Is there any future for felbamate treatment?

Felbamate (2-phenyl-1,3-propanediol dicarbamate), a representative of novel antiepileptic drugs (AESs), proved to have broad-spectrum anticonvulsive activity. Particularly beneficial efficacy was found against partial seizures and Lennox-Gastaut syndrome. Therefore, felbamate started to be indicated not only as an adjunctive antiepileptic drug but also in monotherapy. Unfortunately, it was also evidenced that the drug may induce aplastic anemia or hepatic failure. The former complication was frequently described in patients with previously diagnosed hematopoetic disturbances. Thirty-four cases of well-documented bone marrow suppression, occurred fatal in thirteen cases. Subsequently, felbamate's usage was essentially restricted and at present felbamate is not a first-line AED. However, excluding anemia-prone individuals, new possibilities may open for felbamate position in add-on therapy of drug-resistant epilepsy. Experimental studies provide a good theoretical basis for this kind of treatment.

The immunosuppressant FTY720 is phosphorylated by sphingosine kinase type 2

The potent immunosuppressive drug FTY720, a sphingosine analog, induces redistribution of lymphocytes from circulation to secondary lymphoid tissues. FTY720 is phosphorylated in vivo and functions as an agonist for four G-protein-coupled sphingosine-1-phosphate receptors. The identity of the kinase that phosphorylates FTY720 is still not known. Here we report that although both sphingosine kinase type 1 (SphK1) and type 2 (SphK2) can phosphorylate FTY720 with low efficiency, SphK2 is much more effective than SphK1. FTY720 inhibited phosphorylation of sphingosine catalyzed by SphK2 to a greater extent than it inhibits SphK1. Thus, SphK2 may be the relevant enzyme that is responsible for in vivo phosphorylation of FTY720.

Pharmacodynamics, pharmacokinetics, and safety of multiple doses of FTY720 in stable renal transplant patients: a multicenter, randomized, placebo-controlled, phase I study

BACKGROUND

FTY720, a novel immunomodulator, displays potent immunosuppressive activity in a variety of preclinical transplant models. This study examined the safety, pharmacodynamics, and pharmacokinetics of multiple doses of FTY720 in stable renal transplant patients.

METHODS

This randomized, multicenter, double-blind, placebo-controlled, phase I study included adults who had been maintained on a regimen of cyclosporine A (CsA) microemulsion and prednisone (or its equivalent) for at least 1 year after renal transplantation. Patients received once-daily doses of 0.125, 0.25, 0.5, 1.0, 2.5, or 5.0 mg FTY720, or placebo for 28 days. After completion of study drug administration, the patients were monitored until day 56 by serial laboratory tests, clinical examinations, and recording of adverse events. The study includes 76 treatment courses (61 FTY720 and 15 placebo), with 65 patients enrolled once and 11 reenrolled.

RESULTS

FTY720 doses greater than or equal to 1.0 mg/day produced a significant reduction in peripheral blood lymphocyte count by up to 85%, which reversed within 3 days after discontinuation of study medication. Compared with placebo-treated patients, FTY720 subjects did not show a major increase in adverse events or a change in renal function. Pharmacokinetic measurements revealed that FTY720 displayed linear relations of doses and concentrations over a wide range, but had no effect on CsA exposure.

CONCLUSIONS

At doses up to 5.0 mg/day for 28 days, stable renal transplant patients treated with FTY720 in combination with CsA and prednisone displayed a dose-dependent, reversible decline in peripheral blood lymphocytes without an enhanced incidence of collateral toxicities, except possibly bradycardia.

Brain Access and Anticonvulsant Efficacy of Carbamazepine, Lamotrigine, and Felbamate in ABCC2/MRP2-Deficient TR- Rats

PURPOSE

Different adenosine triphosphate (ATP)-driven multidrug transporters have been described to be expressed in the luminal membrane of blood-brain barrier (BBB) endothelial cells. At this site, multidrug transporters have been suggested to restrict penetration of drugs into the brain. Increasing evidence suggests that overexpression of different multidrug transporters occurs in the region of the epileptic focus of pharmacoresistant epilepsy patients. Based on the assumption that antiepileptic drugs (AEDs) are substrates of these transporters, this overexpression may limit access of AEDs to epileptic neurons and may contribute to drug-refractoriness. In a recent study, overexpression of multidrug resistance protein 2 (ABCC2; MRP2) was reported in BBB endothelial cells of epileptic focal tissue from pharmacoresistant patients. With brain microdialysis, we recently demonstrated that the AED phenytoin is subject to transport by ABCC2 at the BBB, whereas phenobarbital does not seem to be a substrate of ABCC2.

