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Lidocaine was administered to healthy volunteers at different sites in the rectum. Unchanged drug and monoethylglycinexylidide (MEGX) concentrations were measured in plasma with a newly developed gas chromatographic method. Lidocaine was given rectally by means of an osmotic system (Osmet(®)) which delivered 25 mg/h at zero-order rate. In a pilot experiment in two subjects it was shown that lidocaine administration close to the anus for 5 h resulted in higher lidocaine plasma levels as compared to administration at 15 cm from the anus. Six other subjects participated in three separate experiments, in which lidocaine was administered rectally close to the anus and at 7.5 and 15 cm from the anus. A zero-order infusion plasma level profile was found for both the parent compound and its metabolite. The MEGX/lidocaine plasma concentration ratio was calculated for all experiments. After administration most proximal to the anus the mean metabolite/parent drug concentration ratio was significantly less than that obtained after administration at 15 cm from the anus, whereas at approximately 7.5 cm from the anus the values were in-between. Comparison of the AUC lidocaine/AUC MEGX ratios gave similar results; the highest value, 3.2 ± 1.3 (mean ± S. D.), was found after administration close to the anus, while at 15 cm from the anus the ratio was 1.6 ± 0.3 (p0.01). The terminal elimination half-lives of lidocaine and MEGX did not differ for the three sites of administration, and the mean values were 110 and 180 min respectively. The results of this study demonstrate that the site of drug administration in the human rectum determines the degree of hepatic "first-pass" elimination of high-clearance drugs. Maximal avoidance of presystemic elimination is achieved when administration takes place close to the anus.

The extent of "first-pass" elimination of racemic propranolol and dextropropranolol in doses of 0.25 or 0.50 mg was investigated in relation to the site of drug administration in the rectum of rats. The compounds were given orally, i.v., and rectally at distances of 2 and 1 cm from and directly at the anus by low volume zero-order 30 min infusion. Unchanged propranolol was determined in blood, and propranolol and three metabolites were measured in urine. The systemic availability of propranolol after oral administration was approximately 6 %. Rectal administration at 2 cm, at 1 cm and directly at the anus (0.2 cm) gave two, three and six times higher values, respectively. The more distal application site produced urinary metabolite profiles that were comparable to those observed after oral administration, while application directly at the anus was similar to i.v. dosing. In all experiments log-linear elimination phases with comparable elimination half-lives (range 12-18 min) were found, except with the 0.50 mg dose after i.v. and rectal administration close to the anus which showed a non-linear profile. The mean systemic availability after rectal administration of 0.25 mg dextro-propranolol close to the anus was 50 and 64 % as compared to a 0.25 and 0.125 mg i.v. dose, respectively. The rectal route may be used for propranolol to partially prevent hepatic first-pass metabolism. However, avoidance of presys-temic elimination is maximal only in the immediate vicinity of the anus as the venous blood supply of the upper part of the rectum of rats appears to be connected to the portal system and the lower part to the general circulation.

Two model substrates for oxidative hepatic enzyme activity, viz. antipyrine (A) and theophylline (T), were given simultaneously to rats by iv administration. Blood concentrations of A and T were measured by a high-performance liquid chromatographic (HPLC) method. Urinary excretions of A, T, and the major metabolites arising from A-4-hydroxyantipyrine (OHA), norantipyrine (NORA), 3-hydroxymethylantipyrine (HMA), and 4,4'-dihydroxyantipyrine (DOHA)-and from T-1-methyluric acid (1-MU) and 1,3-dimethyluric acid (1,3-DMU)-were also determined by HPLC. It was found that the pharmacokinetic parameters obtained after the simultaneous administration of A and T at relatively low dose levels (A, 5.0 mg; and T, 1.3 mg) were not different from those obtained after the separate administration of A or T at the same dose level. In order to investigate whether the metabolic pathways of A and T are mediated by the same or closely related forms of the cytochrome P-450 system, metabolic clearances of A (CLA,M) and T (CLT,M) and the clearances for production of their various metabolites, obtained in untreated rats and in rats pretreated with 3-methylcholanthrene (MC) or with MC followed by 9-hydroxyellipticine (E), were correlated. These two compounds are a selective cytochrome P-448 inducer and inhibitor, respectively. Strong correlations were found between CLT,M and the clearances for production of OHA, NORA, and DOHA but not HMA. The best correlation, however, was observed between CLT,M and CLOHA, not only when all data points were taken into account (r = 0.99), but also in separate pretreatment groups (r ranging from 0.87 to 0.92). Moreover, the slopes of these correlation lines varied only slightly among groups, while the intercepts were not significantly different from zero. In the separate pretreatment groups, the correlation coefficients for the correlations between CLT,M and the clearance for production of the other metabolites of A were considerably lower, while the slopes of the correlation lines varied substantially. Clearances for production of the metabolites of T were strongly correlated with each other (r = 0.99) and with CLOHA (r = 0.95). It can be concluded that theophylline metabolism and formation of OHA are mediated by the same or very similar forms of cytochrome P-450, whereas formation of the other major metabolites of A is not or only partly. The study of the various pathways of metabolism after simultaneous administration of drugs is a powerful tool in the study of correlations in drug metabolism in vivo.

Memantine is an uncompetitive N-methyl-D-aspartate receptor antagonist which blocks the NMDA receptor with moderate-affinity in a use- and voltage dependent manner. In clinical practice it is used chronically in the treatment of dementia and does not induce psychotomimetic effects as, high affinity, uncompetitive antagonists. Thus, it was of interest to determine dopamine (DA) and metabolite (DOPAC - dihydroxyphenylacetic acid and HVA - homovanillic acid) concentrations in the prefrontal cortex (PFC) in response to 14 days administration of memantine (20 mg/kg/day). It was previously determined that in rats this treatment induces sensitization to the locomotor effect and tolerance to the learning impairing properties of high doses of memantine. Acute administration of memantine (20 mg/kg, i.p.) did not affect dopamine levels in the PFC. It did however increase DA metabolite (DOPAC and HVA) concentrations. Administration of memantine (20 mg/kg/day) for 14 days before the acute challenge only slightly changed memantine's effect on PFC neurochemistry even though pharmacokinetic tolerance was observed. When memantine was administered to the sham group, which had been repeatedly treated with Hypnorm (including neuroleptic), an increase in PFC dopamine and metabolite content was seen. In accordance with the fact that memantine does not possess psychotomimetic activity at therapeutically relevant doses, these experiments showed that it does not affect the prefrontal cortex dopamine levels.

