Studies on the different metabolic pathways of antipyrine in man. I. Oral administration of 250, 500 and 1000 mg to healthy volunteers

Chemical and biological evaluation of some new antipyrine derivatives with particular properties

Starting from 4-amino-antipyrine, six new compounds were synthesized and characterized. The new compounds contain moieties with particular properties, such are ionophore (benzo-15-crown-5), fluorescent (nitrobenzofurazan), stable free radical (nitroxide), or other types of biological active residues, like nitroderivatives, antipyrine or isoniazid residues. They were fully characterized by appropriate means ((1)H and (13)C NMR, IR, UV-Vis, fluorescence, EPR, elemental analysis) and some of their biological properties were evaluated. Hydrophobicity (R(M0), log P), total antioxidant capacity (TAC), and antimicrobial properties are also presented and discussed.

The use of oral fluid for therapeutic drug management: clinical and forensic toxicology

One of the underlying tenets of clinical pharmacology is that only free drugs are pharmacologically active. It is thought that only free drugs can cross biological membranes to interact with a given receptor to alter its function, and that drug responses, both efficacious and toxic, are a function of unbound concentrations. The rationale for measuring drugs in oral fluid is that the free fraction of a drug in plasma reaches equilibrium with the drug in saliva. Although reports concerning the appearance of organic solutes in saliva have been in the literature for over 70 years, it has only been in the past 30 years that there has been emphasis on the appearance of drugs. Although many assumptions for drug level monitoring in saliva are made, the primary requisite for salivary monitoring to be useful is a constant or predictable relationship between the drug concentration in saliva and the drug concentration in plasma. Measurement of oral fluid drug levels for the purpose of managing patients and making dosage adjustments may be useful for select drugs or drug classes. However, it does not appear to be useful for the majority of drugs therapeutically monitored. Some work with antipsychotic medications has indicated that although the measurement of drug concentrations themselves may not be useful for dosage adjustment, the ratio of parent drug to metabolite may reflect altered metabolic status due to either pharmacogenetic variation or other clinical conditions. Furthermore, analysis of saliva may provide a cost-effective approach for the screening of large populations.

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

Exercise training and oxidative stress in the elderly as measured by antipyrine hydroxylation products

Effects of 12 wk exercise training on oxidative stress were examined in elderly humans. We measured oxidative stress during a 45 min cycling test by using antipyrine hydroxylation products. Antipyrine breakdown is independent of blood flow to the liver, which is important during exercise. Furthermore, antipyrine reacts quickly with hydroxyl radicals to form para- and ortho-hydroxyantipyrine. Ortho-hydroxyantipyrine is not formed in man through the mono-oxygenase pathway of cytochrome P450. Twenty subjects (9 women; 60 +/- 3 y) participated in the training program. Thirteen subjects (5 women; 64 +/- 7 y) served as inactive controls. Subjects trained, twice a week for 1 h, at a fitness center. After 12 wk, maximal oxygen uptake (p < .005) and workload capacity (p < .001) were only significantly elevated in the training group. After 12 wk, both groups observed no change in the ratios of antipyrine hydroxylates, para- and ortho-hydroxyantipyrine, to native antipyrine. Furthermore, no differences were observed within or between groups in the exercise-induced increase in the plasma level of thiobarbituric acid reactive species. In conclusion, 12-wk training had no effect on exercise-induced oxidative stress in elderly humans as measured by free radical reaction products of antipyrine. Despite the fact that training in elderly humans improves functional capacity, it appears not to compromise antioxidant defense mechanisms.

Pharmacokinetics of sulfonamides and trimethoprim in the donkey (Equus asinus)

The body disposition of sulfadimidine (SDM), sulfadiazine (SDZ), sulfamethoxypyridazine (SMPZ) and a trimethoprim-sulfadimethoxine combination (TMP-SDMX) was investigated in the donkey. The four sulfonamides and TMP were injected intravenously at doses of 20 mg/kg (SDM, SDZ, SMPZ), 12.5 mg/kg (SDMX) and 2.5 mg/kg (TMP). The body clearance (ClB) of SDZ (1.70 +/- 0.14 ml/min/kg) was significantly higher than those of SDM (1.13 +/- 0.18 ml/min/kg), SMPZ (1.10 +/- 0.09 ml/min/kg) and SDMX (0.75 +/- 0.04 ml/min/kg). In contrast, the volume of distribution at steady state (Vss) was similar for the four sulfonamides (0.68 +/- 0.08 L/kg, 0.63 +/- 0.07 L/kg, 0.47 +/- 0.06 L/kg, and 0.46 +/- 0.05 L/kg for SDM, SDZ, SMPZ and SDMX, respectively). Both ClB and Vss were significantly higher for TMP (4.36 +/- 0.60 ml/min/kg and 2.71 +/- 0.86 L/kg) than for sulfonamides. Antipyrine ClB (3.49 +/- 0.35 ml/min/kg) and Vss (0.66 +/- 0.16 L/kg), determined in order to assess hepatic oxidative function and total body water volume, respectively, were either different from (ClB), or similar to (Vss), values calculated for sulfonamides. The results obtained were compared to those reported in horses.

