Takashi Hirota

Platelet inhibitory activity and pharmacokinetics of prasugrel (CS-747) a novel thienopyridine P2Y12 inhibitor: A single ascending dose study in healthy humans

We assessed the tolerability, pharmacodynamics as measured by inhibition of platelet aggregation (IPA), and pharmacokinetics of prasugrel (CS-747, LY640315), a novel thienopyridine antiplatelet agent in healthy volunteers. Twenty-four subjects were randomized into four groups of six in a double-blind, placebo-controlled trial. One subject in each group received placebo and five subjects received prasugrel orally at single doses of 2.5, 10, 30, or 75 mg. The IPA, assessed using 5 and 20 µM ADP, was periodically measured over a 7-day period by light transmission aggregometry. Plasma concentrations for three major metabolites, R-95913, R-106583, and R-100932, were measured. There were no serious adverse events and no clinically significant changes noted in any laboratory or clinical evaluations in any subject. At 1 h after prasugrel 30 and 75 mg, platelet aggregation induced by 20 µM ADP was inhibited by 43.5 ± 7.8 and 43.2 ± 15.7%, respectively, and this inhibition was significantly greater than that following placebo (5.9 ± 3.5%) (P < 0.05 for both doses). The degree of inhibition observed at 2 h was slightly higher with both prasugrel 30 and 75 mg (59.8 ± 9.9 and 57.0 ± 7.2%) and was maintained through the subsequent 22 h. At 24 h, maximal platelet aggregation induced by 20 µM ADP was reduced to ≤39% in all subjects receiving prasugrel 30 mg and to ≤38% in subjects receiving prasugrel 75 mg. Full recovery of platelet aggregation occurred between 48 h and 7 days suggesting irreversible inhibition by prasugrel and/or its metabolites. With prasugrel 2.5 and 10 mg, there was no measurable effect on platelet aggregation throughout the study (P > 0.05 for 2.5 and 10 mg prasugrel vs. placebo). With prasugrel 75 mg at 4 h postdose, there was a significant increase in the mean bleeding time compared to placebo (682 vs. 161 s; P < 0.05). Prasugrel metabolites obeyed linear pharmacokinetics and the three metabolites appeared in the plasma soon after administration, reaching maximum levels at approximately 1 h. In conclusion, prasugrel 30 and 75 mg were well tolerated and achieved a consistently high level of platelet inhibition with a fast onset of action. Errors appear in the original version of this article. These errors have since been rectified, and a corrected PDF is available here

In Vitro and In Vivo Antibacterial Activities of CS-023 (RO4908463), a Novel Parenteral Carbapenem

ABSTRACT CS-023 (RO4908463, formerly R-115685) is a novel 1β-methylcarbapenem with 5-substituted pyrrolidin-3-ylthio groups, including an amidine moiety at the C-2 position. Its antibacterial activity was tested against 1,214 clinical isolates of 32 species and was compared with those of imipenem, meropenem, ceftazidime, ceftriaxone, ampicillin, amikacin, and levofloxacin. CS-023 exhibited a broad spectrum of activity against gram-positive and -negative aerobes and anaerobes, including methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant Staphylococcus epidermidis, penicillin-resistant Streptococcus pneumoniae (PRSP), β-lactamase-negative ampicillin-resistant Haemophilus influenzae, and Pseudomonas aeruginosa. CS-023 showed the most potent activity among the compounds tested against P. aeruginosa and MRSA, with MICs at which 90% of isolates tested were inhibited of 4 μg/ml and 8 μg/ml, respectively. CS-023 was stable against hydrolysis by the β-lactamases from Enterobacter cloacae and Proteus vulgaris. CS-023 also showed potent activity against extended-spectrum β-lactamase-producing Escherichia coli. The in vivo efficacy of CS-023 was evaluated with a murine systemic infection model induced by 13 strains of gram-positive and -negative pathogens and a lung infection model induced by 2 strains of PRSP (serotypes 6 and 19). Against the systemic infections with PRSP, MRSA, and P. aeruginosa and the lung infections, the efficacy of CS-023 was comparable to those of imipenem/cilastatin and vancomycin (tested against lung infections only) and superior to those of meropenem, ceftriaxone, and ceftazidime (tested against P. aeruginosa infections only). These results suggest that CS-023 has potential for the treatment of nosocomial bacterial infections by gram-positive and -negative pathogens, including MRSA and P. aeruginosa.

Mechanism for covalent binding of rofecoxib to elastin of rat aorta.

