BACKGROUND:
Argatroban, a direct thrombin inhibitor, is an effective anticoagulant for patients who have heparin-induced thrombocytopenia (HIT). Anticoagulation is usually required for renal ...replacement therapy (RRT).
OBJECTIVE:
To prospectively evaluate the pharmacokinetics, pharmacodynamics, and safety of argatroban during RRT in hospitalized patients with or at risk for HIT.
METHODS:
Five patients with known or suspected HIT underwent hemodialysis (n = 4) or continuous venovenous hemofiltration (CVVH, n = 1), while receiving a continuous infusion of argatroban 0.5–2 μg/kg/min. Activated partial thromboplastin times (aPTTs), activated clotting times (ACTs), argatroban concentrations (plasma, dialysate, CVVH effluent), and safety were assessed before, during, and after a 4-hour session of RRT. Systemic and dialytic argatroban clearances were calculated.
RESULTS:
Among the 4 hemodialysis patients, aPTT, ACT, and plasma argatroban concentrations remained stable during RRT, with respective mean ± SD values of 74.3 ± 34.2 seconds, 198 ± 23 seconds, and 499 ± 353 ng/mL before RRT, and 70.6 ± 21.4 seconds, 181 ± 12 seconds, and 453 ± 295 ng/mL 2 hours after starting RRT (p values NS). Systemic clearance was 17.7 ± 12.8 L/h before hemodialysis and 17.0 ± 9.5 L/h during hemodialysis (n = 2). The dialyzer clearance (dialysate recovery method) was 1.5 ± 0.4 L/h (n = 4). Generally similar responses occurred in the CVVH patient: systemic argatroban clearance was 4.8 L/h before CVVH and 4 L/h during CVVH. The hemofilter argatroban clearance was 0.9 L/h. No bleeding or thrombosis occurred.
CONCLUSIONS:
Argatroban provides effective alternative anticoagulation in patients with or at risk for HIT during RRT. Argatroban clearance by high-flux membranes during hemodialysis and CVVH is clinically insignificant, necessitating no dose adjustment.
Due to the exceptional anticonvulsant activity displayed by substituted aniline enaminones, related pyridine derivatives and phenothiazines synthesised in our laboratories, the further investigation ...of various aromatic heterocycles was undertaken. Condensation of cyclic 1,3-diketo esters with 3-, and 5-aminoisoxazole derivatives led to a series of potent anti-maximal electroshock (MES) analogues, three of which occurred in the 3-amino series: ethyl ester (
10), orally (po) active in rats ED
50 68.9 mg kg
−1, TD
50>500 mg kg
−1, protective index (PI=TD
50/ED
50)>49.6; methyl ester (
9), ED
50 68.9 mg kg
−1 intraperitoneally (ip) in mice, TD
50>500 mg kg
−1, PI>7.3, and
tert-butyl ester (
8), ED
50 28.1 mg kg
−1 po in rats, TD
50>500 mg kg
−1, PI>17.8. Sodium channel binding studies, as well as evaluations against pentylenetetrazol, bicuculline, and picrotoxin on isoxazole
10 were all negative, leading to an unknown mechanism of action. X-ray diffraction patterns of a representative of the 3-amino series (isoxazoles
6–
11) unequivocally display the existence of intramolecular hydrogen bonding of the nitrogen to the vinylic proton in the cyclohexene ring, providing a pseudo three ring structure which was also shown previously with the vinylic benzamides. Physicochemical-permeability across the BBB suggested an efflux mechanism for the previously synthesised aniline enaminones, but not with isoxazole
10.
Multidrug resistance (MDR), mediated by P-glycoprotein (Pgp) has been identified as altering the disposition of structurally diverse compounds. Previous in vitro studies in bovine brain microvascular ...endothelial cells and MCF/Adr Adriamycin (doxorubicin)-resistant human breast cancer cells displayed that the transport of enaminone anticonvulsants was influenced by Pgp. Therefore the objectives of this study was to further evaluate the influence of Pgp on the pharmacokinetics and tissue distribution of the enaminone analogs. mdr1ab (+/+) and mdr1ab (-/-) male mice (20 +/- 5 g) were administered DM5 (methyl 4-(4'-chlorophenyl)amino-6-methyl-2-oxo-3-cyclohexene-1-carboxylate) or DM44 (12.5 mg/kg, i.v.). Cohorts (n = 3) were sacrificed over a 12-h period, and samples were analyzed by a validated UV-high performance liquid chromatography assay method. Population analysis was used to estimate pharmacokinetic parameters and partition coefficients were determined for tissues. The clearance (0.51 versus 0.33 l/h/kg) and V(d) (1.25 versus 0.93 l/kg) of DM5 were found to be higher (p < 0.05), however the area under the curve (26.1 versus 38.2 microg/ml. h) was lower (p < 0.05) in mdr1a/1b (-/-) versus mdr1a/1b (+/+) mice, respectively. Similar findings were observed for DM44. Tissues known to express Pgp such as the heart, liver, lung, and brain displayed 2-fold or higher tissue levels in mdr1a/1b (-/-) versus mdr1a/1b (+/+) mice. These results strongly suggest that Pgp may influence enaminone tissue distribution and pharmacokinetics and may play a significant role in the effective treatment of epilepsy with these analogs.