Influence of short-term water deprivation on antipyrine disposition in calves

The effect of four days water deprivation on the metabolism of antipyrine was studied in female Holstein-Friesian calves, aged 24 to 25 days, by measuring the antipyrine plasma clearance and the excretion of three major metabolites of antipyrine in urine. Water deprivation was associated with a statistically significant (P < 0.01) increase in the plasma antipyrine elimination half-life from 10.85(1.14) hours to 14.00(1.05) hours. In water deprived calves the systemic clearance of antipyrine was significantly (P < 0.05) decreased from 0.75(0.07) ml min-1 kg-1 to 0.56(0.05) ml min-1 kg-1. The excretion of three major metabolites of antipyrine: 4-hydroxyantipyrine, 3-hydroxymethylantipyrine and norantipyrine in urine was significantly (P < 0.01) decreased after water deprivation. In the control group no significant differences between the pharmacokinetic parameters of antipyrine in 24 to 25 and 28 to 29 day-old calves were observed. Also urinary profiles of antipyrine in calves from the control group did not differ significantly between 24 to 25 and 28 to 29 days of life. Our data indicate that water deprivation inhibits antipyrine elimination in calves.

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.

Effect of spironolactone on antipyrine metabolism in calves

Ten female calves of the Black and White breed aged seven to eight days were studied before and after seven days of treatment with spironolactone at a dose rate of 1 mg kg bodyweight-1 twice a day. The treatment was associated with a statistically significant decrease in the half-life of antipyrine in plasma and an increase in its rate of metabolic clearance. The excretion of 4-hydroxyantipyrine in urine was significantly increased after the treatment with spironolactone, but there were no changes in the rates of excretion of 3-hydroxymethylantipyrine or norantipyrine. These results indicate that spironolactone enhanced the activity of the microsomal drug-metabolising enzyme system and induced cytochrome P-450 in the calves.

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.

Review article: quantitative tests of liver function

The search continues for a single reliable test of liver function that provides accurate prognostic information in chronic liver disease, in acute liver failure, and about graft function following orthotopic liver transplantation. Although transaminases, the commonly used markers of hepatocellular injury, have a high sensitivity in screening for liver disease, they do not provide any information about prognosis. Rational assessment of liver function using bilirubin, serum albumin and prothrombin-time is limited by the relative lack of sensitivity of these measurements and their inability to identify the functional reserve of the liver. Dynamic liver function tests are an improvement on the static tests but are generally cumbersome. The ideal liver function test would be cheap, easy to perform and analyse, safe, have a simple pharmacokinetic profile with minimal drug interactions, have a high predictive value and provide quick results. Numerous quantitative liver function tests have been developed and have shown promise in some studies. The aim of this review is to assess the place of these tests in the practical management of liver disease.

The effect of zileuton on antipyrine and indocyanine green disposition

The effects of single and multiple oral doses of zileuton on the pharmacokinetics of antipyrine and indocyanine green were studied in 16 healthy, nonsmoking adult men by means of a double-blind, randomized, parallel placebo-controlled design. Indocyanine green disposition was not significantly altered by zileuton. Plasma antipyrine clearance declined by 20% (p < 0.0005) and 52% (p < 0.0005) after single and multiple dose zileuton exposure, respectively. Total urinary recovery of unchanged antipyrine and metabolites decreased with zileuton exposure. Selective declines from baseline of 16% (p = 0.007) and 20% (p = 0.003) after single-dose zileuton and 30% (p < 0.0005) and 43% (p < 0.0005) after multiple-dose zileuton were detected in recovery of 4-hydroxyantipyrine and 3-hydroxymethylantipyrine, respectively. Urinary recovery of the N-demethylantipyrine metabolite norantipyrine and percent of conjugation of 3-hydroxymethylantipyrine were unchanged by zileuton. In conclusion, zileuton therapy has no detectable effect on indocyanine green disposition but exerts marked effects on antipyrine plasma and urine metabolite disposition.

Antipyrine disposition in obesity: evidence for negligible effect of obesity on hepatic oxidative metabolism

Following an overnight fast and 2 days of abstention from caffeine, a single 1.0-g oral dose of antipyrine was administered to 20 obese but otherwise healthy subjects (group A) and 11 healthy volunteers (group B). Weight, Body Mass Index (BMI) and % of Ideal Body Weight (IBW) were significantly greater in the obese than in the lean group. (Mean 110.4 vs 62.7 kg; 38.5 vs 22.3 kg.m-2 and 181 vs 106% respectively). In a subgroup of 6 obese subjects (group C) antipyrine was given again 11.3 months later after a 29.8 kg mean weight loss. Antipyrine apparent volume of distribution (V) and elimination half-life (t1/2) were significantly greater in the obese than in the lean group (V 49.9 vs 34.3 l respectively; t1/2 15.5 vs 12.0 h respectively), but its clearance rate (CL0) values were similar. V corrected for total body weight was significantly reduced in group A than in group B (0.45 vs 0.55 l.kg-1 respectively). Stratified comparison of antipyrine pharmacokinetics between obese and lean subjects according to age, gender and smoking habits did not alter the overall results. In group C, weight reduction was associated with a significant decrease in antipyrine V (from 51.8 to 47.5 l) and t1/2 (from 15.1 to 12.7 h), and a non-significant increase in antipyrine CL0. We conclude that in severely obese subjects, antipyrine total V is mildly increased but V corrected for total body weight is significantly decreased. In addition, obesity is associated with a slight prolongation of antipyrine t1/2 whereas its CL0 is unaltered. These findings may indicate that obesity, even in its extreme form, has a negligible effect on the oxidative metabolic capacity of the liver.

