Safety evaluation of oral calcitonin-gene-related peptide receptor antagonists in patients with acute migraine: a systematic review and meta-analysis.

OBJECTIVE: Calcitonin gene-related peptide (CGRP) receptor antagonists have been suggested as novel treatments for acute migraine. This study aimed to use meta-analysis to compare the safety and tolerability of five existing oral CGRP receptor antagonists (BI44370TA, MK-3207, rimegepant, telcagepant, and ubrogepant) with that of a placebo or triptans against acute migraine. METHODS: Five prominent databases were searched to identify randomized controlled trials on this topic. The primary safety outcomes of interest were any adverse events (AEs) and treatment-related adverse events (TRAEs), and secondary outcomes were individual events, namely diarrhea, dizziness, dry mouth, fatigue, nausea, paresthesia, somnolence, upper abdominal pain, and vomiting. RESULTS: Fifteen studies met the eligibility criteria and were examined in detail. Although, compared to placebo, oral CGRP receptor antagonists significantly increased the incidence of any AEs (risk ratio [RR] = 1.15; 95% confidence interval [CI] = 1.07-1.23), there was no difference in the incidence of TRAEs (RR = 1.18; 95% CI = 1.00-1.38). Moreover, CGRP receptor antagonists were safer than triptans with respect to primary safety outcomes, such as any AEs (RR = 0.78; 95% CI = 0.63-0.98) and TRAEs (RR = 0.68; 95% CI = 0.58-0.79). CONCLUSION: Despite oral CGRP receptor antagonists posing a significantly higher risk of AEs when compared to placebo, CGRP receptor antagonists have a favorable safety profile compared to triptans. Our findings inform strategies to enhance safety and tolerability in the treatment of acute migraine.

Important lack of difference in tacrolimus and mycophenolic acid pharmacokinetics between Aboriginal and Caucasian kidney transplant recipients.

AIM: To examine whether differences in tacrolimus and mycophenolic acid (MPA) pharmacokinetics contribute to the poorer kidney transplant outcomes experienced by Aboriginal Australians. METHODS: Concentration-time profiles for tacrolimus and MPA were prospectively collected from 43 kidney transplant recipients: 27 Aboriginal and 16 Caucasian. Apparent clearance (CL/F) and distribution volume (V/F) for each individual were derived from concentration-time profiles combined with population pharmacokinetic priors, with subsequent assessment for between-group difference in pharmacokinetics. In addition, population pharmacokinetic models were developed using the prospective dataset supplemented by previously developed structural models for tacrolimus and MPA. The change in NONMEM objective function was used to assess improvement in goodness of model fit. RESULTS: No differences were found between Aboriginal and Caucasian groups or empirical Bayes estimates, for CL/F or V/F of MPA or tacrolimus. However, a higher prevalence of CYP3A5 expressers (26% compared with 0%) and wider between-subject variability in tacrolimus CL/F (SD = 5.00 compared with 3.25 L/h/70 kg) were observed in the Aboriginal group, though these differences failed to reach statistical significance (p = .07 and p = .08). CONCLUSION: There were no differences in typical tacrolimus or MPA pharmacokinetics between Aboriginal and Caucasian kidney transplant recipients. This means that Bayesian dosing tools developed to optimise tacrolimus and MPA dosing in Caucasian recipients may be applied to Aboriginal recipients. In turn, this may improve drug exposure and thereby transplant outcomes in this group. Aboriginal recipients appeared to have greater between-subject variability in tacrolimus CL/F and a higher prevalence of CYP3A5 expressers, attributes that have been linked with inferior outcomes.

Gender differences and dose proportionality in the toxicokinetics of udenafil and its active metabolite following oral administration in rodents.