Behavioral changes have previously been reported following administrations of uncompetitive NMDA receptor antagonists memantine, amantadine and MK-801 for 14 days, at the doses that produce plasma levels comparable to those seen in patients (20, 100 and 0.31 mg/kg/day respectively). Using the same doses, the effect on receptor binding (autoradiography) was studied in rats. [3H]MK-801 binding was increased in the dentate gyrus and CA3 region of the hippocampus (35.2 and 24.3% respectively) following 3 days S.C. infusion of memantine by ALZET minipumps. One daily injection of memantine for 14 days, increased [3H]MK-801 binding in the frontal cortex by 40.3%. The same treatment with amantadine did increase [3H]raclopride binding to dopamine D2 receptors by 13.5%. None of these treatments changed the expression of muscarinic receptors. It is concluded that subchronic blockade of the NMDA receptor by uncompetitive antagonists at moderate (therapeutically-relevant) doses induced only minor changes in NMDA and dopamine D2 receptor expression.

Purpose. To determine free brain concentrations of the clinically used uncompetitive NMDA antagonists memantine and amantadine using microdialysis corrected for in vivo recovery in relations to serum, CSF and brain tissue levels and their in vitro potency at NMDA receptors.

1. Interaction between alcohol and bretazenil (a benzodiazepine partial agonist in animals) was studied with diazepam as a comparator in a randomized, double-blind, placebo controlled six-way cross over experiment in 12 healthy volunteers, aged 19-26 years. 2. Bretazenil (0.5 mg), diazepam (10 mg) and matching placebos were given as single oral doses after intravenous infusion of alcohol to a steady target-blood concentration of 0.5 g l-1 or a control infusion of 5% w/v glucose at 1 week intervals. 3. CNS effects were evaluated between 0 and 3.5 h after drug administration by smooth pursuit and saccadic eye movements, adaptive tracking, body sway, digit symbol substitution test and visual analogue scales. 4. Compared with placebo all treatments caused significant decrements in performance. Overall, the following sequence was found for the magnitude of treatment effects: bretazenil+alcoholdiazepam+alcoholor = bretazenildiazepamalcoholplacebo. 5. There were no consistent indications for synergistic, supra-additive pharmacodynamic interactions between alcohol and bretazenil or diazepam. 6. Bretazenil with or without alcohol, and diazepam+alcohol had marked effects. Because subjects were often too sedated to perform the adaptive tracking test and the eye movement tests adequately, ceiling effects may have affected the outcome of these tests. 7. No significant pharmacokinetic interactions were found. 8. Contrary to the results in animals, there were no indications for a dissociation of the sedative and anxiolytic effects of bretazenil in man.

The aim of this study was to determine whether changes in the transport of drugs into the brain could be determined by in vivo intracerebral microdialysis. Atenolol was used as a model drug to determine blood-brain barrier (BBB) transport characteristics. In rats, unilateral opening of the blood-brain barrier was achieved by infusion of hyperosmolar mannitol (25%, w/v) into the left internal carotid artery. BBB transport, expressed as the ratio of the area under the curve (AUC) of atenolol in brain extracellular fluid over plasma, was three times higher for the mannitol treated hemisphere as compared with the contralateral brain or after infusion of saline, being (mean ± SEM) 0.094 ± 0.024 (n = 16), 0.029 ± 0.007 (n = 12) and 0.030 ± 0.009 (n = 12) respectively. Further evaluation of the data indicated that for experiments performed in the morning the mannitol infusion had little effect on the extent of transport of atenolol into the brain, while in the afternoon BBB transport was about 10-fold higher than in the contralateral and saline group. The mean “afternoon” ratios ± SEM were 0.155 ± 0.038 (n = 8), 0.012 ± 0.003 (n = 6) and 0.018 ± 0.006 (n = 6) respectively. It is concluded that intracerebral microdialysis is capable of revealing changes in BBB transport and regional and time-dependent differences in drug levels can be demonstrated with the use of this technique.

1. The effects of metoprolol-Oros 14/190 once daily, propranolol 80 mg twice daily and temazepam 10 mg once daily on central nervous system (CNS) related performance and haemodynamic variables were evaluated in a double-blind, randomized, placebo controlled, crossover study in 12 healthy volunteers. Drugs were administered for 3 consecutive days except for temazepam, which was administered on days 1 and 3 only. Treatment effects were evaluated at 0, 2, 5 and 8 h on days 1 and 3. 2. Neither beta-adrenoceptor blocker had significant effects in a battery of tests after single or 3 days dosing. Temazepam caused a decrease in saccadic peak velocity of 37.4 degrees s-1 (95% CI: 6.0, 68.9) at 2 h and an increase of auditory reaction times of 11.5 ms (0.2, 22.8) at 8 h on day 1. No significant effects of temazepam were detected on day 3. 3. Both beta-adrenoceptor blockers reduced exercise heart rate. Peak effects were measured at 2 h 40 min after propranolol but not metoprolol-Oros (difference, day 1:20 (11, 29) beats min-1, day 3:13 (8, 19) beats min-1). Both beta-adrenoceptor blockers significantly reduced baseline exercise heart rate on day 3. Compared with day 1, metoprolol-Oros caused larger reductions of exercise heart rate at all times on day 3. 4. Metoprolol-Oros and propranolol caused similar reductions of systolic- and diastolic blood pressure on days 1 and 3. Temazepam caused a small reduction in diastolic blood pressure at 5 h 40 min on day 1 but was otherwise devoid of haemodynamic effects.(ABSTRACT TRUNCATED AT 250 WORDS)

This is part II of a review on the transport of drugs across the blood-brain barrier. In this part, the emphasis is on the various experimental techniques that can be used to characterize the blood-brain barrier transport of drugs. Generally speaking, three approaches can be distinguished: in vitro techniques using isolated brain capillaries, cerebrovascular endothelial cells in primary culture or endothelium-derived cell lines; in vivo techniques (both single-passage and multi-passage techniques) and in situ perfusion techniques. Each of these techniques has specific advantages and disadvantages associated with it. Therefore, in many instances, a combination of different approaches is needed to study the fundamental aspects of drug transport across the blood-brain barrier.

