Shun Higuchi

Changing the dosing schedule minimizes the disruptive effects of interferon on clock function

The effectiveness and toxicity of many drugs vary depending on the relationship between the dosing schedule and the 24-hour rhythms of biochemical, physiological and behavioral processes. In addition, several drugs can cause alterations to the 24-hour rhythms leading to illness and altered homeostatic regulation. However, the mechanisms of this drug-based disruption of circadian clock genes remain unclear. Here, we show the disruptive effect of interferon-α on the rhythm of locomotor activity, body temperature and clock-gene mRNA expression in the periphery and suprachiasmatic nuclei, a primary circadian pacemaker. The rhythmicity of clock genes and the photic induction of the Per gene in suprachiasmatic nuclei were disturbed by the repetitive administration of interferon-α. Moreover, alteration of clock function, a new concept of adverse effects, can be overcome by optimizing the dosing schedule to minimize adverse drug effects.

Genetic polymorphisms and functional characterization of the 5′‐flanking region of the human CYP2C9 gene: In vitro and in vivo studies

Genetic polymorphisms were identified in the 5′‐flanking region of the human CYP2C9 gene, and their effects on the phenotype were evaluated on the basis of the luciferase reporter gene assay and the in vivo pharmacokinetics of phenytoin.

P-hydroxylation of phenobarbital: relationship to (S)-mephenytoin hydroxylation (CYP2C19) polymorphism.

The aim of the current study was to compare the pharmacokinetics of phenobarbital (PB) in extensive metabolizers (EMs) and poor metabolizers (PMs) of S-mephenytoin. Ten healthy volunteers (5 EMs and 5 PMs) were given 30 mg PB daily for 14 days. PB and p-hydroxyphenobarbital (p-OHPB) in serum and urine were measured by high-performance liquid chromatography (HPLC). Urinary excretion (12.5% versus 7.7%) and formation clearance (29.8 versus 21.1 mL/h) of p-OHPB, one of the main metabolites of PB, were significantly lower (p < .05) in PMs than in EMs. However, area under the serum concentration–time curve (153.3 in the EMs versus 122.9 &mgr;g · h/mL in the PMs) , total (210.8 versus 254.9 mL/h) and renal clearance (53.1 versus 66.1 mL/h) of PB were identical between the two groups. To compare the inducibility of CYP2C19, mephenytoin was also given prior to and on the last day of PB treatment. The urinary level of 4´-hydroxymephenytoin was analyzed by a validated gas chromatograpy/mass spectrometry (GC/MS) method. The mephenytoin hydroxylation index did not change in either EMs (1.42 versus 1.42) or PMs (341.4 versus 403.5), showing that CYP2C19 was not induced by treatment with PB. These results indicated that the p-hydroxylation pathway of PB co-segregates with the CYP2C19 metabolic polymorphism. However, the overall disposition kinetics of PB were not different between EMs and PMs, and therefore polymorphic CYP2C19 seems have no major clinical implications.

Phenytoin intoxication induced by fluvoxamine.

A patient had phenytoin intoxication after administration of fluvoxamine, a selective serotonin reuptake inhibitor. The serum concentration of phenytoin increased dramatically from 16.6 to 49.1 microg/mL when fluvoxamine was coadministered, although the daily dosage of phenytoin and other drugs had not changed. During phenytoin and fluvoxamine treatment, ataxia, a typical side effect of phenytoin, was observed. The genotypes of CYP2C9 and 2C19, the enzymes responsible for phenytoin metabolism, were homozygous for the wild-type alleles (CYP2C9*1/*1 and 2C19*1/ *1). The interaction may be a result of inhibition of both CYP2C9 and 2C19 by fluvoxamine.

Population pharmacokinetics of digoxin in Japanese patients: a 2-compartment pharmacokinetic model.