We have previously reported that oral administration of [14C]rofecoxib to rats resulted in the long retention of radioactivity by the aorta as a consequence of covalent binding to elastin. Treatment of rats with α-phenyl-α-propylbenzeneacetic acid 2-[diethylamino]-ethyl ester hydrochloride (SKF-525A), a cytochrome P450 inhibitor, significantly decreased the systemic exposure of 5-hydroxyrofecoxib, one of the main metabolites of rofecoxib, whereas there was no statistically significant change in the retention of radioactivity from [14C]rofecoxib in the aorta. On the other hand, the aortic retention of radioactivity closely correlated to the systemic exposure of unchanged rofecoxib in the dose range between 2 and 10 mg/kg. A covalent binding study of [14C]rofecoxib in vitro using rat aorta homogenate in the presence of d-penicillamine, hydralazine, β-aminopropionitrile, and sodium borohydride suggested that the aldehyde group of allysine in elastin was relevant to the covalent binding. In a model reaction using benzaldehyde, rofecoxib but not 5-hydroxyrofecoxib reacted with the aldehyde group of benzaldehyde in a manner of condensation reaction under a physiological pH condition. A histopathological examination using an electron microscope demonstrated that multiple oral administration of rofecoxib to rats caused marked degradation of the elastic fiber system of the aorta. These results suggested that rofecoxib as such is reactive in vivo, undergoing a condensation reaction with allysine, thereby preventing the formation of cross-linkages in elastin, i.e., desmosine and isodesmosine, and causing the degradation of the elastic fibers.

Covalent binding of radioactivity from [14C]rofecoxib, but not [14C]celecoxib or [14C]cs-706, to the arterial elastin of rats

Rofecoxib is a cyclooxygenase-2 (COX-2) inhibitor that has been withdrawn from the market because of an increased risk of cardiovascular (CV) events. With a special focus on the arteries, the distribution profiles of radioactivity in rats orally administered [14C]rofecoxib were investigated in comparison with two other COX-2 inhibitors, [14C]celecoxib and [14C]CS-706 (2-(4-ethoxyphenyl)-4-methyl 1-(4-sulfamoylphenyl)-1H-pyrrole), a novel selective COX-2 inhibitor. Whole-body autoradioluminography and quantitative determination of the tissue concentrations showed that considerable radioactivity is retained by and accumulated in the thoracic aorta of rats after oral administration of [14C]rofecoxib, but not [14C]celecoxib or [14C]CS-706. Acid, organic solvent, and proteolytic enzyme treatments of aorta retaining high levels of radioactivity from [14C]rofecoxib demonstrated that most of the radioactivity is covalently bound to elastin. In agreement with this result, the radioactivity was found to be highly localized on the elastic fibers in the aorta by microautoradiography. The retention of radioactivity on the elastic fibers was also observed in the aortic arch and the coronary artery. These findings indicate that [14C]rofecoxib and/or its metabolite(s) are covalently bound to elastin in the arteries. These data are consistent with the suggestion of modified arterial elasticity leading to an increased risk of CV events after long-term treatment with rofecoxib.

Covalent binding of rofecoxib, but not other cyclooxygenase-2 inhibitors, to allysine aldehyde in elastin of human aorta.

In rats, it has been reported that rofecoxib, a cyclooxygenase-2 (COX-2) inhibitor, reacts with the aldehyde group of allysine in elastin to give a condensation covalent adduct, thereby preventing the formation of cross-linkages in the elastin and causing degradation of the elastic fibers in aortas in vivo. Acid, organic solvent, and proteolytic enzyme treatments of human aortic homogenate after incubation with [14C]rofecoxib demonstrated that most of the radioactivity is covalently bound to elastin. The in vitro covalent binding was inhibited in the presence of β-aminopropionitrile, d-penicillamine, and hydralazine, which suggested that the aldehyde group of allysine in human elastin was relevant to the covalent binding. The in vitro covalent binding of [14C]rofecoxib was significantly decreased by the addition of only nonradiolabeled rofecoxib but not the other COX-2 inhibitors, celecoxib, valdecoxib, etoricoxib, and CS-706 [2-(4-ethoxyphenyl)-4-methyl 1-(4-sulfamoylphenyl)-1H-pyrrole], a novel selective COX-2 inhibitor. All the above COX-2 inhibitors except for rofecoxib had no reactivity with the aldehyde group of benzaldehyde used as a model compound of allysine aldehyde under a physiological pH condition. On the other hand, no retention of the radioactivity of [14C]rofecoxib was observed in human aortic endothelial cells in vitro, suggesting that rofecoxib is not retained in aortic endothelial cells in vivo. These results suggest that rofecoxib, but not other COX-2 inhibitors, is capable of covalently binding to the aldehyde group of allysine in human elastin. This might be one of the main causes of cardiovascular events by rofecoxib in clinical situations.