Generally, oral administration is the route of choice in the daily practice of pharmacotherapy. However, in some circumstances this is impractical or even impossible (during nausea and vomiting or convulsions, in uncooperative patients and before surgery). In these cases, the rectal route may represent a practical alternative and rectal administration is now well accepted for delivering, for example, anticonvulsants, non-narcotic and narcotic analgesics, theophylline, antiemetics and antibacterial agents, and for inducing anaesthesia in children. It may also represent an interesting alternative to intravenous or other injection routes of drug administration. The rate and extent of rectal drug absorption are often lower than with oral absorption, possibly an inherent factor owing to the relatively small surface area available for drug uptake. In addition, the composition of the rectal formulation (solid vs liquid, nature of the suppository base) appears to be an important factor in the absorption process by determining the pattern of drug release. This relation between formulation and drug uptake has been clearly demonstrated for drugs like diazepam, paracetamol (acetaminophen), indomethacin, methadone and diflunisal. Coadministration of absorption-promoting agents (surfactants, sodium salicylate, enamines) represents another approach towards manipulating rectal drug absorption, although this concept requires further research concerning both efficacy and safety. For a number of drugs the extent of rectal absorption has been reported to exceed oral values, which may reflect partial avoidance of hepatic first-pass metabolism after rectal delivery. This phenomenon has been reported for morphine, metoclopramide, ergotamine, lidocaine (lignocaine) and propranolol. Rectal drug delivery in a site- and rate-controlled manner using osmotic pumps or hydrogel formulations may provide opportunities for manipulating systemic drug concentrations and drug effects. The extent of first-pass metabolism may be influenced (lidocaine), depending on the site of drug administration in the rectum. The rate of delivery may determine systemic drug action and side effects (nifedipine), and it may affect the local action of concurrently administered absorption promoters on drug uptake (cefoxitin). Local irritation is increasingly being acknowledged as a possible complication of rectal drug therapy. Long term medication with rectal ergotamine and acetylsalicylic acid, for example, may result in rectal ulceration, and irritation after a single administration of several drugs and formulations has been described. The assessment of tolerability and safety is imperative in the design of rectal formulations. Recent studies corroborate the clinical relevance of rectal drug therapy, and the value of the rectal route as an alternative to parenteral administration has been assessed for several drugs, e.g. diazepam, midazolam, morphine and diclofenac.(ABSTRACT TRUNCATED AT 400 WORDS)

SummaryThe enhancement of the blood fibrinolytic potential by physical exercise is generally attributed to the release of tissue-type plasminogen activator (t-PA) from the vessel wall. In this study we have investigated the possible contribution of urokinase-type plasminogen activator (u-PA).Six healthy male volunteers (age 21–25 years) were screened for their ability to perform maximal exercise for their age-group for 12 min on a bicycle ergometer. Subsequently, on one occasion they were required to remain supine for 2 h (from 8.30 a. m. onwards) and on another they performed maximal exercise (from 9.00 a.m. onwards). During exercise an increase in u-PA antigen and plasmin-activatable pro-urokinase (proUK) activity, concurrent with t-PA antigen and euglobulin t-PA activity, was observed in all six volunteers, while at rest these parameters remained unaffected. Mean u-PA- and t-PA antigen increased, respectively, from 4.2 ± 1.0 ng/ml and 5.8 ± 2.1 ng/ml before exercise to 9.8 ± 3.0 ng/ml and 18.3 ± 3.8 ng/ml (peak). Mean plasminactivatable proUK activity and t-PA activity increased, respectively, from 2.1 ± 0.4 ng/ml and 0.3 ± 0.2 ng/ml before exercise to 4.3 ± 1.7 ng/ml and 7.2 ± 4.0 ng/ml (peak). The increases were statistically significant throughout (paired t-test, pre vs post, antigen P

The transport characteristics of peptide and proteins drugs across various epithelial membrane barriers are outlines. These include transport through the intestinal, buccal, nasal and pulmonary absorptive mucosae, as well as transdermal penetration. Because peptides and proteins are hydrophilic and high molecular weight compounds, they commonly show minor permeability across the mentioned biological membranes. In order to improve their transport properties and thereby their systemic bioavailability, several strategies can be undertaken, such as the synthesis of stabilized and lipophilic analogues, the application of absorption enhancers and protease inhibitors, and the design of suitable dosage forms (e.g., liposomes, biodegradable nanocapsules, bioadhesive microspheres).

Een geriatrische patient krijgt vaak met een veelvoud aan stoornissen te maken zowel op lichamelijk als op psychisch en sociaal gebied. Door veroudering neemt de fysiologische reservecapaciteit af, wat de geriatrische patient kwetsbaar maakt. Er dreigt snel verlies van zelfredzaamheid. Andere kenmerken van de geriatrische patient die in dit hoofdstuk worden besproken, zijn een andere presentatie van ziekten, multipathologie en een gewijzigde farmacokinetiek en -dynamiek.

To investigate whether P-glycoprotein (Pgp) protects the in vitro BBB against the cytotoxic effects of anti-tumour drugs.In an in vitro BBB coculture model the influence of the anti-microtubule drugs vinblastine, colchicine, paclitaxel and the non-anti-microtubule drugs doxorubicin, fluorouracil and etoposide in the absence or presence of Pgp modulators on the trans-endothelial electrical resistance (TEER), which is an indicator for the integrity, was investigated.In the absence of Pgp modulators vinblastine, colchicine and paclitaxel dose dependently decreased TEER values to less than 20% of control. Non-anti-microtubule drugs did not affect TEER values. Following competitive inhibition of Pgp by various Pgp modulators and substrates, even low concentrations of vinblastine, colchicine and paclitaxel substantially decreased TEER. IC50 values of LY 335979, SDZ-PSC 833, cyclosporin A, and verapamil were 0.03, 0.25, 0.46, and 13.7 microM, respectively.These results indicate that Pgp normally protects the in vitro BBB against the disruptive effects of anti-microtubule drugs, but its integrity is lost when anti-microtubule drugs are used in combination with potent Pgp modulators. In addition, this procedure offers the possibility to characterize Pgp modulators and substrates with respect to their efficacy and to elucidate drug interactions at the level of Pgp.

To investigate the influence of astrocytes on P-glycoprotein (Pgp) expression and intracellular accumulation of Pgp substrates, separate from their net transcellular transport across the blood-brain barrier (BBB).An in vitro BBB model was used, comprising of brain capillary endothelial cells (BCEC) monolayers or BCEC co-cultured with astrocytes.BCEC+astrocyte co-cultures seemed to express a higher level of Pgp compared to BCEC monolayers. Inhibition of Pgp results in an increased intracellular accumulation of Pgp substrates in both BCEC monolayers and BCEC+astrocyte co-cultures, and increased the sensitivity for vinblastine mediated disruption of the in vitro BBB (called the vinblastine exclusion assay). BCEC monolayers were more sensitive to vinblastine mediated disruption compared to BCEC+astrocyte co-cultures. In the latter, but not in BCEC monolayers, an inhibitable polar transport of Pgp substrates was only found from the brain to the blood side of the filter.Astrocytes increase the functional expression of Pgp in our in vitro BBB model. These results also illustrate that an important role for Pgp on the BBB is to protect the barrier against intracellular accumulation of cytotoxic BBB disrupting compounds.