Antipyrine clearance and metabolite excretion in patients with chronic hepatitis C

BACKGROUND/AIMS

Our aim was to study whether chronic hepatitis C affects the three metabolic pathways of the model drug antipyrine differently.

METHODS

We measured antipyrine clearance from saliva as well as urinary excretion of its main metabolites 4-hydroxy-antipyrine, 3-hydroxy-methyl-antipyrine, and nor-antipyrine in 24 patients with chronic hepatitis C and in 21 healthy control subjects. Due to incomplete urine collection, 12 liver patients and three controls were excluded.

RESULTS

Antipyrine clearance (mean +/- SD) was significantly lower in patients with chronic hepatitis C, 1.2 +/- 0.7 l.h-1 (n = 12), than in controls (n = 18), 2.2 +/- 1.0 l.h-1 (p = 0.006). The urinary excretion of each of the metabolites was depressed to an equal extent in liver patients. The severity of the liver disease, as assessed by Child Pugh score, serum albumin and bilirubin, correlated significantly with antipyrine clearance and urinary excretion of the metabolite 3-hydroxy-methyl-antipyrine. The hepatitis activity index (Knodell) correlated with 3-hydroxy-methyl-antipyrine and 4-hydroxy-antipyrine, only.

CONCLUSIONS

Moderate-severe chronic hepatitis C does not seem to depress the three main metabolic pathways of antipyrine differently.

Elimination studies of antipyrine and its metabolites in healthy Saudi Arabians

1. We measured the antipyrine clearance in 18 healthy Saudi subjects and determined the urinary excretion of three of its metabolites: 4-hydroxyantipyrine (4-OH AP), norantipyrine (NOR AP) and 3 hydroxymethylantipyrine (3-OHM AP) in 21 subjects. 2. The mean +/- SD of the antipyrine clearance was 2.4 +/- 1.1 h-1 (range 1.0-5.5 l h-1) and the corresponding value per kg body weight was 0.6 +/- 0.2 ml min-1 kg-1. Urinary excretion of antipyrine (AP), 4-OH AP, NOR AP and 3-OHM AP expressed as a percentage of the oral dose of antipyrine given was 2.8 +/- 2.2, 14.5 +/- 6.9, 12.3 +/- 5.6 and 7.6 +/- 3.2 respectively. 3. Compared to Africans, Saudis preferentially metabolize AP to NOR AP and compared to Caucasians to 3-OHM AP, rather than to 4-OH AP. These discrepancies may reflect age differences between the study populations rather than genetic or ethnic variations.

Liver blood flow, antipyrine clearance, and antipyrine metabolite formation clearance in patients with chronic active hepatitis and alcoholic cirrhosis

Duplex scanning was used to measure liver blood flow (hepatic artery and main branches of the portal and hepatic veins) in six healthy subjects, five cirrhotic patients, and six hepatitis patients. Antipyrine clearance and formation clearances to its metabolites were also measured. Compared with healthy control subjects, cirrhotic patients had a lower hepatic vein blood flow (-76%, P < 0.05). This was due primarily to a lower portal vein blood flow (-36%, NS). A statistically significant difference in liver blood flow between patients with hepatitis and normal subjects was not detected. Antipyrine half-life, clearance, and the area under the serum drug concentration vs time curve were significantly different in cirrhotic patients compared with the healthy subjects (mean +/- s.d.-healthy controls: t1/2 = 13.7 +/- 3.0 h, CL = 30.0 +/- 8.6 ml h-1 kg-1, AUC = 549 +/- 139 mg l-1 h; cirrhotic patients: t1/2 = 32.4 +/- 1.7 h, CL = 12.3 +/- 2.1 ml h-1 kg-1, AUC = 1061 +/- 218 mg l-1 h; P < 0.008). Antipyrine half-life, clearance, and the area under the serum drug concentration vs time curve were not significantly different in hepatitis patients compared with the healthy subjects (hepatitis patients: t1/2 = 14.3 +/- 3.7 h, CL = 29.3 +/- 8.5 ml h-1 kg-1, AUC = 498 +/- 142 mg l-1 h). The volume of distribution of antipyrine was similar in all three groups of subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Dose-dependent pharmacokinetic interaction between antipyrine and paracetamol in vivo and in vitro when administered as a cocktail in pig

1. The pharmacokinetic interactions between paracetamol (PA) and antipyrine (AP) were studied in pigs in order to investigate the usefulness of this combination for the simultaneous assessment of oxidative and conjugative metabolism. 2. When both drugs were given at a dose of 5 mg/kg, AP plasma clearance was reduced from 2.22 to 0.96 lh-1 kg-1. PA clearance was not changed in comparison with control values. 3. At a dose of 2 mg/kg no pharmacokinetic interaction between the two drugs was observed. 4. The only oxidative AP metabolite found in urine was 4-hydroxyantipyrine (4-OHA). It accounted for 80% of the dose and, like PA, it was completely glucuronidated. 5. The glucuronidation of PA has been studied in vitro in pig liver microsomes. The apparent Km value for PA glucuronidation was 40 mM with a Vmax = 54 nmol min-1 mg protein-1. To determine if 4-OHA and PA competed for the same UDP-glucuronosyl-transferase, the effect of 4-OHA and AP on PA glucuronidation was studied. It appeared that 4-OHA was a competitive inhibitor with a Ki app = 0.07 microM, whereas AP had no effect. 5. Results suggest a dose-dependent interaction between AP and PA, which may be due to competition at the level of glucuronidation. Therefore, the usefulness of AP and PA in vivo in a cocktail for metabolism studies is limited.

