Pharmacokinetic study of stobadine.

The aim of this paper is to provide a brief overview of most important results of stobadine kinetic studies in rats, dogs, and human volunteers. In these studies, stobadine dihydrochloride and stobadine dipalmitate was used for intravenous and oral administration, respectively. To evaluate kinetic properties of stobadine and its metabolites, TLC, HPLC, GLC, GC-MS, radiometric, and fluorometric methods were developed and used.

Selective uptake of the anticancer drug bendamustine by liver and kidney tissues following its intravenous administration to mice.

Distribution of 14C-bendamustine following intravenous (i.v.) administration to mice was examined by whole body autoradiographic (WBAR) and quantitative techniques. The WBAR study showed that 14C-bendamustine-derived radioactivity was distributed extremely unevenly at each time interval investigated. After 5 min of administration the highest density of radioactive material was found in the liver and in the kidney. At all time intervals investigated the brain remained free of the label. In a detailed quantitative distribution study it was found that 14C-bendamustine-derived radioactivity was also unevenly distributed throughout the mouse tissues. At 5 min postdosing the level of 14C was by one order higher in the liver and in the kidney in comparison to the lungs, heart, spleen, and muscle. The results of both WBAR and quantitative tissue distribution studies suggest that bendamustine was selectively taken up from the blood by liver and kidney tissues. Because of this pharmacokinetic property, dose modification should be taken into consideration when administering the drug to patients suffering from hepatobiliary and kidney disorders.

Structure-photodynamic activity relationships of a series of 4-substituted zinc phthalocyanines.

Radioiodinated zinc phthalocyanine including [125I]ZnPcI4 and differently sulfonated [65Zn]ZnPcS (ZnPcS4, ZnPcS3, ZnPcS2 and ZnPcS1.75, a mixture of adjacent di and 25% mono) were prepared in order to study cell uptake and release kinetics in EMT-6 cells. The same compounds were evaluated for their in vitro phototoxicity and the biological parameters were compared to partition coefficients to arrive at quantitative structure-activity relationships (QSAR). At 1 microM in 1% serum, at 37 degrees C, all dyes showed rapid cell uptake during the first hour followed by a slow accumulation phase. After 24 h, the highest cellular concentration was observed with the lipophilic ZnPcI4, followed by the amphiphilic ZnPcS2 and ZnPcS1.75. The hydrophilic ZnPcS4 and ZnPcS3 showed lower uptake. Dye release from dye-loaded cells during incubation in dye-free medium could reach up to 60% and was shown to depend mainly on the amount of drug incorporated rather than the type of compound. These results suggest that care should be taken in interpreting dye toxicity data, which involve in vitro cell manipulations in dye-free medium, particularly during in vitro-in vivo protocols. The EMT-6 cell survival after 1 h or 24 h incubation with 1 microM dye in 1% serum followed by exposure to red light was assessed by means of the colorimetric 3-(4,5-dimethylthiazol-2-yl)-diphenyl-tetrazolium bromide (MTT) assay. Photocytotoxicities correlated inversely with the tendencies of the dyes to aggregate. Increased dye uptake by the cells also correlated with their activities, except for the lipophilic ZnPcI4, which showed the highest cell uptake but little phototoxicity. The QSAR between phototoxicity and the log of the partition coefficients (phosphate-buffered saline and n-octanol) gave a parabola with optimal partition values corresponding to the adjacent sulfonated ZnPcS2.

High-resolution PET imaging and quantitation of pharmaceutical biodistributions in a small animal using avalanche photodiode detectors.

UNLABELLED: The feasibility of high-resolution PET using BGO-avalanche photodiode detectors for in vivo imaging and quantitation of the biodistribution of radiopharmaceuticals in small animals is demonstrated. A prototype PET camera consisting of two scanning arrays of eight EG&G C30994 solid-state scintillation detectors was used to simulate a 310-mm diameter dual-ring animal tomograph having a 130-mm port and three imaging slices, each about 3.5 mm thick. The spatial resolution (FWHM) is 3 mm or less, isotropic and uniform throughout the 120-mm diameter field of view. METHODS: Female Fischer 344/CRBL rats implanted with subcutaneous mammary adenocarcinoma tumors were injected with copper-tetrasulfophthalocyanine (CuPcS4), a potential sensitizer for the photodynamic therapy of cancer, labeled with 64Cu (T1/2 = 12.7 hr, beta +:19%). RESULTS: In spite of the low specific radioactivity of 64Cu and other inherent limitations, organs such as the liver, kidneys and the tumor could be resolved with sufficient detail for their separation and quantitation. Apart from the tumor, agreement was obtained between the biodistributions measured by PET and by scintillation counting. The discrepancy for the tumor measurement results from averaging the radioactivity over the entire tumor volume when, in fact, CuPcS4 does not completely penetrate the tumor. This incomplete penetration is noted on the PET images. CONCLUSIONS: PET based on avalanche photodiode detectors provides an accurate measurement of target organ and tumor tissue concentrations. These preliminary results demonstrate the potential of very high resolution PET for biodistribution studies in small animals.

