Frusemide and its acyl glucuronide show a short and long phase in elimination kinetics and pharmacodynamic effect in man.

The pharmacokinetics of 80 mg frusemide given orally were investigated in normal subjects using a direct HPLC method for parent drug and its acyl glucuronide conjugate. Two half-lives could be distinguished in the plasma elimination of both frusemide and its conjugate, with values of 1.25 +/- 0.75 and 30.4 +/- 11.5 h for frusemide and 1.31 +/- 0.60 and 33.2 +/- 28.0 h for the conjugate. The renal excretion rate-time profile showed two phases; the rapid elimination phase lasted from 0-15 h and the second and slow phase, from 15-96 h. During the first 15 h, 33.3 +/- 4.8% of the dosed frusemide was excreted; in the remaining period 15-96 h, 4.6 +/- 1.5% was excreted. In the same two periods the excretion of the glucuronide was 13.4 +/- 4.7 and 1.9 +/- 1.1%, respectively. The mean renal clearance of frusemide was 90.2 +/- 16.9 mL min-1 during the first period and 91.5 +/- 29.3 mL min-1 in the remaining period, during which the stimulation of urine production was absent. The renal clearance of the acyl glucuronide was 702 +/- 221 mL min-1 in the first period, but only 109 +/- 51.0 mL min-1 in the second period. The stimulated urine production in the first 6 h after administration amounted to 2260 +/- 755 mL (measured urine production minus baseline value of 1 mL min-1 (360 mL). During the second or rebound period (6-96 h after drug administration), the quantity of urine was 990 +/- 294 mL lower than what would have been expected from the baseline production of 5400 mL. This reduced production (0.82 mL min-1) is equivalent to an 18% reduction in the average urine flow rate of 1 mL min-1.

Comparison of the bioavailability and pharmacokinetics of oral methylergometrine in men and women.

OBJECTIVE: To assess and compare the pharmacokinetics and bioavailability of methylergometrine (ME) in men and non-pregnant women. DESIGN: A cross-over design was used for an oral dose of 0.125 mg and an intravenous dose of 0.200 mg of ME in 6 men and 6 non-pregnant women (parallel-design in gender). RESULTS: After intravenous administration, the pharmacokinetic profile of ME was described with a 2-compartment model. The distribution half-life (t1/2 alpha) in men was 0.19 +/- 0.27 h, in women 0.10 +/- 0.04 h, the elimination half-life (t1/2 beta) 1.85 +/- 0.28 h, respectively, 1.94 +/- 0.34 h and the total body clearance (CL) 33.2 +/- 11.8 l.h-1, and, respectively, 22.18 +/- 3.10 l.h-1. For these intrinsic pharmacokinetic parameters differences between men and women were not statistically significant. After oral administration, the pharmacokinetic profile was described with a 1-compartment model. The lag time was subject dependent and was significantly longer in men 0.33 +/- 0.09 h than in women 0.09 +/- 0.07 h. T1/2 beta in men was 2.08 +/- 0.43 h and was longer than in women 1.42 +/- 0.31 h (p = 0.012). In both men and women a large variation of bioavailability was shown ranging between 22% and 138%. CONCLUSION: This study with oral methylergometrine showed a comparable large interindividual variability in bioavailability in both men and women.

Probenecid inhibits the renal clearance of frusemide and its acyl glucuronide.