METHODS

We investigated whether ABCC2 is functionally involved in transport of the AEDs carbamazepine (CBZ), lamotrigine (LTG), and felbamate (FBM) across the BBB. The distribution of these AEDs into the brain of ABCC2-deficient TR- rats was determined.

RESULTS

AED concentrations in plasma and brain extracellular space of these mutant rats did not differ significantly from those of rats of the corresponding background strain. In the amygdala-kindling model of epilepsy, the anticonvulsant efficacy of LTG and FBM was comparable in both groups of rats. In contrast, CBZ exhibited a higher anticonvulsant activity in kindled ABCC2-deficient rats as compared with nonmutant rats.

CONCLUSIONS

In this present study, the microdialysis results gave no evidence that ABCC2 function modulates entry of CBZ, LTG, and FBM into the CNS of naïve rats. However, ABCC2 deficiency was associated with an increased anticonvulsant response of CBZ in the kindling model. Future investigations are planned to identify the underlying mechanism for this difference, clarifying whether a pharmacokinetic difference is detectable only when brain access of CBZ is compared in kindled ABCC2-deficient rats and kindled nonmutant rats, which may have an increased expression of ABCC2 in response to seizures. The data substantiate that ABCC2-deficient TR- rats are a useful tool for defining the role of ABCC2 for transport of AEDs, and give evidence that the use of kindled TR- rats may provide important supplementary information.

Phosphorylation of the immunomodulatory drug FTY720 by sphingosine kinases

The immunomodulatory drug FTY720 is phosphorylated in vivo, and the resulting FTY720 phosphate as a ligand for sphingosine-1-phosphate receptors is responsible for the unique biological effects of the compound. So far, phosphorylation of FTY720 by murine sphingosine kinase (SPHK) 1a had been documented. We found that, while FTY720 is also phosphorylated by human SPHK1, the human type 2 isoform phosphorylates the drug 30-fold more efficiently, because of a lower Km of FTY720 for SPHK2. Similarly, murine SPHK2 was more efficient than SPHK1a. Among splice variants of the human SPHKs, an N-terminally extended SPHK2 isoform was even more active than SPHK2 itself. Further SPHK superfamily members, namely ceramide kinase and a "SPHK-like" protein, failed to phosphorylate sphingosine and FTY720. Thus, only SPHK1 and 2 appear to be capable of phosphorylating FTY720. Using selective assay conditions, SPHK1 and 2 activities in murine tissues were measured. While activity of SPHK2 toward sphingosine was generally lower than of SPHK1, FTY720 phosphorylation was higher under conditions favoring SPHK2. In human endothelial cells, while activity of SPHK1 toward sphingosine was 2-fold higher than of SPHK2, FTY720 phosphorylation was 7-fold faster under SPHK2 assay conditions. Finally, FTY720 was poorly phosphorylated in human blood as compared with rodent blood, in line with the low activity of SPHK1 and in particular of SPHK2 in human blood. To conclude, both SPHK1 and 2 are capable of phosphorylating FTY720, but SPHK2 is quantitatively more important than SPHK1.

Oral absorption, metabolism and excretion of 1-phenoxy-2-propanol in rats

1. This study was designed to determine the absorption, metabolism and excretion of 1-phenoxy-2-propanol in Fischer 344 rats following oral administration in an effort to bridge data with other propylene glycol ethers. 2. Rats were administered a single oral dose of 10 or 100 mg kg(-1) 14C-1-phenoxy-2-propanol as a suspension in 0.5% methyl cellulose ether in water (w/w). Urine was collected at 0-12, 12-24 and 24-48 h and faeces at 0-24 and 24-48 h post-dosing and the radioactivity was determined. Urine samples were pooled by time point and dose level and analysed for metabolites using LC/ESI/MS and LC/ESI/MS/MS. 3. The administered doses were rapidly absorbed from the gastrointestinal tract and excreted. The major route of excretion was via the urine, accounting for 93 +/- 5% of the low and 96 +/- 3% of the high dose. Most of the urinary excretion of radioactivity occurred within 12 h after dosing; 85 +/- 2% of the low and 90 +/- 1% of the high dose. Total faecal excretion remained < 10%. Rats eliminated the entire administered dose within 48 h after dosing; recovery of the administered dose ranged from 100 to 106%. Metabolites tentatively identified in urine were conjugates of phenol (sulphate, glutathione) with very low levels (< 2%) of hydroquinone (glucuronide), conjugates of parent compound (glucuronide, sulphate) and a ring-hydroxylated metabolite of parent. There was no free parent compound or phenol in non-acid-hydrolysed urine. In acid-hydrolysed urine, 61% of the dose was identified as phenol and 13% as 1-phenoxy-2-propanol. Although the parent compound was stable to acid hydrolysis, some of the phenol in acid hydrolysed urine may have arisen from degradation of acid-labile metabolite(s) as well as hydrolysis of phenol conjugates. 4. Rapid oral absorption, metabolism and urinary excretion of 1-phenoxy-2-propanol in rats were similar to other propylene glycol ethers.