Zonula occludens toxin (Zot), a protein elaborated from Vibrio cholerae, has been shown to be capable of reversibly opening tight junctions. The objective of this work was to determine the stability ...of Zot and to examine the permeability of a series of molecular weight hydrophilic markers and therapeutic agents in the presence of Zot.
The transport of molecular weight markers (i.e., PEG 4000, FITC-dextran 10.000 and inulin) and therapeutic agents (i.e., acyclcovir, cyclopsorin, paclitaxel. doxorubicin) was evaluated with Zot (0, 2, and 4 microg/mL) using Caco-2 cell monolayers.
Zot was found to be stable over a 10-day period. Significantly higher (p < 0.05) permeability of the molecular weight markers, in lin, and PEG4000 were observed with Zot (4 microg/mL). The transport of each therapeutic marker was significantly increased with paclitaxel displaying a >3-fold enhancement in Papp values with Zot (4 microg/mL). A 30% decrease in transepithelial electrical resistance values wa observed, which returned to baseline 30 min after Zot was removed.
Considering the problems of poor oral bioavailability, it is concluded that Zot is a promising drug delivery technology to be used to enhance drug transport across the intestinal mucosa. Future applications are targeted at assessing its usefulness in oral drug delivery using in vivo systems.
SB-424323 is a new, orally active anti-thrombotic agent presently in phase-II clinical development, with limited hemorrhagic risk and a unique mechanism of action involving the induction of ...glycosaminoglycans (GAGs) biosynthesis. The objective of the present study was to develop a simple and rapid high performance liquid chromatography (HPLC) method for determination of endogenous GAGs derived disaccharides in plasma samples from a phase-II clinical study of SB-424323. Sample preparation was a simple heat treatment of the diluted plasma followed by digestion of endogenous GAGs with chondroitinase ABC to yield unsaturated disaccharides, 2-acetamido-2-deoxy-3-
O-(β-
d-gluco-4-enepyranosyluronic acid)-
d-galactose (ΔDi-0S), 2-acetamido-2-deoxy-3-
O-(β-
d-gluco-4-enepyranosyluronic acid)-4-
O-sulfo-
d-galactose (ΔDi-4S), and 2-acetamido-2-deoxy-3-
O-(β-
d-gluco-4-enepyranosyluronic acid)-6-
O-sulfo-
d-galactose (ΔDi-6S). These disaccharides were recovered and purified using centrifugal filtration through a filter with 3000 molecular weight cut-off along with externally added internal standard 2-acetamido-2-deoxy-3-
O-(2-
O-sulfo-β-
d-gluco-4-enepyranosyluronic acid)-
d-galactose (ΔDi-UA2S). A gradient reverse phase HPLC separation was developed on a Waters Symmetry C
18 column (4.6
mm
×
150
mm, 5
μm) with a gradient mobile phase system consisting of 0.8
mM tetrabutylammonium hydrogen sulfate and 2
mM sodium chloride and acetonitrile at a flow rate of 1.0
mL/min. The eluate was monitored with an ultraviolet detector set at 230
nm. Plasma standard curves were linear (
r
2
≥
0.994) in the concentration range 1.0-20
μg/mL with a lower limit of quantification (LLOQ) of 1.0
μg/mL for each of the disaccharide. The mean measured quality control (QC) concentrations for the disaccharides deviated from the nominal concentrations in the range of −8.92 to 5.61% and −16.3 to 16.7%, for inter and intra-day, respectively. The inter and intra-day precision in the measurement of QC samples, were in the range of 3.21 to 18.2% relative standard deviation (R.S.D.) and 0.32 to 20.9% R.S.D., respectively. The inter and intra-day precision in the measurement of endogenous GAGs derived disaccharides in human control plasma, were in the range of 5.8 to 15.9% R.S.D. and 1.17 to 7.74% R.S.D., respectively. Stability of the processed samples was confirmed up to 48
h in the auto-sampler. The method is simple, reliable, and easily adaptable to analysis of large number of samples under logistics of a clinical study. The present method has been used to investigate the GAGs levels in the plasma of patients in a phase II clinical study of SB-424323.
