Influence of adult age on the total and free clearance and protein binding of (R)- and (S)-warfarin

Construction of warfarin population pharmacokinetics and pharmacodynamics model in Han population based on Bayesian method

The purpose of this paper is to study the genetic polymorphisms of related gene loci (CYP2C9*3, VKORC1-1639G > A) based on demographic and clinical factors, and use the maximum a posterior Bayesian method to construct a warfarin individualized dose prediction model in line with the Chinese Han population. Finally, the built model is compared and analyzed with the widely used models at home and abroad. In this study, a total of 5467 INR measurements are collected from 646 eligible subjects in our hospital, and the maximum a posterior Bayesian method is used to construct a warfarin dose prediction that conforms to the Chinese Han population on the basis of the Hamberg model. The model is verified and compared with foreign models. This study finds that body weight and concomitant use of amiodarone have a significant effect on the anticoagulant effect of warfarin. The model can provide an effective basis for individualized and rational dosing of warfarin in Han population more accurately. In the performance of comparison with different warfarin dose prediction models, the new model has the highest prediction accuracy, and the prediction percentage is as high as 72.56%. The dose predicted by the Huang model is the closest to the actual dose of warfarin. The population pharmacokinetics and pharmacodynamics model established in this study can better reflect the distribution characteristics of INR values after warfarin administration in the Han population, and performs better than the models reported in the literature.

Oral anticoagulant therapy in older adults

Patients aged ≥65 years not only account for the majority of patients with atrial fibrillation (AF) and venous thromboembolism (VTE), they are also at a higher risk of morbidity, mortality, and undertreatment than younger patients. Several age-related physiological changes with effects on drug pharmacokinetics/-dynamics and blood vessel fragility as well as the higher prevalence of geriatric conditions such as frailty, multimorbidity, polypharmacy, fall risk, dementia, and malnutrition make older persons more vulnerable to disease- and anticoagulation-related complications. Moreover, because older patients with AF/VTE are underrepresented in oral anticoagulation (OAC) trials, evidence on OAC in older adults with AF/VTE is mainly based on subgroup analyses from clinical trials and observational studies. A growing body of such limited evidence suggests that direct oral anticoagulants (DOACs) may be superior in terms of efficacy and safety compared to vitamin K antagonists in older persons with AF/VTE and that specific DOACs may have a differing risk-benefit profile. In this narrative review, we summarize the evidence on epidemiology of AF/VTE, impact of age-related physiological changes, efficacy/safety of OAC, specifically considering individuals with common geriatric conditions, and review OAC guideline recommendations for older adults with AF/VTE. We also propose a research agenda to improve the evidence basis on OAC older individuals with AF/VTE, including the conduct of advanced age-specific and pragmatic studies using less restrictive eligibility criteria and patient-reported health outcomes, in order to compare the effectiveness and safety of different DOACs, and investigate lower-dose regimens and optimal OAC durations in older patients.

A mathematical model to study low-dose metronomic scheduling for chemotherapy

Metronomic chemotherapy refers to the frequent administration of chemotherapeutic agents at a lower dose and presents an attractive alternative to conventional chemotherapy with encouraging response rates. However, the schedule of the therapy, including the dosage of the drug, is usually based on empiricism. The confounding effects of tumor-endothelial-immune interactions during metronomic administration of drugs have not yet been explored in detail, resulting in an incomplete assessment of drug dose and frequency evaluations. The present study aimed to gain a mechanistic understanding of different actions of metronomic chemotherapy using a mathematical model. We have established an analytical condition for determining the dosage and frequency of the drug depending on its clearance rate for complete tumor elimination. The model also brings forward the immune-mediated clearance of the tumor during the metronomic administration of the chemotherapeutic agent. The results from the global sensitivity analysis showed an increase in the sensitivity of drug and immune-mediated killing factors toward the tumor population during metronomic scheduling. Our results emphasize metronomic scheduling over the maximum tolerated dose (MTD) and define a model-based approach for approximating the optimal schedule of drug administration to eliminate tumors while minimizing harm to the immune cells and the patient's body.

Effect of High Altitude Environment on Pharmacokinetic and Pharmacodynamic of Warfarin in Rats

BACKGROUND

High altitude environment affects the pharmacokinetic (PK) parameters of drugs and the PK parameters are an important theoretical basis for guiding the rational clinical use of drugs. Warfarin is an oral anticoagulant of the coumarin class commonly used in clinical practice, but it has a narrow therapeutic window and wide individual variation. However, the effect of high altitude environment on PK and pharmacodynamic (PD) of warfarin is unclear.

