In vitro and in vivo studies on the complexes of vinpocetine with hydroxypropyl-beta-cyclodextrin

The purpose of this study was to evaluate complexes of vinpocetine (VIN), a poorly water-soluble base type drug, with hydroxypropyl-beta-cyclodextrin (HP-beta-CD) in aqueous environment and in solid state, with or without citric acid (CA) as an acidifier of the complexation medium. The apparent stability constant (Kc) calculated by phase solubility was 282 M(-1) and the complexation in solution was structurally characterized by 1H-NMR which showed VIN was likely to fit into the cyclodextrin cavity with its phenyl ring and ethyl ester bond. Solid complexes of VIN and HP-beta-CD were prepared by kneading (KE), co-evaporating (CE) and freeze-drying (FD) methods. Physical mixtures were prepared for comparison. The study in the solid state included the differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and infrared absorption spectroscopy (IR). From these analyses, CE and FD products were found in amorphous state, allowing to the conclusion of strong evidences of inclusion complex formation. However, the dissolution test showed that only VIN/HP-beta-CD+CA complexes by CE and FD method could provide satisfying dissolution behavior (rapid, complete and lasting) when compared to that of VIN/HP-beta-CD complexes. Interestingly, the addition of CA in inclusion complexes could significantly decrease the amount of HP-beta-CD needed to solubilize the same amount of VIN and thereby reducing the formulation bulk. Furthermore, in-vivo study revealed that the bioavailability of VIN after oral administration to rabbits (n=6) was significantly improved by VIN/HP-beta-CD+CA inclusion complex.

Cyclodextrin Multicomponent Complexation and Controlled Release Delivery Strategies to Optimize the Oral Bioavailability of Vinpocetine

In the present work, to maintain a suitable blood level of vinpocetine (VP) for a long period of time, VP-cyclodextrin-tartaric acid multicomponent complexes were prepared and formulated in hydroxypropylmethylcellulose matrix tablets. In vitro and in vivo performances of these formulations were investigated over a VP immediate release dosage form. Solubility studies were performed to evaluate the drug pH solubilization profile and to assess the effect of multicomponent complexation on VP solubility. The drug release process was investigated using United States Pharmacopeia apparatus 3 and a comparative oral pharmacokinetic study was subsequently undertaken in rabbits. Solubility studies denoted the pH-solubility dependence of VP and solubility improvement attained by complexation. Dissolution results showed controlled and almost complete release behavior of VP over a 12-h period from complex hydroxypropylmethylcellulose-based formulations. A clear difference between the pharmacokinetic patterns of VP immediate release and VP complex-based formulations was revealed. The area under the plasma concentration-time curve after oral administration of complex-based formulations was 2.1-2.9 times higher than that for VP immediate release formulation. Furthermore, significant differences found for mean residence time, elimination half-life, and elimination rate constant values corroborated prolonged release of VP from complex-based formulations. These results suggest that the oral bioavailability of VP was significantly improved by both multicomponent complexation and controlled release delivery strategies.

New HPLC–MS method for quantitative determination of apovincaminic acid in human plasma

A fast and sensitive HPLC-MS method for the quantification of apovincaminic acid, a vinpocetine metabolite, in human plasma has been developed and validated. After protein precipitation with methanol, 10 mL of supernatant was injected at 45 degrees C onto a Zorbax SB-C18 column. Elution was performed in less than three minutes with water containing 0.2% formic acid and acetonitrile (80:20) at 0.75 mL/min. A linearity domain between 4 and 240 ng/mL and a limit of quantification of 4 ng/mL apovincaminic acid were established by monitoring the signal corresponding to m/z = 323. Accuracy and precision were less than 5.2% for within-run assay and 10% for between-run assay. The method was successfully applied in a bioequivalence study of two pharmaceutical products containing 5 mg vinpocetine.