Udenafil is a long-acting oral phosphodiesterase type 5 inhibitor used to treat erectile dysfunction which may also have beneficial effects on cardiovascular diseases. Udenafil is mainly biotransformed to the active metabolite N-dealkylated udenafil via cytochrome P450 3A. The aim of this study was to investigate the gender differences and dose proportionality of the toxicokinetics of udenafil and its metabolite N-dealkylated udenafil in rodents. Udenafil was administered orally by gavage to male and female B6C3F1/N mice (100, 240, 350, and 500 mg/kg) and F344 rats (60, 120, and 240 mg/kg). Plasma concentrations of udenafil and N-dealkylated udenafil were simultaneous measured via liquid chromatography-tandem mass spectrometry. Female mice showed higher systemic exposure to udenafil than male mice, whereas female rats showed lower systemic exposure to udenafil than male rats after repeated administration at high dose. Systemic exposure to the metabolite, N-dealkylated udenafil, was lower in female than male mice and rats. A dose proportionality assessment by power model revealed a lack of dose proportionality in systemic exposure (Cmax, AUC24h and AUCinf) after administration of 100-500 mg/kg of udenafil in mice and 60-240 mg/kg in rats. This study thus demonstrates gender and species differences with regard to the toxicokinetic profiles of udenafil and its active metabolite N-dealkylated udenafil after oral administration of udenafil to mice and rats of both sexes. Our findings suggest the possibility of gender differences in the toxicokinetics of udenafil in humans and suggests that further study is needed in this cohort.

Evaluation of Bayesian Forecasting Methods for Prediction of Tacrolimus Exposure Using Samples Taken on Two Occasions in Adult Kidney Transplant Recipients.

BACKGROUND: Bayesian forecasting-based limited sampling strategies (LSSs) for tacrolimus have not been evaluated for the prediction of subsequent tacrolimus exposure. This study examined the predictive performance of Bayesian forecasting programs/services for the estimation of future tacrolimus area under the curve (AUC) from 0 to 12 hours (AUC0-12) in kidney transplant recipients. METHODS: Tacrolimus concentrations were measured in 20 adult kidney transplant recipients, 1 month post-transplant, on 2 occasions one week apart. Twelve samples were taken predose and 13 samples were taken postdose at the specified times on the first and second sampling occasions, respectively. The predicted AUC0-12 (AUCpredicted) was estimated using Bayesian forecasting programs/services and data from both sampling occasions for each patient and compared with the fully measured AUC0-12 (AUCmeasured) calculated using the linear trapezoidal rule on the second sampling occasion. The bias (median percentage prediction error [MPPE]) and imprecision (median absolute prediction error [MAPE]) were determined. RESULTS: Three programs/services were evaluated using different LSSs (C0; C0, C1, C3; C0, C1, C2, C4; and all available concentrations). MPPE and MAPE for the prediction of fully measured AUC0-12 were <15% for each program/service (with the exclusion of when only C0 was used), when using estimated AUC from data on the same (second) occasion. The MPPE and MAPE for the prediction of a future fully measured AUC0-12 were <15% for 2 programs/services (and for the third when participants who had a tacrolimus dose change between sampling days were excluded), when the occasion 1-AUCpredicted, using C0, C1, and C3, was compared with the occasion 2-AUCmeasured. CONCLUSIONS: All 3 Bayesian forecasting programs/services evaluated had acceptable bias and imprecision for predicting a future AUC0-12, using tacrolimus concentrations at C0, C1, and C3, and could be used for the accurate prediction of tacrolimus exposure in adult kidney transplant recipients.

Oral bioavailability and pharmacokinetics of esculetin following intravenous and oral administration in rats.

Esculetin is the main active ingredient isolated from Artemisia montana (Nakai) Pamp. and Euphorbia lathyris L. The present study investigated the oral bioavailability and pharmacokinetics of esculetin in rats, following intravenous and oral administration.Twenty Sprague-Dawley rats were randomly assigned to receive 10 mg/kg of esculetin either by the intravenous or oral route. Plasma concentrations of esculetin were measured using liquid chromatography-tandem mass spectrometry. Pharmacokinetic parameters were estimated using non-compartmental analysis as well as a compartmental modelling approach using WinNonlinTM and ADAPT 5 software, respectively.According to non-compartmental analysis, the mean oral bioavailability of esculetin was 19%. Mean ± standard deviation values of esculetin half-life, steady-state volume of distribution and clearance, following intravenous dosing, were 2.08 ± 0.46 h, 1.81 ± 0.52 L/kg and 1.27 ± 0.26 L/h/kg, respectively. As indicated by compartmental modelling, a two-compartment pharmacokinetic model with first-order absorption and elimination rate constants of 0.98 ± 0.18 h-1 and 2.47 ± 0.28 h-1, respectively, sufficiently described the plasma concentration-time curve of esculetin.Improving our understanding of the pharmacokinetic properties of esculetin could help with future development of herbal medicine products with appropriate bioactivity.