OBJECTIVE

The objective of this study is to investigate the effect of a high altitude environment on PK and PD of warfarin in rats.

METHOD

Rats were randomly divided into plain group and high altitude group and blood samples were collected through the orbital venous plexus after administration of 2 mg/kg warfarin. Warfarin concentrations in plasma samples were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and PK parameters were calculated by the non-compartment model using WinNonlin 8.1 software. Meanwhile, the expression of PXR, P-gp and CYP2C9 in liver tissues was also determined by western blotting. The effect of high altitude environment on PD of warfarin was explored by measuring activated partial thromboplastin time (APTT) and prothrombin time (PT) values and then calculated international normalized ratio (INR) values based on PT.

RESULTS

Significant changes in PK behaviors and PD of warfarin in high altitude-rats were observed. Compared with the plain-rats, the peak concentration (Cmax) and the area under the plasma concentration-time curve (AUC) increased significantly by 50.9% and 107.46%, respectively. At the same time, high altitude environment significantly inhibited the expression of PXR, P-gp and CYP2C9 in liver tissues. The results of the PD study showed that high altitude environments significantly prolonged PT, APTT and INR values.

CONCLUSION

High altitude environment inhibited the metabolism and increased the absorption of warfarin in rats and increased the effect of anticoagulant effect, suggesting that the optimal dose of warfarin for patients at high altitude should be reassessed.

External Evaluation of a Bayesian Warfarin Dose Optimization Based on a Kinetic-Pharmacodynamic Model

Warfarin is a representative anticoagulant with large interindividual variability. The published kinetic-pharmacodynamic (K-PD) model allows the prediction of warfarin dose requirement in Swedish patients; however, its applicability in Japanese patients is not known. We evaluated the model's predictive performance in Japanese patients with various backgrounds and relationships using Bayesian parameter estimation and sampling times. A single-center retrospective observational study was conducted at Tokyo Women's Medical University, Medical Center East. The study population consisted of adult patients aged >20 years who commenced warfarin with a prothrombin time-international normalized ratio (PT-INR) from June 2015 to June 2019. The published K-PD model modified by Wright and Duffull was assessed using prediction-corrected visual predictive checks, focusing on clinical characteristics, including age, renal function, and individual prediction error. The external dataset included 232 patients who received an initial warfarin daily dose of 3.2 ± 1.28 mg with 2278 PT-INR points (median [range] follow-up period of 23 d [7-28]). Prediction-corrected visual predictive checks carried a propensity for underprediction. Additionally, age >60 years, body mass index ≤25 kg/m², and estimated glomerular filtration rate ≤60 mL/min/1.73 m² had a pronounced tendency to underpredict PT-INR. However, Bayesian prediction using four prior observations reduced underprediction. To improve the prediction performance of these special populations, further studies are required to construct a model to predict warfarin dose requirements in Japanese patients.

To establish a model for the prediction of initial standard and maintenance doses of warfarin for the Han Chinese population based on gene polymorphism: a multicenter study

PURPOSE

The purpose of this paper is to study the correlation between demographic and clinical factors and warfarin dose of patients in Chinese Han population taking warfarin and study gene polymorphisms impact of related gene loci (CYP2C9*3, VKORC1-1639G > A) on warfarin doses, to establish a model to predict initial standard dose and maintenance dose based on CYP2C9*3, VKORC1-1639G > A genotype.

METHODS

The study collects the data of patients in our hospital and other subcenters which incorporates 2160 patients to establish the initial dose model and 1698 patients for the stable dose model, and sequences 26 multigene sites in 451 patients. Based on the patient's dosage, clinical data, and demographic characteristics, the genetic and non-genetic effects on the initial dose and stable dose of warfarin are calculated by using statistical methods, and the prediction model of initial standard dose and maintenance dose can be established via multiple linear regression.

RESULTS

The initial dose of warfarin (mg/day) was calculated as (1.346 + 0.350 × (VKORC1-1639G > A) - 0.273 × (CYP2C9*3) + 0.245 × (body surface area) - 0.003 × (age) - 0.036 × (amine-iodine) + 0.021 × (sex))². This model incorporated seven factors and explained 55.3% of the individualization differences of the warfarin drug dose. The maintenance dose of warfarin (mg/day) was calculated as (1.336 + 0.299 × (VKORC1-1639G > A) + 0.480 × (body surface area) - 0.214 × (CYP2C9*3) - 0.074 × (amine-iodine) - 0.003 × (age) - 0.077 × (statins) - 0.002 × (height))². This model incorporated six factors and explained 42.4% of the individualization differences in the warfarin drug dose.