Metabolism of antipyrine and sulphadimidine in dwarf goats: effects of the enzyme-inducing agents phenobarbital, troleandomycin and rifampicin

1. Antipyrine (AP) and sulphadimidine (SDD) plasma elimination and metabolite formation were studied in dwarf goats before and after treatment with phenobarbital (PB), triacetyloleandomycin (TAO), and rifampicin (RIF). 2. PB treatment significantly increased AP plasma clearance in both male and female goats. With SDD, only male goats were studied, which showed a significant increase of SDD plasma clearance following PB treatment. 3. After PB treatment, partial clearance values of four AP metabolites, 3-hydroxymethylantipyrine (HMA), norantipyrine (NORA), 4-hydroxyantipyrine (OHA) and 4,4'-dihydroxyantipyrine (DOHA), were significantly increased. This induction effect was different for the individual metabolites and also showed sex-dependency. 4. In PB-induced male goats the formation of the hydroxylated SDD metabolites, 6-hydroxymethyl-SDD and 5-hydroxy-SDD, was significantly increased. 5. After TAO treatment, female goats showed a slightly reduced AP plasma clearance and a decreased partial clearance of two AP metabolites, HMA and DOHA. There was no effect on SDD plasma elimination or metabolite excretion. 6. In male goats, RIF had no effect on plasma elimination of AP and SDD. With SDD, it decreased the urinary excretion of the unchanged drug and its N4-acetylated metabolite. 7. Induction/inhibition studies of drug metabolism in food-producing animal species are desirable to gain more insight into the regulation of enzymes involved in the metabolism of xenobiotics.

Solid phase extraction and simultaneous high performance liquid chromatographic determination of antipyrine and its major metabolites in urine

A reversed phase gradient high performance liquid chromatographic method utilizing solid phase extraction has been described for the simultaneous determination of antipyrine (AP), 4-hydroxyantipyrine (4-OHAP), norantipyrine (NorAP) and 3-hydroxymethylantipyrine (3-OHMAP) in human urine after hydrolysis with beta-glucuronidase. The C-18 sorbent cartridges were conditioned and urine samples were applied, washed with 1 x 4 mL of phosphate buffer and eluted with 3 x 100 microL of 20% v/v of acetonitrile in methylene chloride. The eluent was evaporated to dryness, reconstituted in 100 microL phosphate buffer and injected. The calibration ranges were 2.0-250 micrograms/mL (AP), 2.5-250 micrograms/mL (NorAP), 2.0-250 micrograms/mL (3-OHMAP) and 5.0-500 micrograms/mL (4-OHAP) with regression coefficients of 0.998 or greater. Specificity was indicated by the absence of interferences in chromatogram of blank urine from normal as well as cirrhotic patients. The average recovery was 86.7% for AP, 90.5% for NorAP, 85.2% for 4-OHAP and 74.2% for 3-OHMAP. The within-assay precision as indicated by the reproducibility of the assayed spiked urine was less than 9% in all cases and the between-assay precision was less than 12%. The method was applied to studies on antipyrine metabolism in stable cirrhotic patients. Following administration of a single oral dose of about 1000 mg to nine stable cirrhotic patients and eight age-matched healthy volunteers, the cumulative account excreted in the urine up to 48 h for AP and the three metabolites was comparable to other literature reports.

Disposition of antipyrine in patients with extensive metastatic liver disease

In the present study the effect of metastatic liver disease on hepatic drug metabolism has been examined by studying the pharmacokinetics of antipyrine and the urinary excretion of antipyrine and its three major metabolites (4-hydroxyantipyrine, norantipyrine, and 3-hydroxymethylantipyrine) in 12 patients with extensive metastatic liver disease, and in 12 matched healthy controls. In the patients total liver volume, the volume of the liver parenchyma, and the volume of the liver metastases were determined by computed tomography. The volume of liver metastases always exceeded 35% of the total liver volume. There were no significant differences between the patients and controls in plasma half-life, plasma clearance, or apparent volume of distribution of antipyrine. The cumulative urinary excretion of antipyrine and its three major metabolites was significantly lower in patients [44 (18) %] than in controls [71 (8) %]. The excretion of antipyrine itself was unchanged and the decrease in cumulative excretion was due to reduced excretion of the three metabolites. The results show that the activity of the hepatic mixed function oxidases was not impaired even in patients with extensive metastatic liver disease. This may be because liver metastases do not cause a corresponding reduction in the volume of normal hepatic parenchyma. The decreased urinary excretion of the three major metabolites of antipyrine, which are mainly glucuronidated, may have been due to an alteration in the process of conjugation.