Pharmacokinetic interaction between dronedarone and ticagrelor following oral administration in rats.

Dronedarone and ticagrelor have high co-administration potential in patients with both acute coronary syndrome and atrial fibrillation. The objective of the present in vivo study was to investigate the potential interaction between dronedarone (5 and 10 mg/kg) and ticagrelor (5 and 10 mg/kg) when administered orally to rats. Forty Sprague-Dawley rats were randomly distributed into eight groups; consisting of a dronedarone only group, a ticagrelor only group, a dronedarone with ticagrelor-pretreatment group, and a ticagrelor with dronedarone-pretreatment group. Pharmacokinetic exposure (AUCinf = 1472 ng·h/mL) associated with administration of 10 mg/kg of dronedarone increased significantly, with delayed T max in the group that received ticagrelor-pretreatment when compared to the dronedarone only group (AUCinf = 723 ng·h/mL). In addition, pharmacokinetic exposure (AUCinf = 2391 ng·h/mL) associated with administration of 10 mg/kg of ticagrelor increased significantly, with increased K el (0.31 h-1) and decreased V z/F (14.6 L/kg) in the dronedarone-pretreatment group when compared to the ticagrelor only group (AUCinf = 1616 ng·h/mL; K el = 0.21 h-1; V z/F = 31.3 L/kg). Results of our study suggest that further investigation of a potential interaction between dronedarone and ticagrelor in humans is justified and that caution may need to be exercised when dronedarone and ticagrelor pharmacotherapies concomitantly.

Pharmacokinetics of eperisone following oral administration in healthy Korean volunteers.

Eperisone is an oral muscle relaxant used to treat musculoskeletal diseases, which exhibits high pharmacokinetic (PK) variability in bioequivalence studies. The aim of this study was to characterize the PKs of eperisone following its oral administration to Korean volunteers through the conduct of a noncompartmental and population analysis. A total of 360 concentration-time measurements collected on two separate occasions from 15 healthy volunteers during a bioequivalent study of eperisone 50 mg (Murex® ) were used in the PK analysis. Noncompartmental analysis was performed using WinNonLinTM and population analysis was performed using NONMEM® . The possible influence of thirty demographic and pathophysiological characteristics on the PKs of eperisone were explored. Based on noncompartmental analysis mean eperisone elimination half-life, apparent clearance (CL/F), and apparent volume of distribution were estimated to be 3.81 h, 39.24 × 103  l/h × 103  L, respectively. During population PK modeling a two-compartment model with first-order absorption rate constant (typical population K a  = 1.5 h-1 ) and first-order elimination (typical population CL/F and apparent volume of distribution in the central compartment [V c /F] = 30.8 × 103  l/h and 86.2 × 103  l, respectively) best described the PKs of eperisone. Interindividual variability in CL/F and V c /F were estimated to be 87.9% and 130.3%, respectively and interoccasion variability in CL/F and V c /F were estimated to be 23.8% and 30.8%, respectively. Aspartate aminotransferase level and smoking status were identified as potential covariates that may influence the CL/F of eperisone. This is the first study to develop a disposition model for eperisone and investigate the potential influence of covariate factors on it PK variability.

An evaluation of the user-friendliness of Bayesian forecasting programs in a clinical setting.

