Modified-release hydrocortisone to provide circadian cortisol profiles.

Context: Cortisol has a distinct circadian rhythm regulated by the brain's central pacemaker. Loss of this rhythm is associated with metabolic abnormalities, fatigue, and poor quality of life. Conventional glucocorticoid replacement cannot replicate this rhythm.

The Simcyp population-based ADME simulator.

The Simcyp population-based absorption, distribution, metabolism and excretion simulator is a platform and database for 'bottom-up' mechanistic modelling and simulation of the processes of oral absorption, tissue distribution, metabolism and excretion of drugs and drug candidates in healthy and disease populations. It combines experimental data generated routinely during preclinical drug discovery and development from in vitro enzyme and cellular systems and relevant physicochemical attributes of compound and dosage form with demographic, physiological and genetic information on different patient populations. The mechanistic approach implemented in the Simcyp Simulator allows simulation of complex absorption, distribution, metabolism and excretion outcomes, particularly those involving multiple drug interactions, parent drug and metabolite profiles and time- and dose-dependent phenomena such as auto-induction and auto-inhibition.

Contribution of the activities of CYP3A, CYP2D6, CYP1A2 and other potential covariates to the disposition of methadone in patients undergoing methadone maintenance treatment.

Aims: To investigate the influence of different cytochrome P450 (CYP) activities and other potential covariates on the disposition of methadone in patients on methadone maintenance therapy (MMT).

Methods: Eighty-eight patients (58 male; 21-55 years; 84 White) on MMT were studied. CYP2D6 activity [3 h plasma metabolic ratio of dextromethorphan (DEX) to dextrorphan (DOR)] was determined in 44 patients (29 male; 24-55 years), CYP1A2 activity (salivary caffeine elimination half-life) in 44 patients (21 male; 24-55 years) and CYP3A activity (oral clearance of midazolam) in 49 patients (33 male; 23-55 years).

Single-dose pharmacokinetic study of clomiphene citrate isomers in anovular patients with polycystic ovary disease.

The pharmacokinetics of the zuclomiphene (Zu) and enclomiphene (En) isomers of clomiphene citrate following a single oral dose (50 mg) were characterized for the first time in patients receiving the drug (ie, infertile women with polycystic ovary syndrome). Plasma concentrations of Zu and En were measured in 9 patients from the second day of their menstrual cycle (day 1 of dosing) up to 21 days. The mean (+/- coefficient of variation) of C(max), t(max), and AUC of Zu was 15 +/- 41 ng/mL, 7 +/- 87 h, and 1289 +/- 34 ng/mL.

The consequences of 3,4-methylenedioxymethamphetamine induced CYP2D6 inhibition in humans.

3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is a widely abused substituted amphetamine. MDMA is predominantly O-demethylenated in humans by cytochrome P450 isoforms 2D6 and 1A2 (CYP2D6 and CYP CYP1A2, respectively). MDMA is also a mechanism-based inhibitor of CYP2D6.

Covariation of human microsomal protein per gram of liver with age: absence of influence of operator and sample storage may justify interlaboratory data pooling.

Scaling of metabolic clearance values from liver microsomal data or recombinantly expressed cytochrome P450 enzymes to predict human hepatic clearance requires knowledge of the amount of microsomal protein per gram of liver (MPPGL). Identification of physiological covariates of MPPGL requires analysis of values from large diverse populations, which necessitates pooling of data from numerous sources. To ensure compatibility between results obtained within and between studies, the impact of interoperator differences and sample storage on values of MPPGL was investigated.

Metabolism of dextrorphan by CYP2D6 in different recombinantly expressed systems and its implications for the in vitro assessment of dextromethorphan metabolism.

Cytochrome P450 2D6 (CYP2D6) mediated formation of dextrorphan (DOR) from dextromethorphan (DEX) is widely used as a marker to assess the activity of this enzyme both in vitro and in vivo. The sequential metabolism of DOR during in vitro studies, particularly using recombinant systems (rCYPs) expressing human CYP2D6, is assumed to be negligible. The extent of metabolism was investigated for a range of DEX and DOR concentrations in microsomal preparations from three different rCYPs expressing human CYP2D6 (yeast, Supersomes and Bactosomes) containing 10 pmol of the enzyme.

