of renal excretion of hippuric acid only. The heights of resonances for C7 of [7-(13)C]hippuric acid and the glycine carbonyl carbon of [gly-13C]hippuric acid were used to calculate the concentrations of labelled hippuric acids. [7-(13)C]Hippuric acid was excreted more slowly than [gly-13C]hippuric acid by both normal and liver-injured rats. The liver-injured rats excreted the labelled hippuric acids more slowly than the normal rats. The kinetic parameters were computed for the individual rats on the basis of Michaelis-Menten elimination for benzoic acid and first-order elimination for hippuric acid. The maximum rates of metabolism (Vmax) (4.8-5.8 micromol min(-1) kg(-1)) and the renal elimination rate constants of hippuric acid (Kre) (0.010-0.021 min(-1)) in the liver-injured rats were lower than those (Vmax 6.7-11.8 micromol min(-1) kg(-1); Kre 0.026-0.045 min(-1)) in the normal rats. These results have demonstrated that liver function can be evaluated from the Vmax value even though the renal function of hippuric acid excretion (Kre) is impaired. Thus the co-administration methodology is feasible and can remove the defect of the previous hippuric acid test. These results could form the basis for a more convenient and reliable hippuric acid test in man.

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.

Assessment of doxylamine influence on mixed function oxidase activity upon multiple dose oral administration to normal volunteers

The primary purpose of this study was to assess the influence of doxylamine and phenobarbital on antipyrine/metabolites pharmacokinetics and 6 beta-hydroxycortisol urinary excretion. This study was conducted in 48 healthy male human volunteers (16 per treatment group) using a parallel study design. Treatment groups consisted of 12.5 mg of doxylamine succinate, placebo, or 30 mg of phenobarbital administered orally every 6 h for 17 days. Results indicate that no statistically significant differences were observed between the doxylamine and placebo groups that are indicative of enzyme induction. For the phenobarbital group, a significant increase for antipyrine total (36 versus 45 mL/h/kg) and nonrenal (35 versus 44 mL/h/kg) clearances and 6 beta-hydroxycortisol excretion (338 versus 529 micrograms) and a significant decrease in the terminal exponential half-life (11 versus 9 h) of antipyrine were observed.

Trimethadione as a probe drug to estimate hepatic oxidizing capacity in humans

Trimethadione (TMO) has the properties required of probe drugs for the evaluation of hepatic drug-oxidizing capacity in humans in vivo. TMO is demethylated to dimethadione (DMO), its only metabolite, in the liver after oral administration. Involvement of two cytochrome P450's--CYP2C9 and 3A4--in TMO metabolism has been seen in humans, but involvement of 1A2 is not clearly established. In humans with various types of liver disease and hepatectomy, the serum DMO/TMO ratios, which were measured on blood samples obtained by a single collection 4 hr after oral administration of TMO, correlated well with the degree of hepatic damage. This finding suggests that TMO may be used as a probe drug in the rapid determination of the functional reserve mass of the liver as well as hepatic drug-oxidizing capacity in humans in vivo.

Accuracy of the one-sample method for determination of antipyrine clearance in elderly subjects

The purpose of this study was to evaluate the validity of the one-sample abbreviated method for determination of the pharmacokinetic parameters of antipyrine in the elderly. Antipyrine pharmacokinetics were studied in 15 elderly women (mean age 86 years). Antipyrine (1 g) was administered orally and pharmacokinetic parameters were determined by the one-sample (24 h) and multiple-sample (3, 6, 9, 12 and 24 h) methods. Mean antipyrine clearance for the one-sample study (19.72 +/- 1.51) was almost identical to that obtained with the multiple-sample approach (20.73 +/- 1.57), and the two methods were very well correlated (r = 0.989). Relative standard deviations between individual clearances values for multiple-sample vs. one-sample studies averaged 1.6%. Values of elimination half-life were likewise very similar for the abbreviated (17.41 +/- 1.21) and complete (17.99 +/- 1.09) methods, with a significant correlation (r = 0.857). Although values were underestimated by 10% in the one-sample approach, no difference in the volume of distribution with the multiple-sample study was observed. When the unbiased volume of distribution value was determined from the total elimination curve against time, the influence of biased volume of distribution resulted in a 5.1% deviation in antipyrine clearance in the one sample method. The findings indicate that antipyrine pharmacokinetic parameters can be estimated with reasonable precision and accuracy in the elderly using a simplified one-sample procedure.