The effect of oral probenecid (1 g) on the pharmacokinetics of frusemide (80 mg p.o.) and its acyl glucuronide was studied in nine healthy subjects. Probenecid significantly increased the t1/2,z of frusemide from 2.01 +/- 0.68 to 3.40 +/- 1.48 h (P = 0.0015) and significantly decreased oral clearance from 164 +/- 67.0 to 58.3 +/- 28.1 ml min-1 (P = 0.0001). No effect of probenecid on the plasma protein binding of frusemide was detected. Probenecid significantly increased the tmax of the metabolite frusemide acyl glucuronide from 1.4 to 2.6 h, but had no effect on the tlag, Cmax, t1/2,z and plasma protein binding. The urinary recoveries of unchanged frusemide (39.2 +/- 10.2 vs 34.4 +/- 8.6%, P = 0.28) and its acyl glucuronide (12.1 +/- 2.7 vs 11.8 +/- 3.7%, P > 0.8) were not altered by probenecid. However, probenecid decreased the renal clearance of both frusemide (128 +/- 49 vs 44.0 +/- 18.6 ml min-1, P = 0.0002) and the acyl glucuronide (552 +/- 298 vs 158 +/- 94.0 ml min-1, P < 0.0001). The non-renal clearance of frusemide (36.7 +/- 21.0 vs 15.2 +/- 13.4 ml min-1, P = 0.0068) was also decreased. The clinical relevance of the study relates to the possible conjugation of frusemide in the kidney and the role of the conjugate in the pharmacodynamic effect.

Determination of furosemide with its acyl glucuronide in human plasma and urine by means of direct gradient high-performance liquid chromatographic analysis with fluorescence detection. Preliminary pharmacokinetics and effect of probenecid.

Furosemide is metabolized in humans by acyl glucuronidation to the 1-O-glucuronide (Fgluc). Furosemide (F) and the conjugate can be measured directly by gradient high-performance liquid chromatographic analysis without enzymic deglucuronidation. The glucuronide conjugate was isolated by preparative HPLC from human urine samples. Furosemide and its acyl glucuronide were present in plasma. No isoglucuronides were present in acidic urine of a volunteer. Calibration curves were constructed by enzymic deconjugation of samples containing different concentrations of isolated F-acyl glucuronide. The limit of quantitation of F in plasma is 0.007 microgram/ml, Fgluc 0.010 microgram/ml. The limits of quantitation in urine are respectively: F 0.10 microgram/ml, Fgluc 0.15 microgram/ml. A pharmacokinetic profile of furosemide is shown, and some preliminary pharmacokinetic parameters of furosemide obtained from one human volunteer are given. Probenecid does not inhibit the formation of the acyl glucuronide of F, but inhibits the renal clearance of both compounds.

Probenecid inhibits the glucuronidation of indomethacin and O-desmethylindomethacin in humans. A pilot experiment.

Indomethacin is metabolized in humans by O-demethylation, and by acyl glucuronidation to the 1-O-glucuronide. Indomethacin, its metabolite, and their conjugates can be measured directly by gradient high-pressure liquid chromatographic analysis without enzymic deglucuronidation. The pharmacokinetic profile of indomethacin and some preliminary pharmacokinetic parameters of indomethacin obtained from one human volunteer are given. In plasma only the parent drug indomethacin is present, while in urine the acyl and ether glucuronides are present in high concentrations. This confirms other reports that indomethacin and O-desmethylindomethacin may be glucuronidated in the kidney. Probenecid is a known substrate for renal glucuronidation. If indomethacin is glucuronidated in the human kidney like probenecid, then this glucuronidation might be reduced or inhibited under probenecid co-medication. This pilot experiment shows that probenecid reduced the acyl glucuronidation of indomethacin by 50% and completely inhibited the formation of O-desmethylindomethacin acyl and ether glucuronide.

Pharmacokinetics and bioavailability of oral ergometrine in male volunteers.

The aim of this investigation was to assess the pharmacokinetics and bioavailability of ergometrine in six human male subjects after an oral dose of 0.200 mg and after an intravenous dose of 0.075 mg of ergometrine maleate. A large variation in bioavailability of between 34% and 117% in the six volunteers was observed. The lag time was also subject dependent and ranged between 0.0073 h (0.4 min) and 0.47 h (28 min). After intravenous administration, the pharmacokinetic profile can be described by a two-compartment model. The distribution half-life t1/2 alpha is 0.18 +/- 0.20 h, the elimination half-life t1/2 beta is 2.06 +/- 0.90 h, the total body clearance (CL) amounts to 35.9 +/- 13.4 l h-1 and the steady-state volume (Vss) of distribution is 73.4 +/- 22.01. After oral administration, the pharmacokinetic profile can be described by a one-compartment model. The absorption half-life t1/2 abs is 0.19 +/- 0.22 h, and the elimination half-life t1/2 beta 1.90 +/- 0.16 h. This study with oral ergometrine shows such a large interindividual variability in bioavailability that the oral route of administration does not seem not to be the most reliable means of accurate dosing in preventing post-partum haemorrhage.

