Determination of dolasetron and its reduced metabolite in human plasma by GC-MS and LC

Both a GC-MS and an LC method have been developed for the simultaneous quantitation of dolasetron and reduced dolasetron in human plasma. The GC-MS method has been utilized in preliminary human pharmacokinetic studies of dolasetron mesylate. Selected ion monitoring was used in these initial studies to obtain the sensitivity and specificity required for quantitation. The GC-MS method has been used in the range of 1-120 ng ml-1 for dolasetron and 1-240 ng ml-1 for reduced dolasetron in plasma. The limit of quantitation for both compounds by GC-MS was 1 ng ml-1. Recently, an LC method has been utilized for quantitation of both compounds on a routine basis. This method utilizes essentially the same sample preparation procedure as the GC-MS method. The LC method has been used in the range of 5-200 ng ml-1 in plasma for dolasetron and reduced dolasetron. In addition, the relationship between the LC and GC-MS methods has been assessed using data obtained from human male volunteers following intravenous administration of 3.0 mg kg-1 of dolasetron mesylate monohydrate.

[Studies on structures of urinary metabolites of quinotolast, a new oral anti-allergics]

Metabolites of quinotolast in the human, rat and dog urine were isolated chromatographically and their structures were determined spectroscopically. para-Hydroxy substitution to the phenoxyl function of quinotolast, and glucoside or glucuronide conjugate to its tetrazole ring were observed.

Human dolasetron pharmacokinetics: II. Absorption and disposition following single-dose oral administration to normal male subjects

Dolasetron is a 5-hydroxytryptamine antagonist active at type III receptors; it is presently undergoing clinical evaluation for the reduction/prevention of cancer chemotherapy-induced nausea and vomiting. A previous study demonstrated that following intravenous administration to healthy male subjects, dolasetron disappeared extremely rapidly from plasma, and less than 1 per cent of the dose appeared in the urine. A major plasma metabolite, reduced dolasetron, peaked rapidly in the plasma. In this study, dolasetron was administered orally to healthy male subjects at doses ranging from 50 to 400 mg (mesylate monohydrate). Plasma concentrations of dolasetron were low and sporadic, and there was little excreted in urine; this prevented dolasetron pharmacokinetic analysis. Reduced metabolite concentrations peaked rapidly, with a median value of 1.00 h. The median terminal disposition half-life was 7.80 h. Median values for fraction of dose excreted in urine and renal clearance were 22.2 per cent and 2.56 ml min-1 kg-1. Whereas areas under the plasma concentration-time curves were proportional to dose, renal clearance increased with dose (p < 0.05). However, given dose proportionality to AUC, this is probably of little therapeutic consequence. Since reduced dolasetron has significant anti-emetic activity in the ferret model, it appears that this metabolite may play a significant role in pharmacodynamic activity.

Human dolasetron pharmacokinetics: I. Disposition following single-dose intravenous administration to normal male subjects

Dolasetron is a 5-hydroxytryptamine antagonist active at type III receptors; it is presently undergoing clinical evaluation for the reduction/prevention of cancer chemotherapy-induced nausea and vomiting. Following intravenous administration to healthy male subjects of doses ranging from 0.6 to 5 mg kg-1, dolasetron disappeared extremely rapidly from plasma; concentrations were generally measurable for only 2-4 h. Less than 1 per cent of the dose was excreted intact in urine. A major plasma metabolite, reduced dolasetron, peaked rapidly at approximately 0.625 h (median). Its median terminal disposition half-life was 7.56 h; median values for fraction of dose excreted in urine and renal clearance were 31.0 per cent and 2.68 ml min-1 kg-1, respectively. Over the dose-range covered, pharmacokinetics of both dolasetron and reduced metabolite appeared to be independent of dose. The median ratio of the areas under the plasma concentration-time curves for metabolite relative to dolasetron was 11.9. As a result of its activity and significant plasma concentrations, reduced dolasetron may play a significant role in pharmacodynamic activity.