Determination of apovincaminic acid in human plasma by high-performance liquid chromatography using solid-phase extraction and ultraviolet detection

A new, simple and rapid high-performance liquid chromatography (HPLC) method with UV detection has been developed for the determination of apovincaminic acid in human plasma. Apovincaminic acid and internal standard were isolated from plasma samples by solid-phase extraction with OASIS HLB cartridges. The chromatographic separation was accomplished on a reversed-phase C(18) column and UV detection was set at 311 nm. The calibration curves were linear in the concentration range of 2.4-240.0 ng/ml, and the limits of quantification was 2.4 ng/ml. The precision and accuracy ranged from 0.84 to 8.54% and 91.5 to 108.3%, respectively. The developed method was subsequently applied to study the pharmacokinetics of apovincaminic acid in a group of 20 human subjects at a single oral dose of 10mg of vinpocetine tablet.

Pharmacokinetics and comparative bioavailability of two vinpocetine tablet formulations in healthy volunteers by using the metabolite apovincaminic acid as pharmacokinetic parameter

The objective of this study was to evaluate the pharmacokinetics of apovincaminic acid, the main metabolite of vinpocetine ((3alpha, 16alpha) -eburnamenine-14-carboxylic acid ethyl ester, CAS 42971-09-5), and to assess the average bioequivalence of two immediate release formulations of 10 mg vinpocetine tablets in 24 healthy male volunteers. The relative bioavailability of the test (generic) product (Vimpocetina) with respect to the reference product was determined in a single dose, randomized, crossover study. A simple, rapid specific and reliable high performance liquid chromatographic method coupled with mass spectrometry detection has been developed and validated for vinpocetine and apovincaminic acid. However, only the concentrations of the metabolite could be used for bioequivalence determinations because the concentrations of the parent drug were too low to be accurately measured in the biological matrix. The compartmental analysis of the metabolite's appearance-disappearance in blood shows similarity with first-order kinetics of a drug extravascularly administered. The apparent pharmacokinetic constants were determined. The mean values for the Cmax were 49.5 (+/- 16) ng/ml for test and 51.4 (+/- 14) ng/ml for the reference product. The mean values for the AUC0-infinity were 95 (+/- 29) ng/ml x h for test and 96.9 (+/- 26) ng/ml x h for reference, respectively. The 90 % confidence intervals for test/reference mean ratios of the plasma pharmacokinetic variables Cmax and AUC0-infinity lie between 0.83-1.08 and 0.88-1.08, respectively, which is within the conventional bioequivalence range of 80-125 % (Schuirman test). The difference between Tmax of the test and reference products was statistically non-significant (Friedman test). The test product is therefore bioequivalent to the reference product with respect to the rate and extent of apovincaminic acid pharmacokinetics.

Selective reduction of N-oxides to amines: application to drug metabolism

Phase I oxidative metabolism of nitrogen-containing drug molecules to their corresponding N-oxides is a common occurrence. There are instances where liquid chromatography/tandem mass spectometry techniques are inadequate to distinguish this pathway from other oxidation processes, including C-hydroxylations and other heteroatom oxidations, such as sulfur to sulfoxide. Therefore, the purpose of the present study was to develop and optimize an efficient and practical chemical method to selectively convert N-oxides to their corresponding amines suitable for drug metabolism applications. Our results indicated that efficient conversion of N-oxides to amines could be achieved with TiCl(3) and poly(methylhydrosiloxane). Among them, we found TiCl(3) to be a facile and easy-to-use reagent, specifically applicable to drug metabolism. There are a few reports describing the use of TiCl(3) to reduce N-O bonds in drug metabolism studies, but this methodology has not been widely used. Our results indicated that TiCl(3) is nearly as efficient when the reductions were carried out in the presence of biological matrices, including plasma and urine. Finally, we have shown a number of examples where TiCl(3) can be successfully used to selectively reduce N-oxides in the presence of sulfoxides and other labile groups.

[Human positron emission tomography with oral 11C-vinpocetine]

INTRODUCTION

Positron emission tomography (PET) is a useful tool for the investigation of certain physiological changes and for the evaluation of the distribution, and receptor binding of drugs labelled with positron emitting isotopes. Vinpocetine (ethyl-apovincaminate) is a neuroprotective drug widely used in the prevention and treatment of cerebrovascular diseases. In the clinical practice vinpocetine is usually administered to the patients in intravenous infusion followed by long-term oral treatment. Until presently human data describing vinpocetine's kinetics and brain distribution came from ex vivo (blood, plasma, liquor) and post mortem (brain autoradiography) measurements.