Pharmacokinetics of CS-023 (RO4908463), a Novel Parenteral Carbapenem, in Healthy Male Caucasian Volunteers

ABSTRACT The CS-023 concentration in plasma after administration by infusion to healthy volunteers at a dose of 700 mg was decreased, with a half-life of 1.7 h, and the cumulative urinary excretion was 59.4% of the dose. The total clearance, renal clearance, and volume of distribution were 8.12 liters/h, 4.14 liters/h, and 17.2 liters, respectively.

Prediction of pharmacokinetics of CS-023 (RO4908463), a novel parenteral carbapenem antibiotic, in humans using animal data

The pharmacokinetics of CS-023 (RO4908463, formerly R-115685), a novel parenteral carbapenem antibiotic, in humans was successfully predicted using the data collected from mice, rats, rabbits, and dogs; while inclusion of the monkey data led to a significant underestimation of the total plasma clearance (CL). Double logarithmic plots of CL and distribution volume at the steady-state (Vss) vs. body weight in four animal species were linear with high correlation coefficients; and the predicted CL and Vss values in humans agreed well with the observed values after administration of CS-023 by an intravenous drip infusion for 30 min. The plasma concentration-time profile in humans, which was predicted using a bi-exponential equation fitted to a complex Dedrick plot of the animal data, approximated the observed profile. An underestimation of CL caused by including the monkey data in a prediction is quite likely due to the net tubular reabsorption in monkeys, but not at least in rabbits, dogs, and humans.

Experimental study of pharmacokinetics of external, whole-body bathing application of ivermectin.

As a novel method improving the safety of conventional oral ivermectin (IVM) for scabies treatment, we conceived an idea called the “whole‐body bathing method”. In this method, the patients would bathe themselves in a bathing fluid containing IVM at an effective concentration. To evaluate the feasibility of the method, we investigated the IVM concentration in the skin and plasma after bathing rats in a fluid containing 100 ng/mL of IVM. After the bathing, the concentration of IVM in the skin was more than 400 ng/g wet weight and was maintained until 8 h after the bathing. The concentration was clearly higher than that in patients taking IVM p.o. as previously reported; IVM was not detected in plasma in the present study. Thus, the method would be a preferable drug delivery system for the skin application of IVM compared with p.o. administration.

Chloroform distribution and accumulation by combined inhalation plus oral exposure routes in rats

The present investigation was undertaken to determine the distribution and accumulation of chloroform in the blood, liver, kidney and abdominal fat of rats after simultaneous exposure by two routes, inhalation and oral. To distinguish the contribution of each route, unmodified chloroform (CHCl3) was administered by inhalation and deuterated chloroform (CDCl3) was administered orally. Exposure by inhalation and oral administration resulted in CHCl3 and CDCl3 concentrations in the tissues which were significantly higher than when exposure was by either inhalation or oral administration alone. This is the first study to follow the contribution of each of two routes of chloroform exposure on chloroform distribution and accumulation in target tissues. Our results indicate that when assessing the toxicity and carcinogenicity of chloroform, exposure routes, especially the effects of exposure by multiple routes, must be taken into consideration.

Pharmacokinetics and Disposition of CS-023 (RO4908463), a Novel Parenteral Carbapenem, in Animals

ABSTRACT The distribution, metabolism, and excretion of CS-023 (RO4908463), a new carbapenem, were investigated in rats and monkeys after a single intravenous administration of [14C]CS-023. In addition, the drugs pharmacokinetics were examined in rats, dogs, and monkeys. Whole-body autoradioluminograms of rats indicated that the radioactivity is distributed throughout the body immediately after administration except for the central nervous system and testes. The highest radioactivity was found in the kidneys, which are responsible for the excretion of CS-023. R-131624 with an open β-lactam ring, the pharmacologically inactive form, was detected in the plasma and urine as the major metabolite. In rat plasma, the R-131624 levels became higher than CS-023 levels at 30 min postdose and thereafter, while in monkey plasma, CS-023 accounted for most of the radioactivity, with low levels of R-131624. More than 80% of the radioactivity administered was recovered in the urine, and CS-023 and R-131624 accounted for 29.6% and 31.4%, respectively, of the dose in rats and 51.2% and 18.5%, respectively, of the dose in monkeys. The faster metabolism to R-131624 in rats than in monkeys was likely due to the metabolism by dehydropeptidase I in rat lungs. The plasma elimination half-life of CS-023 was 0.16 h in rats, 0.75 h in dogs, and 1.4 h in monkeys. There were no appreciable interspecies differences among the animals tested in either volume of distribution (172 to 259 ml/kg) or serum protein binding (5.0 to 15.6%). The total clearance in monkeys (1.62 ml/min/kg) was lower than that in rats (15.1 ml/min/kg) or dogs (4.19 ml/min/kg).