Species- and sex-related differences in the plasma clearance and metabolite formation of antipyrine. A comparative study in four animal species: cattle, goat, rat and rabbit

1. The plasma disposition of antipyrine, and its urinary metabolite pattern, were studied in both sexes of four animal species: rat, dwarf goat, rabbit and cattle. 2. No sex differences in plasma elimination of antipyrine were found in rabbit and goat; however, in rat and cattle the effect of sex was marked. As expected, male rat showed a higher plasma clearance value than female. In contrast bulls showed a significantly lower clearance value than cows. 3. Metabolite patterns varied widely from one species to another. The major urinary metabolite in rabbit and the two ruminant species was 4-hydroxy-antipyrine (OHA), whereas in rat 3-hydroxymethylantipyrine (HMA) was quantitatively the most important metabolite. 4. HMA was excreted in the 24 h urine in larger amounts by male rats than by females. Metabolism of antipyrine to HMA was also sexually different in the dwarf goat, but in this species females were more active than males. The effect of sex on the metabolite pattern in cattle was marked. 5. It is concluded that in ruminants there may be xenobiotic metabolic pathways which are under hormonal control, just as there are in rats and mice. If hormones influence drug metabolism in food-producing animals, residue levels of xenobiotics or their metabolites in food from animal origin may differ with the sex of the animal, or may be altered after treatment with anabolic hormones.

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

The disposition of phenazone (antipyrine), a low extraction compound with low protein binding, is known to be altered in the presence of various types of hepatic dysfunction. As such, its pharmacokinetics may be useful in the objective characterisation of altered liver function. Understanding the known effects of various liver disease states upon the disposition of this probe may provide insight into future applications. This article provides a review of background information about normal plasma phenazone pharmacokinetics, urinary metabolite disposition and tabulations of reported total body clearances of the drug in the presence of cirrhosis, fatty liver, hepatitis and cholestasis in humans. An estimate is made of the sensitivity and specificity of phenazone testing for the verification of the presence of cirrhosis based on this compiled literature.

Metronidazole and antipyrine as probes for the study of foreign compound metabolism

The aim of the present work was to develop a tool for the study of the enzyme activities relevant for the biotransformation of foreign compounds, their elimination and/or activation to toxic substances. The activity of an enzyme may be assessed by the rate of metabolism of a preferably specific probe or model compound. The cytochrome P450'ies, the key enzymes for the elimination and/or activation of most foreign compounds, exist in multiple forms with variable substrate specificity and regulation. Some cytochrome P450'ies are under genetic control, whereas the activity of others is mainly regulated by the influence from factors in the environment. Only some of the cytochrome P450'ies are relevant for the formation of harmful metabolites. Thus, the activity of as many cytochrome P450 forms as possible should be assessable, preferably simultaneously. The present work evaluated metronidazole in a cocktail with antipyrine as a tool for the study of the regulation of foreign compound metabolism in the liver. The cytochrome P450 catalyzed metabolism of metronidazole and antipyrine was studied in humans and in isolated rat hepatocytes. In humans the influence of dose, route of administration, enzyme induction and inhibition and liver disease was investigated. Rats of either sex were studied with and without pretreatment with specific enzyme inducers and incubations included specific enzyme inhibitors. Evidence was provided that the oxidative formation of the five major metabolites, two from metronidazole and three from antipyrine, depends on different cytochrome P450'ies. In humans it was demonstrated that the clearance of metronidazole and antipyrine could be determined from the same saliva sample collected 16-24 hours after their oral administration and so could the clearance for formation of each metabolite if urine was collected for 48 hours. Thus, with the cocktail of metronidazole and antipyrine and simple non-invasive sampling the activity of five different cytochrome P450'ies can be assessed in vivo. In addition, metronidazole may also be used for assessment of the glucuronidation capacity although this is a minor pathway in man. Because the variation within subjects is much less than between them, the cocktail test is particularly suited for paired designs with measurements before and after an environmental change and the subjects serving as their own control. The metronidazole/antipyrine cocktail may have many applications in the study of the regulation of foreign compound metabolism in man and in animals, in vivo and in vitro.

Effect of subacute oral intake of the food antioxidant butylated hydroxyanisole on clinical parameters and phase-I and -II biotransformation capacity in man

A study is presented in which eight healthy male non-smoking volunteers ingested a daily amount of 0.5 mg/kg butylated hydroxyanisole (BHA) for 10 consecutive days. Blood samples were taken on days -6 and 0 before and on days 4 and 7 after the first BHA administration for the assessment of standard clinical plasma parameters (L-aspartate aminotransferase, L-alanine-aminotransferase, L-gamma-glutamyltranspeptidase, creatine phosphokinase, lactate dehydrogenase, total protein, albumin, urea, creatinine, Na+, and Cl-). Antipyrine (500 mg p.o.) and paracetamol (500 mg p.o) were administered before and during BHA administration as test substances to measure phase-I and phase-II biotransformation capacity. Saliva samples and urine were subsequently collected for the assessment of kinetic parameters (e.g. saliva elimination half-life, saliva clearance, apparent volume of distribution) and urinary excretion of metabolites. Kinetic plasma parameters of BHA itself were determined in plasma samples obtained via a catheter in an arm vein after oral BHA intake on days 0 and 7. Levels of antipyrine, paracetamol, BHA and metabolites in plasma, saliva or urine were quantified by standard or newly developed reversed-phase high-performance liquid chromatography methods. Urinary excretion of Na+, K+, and Cl-, as well as osmolality of urine were measured on three days before and six days during BHA administration. Generally, no significant differences were detected in the parameters measured, indicating that oral administration of BHA to men for 10 days remains without effects on clinical biochemical parameters and phase-I and phase-II biotransformation capacity. In contrast, urinary excretion of metabolites of BHA was significantly increased on days 3 and 7 vs. the first day of BHA administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of alpha-interferon on theophylline pharmacokinetics and metabolism