AIM

The authors wished to investigate the kinetics and distribution of vinpocetine in the brain and body after oral administration with PET in order to prove, that PET is useful in the non-invasive in vivo determination of these parameters.

METHOD

Vinpocetine was labelled with carbon-11 and the radioactivity was measured by PET in the stomach, liver, brain, colon and kidneys in healthy male volunteers. The radioactivity in the blood and urine was also determined.

RESULTS

After oral administration, [11C]vinpocetine appeared immediately in the stomach and within minutes in the liver and the blood. In the blood the level of radioactivity continuously increased until the end of the measurement period, whereas the fraction of the unchanged mother compound decreased. Radioactivity uptake and distribution in the brain were demonstrable from the tenth minute after the oral administration of the labelled drug (average maximum uptake: 0.7% of the administered total dose). Brain distribution was heterogeneous (with preferences in the thalamus, basal ganglia and occipital cortex), similar to the distribution previously reported by the authors after intravenous administration.

CONCLUSIONS

Vinpocetine, administered orally to human volunteers, readily entered the bloodstream from the stomach and the gastrointestinal tract and thereafter passed the blood-brain barrier and entered the brain. Radioactivity from [11C]vinpocetine was also demonstrated in the kidneys and in urine. The study demonstrates that PET might be a useful, direct and non-invasive tool to study the distribution and pharmacokinetics of orally administered labelled drugs active in the central nervous system in the living human body.

PET studies on the brain uptake and regional distribution of [11C]vinpocetine in human subjects

OBJECTIVES

Vinpocetine is a compound widely used in the prevention and treatment of cerebrovascular diseases. It is still not clear whether the drug has a direct and specific effect on neurotransmission or its effects are due to extracerebral actions, such as changes in cerebral blood flow. The main objective of the present investigation was to determine the global uptake and regional distribution of radiolabelled vinpocetine in the human brain in order to explore whether it may have direct central nervous system effects.

MATERIAL AND METHODS

Three healthy subjects were examined with positron emission tomography and [11C]vinpocetine. The regional uptake was determined in anatomically defined volumes-of-interest. The fractions of [11C]vinpocetine and labelled metabolites in plasma were determined using high pressure liquid chromatography.

RESULTS

The uptake of [11C]vinpocetine in brain was rapid and 3.7% (mean; n = 4) of the total radioactivity injected was in brain 2 min after radioligand administration. The uptake was heterogeneously distributed among brain regions. When compared with the cerebellum, an a priori reference region, the highest regional uptake was in the thalamus, upper brain stem, striatum and cortex. Following an initial peak, the total concentration of radioactivity in blood was relatively stable with time, whereas the concentration of the unchanged compound decreased with time in an exponential manner.

CONCLUSION

Vinpocetine, administered intravenously in humans, readily passes the blood-brain barrier and enters the brain. Its regional uptake and distribution in the brain is heterogeneous, indicating binding to specific sites. The brain regions showing increased uptake in the human brain correspond to those in which vinpocetine has been shown to induce elevated metabolism and blood flow. These observations support the hypothesis that vinpocetine has direct neuronal actions in the human brain.

In vitro-in vivo correlation of the pharmacokinetics of vinpocetine

Vinpocetine is extensively metabolized in rats, dogs and humans, and the plasma clearance approximates the hepatic plasma flow in each of the species. In vitro degradation studies with hepatocytes have shown that the activity of human hepatocytes is about one order of magnitude higher than the activity of dog hepatocytes, and two orders of magnitude higher than that of rat hepatocytes. These differences can explain the differences in bioavailabilities of vinpocetine in the three species (52% in rats, 21.5+/-19.3% in dogs and 6.2+/-1.9% in humans). In dogs and humans, the compound seems to be metabolized exclusively in the liver whereas in rats extrahepatic metabolism seems also to be important. The in vivo clearance predicted from the activity of hepatocytes is in good agreement with the values measured in vivo in the case of humans and dogs. The estimated values for bioavailability showed good correlation with in vivo data in each species if the free drug ratio was assumed to equal 1.

