Biliary excretion of benzbromarone and its hydroxilated main metabolites in humans.

Hepatic metabolism of the uricosuric drug benzbromarone results in the formation of two hydroxilated main metabolites M1 (1'-hydroxybenzbromarone) and M2 (6-hydroxybenzbromarone). As urinary excretion of benzbromarone and its metabolites is very low, we investigated biliary and plasma concentrations of the parent drug and the metabolites after oral administration of a single 100 mg dose of benzbromarone in 6 patients requiring diagnostic gastroduodenoscopy. Benzbromarone, M1 and M2 were detectable in bile samples 12 hours after drug application. No dehalogenated derivatives (bromobenzarone, benzarone) were present in the bile. 12h, 24h, and 36h plasma concentrations of the parent drug and the main metabolites varied substantially. Our data provide direct evidence of biliary excretion of benzbromarone and its hydroxilated main metabolites 1'-OH-bzbr (M1) and 6-OH-bzbr (M2) and demonstrate the lack of excretion of debrominated products.

Disease-specific noncompliance with drug treatment as a cause of persistent hyperuricemia and gout in anorexia nervosa.

A 49 year old female patient with anorexia nervosa was admitted to the hospital because of treatment-refractory hyperuricemia and gout. Medical history and clinical findings were compatible with primary gout and uric acid nephropathy. The patient stated that she regularly took allopurinol. In the hospital she initially received 300 mg allopurinol daily after breakfast. In order to ensure allopurinol ingestion and absorption the plasma concentrations of both allopurinol and its active metabolite oxipurinol were determined in addition to serum uric acid and further clinical chemistry data. Despite allopurinol treatment no decrease of serum uric acid was observed for three days. Therefore the head nurse was instructed to supervise the intake of allopurinol carefully. During the following days serum uric acid decreased and plasma oxipurinol concentrations rose. On day 9 of treatment serum uric acid fell into the upper normal range. Therefore the patient was allowed to leave the hospital within a few days. However serum uric acid thereafter increased again while plasma oxipurinol declined. Later on it became evident that the patient had vomited self-induced approximately 15 minutes after allopurinol intake. In the meantime her husband had urged her to return home. Starting with day 18 benzbromarone treatment was added. Combined therapy with 400 mg allopurinol and 50 mg benzbromarone daily finally resulted in a serum uric acid concentration of 4.5 mg/dl at discharge from the hospital. About three weeks later the private physician again diagnosed hyperuricemia with serum uric acid values between 10 and 12 mg/dl. Meanwhile the patient needs to be dialysed due to end stage renal disease. Our observations show that self-induced vomiting to prevent effective treatment may be a disease-specific pattern of noncompliance with drug therapy in anorexia nervosa.

Fasting and postprandial disposition of R(-)- and S(+)-ibuprofen following oral administration of racemic drug in healthy individuals.

The effects of preceding food intake on the plasma concentrations of R(-)-ibuprofen and the pharmacologically active enantiomer S(+)-ibuprofen were investigated in healthy subjects. A single oral dose of 400 mg racemic ibuprofen was administered either fasting or following a standardized meal. As compared to fasting administration postprandial drug intake resulted in a clear reduction of R(-) and S(+)- ibuprofen plasma concentrations mainly during the initial three hours. The ratio of S(+)/R(-)-ibuprofen postprandially was increased for Cmax and AUC o-tmax as well as for AUC o-infinity. These data are compatible with a meal-induced enhancement of chiral inversion of R(-) to S(+)-ibuprofen. The significant reduction of plasma concentrations of ibuprofen mainly during the initial three hours suggests that the analgesic efficacy is diminished when the drug is taken after a meal. This may to a slight extent be compensated for by a small increase of the metabolic inversion of the R(-)-enantiomer into the active S(+)-form of the drug.

Uric acid lowering effect of oxipurinol sodium in hyperuricemic patients - therapeutic equivalence to allopurinol.