Hydrolysis kinetics of propylene glycol monomethyl ether acetate in rats in vivo and in rat and human tissues in vitro

The kinetic equivalency of propylene glycol monomethyl ether (PGME), derived from propylene glycol monomethyl ether acetate (PGMEA), as well as the parent compound (PGME) following intravenous administration to Fischer 344 rats was evaluated. In addition, in vitro hydrolysis rates of PGMEA in blood and liver tissue from rats and humans were determined. The blood kinetics were determined following iv administration to rats of PGME and PGMEA of low [10 and 14.7 mg/kg body weight (bw)] or high (100 and 147 mg/kg) equimolar dosages of PGME and PGMEA, respectively. The blood time courses of PGME elimination for both dosages of both compounds were identical. Half-lives of PGMEA elimination following iv administration of 14.7 or 147 mg PGMEA/kg bw were calculated to be 1.6 and 2.3 min, respectively. Rat and human in vitro hydrolysis rates of PGMEA were determined by incubation of 5 or 50 microg PGMEA/ml in whole blood or liver homogenate. The rate of loss of PGMEA was more rapid in rat blood than in human blood, with hydrolysis half-lives of 36 and 34 min in human blood and 16 and 15 min in rat blood for the 5 and 50 microg/ml concentrations of PGMEA, respectively. In contrast the rate of loss of PGMEA in human and rat liver homogenate incubations was similar, 27-30 min and 34 min, respectively. These data demonstrate the rapid hydrolysis of PGMEA in vivo to its parent glycol ether, PGME and that, once hydrolyzed, the kinetics for PGME derived from PGMEA are identical to that for PGME. This study supports the use of the toxicological database on PGME as a surrogate for PGMEA.

Is the interaction between felbamate and valproate against seizures induced by 4-aminopyridine and pentylenetetrazole in mice beneficial?

We compared the effects of adding a non-protective dose of valproate (VPA) to increasing single doses of felbamate (FBM) with those of monotherapy and vice versa in CD1 mice. Anticonvulsant effects were evaluated against seizures induced by 14 mg kg(-1) of 4-aminopyridine (4-AP) and by 110 mg kg(-1) of pentylenetetrazole (PTZ), and neurotoxicity by the rotarod test. The study also assessed changes in concentrations of anticonvulsants, gamma-aminobutyric acid (GABA) and glutamate in the whole brain. VPA increased the potency ratio of FBM against 4-AP (1.94, P<0.05) but not against PTZ. VPA increased the neurotoxicity of FBM (3.30, P<0.05) and the protective index of FBM was, therefore, reduced from 12.0 to 7.0 for the 4-AP model and from 11.8 to 5.2 for the PTZ model; VPA reduced brain FBM, and increased brain GABA in relation to FBM monotherapy. On the other hand, FBM increased the potency ratio of VPA against 4-AP (1.60, P<0.05) but not against the PTZ, and had no effect on the rotarod model. Therefore, the protective index increased from 1.1 to 1.6 for the 4-AP model and decreased from 1.9 to 1.7 for the PTZ model. FBM did not change brain VPA, and changes in brain GABA and glutamate were not clearly related to anticonvulsant effects. In conclusion, although the addition of a low dose of FBM to VPA was beneficial in the 4-AP model, the addition of a low dose of VPA to FBM was not; both combinations were disadvantageous in the PTZ model. This interaction appears to be pharmacodynamic because a pharmacokinetic mechanism was discarded.

FTY720: A new kid on the block for transplant immunosuppression

FTY720, a synthetic analogue of myriocin (ISP-1), is derived from culture filtrates of the fungus Isaria sinclairii. As a sphingosine analogue, FTY720 appears to undergo phosphorylation and thereby interact with specific G-protein-linked receptors. In vivo, FTY720 causes emigration of lymphocytes from peripheral blood to secondary lymphoid structures. Thus, the drug is the archetype of a new class of agents that alter cellular homing patterns: the adhesion-migration paradigm. Since FTY720 seems to spare nonspecific elements of host resistance, it may address the not infrequent complications of infections associated with existing therapies. In experimental rodent, canine and non-human primate models, FTY720 produces lymphopenia and immunosuppression, prolonging the survival of allografts. Because of synergistic interactions, it promotes the immunosuppressive effects not only of calcineurin antagonists, but also of proliferation signal inhibitors. These interactions proffer the possibility of large reductions in exposure to and mitigated toxicity of existing drugs. In humans, FTY720 causes dose-dependent peripheral blood lymphopenia, a reduced incidence of acute rejection episodes and only one apparent adverse reaction - a negative chronotropic effect - particularly after the loading dose. While the clinical utility of FTY720 is difficult to predict before completion of Phase III studies that elucidate its benefits versus unanticipated side effects, the initial data suggest several potential advantages: it does not produce hyperlipidaemia, diabetes mellitus, nephrotoxicity, neurotoxicity or myelosuppression, which are characteristic of other immunosuppressants. Furthermore, it displays high oral bioavailability and a low interindividual coefficient of variation. Clearly, structural analogues, as well as other agents that alter the balance of chemokines or affect cellular adhesion to activated endothelium, will represent important components of future regimens.