AIMS: To evaluate 3 Bayesian forecasting (BF) programs-TDMx, InsightRx and DoseMe-on their user-friendliness and common liked and disliked features through a survey of hospital pharmacists. METHODS: Clinical pharmacists across 3 Australian hospitals that did not use a BF program were invited to a BF workshop and complete a survey on programs they trialled. Participants were given 4 case scenarios to work through and asked to complete a 5-point Likert scale survey evaluating the program's user-friendliness. Liked and disliked features of each program were ascertained through written responses to open-ended questions. Survey results were compared using a χ2 test of equal or given proportions to identify significant differences in response. RESULTS: Twenty-seven pharmacists, from hospitals, participated. BF programs were rated overall as user-friendly with 70%, 41% and 37% (P = .02) of participants recording a Likert score of 4 or 5 for DoseMe, TDMx and InsightRx, respectively. Participants found it easy to access all required information to use the programs, understood dosing recommendations and visualisations given by each program, and thought programs supported decision-making with >50% of participants scoring a 4 or 5 across the programs in these categories. Common liked features across all programs were the graphical displays and ease of data entry, while common disliked features were related to the units, layout and information display. CONCLUSION: Although differences exist between programs, all 3 programs were most commonly rated as user-friendly across all themes evaluated, which provides useful information for healthcare facilities wanting to implement a BF program.

Prednisolone Concentrations in Plasma (Total and Unbound) and Saliva of Adult Kidney Transplant Recipients.

BACKGROUND: Prednisolone displays significant pharmacokinetic variability and exposure-outcome relationships in renal transplant recipients, suggesting a role for drug monitoring in some scenarios. It is highly protein-bound, and the free form is pharmacologically active but cumbersome to measure. Saliva concentrations might reflect free plasma prednisolone and present an alternative measurement. The aim of this study was to examine the correlation between total and free plasma and saliva prednisolone in adult renal transplant recipients. METHODS: Total and free plasma and saliva prednisolone concentrations were measured in 20 patients receiving oral prednisolone 1-2 months after transplant, between pre-dose and 12 hours post-dose. Prednisolone was determined using high-performance liquid chromatography mass spectrometric detection. The Pearson coefficient was used to assess the association between plasma and salivary prednisolone concentrations and area under the concentration-time curves (AUC0-12). RESULTS: When considering all time points, the total and free plasma prednisolone concentrations correlated well (r = 0.81), but there was poor correlation between saliva and free (r = 0.003) and total (r = 0.01) plasma concentrations. When concentrations before the maximum free prednisolone plasma value were excluded, the correlation between free plasma and saliva concentrations improved (r = 0.57). There was a moderate correlation between free and total plasma prednisolone AUC0-12 (r = 0.62) using all time points, but a poor correlation between free and total plasma prednisolone AUC0-12 and saliva AUC0-12 (r = 0.07; r = 0.17). CONCLUSIONS: Total and free plasma prednisolone measurements correlated poorly with saliva measurements; however, correlation improved when concentrations early in the dosing interval were excluded.

Evaluation of Multiple Linear Regression-Based Limited Sampling Strategies for Enteric-Coated Mycophenolate Sodium in Adult Kidney Transplant Recipients.

BACKGROUND: Although multiple linear regression-based limited sampling strategies (LSSs) have been published for enteric-coated mycophenolate sodium, none have been evaluated for the prediction of subsequent mycophenolic acid (MPA) exposure. This study aimed to examine the predictive performance of the published LSS for the estimation of future MPA area under the concentration-time curve from 0 to 12 hours (AUC0-12) in renal transplant recipients. METHODS: Total MPA plasma concentrations were measured in 20 adult renal transplant patients on 2 occasions a week apart. All subjects received concomitant tacrolimus and were approximately 1 month after transplant. Samples were taken at 0, 0.33, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 6, and 8 hours and 0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 2, 3, 4, 6, 9, and 12 hours after dose on the first and second sampling occasion, respectively. Predicted MPA AUC0-12 was calculated using 19 published LSSs and data from the first or second sampling occasion for each patient and compared with the second occasion full MPA AUC0-12 calculated using the linear trapezoidal rule. Bias (median percentage prediction error) and imprecision (median absolute prediction error) were determined. RESULTS: Median percentage prediction error and median absolute prediction error for the prediction of full MPA AUC0-12 were <15% for 4 LSSs, using the data from the same (second) occasion. One equation (1.583C1 + 0.765C2 + 0.369C2.5 + 0.748C3 + 1.518C4 + 2.158C6 + 3.292C8 + 3.6690) showed bias and imprecision <15% for the prediction of future MPA AUC0-12, where the predicted AUC0-12 from the first occasion was compared with the full AUC0-12 from the second. All LSSs with an acceptable predictive performance included concentrations taken at least 6 hours after the dose. CONCLUSIONS: Only one LSS had an acceptable bias and precision for future estimation. Accurate dosage prediction using a multiple linear regression-based LSS was not possible without concentrations up to at least 8 hours after the dose.