OBJECTIVE: Oxipurinol has been shown to be sufficiently absorbed after oral administration as a rapid release preparation of oxipurinol sodium. We compared the uric acid lowering affect of allopurinol and oxipurinol. METHODS: In a multicenter, randomized, double blind crossover trial in 99 hyperuricemic patients with normal renal function we investigated the uric acid lowering effect of oxipurinol sodium (O) in daily amounts equimolar to 300 mg allopurinol (A). Mean pretreatment plasma uric acid concentrations in groups A/O and O/A were 8.3 +/- 1.4 and 8.7 + /- 1.4 mg/dl, respectively. RESULTS: In group A/O the mean plasma uric acid decreased to 5.4 +/- 1.2 mg/dl with allopurinol treatment, and increased slightly to 5.7 + /- 1.3 mg/dl during the consecutive oxipurinol period. In group O/A plasma uric acid declined to 6.0 +/- 1.4 mg/dl with oxipurinol and was 5.6 + /- 1.3 mg/dl at the end of the allopurinol period. The overall average reduction compared to baseline was 3.0 mg/dl with allopurinol and 2.6 mg/dl with oxipurinol. The difference between the 2 treatments was small but significant (multiple p=0.027,2 tailed). The corresponding mean plasma oxipurinol concentrations were 9.24 mu g/dl at the end of the allopurinol period and 9.9 mu g/dl after treatment with oxipurinol (NS). CONCLUSION: Oxipurinol is well absorbed and sufficiently effective in hyperuricemic patients when administered as a rapid release preparation of oxipurinol sodium. Oxipurinol sodium could be a substitute for allopurinol in hyperuricemic patients and possibly also with new uses for allopurinol.

Biotransformation and uric acid lowering effect of benzbromarone in patients with liver cirrhosis - evidence for active benzbromarone metabolites?

The disposition of benzbromarone and its uric acid lowering effect were investigated in 8 patients with compensated liver cirrhosis in order to obtain evidence whether dose requirements differ from subjects with normal liver function. Following a single oral dose of 100 mg benzbromarone, the plasma concentrations of the parent drug and the two hydroxylated main metabolites M1 and M2 as well as uric acid were determined up to at least 72 h. All patients were found to be rapid benzbromarone eliminators. In patients 2-8 the extent of systemic availability of benzbromarone, as estimated by the average AUC(0-infinite), was similar to previous observations in healthy individuals, whereas the values of both metabolites M1 and M2 tended to be lower in patients with liver cirrhosis. Cmax of benzbromarone and M1 also were lower in patients, M2 was equivalent to the data in subjects with normal liver function. tmax and the plasma elimination half-life t(1/2) varied within the same range as previously observed in healthy individuals. One patient exhibited much higher values in AUC(0-infinite); and Cmax of benzbromarone and both metabolites, and in addition of the elimination half-life of M1 and M2, whereas the plasma elimination of benzbromarone itself was not delayed. An effect of altered liver function cannot be excluded in this patient. Ten hours after benzbromarone administration the mean plasma uric acid in patients 2-8 was reduced by 31.5% and in patient 1 by 44.2% as compared to pretreatment values. Baseline levels were not regained until 72 h. These data are compatible with a prolonged uric acid lowering effect of an active benzbromarone metabolite. Altogether, the present observations do not suggest dose adjustment to be necessary in patients with compensated liver cirrhosis Child A and B.

Disposition and uric acid lowering effect of oxipurinol: comparison of different oxipurinol formulations and allopurinol in healthy individuals.

We have investigated the disposition and plasma uric acid lowering effect of oxipurinol in ten healthy individuals following oral administration of three different formulations of oxipurinol and of allopurinol in equimolar doses. The reduction of plasma uric acid was clearcut up to 48 h. As estimated from plasma AUC0-infinity, Cmax, tmax, tlag, and urinary drug excretion, a conventional rapid release preparation of oxipurinol sodium was clearly superior to oxipurinol as free acid and to enteric coated microtablets of oxipurinol sodium. Plasma oxipurinol concentrations following a single dose of the conventional formulation of oxipurinol sodium were approximately 25% lower than those observed after an equimolar dose (300 mg) of allopurinol, but mean Cmax reached the value reported to be necessary for 90% inhibition of xanthine oxidase. Since prolonged administration will result in accumulation of oxipurinol because of its slow elimination, this type of oxipurinol formulation can be expected to meet the therapeutic requirements for a drug to lower plasma uric acid.