ObjectiveTo clarify the observed variability of digoxin disposition by performing a population pharmacokinetic analysis in a Japanese population.DesignRetrospective analysis of clinical pharmacokinetic data.Patients and participantsData were obtained from 106 patients with heart failure and atrial fibrillation (43 males and 63 females).MethodsDigoxin concentrations in serum were measured by fluorescence polarisation immunoassay. Population pharmacokinetic analysis was performed using a 2-compartment open pharmacokinetic model with the computer program NONMEM.Results246 serum concentrations were obtained. Final pharmacokinetic parameters were: CL (L/h) = (0.036 □TBW + 0.112 □CLCR) □0.77SPI □0.784CCB, V1 = 1.83 L/kg, V2 = 22.6 L/kg and Q = 0.629 L/h/kg, where CL is total body clearance, V1 and V2 are the apparent volumes of distribution in the central and peripheral compartments, Q is intercompartmental clearance, TBW is total bodyweight (in kg), CLCR is creatinine clearance (in ml/min), SPI = 1 for concomitant administration of spironolactone (and zero otherwise) and CCB = 1 for concomitant administration of calcium antagonists (and zero otherwise). Concomitant administration of digoxin and spironolactone resulted in a 23% decrease in digoxin clearance. Concomitant administration of digoxin and calcium antagonists (diltiazem, nicardipine, nifedipine or verapamil) resulted in a 21.6% decrease in digoxin clearance.ConclusionsThe estimated population parameter values may assist clinicians in the individualisation of digoxin dosage regimens.

Estimation of rhG-CSF absorption kinetics after subcutaneous administration using a modified Wagner-Nelson method with a nonlinear elimination model.

The clearance of recombinant human granulocyte-colony stimulating factor (rhG-CSF) is known to decrease with dose increase, and to be saturable. The average clearance after intravenous administration will be lower than that after subcutaneous administration. Therefore, the apparent absolute bioavailability with subcutaneous administration calculated from the AUC ratio is expected to be an underestimate. The absorption pharmacokinetics after subcutaneous administration was examined using the results of the bioequivalency study between two rhG-CSF formulations with a dose of 2 microg/kg. The analysis was performed using a modified Wagner-Nelson method with the nonlinear elimination model. The apparent absolute bioavailability for subcutaneous administration was 56.9 and 67.5% for each formulation, and the ratio between them was approximately 120%. The true absolute bioavailability was, however, estimated to be 89.8 and 96.9%, respectively, and the ratio was approximately 108%. The absorption pattern was applied to other doses, and the predicted clearance values for subcutaneous and intravenous administrations were then similar to the values for several doses reported in the literature. The underestimation of bioavailability was around 30%, and the amplification of difference was 2.5 times, from 8 to 20%, because of the nonlinear pharmacokinetics. The neutrophil increases for each formulation were identical, despite the different bioavailabilities. The reason for this is probably that the amount eliminated through the saturable process, which might indicate the amount consumed by the G-CSF receptor, was identical for each formulation.

Effect of Dosing Schedule on Pharmacokinetics of Alpha Interferon and Anti-Alpha Interferon Neutralizing Antibody in Mice

ABSTRACT The influences of dosing time and dosing schedule on the plasma alpha interferon (IFN-α) concentration and the production of anti-IFN-α neutralizing antibodies were investigated in ICR male mice adapted to cycles of 12 h of light and 12 h of dark. In mice pretreated with IFN-α for 21 days, the plasma IFN-α concentrations were significantly lower than those in control mice (P< 0.01). The clearance of IFN-α and its volume of distribution obtained at steady state were significantly higher in the animals with IFN-α pretreatment than in the mice without IFN-α pretreatment. The area under the concentration-time curve and the mean residence time of IFN-α were significantly smaller in IFN-α-pretreated animals than in control animals. The plasma IFN-α levels (measured 2 h after dosing) were significantly lower in mice treated daily with IFN-α, while the anti-IFN-α neutralizing antibody levels (measured 24 h after dosing) were significantly increased on days 15 and 21 of treatment. Plasma IFN-α levels were significantly decreased in association with the production of anti-IFN-α neutralizing antibodies in mice treated with IFN-α daily at either 0900 or 2100 h. By contrast, the plasma IFN-α levels (measured 2 h after dosing) remained stable in mice treated with IFN-α at 0900 h on alternate days, while they were significantly lower after 21 days of treatment in mice treated with IFN-α at 2100 h on alternate days. These changes were associated with a significant increase in the levels of anti-IFN-α neutralizing antibodies in the latter group. The present findings suggest that an appropriate dosing schedule and/or dosing time for IFN-α may reduce the level of production of anti-IFN-α neutralizing antibodies in experimental and clinical situations.