Cytochrome p450 turnover: regulation of synthesis and degradation, methods for determining rates, and implications for the prediction of drug interactions.

In vivo enzyme levels are governed by the rates of de novo enzyme synthesis and degradation. A current lack of consensus on values of the in vivo turnover half-lives of human cytochrome P450 (CYP) enzymes places a significant limitation on the accurate prediction of changes in drug concentration-time profiles associated with interactions involving enzyme induction and mechanism (time)-based inhibition (MBI). In the case of MBI, the full extent of inhibition is also sensitive to values of enzyme turnover half-life.

CYP2D6 is primarily responsible for the metabolism of clomiphene.

Clomiphene is a first line treatment for anovulation, a common cause of infertility. Response to clomiphene is variable and unpredictable. Tamoxifen is structurally related to clomiphene, and also shows considerable variation in response.

Evaluation of the relationship between plasma concentrations of en- and zuclomiphene and induction of ovulation in anovulatory women being treated with clomiphene citrate.

Objective: To investigate the relationship between the plasma concentrations of clomiphene citrate (CC) isomers zu- (Zu) and enclomiphene (En), and ovulation outcome.

Design: Prospective, cohort study.

Setting: Reproductive medicine and fertility center in a university teaching hospital, United Kingdom.

Prediction of intestinal first-pass drug metabolism.

Despite a lower content of many drug metabolising enzymes in the intestinal epithelium compared to the liver (e.g. intestinal CYP3A abundance in the intestine is 1% that of the liver), intestinal metabolic extraction may be similar to or exceed hepatic extraction.

Mechanism-based inactivation of human cytochrome P450 enzymes: strategies for diagnosis and drug-drug interaction risk assessment.

Among drugs that cause pharmacokinetic drug-drug interactions, mechanism-based inactivators of cytochrome P450 represent several of those agents that cause interactions of the greatest magnitude. In vitro inactivation kinetic data can be used to predict the potential for new drugs to cause drug interactions in the clinic. However, several factors exist, each with its own uncertainty, that must be taken into account in order to predict the magnitude of interactions reliably.

Modified-release hydrocortisone for circadian therapy: a proof-of-principle study in dexamethasone-suppressed normal volunteers.

Background: All existing long-term glucocorticoid replacement therapy is suboptimal as the normal nocturnal rise and waking morning peak of serum cortisol is not reproduced.

Aim: To test whether it is possible to reproduce the normal overnight rise and morning peak in serum cortisol using an oral delayed and sustained release preparation of hydrocortisone (Cortisol(ds)).

Subjects And Methods: Six healthy normal male volunteers attended on two occasions, in a single-dose, open-label, nonrandomized study.

Influence of beta2-adrenoceptor gene polymorphisms on beta2-adrenoceptor-mediated responses in human lung mast cells.

Background And Purpose: Previous studies have shown that beta(2)-adrenoceptor-mediated responses in human lung mast cells are highly variable. The aims of the present study were to establish whether polymorphisms of the beta (2)-adrenoceptor gene (ADRB2) influence this variability in (a) beta(2)-adrenoceptor-mediated inhibition and (b) desensitization of beta(2)-adrenoceptor-mediated responses in human lung mast cells.

Experimental Approach: Mast cells were isolated from human lung tissue.

Disparity in holoprotein/apoprotein ratios of different standards used for immunoquantification of hepatic cytochrome P450 enzymes.

An analysis of reported hepatic abundances of CYP3A4 and 3A5 indicated that values determined by immunoquantification using commercially available, unpurified recombinant enzymes as standards are significantly lower than those determined using purified enzymes or human liver microsomes characterized with lysosomal peptides (CYP3A4: mean 45 versus 121 pmol/mg protein, p < 0.01; CYP3A5: mean 28 versus 83 pmol/mg protein, p < 0.05).

Inactivation of CYP2D6 by methylenedioxymethamphetamine in different recombinant expression systems.