Interaction of allopurinol and hydrochlorothiazide during prolonged oral administration of both drugs in normal subjects. I. Uric acid kinetics.

The interaction of allopurinol (300 mg/day) and hydrochlorothiazide (50 mg/day) was studied in seven healthy male volunteers during prolonged coadministration of the two drugs using defined dietary conditions. A formula diet was administered with the allopurinol throughout the 24-day study, while hydrochlorothiazide was added during days 11-21. After the addition of hydrochlorothiazide both plasma uric acid and plasma oxipurinol rose for 6 days--24% and 30%, respectively, compared to steady-state levels during allopurinol alone (P < 0.01 each). In neither substance were variations in renal excretion significant. By the end of combined treatment (day 21), the changes induced by hydrochlorothiazide had already been reversed to a considerable extent. It is concluded that both in normal individuals and in patients with normal renal clearance of uric acid the effect of hydrochlorothiazide on the plasma concentration and renal excretion of oxipurinol is small. When taking both drugs, there is no increased risk during long-term treatment, and a risk is even questionable during the first days.

Interaction of allopurinol and hydrochlorothiazide during prolonged oral administration of both drugs in normal subjects. II. Kinetics of allopurinol, oxipurinol, and hydrochlorothiazide.

The kinetics of allopurinol and hydrochlorothiazide were investigated in seven healthy male subjects during prolonged coadministration of two drugs. Subjects were maintained on an isoenergetic, purine-free formula diet with RNA supplementation for 24 days. Allopurinol (300 mg) was given orally on days 1-24. Hydrochlorothiazide (50 mg daily) was added to days 11-21. On day 43 a single oral dose of 50 mg hydrochlorothiazide was administered. Plasma concentration-time profiles of allopurinol and its main metabolite oxipurinol were obtained on days 1, 10, and 21; hydrochlorothiazide profiles were assessed on days 21 and 43. In addition, 24-h plasma concentrations of oxipurinol were measured repetitively, and 24 h urine samples were collected for the determination of allopurinol, oxipurinol, and hydrochlorothiazide. For oxipurinol, mean Cmax was not altered on hydrochlorothiazide treatment (13.8 +/- 1.4 micrograms/ml and 14.7 +/- 2.6 micrograms/ml, respectively); mean AUC0-24 was 259 and 290 micrograms h-1 ml-1, respectively. The small difference in AUC0-24 values does not explain the increase in plasma uric acid concentration during hydrochlorothiazide treatment, nor do the variations in allopurinol and hydrochlorothiazide kinetics.

Determination of the coumarin anticoagulant phenprocoumon and metabolites in human plasma, urine and breast milk by high-performance liquid chromatography after solid-phase extraction.

The coumarin anticoagulant phenprocoumon (PH) and metabolites (6-, 7- and 4'-hydroxyphenprocoumon) were analysed in plasma and urine samples from anticoagulated patients using solid-phase extraction and high-performance liquid chromatography with reversed-phase columns and ultraviolet and fluorescence detection; a simpler handling of samples, higher selectivity, precision, accuracy and analytical recovery were obtained compared to analysis using liquid-liquid extraction. Similarly, a method for the analysis of PH in human breast milk was developed to assess the passage of anticoagulants into breast milk in anticoagulated lactating women.

Metabolism of benzbromarone in man: structures of new oxidative metabolites, 6-hydroxy- and 1'-oxo-benzbromarone, and the enantioselective formation and elimination of 1'-hydroxybenzbromarone.