Biological activities of phthalocyanines--XV. Radiolabeling of the differently sulfonated 67Ga-phthalocyanines for photodynamic therapy and tumor imaging.

Phthalocyanines have been advanced as photosensitizers for the photodynamic therapy of cancer and selectively sulfonated derivatives have shown promise as tumor imaging agents. In order to study the effect of the degree of sulfonation on their biodistribution pattern, we prepared a series of sulfophthalocyanines (PcS) labeled with 67Ga. Direct chelation of metal free phthalocyanines with 67Ga gave chelates which demetallated on further purification whereas condensation of 67Ga with phthalic acid precursors, following purification and fractionation on Sep-Pak C18 cartridges, gave stable products. The distribution pattern of the [67Ga]GaPcS among human plasma proteins was strongly affected by the degree of sulfonation of the PcS. The lower sulfonated GaPcS showed significant binding to the various lipoprotein fractions whereas increased sulfonation favored association to albumin. The use of the 67Ga allowed for the validation of spectrophotometric quantification of GaPcS in biological samples and confirmed the in vivo stability of the radiolabeled complex.

Hepatobiliary elimination of bendamustin (Cytostasan) in rats.

Biliary excretion of bendamustin (Cytostasan, 5-[bis(2-chloroethyl)amino]-i-methylbenzimidazole-2-butyric acid; 1) and its metabolites was studied in rats after i.v. administration of 14C-1. The most significant finding was the rapid excretion of 1 related radioactivity in the bile occurring shortly after injection. While radioactivity eliminated by bile within 2 h was 41.8%, in the course of subsequent 22 h it amounted only to 3.2%. Bile samples analyzed by TLC indicated that the total amount of radioactivity was excreted in the form of conjugates and two hydroxy metabolites. A significant amount of radioactivity was excreted in urine. The diversion of bile by cannulation of the bile duct led to a significant decrease of elimination by feces.

The effect of high energy electron irradiation on blood-brain barrier permeability to haloperidol and stobadin in rats.

The heads of rats were irradiated by 4 MeV electrons in doses 90, 180, and 360 Gy. The observed times of deaths ranged 120-600, 60-420, and 150-370 min after 90, 180, and 360 Gy, respectively. A dose dependent decrease of the brain uptake index of haloperidol was observed 1 and 3 h post radiation. On the other hand an increased brain uptake index was found for stobadin after head irradiation with doses of 180 and 360 Gy. Regional cerebral blood flow, blood pressure, and heart rate were not significantly altered in the period following irradiation with 180 Gy. The observed changes in blood-brain barrier (BBB) permeability seem to be the result of the damaged function of morphological structures forming the BBB rather than altered regional blood flow.

Irradiation of the head by 60Co opens the blood-brain barrier for drugs in rats.

The passage of 6 model drugs; acetylsalicylic acid, chloramphenicol, ethimizol, carbisocaine, heptacaine, and diazepam, through the blood-brain barrier, was determined in unirradiated control rats and in animals 1, 3, and 7 days after irradiation of the head only with a dose of 25 Gy from a 60Co source. The brain uptake index (BUI), which compares the uptake of the test substance with that of 3H2O 5 s after their injection into the common carotid artery, was significantly increased in comparison with unirradiated controls 7 days after irradiation, for all substances tested except for ethimizol. For acetylsalicylic acid and chloramphenicol it was also significantly increased in the other time intervals. The less lipophilic substances showed a greater relative increase of BUI than the more lipophilic ones.

Effects of inducers and inhibitors of mixed-function oxidases on the biliary excretion of pentacaine metabolites.