The effects of cimetidine, ranitidine and famotidine on the single-dose pharmacokinetics of naproxen and its metabolites in humans.

We studied the effects of cimetidine, ranitidine and famotidine on the kinetics of naproxen. The mean t1/2 beta of naproxen in 6 subjects was 25.7 +/- 5.4 h (range 16 to 36). Naproxen acyl glucuronide accounts for 50.9 +/- 6.9% of the dose, its isomerized isoglucuronide for 6.8 +/- 2.6%, O-desmethylnaproxen acyl glucuronide for 14.3 +/- 4.1% and its isoglucuronide for 5.5 +/- 1.5% (n = 6). Naproxen (1.3 +/- 1.1%) and O-desmethylnaproxen (0.6 +/- 0.4%) are excreted in negligible amounts. Cimetidine, ranitidine and famotidine all reduced significantly the t1/2 beta of naproxen by 50% from 25 h to 13 h and the t1/2 alpha from 4.0 h to 1.1 h. No effect of the H2 antagonists was observed on the absorption of naproxen. They also reduced the Vss of naproxen by 50%. The amount of naproxen acyl glucuronide, naproxen isoglucuronide and O-desmethylnaproxen acyl glucuronide excreted in the urine, remained unchanged, 60%, 7%, and 14% respectively.

Pharmacokinetics of naproxen, its metabolite O-desmethylnaproxen, and their acyl glucuronides in humans.

The aim of this investigation was to assess the pharmacokinetics of naproxen in 10 human subjects after an oral dose of 500 mg using a direct HPLC analysis of the acyl glucuronide conjugates of naproxen and its metabolite O-desmethylnaproxen. The mean t1/2 of naproxen in 9 subjects was 24.7 +/- 6.4 h (range 16 to 36 h). The t1/2 of 7.4 as found in subject number 10 must, therefore, be regarded as an extraordinary case (p < 0.0153). Naproxen acyl glucuronide accounts for 50.8 +/- 7.32 per cent of the dose, its isomerized conjugate isoglucuronide for 6.5 +/- 2.0 per cent, O-desmethylnaproxen acyl glucuronide for 14.3 +/- 3.4 per cent, and its isoglucuronide for 5.5 +/- 1.3 per cent (n = 10; 100 h collection period). Naproxen and O-desmethylnaproxen are excreted in negligible amounts (< 1 per cent). Even though urine pH of the subjects was kept acid (range pH 5.0-5.5) in order to stabilize the acyl glucuronides, isomerization takes place in blood when the acyl glucuronide is released from the liver for excretion by the kidney. Binding to plasma proteins was measured as 98 per cent and 100 per cent, respectively for the unconjugated compounds naproxen and O-desmethylnaproxen. Binding of the acyl glucuronides was less, being 92 per cent; for naproxen acyl glucuronide, 66 per cent for naproxen isoglucuronide, 72 per cent for O-desmethylnaproxen acyl glucuronide and 42 per cent for O-desmethylnaproxen isoglucuronide.

Probenecid inhibits the renal clearance and renal glucuronidation of nalidixic acid. A pilot experiment.