CONCLUSION

The genetic and non-genetic factors affecting warfarin dose in Chinese Han population were studied systematically in this study. The pharmacogenomic dose prediction model constructed in this study can predict anticoagulant efficacy of warfarin and has potential application value in clinical practice.

Drug metabolism in severe chronic obstructive pulmonary disease: A phenotyping cocktail study

AIMS

To evaluate the effect of severe chronic obstructive pulmonary disease (COPD) on drug metabolism by comparing the pharmacokinetics of patients with severe COPD with healthy volunteers and using the modified Inje drug cocktail.

METHODS

This was a single-centre pharmacokinetic study with 12 healthy participants and 7 participants with GOLD D COPD. Midazolam 1 mg, dextromethorphan 30 mg, losartan 25 mg, omeprazole 20 mg, caffeine 130 mg and paracetamol 1000 mg were simultaneously administered and intensive pharmacokinetic sampling was conducted over 8 hours. Drug metabolism by CYP3A4, CYP2D6, CYP2C9, CYP2C19, CYP1A2, UGT1A6 and UGT1A9 in participants with COPD were compared with phenotypes in healthy controls.

RESULTS

The oral clearance (95% confidence interval) in participants with COPD relative to controls was: midazolam 63% (60-67%); dextromethorphan 72% (40-103%); losartan 53% (52-55%); omeprazole 35% (31-39%); caffeine 52% (50-53%); and paracetamol 73% (72-74%). There was a 5-fold increase in AUC for omeprazole and approximately 2-fold increases for caffeine, losartan, dextromethorphan, and midazolam. The AUC of paracetamol, which is mostly glucuronidated, was increased by about 60%.

CONCLUSION

Severe COPD is associated with a clinically significant reduction in oral drug clearance. This may be greater for cytochrome P450 substrates than for glucuronidated drugs. This supports reduced starting doses when prescribing for patients with severe COPD.

Lack of effect of Imrecoxib, an innovative and moderate COX-2 inhibitor, on pharmacokinetics and pharmacodynamics of warfarin in healthy volunteers

Imrecoxib is a registered treatment for osteoarthritis pain symptoms in China. This study aims to assess the effect of imrecoxib on the pharmacodynamics and pharmacokinetics of warfarin. 12 healthy male volunteers with CYP2C9*3 AA and VKORC1 AA genotypes took a 5 mg dose of warfarin both alone and concomitantly with steady-state imrecoxib. Both warfarin alone and concomitantly with imrecoxib have safey and good tolerance across the trial. Following warfarin and imrecoxib co-administration, neither C_max, AUC_0-t and t_1/2 of warfarin enantiomers nor AUC of international normalized ratio (INR) were markedly different from those of warfarin alone. The geometric mean ratios (GMRs) (warfarin + imrecoxib: warfarin alone) of INR_(AUC) was 1 (0.99, 1.01). The GMRs of warfarin AUC_0-∞ (90% confidence interval, CIs) for warfarin + imrecoxib: warfarin alone were 1.12 (1.08, 1.16) for R-warfarin and 1.13 (1.07, 1.18) for S- warfarin. The 90% CIs of the GMRs of AUC_0-∞, C_max and INR _(AUC) were all within a 0.8–1.25 interval. The combination of warfarin and imrecoxib did not impact the pharmacodynamics and pharmacokinetics of single-dose warfarin; therefore, when treating a patient with imrecoxib and warfarin, it is not required to adjust the dosage of warfarin.

Influence of Age on Warfarin Dose, Anticoagulation Control, and Risk of Hemorrhage

OBJECTIVE

We assessed the influence of age on warfarin dose, percentage time in target range (PTTR), and risk of major hemorrhage.

DESIGN

Warfarin users recruited into a large prospective inception cohort study were categorized into three age groups: young (younger than 50 yrs), middle aged (50-70 yrs), and elderly (older than 70 yrs). The influence of age on warfarin dose and PTTR was assessed using regression analysis; risk of major hemorrhage was assessed using proportional hazards analysis. Models were adjusted for demographic, clinical, and genetic factors.

SETTING

Two outpatient anticoagulation clinics.