1. The influence of alpha-interferon (Roferon-A) on the pharmacokinetics and metabolism of theophylline was studied in healthy adults. Roferon-A was administered as an intra-muscular injection (3 x 10(6) iu) once-a-day over 3 days. One week prior to and immediately after this course a single 20 min aminophylline infusion (4 mg kg-1) was given. 2. Blood samples for theophylline analysis were taken over 48 h. Urine was collected up to 72 h and assayed for theophylline and its major metabolites 3-methylxanthine, 1,3-dimethyluric acid and 1-methyluric acid. 3. Pharmacokinetic parameters for theophylline in plasma were calculated. From urinary excretion data the overall metabolic clearance of theophylline and clearances for formation of the metabolites were calculated. 4. After interferon administration, there was a significant increase of approximately 15% in the mean values of the terminal elimination half-life, area under the curve and mean residence time of theophylline in association with a similar decrease in plasma clearance (P less than 0.05). Formation clearances of the metabolites tended to be smaller after treatment, but only the change in the overall clearance of theophylline was significantly different (P less than 0.05). There was no systematic shift in the metabolic pattern of theophylline. 5. Additional investigations of the influence of the duration of alpha-interferon treatment are necessary before definite conclusions can be drawn about the mechanism and the clinical relevance of the described interaction.

Inhibition of drug metabolism by quinolone antibiotics

A number of quinolone antibiotics have been found to reduce the hepatic clearance of coadministered drugs such as theophylline. Enoxacin appears to be the most potent inhibitor, consistently decreasing theophylline clearance by more than 50%, while a single study suggests a similar degree of inhibition with pipemidic acid. Ciprofloxacin and pefloxacin reduce theophylline clearance to a smaller extent (approximately 20 to 30%). However, with ciprofloxacin, larger changes and theophylline toxicity have been reported in some subjects. Norfloxacin, ofloxacin and nalidixic acid appear to have minimal effects on theophylline clearance. Enoxacin and ciprofloxacin have also been found to reduce the clearance of caffeine, while ofloxacin has no effect. Few other substrates have been studied. Enoxacin decreases the clearance of R-warfarin with no effect on S-warfarin. In addition, enoxacin has been reported to reduce the clearance of antipyrine, with no effect on chlorpropamide, glibenclamide (glyburide) or phenytoin. The mechanism of these interactions is largely unexplored. It has been suggested that inhibition may be related to the production of 4-oxoquinolone metabolites; however, this hypothesis has not been confirmed. No unique structural feature has been identified to date which explains differences between these compounds in their propensity to affect drug metabolism. Further studies are needed to evaluate the effects of these drugs on other substrates not yet examined and to assess whether or not inhibition is dose related. Clinically, caution is advised when using a quinolone, particularly enoxacin, pipemidic acid, ciprofloxacin or pefloxacin, in combination with theophylline. Close monitoring of theophylline concentrations is recommended in any patient receiving these drugs. The clinical significance of inhibited metabolism of other substrates remains unclear at present. Until further data are available, clinicians should be aware of the possibility of reduced drug clearance resulting in adverse effects whenever the fluoroquinolones are coadministered with drugs that depend on hepatic metabolism for their elimination.

The influence of ranitidine on the pharmacokinetics and toxicity of doxorubicin in rabbits

The influence of ranitidine on the pharmacokinetics and toxicity of doxorubicin was studied in six female New Zealand white rabbits. Plasma pharmacokinetic data were first obtained from rabbits given 3 mg/kg doxorubicin. After 1 month, the same rabbits were treated with ranitidine, 2.5 mg/kg or 25 mg/kg, before and during doxorubicin administration. The plasma doxorubicin assays to determine pharmacokinetic parameters were repeated. Drug toxicity was evaluated using complete blood counts, and hepatic function was measured using a 14C-aminopyrine breath test. High-dose ranitidine increased the total exposure to doxorubicin (area under the curve of doxorubicin alone = 1.44 +/- 0.88 microM.h/ml vs 4.49 +/- 2.35 microM.hr/ml for doxorubicin given with high-dose ranitidine; P = 0.06). Low-dose ranitidine did not alter doxorubicin pharmacokinetics. Exposure to doxorubicinol was altered by either high-dose or low-dose ranitidine. 14C-Aminopyrine half-life was altered by a ranitidine dose of 25 mg/kg (aminopyrine half-life after placebo control = 97 +/- 6 min as against aminopyrine half-life after ranitidine = 121 +/- 7 min; mean +/- SEM; P less than 0.02). Low-dose ranitidine did not exacerbate doxorubicin-induced myelosuppression. High-dose ranitidine enhanced doxorubicin-induced erythroid suppression while sparing the myeloid series. At cytochrome P-450-inhibitory doses, ranitidine's effects upon doxorubicin plasma pharmacokinetics are similar to those previously seen with cimetidine. These changes did not appear to alter drug detoxification and are not related to microsomal inhibition of doxorubicin detoxification. Low doses of ranitidine do not alter doxorubicin plasma pharmacokinetics or toxicity in rabbits.

Studies on in vitro antipyrine metabolism by 13C,15N double labeled method

The capacities of forms of cytochrome P-450 to oxidize antipyrine were compared. An isotope dilution gas chromatography/mass spectrometry/selected ion monitoring assay was developed to quantify the three main metabolites, norantipyrine, 3-hydroxymethylantipyrine and 4-hydroxyantipyrine. 13C,15N-Double labeled antipyrine was used as a substrate and the metabolites were analyzed as their trimethylsilyl derivatives. Among forms of cytochrome P-450 examined, a male-specific form of P-450, namely P-450-male, showed higher activity to form all the three metabolites. The other forms were responsible only for the formation of norantipyrine and 4-hydroxyantipyrine. The activities of liver microsomes from untreated male and female rats and rats treated with phenobarbital, 3-methylcholanthrene or polychlorinated biphenyl were expressed dependent on the activities of forms of cytochrome P-450 examined.

