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170 results on '"Duffull, S. B."'

21. Incidence and risk factors of major bleeding following major orthopaedic surgery with fondaparinux thromboprophylaxis. A time‐to‐event analysis

Author

Zufferey, P. J., Ollier, E., Delavenne, X., Laporte, S., Mismetti, P., and Duffull, S. B.

Subjects
Adult, Aged, 80 and over, Male, Time Factors, Dose-Response Relationship, Drug, Incidence, Original Articles, Venous Thromboembolism, Middle Aged, Postoperative Hemorrhage, Kidney, Prognosis, Risk Assessment, Renal Elimination, Fondaparinux, Risk Factors, Creatinine, Humans, Female, Orthopedic Procedures, Prospective Studies, Aged, Factor Xa Inhibitors, Follow-Up Studies, Glomerular Filtration Rate
Abstract

AIMS: Increased exposure to fondaparinux, as observed in patients with renal impairment, may increase bleeding risk. This study aims to determine the time course of major bleeding after major orthopaedic surgery, identify predictors of bleeding and simulate the effect of a reduced dose of fondaparinux on bleeding for patients with moderate renal impairment (creatinine clearance = 20–50 ml min(−1)). METHODS: Data including fondaparinux anti‐Xa activities from two multicentre prospective cohorts were used. In the first cohort, patients (n = 957) received fondaparinux 2.5 mg once a day. In the second, patients with moderate renal impairment (n = 436) received 1.5 mg once per day. The time‐to‐major bleeding after the end of surgery was modelled using a parametric survival analysis in NONMEM. RESULTS: The observed rate of major bleeding up to day 11 was 5.2%. The time‐to‐event analysis indicated that the hazard of bleeding was highest in the first days following surgery and then remained low thereafter. Independent significant predictors of an increased hazard of major bleeding were male sex, lower body weight and increased drug exposure. Simulated rates of major bleeding up to day 11 in patients with moderate renal impairment were 6.5% with fondaparinux 2.5 mg once daily and 3.8% with fondaparinux 1.5 mg once daily. CONCLUSION: The hazard of major bleeding is highest in the first postoperative days and increases with fondaparinux exposure. To reduce the risk of bleeding in patients with moderate renal impairment, this study supports the use of a lower dose of fondaparinux 1.5 mg once daily.

Published
2018

28. Population pharmacokinetic analysis of mycophenolic acid in renal transplant recipients following oral administration of mycophenolate mofetil

Author

Shum, B, Duffull, S B, Taylor, P J, and Tett, S E

Subjects
Adult, Male, Administration, Oral, Humans, Pharmacokinetics, Female, Enzyme Inhibitors, Middle Aged, Mycophenolic Acid, Kidney Transplantation, Immunosuppressive Agents, Aged
Abstract

To develop a population pharmacokinetic model for mycophenolic acid in adult kidney transplant recipients, quantifying average population pharmacokinetic parameter values, and between- and within-subject variability and to evaluate the influence of covariates on the pharmacokinetic variability.Pharmacokinetic data for mycophenolic acid and covariate information were previously available from 22 patients who underwent kidney transplantation at the Princess Alexandra Hospital. All patients received mycophenolate mofetil 1 g orally twice daily. A total of 557 concentration-time points were available. Data were analysed using the first-order method in NONMEM (version 5 level 1.1) using the G77 FORTRAN compiler.The best base model was a two-compartment model with a lag time (apparent oral clearance was 27 l h(-1), and apparent volume of the central compartment 98 l). There was visual evidence of complex absorption and time-dependent clearance processes, but they could not be successfully modelled in this study. Weight was investigated as a covariate, but no significant relationship was determined.The complexity in determining the pharmacokinetics of mycophenolic acid is currently underestimated. More complex pharmacokinetic models, though not supported by the limited data collected for this study, may prove useful in the future. The large between-subject and between-occasion variability and the possibility of nonlinear processes associated with the pharmacokinetics of mycophenolic acid raise questions about the value of the use of therapeutic monitoring and limited sampling strategies.

Published
2003

29. The effect of decontamination procedures on the pharmacokinetics of venlafaxine in overdose

Author

Kumar, V V P, Oscarsson, S., Friberg, L .E., Isbister, G K, Hackett, L P, Duffull, S B, Kumar, V V P, Oscarsson, S., Friberg, L .E., Isbister, G K, Hackett, L P, and Duffull, S B

Abstract

The aim of this work was to investigate the pharmacokinetics (PK) of venlafaxine in overdose and the effects of single-dose activated charcoal (SDAC) and whole-bowel irrigation (WBI), alone or in combination, as methods of decontamination. The data included 339 concentration-time points from 76 venlafaxine overdose events (median dose 2,625 (150-13,500 mg)); 69 were slow-release doses. SDAC, WBI, a combination of both, or no decontamination were administered to patients as decided by the treating clinician. The data were modeled using WinBUGS (Windows Bayesian Inference Using Gibbs Sampling). A one-compartment model with first-order input and elimination provided an adequate description of the data. SDAC increased clearance (CL) of venlafaxine by 35%, and SDAC and WBI combined reduced the fraction absorbed by 29%. However, the latter produced a greater reduction in maximum plasma concentration (C(max)) for a similar drop in area under the plasma concentration-time curve (AUC). Both SDAC alone, and a combination of SDAC and WBI, decreased the AUC after venlafaxine overdose, but the combination may be more beneficial because it reduces peak concentrations to a greater extent.

