Variation In Drug Pharmacokinetics Research Articles

Pharmacogenomics Biomarker Discovery and Validation for Translation in Clinical Practice.

Interindividual variability in drug efficacy and toxicity is a major challenge in clinical practice. Variations in drug pharmacokinetics (PKs) and pharmacodynamics (PDs) can be, in part, explained by polymorphic variants in genes encoding drug metabolizing enzymes and transporters (absorption, distribution, metabolism, and excretion) or in genes encoding drug receptors. Pharmacogenomics (PGx) has allowed the identification of predictive biomarkers of drug PKs and PDs and the current knowledge of genome‐disease and genome‐drug interactions offers the opportunity to optimize tailored drug therapy. High‐throughput PGx genotyping, from targeted to more comprehensive strategies, allows the identification of PK/PD genotypes to be developed as clinical predictive biomarkers. However, a biomarker needs a robust process of validation followed by clinical‐grade assay development and must comply to stringent regulatory guidelines. We here discuss the methodological challenges and the emerging technological tools in PGx biomarker discovery and validation, at the crossroad among molecular genetics, bioinformatics, and clinical medicine.

Characterization of Seasonal Pharmacokinetic Variability in Woodchucks.

The eastern woodchuck (Marmota monax) is a hibernating species extensively used as an in vivo efficacy model for chronic human hepatitis B virus infection. Under laboratory conditions, woodchucks develop a pseudohibernation condition; thus, the pharmacokinetics (PK) of small-molecule therapeutics may be affected by the seasonal change. The seasonal PK of four probe compounds were characterized over 12 months in seven male and nine female laboratory-maintained woodchucks. These compounds were selected to study changes in oxidative metabolism [antipyrine (AP)], glucuronidation [raltegravir (RTG)], renal clearance [lamivudine (3TC)], and hepatic function [indocyanine green (ICG)]. Seasonal changes in physiologic parameters and PK were determined. Seasonal body weight increases were ≥30%. Seasonal changes in body temperature and heart rate were <10%. The mean AP exposure remained unchanged from April to August 2017, followed by a significant increase (≥1.0-fold) from August to December and subsequent decrease to baseline at the end of study. A similar trend was observed in RTG and 3TC exposures. The ICG exposure remained unchanged. No significant sex difference in PK was observed, although female woodchucks appeared to be less susceptible to seasonal PK and body weight changes. Significant seasonal PK changes for AP, RTG, and 3TC indicate decreases in oxidative metabolism, phase II glucuronidation, and renal clearance during pseudohibernation. The lack of seasonal change in ICG exposure suggests there are no significant changes in hepatic function. This information can be used to optimize the scheduling of woodchuck studies to avoid seasonally driven variation in drug PK. SIGNIFICANCE STATEMENT: Woodchuck is a hibernating species and is commonly used as a nonclinical model of hepatitis B infection. Investigation of seasonal PK changes is perhaps of greater interest to pharmaceutical industry scientists, who use the woodchuck model to optimize the scheduling of woodchuck studies to avoid seasonally driven variation in drug PK and/or toxicity. This information is also valuable to drug metabolism and veterinary scientists in understanding woodchuck's seasonal metabolism and behavior under the pseudohibernation condition.

A101 USTEKINUMAB LEVELS MEASURED DURING INDUCTION ARE ASSOCIATED WITH CLINICAL AND BIOCHEMICAL OUTCOMES AT WEEK 12 OF TREATMENT IN CROHN’S DISEASE