Brain uptake and plasma metabolism of [11C]vinpocetine: a preliminary PET study in a cynomolgus monkey

Vinpocetine, a vinca alkaloid, is a widely used therapeutic agent in patients with acute and chronic stroke. To reveal the mechanisms of vinpocetine action in the brain, vinpocetine was labeled with 11C. Positron emission tomography (PET) was used to determine the uptake and distribution of [11C]vinpocetine in brain regions and the trunk of a cynomolgous monkey in two independent measurements. The concentration of vinpocetine and its labeled metabolites was determined in blood and plasma using high-performance liquid chromatography (HPLC). Almost identical measurements were obtained in the two independent studies. After intravenous administration, following an initial peak, the total concentration of radioactivity in blood was relatively stable with time, whereas the concentration of the unchanged compound decreased with time in an exponential manner. The uptake of [11C]vinpocetine in brain was rapid, and 5% of the radioactivity totally injected was present in the brain 2 minutes after drug administration, indicating that the compound entered the brain readily. The radioactivity uptake was heterogeneously distributed among brain regions and was highest in the thalamus, the basal ganglia, and certain neocortical regions. The high brain uptake and the heterogeneous regional distribution indicate that direct central nervous system (CNS) effects of vinpocetine must be considered as explanation for the therapeutic effects. The detailed exploration of this suggestion requires further studies.

Improved gas chromatographic-mass spectrometric method for the quantitative determination of vinpocetine in human plasma

An improved and validated method for the determination of vinpocetine in human plasma using a combination of a solid-phase extraction as a cleaning step followed by gas chromatography-mass spectrometry (GC-MS) has been presented. Quantitation has been carried out with apovincaminic acid methyl ester as internal standard. A limit of detection of 0.01 ng/ml, limit of quantitation of 0.10 ng/ml, as well as a satisfactory accuracy, improved precision and prolonged capillary column life have been achieved.

Determination of vinca alkaloids in human plasma by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

A sensitive assay was developed for the quantitation of vinblastine, desacetylvinblastine and vincristine using liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (LC-APCI-MS). Analyses were performed on an Ultrasphere C18 microbore column using ammonium acetate as mobile phase. The calibration curves were linear across the range of 0.51-4.00 ng/ml (0.63-4.93 nM) for vinblastine, 0.74-3.93 ng/ml (0.96-5.11 nM) for desacetylvinblastine and 0.30-3.95 ng/ml (0.36-4.79 nM) for vincristine. Vinca alkaloid concentrations were measured with an accuracy and precision within 11%. This assay could be implemented to determine the plasma concentrations for pharmacokinetic studies of vinblastine, desacetylvinblastine and vincristine in conjunction with clinical trials.

Determination of apovincaminic acid in human plasma by high-performance liquid chromatography

An isocratic high-performance liquid chromatographic method is described for the quantitative analysis of low concentrations of apovincaminic acid (AVA) in blood plasma. AVA, interfering plasma components and primidone (used as the internal standard) were separated on a reversed-phase column of LiChrospher 60 RP-Select B (125 mm x 3 mm i.d.; 5 microns) (Merck). A UV-Vis detector was used at a wavelength of 254 nm. Each chromatographic separation was completed in 14 min and the results showed a relative recovery which varied between 95.9 and 116%, a good overall precision (relative standard deviation, 7.00%) and sensitivity over a linear range of 5.00-300 ng ml-1 (R = 0.999) for AVA in plasma. The method was applied to the analysis of plasma samples obtained from healthy subjects treated with one single oral dose of 20 mg of vinpocetine. The results indicate the method to be suitable for pharmacokinetic studies.

Lack of pharmacokinetic interaction between vinpocetine and oxazepam

The influence of multiple doses of vinpocetine (10 mg three times daily) on the steady state plasma concentrations of oxazepam (10 mg three times daily) was studied in 16 healthy subjects. The mean (+/- s.d.) AUC (ng ml-1h-1) of oxazepam over 24 h during combined treatment was 4716 +/- 2296 and for oxazepam treatment alone it was 4737 +/- 2448 (95% confidence intervals for ratio of means = 95.4-103.7%). The degree of plasma protein binding of oxazepam was 98.11 +/- 0.32% and was not affected by vinpocetine. Independent of vinpocentine treatment a significant diurnal change in the plasma binding of oxazepam was observed; the free drug fraction was 20% higher during the night than during the day. Cmax and AUC values based on total oxazepam in plasma were 10% lower during the night. The results indicate a lack of influence of vinpocetine on oxazepam kinetics. Diurnal changes in the plasma binding of oxazepam probably have no clinical consequences.