PARTICIPANTS

A total of 1498 anticoagulated patients.

OUTCOMES

Warfarin dose (mg/day), PTTR, major hemorrhage.

RESULTS

Of the 1498 patients, 22.8% were young, 44.1% were middle aged, and 33.1% were elderly. After accounting for clinical and genetic factors, compared with young warfarin users, warfarin dose requirements were 10.6% lower among the middle aged and an additional 10.6% lower for the elderly. Compared with young patients, middle-aged and elderly patients spent more time in target international normalized ratio (INR) range (p<0.0001), despite having fewer INR assessments (p<0.0001). Compared with young warfarin users, absolute risk of hemorrhage was marginally higher among the middle aged (p=0.08) and significantly higher among the elderly (p=0.016). Compared with young warfarin users, after adjustment, the relative risk of hemorrhage increased by 31% for each age category (p=0.026).

CONCLUSIONS

In a real-world setting, despite achieving better anticoagulation control, elderly patients had a higher risk of major hemorrhagic events. As the population ages and the candidacy for oral anticoagulation increases, strategies that mitigate the elevated risk of hemorrhage need to be identified.

Quantitative Assessment of CYP2C9 Genetic Polymorphisms Effect on the Oral Clearance of S-Warfarin in Healthy Subjects

BACKGROUND

Genetic polymorphisms in CYP2C9 account for 10-20% of the variability in warfarin dose requirement. As such CYP2C9 genetic polymorphisms are commonly included in algorithms aimed to optimize warfarin therapy as a way to account for variability in warfarin responsiveness that is due to altered pharmacokinetics. However, most of the currently available pharmacokinetic data were derived from studies among patients on chronic warfarin therapy and therefore suffer from the confounding effects of disease states and drug interactions.

OBJECTIVE

The purpose of the present study was to provide an accurate quantitative estimate of S-warfarin oral clearance (CL_S) among healthy subjects carrying different CYP2C9 genotypes.

METHODS

Single dose of warfarin was administered to 150 non-smokers, age (mean ± SD) 23.3 ± 4.5 years, 60% male, non-obese, healthy subjects. Blood samples were taken for up to 168 h and urine was collected over the entire study period.

RESULTS

Compared with carriers of the wild-type CYP2C9*1/*1 genotype (n = 69), CL_S was reduced by 25, 39 and 47% among heterozygote for CYP2C9*2 (n = 41) CYP2C9*3 (n = 26) and carriers of 2 variant alleles (n = 14), respectively (p < 0.001). The corresponding decrease in the formation clearance of 6 and 7 S-hydroxy-warfarin was 45, 65 and 75%, respectively (p < 0.001).

CONCLUSIONS

The current study provides an estimate concerning the effect of CYP2C9 polymorphisms on S-warfarin pharmacokinetics among healthy subjects. As such it is free of the confounding effects of disease states and drug interactions. Further research is needed to evaluate whether the incorporation of quantitative data obtained in the present study into pharmacogenetic warfarin algorithm may enhance its precision.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier NCT00162474.

Effects of aging and rifampicin pretreatment on the pharmacokinetics of human cytochrome P450 probes caffeine, warfarin, omeprazole, metoprolol and midazolam in common marmosets genotyped for cytochrome P450 2C19

1. The pharmacokinetics were investigated for human cytochrome P450 probes after single intravenous and oral administrations of 0.20 and 1.0 mg/kg, respectively, of caffeine, warfarin, omeprazole, metoprolol and midazolam to aged (10-14 years old, n = 4) or rifampicin-treated/young (3 years old, n = 3) male common marmosets all genotyped as heterozygous for a cytochrome P450 2C19 variant. 2. Slopes of the plasma concentration-time curves after intravenous administration of warfarin and midazolam were slightly, but significantly (two-way analysis of variance), decreased in aged marmosets compared with young marmosets. The mean hepatic clearances determined by in silico fitting for individual pharmacokinetic models of warfarin and midazolam in the aged group were, respectively, 23% and 56% smaller than those for the young group. 3. Significantly enhanced plasma clearances of caffeine, warfarin, omeprazole and midazolam were evident in young marmosets pretreated with rifampicin (25 mg/kg daily for 4 days). Two- to three-fold increases in hepatic intrinsic clearance values were observed in the individual pharmacokinetic models. 4. The in vivo dispositions of multiple simultaneously administered drugs in old, young and P450-enzyme-induced marmosets were elucidated. The results suggest that common marmosets could be experimental models for aged, induced or polymorphic P450 enzymes in P450-dependent drug metabolism studies.