Abstract Background Therapeutic drug monitoring (TDM) helps guide use of anti-TNF drugs in IBD patients. In addition, higher anti-TNF levels during induction therapy have been shown to be associated with better clinical and endoscopic outcomes. The role of TDM for more novel biologics such as ustekinumab (an anti- IL-12/23 antibody used to treat Crohn’s disease) remains to be elucidated. Aims We set out to investigate correlations between ustekinumab drug levels measured during induction with clinical and biochemical outcomes in patients with Crohn’s disease. Methods Patients with Crohn’s disease commencing treatment with ustekinumab were recruited from a single tertiary referral centre. Standard weight-based induction dosing was used. TDM was performed at week 2 and week 6 following IV induction dose. A drug-tolerant assay (Prometheus) was used. Kruskal-Wallis test was used to examine association between induction dose and ustekinumab levels. CDAI, CRP, and faecal calprotectin (FCP) were measured at week 12. Pearson correlation co-efficient was used to assess the relationship between ustekinumab levels and i)CDAI ii)CRP and iii)FCP at week 12. Results A total of 38 ustekinumab levels in 21 patients were measured. Week 2 ustekinumab levels were available for 17 patients, 16 (94.1%) of whom had levels of greater or equal to 25μg/mL. (1 patient had a level of 19.5μg/mL.) Week 6 ustekinumab levels were available for 21 patients; median 15μg/mL (IQR 9.9–21.3). No patients had detectable antibodies to ustekinumab. There was no significant association between absolute induction dose and week 6 ustekinumab levels; p=0.46. Of the 21 patients with week 6 levels, CDAI, CRP and FCP were available for 18, 18 and 16 patients respectively; Median CDAI 103(IQR 42–249), median CRP 2.3mg/L(IQR 1.0–11.3), median FCP 269μg/g(IQR109-932). There was a significant negative correlation between week 6 ustekinumab levels and CDAI; r=-.609, p=0.007. A negative correlation between week 6 ustekinumab levels and FCP was also significant; r=-.526, p=0.037. There was no significant correlation between week 6 ustekinumab levels and CRP; r=-.259, p=0.298. Conclusions We have demonstrated inter-patient variation in drug pharmacokinetics at week 6 following induction dose of ustekinumab in patients with Crohn’s disease. Drug levels at week 6 are significantly associated with clinical and biochemical markers of disease activity (CDAI, faecal calprotectin) at week 12. Measurement of week 6 ustekinumab levels may aid early identification of patients at risk of primary non-response to ustekinumab. Funding Agencies Testing provided by Prometheus

Daily rhythms of cortisol and glucose and the influence of the light/dark cycle on anaesthesia in Nile tilapia ( Oreochromis niloticus ): Does the timing of anaesthetic administration affect the stress response?

Although daily variations in drug pharmacokinetics have been reported for a variety of teleost species, the influence of this daily variation on the cortisol response following anaesthesia remains poorly understood. To address this, two experiments were performed. The first experiment described the daily patterns of cortisol and glucose secretion in tilapia (Oreochromis niloticus). The second experiment investigated how the timing of anaesthetic administration (specifically at mid-light [ML] or at mid-dark [MD]) affects the induction and recovery times and plasma cortisol and glucose levels of juvenile Nile tilapia exposed to benzocaine, clove oil or tricaine methanesulphonate (MS-222). The results revealed that the effect on the stress response associated with the moment when anaesthesia took place (ML or MD) varied according to the treatment (p < 0.05). Cortisol levels were significantly higher at ML for MS-222 (ML = 116.23 ± 25.55; MD = 48.25 ± 22.33 ng/dl) (p < 0.05) and clove oil (ML 59.73 ± 14.27; MD 38.26 ± 12.07 ng/dl) (p < 0.05), whereas no significant differences were found between ML and MD cortisol levels for the control treatment (ML = 72.91 ± 18.42; MD = 64.80 ± 10.68 ng/dl) (p > 0.05) or in the benzocaine-treated group (ML = 38.7 ± 4.90; MD = 38.60 ± 3.69 ng/dl) (p > 0.05). The highest plasma cortisol level in ML was found in the MS-222-treated group. All the tested anaesthetics had similar cortisol levels at MD (p > 0.05).

O-108 Pharmacokinetics Of Melatonin In Preterm Infants

<h3>Background</h3> Evidence from neonatal studies is critical in understanding developmental variations in drug pharmacokinetics and can guide dosing adjustments. Melatonin has been shown previously in a single dose study to have slow clearance and prolonged half-life in preterm infants. <h3>Aim</h3> To determine the melatonin pharmacokinetic profile in preterm infants on exogenous supplementation and to determine the melatonin concentrations in donor and maternal breast milk. <h3>Methods</h3> The study was part of an exploratory; double-blinded randomised placebo controlled trial evaluating the neuroprotective effect of melatonin in preterm infants less than 31 weeks gestation. Infants in the melatonin arm (n = 29) received an intravenous infusion 0.1 mcg/kg/hr for 2 h once daily for 7 days starting by 48 h after birth. The placebo group (n = 28) received same volume of saline. Plasma and milk melatonin concentrations were analysed by radioimmunoassay. Population pharmacokinetics was carried out using NONMEM. <h3>Results</h3> The median plasma melatonin levels on day 4 was 152pg/ml in the melatonin group and was 0pg/ml in the saline group. On nonlinear mixed effect modelling, using first order conditional estimation with interaction, the clearance was 0.05L/hr with a half-life of 15.61 h. Effect of covariates: gender and race were not significant in this study unlike previously reported. Mean melatonin concentrations in donor breast milk were 63pg/ml, higher than that of maternal breast milk even on day 4 (16.6 pg/ml). <h3>Conclusions</h3> Preterm infants have delayed clearance and prolonged half-life of melatonin. This data can be used for simulation of future dose studies in preterm infants.