Pharmacodynamics of single doses of the novel immunosuppressant FTY720 in stable renal transplant patients

FTY720, a new and potent immunosuppressant, causes in animal models a rapid, reversible reduction of all subsets of peripheral blood lymphocytes, inducing their migration to secondary lymphoid organs. In this human phase I trial, the pharmacodynamics of single oral doses of FTY720 were evaluated. A randomized, double-blind, placebo-controlled, time-lagged study of six different single ascending oral doses of FTY720 ranging from 0.25 to 3.5 mg was conducted in stable renal transplant patients receiving a cyclosporine-based regimen. Absolute and subset lymphocyte counts, as well as absolute differential leukocyte counts, were determined by differential blood counts and flow cytometry at screening and multiple intervals thereafter. A pharmacodynamic model was established. Twenty-four single doses of FTY720 that were administered caused a transient, reversible pan-lymphopenia within 4 h. Lymphocyte subgroup analysis revealed that almost all subsets declined, with CD4- and CD45RA-positive cells being affected the most. Natural killer cells, granulocytes and monocytes were not influenced by FTY720. The lymphocyte count returned to baseline within 72 h in all dosing cohorts except the highest. Pharmacokinetik/pharmacodynamic modelling revealed a nonlinear dose effect and resulted in a good fit with observed values. These data show that FTY720 is highly effective in humans, with single oral doses of FTY720 ranging from 0.25 to 3.5 mg causing a reversible selective panlymphopenia.

The ideal pharmacokinetic properties of an antiepileptic drug: how close does levetiracetam come?

The pharmacokinetic properties of a drug are the primary deter-minant of the extent and duration of drug action, and influence susceptibility to clinically important drug interactions. Most of the older-generation antiepileptic drugs (AEDs) are far from ideal in terms of pharmacokinetics and interaction potential. For example, phenytoin, carbamazepine, and valproic acid exhibit non-linear kinetics; carbamazepine and valproic acid have relatively short half-lives; and most of these drugs cause either enzyme induction (phenytoin, phenobarbital, primidone, carbamazepine) or enzyme inhibition (valproic acid). Compared with older agents, certain new-generation AEDs offer a num-ber of pharmacokinetic advantages, particularly in terms of reduced inter-patient variability in drug clearance and a lower interaction potential. One of the most recently developed of these drugs, levetiracetam, comes especially close to fulfilling the desirable pharmacokinetic characteristics for an AED: (1) it has a high oral bioavailability, which is unaffected by food; (2) it is not significantly bound to plasma proteins; (3) it is eliminated partly in unchanged form by the kidneys and partly by hydrolysis to an inactive metabolite, without involvement of oxidative and conjugative enzymes; (4) it has linear kinetics; and (5) it is not vulnerable to important drug interactions, nor does it cause clinically significant alterations in the kinetics of concomitantly administered drugs. Although its half-life is relatively short (6 to 8 hours), its duration of action is longer than anticipated from its pharmacokinetics in plasma, and a twice-daily dosing regimen is adequate to produce the desired response.

Synergistic interaction between felbamate and lamotrigine against seizures induced by 4-aminopyridine and pentylenetetrazole in mice

We compared the effects of adding a nonprotective dose of felbamate to increasing single doses of lamotrigine with those of monotherapy and vice versa in CD1 mice. Anticonvulsant effects were evaluated against seizures induced by both 14 mg/kg of 4-aminopyridine and 110 mg/kg of pentylenetetrazole, and neurotoxic effects were evaluated by the rotarod test. Changes in anticonvulsants, gamma-aminobutyric acid (GABA) and glutamate concentrations in the whole brain were also assessed. Lamotrigine increased the potency ratio of felbamate against 4-aminopyridine (1.80, 95% confidence interval (CI) 1.23-2.65, P<0.05) but not against pentylenetetrazole nor on rotarod, the protective index being increased from 12.0 to 17.1 for 4-aminopyridine, with a reduction in brain felbamate, and with an increase in brain GABA. Felbamate increased the potency ratio of lamotrigine against 4-aminopyridine (4.35, 95% CI 2.05-9.25, P<0.05) but not on rotarod, the protective index being increased from 4.4 to 15.7; there were no changes in brain lamotrigine, and changes in brain GABA and/or glutamate were unrelated to the pharmacodynamic effects. In conclusion, a nonprotective dose of lamotrigine increased the therapeutic index of felbamate and vice versa, and these effects appeared to be pharmacodynamic.