Warfarin and Flavonoids Do Not Share the Same Binding Region in Binding to the IIA Subdomain of Human Serum Albumin

Human serum albumin (HSA) binds a variety of xenobiotics, including flavonoids and warfarin. The binding of another ligand to the IIA binding site on HSA can cause warfarin displacement and potentially the elevation of its free concentration in blood. Studies dealing with flavonoid-induced warfarin displacement from HSA provided controversial results: estimated risk of displacement ranged from none to serious. To resolve these controversies, in vitro study of simultaneous binding of warfarin and eight different flavonoid aglycons and glycosides to HSA was carried out by fluorescence spectroscopy as well as molecular docking. Results show that warfarin and flavonoids do not share the same binding region in binding to HSA. Interactions were only observed at high warfarin concentrations not attainable under recommended dosing regimes. Docking experiments show that flavonoid aglycons and glycosides do not bind at warfarin high affinity sites, but rather to different regions within the IIA HSA subdomain. Thus, the risk of clinically significant warfarin-flavonoid interaction in binding to HSA should be regarded as negligible.

Analysis of the first therapeutic-target-achieving time of warfarin therapy and associated factors in patients with pulmonary embolism

The present study aimed to investigate the factors affecting the first therapeutic-target-achieving (TTA) time of warfarin therapy in patients with acute pulmonary embolism (PTE). Between January 2008 and June 2013, patients with PTE confirmed by transpulmonary arterial enhanced computed tomographic pulmonary angiography or pulmonary ventilation perfusion scanning were included in the present study. Data collected included demographic information, history of tobacco and alcohol intake, basic diseases (stable and unstable hypertension, diabetes, heart failure, cancer/cerebral infarction, old myocardial infarction and atrial fibrillation), liver and kidney function, the haemoglobin and platelet count of the blood, international normalized ratio monitoring, warfarin dosage adjustment and medication combinations. Dynamic changes in international normalized ratio, anticoagulant efficacy, and adverse events within 90 days were monitored and analyzed. Univariate analysis demonstrated that the following factors affect the first TTA time: Initial dose, body mass index (BMI), liver function, heart failure, and the administration of levofloxacin, cephalosporins, and blood circulation-activating drugs. Logistic regression analysis revealed that the following were independent factors of the first TTA time: Initial dose, BMI, liver function, heart failure and levofloxacin. Therefore, the results of the present study demonstrated that various factors may affect the first TTA time of warfarin therapy, including the initial dose, BMI, liver function, heart function and concomitant medication.

In vitro and in vivo evaluation of cucurbitacin E on rat hepatic CYP2C11 expression and activity using LC-MS/MS

This study explored the effects of cucurbitacin E (CuE), a bioactive compound from Cucurbitaceae, on the metabolism/pharmacokinetic of tolbutamide, a model CYP2C9/11 probe substrate, and hepatic CYP2C11 expression in rats. Liquid chromatography-(tandem) mass spectrometry (LC-MS/MS) assay was used to detect tolbutamide as well as 4-hydroxytolbutamide, and then successfully applied to the pharmacokinetic study of tolbutamide in rats. The effect of CuE on CYP2C11 expression was determined by western blot. CuE (1.25-100 μmol L^-1) competitively inhibited tolbutamide 4-hydroxylation (CYP2C11) activity only in concentration-dependent manner with a K _i value of 55.5 μmol L^-1 in vitro. In whole animal studies, no significant difference in metabolism/pharmacokinetic of tolbutamide was found for the single pretreatment groups. In contrast, multiple pretreatments of CuE (200 μg kg^-1 d^-1, 3 d, i.p.) significantly decreased tolbutamide clearance (CL) by 25% and prolonged plasma half-time (T _1/2) by 37%. Moreover, CuE treatment (50-200 μg kg^-1 d^-1, i.p.) for 3 d did not affect CYP2C11 expression. These findings demonstrated that CuE competitively inhibited the metabolism of CYP2C11 substrates but had no effect on rat CYP2C11 expression. This study may provide a useful reference for the reasonable and safe use of herbal or natural products containing CuE to avoid unnecessary drug-drug interactions.

