Published papers

To compare vitreous concentrations of triamcinolone acetonide (TA) achieved by prior therapeutic intravitreal and subtenon injections. Interventional case series. Vitreous samples were collected from patients who required vitreous surgery, six having received a subtenon injection of TA and another six, an intravitreal injection. Vitreous concentrations of TA were measured by high-performance liquid chromatography. Vitreous concentrations of TA after intravitreal injection were 1.22 ± 0.24 μg/ml, significantly higher than those after subtenon injection (<0.001 μg/ml, P =. 003). Vitreous concentrations of TA after subtenon injection and TA-assisted vitrectomy performed in a few patients to visualize the transparent vitreous gel were 0.20 ± 0.11 μg/ml, an intermediate amount between these two groups. Much higher vitreous concentrations of TA after intravitreal injection than subtenon injection may accelerate therapeutic effect when intravitreal injections are given to reduce macular edema. Subtenon injections of TA may act via the sclera as opposed to the vitreous. © 2004 by Elsevier Inc. All rights reserved.

N-desmethylclobazam (N-CLB), the major metabolite of clobazam (CLB), exerts a large influence on therapeutic and adverse effects of CLB. A substantial inter-individual variability has been observed in the ratios of N-CLB concentration/CLB dose and of the N-CLB/CLB concentration. We document here a genotype-phenotype correlation between CYP2C19 polymorphisms and those ratios. Patients with two mutated CYP2C19 alleles show significantly higher ratios than those with the wild type genotype: patients with one mutated allele exhibited intermediate trait. That is, the degree of elevation in the ratios was dependent on the number of mutated alleles of CYP2C19 (gene-dose effect). The N-CLB concentration/CLB dose ratio of patients with two mutated alleles was more than six fold higher than that of wild type patients. Thus, the serum N-CLB/CLB concentration ratio may be a valuable parameter to screen for patients at risk for side effects. Such precautions may be clinically relevant in populations where the mutant allele frequency is high, such as in Asian populations (∼35%). Patients co-medicated with CYP3A4 inducer showed lower CLB concentration/CLB dose ratios and higher N-CLB/CLB concentration ratios. The overall effect of CYP3A4 inducer on N-CLB metabolism, however, was small and, thus, we conclude that the CYP2C19 genotype is the major determinant of the N-CLB concentration. For this reason it is crucial for the better management of epilepsy and other chronic illnesses in general to establish the correlation of genotype of CYP enzymes and pharmacokinetics/dynamics of drugs. © 2004 Elsevier B.V. All rights reserved.

Background: KRN5500, a novel spicamycin derivative, shows an inhibitory effect on protein synthesis. This phase I study was aimed at investigating the toxicity, maximum tolerated dose (MTD) and pharmacokinetics of this compound. Patients and methods: Patients with solid tumors not amenable to standard forms of treatment were eligible. KRN5500 was administered as a 2 h intravenous infusion every 4 weeks at doses of 3, 6, 10, 15 and 21 mg/m2. Pharmacokinetic evaluation was performed at the first cycle. Results: Eighteen patients with advanced solid tumors were enrolled. A total of 26 cycles of KRN5500 were administered. The major toxicities were nausea, vomiting, diarrhea, fatigue and a mild reversible prolongation of prothrombin time. Grade 4 pulmonary toxicity (interstitial pneumonitis) was observed in one patient at a dose level of 15 mg/m2. Severe fatigue was observed in one patient at a dose level of 21 mg/m2 and the duration of fatigue tended to increase with the dose of KRN5500. Nausea and vomiting were frequently observed and became prolonged with increasing dose of KRN5500. These toxicity profiles were identified as unacceptable and further dose escalation above 21 mg/m2 was withheld. The MTD was therefore determined as 21 mg/m2. The peak plasma concentration and the area under the concentration-time curve of KRN5500 increased proportionally to the dose, suggesting linear pharmacokinetics. No objective antitumor response was observed. Conclusion: KRN5500, a structurally novel protein synthesis inhibitor, warrants further investigation to overcome these toxicity profiles and improve its efficacy. © 2003 Foundation for Promotion of Cancer Research.