Significance of 2-methoxypropionic acid formed from beta-propylene glycol monomethyl ether: integration of pharmacokinetic and developmental toxicity assessments in rabbits

Commercial grade propylene glycol monomethyl ether (PGME), which is composed of > 99.5% alpha-isomer and < 0.5% beta-isomer, has been shown in several studies to have a low potential for developmental toxicity. Nonetheless, questions have been raised about potential human developmental toxicity due to beta-PGME, because it can be metabolized to 2-methoxypropionic acid (MPA), a compound bearing structural similarity to the teratogen, methoxyacetic acid (MAA). Accordingly, a series of in vivo developmental toxicity, whole embryo culture, and in vivo pharmacokinetic experiments were conducted in New Zealand White rabbits (highly sensitive to these compounds) to better understand the developmental toxicity potential of MPA and the kinetics of its formation from beta-PGME. For the in vivo developmental toxicity studies, groups of 20 inseminated rabbits were gavaged with 0, 10, 26, or 78 mg/kg/day of MPA on gestation day (GD) 7-19, followed by fetal evaluation on GD 28. Results with MPA were compared with those of rabbits similarly dosed with 0, 2.5, 7.5, or 15 mg/kg/day of MAA. Developmental toxicity no-observable-effect levels (NOEL) were approximately 10-fold higher for MPA (26 mg/kg/day) than for MAA (2.5 mg/kg/day). Also, the severity of effects caused by MPA was less than that of MAA, and unlike MAA, MPA was not selectively toxic to the fetus. This differential toxicity was also seen in whole embryo cultures of GD 9 rabbit embryos, in which there were no adverse effects of MPA (1.0, 5.0 mM) or its parent compound, beta-PGME (0.5, 2.0 mM), but severe dysmorphogenesis in 100% of embryos cultured in 5.0 mM MAA. The pharmacokinetics study showed rapid and complete conversion of beta-PGME to MPA, with a relatively long elimination half-life (33-44 h) for MPA. However, peak and AUC concentrations of MPA in blood associated with the MPA LOEL dose of 78 mg/kg/day were 1.3 mM and 52.9 mM-h/l, respectively, suggesting a relatively high threshold based on internal dosimetry. Taken together, these data indicate a negligible risk of developmental toxicity due to MPA formation from the small amounts of beta-isomer present in commercial PGME.

Effects of cellulose derivatives and poly(ethylene oxide)-poly(propylene oxide) tri-block copolymers (Pluronic)surfactants) on the properties of alginate based microspheres and their interactions with phagocytic cells

The goal of this study was to examine the phagocytosis of alginate based microspheres with different surface properties. Favorable interaction with macrophages is critical for uptake subsequent processing of the microspheres used for oral vaccine delivery. We examined the effects of size of alginate microspheres and hydrophobicity on cellular uptake. We also examined the toxicity of formulation components to phagocytic cells. Alginate microspheres were made by the emulsion-cross-linking technique. Five different formulations of microspheres were evaluated for size, hydrophobicity, cellular uptake and toxicity to macrophages. The formulations examined were: alginate alone (A), alginate with methylcellulose (AA) AA with Pluronic L61 (AA61), alginate with hydroxypropyl methylcellulose (AK3), and AK3 with Pluronic (L61 (AK3 61). Microspheres with without poly-L-lysine (PLL) coating were tested. The mean volume sizes of A, AA, AA61, AK3, AK3 61 microspheres (MS) were 11, 10.5, 3.8, 8.7 and 3.9 mocrom, respectively. After coating them with PLL the mean volume sizes were 10.4, 10, 3.7, 8.8 and 3.5 microm, respectively. Hydrophobicity of the microspheres was evaluated by measuring contact angle on a glass slide coated with the microspheres. The contact angles measured using a goniometer on A, AA, AA61, AK3, AK3 61 MS were 20, 34.8, 71, 29 and 80 degrees, respectively whereas those MS coated with PLL were 49.7, 55.8, 91, 48.25 and 84.4 degrees, respectively. Cellular uptake studies using flow cytometery revealed that AA61 MS coated with PLL were phagocytosed most often by mouse macrophages. There was no statistically significant difference in cellular uptake among those MS without PLL coating. Toxicity to macrophages was shown to depend on the ratio of microspheres to cells. These studies suggest that formulation can dramatically affect the physical characteristics of alginate MS in ways that can affect how they will interact with cells in the body when administered as a vaccine delivery system.