The disposition of antipyrine and its metabolites in young and elderly healthy volunteers

1 Oxidative metabolism of antipyrine (AP) was compared in 11 elderly (greater than 65 years) and 12 young (less than 40 years) volunteers. All subjects were non-smokers, consumed little if any alcohol and were in good health. 2 After a single dose of AP 500 mg, its clearance from saliva and profiles of the parent drug and its major metabolites in urine were determined using high-performance liquid chromatography. 3 Mean total AP clearance from saliva was lower in the elderly (P less than 0.05). Mean weight-normalised volume of distribution was also smaller (P less than 0.01) so that elimination half-life in the elderly was not significantly different from that in the young. 4 The percentage dose excreted in 48 h urine as norantipyrine (NORA) and its clearance for production were lower in the elderly (P less than 0.001 and P less than 0.01 respectively). Urinary 3-hydroxymethylantipyrine (HMA) and free antipyrine were present in greater quantities in 48 h urine in the elderly (P less than 0.001 and P less than 0.05) while the amounts of 4-hydroxyantipyrine (OHA) were almost identical in the two age groups. 5 The findings suggest that there is a selective impairment of N-demethylation in the elderly which may have important implications for dosage of elderly patients with drugs metabolised by this route.

Plasma antipyrine half-life can be determined from urine data

Antipyrine half-life has been determined from measurements of antipyrine concentrations in spontaneously voided urine specimens in eleven subjects, studied on a total of forty-seven different occasions while receiving no drugs, interferon or ketoconazole. Plasma and saliva half-lives show good intrasubject correlation. Plasma and urine half-lives show good intrasubject correlation provided total urine output is at least 1.1 l day-1. The range of intrasubject correlation coefficients for plasma and urinary half-lives was 0.76 to 0.98, with a median value of 0.85. Saliva and urine half-lives show good intrasubject correlation, with the range of intrasubject correlation coefficients from 0.74 to 0.98, and with a median value of 0.75. There is a small but consistent bias towards shorter urinary half-life estimates; this averaged 0.75 h for the plasma-urine studies and 0.192 h for the saliva-urine studies. There were parallel changes in antipyrine half-life estimated from plasma and urine for one of our subjects who received multiple doses of recombinant beta-interferon and had a 150% increase in antipyrine half-life over the study period.

Induction of mixed function oxidase activity in man by rifapentine (MDL 473), a long-acting rifamycin derivative

The effects of rifapentine (MDL 473) administration on hepatic mixed function oxidase activity in man have been investigated in six healthy volunteers. Administration of rifapentine (600 mg 48 h-1) for 10 days resulted in a significant reduction in antipyrine half-life (from 13.2 +/- 1.0 h to 7.7 +/- 0.4 h) and a corresponding increase in its total body clearance (from 41.8 +/- 5.5 ml min-1 to 67.4 +/- 5.6 ml min-1). Twelve days after stopping rifapentine administration, these values had largely returned to base-line. 24-Hour excretion of 6 beta-hydroxycortisol was significantly increased, by approximately three-fold, following administration of rifapentine for 10 days. Again, 12 days after stopping drug administration, 6 beta-hydroxycortisol excretion had returned to pretreatment values. Clearance of antipyrine to its three oxidative metabolites was increased by rifapentine administration, although the increase for 3-hydroxymethylantipyrine was not significant. The greatest increase (+140%) was observed for norantipyrine. Twelve days after the last dose of rifapentine, all values had returned to control levels. It is concluded that, like rifampicin, rifapentine is a potent inducer of mixed function oxidase activity in man and that the possibility of clinically significant drug interactions should be anticipated in the therapeutic use of this compound.

Antipyrine metabolism during hepatic regeneration in the rat

We investigated antipyrine clearance and urinary excretion of 4-hydroxyantipyrine, 3-hydroxymethylantipyrine and nor-antipyrine in rats after 70% partial hepatectomy. Antipyrine clearance recovered more slowly than liver weight but after 240 h both liver weight and antipyrine clearance had reached control values. During hepatic regeneration conversion of antipyrine to the three major metabolites was reduced, conversion to 3-hydroxymethylantipyrine being reduced more than conversion to the other metabolites. Antipyrine clearance was closely correlated to liver weight (r = 0.81), indicating a close relation between the functional hepatic mass and the liver weight during hepatic regeneration.

Effect of rifampicin treatment on hepatic drug metabolism and serum bile acids in patients with primary biliary cirrhosis

Six patients with primary biliary cirrhosis (PBC) were treated with a daily oral dose of 600 mg rifampicin for 2 weeks to induce the hepatic metabolism of drugs and bile acids. On rifampicin 5 of 6 patients experienced a pronounced decrease of their pruritus. In all patients the oxidative cytochrome P-450 dependent drug metabolism was induced as shown by an increase of antipyrine-clearance from 36.3 +/- 8.8 to 80.6 +/- 20.1 ml/min and an enhanced urinary excretion of 6-beta-hydroxycortisol from 454 +/- 1.99 to 1607 +/- 362 micrograms/24 h. Furthermore, in all 6 patients the serum alkaline phosphatase declined. In the 3 cholestatic patients (bilirubin greater than 1.0 mg/dl) the serum concentration of total and conjugated bile acids was strikingly reduced. Thus, rifampicin is an inducer of hepatic metabolism in PBC-patients, ameliorates the pruritus and can lower serum concentrations of alkaline phosphatase and bile acids.