The biliary excretion of 3H-pentacaine and its metabolites was studied in rats pretreated with an inducer or inhibitor of mixed-function oxidases. Over one-fourth (25.8 per cent) of a 2 mg kg-1 intraportal dose of 3H-pentacaine was excreted in bile in urethaneanaesthetized control rats within 3 h. The radioactivity appeared in the form of the parent drug, basic metabolites, and metabolite conjugates, 3.1, 86.5, and 10.4 per cent of the total radioactivity excreted, respectively. Pretreatment of rats with phenobarbital enhanced only slightly the biliary excretion of basic metabolites, and pretreatment with 3-methylcholanthrene had no effect. Phenobarbital also increased the initial rate of excretion of conjugates, but this effect was not sustained. 3-Methylcholanthrene had a tendency to impair excretion of conjugates by bile. Pretreatment of rats with SKF 525-A decreased the biliary excretion of both basic metabolites and conjugates while cimetidine did not alter significantly the biliary excretion of pentacaine metabolites. These results suggest that the canalicular transport of metabolites may be the most important factor in controlling pentacaine metabolite excretion in bile.

Kinetics of biliary elimination of pentacaine in rats.

Pentacaine, a local anaesthetic of the carbanilate type, administered intravenously as 3H-pentacaine, 2 mg kg-1 to rats, was eliminated in the bile mainly in the form of metabolites (20.5 +/- 1.5 per cent of the dose) and as parent drug (0.1 per cent of the dose) within 3 days. In control rats 32.2 +/- 2.5 and 37.8 +/- 2.5 per cent of 3H-dose, representing pentacaine metabolites, were excreted in the urine and faeces, respectively. In bile-duct-cannulated rats 35.7 +/- 6.8, 11.2 +/- 3.4, and 20.5 +/- 1.5 per cent of 3H-dose were excreted in the urine, faeces, and bile, respectively. The high 3H recovered in faeces in animals with diverted bile flow indicated passage of pentacaine metabolites through the intestinal wall. The excretion of pentacaine and its metabolites in bile was an active process, since the ratio bile/plasma concentration rapidly attained values approaching 10. In rats with ligated ureters the biliary elimination of pentacaine and its metabolites was enhanced, compensating for impaired urinary excretion. This was accompanied by increased plasma and brain levels of 3H compared with untreated controls.

[Transplacental transfer, tissue localization and morphological study of the rabbit placenta after the administration of pentacaine]. / Transplacentárny prechod, tkanivová lokalizácia a morfologická stúdia placenty králika po podaní pentakaínu.

On day 29 of gravidity, the New Zealand white breed rabbits were intravenously administered 3H-pentacaine (0.5 mg.kg-1), a new local anaesthetic agent with anti-ulcerous effect in order to study the distribution in pregnant females. Transplacental passage and a relatively homogenous distribution of unchanged pentacaine were found in the organs of females with the largest accumulation in the lungs. Pentacaine is distributed in the same manner in the fetal organs as in the organs of the mother, but the levels in the foetuses were significantly lower. A morphological study of the rabbit placenta on day 29 of gravidity after the doses of 1, 10 and 50 mg.kg-1 of pentacaine did not show any pathological changes.

Stability studies of 14C-Cytostasan solutions and its extraction using dicarbolide of cobalt.

In this study the stability of 14C-Cytostasan (1, bendamustine), in water solutions was investigated. In distilled water a rapid degradation of carrier-free 14C-1 occurred. The degradation products of 14C-1 are 14C-monohydroxy-1 and 14C-dihydroxy-1 (evidence with the TLC). The degradation rate of 14C-1 was reduced by addition of nonlabelled 1 to the 14C-1 stock solution. The possibility of using distribution coefficient as a stability indicator of 14C-1 solutions was investigated. A number of organic solvents ranging from polar to nonpolar were used for extraction of 14C-1 from water solution. Only ethyl acetate was slightly effective. The distribution coefficient of 14C-1 was dramatically enhanced in presence of dicarbolide of cobalt (DC-H+) in benzene at extraction from HClO4 (0.5 mol.l-1).

Pharmacokinetics of carbisocaine in rats and mice.