Methods for the analysis of the new vinca alkaloid derivative, S 12363, in plasma by high-performance liquid chromatography with fluorescence detection

Two sensitive analytical methods for the analysis of S 12363 in plasma are described. A highly sensitive procedure for human and dog plasma using cyanopropyl solid-phase extraction with ion pairing chromatography and fluorescence detection, has a limit of quantification of 0.1 ng ml-1. The technique has an overall precision and accuracy of 4.8 and 5.4% respectively over the concentration range 0.1-20 ng ml-1. A second, less sensitive, assay specifically adapted for rodent plasma, uses benzene sulphonyl cation-exchange solid-phase extraction followed by reversed-phase chromatography, with post-column fluorescence enhancement. This method has a limit of quantitation of 1.0 ng ml-1, with overall accuracy and precision of 7.2 and 11.6% respectively, over the concentration range 1.0-20.0 ng ml-1. Both assays have been successfully applied to dog and mouse toxicokinetic studies.

Binding of a new vinca alkaloid derivative, S12363, to human plasma proteins and platelets. Usefulness of an erythrocyte partitioning technique

The interactions of S12363 with human plasma proteins have been investigated in vitro by an erythrocyte partitioning technique that allows a quantitative estimation of the plasma and erythrocytes binding. S12363 was 85-95% plasma-bound and 97-98% blood-bound. The main binding protein in plasma was alpha-acid glycoprotein, with a binding constant of 0.6 x 10(6) M-1, accounting for 70% of total S12363 in plasma. Owing to extensive binding to platelets (40-50% of total blood amount), S12363 was mainly distributed in the non plasma blood compartment, with blood-to-plasma concentrations ratio of 1.2-1.4. These results indicate that, in vivo, the fraction of blood S12363 available for tissue diffusion, i.e., the free drug fraction in blood, should depend on both alpha 1-acid glycoprotein concentration in plasma and blood platelet count.

Development of a sensitive enzyme immunoassay for the determination of vinpocetine in human plasma

An Enzyme immunoassay for the quantitative determination of vinpocetine (CAS-42971-09-5) in human plasma has been developed. The lower limit of quantification is 0.1 ng/ml plasma. The assay shows no cross reactivity with the major metabolite apovincaminic acid. Because of a strong unspecific binding of vinpocetine to plasma proteins an extraction step was necessary. The inter- and intra-assay reproducibility of the test (coefficient of variation) is in a range of 1.1 and 18.3%.

Determination of apovincaminic acid in serum by means of high-performance liquid chromatography

A high-performance liquid chromatographic method for the determination of low concentrations in serum of apovincaminic acid, the main metabolite of vinpocetine, is reported. The assay includes a two-step ion-pair extraction with tetrabutylammonium as counter ion. Recovery is ca. 40%. Separation is performed on a narrow-range 5 microns particle size octadecylsilane modified silica packing. Heptanesulphonic acid is the pairing ion in the eluent, and the ultraviolet detection wavelength is 224 nm. Yohimbine serves as the internal standard. The assay is fast, accurate and sensitive quantifying at least 5 ng/ml apovincaminic acid in serum. The method was applied to the analysis of serum samples from aged subjects, treated with a 20-mg dose of vinpocetine.

Investigation of the possible influence of the absorption of vinpocetine with concomitant application of magnesium-aluminium-hydroxide gel

The concomitant application of magnesium-aluminium-hydroxide gel does not influence the absorption of vinpocetine (CAS 42971-09-5). The pharmacokinetics of vinpocetine under the influence of a concomitant application of magnesium-aluminium-hydroxide gel was investigated. 18 healthy male volunteers were included in the study. Vinpocetine was administered in the galenic form of a film-coated tablet in a dosage of 20 mg t.i.d. over 10 days. On days 5 and 6 of the study, blood samples were taken at 16 different moments over 24 h and analyzed as to their vinpocetine content. Starting with the 6th day of the study, the patients were administered in addition 1 sachet of an magnesium-aluminium-hydroxide gel 4 times a day. On day 9 of the trial, blood samples were taken again over 24 h. The parameters examined were AUC, Cmin, Cmax, tmax and Mean Residence Time. The results as to these parameters of day 5 were compared with those of day 9. As a further parameter, apovincaminic acid plasma levels were determined. There was no difference as to the vinpocetine amount absorbed with or without concomitant application of magnesium-aluminium-hydroxide gel. Apovincaminic acid plasma levels were lowered by approx. 11% when associated with the antacid.