We describe a new simple, selective and sensitive micromethod based on HPLC and fluorescence detection to measure debrisoquine (D) and 4-hydroxydebrisoquine (4-OHD) in urine for the investigation of xenobiotic metabolism by debrisoquine hydroxylase (CYP2D6). Four hundred microl of urine was required for the analysis of D and 4-OHD. Peaks were eluted at 8.3 min (4-OHD), 14.0 min (D) and 16.6 min for the internal standard, metoprolol (20 microg/ml). The 5-microm CN-reverse-phase column (Shimpack, 250 x 4.6 mm) was eluted with a mobile phase consisting of 0.25 M acetate buffer, pH 5.0, and acetonitrile (9:1, v/v) at 0.7 ml/min with detection at lambdaexcitation = 210 nm and lambdaemission = 290 nm. The method, validated on the basis of measurements of spiked urine, presented 3 ng/ml (D) and 6 ng/ml (4-OHD) sensitivity, 390-6240 ng/ml (D) and 750-12000 ng/ml (4-OHD) linearity, and 5.7/8.2% (D) and 5.3/8.2% (4-OHD) intra/interassay precision. The method was validated using urine of a healthy Caucasian volunteer who received one 10-mg tablet of Declinax(R), po, in the morning after an overnight fast. Urine samples (diuresis of 4 or 6 h) were collected from zero to 24 h. The urinary excretion of D and 4-OHD, Fel (0-24 h), i.e., fraction of dose administered and excreted into urine, was 6.4% and 31.9%, respectively. The hydroxylation capacity index reported as metabolic ratio was 0.18 (D/4-OHD) for the person investigated and can be compared to reference limits of12.5 for poor metabolizers (PM) and12.5 for extensive metabolizers (EM). In parallel, the recovery ratio (RR), another hydroxylation capacity index, was 0.85 (4-OHD: SigmaD + 4-OHD) versus reference limits of RR0.12 for PM and RR0. 12 for EM. The healthy volunteer was considered to be an extensive metabolizer on the basis of the debrisoquine test.

The purpose of the present study was to determine whether the probenecid-sensitive organic acid transporter is responsible for the short duration of action of a new group of N-methyl-D-aspartate receptor glycine(B)-site antagonists, MRZ 2/570, 2/571, and 2/576. A prolongation of their anticonvulsant activity from 60 to 180 to 240 min, was found in mice after pretreatment with probenecid (200 mg/kg i.p.). Microdialysis studies in rats showed that this is likely due to a change in central nervous system concentrations of these drugs because cotreatment with probenecid caused an increase in the brain extracellular fluid half-life (0.5- to 4-fold) and the brain area under the curve (1.8- to 3.6-fold). In serum the half-life of MRZ 2/576 (30 mg/kg) was also increased by coadministration of probenecid from 15.6 +/- 1.3 to 40.6 +/- 6.0 min. At steady state (MRZ 2/576, 20 mg/kg/h i.v.), brain extracellular fluid concentration was elevated 2.5-fold by concomitant administration of probenecid. These results clearly show that these glycine(B)-site antagonists are rapidly cleared from the systemic circulation and the central nervous system by the probenecid-sensitive organic acid transport system. Moreover, the present data show that MRZ 2/570, 2/571, and 2/576 reach the brain in concentrations (1.34-2.32 microM) above the range of their in vitro potencies at the glycine site of the N-methyl-D-aspartate receptor (0.1-1.0 microM).

To determine free brain concentrations of the clinically used uncompetitive NMDA antagonists memantine and amantadine using microdialysis corrected for in vivo recovery in relations to serum, CSF and brain tissue levels and their in vitro potency at NMDA receptors.Microdialysis corrected for in vivo recovery was used to determine brain ECF concentrations after steady-state administration of either memantine or amantadine. Additionally CSF, serum, and brain tissue were analyzed.Following 7 days of infusion of memantine or amantadine (20 and 100 mg/kg/day respectively) whole brain concentrations were 44-and 16-fold higher than free concentrations in serum respectively. The free brain ECF concentration of memantine (0.83 +/- 0.05 microM) was comparable to free serum and CSF concentrations. In case of amantadine, it was lower. A higher in vivo than in vitro recovery was found for memantine.At clinically relevant doses memantine reaches a brain ECF concentration in range of its affinity for the NMDA receptor and close to its free serum concentration. This is not the case for amantadine and different mechanisms of action may be operational.

The blood-brain barrier prevents an indifferent medicine existing in the blood to enter also in the brain. This barrier has got an anatomical base: it is first consisting in a cerebrovascular layer of endothelial capillary vessels of the peripheral tissue. It is moreover covered by outgrowths of the flial cells, which are called astrocytes. There are, for that reason, important limits to a size of molecules which can reach the cerebral tissue through a paracellular way (through what is called in English "tight-junctions"). Most medicines must use the transcellular way. Lipophily is necessary to follow that way. Year after year, it appeared, thanks to a comparative study of the substances, that there exists--grosso modo--a positive correlation between the lipophilic level and the permeation-level of a substance in the cerebral tissue. There are, however, several exceptions: it is so that hydrophilic substances, possessing an important nourishing function (such as glucosis, amino-acids) seem to penetrate much more easily than we could expect when we consider their physicochemical characteristics. This is the result of the fact that there exist specifical transport-mechanisms for these substances at the level of the endothelial cell-membranes, allowing the penetration of such substances. There exist, on the contrary, lipophilic components that penetrate the cerebral tissue much less strongly than we should expect. This happens because there also exist pumping-mechanisms at the level of the hemato-encephalic barrier. The concerning substance, which was recently discovered is the "glycoprotein P", which is also responsible for the "multi-drug-resistance" and for the resistance of tumors to cytostatics. This phenomenon relies on a very efficient pumping of substances which have penetrated cells in which this protein expressed itself in the membranous structure. In order to obtain a better understanding of the function of the hemato-encephalic barrier, comprising the transport of medicines, it is most important to have reliable experimental models. It is to that aim that, during former years, the technique of cultivating endothelial cerebrovascular cells was developed. These cells are isolated from brains of calves or rats and, subsequently, cultivated on a laboratory medium; about a week later, they have grown a single and confluent layer. This layer represents a kint of "hemato-encephalic barrier" in vitro, which allows us to study the transfer of substances through the layer and thus also the details concerning the transport mechanisms, as well as the factors influencing the permeability of the cells-layer (for instance the inflammatory stimuli). Concerning the "in vivo" research, the technique of intracerebral microdialysis in lab-animals proved to be very promising. In order to effect this microdialysis, a semipermeable microcannula is introduced in the brain tissue, across which an iso-osmotic liquid is being injected continuously. The substances staying in the interstitial liquid of the cerebral tissue will diffuse under the influence of a concentration gradient, into the dialysing liquid and they will also be ready to be analysed. Thanks to this technique, it is possible to follow, in the same animal, the evolution of the concentration in the brain of a substance which has, for instance been injected in a peripheral region. In this way, we obtain, indirectly and in vivo, informations about the functioning-process of the "hemato-encephalic barrier". We can, moreover, effect measures on a specific spot, for instance in tumoral brain tissue: this allows us to study the influence of specific transport-mechanisms. These rather recent techniques, as well in vitro as in vivo, will allow us, in consequence, to increase, during the next years, our understanding of the way the hemato-encephalic barrier functions as to the transfer of medicines towards the central nervous system. This understanding may lead us to new strategies allowing