[14C]carbisocaine, N-(2-(2-[1-14C]-heptyloxyphenylcarbamoyloxy)-propyl)-diethylammoni um chloride was administered to male Wistar rats, weighing 180-210 g IV in doses of 0.425, 1.425, 2.425 or 4.425 mg/kg or orally in a dose of 2.425 mg/kg. Extraction of carbisocaine from alkaline media into n-heptane was used for assessment of the unchanged drug in plasma, organs and excreta in predetermined time intervals. The two-way analysis of variance confirmed the insignificant effect of subject variability of experimental animals (p greater than 0.05) on plasma data after IV administration. Plasma data following the IV administration were approximated by a linear open two-compartment model with elimination from the central compartment. Regression analysis indicated linearity between carbisocaine plasma AUC and the IV administered dose within the range tested. The following model parameters were obtained: elimination half-life 161.2 +/- 37.5 min, total body clearance 59.5 ml/min/kg, distribution volume in steady state 5616.2 ml/kg and mean residence time 96.7 min. The systemic availability of the orally given carbisocaine was 45.2%, assessed by AUCpo/AUCiv (0-360 min). The brain uptake index of carbisocaine in relation to 3H2O was 57.7 +/- 3.9%. Whole body autoradiographs of mice injected with [14C]carbisocaine documented accumulation of 14C in gall and urinary bladder and in the gut contents and the effective placental barrier against carbisocaine and its metabolites.

Biotransformation of stobadine, a gamma-carboline antiarrhythmic and cardioprotective agent, in rat liver microsomes.

1. The metabolism of stobadine, a gamma-carboline antiarrhythmic and cardioprotective agent, was investigated in vitro using fortified rat liver microsomal preparations. 2. Two metabolic products, N-desmethyl stobadine and stobadine N-oxide were isolated and identified by means of t.l.c.,g.l.c. -mass spectrometry, n.m.r. spectrometry and comparison with synthetic reference compounds. 3. Stobadine N-oxide was resolved into two optically active stereoisomers which were produced enzymically in approximately equal quantities.

Pharmacokinetics of the new local anaesthetic N-[2-(2-Heptyloxyphenylcarbamoyloxy)ethyl]piperidinium chloride in rats and mice.

Pharmacokinetics of a local anaesthetic of the carbanilate type (Heptacaine; in the following briefly called HCP), was studied using a labelled product, N-[2-(2-[1-14C]-heptyloxyphenylcarbamoyloxy)ethyl]piperidinum++ + chloride. Determination of HCP in biological material was based on double extraction of HCP from alkaline media into n-heptane. The plasma concentration of HCP following i.v. administration to rats was approximated by a biexponential function. An open two-compartment pharmacokinetic model was conferred to the data. The model parameter estimates are as follows: terminal elimination half-life 3.80 +/- 0.15 h, distribution volume at steady state 9.31 l/kg, total body clearance 73.4 ml/min/kg, mean residence time 2.1 h. The systemic availability of the orally given HCP in solution was 35.8%. The HCP plasma AUC vs. dose relationship was linear within doses ranging from 2.78 to 4.33 mg/kg. The brain uptake index of HCP in comparison with 3H2O was 62.2%. Autoradiography in mice injected i.v. showed a heterogeneous distribution of the label in the tissues and its excretion by the urinary and biliary pathways. HCP showed strong affinity to the lung tissue. During 96 h after i.v. administration, 21% and 62% of the 14C dose was excreted into urine and faeces, respectively, and after oral administration, the excretion was 17% and 43%, respectively.

The disposition of the local anaesthetic, pentacaine, in rats and mice.

The pharmacokinetics of pentacaine, a new local anaesthetic agent from the group of carbanilates, was investigated in the rat at a dose of 2 mg kg-1 i.v. and per os. A three-compartment open model gave the best fit to the data. The model parameters are: t1/2 99.0 +/- 14.1 min, Vss 7411.1 ml kg-1, Cl 77.9 ml min-1 kg-1; after oral administration t1/2ab 4.9 +/- 1.9 min, bioavailability 59.1 per cent, and extent of absorption 79.3 per cent. Pentacaine is eliminated almost entirely by metabolism. The metabolites are excreted equally in the urine and faeces at a relatively slow rate. The pharmacokinetics of pentacaine was linear in the dose range 0.008-4 mg kg-1. The whole-body autoradiography in mice showed rapid transfer of 3H radioactivity from the vessels to tissues and a markedly heterogeneous disposition pattern in organs.