1. The uricosuric drug benzbromarone is extensively metabolized in man and two main metabolites are formed: the previously characterized 1'-hydroxybenzbromarone (metabolite M1) and an arylhydroxybenzbromarone (metabolite M2) of unknown structure. A dimethyl derivative was isolated from urine after methylation and was characterized by gas chromatography-mass spectrometry (g.l.c.-m.s.) and high resolution nuclear magnetic resonance spectroscopy as 4''-O-methyl-6-methoxybenzbromarone; the structure of M2 therefore is 6-hydroxybenzbromarone. 2. A minor metabolite was similarly characterized as 1'-oxobenzbromarone by comparison with authentic synthetic samples and is a product of biodegradation and not an artifact derived from the in vitro oxidation of 1'-hydroxybenzbromarone. Further minor metabolites were detected and were provisionally characterized by g.l.c.-m.s. after derivatization and include: 2'-hydroxybenzbromarone (an isomer of 1'-hydroxybenzbromarone); 1',6-dihydroxybenzbromarone; dihydroxy-aryl-benzbromarone; and two structure isomers of 6-hydroxybenzbromarone. Debrominated metabolites were not detectable. 3. Benzbromarone is hydroxylated in vivo at the prochiral centre C1' to 1'-hydroxybenzbromarone; analysis of 1'-hydroxybenzbromarone from plasma and urine extracts by h.p.l.c. using a chiral column revealed that two peaks were eluted which showed a mean enantiomeric ratio of 2.1 for plasma and 7.3 for urine; these data demonstrate that the formation and elimination of this metabolite is enantioselective; the absolute configuration of the 1'-chiral centre is presently unknown.

Benzbromarone hydroxylation in man: defective formation of the 6-hydroxybenzbromarone metabolite.

To determine the elimination phenotype of the uricosuric agent benzbromarone 100 mg of the drug was administered as a single oral dose to 11 volunteers on a formula diet; plasma concentration-time profiles of the parent drug and the main metabolites M1 (1'-hydroxybenzbromarone) and M2 (6-hydroxy-benzbromarone) were measured by high-performance liquid chromatography for 168 h. Of the 11 subjects 2 showed higher plasma concentrations and delayed elimination of benzbromarone and metabolite M1 but reduced formation of metabolite M2 compared to the other 9 subjects. However, the plasma concentration-time profiles of the metabolites in these two slow eliminators, termed type 2, differed from those of a poor eliminator characterized during a previous study; the latter, termed type 1, eliminated benzbromarone as well as both metabolites M1 and M2 slowly. The differences in the elimination of benzbromarone and its metabolites are probably caused by differences in the activities of the cytochrome P450 mono-oxygenase isozymes. The results show that determination of the phenotype solely by measurement of the 24-h benzbromarone plasma concentration does not unequivocally characterize slow benzbromarone eliminators; additional plasma concentration-time profiles of the parent drug and metabolites are necessary. Metabolite M2 is characterized as 6-hydroxybenzbromarone; the formation and elimination of the chiral metabolite M1 is enantioselective.

Simultaneous determination of allopurinol and oxipurinol in human plasma and urine by high-performance liquid chromatography.

The uricostatic drug allopurinol (CAS 315-30-0) is used for treatment of hyperuricaemia and is mainly bio-transformed to the active metabolite oxipurinol (CAS 2465-59-0) in humans. A new assay was developed for the simultaneous determination of both compounds in plasma and urine using ultrafiltration and ion exchange purification steps for plasma and urine, respectively. Reversed-phase high-performance liquid chromatography with ultraviolet detection was applied for the separation and quantitation of both compounds. The limit of detection was 0.1 microgram/ml for both compounds in plasma and 0.2 and 0.5 microgram/ml for allopurinol and oxipurinol, respectively, in urine. Within-run and day-to-day precision of 3-5% and 5-7% was determined for plasma and 6-8% and 8-10% for urine analysis. The assays were further validated using liquid chromatography with photodiode array detection and by comparison with methods using protein precipitation as the purifying step. The high analytical recoveries, selectivity, sensitivity, accuracy and reproducibility were adequate for the measurement of both compounds in pharmacokinetic studies and for drug monitoring in patients on allopurinol therapy.