Antimicrobial stewardship in paediatric oncology: Impact on optimising gentamicin use in febrile neutropenia.

OBJECTIVES: To evaluate the impact of an antimicrobial stewardship (AMS) intervention, involving introduction of new guidelines on the treatment of febrile neutropenia (FN), on improving the use of gentamicin in paediatric oncology patients. DESIGN AND INTERVENTION: Updated guidelines for gentamicin usage in paediatrics with FN were implemented at a tertiary children's teaching hospital, in Brisbane, Australia. Data on gentamicin usage before and after the guideline change were collected retrospectively from children with cancer admitted to hospital with FN between January 2012 and December 2013. Gentamicin use, duration of gentamicin therapy and therapeutic monitoring practice were compared against bacterial culture status for admissions before and after the guideline change to assess the impact on practice. RESULTS: Data were collected from 227 children corresponding to 453 separate admissions, 195 preguideline and 257 post-guideline change. Following guideline change, the proportion of admissions in which gentamicin was administered reduced from 79.0 to 20.9% (P-value < 0.001) and administrations not associated with a cultured Gram-negative organism dropped from 87.2 to 58.2% (P-value < 0.001), indicating a change in practice according to the new guideline. Following guideline change, admissions in which gentamicin was used for >48 hr despite the absence of a confirmed Gram-negative infection decreased from 85.6 to 46.9% (P-value < 0.001). CONCLUSIONS: Guideline changes driven through an AMS initiative involving paediatric oncology patients significantly improved targeted- and nontargeted-antimicrobial use potentially reducing the risk of emergence of resistance against gentamicin in this cohort.

Patterns in use and costs of conventional and biologic disease-modifying anti-rheumatic drugs in Australia.

OBJECTIVES: The aim of this study was to characterise the use and costs of subsidising conventional disease-modifying anti-rheumatic drugs (DMARDs) and biologic DMARDs in Australia from 2004-2014 through pharmaceutical benefits schemes. METHODS: Dispensing and expenditure data on conventional and biologic DMARDs were extracted from Medicare Australia and temporal trends were analysed. Medicine use was standardised in terms of the defined daily dose (DDD) per 1,000 population per day (DDD/1,000 population/day). RESULTS: Conventional and biologic DMARD use increased 74% over the study period (4.86 to 8.46 DDD/1,000 population/day; average annual increase 6.7%). Conventional DMARDs accounted for the vast majority of total use and increased 55% (4.81 to 7.43 DDD/1,000 population/day), while biologic DMARD use increased 1,784% (0.055 to 1.030 DDD/1,000 population/day). The most frequently used conventional DMARD was methotrexate (56% total conventional DMARD use) and use increased 95%. Hydroxychloroquine and leflunomide use increased marginally while sulfasalazine use declined 4.2%. Etanercept was the most commonly used biologic DMARD in 2004 and adalimumab in 2014. Conventional DMARD expenditure decreased 4.2% to AUD$33.3 million but biologic DMARD expenditure increased 2,089% to AUD$585.4 million. CONCLUSIONS: The use of conventional and biologic DMARDs increased substantially over a decade in Australia. Patterns of use of conventional DMARDs have changed, and costs have decreased. In contrast a significant escalation in both the use and cost of biologic DMARDs has occurred. Further research is required to address cost-effectiveness, regulation and quality use of these medicines in clinical practice.

Assessing Predictive Performance of Published Population Pharmacokinetic Models of Intravenous Tobramycin in Pediatric Patients.

