Effects of ursodeoxycholic acid on the pharmacokinetics and pharmacodynamics of intravenous and oral midazolam in healthy volunteers

Prediction of Pharmacokinetics for CYP3A4-Metabolized Drugs in Pediatrics and Geriatrics Using Dynamic Age-Dependent Physiologically Based Pharmacokinetic Models

Background/Objectives: The use of medicines in pediatrics and geriatrics is widespread. However, information on pharmacokinetics of therapeutic drugs mainly comes from healthy adults, and the pharmacokinetic parameters of therapeutic drugs in other age stages, including pediatrics and geriatrics, are limited. The aim of the study was to develop a dynamic age-dependent physiologically based pharmacokinetic (PBPK) model to predict the pharmacokinetics of drugs in humans at different ages. Method: The PBPK models characterizing dynamic age-dependence were developed in adults (20-59 years old) and 1000 virtual individuals were constructed. Four CYP3A substrates, namely midazolam, fentanyl, alfentanil and sufentanil, served as model drugs. Following validation using clinic observations in adult populations, the developed PBPK models were extrapolated to other age populations, such as pediatrics and geriatrics, via replacing their physiological parameters and pharmacokinetic parameters, such as organ volume, organ blood flow, clearance, fu,b and Kt:p. The simulations were compared with clinic observations in corresponding age populations. Midazolam served as an example, the dose transitions between adult pediatrics and adult geriatrics were visualized using the developed PBPK models. Results: Most of observed plasma concentrations fell within the 5th-95th percentile of the predicted values in the 1000 virtual individuals, and the predicted AUC0-t and Cmax were almost within between 0.5 and 2 times of the observations. The optimization of dosages in pediatrics and geriatrics were further documented. Conclusions: The developed PBPK model may be successfully used to predict the pharmacokinetics of CYP3A4-metabolized drugs in different age groups and to optimize their dosage regiments in pediatrics and geriatrics.

Physiologically based pharmacokinetic/pharmacodynamic modeling to evaluate the absorption of midazolam rectal gel

OBJECTIVE

We aimed to 1) develop physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) models of a novel midazolam rectal gel in healthy adults, 2) assess the contribution of different physiologically relevant factors in rectal absorption, and 3) to provide supports for future clinical studies of midazolam rectal gel.

METHODS

We developed the rectal PBPK model after built the intravenous and the oral PBPK model. Then, the physiological progress of rectal route was described in terms of the drug release, the rectal absorption and the particle first-pass elimination. Next, the validated PBPK model was combined with the sigmoid E_max PD model. This PBPK/PD model was used to identify the dose range and the critical parameters to ensure safety sedation.

RESULTS

Based on the simulations, the recommended maximum dose for adults' sedation was 15 mg. And the retention time of midazolam rectal gel should be longer than 3 h to reach over 80% pharmacokinetics and pharmacodynamics effects.

CONCLUSION

We successfully developed a PBPK/PD model for the midazolam rectal gel, which accurately described the PK/PD behavior in healthy adults and indicated the transit time of rectum was the most sensitive parameter for absorption. This PBPK/PD model would be expected to support the future clinical studies and pediatric application.

In vitro-in vivo extrapolation of metabolic clearance using human liver microsomes: factors showing variability and their normalization

In vitro-in vivo extrapolation (IVIVE) using human liver microsomes has been widely used to predict metabolic clearance, but some of the factors used in the process of prediction show variability for the same compound: notably, microsomal intrinsic clearance values corrected by the unbound fraction (CL_{int, u}), physiological parameters used for scale-up, and the source of in vivo clearance data.The purpose of this study was to assess the correlation between in vitro and in vivo CL_int with a focus on factors showing variability using four cytochrome P450 (CYP)3A substrates.We surveyed in vivo clearance values in literature and also determined the microsomal CL_{int, u} values. A scaling factor (SF_direct) was defined as in vivo CL_int divided by the microsomal CL_{int, u}, which ranged from 1190 to 2310 (mg protein per kg body weight). The application of a mean SF_direct of 1600 (mg protein per kg body weight) and further normalization by the microsomal CL_{int, u} values of midazolam, the most commonly used substrate, resulted in improved prediction accuracy for CL_{int, u} values from various microsomal batches.The results suggest the normalization of variability might be useful for predicting the in vivo CL_int.

Ursodeoxycholic acid in pregnancy?

The case of a 34-year-old woman with primary biliary cholangitis (PBC) before, during and after pregnancy is described. The use of ursodeoxycholic acid (UDCA) during and after pregnancy is discussed. UDCA has not been approved by the drug regulatory authorities as a pregnancy-safe drug; therefore, the reluctance of clinicians to prescribe UDCA during pregnancy is understandable. This Grand Round aims to provide a detailed analysis of the current evidence, safety data and clinical experience with UDCA (and alternative drugs) during pregnancy and lactation. Based on this analysis, advice for clinicians regarding the use of UDCA during pregnancy and lactation is given.