The role of competitive binding to human serum albumin on efavirenz-warfarin interaction: a nuclear magnetic resonance study

The potential for co-prescription of the anti-human immunodeficiency virus (anti-HIV) drug efavirenz (EFV) and the oral anticoagulant warfarin (WAR) is currently high as EFV is a drug of choice for HIV type 1 infection and because cardiovascular disease is increasing among HIV-infected individuals. However, clinical reports of EFV-WAR interaction, leading to WAR overdosing, call for elucidation of the mechanisms involved in this drug-drug interaction. Here we present the first report demonstrating competition of the two drugs for the same binding site of human serum albumin. Using ligand-based nuclear magnetic resonance experiments, this study proves that EFV has an effect on the concentration of free WAR. This previously unidentified EFV-WAR interaction represents a potential risk factor that should be taken into account when considering treatment options.

Effects of etravirine on the pharmacokinetics and pharmacodynamics of warfarin in rats

BACKGROUND AND PURPOSE

Warfarin is often used with etravirine (ETV) to prevent HIV-related thromboembolic events. As both warfarin and ETV bind to plasma proteins and are metabolized by hepatic cytochrome P450s, they are likely to interact. Hence, we evaluated the effect of ETV on the pharmacokinetics and blood clotting time of racemic warfarin in rats.

EXPERIMENTAL APPROACH

Two groups of male Sprague-Dawley rats, in which the jugular vein had been cannulated, were studied. The control group (n = 10) received 1 mg·kg(-1) racemic warfarin i.v., and the test group (n = 13) 1 mg·kg(-1) of racemic warfarin followed by 25 mg·kg(-1) ETV i.v. Serial blood samples were collected for up to 144 h and the blood clotting time (calculated as international normalized ratio [INR]) measured in blood plasma at each sample point. Plasma concentrations of R-warfarin, S-warfarin, R-7-hydroxywarfarin and S-7-hydroxywarfarin were measured by a LC/MS/MS method using a chiral lux cellulose-1 column. Pharmacokinetic parameters were analysed using non-compartmental methods.

KEY RESULTS

ETV significantly increased, by threefold, the systemic clearance and volume of distribution of S-warfarin, but not those of R-warfarin. ETV decreased the total AUC of warfarin, but had no effect on its elimination half-life. ETV also increased the systemic clearance of both R-7-hydroxywarfarin and S-7-hydroxywarfarin but only increased the volume of distribution of R-7-hydroxywarfarin. Interestingly, the effect of warfarin on blood clotting time (INR) was significantly increased in the presence of etravirine.

CONCLUSION AND IMPLICATIONS

Our data suggest that etravirine may potentiate the anticoagulant effect of warfarin and this could have clinical significance.

Predicted metabolic drug clearance with increasing adult age

AIM

To determine the effect of increasing adult age on predicted metabolic drug clearance.

METHOD

Predicted metabolic drug clearances (CLPT ) were determined using in vitro-in vivo extrapolation coupled with physiological-based pharmacokinetic modelling and simulation (IVIVE-PBPK) in Simcyp®. Simulations were conducted using CYP-selective 'probe' drugs with subjects in 5 year age groups (20-25 to 90-95 years). CLPT values were compared with human pharmacokinetic data stratified according to age (young = 20-40 years and elderly = 65-85 years) and gender. Age-related changes in the physiological parameters used for IVIVE of CLPT were described.

RESULTS

Predicted metabolic drug clearances decreased with increasing adult age to approximately 65-70 years: caffeine from 1.5 to 1.0 ml min(-1)  kg(-1) (a 33% decrease), S-warfarin from 0.100 to 0.064 ml min(-1)  kg(-1) (36%), S-mephenytoin from 4.1 to 2.5 ml min(-1)  kg(-1) (39%), desipramine from 10.6 to 7.3 ml min(-1)  kg(-1) (31%) and midazolam from 5.4 to 3.9 ml min(-1)  kg(-1) (27%). Except for S-mephenytoin, predictions were within 3.5-fold of clearances from clinical studies when stratified by age and gender. A trend towards higher CLPT was observed in females, but this was only statistically significant in larger virtual trials. Physiological parameters that determine CLPT decreased with increasing adult age: mean microsomal protein g(-1) of liver, liver weight, hepatic blood flow and human serum albumin concentration.

CONCLUSION

Decreased metabolic clearance in the elderly was predicted by Simcyp® and was generally consistent with limited clinical data for four out of five drugs studied and the broader literature for drugs metabolized by CYP enzymes. IVIVE-PBPK may be increasingly useful in predicting metabolic drug clearance in the elderly.