[3H]-MK 912 binding delineates two alpha 2-adrenoceptor subtypes in rat CNS one of which is identical with the cloned pA2d alpha 2-adrenoceptor

1. Simultaneous computer modelling of control and guanfacine-masked [3H]-MK 912 saturation curves as well as guanfacine competition curves revealed that the drugs bound to two alpha 2-adrenoceptor subtypes in the rat cerebral cortex with very different selectivities. These alpha 2-adrenoceptor subtypes were designated alpha 2A and alpha 2C. The Kd value of [3H]-MK 912 for the alpha 2A-subtype was 1.77 nM and for the alpha 2C-subtype 0.075 nM; the receptor sites showing capacities 296 and 33 fmol mg-1 protein, respectively. The Kds of guanfacine were 19.9 and 344 nM, respectively. 2. Binding constants of 26 compounds for the two rat cerebral cortex alpha 2-adrenoceptor subtypes were determined by simultaneous computer modelling of control and guanfacine-masked drug competition curves as well as plain guanfacine competition curves using [3H]-MK912 as labelled ligand (i.e. a '3-curve assay'). Of the tested drugs WB4101, corynanthine, rauwolscine, yohimbine, ARC 239 and prazosin were found to be clearly alpha 2C-selective with selectivities ranging from 16 to 30 fold whereas guanfacine, oxymetazoline, BRL 44408 and BRL 41992 were found to be alpha 2A-selective with selectivities ranging from 9 to 22 fold. 3. The Kds of compounds obtained for the cerebral cortex alpha 2C-adrenoceptors showed an almost 1:1 correlation with the corresponding Kds for alpha 2-adrenoceptors expressed by the pA2d-gene (the rat 'alpha 2-C4' adrenoceptor) in CHO-cells. The cerebral cortex alpha 2A-adrenoceptors did not correlate well with the pA2d alpha 2-adrenoceptor Kds. 4. In the rat spinal cord [3H]-MK 912 bound to alpha 2A- and alpha 2C-adrenoceptor sites with similar affinities as in the cerebral cortex and with densities 172 and 7.4 fmol mg-1 protein, respectively. Drug affinities for some compounds showing major selectivity for alpha 2A- and alpha 2C-adrenoceptors were fully compatible with the notion that the spinal cord sites were alpha 2A- and alpha 2C-adrenoceptors.

Direct-gradient high-performance liquid chromatographic analysis and preliminary pharmacokinetics of flumequine and flumequine acyl glucuronide in humans: effect of probenecid

A gradient high-performance liquid chromatographic analysis for the direct measurement of flumequine, with its acyl glucuronide, in plasma and urine of humans has been developed. In order to prevent hydrolysis and isomerization of flumequine acyl glucuronide, the samples were acidified by the oral intake of four 1.2-g amounts of ammonium chloride per day. In contrast to the acyl glucuronides of non-steroidal anti-inflammatory drugs, flumequine and its acyl glucuronide were stable in urine of pH 5.0-8.0. Flumequine acyl glucuronide is unstable at pH 1.5. In acidic urine (pH 5-6), almost no flumequine is excreted unchanged (1%): it is excreted chiefly as acyl glucuronide (84.2%). Probenecid co-medication reduces the renal excretion rate of flumequine acyl glucuronide from 662 to 447 micrograms/min (p = 0.00080), but not the percentage of glucuronidation.

Synthesis and biodistribution of the alpha 2-adrenergic receptor antagonist (11C)WY26703. Use as a radioligand for positron emission tomography

The purpose of these experiments was to label an alpha 2-adrenergic receptor ligand with a positron emitting isotope and then test this radioligand in vivo. No-carrier-added [11C]WY26703 was synthesized by methylation of its desmethyl precursor, WY27050 with [11C]H3I followed by purification with HPLC in 14% yield in a synthesis time of 35 min from EOB. Ki values for unlabeled WY26703, ranged from 0.52-1.55 nM in tissues that express a single alpha 2-adrenergic receptor subtype. Tail vein injections of [11C]WY26703 in mice revealed that the compound was distributed in the brain, heart, lungs, spleen, and kidneys. In the brains of rats treated with atipamezole, an alpha 2-adrenergic receptor antagonist, there was no decrease in [11C] accumulation indicating a lack of observable specific binding of the radioligand. When brain tissue was homogenized and filtered, however, atipamezole decreased [11C] activity by 53%. Therefore, [11C]WY26703 crosses the blood-brain barrier and specifically binds to alpha 2-adrenergic receptors with high affinity. Atipamezole treatment decreased only the area of the locus coeruleus [11C] value of the various regions of the brain. The affinity, however, of [11C]WY26703 does not appear to distinguish alpha 2-receptors from nonspecific binding sites. PET study of [11C]WY26703 in a Rhesus monkey showed that influx of [11C]WY26703 into the brain was high for the first few minutes but radioactivity then declined rapidly and did not retain in a specific brain region. This suggests that [11C]WY26703 may not be a useful ligand for imaging human alpha 2-adrenergic receptors by positron emission tomography.

