The British Journal of Clinical Pharmacology: The first 50 years.

The British Journal of Clinical Pharmacology celebrates its 50th anniversary of publication in 2023. Here four previous Editors-in-Chief and the current Editor reflect on the Journal's history and the changes that have occurred during that time.

When Regional Anesthesia Met Pharmacokinetics.

Pharmacokinetics of Local Anaesthetic Agents. By Tucker GT, Mather LE. Br J Anaesth 1975; 47(suppl 1):213-24 Information derived from measurements of blood concentrations of local anaesthetics can be extended by the application of pharmacokinetic analysis. A better understanding of quantitative aspects of the disposition and absorption of these drugs should assist the anaesthetist in deciding the optimal agent and dosage for regional block techniques.

A series acceleration algorithm for the gamma-Pareto (type I) convolution and related functions of interest for pharmacokinetics.

The gamma-Pareto type I convolution (GPC type I) distribution, which has a power function tail, was recently shown to describe the disposition kinetics of metformin in dogs precisely and better than sums of exponentials. However, this had very long run times and lost precision for its functional values at long times following intravenous injection. An accelerated algorithm and its computer code is now presented comprising two separate routines for short and long times and which, when applied to the dog data, completes in approximately 3 min per case. The new algorithm is a more practical research tool. Potential pharmacokinetic applications are discussed.

Prediction of olanzapine exposure in individual patients using physiologically based pharmacokinetic modelling and simulation.

AIM: The aim of the present study was to predict olanzapine (OLZ) exposure in individual patients using physiologically based pharmacokinetic modelling and simulation (PBPK M&S). METHODS: A 'bottom-up' PBPK model for OLZ was constructed in Simcyp® (V14.1) and validated against pharmacokinetic studies and data from therapeutic drug monitoring (TDM). The physiological, demographic and genetic attributes of the 'healthy volunteer population' file in Simcyp® were then individualized to create 'virtual twins' of 14 patients. The predicted systemic exposure of OLZ in virtual twins was compared with measured concentration in corresponding patients. Predicted exposures were used to calculate a hypothetical decrease in exposure variability after OLZ dose adjustment. RESULTS: The pharmacokinetic parameters of OLZ from single-dose studies were accurately predicted in healthy Caucasians [mean-fold errors (MFEs) ranged from 0.68 to 1.14], healthy Chinese (MFEs 0.82 to 1.18) and geriatric Caucasians (MFEs 0.55 to 1.30). Cumulative frequency plots of trough OLZ concentration were comparable between the virtual population and patients in a TDM database. After creating virtual twins in Simcyp®, the R2 values for predicted vs. observed trough OLZ concentrations were 0.833 for the full cohort of 14 patients and 0.884 for the 7 patients who had additional cytochrome P450 2C8 genotyping. The variability in OLZ exposure following hypothetical dose adjustment guided by PBPK M&S was twofold lower compared with a fixed-dose regimen - coefficient of variation values were 0.18 and 0.37, respectively. CONCLUSIONS: Olanzapine exposure in individual patients was predicted using PBPK M&S. Repurposing of available PBPK M&S platforms is an option for model-informed precision dosing and requires further study to examine clinical potential.

Inhibition of human UDP-glucuronosyltransferase enzymes by lapatinib, pazopanib, regorafenib and sorafenib: Implications for hyperbilirubinemia.

Kinase inhibitors (KIs) are a rapidly expanding class of drugs used primarily for the treatment of cancer. Data relating to the inhibition of UDP-glucuronosyltransferase (UGT) enzymes by KIs is sparse. However, lapatinib (LAP), pazopanib (PAZ), regorafenib (REG) and sorafenib (SOR) have been implicated in the development of hyperbilirubinemia in patients. This study aimed to characterise the role of UGT1A1 inhibition in hyperbilirubinemia and assess the broader potential of these drugs to perpetrate drug-drug interactions arising from UGT enzyme inhibition. Twelve recombinant human UGTs from subfamilies 1A and 2B were screened for inhibition by LAP, PAZ, REG and SOR. IC50 values for the inhibition of all UGT1A enzymes, except UGT1A3 and UGT1A4, by the four KIs were <10µM. LAP, PAZ, REG and SOR inhibited UGT1A1-catalysed bilirubin glucuronidation with mean IC50 values ranging from 34nM (REG) to 3734nM (PAZ). Subsequent kinetic experiments confirmed that REG and SOR were very potent inhibitors of human liver microsomal ß-estradiol glucuronidation, an established surrogate for bilirubin glucuronidation, with mean Ki values of 20 and 33nM, respectively. Ki values for LAP and PAZ were approximately 1- and 2-orders of magnitude higher than those for REG and SOR. REG and SOR were equipotent inhibitors of human liver microsomal UGT1A9 (mean Ki 678nM). REG and SOR are the most potent inhibitors of a human UGT enzyme identified to date. In vitro-in vivo extrapolation indicates that inhibition of UGT1A1 contributes significantly to the hyperbilirubinemia observed in patients treated with REG and SOR, but not with LAP and PAZ. Inhibition of other UGT1A1 substrates in vivo is likely.