The aim of this pilot study was to demonstrate the possible inhibitory effect of probenecid on the renal glucuronidation and on the renal clearance of nalidixic acid in a human volunteer. Under acidic urine conditions, hardly any nalidixic acid is excreted unchanged (0.2%). It is excreted as acyl glucuronide (53.4%), 7-hydroxymethylnalidixic acid (10.0%), the latter's acyl glucuronide 30.9%, and 7-carboxynalidixic acid (4.2%). Under probenecid co-medication the renal glucuronidation of nalidixic acid is reduced from 53% to 16%; the renal clearance of both nalidixic acid and 7-hydroxymethylnalidixic acid are reduced (p < 0.001); the intrinsic t1/2 of the metabolite 7-hydroxymethylnalidixic acid increased from 0.48 h to 4.24 h. The amount of acyl glucuronidation of 7-hydroxymethylnalidixic acid was not altered. The in vitro protein binding of both acyl glucuronides was increased, while no effect on the unconjugated compounds was seen. Nalidixic acid had no effect on the maximal renal excretion rate of probenecid acyl glucuronide.

Determination of indomethacin, its metabolites and their glucuronides in human plasma and urine by means of direct gradient high-performance liquid chromatographic analysis. Preliminary pharmacokinetics and effect of probenecid.

Indomethacin is metabolized in humans by O-demethylation, and by acyl glucuronidation to the 1-O-glucuronide. Indomethacin, its metabolite O-desmethylindomethacin (DMI) and their conjugates can be measured directly by gradient high-performance liquid chromatographic analysis without enzymic deglucuronidation. The glucuronide conjugates were isolated by preparative HPLC from human urine samples. In plasma only indomethacin was present. No isoglucuronides were present in acidic urine of the volunteer. The possible metabolite deschlorobenzoylindomethacin (DBI) was not detectable in urine. Calibration curves were constructed by enzymic deconjugation of samples containing different concentrations of isolated indomethacin acyl glucuronide, DMI acyl glucuronide and DMI ether glucuronide. The limit of quantitation of indomethacin in plasma is 0.060 microgram/ml. The limits of quantitation in urine are: indomethacin 0.053 microgram/ml, DMI 0.065 microgram/ml, DMI acyl glucuronide 0.065 microgram/ml and DMI ether glucuronide 0.254 microgram/ml. A pharmacokinetic profile of indomethacin is shown, and some preliminary pharmacokinetic parameters of indomethacin obtained from one human volunteer are given. Probenecid inhibits the formation of both the ether and the acyl glucuronide of DMI.

Direct gradient reversed-phase HPLC analysis and preliminary pharmacokinetics of nalidixic acid, 7-hydroxymethylnalidixic acid, 7-carboxynalidixic acid, and their corresponding glucuronide conjugates in humans.

A gradient reversed-phase high pressure liquid chromatographic analysis was developed for the direct measurement of nalidixic acid with its acyl glucuronide, 7-hydroxymethylnalidixic acid with its acyl and ether glucuronides, and 7-carboxynalidixic acid in human plasma and urine. The glucuronides and 7-carboxynalidixic acid were not present in plasma after an oral dose of 1,000 mg nalidixic acid. The acyl glucuronides of 7-carboxynalidixic acid were not present in plasma and urine. The acyl glucuronides are stable in urine at pH 5.0-5.5. The subject's urine must therefore be acidified by the oral intake of 4 x 1 g of ammonium chloride per day. With acidic urine, hardly any nalidixic acid was excreted unchanged (0.2%). It was excreted as acyl glucuronide (53.4% of dose), 7-hydroxymethyl-nalidixic acid (10.0%), the latter's acyl glucuronide (30.9%), and 7-carboxynalidixic acid (4.2%).

The pharmacokinetics of naproxen, its metabolite O-desmethylnaproxen, and their acyl glucuronides in humans. Effect of cimetidine.