Pharmacoepidemiologic investigation of a clonazepam-carbamazepine interaction by mixed effect modeling using routine clinical pharmacokinetic data in Japanese patients.

Nonlinear mixed effects modeling was used to estimate the effects of clonazepam-carbamazepine interaction on clearance values using 359 serum levels gathered from 183 pediatric and adult epileptic patients (age range, 0.3–26.8 years) during their clinical routine care. Patients received the administration of clonazepam and/or carbamazepine. The final model describing clonazepam clearance was CL = 179.0 · TBW −0.231 · 1.22 CBZ , where CL is total body clearance (mL/kg/h) and TBW is total body weight (kg); CBZ = 1 for concomitant administration of carbamazepine and CBZ = zero otherwise. The final model describing carbamazepine clearance was CL = 92.7 · TBW −0.394 · DOSE 0.397 · 0.795 CZP , where DOSE is the daily dose of carbamazepine (mg/kg/day); CZP = 1 for concomitant administration of clonazepam and CZP = zero otherwise. Concomitant administration of clonazepam and carbamazepine resulted in a 22% increase in clonazepam clearance and a 20.5% decrease in carbamazepine clearance.

Population-based investigation of relative clearance of digoxin in Japanese neonates and infants by multiple-trough screen analysis

Abstract. Objective: The steady-state concentrations of digoxin at trough levels were studied to establish the role of patient characteristics in estimating doses for digoxin using routine therapeutic drug monitoring data. Method: The data (n=448) showing steady state after repetitive oral administration in 172 hospitalized neonates and infants were analyzed using Nonlinear Mixed Effect Model (NONMEM), a computer program designed to analyze pharmacokinetics in study populations by allowing pooling of data. Analysis of the pharmacokinetics of digoxin was accomplished using a simple steady-state pharmacokinetic model. The effects of a variety of developmental and demographic factors on the clearance of digoxin were investigated. Results: Estimates generated using NONMEM indicated that clearance of digoxin (l·h–1) was influenced by the demographic variables of age, total body weight, serum creatinine, the coadministration of spironolactone, and the presence or absence of congestive heart failure. The interindividual variability in digoxin clearance was modeled with proportional errors with an estimated coefficient of variation of 32.1%, and the residual variability was 28.9%. In the validation set of 66 patients, the performance (bias, precision) of the final population model was good (mean prediction error –0.04xa0ng·ml–1; mean absolute prediction error 0.20xa0ng·ml–1).

Relationship between diurnal rhythm of cell cycle and interferon receptor expression in implanted-tumor cells

Whether the diurnal rhythm of cell cycle is associated with that of interferon-alpha/beta receptor (IFNAR) expression was investigated in implanted-tumor cells. The expression of IFNAR mRNA significantly increased when the proportion of tumor cells in DNA synthesis (S) phase increased in vitro. A diurnal rhythm was observed for cell cycle distribution in implanted-tumor cells. The specific binding of interferon-alpha to receptor and IFNAR mRNA increased when the proportion of tumor cells in S phase increased in vivo. The time-dependent expression of IFNAR was supported by that of transcription factor level induced by interferon-beta. The present result suggests that the rhythm of IFNAR expression is closely related to that of cell cycle distribution in implanted-tumor cells.