Results from this study suggest that DBP and E4BP4 might consist of a reciprocating mechanism in which DBP activates the transcription of the CYP3A4 gene during the time of day when DBP is abundant, and E4BP4 suppresses the transcription at other times of day. Our current findings provide a molecular link between the circadian clock and the xenobiotic metabolism.

We developed a new model for neonate and infant dosing of phenobarbital with good predictive performance. Clinical application of our model should permit more accurate selection of initial and maintenance doses to achieve target phenobarbital concentrations in Japanese neonates and infants, thereby enabling the clinician to achieve the desired therapeutic effect. A similar approach can be used to validate our model for use in other neonate and infant populations.

Cytochrome P450 2E1 (CYP2E1) is clinically and toxicologically important and exhibits 24-hour periodicity in its activity. In the present study, we investigated whether hepatic nuclear factor-1␣ (HNF-1␣) and clock genes with a striking 24-hour rhythm in mouse liver contributed to the 24-hour regulation of CYP2E1 expression. The results demonstrated that the expression of CYP2E1 messenger RNA (mRNA) in the liver was affected by HNF-1␣ and the circadian organization of molecular clocks. The mRNA levels of CYP2E1 in the liver increased from the late light phase to the early dark phase. Luciferase reporter gene analysis revealed that HNF-1␣ activated CYP2E1 promoter activity, which was restricted by CRY1, a member of the circadian organization of molecular clocks. Repressor activity of CRY1 was observed on the HNF-1␣ binding site of the CYP2E1 promoter region with mutated E-box. The effectiveness and toxicity of many drugs vary depending on the dosage in association with 24-hour rhythms of biochemical, physiological, and behavioral processes under the control of the circadian clock. 2,3 Recently, several clock genes have been identified that control an array of circadian rhythms in physiology and behavior. According to the currently held model, the core circadian oscillator consists of an autoregulatory transcription-translation feedback loop. CLOCK and BMAL1 proteins form a heterodimer and then activate the transcription of Per and Cry genes. Once PER and CRY proteins have reached a critical concentration, they attenuate CLOCK/BMAL1-mediated activation of their own genes in a negative feedback loop. 4,5 The existence of peripheral clocks has been suggested in the liver, kidney, lung, and other organs, serving as endogenous oscillators to regulate peripheral circadian rhythms on the one hand and synchronized by a master clock on the other hand. [6][7][8] Cytochrome P450 2E1 (CYP2E1) is clinically and toxicologically important. Compared with other CYP genes,

We developed a new model for elderly patient dosing of digoxin with good predictive performance. Clinical application of the findings of the present study to patient care may permit selection of an appropriate initial digoxin maintenance dose, thus enabling the clinician to achieve a desired therapeutic effect. However, the digoxin dosage regimen should be based on an appraisal of the individual patient's clinical need for the drug.

To establish the role of patient characteristics in estimating doses of digoxin for infants and young children using routine therapeutic drug monitoring data, the steady-state blood-level data (n = 245) after repetitive oral administration in 117 hospitalized infants and young children were analyzed using nonlinear mixed effects modeling (NONMEM), a computer program designed for analyzing drug pharmacokinetics in study populations through pooling of data. Analysis of the pharmacokinetics of digoxin was accomplished using a 1-compartment pharmacokinetic model. Estimates generated by NONMEM indicated that the clearance of digoxin (CL/F; L/h) was influenced by the following demographic variables: total body weight (TBW), presence of congestive heart failure (CHF), and infant-young children clearance factor (trough serum concentration of digoxin; Conc). These influences could be modeled by the equation CL/F (L/h) = 0.302 · TBW (kg)¹·¹⁷ · 0.905(CHF) · Conc (trough serum digoxin concentration >1.7 ng/mL)⁻⁰·⁵⁴⁰; F = 0.754, where CHF is 1 for presence of congestive heart failure, 0 otherwise; F is bioavailability, 1 for elixirs, 0.754 for powders; and Conc⁻⁰·⁵⁴⁰ is 1 for digoxin concentration <1.7 ng/mL. Clinical application of the model to patient care may permit selection of an appropriate initial maintenance dose, thus enabling the clinician to achieve the desired therapeutic effect. However, the digoxin dosage regimen for the individual patient should be based on a careful appraisal of his or her clinical need for the drug.