1. The pharmacokinetics of 500 mg naproxen given orally were described in 10 subjects using a direct h.p.l.c. analysis of the acyl glucuronide conjugates of naproxen and its metabolite O-desmethylnaproxen. 2. The mean elimination half-life of naproxen was 24.7 +/- 6.4 h (range 7 to 36 h). 3. Naproxen acyl glucuronide accounted for 50.8 +/- 7.3% of the dose recovered in the urine, its isomerised conjugate isoglucuronide for 6.5 +/- 2.0%, O-desmethylnaproxen acyl glucuronide for 14.3 +/- 3.4%, and its isoglucuronide for 5.5 +/- 1.3%. Naproxen and O-desmethylnaproxen were excreted in negligible amounts (< 1%). 4. Even though the urine pH of the subjects was kept acid in order to stabilize the acyl glucuronides, isomerisation took place in blood. 5. The extents of plasma binding of the unconjugated compounds were 98% (naproxen) and 100% (O-desmethylnaproxen), while naproxen acyl glucuronide binding was 92%; that of its isomer isoglucuronide 66%. O-desmethylnaproxen acyl glucuronide was 72% bound and its isoglucuronide was 42% bound. 6. Cimetidine (400 mg twice daily) decreased the t1/2 of naproxen by 39-60% (mean 47.3 +/- 11.5%; P = 0.0014) from 24.7 +/- 6.4 h to 13.2 +/- 1.0 h. It increased (10%) the urinary recovery of naproxen acyl glucuronide (P = 0.0492). The urinary recoveries of naproxen isoglucuronide and O-desmethylnaproxen acyl glucuronide remained unchanged.

High-performance liquid chromatography of ergometrine and preliminary pharmacokinetics in plasma of men.

An isocratic high-performance liquid chromatographic (HPLC) method with fluorescence detection has been developed for the measurement of ergometrine in human plasma. The quantitation limit in plasma was 75 pg/ml. An example of the plasma concentration-time curves obtained after both oral and intravenous administration of ergometrine in one volunteer is shown. This HPLC method makes it possible to describe the pharmacokinetic parameters of oral ergometrine.

Determination of naproxen and its metabolite O-desmethylnaproxen with their acyl glucuronides in human plasma and urine by means of direct gradient high-performance liquid chromatography.

Naproxen is metabolized in humans by O-demethylation, and by acyl glucuronidation to the 1-O-glucuronide. Naproxen, its metabolite and the conjugates can be measured directly by gradient high-performance liquid chromatographic analysis without enzymic deglucuronidation. The glucuronide conjugates were isolated by preparative chromatography from human urine samples. Mild acidic hydrolysis of one urinary conjugate resulted in naproxen. This conjugate was also formed by alkaline isomerization of isolated naproxen acyl glucuronide, indicating that the structure of this urinary conjugate must have been naproxen isoglucuronide (4-O-glucuronide). Mild acidic hydrolysis of another urinary conjugate resulted in O-desmethylnaproxen. This conjugate was also formed by alkaline isomerisation of isolated O-desmethylnaproxen acyl glucuronide, indicating that the structure of this urinary conjugate must have been O-desmethylnaproxen isoglucuronide (4-O-glucuronide). Calibriation curves were constructed by enzymic deconjugation of samples containing different concentrations of isolated naproxen acyl glucuronide, O-desmethylnaproxen acyl glucuronide, and the isoglucuronides of naproxen and O-desmethylnaproxen by mild acidic hydrolysis. The limit of quantitation of naproxen in plasma is 1.5 microgram/ml. The limits of quantitation in urine are: naproxen, O-desmethylnaproxen, naproxen acyl glucuronide and O-desmethylnaproxen acyl glucuronide, 1 microgram/ml; the isoglucuronide of naproxen and O-desmethylnaproxen, 1.5 microgram/ml. A pharmacokinetic profile of naproxen is shown, and some preliminary pharmacokinetic parameters of naproxen obtained from two human volunteers are given.

High performance liquid chromatography and preliminary pharmacokinetics of rufloxacin and its metabolites N-desmethylrufloxacin and rufloxacinsulfoxide in plasma and urine of humans.