Bile Acids, Nuclear Receptors and Cytochrome P450

This review summarizes the importance of bile acids (BA) as important regulators of various homeostatic mechanisms with detailed focus on cytochrome P450 (CYP) enzymes. In the first part, synthesis, metabolism and circulation of BA is summarized and BA are reviewed as physiological ligands of nuclear receptors which regulate transcription of genes involved in their metabolism, transport and excretion. Notably, PXR, FXR and VDR are the most important nuclear receptors through which BA regulate transcription of CYP genes involved in the metabolism of both BA and xenobiotics. Therapeutic use of BA and their derivatives is also briefly reviewed. The physiological role of BA interaction with nuclear receptors is basically to decrease production of toxic non-polar BA and increase their metabolic turnover towards polar BA and thus decrease their toxicity. By this, the activity of some drug-metabolizing CYPs is also influenced what could have clinically relevant consequences in cholestatic diseases or during the treatment with BA or their derivatives.

In vitro inhibition and induction of human liver cytochrome P450 enzymes by gentiopicroside: potent effect on CYP2A6

Gentiopicroside (GE), a naturally occurring iridoid glycoside, has been developed into a Novel Traditional Chinese Drug named gentiopicroside injection, and it was approved for the treatment of acute jaundice and chronic active hepatitis by SFDA. However, the inhibitory and inducible effects of GE on the activity of cytochrome P450 (CYP450) are unclear. The purpose of this study was to evaluate the ability of GE to inhibit and induce human cytochrome P450 enzymes in vitro. In human liver microsomes, GE inhibited CYP2A6 and CYP2E1 in a concentration-dependent manner, with IC₅₀ values of 21.8 µg/ml and 594 µg/ml, respectively, and the IC₅₀ of CYP2A6 was close to the C(max) value observed clinically. GE was a non-competitive inhibitor of CYP2A6 at lower concentrations and a competitive inhibitor at higher concentrations. GE did not produce inhibition of CYP2C9, CYP2D6, CYP1A2 or CYP3A4 activities. However, a significant increase of CYP1A2 and CYP3A4 activity was observed at high concentrations. In cultured human hepatocytes no significant induction of CYP1A2, CYP3A4 or CYP2B6 was observed. Given these results, the in vivo potential inhibition of GE on CYP2A6 deserves further investigation, and it seems that the hepatoprotective effect of GE is irrelevant to its effect on P450s.

Effect of 2 weeks' consumption of pomegranate juice on the pharmacokinetics of a single dose of midazolam: an open-label, randomized, single-center, 2-period crossover study in healthy Japanese volunteers

BACKGROUND

It has been reported that pomegranate juice significantly increased the AUC of orally administered carbamazepine in rats, which suggests that pomegranate may inhibit the cytochrome P450 3A (CYP3A)-mediated carbamazepine metabolism.

OBJECTIVE

The aim of the present study was to clarify the effect of repeated consumption of pomegranate juice on CYP3A activity by assessing the pharmacokinetics of midazolam, a typical CYP3A probe drug, and its metabolites in healthy volunteers.

METHODS

An open-label, randomized, single-center, 2-period crossover study was conducted on healthy Japanese volunteers. Each subject received 200 mL of pomegranate juice twice daily for 2 weeks. On day 14, they were administered 15 μg/kg midazolam orally with either pomegranate juice or water. Plasma concentrations and urinary excretions of midazolam, 1'-hydroxymidazolam, and 4-hydroxymidazolam were determined up to 24 hours using LC/MS/MS and analyzed by a noncompartmental method.

RESULTS

Sixteen subjects (11 men and 5 women) were enrolled and completed the study. The mean (SD) age was 24.1 (4.8) years (range 22-40), mean body weight was 62.9 (8.8) kg (range 45.6-79.9). Differences in the mean AUC(0-∞) were 12.7 (4.4) and 14.2 (6.6) ng/mL/h in pomegranate juice and control groups, respectively (geometric mean ratio: 1.02 [95% CI, 0.95-1.09]; P = 0.40). Differences in C(max) for midazolam did not reach the level of statistical significance (5.1 [1.7] vs 5.0 [2.0] ng/mL, geometric mean ratio: 0.95 [95% CI, 0.79-1.11]; P = 0.68). Excretions of 1'-hydroxymidazolam (P = 0.34) and 4-hydroxymidazolam (P = 0.32) were not significantly altered by ingestion of pomegranate juice.

CONCLUSION

In this small Japanese adult volunteer population receiving single subtherapeutic doses of midazolam, 2 weeks' consumption of pomegranate juice did not significantly alter the pharmacokinetic profile of midazolam compared with that of the control. Protocol identifier: UMIN000004459.