Pharmacokinetics of trapidil in patients with chronic liver disease

The pharmacokinetics of trapidil were studied in 15 patients with chronic liver disease (12 with hepatic cirrhosis, 2 with alcoholic fatty liver, 1 with liver fibrosis). Trapidil was administered intravenously as a 100-mg bolus. Serum samples were analyzed for trapidil by means of high-performance liquid chromatography. Mean pharmacokinetic parameters were compared with those found in a previous study of 12 healthy volunteers. Total plasma clearance was decreased significantly in patients with hepatic cirrhosis (96 mL/ min versus 258 mL/min in healthy individuals and 252 mL/min in patients with noncirrhotic liver disease). No difference in clearance was observed between patients with compensated or decompensated cirrhosis, and portal hypertension did not affect this clearance of trapidil. It can be concluded that trapidil clearance is a parameter that is very sensitive to alterations in hepatic clearance caused by liver cirrhosis, and that the dosage of trapidil should be adjusted accordingly in such patients.

The absolute bioavailability and pharmacokinetics of butorphanol nasal spray in patients with hepatic impairment

OBJECTIVE

The objective of the study was to investigate the effects of hepatic impairment on the absolute transnasal bioavailability and pharmacokinetics of butorphanol.

STUDY DESIGN

Twelve (eight men and four women) healthy subjects and 12 (eight men and four women) patients with hepatic impairment received a 1 mg dose of butorphanol by intravenous or transnasal administration on two separate occasions. Hepatic function was assessed by antipyrine and indocyanine green clearance tests. Serial blood and urine samples were collected after each dose. Plasma samples were analyzed for butorphanol, and urine samples were analyzed for butorphanol and its metabolites.

RESULTS

No statistical difference in maximum plasma concentration (Cmax) for butorphanol was observed between the two groups of volunteers after transnasal administration. However, total plasma clearance (CL), steady-state volume of distribution, area under the concentration-time curve [AUC(0-infinity)], and elimination half-life of butorphanol in patients with hepatic impairment were significantly altered (approximately twofold to threefold). The absolute transnasal bioavailability of butorphanol was significantly higher (approximately 20%) in patients with hepatic impairment. A greater fraction of the administered dose was recovered from the urine in hepatically impaired patients compared to that in healthy subjects (23% to 31% versus 10% to 11%). There was a significant reduction in CL of indocyanine green and antipyrine in hepatically impaired patients. The percentage of reduction in butorphanol CL was highly correlated to the estimated degree of portosystemic shunts in the patients with hepatic impairment.

CONCLUSION

Based on the comparable Cmax but the increased AUC in patients with liver dysfunction, the initial dose of butorphanol nasal spray may not need to be adjusted. However, the subsequent dosing intervals for butorphanol should be prolonged.

Influence of nutrition on liver oxidative metabolism

The liver plays a major role in the disposition of the majority of drugs. This is due to the presence of several drug-metabolizing enzyme systems, including a group of membrane-bound mixed-function oxidative enzymes, mainly the cytochrome P450 system. Hepatic oxidative capacity can be assessed by changes in antipyrine metabolism. Different drugs and other factors may induce or inhibit the cytochrome P450-dependent system. This effect is important in terms of the efficacy or toxicity of drugs that are substrates for the system. Microsomal oxidation in animals fed with protein-deficient diets is depressed. The mixed-function oxidase activity recovers after a hyperproteic diet or the addition of lipids. Similar findings have been reported in patients with protein-calorie malnutrition, although results in the elderly are conflicting. Different studies have revealed that microsomal oxidation is impaired by total parenteral nutrition and that this effect is absent when changing the caloric source from carbohydrates to a conventional amino acid solution or after lipid addition, especially when administered as medium-chain/long-chain triglyceride mixtures. Peripheral parenteral nutrition appears to increase antipyrine clearance.

The use of lidocaine as a test of liver function in liver transplantation

The hepatic metabolism of lidocaine to monoethyl-glycinexylidide (MEGX) is the basis of a dynamic test of liver function. To understand its potential value in liver transplantation, the latter has been considered in the following three separate stages: pretransplantation assessment of potential candidates, potential liver donors, and the transplant recipient. In pretransplantation patients, data support its role in assessing risk of morbidity and mortality. In assessment of the liver transplant donor, there are differences concerning apparent usefulness, and these must be resolved. In the liver transplant recipient, serial measurements are useful to measure real-time hepatic metabolic activity. Low MEGX values reflect the clinical condition of the patient, and the importance of entirely assessing the patient, not just noting the test result, is paramount. This review has considered the role of the MEGX test in liver transplantation.