Mechanisms of idiosyncratic drug reactions: the case of felbamate

Idiosyncratic drug reactions (IDR) are a specific type of drug toxicity characterized by their delayed onset, low incidence and reactive metabolite formation with little, if any, correlation between pharmacokinetics or pharmacodynamics and the toxicological outcome. As the name implies, IDR are unpredictable and often result in the post marketing failure of otherwise useful therapies. Examples of drugs, which have failed as a result of IDR in recent years, include trovafloxacin, zileuton, troglitazone, tolcapone and felbamate. To date there exists no pre-clinical model to predict these adverse drug reactions and a mechanistic understanding of these toxicities remains limited. In an attempt to better understand this class of drug toxicities and gain mechanistic insight, we have studied the IDR associated with a model compound, felbamate. Our studies with felbamate are consistent with the theory that compounds which cause IDR undergo bioactivation to a highly reactive electrophilic metabolite that is capable of forming covalent protein adducts in vivo. In additon, our data suggest that under normal physiological conditions glutathione plays a protective role in preventing IDR during felbamate therapy, further emphasizing a correlation between reactive metabolite formation and a toxic outcome. Clinical studies with felbamate have been able to demonstrate an association between reactive metabolite formation and a clinically relevant toxicity; however, additional research is required to more fully understand the link between reactive metabolite formation and the events which elicit toxicity. Going forward, it seems reasonable that screening for reactive metabolite formation in early drug discovery may be an important tool in eliminating the post-marketing failure of otherwise useful therapies.

Effects of experimental conditions on absorption of glycol ethers through human skin in vitro

OBJECTIVES

To determine effects of experimental variables on the dermal absorption of 2-ethoxyethanol (EE), 2-butoxyethanol (BE) and 1-methoxy-2-propanol (M2P) through human skin in vitro.

METHODS

Percutaneous absorption of EE, BE and M2P, in aqueous solution (3 mg ml(-1), 200 microl) or undiluted (10.5 microl), though full thickness or dermatomed human breast skin (0.64 cm(2) exposed area) was measured for 24 h using flow-through diffusion cells. Tissue culture medium was used as receptor fluid, with 2% (w/v) bovine serum albumin (BSA) or 2%-6% (w/v) polyethylene glycol 20 oleyl ether (PEG 20) added for some studies. Volatilised test compounds were trapped on charcoal filters placed above cells.

RESULTS

In aqueous solution, steady-state flux of BE (544+/-64 nmol cm(-2) h(-1)) exceeded that of EE (143+/-19 nmol cm(-2) h(-1)) and M2P (48+/-6 nmol cm(-2) h(-1)). Reducing the dose volume to 100 microl decreased the steady-state flux of BE by about 55%, though the flux of EE was approximately doubled. Doubling the dose concentration of EE increased the flux by about eight-fold. Using full thickness skin increased tau of both EE and BE and reduced the steady-state flux of BE. Absorption rates of undiluted solvents in finite doses exceeded those measured with aqueous solutions, though the apparent permeability coefficient was higher with aqueous doses. Addition of BSA or PEG 20 to receptor fluid markedly increased absorption in both aqueous and undiluted doses.

CONCLUSIONS

The dermal absorption potential of M2P from a liquid application was markedly lower than from EE or BE in all but infinite undiluted doses. The influence of receptor fluid on dermal absorption of glycol ethers could be relevant to prediction of absorption in vivo.

Renal chemoembolization with mitomycin c/Ethibloc: pharmacokinetics and efficacy in an animal model

BACKGROUND AND PURPOSE

Arterial embolization can be an alternative treatment for kidney malignancy. We investigated the efficacy of renal embolization with a combination of an occlusive agent (Ethibloc) and the cytotoxic substance mitomycin C (MMC) in an animal model.

MATERIALS AND METHODS

In 32 rats with implanted Yoshida sarcoma, nephrectomy was carried out 15, 30, 60, or 90 minutes after chemoembolization (1 mg v 2 mg of MMC/mL of Ethibloc) or chemoperfusion (1 mg of MMC/mL of NaCl) of the tumor-bearing kidney. The MMC tissue concentration was measured in the kidney specimens. Six dogs also underwent chemoembolization or chemoperfusion with monitoring of MMC serum concentration at the same intervals. We compared the survival time of rats with Yoshida sarcoma after chemoembolization (N = 15), chemoperfusion (N = 18), embolization (N = 18), nephrectomy (N = 21), and no treatment (N = 25).