Personalized Drug Dosage - Closing the Loop.

A brief account is given of various approaches to the individualization of drug dosage, including the use of pharmacodynamic markers, therapeutic monitoring of plasma drug concentrations, genotyping, computer-guided dosage using 'dashboards', and automatic closed-loop control of pharmacological action. The potential for linking the real patient to his or her 'virtual twin' through the application of physiologically-based pharmacokinetic modeling is also discussed.

The absorption kinetics of ketoconazole plays a major role in explaining the reported variability in the level of interaction with midazolam: Interplay between formulation and inhibition of gut wall and liver metabolism.

The impact of different single oral doses of ketoconazole (KTZ) (100, 200 and 400 mg) and of staggering its dosage (400 mg at -12, -2, 0, 2 and 4 h), with respect to the administration of a single 5 mg oral dose of midazolam (MDZ) on the extent of inhibition of the metabolism of the latter, was evaluated in healthy subjects in two separate studies. Escalation of the ketoconazole dosage resulted in 2.3 (1.9), 2.7 (1.7) and 4.2 (2.5) -fold increases in the mean AUC(0,12h) (and Cmax ) values of midazolam. Dose-staggering was associated with 3.9 (2.5), 4.9 (2.9), 5.4 (2.8), 2.0 (1.3) and 1.2 (0.9) -fold increases in the mean AUC(0,12h) (and Cmax ) of midazolam. These findings could be predicted by physiologically based pharmacokinetic (PBPK) modelling using the ADAM (advanced dissolution absorption and metabolism) model within the Simcyp Simulator (Version 12 Release 2) to characterize the absorption kinetics of ketoconazole with respect to disintegration time, supersaturation ratio and precipitation rate. This study also emphasizes a need to account for inter-individual variability in the gut wall and systemic exposure of inhibitors with physicochemical properties similar to ketoconazole, in particular in their rate of oral absorption and when using different pharmaceutical formulations, in designing and evaluating the extent of drug-drug interactions. Copyright © 2016 John Wiley & Sons, Ltd.

Current Challenges and Potential Opportunities for the Pharmaceutical Sciences to Make Global Impact: An FIP Perspective.

The chairs of each of the 8 Special Interest Groups of the Board of Pharmaceutical Sciences of the International Pharmaceutical Federation have compiled opinions with regard to major challenges for the pharmaceutical sciences over the next 5-10 years. Areas covered are drug design and discovery, natural products, formulation design and pharmaceutical technology, pharmacokinetics/pharmacodynamics and systems pharmacology, translational and personalized medicine, biotechnology, analytical sciences and quality control, and regulatory science.

In Vitro Characterization of the Human Liver Microsomal Kinetics and Reaction Phenotyping of Olanzapine Metabolism.

Olanzapine (OLZ) is an atypical antipsychotic used in the treatment of schizophrenia and related psychoses. The metabolism of OLZ is complex and incompletely characterized. This study aimed to elucidate the enzymes and pathways involved in the metabolism of OLZ and to determine the kinetics of OLZ oxidation and glucuronidation by human liver microsomes, recombinant cytochrome P450 (rP450) enzymes, and recombinant UDP-glucuronosyltransferase (rUGT) enzymes. An ultra-performance liquid chromatography-mass spectrometry method was developed and validated to quantify OLZ, its four oxidative metabolites (N-desmethyl-OLZ, 2-hydroxymethyl-OLZ, 7-hydroxy-OLZ, and OLZ-N-oxide), and two N-glucuronides (OLZ-10-N-glucuronide and OLZ-4'-N-glucuronide). Consistent with previous reports, UGT1A4, CYP1A2, and flavin-containing monooxygenase 3 play major roles in catalyzing the formation of OLZ-10-N-glucuronide, 7-hydroxy-OLZ, and OLZ-N-oxide, respectively. In addition, a previously uncharacterized major contribution of CYP2C8 to OLZ-N-demethylation was demonstrated. The kinetics of OLZ metabolite formation (Km and Vmax) by human liver microsomes, rP450 enzymes, and rUGT enzymes were characterized in the presence of bovine serum albumin [2% (w/v)]. Consistent with the known effect of bovine serum albumin on CYP1A2, CYP2C8, and UGT1A4 activities, Km values reported here are lower than previously reported values for OLZ metabolic pathways. In addition to CYP1A2-mediated OLZ-N-demethylation, these results suggest that other P450 enzymes, particularly CYP2C8, contribute significantly to oxidative OLZ metabolism through catalysis of OLZ-N-demethylation.