Steady-state pharmacokinetics of nefazodone in subjects with normal and impaired renal function

The steady-state pharmacokinetics of nefazodone (NEF) and its metabolites hydroxynefazodone (HO-NEF) and m-chlorophenylpiperazine (mCPP) were compared in subjects with normal and impaired renal function.

PATIENTS

The Study was of parallel group design which included 7 subjects with normal (NOR) renal function, CLCR > or = 72 ml.min-1 x 1.73 m-2, 6 with moderate (MOD) renal impairment, CLCR 31-60 ml.min-1 x 1.73 m-2 and 9 with severe (SEV) renal impairment, CLCR < or = 30 ml.min-1 x 1.73 m-2. Subjects in each renal function group received a 100-mg oral dose of nefazodone hydrochloride BID for 7 days and a single morning dose on day 8. Starting 48 h after the last 100-mg dose, 200-mg doses were administered on a similar schedule to 3, 4 and 3 subjects from each renal function group (NOR, MOD and SEV, respectively). Single trough blood samples just prior to each morning dose (Cmin) and serial samples after the dose on day 8 were obtained at each dose level for pharmacokinetic analysis. Plasma samples were assayed by a specific HPLC method for NEF, HO-NEF and mCPP. The CMIN data indicated that steady state was attained by the third day of BID administration of both the 100- and 200-mg doses of nefazodone, regardless of degree of renal function. Both NEF and HO-NEF attained steady-state Cmax within 2 h after administration of nefazodone; tmax for mCPP was less defined and more delayed. HO-NEF and mCPP plasma levels were about 1/3 and < 1/10 those of NEF, respectively, regardless of the status of renal function. Steady-state systemic exposure of NEF and HO-NEF, as reflected by AUC and Cmax, and elimination t1/2 values did not differ significantly among renal function groups.

CONCLUSION

The study results suggest that dose adjustments may not be necessary, but nefazodone should be used with caution in the presence of severe renal impairment.

Effects of aging on antipyrine clearance: predictive factors of metabolizing capacity

The purpose of this study was to identify variables that can account for the decline of antipyrine clearance (CLAP) in elderly adults and that may help predict a reduction in metabolizing capacity. For comparison, ClAP was determined in 177 elderly (mean age 82 years) and 25 young (mean age 29 years) volunteers. Antipyrine (1 g) was administered orally and ClAP was determined by the one-sample saliva method. Mean ClAP was reduced by 38% and antipyrine half-life increased by 64% in old subjects. Multiple regression analysis of ClAP revealed an independent value for age, serum aspartate transaminase (AST), and height in the elderly. The independent variables collectively accounted for 27% of the variance explained. Age, high serum AST, use of diuretics, and no consumption of drugs known to stimulate oxidative metabolism were selected by multivariate analysis (logistic model) as independent predictors of a low metabolizing capacity. The findings indicate that factors other than age may contribute to impaired hepatic oxidative metabolism in the elderly.

Antipyrine clearance and metabolite excretion in Saudi patients with non-alcoholic chronic liver disease

In this report, we examined the hepatic microsomal enzyme activity in 34 Saudi patients with chronic liver disease (CLD) and in 21 healthy Saudi subjects by measuring antipyrine clearance (APCI) and the fraction (%) of antipyrine (AP) dose excreted in urine unchanged (fAP) and in the form of its main metabolites: 3-hydroxymethylantipyrine (fHMAP), norantipyrine(fNORAP), and 4-hydroxyantipyrine (f4OHAP). While APCI, fHMAP, fNORAP, f4OHAP were significantly reduced in patients with CLD, fAP was significantly higher in these patients. Correlation was observed between serum albumin and APCI, fHMAP, fNORAP, or f4OHAP and between each two of the last three variables. We conclude that Saudis with CLD have uniform rather than selective reduction of hepatic microsomal enzyme activity and that serum albumin is a sensitive indicator of this activity.

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.