Further investigation of the potential anticonvulsant activity of the enaminones was attempted to discern the possible role of metabolites as the active/co-active entities of the esters of the ...enaminones. A series of 5-methyl-2-cyclohexene enaminones, the hypothesised metabolites corresponding to a sequence of active and inactive esters were synthesised and evaluated for anticonvulsant activity. With two exceptions, ethyl 4-(4-cyanophenyl)amino-6-methyl-2-oxocyclohex-3-ene-1-carboxylate (
1k), and 3-
N-(4-cyanophenyl)amino-5-methyl-2-cyclohexenone (
3g), and ethyl 4-(phenylamino)-6-methyl-2-cyclohexenone (
1n), and 3-
N-(phenylamino)-5-methyl-2-cyclohexenone (
3j), anticonvulsant screening data were parallel, with the ester and their putative decarboxylated analogue displaying similar activity. The most active analogue evaluated in this series, ethyl 4-(4-chlorophenyl)amino-6-methyl-2-oxocyclohex-3-ene-1-carboxylate (
1e), which displayed an ED
50 of 16.7 mg kg
−1 and a TD
50 of 110.7 mg kg
−1 (protective index, PI=TD
50/ED
50=6.6) in the maximal electroshock seizure (MES) test in mice and an ED
50 of 3.0 mg kg
−1 and a TD
50 >250 mg kg
−1 (PI >83.3) in rats in the same evaluation, making this compound the most potent enaminone emanating from our laboratories. Pharmacokinetic evaluation of compound
1e in rats using LC/MS analysis unequivocally provides evidence that this compound is converted into the decarboxylated analogue
3a in the brain and the urine.
Zonula occludens toxin (Zot), a protein elaborated from Vibrio cholerae, has been shown to be capable of reversibly opening tight junctions between intestinal cells The objective of this study was to ...examine the effect of Zot on the flux of various molecules across Caco-2 cell monolayers. In addition, the transport of a series of anticonvulsants, the enaminones was also evaluated in the presence of Zot. The flux of (14)Cmannitol, (14)Cinulin and various enaminones across Caco-2 cell monolayers (n=6) was examined after pre-incubation for 1h with Zot (0 or 4000ng/ml) or phosphate-buffered saline (PBS). At the end of the incubation period, the flux of radiolabeled compounds or enaminones (1x10(-4)M) was assessed over a 2-h period. In addition, dose-response studies with Zot (0, 1000, 2000 or 4000ng/ml) were performed using mannitol. The flux of both mannitol and inulin significantly increased (P<0.05) in the presence of Zot. The transport of the enaminones with Zot ranged from 9.42 to 26.83x10(-5)cm/s vs. 4.68 to 13.83x10(-5)cm/s without Zot. Zot significantly increased the transport of all agents tested. This suggests that the co-administration of drugs with Zot may be a useful delivery strategy to increase the intestinal permeability and hence oral absorption of poorly bioavailable agents.
The pharmacokinetic-pharmacodynamic (PK-PD) relationship of argatroban, administered in combination with a platelet glycoprotein IIb/IIIa receptor antagonist, was characterized in patients undergoing ...percutaneous coronary intervention (PCI). Plasma argatroban and activated clotting times (ACTs) were assessed periprocedurally in 152 patients administered argatroban (250- or 300-microg/kg bolus, then 15-microg/kg/min infusion) in combination with abciximab or eptifibatide during PCI. The PK and PK-PD models were developed utilizing a sequential population approach in NONMEM. Population PK estimates for clearance, central volume, and peripheral volume were 22.0 L/h, 11.0 L, and 13.0 L, respectively (coefficients of variation CVs </= 10%). By covariate analysis, clearance increased linearly with body weight. Plasma argatroban and ACT effect were well described using a sigmoidal E(max) model. For argatroban in combination with platelet glycoprotein IIb/IIIa receptor blockade in patients undergoing PCI, population PK parameters are consistent with values reported for argatroban in healthy subjects. A predictable relationship exists between argatroban concentration and effect in this setting.