Pharmacokinetics of vinpocetine and its main metabolite apovincaminic acid before and after the chronic oral administration of vinpocetine to humans

The pharmacokinetics of vinpocetine (Cavinton) and of its main metabolite apovincaminic acid (AVA), has been studied in 5 healthy male volunteers after the administration of 3 x 5 and 3 x 10 daily doses of vinpocetine for seven days. The pharmacokinetic curves of both vinpocetine and AVA have been determined prior to the chronic administration and on the last day of the treatment, whereas between the 2nd and 6th days, concentration was measured once daily. On the basis of these pharmacokinetic studies it can be concluded that both vinpocetine and AVA show linear pharmacokinetics at the doses used and that there is no accumulation or autoinduction.

Vinpocetine pharmacokinetics in elderly subjects

The pharmacokinetics of vinpocetine (Eusenium) were investigated in 20 elderly, healthy volunteers. Plasma levels of the drug were determined during one dose interval of either repeated intravenous infusion or oral administration. AUC, Cmax and tmax values were derived for oral application, AUC values in case of intravenous application. Oral administration of 20 mg vinpocetine resulted in 4.60 x 10(-8) mol l-1 h, 1.71 x 10(-8) mol l-1 and 2.33 h for AUC, Cmax and tmax, respectively. The appropriate values for apovincaminic acid were 1.92 x 10(-6) mol l-1 h, 6.39 x 10(-7) mol l-1 and 2.41 h. When 10 mg vinpocetine were infused for 1 h, AUC values for vinpocetine and apovincaminic acid were 3.42 x 10(-7) mol l-1 h and 1.69 x 10(-6) mol l-1 h. Absolute bioavailability of vinpocetine was 6.7%. These data were in good agreement with the literature on young and elderly subjects. Marked deviations of apovincaminic acid kinetics in elderly subjects as described earlier could not be demonstrated in this study.

Determination of vinca alkaloids in plasma and urine using ion-exchange chromatography on silica gel and fluorescence detection

The development of a method for the determination of the antineoplastic vinca alkaloids vinblastine and vindesine in biological samples is described. The selectivity of the assay is high owing to the use of solid-phase extraction on a cyanopropyl extraction column prior to isocratic chromatography on unmodified silica gel with fluorescence detection. The influence of acetonitrile concentration and mobile phase pH on the capacity factors of the drugs was studied in order to optimize the separation between the drugs and endogenous components. The effect of varying the type and concentration of competing cations in the mobile phase was also examined. The limit of determination (signal-to-noise ratio = 3) for vinblastine is 0.5 ng/ml in plasma and urine and for vindesine 2.5 ng/ml. The assay is suitable for determining the concentrations of both compounds in plasma and urine samples from patients.

[Simultaneous determination of vinburnine and 6-hydroxyvinburnine in human plasma by high-performance liquid chromatography]

An isocratic high-performance liquid chromatographic method has been developed to allow the simple and rapid determination of both vinburnine (I) and its main metabolite, 6-hydroxyvinburnine (II), in heparinized human plasma (0.5 ml). Compounds I and II and p-chlorodisopyramide (internal standard) were first extracted with alkalinized ethyl acetate and then with sulphuric acid. Separation was achieved on a reversed-phase muBondapak C18 column with a mobile phase of acetonitrile-water-0.1 M heptanesulphonate in acetic acid and with detection at 254 nm. Each run required 20 min. The within-day coefficients of variation for identical samples (20 ng/ml) were 7 and 6% and between-day coefficients of variation 8 and 26% for I and II, respectively. The detection limit was 5 ng/ml (normal therapeutic concentration, 10-300 ng/ml). The application of the method to drug monitoring was compared to that of a thin-layer chromatographic procedure.