Body fat composition impacts the hematologic toxicities and pharmacokinetics of doxorubicin in Asian breast cancer patients

Body surface area (BSA)-based dosing leads to wide inter-individual variations in drug pharmacokinetics and pharmacodynamics, whereas body composition has been shown to be a more robust determinant of efficacy and toxicity of certain chemotherapeutic agents. We correlated various parameters of body composition with doxorubicin pharmacokinetics and hematologic toxicities in Asian patients with locally advanced or metastatic breast cancer. Our analysis included 84 patients from two studies who received pre- or post-operative single-agent doxorubicin; pharmacokinetic parameters were available for 44 patients. Body composition parameters were derived from CT cross-sectional images and population pharmacokinetic analysis was conducted using mixed-effects modeling. Higher intra-abdominal fat volume and fat ratio (intra-abdominal:total abdominal fat volume) correlated with greater incidence of grade 4 leukopenia on cycle 1 day 15 (mean intra-abdominal fat volume: 97.4 ± 46.5 cm(3) vs 63.4 ± 30.9 cm(3), p = 0.014; mean fat ratio: 0.43 ± 0.11 vs 0.33 ± 0.09, p = 0.012, grade 4 vs grade 0-3 leukopenia). On subset analysis, this relationship was maintained even in underweight patients. Concordantly, there were positive correlations between doxorubicin AUC and intra-abdominal fat volume as well as total abdominal fat volume (r (2) = 0.324 and 0.262, respectively, all p < 0.001). BSA and muscle volume did not predict for doxorubicin pharmacokinetics or toxicities. High-intra-abdominal fat volume but not BSA predicted for greater doxorubicin exposure and hematologic toxicities, suggesting that body composition is superior to BSA in determining doxorubicin pharmacokinetics and pharmacodynamics. Body composition has an emerging role in chemotherapy dose determination.

DxS Ltd.

DxS is a personalized medicine company focused on providing genetic analysis services and technologies to enable the delivery of safe and effective medicines. The services provide support for drug development, diagnostic product development and pharmacodiagnostics. There is an increasing demand from the pharmaceutical industry for genetic analysis of clinical trial populations to help to understand individual variation in drug pharmacokinetics and pharmacodynamics. Since these studies are part of a clinical trial it is essential that they are performed in a high quality environment that meets relevant regulatory standards. DxS operates a genotyping service operation that fulfils all of these requirements. One of the expectations deriving from the growing use of pharmacogenetics during clinical development is that some of the genetic markers will be required as diagnostics to allow the identification of suitable patients for a therapy. This combination of a drug and a diagnostic is called personalized medicine. DxS have established a global network of alliance laboratories to allow the rapid translation of tests from clinical development into clinical diagnostics.

Implications of cytochrome P450 genetic polymorphisms on the toxicity of antitumor agents.

In the treatment of cancer, a narrow therapeutic window generally exists between toxicity and suboptimal therapy. In addition, interindividual variation in drug metabolism seriously complicates therapy. Genetic polymorphisms in phase 1 and phase 2 enzymes are present in the population and may explain part of the observed interindividual variation in drug pharmacokinetics. For the cytochrome P450 superfamily, information on variant alleles encoding enzymes with decreased activity is rapidly on the increase. The potential of applying pharmacogenetic screening before therapy in the treatment of cancer seems to be greatest for CYP2B6 (cyclophosphamide treatment), CYP2C8 (paclitaxel therapy), and CYP3A5; however, the drugs of interest still need to be identified for this latter enzyme.

Impact of interpatient pharmacokinetic variability on design considerations for therapy with radiolabeled MAbs.

Radionuclides provide biologically-distributed vehicles for radiotherapy of multifocal cancer. Two algorithms, fixed vs individualized, have been used to prescribe the therapeutic dose of radionuclide (GBq) for the patient. The individualized method for prescribing radionuclide dose takes variations in drug pharmacokinetics into consideration, whereas the fixed method depends, in part, on documentation that there is little interpatient pharmacokinetic variability for the radiolabeled drug. Two data bases, selected to compare iodine-131((131)I) and indium-111((111)In) labeled MAbs, were used to assess interpatient pharmacokinetic variability and its impact on radionuclide dose prescription. Pharmacokinetic data obtained over 7 days for non-Hodgkins lymphoma (NHL) patients given (131)I-Lym-1 (n = 46) or (111)In-Lym-1 (n = 13) were used to obtain cumulated activities. Although (131)I-Lym-1 often showed greater interpatient variability, (111)In-Lym-1 showed several-fold variability for many tissues. Both (131)I- and (111)In-Lym-1 had sufficient interpatient variability to be significant for radionuclide dose prescription, depending on the dose-limiting critical tissue. Interpatient variability exceeded intra- and interoperator variability and intrapatient variability over time for a single institution. In summary, the magnitude of interpatient pharmacokinetic variability for (131)I- and (111)In-Lym-1 suggested that an optimally safe and effective therapy can be best achieved when radionuclide dose is influenced by estimated radiation dose, if the latter is reproducible from institution to institution.