RESULTS

The MMC tissue concentration in the rat model was much higher after chemoembolization than after chemoperfusion for at least 1.5 hours. The MMC serum concentration in the dogs showed a high initial peak (0.6 mg/L) after chemoperfusion, then dropped quickly to the same level seen 30 minutes after chemoembolization with 1 mg of MMC/mL of Ethibloc (0.15 mg/L). The MMC serum concentration following chemoembolization with 2 mg of MMC/mL of Ethibloc stayed higher (0.3-0.25 mg/L) for 60 minutes. The survival rates after nephrectomy were equal to those after chemoembolization (80% survival after 30 days), with poorer survival being seen after embolization (75%) and chemoperfusion (70%). In the control group, all rats were dead at the 27th day.

CONCLUSION

Chemoembolization produces persistently high tissue concentrations of MMC and avoids toxic peak serum levels. It improves the efficacy of organ ablative vasoocclusion in renal malignancies.

P-Glycoprotein-mediated efflux of phenobarbital, lamotrigine, and felbamate at the blood-brain barrier: evidence from microdialysis experiments in rats

Although a series of new antiepileptic drugs (AEDs) have been launched in the last two decades, drug-refractoriness remains a major problem concerning 20-30% of epileptic patients. The fact that most patients with refractory epilepsy are resistant to several AEDs acting via different targets points to an involvement of unspecific mechanisms like changes in local uptake of AEDs in the epileptic focus region. Increased expression of multidrug transporters has been reported in epileptogenic brain tissue from pharmacoresistant patients undergoing epilepsy surgery. However, only limited information exists on the extent to which AEDs are transported by multidrug transporters like P-glycoprotein (PGP). In the present study, the effect of PGP inhibition by verapamil on brain access of the AEDs phenobarbital, lamotrigine, and felbamate was investigated by in vivo microdialysis in rats. Local perfusion of verapamil via the microdialysis probe increased the concentration of the three AEDs in the extracellular fluid of the cerebral cortex in a significant manner. The data indicate that overexpression of PGP in epileptic tissue is likely to limit brain access of the AEDs phenobarbital, lamotrigine, and felbamate, thus favoring the hypothesis that multidrug transporters play a crucial role in the phenomenon of drug-refractory epilepsy.

Pharmacokinetics of new anticonvulsants in psychiatry

The newer AEDs have potential in the treatment of psychiatric disorders. In light of this expanding spectrum of activity, it is necessary to refine and focus the safety and efficacy of the use of these agents among a wider population. The classic AEDs had numerous problems, ranging from inconvenient dosing schedules to frequent side effects due to active metabolites and common drug interactions; newer agents have been developed to avoid some of these pitfalls. Indeed, a generation of drugs that appears to have relatively simple pharmacokinetics and limited drug interactions--making them safer and easier to administer--is now available. The use of these agents in psychiatry will necessitate additional investigation into their dosing and administration guidelines, as well as their interactions with other common psychiatric or concomitant drugs. Certainly, over time, they will be evaluated for these parameters in the newer indications. In the meantime, a review of the established pharmacokinetic and pharmacodynamic activities of these agents is the first step in defining their optimal uses and limitations in the psychiatric setting.

Pharmacokinetics and cell trafficking dynamics of 2-amino-2-[2-(4-octylphenyl)ethyl]propane-1,3-diol hydrochloride (FTY720) in cynomolgus monkeys after single oral and intravenous doses

The pharmacokinetics and cell trafficking dynamics of 2-amino-2-[2-(4-octylphenyl)ethyl]propane-1,3-diol hydrochloride (FTY720), a novel immunosuppressive agent, were examined in cynomolgus monkeys (three males and three females). After single doses of 0.1 mg/kg p.o. or i.v. bolus and 1 mg/kg p.o. were administered to the animals, the concentrations of FTY720, and the numbers of lymphocytes, CD20+CD2-B cells, and CD2+CD20-T cells in blood were measured over 23 days. A linear three-compartment model characterized the time course of FTY720 concentrations with a terminal half-life of about 31 h, clearance of about 0.53 l/h/kg, and bioavailability of about 38%. The dynamic responses were not area under the curve (or dose) proportional for either males or females. An indirect response model with a distribution pool captured the cell trafficking data for all doses for each cell type, where initial blood counts (R(0)) were about 7650, 2100, and 5250 cells/microl; maximum fractional inhibition (I(max)) about 0.88, 0.85, and 0.91; influx (k(in)) about 6014, 1312, and 5662 cells/microl/h; efflux (k(out)) about 0.798, 0.555, and 1.08 h(-1); intercompartmental k(cp) about 0.134, 0.192, and 0.082 h(-1); and intercompartmental k(pc) rate constants about 3.9 x 10(-4), and 0.016 and 8.9 x 10(-6) h(-1) for lymphocytes, B cells, and T cells, respectively. The inhibition concentration IC(50) was about 0.48 microg/l for all cells, which was remarkably low. The apparent distribution volumes of peripheral pool (V(p)) were markedly larger than blood volume (V(b)) for all cells. The I(max) for cell trafficking was achieved at doses smaller than that producing graft protection, indicating stronger central than peripheral effects of this drug. The profound cell trafficking effects of FTY720 can be readily captured and interpreted with an extended indirect response model.