[Transfer of phenprocoumon in breast milk. Is oral anticoagulation with phenprocoumon a contraindication for breastfeeding?]. / Transfer von Phenprocoumon in die Muttermilch. Ist eine orale Antikoagulation mit Phenprocoumon eine Kontraindikation für das Stillen?

UNLABELLED: As the passage of phenprocoumon into human milk has not been studied yet, mothers on oral anticoagulation with Phenprocoumon are advised to stop breastfeeding in order to avoid the potential hazards of vitamin K deficiency haemorrhage in their babies. We analysed the passage of Phenprocoumon into human milk in a breastfeeding mother of a premature baby (gestational age 32 weeks), who required oral anticoagulation on day 19 post partum. The mother was advised to continue collecting her milk with an electric pump, and to resume breastfeeding, if a significant passage of the drug was excluded. Milk Sampling (fore and hind milk pairs (n = 2), for milk (n = 4), 24 h pooled collections) for the Phenprocoumon analyses with an HPLC method was performed on days 27, 28, and 31 when the Quick's Prothrombin time was stable in the therapeutic range (Phenprocoumon plasma concentrations: 1.8-2.2 micrograms/ml). RESULTS: Phenprocoumon was higher in hind than in foremilk. With constant plasma concentrations the variability between different foremilk samples was 26-76 ng/ml. The Phenprocoumon concentration in the 24 h pooled sample was 33 ng/ml. Estimates of the Phenprocoumon secretion into human breast milk should be from pooled milk samples of a 24 h collection. Phenprocoumon in human milk is only about 1/50 of the corresponding maternal plasma concentrations. The estimated daily Phenprocoumon intake from maternal milk in a baby drinking about 200 ml/kg/day is 6-8 micrograms/kg. This is much less the average maintenance requirement for anticoagulation with Phenprocoumon in children (about 50 micrograms/kg/day).(ABSTRACT TRUNCATED AT 250 WORDS)

Bioequivalence of allopurinol preparations: to be assessed by the parent drug or the active metabolite?

Allopurinol is converted almost completely into a single active metabolite, oxipurinol, which has the same therapeutic pattern but a much longer elimination half-life than the parent compound. Therefore both allopurinol and oxipurinol were evaluated in our bioequivalence study in healthy volunteers comparing two allopurinol brands. Bioequivalence determination was based on the 90% confidence intervals (CI) of the area under the plasma concentration time curve from time zero to infinity (AUC0-infinity), of the area from time zero to the last measurable plasma concentration (AUC0-t (last)), and Cmax. Because of the lack of compound-specific criteria we used conventional limits for the bioequivalence range. Under these conditions the brand chosen as test preparation was judged to be bioequivalent to the reference form with respect to the extent of bioavailability, AUC0-infinity, and AUC0-t (last) of the parent drug. The CI of Cmax of allopurinol slightly exceeded the upper limit of 130%, so that bioequivalence was not confirmed with regard to the rate of bioavailability of the parent compound. The CI values of both AUC and Cmax of the active metabolite were tighter than those of allopurinol. In addition, the CI values of Cmax of oxipurinol were smaller than those of the corresponding AUC. As a consequence the test drug can clearly be accepted as bioequivalent, based on metabolite data. Since the active metabolite is of greater therapeutic significance than the parent drug, assessment of the bioequivalence of allopurinol preparations needs to be based on oxipurinol rather than allopurinol.(ABSTRACT TRUNCATED AT 250 WORDS)

Simple determination of hydrochlorothiazide in human plasma and urine by high performance liquid chromatography.

The diuretic drug hydrochlorothiazide (HCT) is used mainly for treatment of mild to moderate hypertension and is usually administered with other drugs. An assay for the determination of HCT in human plasma and urine by high performance liquid chromatography (HPLC) has been developed. Samples were purified by solvent extraction and analysed by reversed phase HPLC with ultraviolet detection, using hydroflumethiazide as the internal standard; plasma was eluted using gradient elution and urine was analysed isocratically. The method is simple to perform, is sensitive (detection limit 0.01 micrograms/mL in plasma and 0.2 micrograms/mL for urine); it showed good reproducibility (3-8%). A great number of drugs did not interfere with the assay and the method was used for pharmacokinetic studies in healthy subjects, but samples from patients can also be analysed with high selectivity.