Several population pharmacokinetic models describe the dose-exposure relationship of tobramycin in pediatric patients. Before the implementation of these models in clinical practice for dosage adjustment, their predictive performance should be externally evaluated. This study tested the predictive performance of all published population pharmacokinetic models of tobramycin developed for pediatric patients with an independent patient cohort. A literature search was conducted to identify suitable models for testing. Demographic and pharmacokinetic data were collected retrospectively from the medical records of pediatric patients who had received intravenous tobramycin. Tobramycin exposure was predicted from each model. Predictive performance was assessed by visual comparison of predictions to observations, by calculation of bias and imprecision, and through the use of simulation-based diagnostics. Eight population pharmacokinetic models were identified. A total of 269 concentration-time points from 41 pediatric patients with cystic fibrosis were collected for external evaluation. Three models consistently performed best in all evaluations and had mean errors ranging from -0.4 to 1.8 mg/liter, relative mean errors ranging from 4.9 to 29.4%, and root mean square errors ranging from 47.8 to 66.9%. Simulation-based diagnostics supported these findings. Models that allowed a two-compartment disposition generally had better predictive performance than those that used a one-compartment disposition model. Several published models of the pharmacokinetics of tobramycin showed reasonable low levels of bias, although all models seemed to have some problems with imprecision. This suggests that knowledge of typical pharmacokinetic behavior and patient covariate values alone without feedback concentration measurements from individual patients is not sufficient to make precise predictions.

Population Pharmacokinetics of Doripenem in Critically Ill Patients with Sepsis in a Malaysian Intensive Care Unit.

Doripenem has been recently introduced in Malaysia and is used for severe infections in the intensive care unit. However, limited data currently exist to guide optimal dosing in this scenario. We aimed to describe the population pharmacokinetics of doripenem in Malaysian critically ill patients with sepsis and use Monte Carlo dosing simulations to develop clinically relevant dosing guidelines for these patients. In this pharmacokinetic study, 12 critically ill adult patients with sepsis receiving 500 mg of doripenem every 8 h as a 1-hour infusion were enrolled. Serial blood samples were collected on 2 different days, and population pharmacokinetic analysis was performed using a nonlinear mixed-effects modeling approach. A two-compartment linear model with between-subject and between-occasion variability on clearance was adequate in describing the data. The typical volume of distribution and clearance of doripenem in this cohort were 0.47 liters/kg and 0.14 liters/kg/h, respectively. Doripenem clearance was significantly influenced by patients' creatinine clearance (CL(CR)), such that a 30-ml/min increase in the estimated CL(CR) would increase doripenem CL by 52%. Monte Carlo dosing simulations suggested that, for pathogens with a MIC of 8 mg/liter, a dose of 1,000 mg every 8 h as a 4-h infusion is optimal for patients with a CL(CR) of 30 to 100 ml/min, while a dose of 2,000 mg every 8 h as a 4-h infusion is best for patients manifesting a CL(CR) of >100 ml/min. Findings from this study suggest that, for doripenem usage in Malaysian critically ill patients, an alternative dosing approach may be meritorious, particularly when multidrug resistance pathogens are involved.

Gentamicin Pharmacokinetics and Monitoring in Pediatric Patients with Febrile Neutropenia.