The involvement of mdr1a P-glycoprotein (P-gP) on the tissue distribution of the multidrug resistance-reversing agent SDZ PSC 833 was assessed by use of mdr1a (-/-) mice. The mdr1a (-/-) and wild-type mdr1a (+/+) mice received a 4-h constantrate i.v. infusion (2 micrograms/min) of [14C]SDZ PSC 833. Mice were sacrificed at 0, 0.5, 1, 2 and 4 h during infusion and at 0.5, 1, 3, 8 and 24 h after stopping the infusion. Blood and tissues were analyzed on total (14C) and parental SDZ PSC 833 concentrations. Mdr1a (-/-) mice exhibited increased SDZ PSC 833 accumulation in cerebrum, cerebellum and somewhat in testes and small intestine compared with the wild-type mice. The difference between mdr1a (-/-) and (+/+) brain (cerebrum and cerebellum) penetration depended on SDZ PSC 833 blood concentrations, because this cyclosporin analog apparently governs its own brain penetration by inhibiting the P-glycoprotein pump in mdr1a (+/+) mice. Thus the mdr1a (-/-)/(+/+) ratio of brain concentrations tended to decrease and increase at high and low blood concentrations, respectively. These findings clearly demonstrate the interaction of SDZ PSC 833 with the P-glycoprotein present at the blood-brain barrier. The SDZ PSC 833 distribution in other mdr1a P-glycoprotein-expressed tissues, as well as its metabolism and elimination, was not affected by the mdr1a gene disruption. This suggests that factors other than mdr1a P-gP are involved in the disposition of this multidrug resistance-reversing agent.

Aminopyrine, antipyrine and trimethadione have been widely used for some time as probe drugs to assess non-selective P450 liver function. They have proved useful in evaluating pre- and post-operative liver function when performing surgery, transplantations, etc., in addition to a general evaluation of liver function and drug interactions. Progress has recently been made both in these non-selective P450 function tests and in the analysis of drug-metabolizing enzymes at a molecular level, which has resulted in more selective P450 function tests. The caffeine (CYP1 A2), chlorzoxazone (CYP2E1), lidocaine (CYP3 A) and midazolam (CYP3 A) function tests and the erythromycin breath test (CYP3 A) are currently being used as specific probes. The future use of these tests needs to be discussed in terms of potential clinical implications.

Epidural administration of an aqueous suspension of n-butyl-p-aminobenzoate (BAB) to humans results in long-lasting sensory blockade without motor block. The dose-response of BAB administered epidurally and intrathecally as a solution was studied in rats to define the local anesthetic properties in an established animal model.The time course of changes in tail withdrawal latency and motor function were determined in rats after epidural or intrathecal administration of solutions of BAB or bupivacaine. The dose-response relation was determined and median effective dose values were calculated.After epidural and intrathecal administration of BAB solutions, the onset and duration of the antinociceptive action were comparable to bupivacaine. Median effective dose values for tail-withdrawal latency of 6 s or more were significantly greater for BAB. After both routes of administration, BAB clearly affected motor function.When administered epidurally and intrathecally as a solution, BAB is a local anesthetic of relative low potency with onset and duration of action comparable to those of bupivacaine. These findings suggest that the long-lasting action obtained after applying BAB suspension results from the slow dissolution (continuous release) of the solid BAB deposited in the epidural space.

The effect of lipopolysaccharide (LPS) on cultured cerebral endothelial cells was investigated to assess the changes in the trans endothelial electrical resistance (TEER) across the blood-brain barrier that may occur during inflammatory diseases of the central nervous system. Primary cultures of bovine cerebral endothelial cells were cultured to tight monolayers with a TEER of 250 to 300 omega.cm2 on polycarbonate Transwell filters. LPS induced a time- and dose-dependent decline in TEER. Transport of the hydrophilic model compounds sodium fluorescein and fluorescein dextran (MR, 4 kDa) across monolayers of bovine cerebral endothelial cells increased more than 3-fold after treatment of the cells with LPS (50 ng/ml). Treatment of the monolayers with various concentrations of LPS caused a 3-to 4-fold increase in the permeability of bovine cerebral endothelial cells for [125I]bovine serum albumin, which was also preceded by a decrease in TEER. The reduction of TEER by LPS could be inhibited completely by indomethacin (10(-6)M for 30 min), a cyclooxygenase inhibitor, but not by dexamethasone, a glucocorticoid (10(-7) M for 16 hr). In conclusion, LPS administration to blood-brain barrier endothelial cells causes a decrease in TEER which leads to enhanced transport of low and high molecular weight molecules. During this process the production of eicosanoids by the endothelial cells seem to play a key role.

The transport of the hydrophilic model compound sodium fluorescein into the cerebrospinal fluid (CSF) of rats was studied during experimental allergic encephalomyelitis (EAE), as a model for local central nervous system (CNS) inflammatory disease, and after a single injection of a pyrogenic dose of lipopolysaccharide (LPS), as a model for a general inflammation.Transport of sodium fluorescein was measured by means of serial CSF and plasma sampling. Transport of this hydrophilic model compound was studied in Lewis rats suffering from EAA and three hours after LPS administration in male Wistar rats.During acute EAE, sodium fluorescein concentrations in the CSF increased twofold compared to control animals, whereas plasma kinetics were comparable within both groups. After i.v. LPS administration, however, plasma as well as CSF kinetic parameters of sodium fluorescein concentration were significantly changed from those seen in control animals. Transport of sodium fluorescein from plasma into the CSF was calculated as the ratio Area Under the Curve (AUC)CSF/AUCPLASMA. During acute EAE this ratio increased 2-fold compared to control animals, whereas after i.v. LPS administration it was not significantly different from the one obtained in control animals.These results suggest an opening of the blood-brain barrier (BBB) during a cerebral inflammatory response, like acute EAE, but not after LPS administration.