Development and testing in healthy adults of oral hydrocortisone granules with taste masking for the treatment of neonates and infants with adrenal insufficiency.

BACKGROUND: Treatment of neonates and infants with adrenal insufficiency is unsatisfactory because unlicensed hydrocortisone formulations are used. OBJECTIVES: The objectives were to survey current hydrocortisone prescribing practice and develop a novel hydrocortisone formulation, Infacort. METHODS: The use of hydrocortisone by European pediatric endocrinologists was surveyed. Based on this, an oral hydrocortisone granule formulation, Infacort, with taste masking was developed and evaluated in vitro and then in vivo in a phase I pharmacokinetic study. RESULTS: The survey showed that pediatricians use a variety of unlicensed compounded adult medications at doses of between 0.5 and 5 mg. Infacort was formulated with a taste-masking layer stable for at least 5 minutes in aqueous media and was produced in unit doses of 0.5, 1, 2, and 5 mg. Infacort 10 mg is the bioequivalent of a 10-mg hydrocortisone tablet (mean area under the curve from zero to infinity [AUC(0-inf)] ratio, 101%; 90% confidence interval, 96-107%). Mean cortisol maximum concentration (C(max)) and AUC(0-inf) values after administration of Infacort were linear with dose and dose proportional when adjusted for saturable plasma protein binding. Subjects rated Infacort as "not good or bad" for smell (86%), feel in the mouth (71%), and taste (79%). No serious adverse events were reported. CONCLUSIONS: This phase 1 study demonstrates that Infacort is safe, well tolerated, of neutral taste, bioequivalent to hydrocortisone licensed for adults, and shows dose proportionality with respect to cortisol exposure. Infacort is expected to facilitate optimization of hydrocortisone dosing in neonates and children with adrenal insufficiency; however, clinical studies will be required to demonstrate efficacy in this patient age group.

Does age affect gastric emptying time? A model-based meta-analysis of data from premature neonates through to adults.

PURPOSE: Gastric emptying (GE) is often reported to be slower and more irregular in premature neonates than in older children and adults. The aim of this study was to investigate the impact of age and other covariates on the rate of GE. METHODS: The effect of age on the mean gastric residence times (MGRT) of liquid and solid food was assessed by analysing 49 published studies of 1457 individuals, aged from 28 weeks gestation to adults. The data were modelled using the nonlinear mixed-effects approach within NONMEM version 7.2 (ICON, Dublin, Ireland), with evaluation of postnatal age, gestational age and meal type as covariates. A double Weibull function was selected as a suitable model since it could account for the typical biphasic nature of GE. RESULTS: Age was not a significant covariate for GE but meal type was. Aqueous solutions were associated with the fastest emptying time (mean simulated gastric residence time of 45 min) and solid food was associated with the slowest (98 min). CONCLUSIONS: These findings challenge the assertion that GE is different in neonates, as compared with older children and adults due to age, and they reinforce the significance of food type in modulating GE.

A re-evaluation and validation of ontogeny functions for cytochrome P450 1A2 and 3A4 based on in vivo data.