The effects of 12 Ca2+ antagonists on MDR1 were examined by two independent models: the inhibitory effect on MDR1-mediated transport of [3H]digoxin using MDR1-overexpressing LLC-GA5-COL150 cell monolayers and the reversal effect on cytotoxicity of vinblastine or paclitaxel using MDR1-overexpressing Hvr100-6 cells. The inhibitory effects on [3H]digoxin transport were assessed as the 50% inhibitory concentration during 4 h exposure, and the values were the lowest for nicardipine (4.54 μM), manidipine (4.65 μM) and benidipine (4.96 μM), followed by bepridil (10.6 μM), barnidipine (12.6 μM), efonidipine (13.0 μM), verapamil (13.2 μM) and nilvadipine (18.0 μM). The reversal effect on cytotoxicity was assessed by the 50% growth inhibitory concentration after 3 days exposure, and the resistance to vinblastine or paclitaxel in Hvr100-6 cells was reversed by manidipine, verapamil, benidipine, barnidipine, and nicardipine, in that order. Bepridil, barnidipine, efonidipine, verapamil and nilvadipine showed similar inhibitory effects on [3H]digoxin transport, but barnidipine and verapamil showed a stronger effect in reversal of cytotoxicity. Real-time quantitative RT-PCR assay indicated a decrease in MDR1 mRNA expression by barnidipine and verapamil. It is concluded that Ca2+ antagonists cannot only be direct inhibitors of MDR1 but that some may at the same time act as inhibitors of expression of MDR1 via down-regulation of MDR1 mRNA. © 2002 Elsevier Science B.V. All rights reserved.

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, pravastatin, was compared with simvastatin and lovastatin from the viewpoint of susceptibility to interaction with or via the multidrug transporter, MDR1 (P-glycoprotein). This was carried out using the MDR1-overexpressing cell line LLC-GA5-COL150, established by transfection of MDR1 cDNA into porcine kidney epithelial LLC-PK1 cells, and [3H]digoxin, which is a well-documented substrate for MDR1. Pravastatin, at 25-100 μM, had no effect on the transcellular transport of [3H]digoxin whereas simvastatin and lovastatin suppressed the basal-to-apical transport of [3H]digoxin and increased the apical-to-basal transport. It was suggested that recognition by MDR1 was due to the hydrophobicity. In conclusion, simvastatin and lovastatin are susceptible to interaction with or via MDR1, but pravastatin is not. This is important information when selecting the HMG-CoA reductase inhibitors for patients taking drugs that are MDR1 substrates.

The population pharmacokinetics of theophylline were studied in 55 patients with stable chronic airway obstruction. Two hundred and seventy six theophylline serum concentrations after intravenous short infusion were analyzed using a nonlinear mixed-effect model. The influence of hepatic dysfunction, smoking habit, age and the measurement of arterial blood gases (oxygen tension: PaO2, carbon dioxide tension: PaCO2, blood pH) and clinical laboratory tests (serum albumin concentration, haematocrit) on the pharmacokinetic parameters of theophylline was examined by the likelihood ratio test. Assessment of each factor was made by a forward selection method. In the final regression model, the total body clearance (CL, l/h/kg) was related to the value of PaCO2 as well as to the presence of hepatic dysfunction, and the volume of distribution (V(d), l/kg) was related with the PaCO2 value as expressed in the following equations: CL=exp(- 3.78 - 0.525. HF+ 0.0233. PaCO2) and V(d)=exp(- l.12 + 0.00934. PaCO2), where HF is a categorical variable with a value of unity if a patient has hepatic dysfunction otherwise zero. The interactions among blood gas measurements were observed and the CL and V(d) of theophylline would be inversely correlated with PaO2 or pH, if we selected PaO2 or blood pH to be a more important factor than PaCO2. The inter-individual variabilities in CL and V(d) were 38.5% and 12.5%, respectively, and the residual variability in theophylline serum concentrations was 10.6% as a coefficient of variation. This final model and the population parameters of theophylline will be useful for individualization of a drug dosage regimen by means of the Bayesian method. Significant correlation between arterial blood gas measurements and pharmacokinetic parameters observed in this study indicates that the pharmacokinetics of theophylline can vary in association with the severity of respiratory diseases.