Analysis of vinca alkaloids in plasma and urine using high-performance liquid chromatography with electrochemical detection

The reversed-phase high-performance liquid chromatography with electrochemical detection was used to quantify plasma and urine levels of vinblastine, vincristine, vindesine and a metabolite of vinblastine, desacetylvinblastine. Sample clean-up consisted of solid-phase extraction with a Bond Elut CN column. The extracts were separated on a Hypersil ODS column. The mobile phase consisted of a mixture of methanol and 10 mM phosphate buffer (pH 7.0). The limit of sensitivity using electrochemical detection was 100 pg on-column for all compounds with a signal-to-noise ratio of 3. Quantification of the compounds in human plasma and urine was possible down to 1 ng/ml (ca. 1 pmol). Pharmacokinetic results show that the sensitivity of the method is adequate for drug monitoring in clinical research.

Pharmacokinetic and metabolic studies of vinpocetine on dogs. I. Pharmacokinetics

The pharmacokinetics of tritiated vinpocetine has been studied on dogs. The drug, when administered orally, was readily absorbed from the gastrointestinal tract (T1/2 0.3 h) and underwent similarly fast distribution (T1/2 0.8 h) in the organism. The mean value of the elimination half-life was 8.2 h. Approx. 75% of the administered radioactivity was excreted with urine and feces within 72 h. The pharmacokinetics of the intravenously administered, labelled compound showed that a similarly rapid distribution but a somewhat slower elimination took place. Fecal and urinary excretion of radioactivity applied amounted to about 82%. Investigation of the distribution of radioactivity between plasma and blood cells revealed that the radioactivity content did not bind to the cellular fraction of the blood. Pharmacokinetic studies of the same design in the literature allowed us to make some comparison between dogs, rats and humans in respect to the kinetic behavior of labelled vinpocetine.

Clinical pharmacology of vinzolidine

Vinzolidine (VZL), a new semisynthetic vinca alkaloid, was studied by using 3H-labeled VZL administered PO in four patients. At single doses from 1.5 to 36.5 mg/m2 (0.034-0.919 mg/kg) radioactivity was rapidly absorbed with a half-life of absorption of 1 h and a peak at 4 h. Plasma decay of radiolabel followed a biphasic pattern with an alpha half-life of 10.48 h and a beta half-life of 172 h. The apparent plasma clearance was dose-dependent. The total radiolabel recovered was 52.9% +/- 11.4% of the administered label, with 90% in the feces. HPLC analysis revealed that in all extracted plasma, urine, and feces the predominant material was unchanged VZL. Several metabolites were observed but not identified.

High-performance liquid chromatographic determination of vinca-alkaloids in plasma and urine

A liquid chromatographic method is described for separating and determining vinblastine, vincristine and vindesine in plasma and urine. The drugs are extracted from the biological material using an ion-pair extraction, with sodium octylsulphate as counter-ion at pH 3. The extracts are injected on a reversed-phase system with a cyano column as stationary phase and a mobile phase composed of acetonitrile-phosphate buffer, pH 3 (65:35, vol. %). Stability studies are carried out for stock solutions of the drugs in water at different temperatures and pH values. The stability of these compounds in plasma is also investigated in the presence of an antioxidant. The method is applied to determine drug levels of vindesine and vinblastine in preliminary pharmacokinetic studies, using vincristine as the internal standard.

Slow infusion of vinca alkaloids in the treatment of idiopathic thrombocytopenic purpura

Vinca alkaloids are useful in the treatment of idiopathic thrombocytopenic purpura, a disorder in which macrophages remove platelets sensitized with antibody. Because vinca alkaloids avidly bind to platelets, drugs can be delivered selectively to macrophages. However, drugs given by bolus injection are cleared too rapidly to bind optimally to autologous platelets, and the use of allogeneic platelets loaded with drug in vitro is cumbersome, expensive, and dangerous. Therefore, slow infusions were devised to prolong the duration of enhanced plasma drug concentrations, thereby providing better conditions for in-vivo drug loading into autologous platelets. Twenty-four patients with refractory idiopathic thrombocytopenic purpura were given slow infusions; 17 had good to excellent responses. Eleven of eighteen patients who had been treated with bolus injections had better results when treated with slow infusions. Patients with improved responses had slower plasma clearance rates than did patients with poor responses. Slow infusion therapy had fewer side effects than bolus injection therapy. Slow infusions are the best method for long-term management.