Heterogeneity of dehydrogenases of Stenotrophomonas maltophilia showing dye-linked activity with polypropylene glycols

Distinct enzyme activities were found in extracts from Stenotrophomonas maltophilia showing dye-linked oxidation of polypropylene glycols. The activities were induced when polypropylene glycols served as sole carbon and energy sources for the bacterium. In the logarithmic phase, most of the enzyme activities (88%) were found in the cytoplasm. In the stationary phase, more than half of the activities (54%) were found on the membrane, but significant activities were also distributed in the periplasm (34%) and the cytoplasm (12%). The enzyme activities differed from each other in their localization, time of induction in the growth cycle, specificity toward electron acceptor, and electrophoresis mobility.

First human trial of FTY720, a novel immunomodulator, in stable renal transplant patients

FTY720 is a novel immunomodulator to be developed for use in organ transplantation. The primary objective of this study was to measure safety, single-dose pharmacokinetics, and pharmacodynamics in stable renal transplant patients-the first human use of FTY720. This study used a randomized, double-blind, placebo-controlled design that explored single oral doses of FTY720 from 0.25 to 3.5 mg in 20 stable renal transplant patients on a cyclosporine-based regimen. Safety assessments and blood samples were taken predose and at multiple time points during a 96-h period postdose. Standard pharmacokinetic parameters were derived from the FTY720 whole blood concentrations, measured by HPLC/MS/MS. FTY720 was well tolerated, with no serious adverse events. Transient, asymptomatic bradycardia occurred after administration in 10 of 24 doses of FTY720. Pharmacokinetics are characterized by a prolonged absorption phase; the terminal elimination phase started 36 h after the administration, with elimination half-life (t(1/2)) ranging from 89 to 157 h independent of dose. Maximum plasma concentration and AUC were proportional to dose with low intersubject variability, the apparent volume of distribution (V(d)/F) ranged from 1116 to 1737 L. FTY pharmacodynamics were characterized by a reversible transient lymphopenia within 6 h, the nadir being 42% of baseline. The lymphocyte count returned to baseline within 72 h in all dosing cohorts except the highest. Single oral doses of FTY720 ranging from 0.25 to 3.5 mg were well tolerated and caused a reversible selective lymphopenia. Transient, but asymptomatic bradycardia was the most common adverse event. The long t(1/2) suggests less frequent dosing intervals. The size of V(d)/F is in excess of blood volume, consistent with widespread tissue distribution

Update on pharmacokinetic/pharmacodynamic studies with FTY720 and sirolimus

Expanding the cytokine paradigm beyond the use of calcineurin inhibitors as baseline therapy provides new strategies in immunosuppression. Drugs such as FTY720 alter the sensitivity of lymphocytes to homing chemokines, and agents such as sirolimus (SRL) disrupt downstream cytokine signal transduction. Confirming studies in rodents and nonhuman primates, administration of either FTY720 or both of these drugs afford synergistic interactions with cyclosporine to renal transplant patients to rapidly and dramatically deplete peripheral blood lymphocytes (PBL) but neither granulocytes nor monocytes. Present information suggests that FTY720 facilitates lymphocyte homing mechanisms, leading to T and B cell sequestration in secondary lymphoid structures. Interestingly, FTY720 displays pharmacokinetic characteristics suggesting that therapeutic drug monitoring (TDM) will not be essential for clinical applications. In contrast, SRL is a critical-dose drug that requires TDM. SRL disrupts costimulatory and cytokine-stimulated T cell activation by inhibiting a multifunctional kinase, mammalian target of sirolimus (mTOR). Two pivotal trials including more than 1,300 patients demonstrated that addition of SRL to a CsA-based regimen reduces the incidence, time to onset, and severity of acute rejection episodes. When used alone, SRL seems therapeutically equivalent to CsA. In the coming decade, SRL is likely to be used in a variety of drug combination regimens both simultaneously and sequentially, not only to avert acute rejection episodes, but also to forestall chronic nephropathic processes. These two new agents are likely to usher in a new era of transplant therapy.