Comparative plasma disposition and anticoagulant activities of racemic phenprocoumon and its metabolites in rats.

The anticoagulant phenprocoumon (PH) and its metabolites 6-hydroxy-, 7-hydroxy- and 4'hydroxy-phenprocoumon (6-OH-PH, 7-OH-PH and 4'-OH-PH, respectively) were separately administered intravenously as racemates to rats in order to measure the potential effects of the major metabolites of PH on coagulation. Plasma samples were assayed for total concentrations of the administered compounds and the corresponding prothrombin times; kinetic parameters and anticoagulant activities were estimated using a pharmacodynamic model based on the rate of synthesis of clotting factors. The relative potencies were in the order PH > 4'-OH-PH > 6-OH-PH > 7-OH-PH the latter showing no activity. Patients on PH therapy showed lower plasma concentrations of metabolites than of PH; in humans the metabolites of PH will not contribute significantly to the overall anticoagulant activity of the drug.

Lack of accumulation of midazolam in plasma and lipoprotein fractions during intravenous lipid infusions in patients on artificial respiration.

Severely ill patients often require total parenteral nutrition including intravenous lipid emulsions concurrently administered with lipophilic drugs. Therefore we investigated whether therapeutic application of a mixed medium chain/long chain triglyceride infusion affects the disposition of midazolam necessary for sedation in patients on artificial respiration. The concentrations of midazolam were measured in unfractionated plasma, and in lipoprotein fractions isolated from ex vivo blood samples, including determination of triglycerides and cholesterol; the albumin level was also analysed. Midazolam in the VLDL fraction was only 0.246 microgram.ml-1, whereas the total plasma concentration averaged 1.101 micrograms.ml-1, and the midazolam content of the LDL plus HDL fractions amounted to 1.771 micrograms.ml-1. Albumin in these lipoprotein fractions was just as unequally distributed. A lipid infusion resulted in a significant elevation of total triglycerides from 157 to 221 mg.dl-1 and VLDL-triglycerides from 77 to 155 mg.dl-1. The triglyceride content of the LDL plus HDL fraction rose from 102 to 139 mg.dl-1. At the same time the midazolam concentration in unfractionated plasma and in the VLDL and the LDL + HDL fractions decreased to 0.899 microgram.ml-1, 0.130 micrograms.ml-1, and 1.265 micrograms.ml-1, respectively. Cholesterol and albumin concentrations were not affected. The data show for the first time that a significant increase in plasma triglycerides during an intravenous lipid infusion does not result in accumulation of midazolam in lipoproteins, probably because albumin binding of the drug is very strong. The lack of midazolam trapping is important with respect to the safety of concurrent use of lipophilic drugs and intravenous lipid infusions.

Thermospray and particle beam liquid chromatographic-mass spectrometric analysis of coumarin anticoagulants.

Positive ion mass spectra were obtained from several coumarin oral anticoagulants (phenprocoumon, warfarin, acenocoumarol and dicoumarol) and derivatives by liquid chromatography-thermospray mass spectrometry (LC-TSP-MS) and liquid chromatography-electron impact mass spectrometry (LC-EI-MS) to assess the use of LC-MS methods for the determination of these compounds in biological materials. LC-TSP mass spectra showed a single [M + 1]+ ion with no fragmentation; LC-EI mass spectra showed fragment ions which were similar in mass and relative intensities to those obtained by conventional EI-MS. These data should serve as a basis for the development of LC-MS methods for the qualitative and quantitative analysis of coumarin anticoagulants in biological samples. LC-TSP-MS was applied to the determination of phenprocoumon in a plasma extract from an anticoagulated patient.