Kinetic study of the transformation from tetrahydrate to monohydrate of a new antiallergic, sodium 5-(4-oxo-phenoxy-4H-quinolizine-3-carboxamide)-tetrazolate

Two hydrates (tetrahydrate, I, and monohydrate, II) of a new antiallergic, sodium 5-(4-oxo-phenoxy-4H-quinolizine-3-carboxamide)-tetrazolate (FR71021), were prepared and characterized by means of infrared spectrometry, thermal analysis, and power X-ray diffraction spectrometry. While I was confirmed to dehydrate readily resulting in an anhydrate form (noncrystalline form) below its critical relative humidity for dehydration, I was also transformed into II under humid conditions. The transformation kinetics from I to II were investigated under varying temperature and humidity conditions by a powder X-ray diffraction technique. The transformation mechanism followed a zero-order reaction, and the apparent transformation rate constant (k) could be described as a function of water vapor pressure (P), temperature (T), and the interaction orders between water vapor pressure and the samples (s): k = A.exp(-Ea/RT).Ps, where Ea is the activation energy and R is the gas constant.

Reservoir of quinolone residues in fish

Different tissues from salmon treated with the quinolones oxolinic acid, flumequine, enrofloxacin and sarafloxacin were analysed in search of possible reservoirs of the drugs. Residues of oxolinic acid and flumequine seem to be especially bound to bone, enrofloxacin to skin, and sarafloxacin to both skin and bone. The results showed that residues of these drugs were present in the fish for prolonged periods after the end of treatment.

Effect of plasma exchange on flumequine pharmacokinetics: comparison with control kinetics

The effect of plasma exchange (PE) on the pharmacokinetics of flumequine (Apurone) was studied in eight patients receiving a single oral dose of 800 mg. The maximum concentration (38 micrograms/ml) and time to maximum concentration (2.6 h) values were not significantly altered by PE beginning 3 h after administration of flumequine. There was no change in the terminal elimination half-lives (6.6 h), in the steady-state volume of distribution (29 L), or in the apparent plasma clearance (2.5 L/h). By contrast, PE decreased the mean residence time by 30% (14.3 +/- 4.1 h without PE; 9.88 +/- 1.36 h with PE; p less than 0.05). The amount of flumequine extracted by PE (72 mg) was proportional to the plasma concentration at the beginning of the exchange. The elimination half-life during PE (3.15 +/- 1.23 h) decreased by 40%. Renal clearance (0.3 L/h) was not affected. PE only partially modifies the pharmacokinetics of flumequine administered in a single oral dose before PE.

Effects of experimentally induced Pasteurella haemolytica infection in dairy calves on the pharmacokinetics of flumequine

The effect of experimental Pasteurella haemolytica infection on the intravenous and intramuscular pharmacokinetics of flumequine was studied in dairy calves. The plasma concentration-time curve of flumequine after intravenous injection of 5 mg/kg bodyweight flumequine of a 10% solution before and after experimental infection, was best described by a three-compartment open model. After intramuscular injection of the same dosage rate of a 3% flumequine suspension is was best described by the one-compartment open model with first-order absorption. The experimental infection by intratracheal administration of infectious bovine rhinotracheitis (IBR)-virus and 5 days later intrapulmonary administration of Pasteurella haemolytica produced a clear temperature rise and signs of disease expressed as Average Health Status. Subsequently, plasma Fe and Zn concentration decreased after infection. The distribution volumes Vc, Vd(area) and Vd(ss) after infection (0.07 +/- 0.04, 1.38 +/- 0.36 and 0.50 +/- 0.11 l/kg, respectively) were smaller than those before infection, but the differences were not significant (P less than or equal to 0.1). The intravenous AUC infinity was significantly increased (21.86 +/- 3.51 to 33.85 +/- 2.97 mg.h/l, P less than or equal to 0.01) and the total body clearance (ClB) significantly decreased (0.24 +/- 0.02 to 0.15 +/- 0.01, P less than or equal to 0.01) after infection. After intramuscular injection of flumequine at 5 mg/kg as a 3% suspension, only the bioavailability, F, was significantly decreased after infection (78.5 +/- 14.3 to 59.7 +/- 21.2%, P less than or equal to 0.02). However, this had no consequences for the dosage regimen used. The urine concentration ratio flumequine:7-hydroxy-flumequine:conjugated flumequine changed from 2:1:10 before infection to 6:1:15 after infection, which indicates that hydroxylation and glucuronidation as metabolic pathways for flumequine were decreased after Pasteurella sp. infection.