Quantitation of norantipyrine sulphate and norantipyrine glucuronide as major metabolites of antipyrine in man and rat

Two assay procedures are described for the quantitation of norantipyrine sulphate and norantipyrine glucuronide present in biological material. One, a selective acid hydrolytic assay procedure that affords the discriminative determination of both conjugates without prior separation, measures free norantipyrine by tlc-uv. The other is a tlc separation procedure for intact norantipyrine conjugates, which, in conjunction with radiolabelled material, derived from [3-14C]antipyrine, enables the direct quantitation of both conjugates independently. In man, about 25% of dose of antipyrine (1200 mg) was excreted as norantipyrine glucuronide within 48 h. The amount of norantipyrine sulphate was small. In the rat, norantipyrine sulphate represented about 15-20% of the dose of antipyrine (40-50 mg kg-1); no norantipyrine glucuronide was formed. Free norantipyrine has not been detected in urine of either species after antipyrine dosage. Pretreatment with 3-methylcholanthrene in the rat substantially enhanced excretion of norantipyrine sulphate, whereas induction with phenobarbitone was without effect on the microsomal N-demethylation of antipyrine. The lability of free norantipyrine was examined under different conditions and contrasted with the relative stability of norantipyrine conjugates. Two of the main degradation products of norantipyrine were identified as 4-phenylazo-norantipyrine and a 4,4'-bipyrazole-derivative.

Effect of chloroquine and primaquine on antipyrine metabolism

The effects of two antimalarial drugs, chloroquine and primaquine on antipyrine kinetics and metabolism have been studied in volunteers. Chloroquine (250 mg) given 2 h before antipyrine (600 mg orally) had no effect on salivary kinetics of antipyrine or on the urinary recovery of metabolites. Primaquine (45 mg) given 2 h before antipyrine (300 mg orally), increased antipyrine half-life (calculated from 0-24 h) from 12.7 +/- 3.2 (mean +/- s.d.) to 25.3 +/- 3.9 h and decreased clearance from 3.01 +/- 0.67 to 1.32 +/- 0.32 1 h-1. There was no change in the apparent volume of distribution. Antipyrine half life changed with time in the presence of primaquine and when calculated between 24 and 48 h had returned to control. After primaquine, the metabolic clearance (calculated from 0-24 h) of antipyrine to its three main metabolites, 3-hydroxymethylantipyrine, 4-hydroxyantipyrine and norantipyrine was significantly reduced. There was no selective effect on a particular metabolic pathway. There was no change in 6 beta-hydroxycortisol excretion (expressed as a ratio of total 17-hydroxy-corticosteroids) in the period 0-48 h following primaquine administration. The inhibition of hepatic metabolism by primaquine but not the structurally related chloroquine may be an example of a structure activity phenomenon and could be of clinical significance.

Time course of phenobarbital and cimetidine mediated changes in hepatic drug metabolism

Four healthy subjects were investigated weekly for 14 weeks by the antipyrine one sample saliva test, the 48-h urinary excretion of major antipyrine metabolites and the 2-h aminopyrine breath test before, during and after stimulation and inhibition of drug metabolism with phenobarbital and cimetidine, respectively. The phenobarbital-induced enhancement of antipyrine clearance (1.33-2.03 times) and of the aminopyrine breath test (0.94-1.19 times) occurred one week after beginning drug administration and persisted for 10 days after its cessation. The cimetidine-related inhibition of antipyrine clearance (0.62-0.85 times) and of the aminopyrine breath test (0.52-0.93 times) was observed 24 h after beginning cimetidine administration and subsided within two days after the last dose. During enhancement and inhibition the clearance of antipyrine to 3-hydroxymethyl-, 4-hydroxy- and norantipyrine varied as the total antipyrine clearance. The intraindividual variation in antipyrine clearance was 6-8%, and the corresponding variation in urinary excretion of antipyrine metabolites was 10-20%. It is concluded that the influence of phenobarbital and cimetidine on hepatic microsomal enzyme activity can be monitored simply by measurement of the blood concentration of the drug. Whether this simple relationship applies to other microsomally mediated drug interactions requires further evaluation.

Antipyrine metabolism in relation to polymorphic oxidations of sparteine and debrisoquine

Thirty-five healthy subjects who had been classified as extensive or poor metabolizers of both sparteine and debrisoquine were given a single oral dose of antipyrine. Saliva concentration of antipyrine and urinary excretion of its three major oxidation metabolites were measured. All the parameters of antipyrine metabolism which were estimated had similar distributions in both the 28 EM and 7 PM genetic phenotypes defined by the metabolism of sparteine and debrisoquine. The clearance of antipyrine by the formation of 4-hydroxy-antipyrine and 3-hydroxy-antipyrine respectively were closely correlated (r = 0.83, P less than 0.001) and both were significantly higher in smokers than in non-smokers. Demethylation of antipyrine also seemed to be influenced by smoking, but not to a statistically significant extent. These findings confirm the influence of the environmental factor of smoking in antipyrine oxidative biotransformations.