The use of intracerebral microdialysis as a tool to measure the penetration of anticancer agents in brain tumor was investigated.Following intravenous (iv) administration of 75 mg/kg. concentration-time profiles of methotrexate (MTX) were determined in brain cortical dialysate and in plasma. The individual ratio of the area under the curve of MTX in brain dialysate over that in plasma (MTX penetration) was determined in normal brain, in tumor-bearing brain and in brain after sham tumor implantation. Individual brains were examined histologically on the presence of tumor, as well as for other factors that might influence local MTX penetration. Histological scores were related to the individual data on penetration of MTX.MTX penetration values were higher in cortical brain at the site of the tumor, as compared to the levels measured in normal or sham implanted brain (mean increase to 250%). In the cortical brain contralateral to the tumor, MTX penetration values were found to be lower than in normal brain (mean reduction of 65%). Furthermore, it appeared that in the absence of tumor tissue, the presence of exudate around the probe was independently associated with increased penetration of MTX into the brain.Tumor tissue appeared to be the most important parameter in changing local MTX penetration in brain after tumor implantation. In general, it is anticipated that intracerebral microdialysis combined with histological examination can be used to investigate effects of brain tumor presence on regional (periprobe) penetration of anticancer drugs into the brain.

Several studies have suggested that the glutathione/glutathione S-transferase (GSH/GST) system is involved in resistance of tumors toward ifosfamide and other cytostatic agents. Besides, ifosfamide metabolites (in vitro) as well as ifosfamide treatment (in vivo) have been shown to decrease cellular GSH availability. In the present study, the in vivo effects of three different ifosfamide treatment schedules on the GSH/GST system were studied in patients with advanced cancers (n = 24): continuous i.v. infusions of 1300 mg/m2 daily for 10 days and 5000 mg/m2/day for 24 h, as well as a 4-h infusion of 3000 mg/m2 daily for 3 days. The GSH/GST system was characterized by administering bromisoval, a probe drug to assess GSH conjugation activity in vivo, as well as by daily monitoring of GSH concentrations in blood cells and plasma. Bromisoval pharmacokinetics was assessed before and at the end of the ifosfamide treatment. Blood cell GSH levels decreased significantly (P0.05) during the 3- and 10-day ifosfamide treatment schedules; the 24-h treatment had no effect. The ifosfamide treatment schedules had only minimal effects on bromisoval pharmacokinetics. Assuming that the kinetics of the probe drug provide an accurate reflection of enzyme activity, this suggests that GST activity remains unchanged. Because GSH conjugation of bromisoval enantiomers requires both GST activity and GSH availability, these results also indicate that, despite the 35% decrease in GSH in blood cells of two patient groups, the GSH availability of the cancer patients was not rate-limiting for GSH conjugation of bromisoval enantiomers. If GSH levels in blood cells reflect those in tumors/other tissues, the present results indicate that ifosfamide may be used clinically to decrease GSH levels. However, whether a 35% decrease is sufficient to increase tumor sensitivity toward (other) cytostatics remains uncertain.

The influence of ageing and dietary restriction (DR) on the in vivo activities of different P450 enzymes was studied longitudinally in female BN/BiRij rats. For this purpose, antipyrine (AP) and theophylline (TH) were used as substrates. The metabolic clearances of AP (CIm AP) and TH (CIm TH) were used as indicators for P450 enzyme activities in vivo. Therefore, we also included the assessment of the clearances of formation of three AP metabolites, i.e., 3-hydroxymethylantipyrine (CI--HMA), 4-hydroxyantipyrine (CI--OHA) and norantipyrine (CI--NORA). Ninety, 50 and 10% survival times were prolonged significantly in DR rats. In control animals, the contribution to the metabolism of AP in the formation of HMA, OHA and NORA, expressed as percentage of the dose, decreased with ageing, indicating that other pathways compensate for this decrease. Only a significant decrease in the metabolism to OHA was observed in DR animals. CI--HMA, CI--OHA and CI--NORA showed an age-related decrease in the control rats, whereas in the DR rats an age-related decrease was observed for CI--HMA and CI--OHA. The results of the present study suggest that the decrease in the activities of the P450 enzymes involved in the formation of HMA, OHA and NORA have a later onset in the DR rats. In conclusion, DR not only has a strong positive influence on the health and life span of the rats, but also results in a delayed onset of the decrease in activity of certain P450 enzymes.

The aim of this study was to determine whether changes in the transport of drugs into the brain could be determined by in vivo intracerebral microdialysis. Atenolol was used as a model drug to determine blood-brain barrier (BBB) transport characteristics. In rats, unilateral opening of the blood-brain barrier was achieved by infusion of hyperosmolar mannitol (25%, w/v) into the left internal carotid artery. BBB transport, expressed as the ratio of the area under the curve (AUC) of atenolol in brain extracellular fluid over plasma, was three times higher for the mannitol treated hemisphere as compared with the contralateral brain or after infusion of saline, being (mean +/- SEM) 0.094 +/- 0.024 (n = 16), 0.029 +/- 0.007 (n = 12) and 0.030 +/- 0.009 (n = 12) respectively. Further evaluation of the data indicated that for experiments performed in the morning the mannitol infusion had little effect on the extent of transport of atenolol into the brain, while in the afternoon BBB transport was about 10-fold higher than in the contralateral and saline group. The mean "afternoon" ratios +/- SEM were 0.155 +/- 0.038 (n = 8), 0.012 +/- 0.003 (n = 6) and 0.018 +/- 0.006 (n = 6) respectively. It is concluded that intracerebral microdialysis is capable of revealing changes in BBB transport and regional and time-dependent differences in drug levels can be demonstrated with the use of this technique.