Chromatographic analysis of Vinca alkaloids in human neoplastic tissues and host (mouse) tissues after injection in vivo or after incubation in vitro

A method for extracting from biological tissues vincristine, vinblastine, and their metabolites and analysis by high-performance liquid chromatography has been developed. After excision tissues are rapidly frozen in liquid nitrogen (less than 10 s) and powders are made under liquid N2. Extraction of blood, plasma, or tissue powders was achieved using ethanol (95%) acidified to pH 4.9 with acetic acid. Extracts were analyzed using reverse-phase chromatography capable of separating Vinca alkaloids with substitutions on the vindoline or catharanthine moiety. This technique has been used to elucidate the metabolism of [3H]vincristine and [3H]vinblastine in vivo and in vitro.

Determination of apovincaminic acid in human plasma by gas-liquid chromatography

High-resolution capillary gas-liquid chromatography (GLC) and highly sensitive and selective nitrogen-phosphorus flame ionization detection were applied for the detection of apovincaminic acid (AVA), the main metabolite of the cerebral vasodilator vinpocetine in human plasma. AVA was recovered from plasma by ion-pair extraction and determined by GLC as its methyl ester after derivation with diazomethane. An acid-base washing technique was used in order to reduce the contamination of GLC samples by material of endogenous origin to a minimum. The lowest detection limit of the method is 2 ng of AVA per ml of plasma.

Determination of apovincaminic acid in biological samples by high-performance liquid chromatography

A method is described for measuring the concentrations of apovincaminic acid and vincaminic acid (internal standard) in blood plasma and urine by high-performance liquid chromatography using ion pair extraction. The main metabolite of vinpocetine, apovincaminic acid, and vincaminic acid were extracted from 1 ml of plasma and urine into chloroform as an ion pair using tetrabutylammonium hydroxide as counter ion. Analysis was carried out on a reversed-phase column of RP-8 with acetonitrile-0.0075 M phosphate buffer (28:72) at pH 3.5 as mobile phase. The eluted derivatives were detected by UV absorption at 254 nm. The sensitivity of the method is 20 ng/ml for AVA in plasma and urine samples. The relative recovery of these compounds added to plasma was about 50%.

The pharmacokinetics and metabolism of N-desmethyl-N-formyl-leurosine (F-leurosine) in the rat

Absorption, tissue distribution, excretion, protein binding, and the metabolism of 14C labelled F-leurosine were studied in the rat. A triphasic curve for the disappearance of the drug from blood was found. The bile was the major route of excretion: 80% of radioactivity was recovered in the bile during the first 28 h after i.v. administration. 54% of the F-leurosine binds, in the concentration range of 0.1 mumol/1-0.5 mmol/l to plasma proteins. The TLC and HPLC data suggested that the bile of rats administered [14C]-F-leurosine contained either none or only small amount of metabolic products, which were most probably due to chemical decomposition rather then metabolism. Rat liver homogenates did not metabolize [14C] F-leurosine to any detectable extent.

Determination of vincamine in human plasma using automated high-performance liquid chromatography

A specific and sensitive high-performance liquid chromatographic method for the quantitative determination of vincamine at therapeutic concentrations in plasma is described. The column was packed with Spherisorb ODS 5 micrometer, and the mobile phase was acetonitrile-potassium phosphate (0.02 M, pH 2.3) (50:50) with a flow-rate of 10 ml/min. Detection was at 230 nm. Using automated large-volume injection of a non-eluting solvent (0.02 M potassium phosphate) the method was capable of the analysis of a large number of samples daily. The coefficient of variation of the procedure was 4.8% at a plasma vincamine concentration of 10 ng/ml

Determination of vincamine in plasma by selected ion monitoring

A sensitive and specific method for the determination of vincamine in plasma is described. The molecular ion (m/e 426) and the parent peak (m/e 367) of the TMS derivative are assayed simultaneously by selected ion monitoring. Sensitivity is 30 pg ml plasma. The suitability of the method for pharmacokinetic studies is assessed by measuring plasma level profiles in six volunteers receiving 20 mg of vincamine orally.