Recombinantly expressed CYP450 systems (rCYPs) are often used to screen for irreversible/quasi-irreversible enzyme inhibitors during drug development. The concentration- and time-dependent inactivation of CYP2D6 by methylenedioxymethamphetamine (MDMA) was compared in three different rCYP2D6 systems (yeast microsomes, Supersomestrade mark and Bactosomestrade mark) under the conditions of the most commonly used protocols in assessing mechanism-based inactivation (MBI). MDMA (2-20microM) was pre-incubated with enzyme for 0, 2.

Theoretical assessment of a new experimental protocol for determining kinetic values describing mechanism (time)-based enzyme inhibition.

We have shown previously that the conventional experimental protocol (CEP) used to characterise mechanism-based enzyme inhibition (MBI) of drug metabolism in vitro may introduce substantial bias in estimates of the relevant kinetic parameters. The aim of this study was to develop and assess, by computer simulation, an alternative, mechanistically-based experimental protocol (MEP). This protocol comprises three parts viz.

Kinetics of the time-dependent inactivation of CYP2D6 in cryopreserved human hepatocytes by methylenedioxymethamphetamine (MDMA).

Methylenedioxymethamphetamine (MDMA) was investigated in cryopreserved human hepatocytes as a time-dependent inactivator (TDI) of CYP2D6 using dextromethorphan (DEX) as a probe substrate. Inhibition kinetic parameters k(inact), the maximal rate of inactivation, and K(I), the inhibitor concentration at half the maximal activation rate, were determined. Time- and concentration-dependent inhibition were confirmed, and the influence of different elements of study design (e.

The use of mechanistic DM-PK-PD modelling to assess the power of pharmacogenetic studies -CYP2C9 and warfarin as an example.

Aim: To assess the power of in vivo studies needed to discern the effect of genotype on pharmacokinetics (PK) and pharmacodynamics (PD) using CYP2C9 and (S)-warfarin as an example.

Methods: Information on the in vitro metabolism of (S)-warfarin and genetic variation in CYP2C9 was incorporated into a mechanistic population-based PK-PD model. The influence of study design on the ability to detect significant differences in PK (AUC(0-12 h)) and PD (AUEC(0-12 h) INR) between CYP2C9 genotypes was investigated.

Simulation and prediction of in vivo drug metabolism in human populations from in vitro data.

The perceived failure of new drug development has been blamed on deficiencies in in vivo studies of drug efficacy and safety. Prior simulation of the potential exposure of different individuals to a given dose might help to improve the design of such studies. This should also help researchers to focus on the characteristics of individuals who present with extreme reactions to therapy.

Scaling factors for the extrapolation of in vivo metabolic drug clearance from in vitro data: reaching a consensus on values of human microsomal protein and hepatocellularity per gram of liver.

Reported predictions of human in vivo hepatic clearance from in vitro data have used a variety of values for the scaling factors human microsomal protein (MPPGL) and hepatocellularity (HPGL) per gram of liver, generally with no consideration of the extent of their inter-individual variability. We have collated and analysed data from a number of sources, to provide weighted meangeo values of human MPPGL and HPGL of 32 mg g-1 (95% Confidence Interval (CI); 29-34 mg.g-1) and 99x10(6) cells.

Incorporating in vitro information on drug metabolism into clinical trial simulations to assess the effect of CYP2D6 polymorphism on pharmacokinetics and pharmacodynamics: dextromethorphan as a model application.

In vitro-in vivo extrapolation of clearance, embedded in a clinical trial simulation, was used to investigate differences in the pharmacokinetics and pharmacodynamics of dextromethorphan between CYP2D6 poor and extensive metabolizer phenotypes. Information on the genetic variation of CYP2D6, as well as the in vitro metabolism and pharmacodynamics of dextromethorphan and its active metabolite dextrorphan, was integrated to assess the power of studies to detect differences between phenotypes. Whereas 6 subjects of each phenotype were adequate to achieve 80% power in showing pharmacokinetic differences, the power required to detect a difference in antitussive response was less than 80% with 500 subjects in each study arm.