The purpose of this investigation was to determine the effect of experimental conditions on the concentrations of atenolol and acetaminophen in brain microdialysate, and to investigate the feasibility of performing repeated experiments within individual rats. Following intravenous bolus administration, reproducible concentration-time profiles were obtained in plasma and in brain dialysate. Based on corrections for in vitro recoveries of the intracerebral probe, the estimated ratio of the AUC in brain extracellular fluid (AUCbrain ECF) over the AUC in plasma (AUCplasma) +/- S.E.M. was 3.8 +/- 0.6% (n = 6) for atenolol and 18 +/- 2% (n = 6) for acetaminophen. Upon intracerebroventricular administration, interanimal differences in kinetics of acetaminophen in brain dialysate were observed while the concentrations of atenolol were below the detection limit of the assay. The influence of the use of isotonic versus hypotonic perfusate solutions on AUCbrain ECF values after intravenous bolus administration of both drugs was determined. Repeated experiments with the isotonic perfusate (24, 48 and 78 h post-surgery) resulted in AUCbrain ECF values with the ratio of 100: 98: 76% for acetaminophen and 100: 103: 98% for atenolol. Using a hypotonic perfusion solution the ratio of AUCbrain ECF values was 100: 154: 114% for acetaminophen and 100: 378: 427% for atenolol. A clear effect of the temperature of the hypotonic perfusate (24 vs 38 degrees C) on acetaminophen AUCbrain ECF values was revealed. The ratio of AUCbrain ECF values obtained at 24: 38 degrees C was 192: 100%.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of anisotonic solutions on the enhancement of the transport of hydrophilic model compounds across monolayers of Caco-2 and HT-29.cl19A intestinal epithelial cells was studied. In filter-grown monolayers of the highly differentiated villus-like Caco-2 cell line, a profound and dose-dependent drop in the transepithelial electrical resistance was found after apical treatment with a 30 or a 50% hypotonic solution (200 and 150 mOsmol, respectively). This drop was not observed after basolateral and two-sided application of a 50% hypotonic solution. During apical hypotonic treatment a 12- and 8-fold increase also was observed in transepithelial transport of two hydrophilic model compounds, i.e., fluorescein-Na and fluorescein-isothiocyanate-labeled dextran, MW 4000, respectively. Through confocal laser scanning microscopy, it was revealed that this enhanced transport was predominantly via the paracellular route. Moreover, morphological changes in the cell layers indicating cell swelling were observed after apical hypotonic, but not after basolateral or bilateral treatment, probably resulting from an incomplete regulatory volume decrease response. This swelling, and slight lateral retraction of the cells, allowed the hydrophilic compounds to pass between the cells. The effects of hypotonic challenge also were studied in monolayers of the more crypt cell-like HT-29.cl19A cell line. After apical hypotonic shock, these cells showed no effect on transepithelial electrical resistance, whereas an increase was observed after basolateral and bilateral treatment. Hypotonic shock failed to increase the transport of the hydrophilic model compounds in this cell line.(ABSTRACT TRUNCATED AT 250 WORDS)

Confocal laser scanning microscopy (CLSM) was used to quantify and visualize the transport of the octapeptide and somatostatin analogue, octreotide (SMS 201-995, Sandostatin), across monolayers of bovine cerebrovascular endothelial cells, an in vitro model of the blood-brain barrier. The concentrations of octreotide and its conjugates in the cell culture medium were determined by radioimmunoassay (RIA). Two fluorescent conjugates of octreotide (FITC- and NBD-octreotide) were used to obtain CLSM images. The peptides did not undergo significant degradation in the presence of brain endothelial cell monolayers. The transport rate of octreotide expressed as clearance (Cl) and endothelial permeability (Pe) did not depend on either the initial concentration (between 10 nM and 1 microM) or the site of administration (luminal or abluminal side of the monolayer), indicating the absence of saturable and/or asymmetrical transport mechanisms. The Pe of octreotide and that of the paracellular permeability marker fluorescein correlated well. Although the conjugates are more lipophilic than octreotide itself, they exhibited lower Cl and Pe, values probably because of their larger molecular size. On the CLSM images, FITC-octreotide was present only in the intercellular space, while the cells did not exhibit detectable fluorescence. Transport studies and CLSM images suggest that octreotide passes the endothelial monolayer primarily via the paracellular route without significant contribution of carrier-mediated transport.

The transport of the antiviral nucleoside analogue zidovudine (3'-azido-3'-deoxythymidine; AZT) into the central nervous system (CNS) was characterized in vitro and in vivo. The in vitro model consisted of primary cultures of isolated bovine capillary endothelial cells. The transport rate of AZT across the monolayer, expressed as endothelial permeability P, was determined following luminal and abluminal administration. P did not differ between the two administration sites (luminal, 1.65 +/- 0.44 cm/min/10(3); abluminal, 1.63 +/- 0.28 cm/min/10(3)). The transport of AZT across the endothelial cell monolayer was found to be concentration independent in the range between 0.4 and 50 micrograms/mL. AZT transport was not affected by pretreatment of the cells with either metabolic inhibitors (DODG and DODG/NaN3) or probenecid. This suggests that AZT passes the monolayer mainly by passive diffusion. The in vivo transport of AZT across the blood-brain barrier and the blood-CSF barrier was studied in male Wistar rats after coadministration of potential inhibitors of active transport of AZT: probenecid (organic anion transport) and thymidine (nucleoside transport). Intracerebroventricular and intravenous coadministration of probenecid caused a significant (P0.001) increase in the CSF/plasma concentration ratio compared to the control phase, indicating that the organic anion carrier is involved in AZT transport from CSF to blood. Since there was no effect of probenecid on the transport of AZT in vitro, it is suggested that this carrier is located at the choroid plexus. Coadministration of thymidine did not affect the CSF/plasma concentration ratio, suggesting that a nucleoside carrier system is not involved in AZT transport into or out of the CNS.

The influence of aging on the metabolism of antipyrine (AP) and hexobarbital enantiomers (R-HB and S-HB) with and without phenobarbital (PB) induction was investigated in a longitudinal study in rats aged 6, 12, 24 and 30 months. The metabolic clearances of AP (Clm AP), R-HB (Clm R-HB) and S-HB (Clm S-HB) were used as indicators for P450 enzyme activities in vivo. This also included the assessment of the clearances of formation of three AP metabolites, 3-hydroxymethylantipyrine (Cl--HMA), 4-hydroxyantipyrine (Cl--OHA) and norantipyrine (Cl--NORA). Aging appeared to have little influence on the pharmacokinetics of the model compounds. By contrast, the influence of PB pretreatment on Clm AP changed dramatically with aging. The extent of induction decreased from 4.5-fold at 6 months to 1.7-fold at 30 months. Aging influenced the clearances of formation of the three metabolites differentially. Clm S-HB was about six times higher than Clm R-HB without induction. After PB induction, S-HB did not reach detectable levels in plasma at 6, 12 and 24 months. At 30 months, PB pretreatment resulted in a significantly decreased Clm S-HB when compared with the uninduced state. The extent of induction of R-HB metabolism had decreased strongly at 24 and 30 months. The present results clearly indicate that in the aged rat, the P450 enzyme system is much less sensitive to PB induction.

Human beings live in changing environments in which some factors change very rapidly and others more slowly. Organisms must adapt themselves to these changes if they are to survive and reproduce. A specific aspect of the adaptation is the mechanism by which organisms try to maintain homeostasis in respect to the chemical environment. Organisms are endowed with the enzyme machinery which disposes of chemicals that have entered the body. These enzymes are called drug- or xenobiotic-metabolizing enzymes and they have been dealt with in numerous monographs, review articles, and symposia during the past 30 years or so (see, e.g., Jenner and Testa 1980; Ortiz De Montellano 1986; Benford et al. 1987; Alvares and Pratt 1990; Tukey and Johnson 1990).