BACKGROUND AND OBJECTIVES: Current cytochrome P450 (CYP) 1A2 and 3A4 ontogeny profiles, which are derived mainly from in vitro studies and incorporated in paediatric physiologically based pharmacokinetic models, have been reported to under-predict the in vivo clearances of some model substrates in neonates and infants. METHOD: We report ontogeny functions for these enzymes as paediatric to adult relative intrinsic clearance per mg of hepatic microsomal protein, based on the deconvolution of in vivo pharmacokinetic data and by accounting for the impact of known clinical condition on hepatic unbound intrinsic clearance for caffeine and theophylline as markers of CYP1A2 activity and for midazolam as a marker of CYP3A4 activity. RESULTS: The function for CYP1A2 describes an increase in relative intrinsic metabolic clearance from birth to 3 years followed by a decrease to adult values. The function for CYP3A4 describes a continuous rise in relative intrinsic metabolic clearance, reaching the adult value at about 1.3 years of age. The new models were validated by showing improved predictions of the systemic clearances of ropivacaine (major CYP1A2 substrate; minor CYP3A4 substrate) and alfentanil (major CYP3A4 substrate) compared with those using a previous ontogeny function based on in vitro data (alfentanil: mean squared prediction error 3.0 vs. 6.8; ropivacaine: mean squared prediction error 2.3 vs.14.2). CONCLUSIONS: When implementing enzyme ontogeny functions, it is important to consider potential confounding factors (e.g. disease) that may affect the physiological conditions of the patient and, hence, the prediction of net in vivo clearance.

Differences in cytochrome p450-mediated pharmacokinetics between chinese and caucasian populations predicted by mechanistic physiologically based pharmacokinetic modelling.

BACKGROUND: International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) guidelines emphasize the need for better understanding of the influence of ethnicity on drug response to minimize duplication of clinical studies, thereby expediting drug approval. OBJECTIVES: We have developed a Chinese database for the prediction of differences in the population kinetics of drugs mainly metabolized by cytochromes P450 (CYPs) relative to Caucasian populations. Such predictions should help to inform the need for duplication of in vivo pharmacokinetic studies in the two ethnic groups and the design of such studies. METHODS: Demographic and physiological data for Chinese, along with information on CYP abundances and the frequencies of associated genetic polymorphisms in Chinese, were collated from literature sources and incorporated within the Simcyp Population-based Simulator(®) (v11.1). Default Simcyp parameter values for a virtual Caucasian population and for model compounds metabolized principally by specific CYPs were used as the point of reference. The drugs and the main CYPs involved in their metabolism were phenacetin (CYP1A2), desipramine (CYP2D6), tolbutamide (CYP2C9), omeprazole (CYP2C19), and alprazolam and midazolam (CYP3A). Hydroxy bupropion formation was used as a more sensitive marker of CYP2B6 activity than bupropion kinetics. Observed plasma drug concentration-time profiles and pharmacokinetic parameters after oral and, where possible, intravenous dosing were obtained from published in vivo studies in both Chinese and Caucasian subjects. Virtual subjects generated within Simcyp were matched to the subjects used in the in vivo studies with respect to age, sex, dosage and, where possible, CYP phenotype frequency. Predicted and observed plasma drug concentrations and weight-normalized clearances were compared between the ethnic groups. RESULTS: Significant differences were identified between Chinese and Caucasian populations in the frequency of CYP2C19 poor metabolizers (PMs) [Chinese 13 %; Caucasian 2.4 %], CYP2D6 PMs and intermediate metabolizers (IMs) [Chinese PMs 0.3 %, IMs 39 %; Caucasian PMs 8 %, IMs <1 %], the hepatic abundance of CYP2C19 (mean values: Chinese 8 pmol/mg; Caucasian 14 pmol/mg) and liver weight (mean values: Chinese 1198 g; Caucasian 1603 g). The observed plasma drug concentration-time profiles and weight-normalized clearances were predicted with reasonable accuracy (100 % within twofold; 89 % within 1.5-fold) in both ethnic groups. The predicted phenacetin, tolbutamide, omeprazole, desipramine, midazolam (intravenous), midazolam (oral), alprazolam (intravenous) and alprazolam (oral) clearances were 36, 25, 51, 43, 24, 17, 21 and 22 % lower, respectively, in Chinese than in Caucasians; the observed clearances were 28, 2, 75, 42, 19, 62, 20 and 21 % lower, respectively. Predicted and observed formation of hydroxy bupropion was lower in Caucasians than in Chinese (6 and 20 %, respectively). Differences between ethnic groups were less after normalization for body weight. CONCLUSION: The results of this study indicate the value of simulation based on mechanistic physiologically based pharmacokinetic modelling (PBPK) in anticipating the likely extent of any differences in the kinetics of CYP substrates in Chinese and Caucasian populations arising from demographic, physiological and genetic differences.