An HPLC analysis was developed for the measurement of rufloxacin and two of its possible metabolites N-desmethylrufloxacin and rufloxacinsulfoxide. Humans are unable to form these two metabolites, while no other metabolites could be detected in the HPLC chromatogram. The half-life of elimination of rufloxacin in two human subjects was 27 and 38 h respectively, while a constant percentage of 25-26% of the dose is excreted unchanged in the urine.

High-performance liquid chromatography and preliminary pharmacokinetics of rufloxacin and its metabolites, N-desmethylrufloxacin and rufloxacinsulfoxide, in urine of rhesus monkey Macaca mulatta.

A gradient high-performance liquid chromatographic method for the quantification of rufloxacin and two of its metabolites in urine, N-desmethylrufloxacin and rufloxacinsulfoxide, has been developed and validated. Monkey urine samples were diluted ten times with distilled water and 20 microliters were injected onto a Cp Spher 5-ODS column, 5 microns particle size. The mobile phase was a mixture of 4% acetonitrile and 96% buffer at time 0, which changed linearly over 37 min to 26% acetonitrile and 74% buffer. Detection was achieved at 246 nm. The limit of detection of the three compounds was 0.50 microgram/ml. An example of a pharmacokinetic study of rufloxacin and its metabolites in monkeys is shown.

The effect of multiple-dose oral lomefloxacin on theophylline metabolism in man.

Single-dose plasma pharmacokinetics of theophylline (6 mg/kg intravenously) and renal excretion of theophylline and its metabolites, resulting from 8-oxidation and N-demethylation, were investigated in eight healthy volunteers before and at day 3 of concomitant oral administration of the quinolone derivative lomefloxacin (400 mg twice daily). Plasma samples were collected until 24.5 h, and urine samples were collected until 72 h after theophylline administration. The concentrations of theophylline and the major metabolites, resulting from N-demethylation and 8-oxidation, were measured utilizing a high-pressure liquid chromatography (HPLC) technique. No significant changes in theophylline half-life, volume of distribution, protein binding, total body clearance, or renal clearance were noted. In addition, renal excretion of unchanged theophylline, the products of the N-demethylation, 3-methylxanthine, and 1-methyluric acid, and the product of the 8-oxidation, 1,3-dimethyluric acid, were not altered by simultaneous administration of lomefloxacin. Orally administered lomefloxacin is absorbed quickly and to a high extent. During administration of 400 mg twice daily, plasma concentrations reached are well above minimum inhibitory concentration (MIC) values of pathogens that are frequently isolated in lower respiratory tract infections. This study shows that lomefloxacin in a twice daily dose of 400 mg does not effect theophylline metabolism. Lomefloxacin and theophylline can be coadministered without concern about effects of lomefloxacin on theophylline pharmacokinetics.

Pharmacokinetics, N1-glucuronidation and N4-acetylation of sulfadimethoxine in man.

Sulfadimethoxine is metabolized by O-dealkylation, N4-acetylation and N1-glucuronidation. In man, only N1-glucuronidation and N4-acetylation takes place, leading to the final double conjugate N4-acetylsulfadimethoxine-N1-glucuronide. The N1-glucuronides are directly measured by high pressure liquid chromatography. When N4-acetylsulfadimethoxine is administered as parent drug, 30% of the dose is N1-glucuronidated and excreted. Fast acetylators show a shorter half-life for sulfadimethoxine than slow acetylators (27.8 +/- 4.2 h versus 36.3 +/- 5.4 h; P = 0.013), similarly the half-life of the N4-acetyl conjugate is also shorter in fast acetylators (41.3 +/- 5.2 h versus 53.5 +/- 8.5 h, P = 0.036). No measurable plasma concentrations of the N1-glucuronides from sulfadimethoxine are found in plasma. N1-glucuronidation results in a 75% decrease in protein binding of sulfadimethoxine. N4-acetylsulfadimethoxine and its N1-glucuronide showed the same high protein binding of 99%. Approximately 50-60% of the oral dose of sulfadimethoxine is excreted in the urine, leaving 40-50% for excretion into bile and faeces.