Pharmacokinetics, metabolism and renal clearance of flumequine in veal calves

The pharmacokinetics of flumequine was studied in 1-, 5- and 18-week-old veal calves. A two-compartment model was used to fit the plasma concentration-time curve of flumequine after the intravenous injection of 10 mg/kg of a 10% solution. The elimination half-life (t1/2 beta) of the drug ranged from 6 to 7 h. The Vd beta and ClB of 1-week-old calves (1.07 l/kg, 1.78 ml/min/kg) were significantly lower than those of 5-week-old (1.89 l/kg, 3.23 ml/min/kg) and 18-week-old calves (1.57 l/kg, 3.10 ml/min/kg). After the oral administration of 10 mg/kg of a 2% flumequine formulation mixed with milk replacer, the Cmax was highest in 1-week-old (9.27 micrograms/ml) and lowest in 18-week-old calves (4.47 micrograms/ml). The absorption was rapid (Tmax of approximately 3 h) and complete. When flumequine itself and a formulation containing 2% flumequine and 20 X 10(6) iu of colistin sulphate were mixed with milk replacer and administered at the same dose rate, absorption was incomplete and Cmax was lower. The main urinary metabolite of flumequine was the glucuronide conjugate (approximately 40% recovery within 48 h of intravenous injection) and the second most important metabolite was 7-hydroxy-flumequine (approximately 3% recovery within 12 h of intravenous injection). Only 3.2-6.5% was excreted in the urine unchanged. After oral administration a 'first-pass' effect was observed, with a significant increase in the excretion of conjugated drug. For 1-week-old calves it is recommended that the 2% formulation should be administered at a dose rate of 8 mg/kg every 24 h or 4 mg/kg every 12 h; for calves over 6 weeks old, the dose should be increased to 15 mg/kg every 24 h or 7.5 mg/kg every 12 h. The formulation containing colistin sulphate should be administered to 1-week-old calves at a flumequine dose of 12 mg/kg every 24 h or 6 mg/kg every 12 h.

Oral absorption and bioavailability of flumequine in veal calves

The oral absorption and bioavailability of flumequine was studied in 1-, 5- and 18-week-old calves following intravenous and oral administration of different formulations of flumequine (Flumix, Flumix C and pure flumequine). Increasing age had a negative influence on the Cmax after the administration of Flumix, based on a larger VD in the older calves. The Cmax decreased from 5.02 +/- 1.46 micrograms/ml in the first week to 3.28 +/- 0.42 micrograms/ml in the 18th week. Adding colistin sulfate to the flumequine formulation and administring pure flumequine mixed with milk replacer had a negative effect on the Cmax of flumequine after oral administration of 5 and 10 mg/kg body weight. The bioavailability of the orally administered flumequine formulations was 100% in all cases except after the administration of Flumix C, for which it was 75.9 +/- 18.2%. The urinary recovery of flumequine after intravenous injection of a 10% solution varied from 35.2 +/- 2.3% for Group B, to 41.2 +/- 6.3% for Group C. The dosage of 5 mg/kg body weight Flumix twice daily in 1-week-old veal calves is sufficient to reach therapeutic plasma concentrations, based on a MIC value of 0.8 micrograms/ml of the target bacteria. In older calves it is advisable to increase the dosage 7.5 or 10 mg/kg body weight every 12 hours. In combination with colistin sulfate it is also advisable to increase the dosage slightly because of the negative effect of the colistin sulfate on the Cmax of flumequine.