Published
2009
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31. Pharmacokinetics of quetiapine in overdose and the effect of activated charcoal

Author

Isbister, G. K., Friberg, Lena, Hackett, L. P., Duffull, S. B., Isbister, G. K., Friberg, Lena, Hackett, L. P., and Duffull, S. B.

Abstract

The aim of the study was to investigate the pharmacokinetics of quetiapine overdose and the effect of charcoal. The data set included 204 concentration-time points from 54 quetiapine overdose events (median dose 2,700 mg (300-24,000 mg)). Charcoal was administered 0.5-6 h after 19 overdoses. A fully Bayesian methodology for population pharmacokinetic analysis was used and data were modelled using WinBUGS. Uncertainty in the dose history was considered in model building by estimating dose amount and dose time within a possible range. Inclusion of informative priors stabilized the model and population parameter values could be estimated well. A one-compartment model with first-order input and first-order elimination described the data. The final model included uncertainty in dose time. The median and interquartile range of the half-life for individual patients was 6.6 h (4.9-8.4 h). Charcoal was estimated to reduce fraction absorbed by 35%. Co-ingested CYP3A4 inhibitors appeared to decrease clearance and CYP3A4 inducers increase clearance. Charcoal administration may be beneficial after quetiapine overdose.

Published
2007
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38. A model-based meta-analysis of the influence of factors that impact adherence to medications.

Author

Assawasuwannakit, P., Braund, R., and Duffull, S. B.

Subjects
AGE distribution, CONFIDENCE intervals, DRUGS, HIV-positive persons, HYPERTENSION, MEDLINE, META-analysis, PATIENT compliance, RESEARCH, SYSTEMATIC reviews
Abstract

What is known and objective Several studies have investigated factors that may influence adherence for a given disease. The influence of disease on adherence has received limited attention. Less work has been conducted to investigate the influence of other factors in conjunction with disease on adherence. The aim of this study was to determine the independent influence of disease and other factors on adherence. Methods A literature search was conducted to retrieve adherence studies using medication event monitoring system devices. Studies were categorized into different therapeutic areas. Only the two most commonly studied therapeutic areas were selected. Pseudopatient-level data were extracted from each study. The extracted data were analysed using a model-based meta-analysis technique. Univariate and multivariate models were developed. Model selection was based on a likelihood ratio test and visual plots. Results The most commonly studied therapeutic areas were HIV and hypertension. The most commonly recorded adherence criterion was percentage of prescribed doses taken per day. Based on this adherence criterion, ultimately, 24 HIV papers and 12 hypertension papers were included for data extraction. The statistically significant factors were disease, age and dosing regimen. The independent influences of each factor on adherence were as follows: an increase in adherence of approximately 8% per 10-year increase of age, a 15-19% reduction from once to thrice daily dosing and that patients with HIV were 5% more adherent than those with hypertension. What is new and conclusion Although the influence of disease on adherence was significant, it was of limited clinical significance in the diseases studied here. Adherence appears to improve with age and decline with more frequent dosing. Additionally, the influence of dosing regimen wanes with increasing age. These results should be treated as exploratory and require prospective assessment. [ABSTRACT FROM AUTHOR]

Published
2015
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45. Reply

Author

BARCLAY, M. L., primary, DUFFULL, S. B., additional, and BEGG, E. J., additional

Published
1996
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49. Pharmacokinetics and efficacy of rectal versus oral sustained-release morphine in cancer patients.

Author

Wilkinson, Timothy, Robinson, Bridget, Begg, Evan, Duffull, Steven, Ravenscroft, Peter, Schnieder, Jennifer, Wilkinson, T J, Robinson, B A, Begg, E J, Duffull, S B, Ravenscroft, P J, and Schneider, J J

Subjects
CLINICAL trials, COMPARATIVE studies, CONTROLLED release preparations, RESEARCH methodology, MEDICAL cooperation, MORPHINE, ORAL drug administration, PAIN, RECTAL medication, RESEARCH, TIME, TUMORS, EVALUATION research, PAIN measurement, RANDOMIZED controlled trials
Abstract

Sustained-release morphine (MST) given by the rectal route was compared with oral MST in an open randomised cross-over trial in ten patients with cancer who received stable doses of MST. No significant difference was found in the areas under the curve of the concentration-time profiles (AUC) following oral or rectal administration for parent morphine. The AUCs determined for morphine-6-glucuronide (M6G) and morphine-3-glucuronide (M3G) after oral administration were approximately twice those obtained following rectal administration. The maximal concentration achieved was lower and the time to maximal concentration was longer following rectal administration for morphine, M6G and M3G. The relative mean arrival times following rectal administration were significantly longer for morphine and M3G but not for M6G. These findings suggest slower absorption but less first-pass metabolism of MST after rectal administration. No significant difference was noted between the oral and the rectal route in measurements on visual-analogue scales for pain or side effects. We recommend the rectal route as being suitable for MST administration when the oral route is no longer available. In changing from oral to rectal administration, the same dose and dose interval may be used, but dose adjustment may be needed. [ABSTRACT FROM AUTHOR]

Published
1992
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