The effects of sodium salicylate and sodium tauro-24,25-dihydrofusidate (STDHF) on the aqueous permeability of confluent monolayers of Caco-2 cells were studied. Measurements of transepithelial electrical resistance (TEER) showed a concentration-dependent effect of both compounds after apical incubation for 1 hr. Reductions in TEER resulting from EC50 concentrations (2.8 mM for STDHF; 173 mM for salicylate) were reversible within 5.75 hr. The transpithelial fluxes of two hydrophilic model compounds, sodium fluorescein F (molecular weight 376) and a fluorescein isothiocyanate-labeled dextran (mean molecular weight 4000) was significantly increased by STDHF (2.8 mM). Sodium salicylate (173 mM) only enhanced the transport of sodium fluorescein significantly. At the EC50 concentrations, confocal laser scanning microscopy (CLSM) visualized both fluorescent tracers mainly in the paracellular route. With higher enhancer concentrations (373 mM sodium salicylate and 8 mM STDHF), both transport markers appeared intracellularly as a result of cell death. STDHF rapidly extracted an exogenous lipophilic membrane probe, 5-(N-hexadecanoyl)aminofluorescein (HEDAF), from the apical part of Caco-2 plasma membranes, indicating qualitatively that STDHF interacts with the lipid portion of cell membranes. These results suggest that both sodium salicylate and STDHF can be used to reversibly increase paracellular permeability of Caco-2 cell monolayers, whereby STDHF appears to be advantageous compared to sodium salicylate. By adapting the Costar cell culture system to CLSM, we have shown that this technique is suitable to study membrane interactions qualitatively and for visualizing transport routes of hydrophilic tracers through nonfixed, filter-grown monolayers.

Primary cultures of bovine brain capillary endothelial cells (BCEC), possessing tight junctions and high levels of gamma-glutamyl transpeptidase, were used as an in vitro model for the blood-brain barrier. The interaction of acetylated low density lipoprotein (AcLDL) with BCEC was studied to characterize the scavenger receptor on these cells. A saturable high affinity binding site was found with a dissociation constant of AcLDL of 5.4 micrograms/ml (3.1 nM) and a maximal binding ranging from 284 to 626 ng of AcLDL/mg of cell protein for eight primary cultures, and independent of the presence of calcium. Cell association was coupled to degradation, and both could be effectively competed for by polyinosinic acid and AcLDL but not by low density lipoprotein or by high density lipoprotein. Prolonged incubation showed an accumulation of the ligand in the cells. The rate of degradation of AcLDL was approximately 10-20-fold lower in BECEC than that of peripheral endothelial cells. No evidence for lysosomal degradation could be obtained. Binding of 1,1'-dioctadecyl-3,3,3'-tetramethylindocarboxyamine perchlorate-labeled AcLDL by BCEC was observed, which could be competed for by an excess of unlabeled AcLDL and polyinosinic acid. We have shown that in vitro BCEC possesses specific binding sites for AcLDL, whereas these cells show a relatively low degradative capacity.

1. In a previous study it was demonstrated that a decrease in liver blood flow produced a decrease in clearance of recombinant human tissue-type plasminogen activator (rt-PA). 2. The purpose of this randomized, double-blind, placebo-controlled, three-way, cross-over investigation was to determine the effect of nifedipine (20 mg orally), a compound that increases liver blood flow, on plasma concentrations of steady state endogenous and recombinant tissue-type plasminogen activator (t-PA and rt-PA) (35 mg of rt-PA over 2 h) in nine healthy male volunteers. 3. Nifedipine increased liver blood flow by 95% (42-167%) (mean (95% confidence interval)) as assessed by indocyanine green (ICG, 0.5 mg kg-1 i.v. bolus injection) clearance. 4. Nifedipine did not influence the plasma concentrations of total rt-PA antigen and activity as evaluated by the areas under the rt-PA curves from 30 min (time at which nifedipine was ingested) to 90 min during the rt-PA infusion (P > 0.05) and by analysis of a possible treatment x time interaction (P > 0.05). In addition, the plasma concentrations of endogenous t-PA remained unchanged when nifedipine was given alone. 5. In conclusion, by using nifedipine as a model compound it was demonstrated that the combination of rt-PA and a compound which increases liver blood flow probably does not lead to substantial changes in plasma concentrations of rt-PA.

The disposition of ciprofloxacin and pefloxacin in the rat cerebrospinal fluid (CSF) was investigated after i.v. and i.c.v. administration. After injection into the lateral ventricle, the terminal half-life of pefloxacin was shorter than that of ciprofloxacin. After i.v. infusions, the relative CSF exposure, expressed as CSF: area under the plasma concentration time curve ratio, were found to be 10.4 +/- 2.8% for ciprofloxacin and 42.4 +/- 3.0% for pefloxacin. The unit impulse response methodology was applied in order to assess the CSF transport profile. The plasma-CSF transport clearance of pefloxacin and the total amount of drug transported into the CSF were significantly higher compared with ciprofloxacin. Although pefloxacin exhibited a linear CSF transport profile, the plasma-CSF transport clearance of ciprofloxacin was found to be nonlinear at the dose level studied. Pefloxacin was converted in the brain to the active metabolite norfloxacin (N-desmethyl pefloxacin). The difference in CSF exposure of both quinolones and the presence of active metabolites of N-methylated quinolones in the CSF may be of clinical relevance in the treatment of CNS infections, but differences in antimicrobial activity have to be taken into account as well.

The effects of heparin (5,000 IU i.v.) and the low molecular weight heparinoid Org 10172 (Orgaran) (3,250 anti-Xa units i.v.) on components of the fibrinolytic system were studied in two double-blind, randomised, placebo-controlled, cross-over trials using healthy subjects. In study A (n = 6) the effects were studied during rest and standardized exercise and in study B (n = 6) during a low dose infusion of recombinant tissue-type plasminogen activator (rt-PA; 80 micrograms over 16 min). At rest, heparin and Org 10172 did not influence the plasma concentrations of endogenous t-PA antigen and activity, urokinase-type PA (u-PA) antigen, plasmin activatable pro-urokinase (scu-PA), active urokinase (tcu-PA) and plasminogen activator inhibitor-1 (PAI-1) antigen. Recombinant t-PA antigen and activity during rt-PA infusion were also not affected. During exercise, neither heparin nor Org 10172 influenced the area under the curve (AUC) of t-PA and u-PA antigen and t-PA activity when compared with placebo. Unexpectedly, after heparin the AUC of t-PA activity was 49% larger (range +19 to +245%) than after Org 10172 (p0.05). The last difference was considered spurious, scu-PA, tcu-PA and PAI-1 antigen levels at 2 min after termination of exercise were unaffected by both compounds (p0.05). Sulphated polysaccharides do not increase fibrinolytic activity of the plasma by changing the concentrations of the components of the fibrinolytic system.