The population pharmacokinetics of theophylline during constant-rate intravenous infusion has been studied in 66 children (8.7 ± 4.7 year of age; 26.0 ± 12.8 kg, mean ± S.D.) with an episode of acute asthma. One hundred and twelve theophylline serum concentrations (13.9 ± 4.8 μg/ml) collected retrospectively were analyzed using a nonlinear mixed-effect model. The influence of hepatic dysfunction, age, gender, days after admission, blood gas measurements (PaO2, PaCO2, blood pH) and clinical analyses data (total serum protein, albumin concentration, haemoglobin concentration, haematocrit) on theophylline clearance was examined by the likelihood ratio test. A final estimate of population mean clearance was 58.6 ml/kg/h, which was decreased by 36% in patients with hepatic dysfunction. Other factors tested displayed no statistically significant effect on theophylline clearance. The inter-individual variability in clearance was 26% while the intra-individual variability in theophylline concentrations was 2.6 μg/ml as a standard deviation, which was almost double that observed for stable patients. Taking into account that the therapeutic window of this drug is 10-20 μg/ml, this value indicates a relatively large intra-individual variability and suggests that frequent (daily) monitoring of serum concentrations is necessary for patients with an episode of acute asthma.

The mechanism of a renal tubular digoxin-cyclosporin A interaction was elucidated using a kidney epithelial cell line and the isolated perfused rat kidney. The cells expressed an excess amount of human P-glycoprotein on the apical membranes by transfection with MDR1 cDNA. Cyclosporin A inhibited the trans-epithelial transport of digoxin mediated by human P-glycoprotein; net basal-to-apical transport across the cell monolayer was 22.8, 21.2, 6.61 and 0.91 pmol/mg of protein/3 hr in the presence of 0, 1, 5 and 10 μM cyclosporin A, respectively. Cyclosporin A also reduced the renal tubular secretion of digoxin by the kidney. The ratio of fractional excretion/filtration fraction for digoxin was 2.88 ± 0.71 (mean ± S.D.) in the control, and this was decreased to 1.21 ± 0.09 and 1.05 ± 0.13 in the presence of 1 and 5 μM cyclosporin A, respectively. Because no signs of acute nephrotoxicity were observed, a direct effect of cyclosporin A accounted for the reduced secretion. On the other hand, digoxin did not affect cyclosporin A transport by P-glycoprotein. These findings indicate that serum concentrations of digoxin in patients should be carefully monitored when administered concurrently with cyclosporin A. The present transepithelial transport system using the transfectant cells is a simple and useful screening system for predicting drug interactions that can occur in a clinical situation.

The mechanism for renal tubular secretion of digoxin as well as its interaction with quinidine or verapamil were investigated using the isolated perfused rat kidney. [3H]Digoxin was instantaneously administered into the renal artery together with [14C]inulin and Evans blue-albumin, and renal venous and urinary outflow curves were measured. The ratio of fractional excretion to filtration fraction for digoxin was 2.40 ± 0.40, indicating involvement of tubular secretion. Quinidine and verapamil decreased the ratio of fractional excretion to filtration fraction in a concentration-dependent manner, and this inhibition was indicated to occur at transport from cells to lumen across luminal membranes. Neither tetraethylammonium nor p- aminohippurate affected the renal handling of digoxin. Because ouabain and digitoxose showed no influence on the value of fractional excretion to filtration fractions, Na+,K+-ATPase is not involved in the tubular secretion of digoxin. A metabolic inhibitor, 2,4-dinitrophenol, markedly inhibited digoxin secretion. Agents that bind to P-glycoprotein, such as vinblastine, daunorubicin and reserpine, markedly inhibited the secretion of digoxin. Recently, we have found that digoxin is a substrate transported by P-glycoprotein. The findings obtained here support the hypothesis that digoxin is secreted by P-glycoprotein located on the luminal membrane of renal tubular epithelial cells, and that clinically important interactions with quinidine and verapamil are caused by the inhibition of P-glycoprotein.

Understanding of the interactions between P-glycoprotein and multidrug resistance (MDR) reversing agents is important in designing more effective MDR modulators. We examined transcellular transport of several MDR modulators by using a drug-sensitive epithelial cell line, LLC-PK1 and its transformant cell line, LLC-GA5-COL300, which expresses human P-glycoprotein on the apical surface. Basal-to-apical transports of azidopine and diltiazem across the LLC-GA5-COL300 monolayer were increased and apical-to-basal transports were decreased compared to those across the LLC-PK1 monolayer, indicating that P-glycoprotein transports azidopine and diltiazem. Movements of nitrendipine and staurosporine across the epithelial monolayer were not affected by P-glycoprotein. These results suggests that some MDR modulators exert their inhibitory effect not only by blocking the initial binding of anticancer drugs but throughout the course of the transport process. © 1993.