Assessment of liver metabolic function. Clinical implications

Inter- and intraindividual variability in pharmacokinetics of most drugs is largely determined by variable liver function as described by parameters of hepatic blood flow and metabolic capacity. These parameters may be altered as a result of disease affecting the liver, genetic differences in metabolising enzymes, and various types of drug interactions, including enzyme induction, enzyme inhibition or down-regulation. With the now known large number of drug metabolising enzymes, their differential substrate specificity, and their differential induction or inhibition, each test substance of liver function should be used as a probe for its specific metabolising enzyme. Thus, the concept of model test-substances providing general information about liver function has severe limitations. To test the metabolic activity of several enzymes, either several test substances may be given (cocktail approach) or several metabolites of a single test substance may be analysed (metabolic fingerprint approach). The enzyme-specific analysis of liver function results in a preference for analysis of the metabolites rather than analysis of the clearance of the parent test substance. There are specific methods to quantify the activity of cytochrome P450 enzymes such as CYP1A2, CYP2C9, CYP2C19MEPH, CYP2D6, CYP2E1, and CYP3A, and phase II enzymes, such as glutathione S-transferases, glucuronyl-transferases or N-acetyltransferases, in vivo. Interactions based on competitive or noncompetitive inhibition should be analysed specifically for the cytochrome P450 enzyme involved. At least 5 different types of cytochrome P450 enzyme induction may result in major variability of hepatic function; this may be quantified by biochemical parameters, clearance methods, or highly enzyme-specific methods such as Western blot analysis or molecular biological techniques such as mRNA quantification in blood and tissues. Therapeutic drug monitoring is already implicitly used for quantification of the enzyme activities relevant for a specific drug. Selective impairment of hepatic enzymes due to gene mutations may have an effect on the pharmacokinetics of certain drugs similar to that caused by cirrhosis. Assessment of this heritable source of variability in liver function is possible by in vivo or ex vivo enzymological methods. For genetically polymorphic enzymes and carrier proteins involved in drug disposition, molecular genetic methods using a patient's blood sample may be used for classification of the individual into: (i) the impaired or poor metaboliser (homozygous deficient); (ii) the extensive (homozygous active) metaboliser group; and (iii) the moderately extensive metaboliser (heterozygous) group. For hepatic blood flow determinations, galactose or sorbitol given at relatively low doses may be much better indicators than the indocyanine green.(ABSTRACT TRUNCATED AT 400 WORDS)

Isolation and purification of three glucuronides of antipyrine. Proposal for an original analytical method for quantitation of sulpho- and glucuroconjugated metabolites

The determination of the concentrations of antipyrine metabolites in biological fluids is hampered by the difficulty in obtaining pure conjugated compounds to be used as standards. Most authors have proposed determination of total forms by high performance liquid chromatography (HPLC) after deconjugation of these metabolites using chemical or enzymatic hydrolysis. Up to now there is no satisfactory hydrolysis method for the study of all antipyrine metabolites. The situation is further complicated by the fact that the deconjugated metabolites are highly unstable whichever technique is being used. Because of the lack of stability of all these molecules it has been necessary to isolate the glucuroconjugated compounds from urine. We describe a method which allows us to obtain highly purified glucuroconjugated metabolites of antipyrine. Sulphoconjugated compounds have been synthesized previously. We are thus able to propose a chromatographic procedure which allows us to determine simultaneously all stable phase I and phase II metabolites of antipyrine in biological fluids without any step of extraction. This analytical technique allows us to study the activity of the different isoenzymes implicated in the metabolism of antipyrine.

Antipyrine kinetics in patients with primary biliary cirrhosis

Fourteen antimitochrodrial antibody-positive patients (13 women, 1 man) with biopsy-proven primary biliary cirrhosis, aged 40 to 71 years (mean, 57 years) weighing 43 to 102 kg (mean, 63 kg), along with 14 age- and sex-matched healthy controls, received a single 1.0- to 1.2-g dose of intravenous antipyrine. Plasma antipyrine levels were determined during a 12- to 24-hour period. Patients' mean serum chemistry values were: albumin, 3.9 g/dL (range, 3.1-4.4) and total bilirubin, 1.9 mg/dL (range, 0.3-10.9). Seven of the fourteen patients had cirrhosis. Mean kinetic variables for antipyrine in controls and primary biliary cirrhosis patients were: Vd, .54 versus .49 L/kg; half-life, 12.0 versus 15.1 hours (P < .07); clearance, .55 versus .41 mL/min/kg (P < .04). Within the primary biliary cirrhosis group, there was no correlation between total bilirubin and clearance (r = .09), nor did clearance vary significantly among histologic categories. Clearance of antipyrine in primary biliary cirrhosis patients is reduced by an average of 25%, but the clinical prognosticators of serum bilirubin levels and histologic grade do not correlate with or predict the degree of clearance impairment.