Rational dosing of antimicrobial drugs: animals versus humans

The rational dosing of antimicrobial drugs depends on knowledge of physiology, anatomy and pathology, including disease condition, and in major respects these differ between animals and humans and between species of animal. These differences lead to species variation in drug pharmacokinetics, which can be profound. This review highlights selected aspects of species differences in pharmacokinetics and considers underlying mechanisms by reference to ruminant and non-ruminant mammals, birds, fish and bees. For all species it is desirable and should be possible to design dosage schedules based on knowledge of drug pharmacokinetics and pharmacodynamics. There have been many attempts to integrate pharmacokinetic and pharmacodynamic data to provide dosage schedules which optimize efficacy and minimize opportunities for the development of antimicrobial resistance in both laboratory animal studies and human clinical trials. However, there have been relatively few studies in animal species of major veterinary interest. This review summarizes recent studies in four ruminant species (calf, sheep, goat and camel) which have used PK–PD integration to determine for the fluoroquinolone, danofloxacin, AUC/MIC ratios producing (a) bacteriostasis (b) bactericidal activity and (c) elimination of bacteria. Future possible developments in dosage schedule design are considered.

Cyclophosphamide, cisplatin, and carmustine: pharmacokinetics of carmustine following multiple alkylating-agent interactions.

Cyclophosphamide, cisplatin, and carmustine (CPA/cDDP/BCNU) constitute a combination alkylating-agent regimen commonly used with autologous marrow support. Its therapeutic effectiveness is accompanied by sporadic life-threatening and fatal toxicities, the most common of which is acute lung injury. We have previously shown that variation in the BCNU AUC can be correlated to the risk of pulmonary injury in patients receiving CPA/cDDP/BCNU. In an attempt to understand further the role of interpatient variation in drug pharmacokinetics (PK) with respect to pharmacodynamic outcomes, we evaluated the effect of pretreatment with CPA, cDDP, or both on BCNU PK in male Sprague-Dawley rats. The drug-administration pattern was designed to mimic that of the CPA/cDDP/BCNU regimen in patients. Each pretreatment increased both the absolute value of and the variation in BCNU AUC relative to the control values. These findings are consistent with an important rate-limiting elimination pathway for BCNU in rats and may explain the wide interpatient variability of BCNU AUC and the sporadic pulmonary toxicity seen in patients receiving CPA/cDDP/BCNU.

Chronopharmacokinetics of 5-methoxypsoralen.

Diurnal variations in drug pharmacokinetics are a well known phenomenon. Chronopharmacology studies now appear to be attracting increasing interest with a view to establishing an optimum therapeutic prescription. In order to determine possible chronobiological variations of 5-methoxypsoralen (5-MOP) pharmacokinetic, 5-MOP blood concentrations were quantified in 8 healthy subjects after drug ingestion at different times during the day. Stolk's High Performance Liquid Chromatography technique was used to assess the 5-MOP serum concentrations. Each subject underwent three pharmacokinetic studies after oral ingestion of 5-MOP (1.2 mg/kg), in conjunction with a standardized low-lipid meal. The first pharmacokinetic study was started in the morning, the second in the afternoon and the third in the evening. Drug intake was at intervals of 2 days, to avoid drug accumulation. The results showed that the evening intake of the drug induced a higher 5-MOP maximum concentration and a higher 'area under curve' than morning or afternoon ingestion. This study suggests an optimized PUVA therapy, when performed in the evening.

Chronopharmacokinetics of 5-methoxypsoralen.

Diurnal variations in drug pharmacokinetics are a well known phenomenon. Chronopharmacology studies now appear to be attracting increasing interest with a view to establishing an optimum therapeutic prescription. In order to determine possible chronobiological variations of 5-methoxypsoralen (5-MOP) pharmacokinetic, 5-MOP blood concentrations were quantified in 8 healthy subjects after drug ingestion at different times during the day. Stolk's High Performance Liquid Chromatography technique was used to assess the 5-MOP serum concentrations. Each subject underwent three pharmacokinetic studies after oral ingestion of 5-MOP (1.2 mg/kg), in conjunction with a standardized low-lipid meal. The first pharmacokinetic study was started in the morning, the second in the afternoon and the third in the evening. Drug intake was at intervals of 2 days, to avoid drug accumulation. The results showed that the evening intake of the drug induced a higher 5-MOP maximum concentration and a higher 'area under curve' than morning or afternoon ingestion. This study suggests an optimized PUVA therapy, when performed in the evening.