BACKGROUND: The pharmacokinetics of gentamicin in pediatric patients with febrile neutropenia is described, and the adequacy of initial dosing of once-daily gentamicin assessed at Queensland's largest Children's Hospital. METHODS: Data were retrospectively collected from all pediatrics with febrile neutropenia admitted over a 2-year period who had at least 2 gentamicin concentration-time measurements (a paired set within 1 dosing interval). Gentamicin clearance, volume of distribution, area under the concentration-time curve from 0 to 24 hours postdose (AUC0-24), and maximum concentration values were estimated with log-linear regression using each paired set. The percentage of paired sets associated with gentamicin exposure within predefined hospital targets was calculated, and exposure was examined in relation to the bacterial culture status. RESULTS: Data were collected from 69 patients [median (interquartile range) age 3.7 years (2.2-8.9)] and comprised 121 paired concentration sets characterizing 80 separate admissions. Median (interquartile range) gentamicin clearance and volume of distribution were 8.1 L·h·70 kg (5.8-12.4) and 21.8 L/70 kg (16.9-29.5), respectively. Predefined hospital exposure targets were achieved for both AUC0-24 and maximum concentration for 10% of paired sets; one or the other of these targets were met for 36% of paired sets, and neither target was achieved for 54% of paired sets. Achievement of targets improved with repeated monitoring during the same admission. Median AUC0-24 achieved was significantly higher in patients with a confirmed Gram-negative infection compared with those without 71 (50-91) mg·h·L versus 55 (40.8-67.5) mg·h·L, respectively (P = 0.003). Over the study period, a median gentamicin dose of 10.8 and 6.4 mg/kg was estimated to be necessary to achieve an AUC target of 80 mg·h·L in children ≤10 years and >10 years of age. CONCLUSIONS: Based on a log-linear method of analysis, current dosing seems to be consistently producing gentamicin exposure below predefined pharmacokinetic targets, suggesting that an increase in the recommended starting dose of gentamicin may be required.

Exposure-effect relationship of mycophenolic acid and prednisolone in adult patients with lupus nephritis.

AIMS: The aim was to examine relationships between total and unbound mycophenolic acid (MPA) and prednisolone exposure and clinical outcomes in patients with lupus nephritis. METHODS: Six blood samples were drawn pre- and at 1, 2, 4, 6 and 8 h post-dose and total and unbound MPA and prednisolone pre-dose (C0 ), maximum concentration (Cmax ) and area under the concentration-time curve (AUC) were determined using non-compartmental analysis in 25 patients. The analyses evaluated drug exposures in relation to treatment response since starting MPA and drug-related adverse events. RESULTS: Dose-normalized AUC varied 10-, 8-, 7- and 19-fold for total MPA, unbound MPA, total prednisolone and unbound prednisolone, respectively. Median values (95% CI) of total MPA AUC(0,8 h) (21.5 [15.0, 42.0] vs. 11.2 [4.8, 30.0] mg l(-1) h, P= 0.048) and Cmax (11.9 [6.7, 26.3] vs. 6.1 [1.6, 9.2] mg l(-1) , P = 0.016) were significantly higher in responders than non-responders. Anaemia was significantly associated with higher total (37.8 [14.1, 77.5] vs. 18.5 [11.7, 32.7] mg l(-1) h, P = 0.038) and unbound MPA AUC(0,12 h) (751 [214, 830] vs. 227 [151, 389] mg l(-1) h, P = 0.004). Unbound prednisolone AUC(0,24 h) was significantly higher in patients with Cushingoid appearance (unbound: 1372 [1242, 1774] vs. 846 [528, 1049] nmol l(-1) h, P = 0.019) than in those without. Poorer treatment response was observed in patients with lowest tertile exposure to both total MPA and prednisolone as compared with patients with middle and higher tertile exposure (17% vs. 74%, P = 0.023). CONCLUSIONS: This study suggests a potential role for therapeutic drug monitoring in individualizing immunosuppressant therapy in patients with lupus nephritis.

Improved prediction of tacrolimus concentrations early after kidney transplantation using theory-based pharmacokinetic modelling.

AIMS: The aim was to develop a theory-based population pharmacokinetic model of tacrolimus in adult kidney transplant recipients and to externally evaluate this model and two previous empirical models. METHODS: Data were obtained from 242 patients with 3100 tacrolimus whole blood concentrations. External evaluation was performed by examining model predictive performance using Bayesian forecasting. RESULTS: Pharmacokinetic disposition parameters were estimated based on tacrolimus plasma concentrations, predicted from whole blood concentrations, haematocrit and literature values for tacrolimus binding to red blood cells. Disposition parameters were allometrically scaled to fat free mass. Tacrolimus whole blood clearance/bioavailability standardized to haematocrit of 45% and fat free mass of 60 kg was estimated to be 16.1 l h−1 [95% CI 12.6, 18.0 l h−1]. Tacrolimus clearance was 30% higher (95% CI 13, 46%) and bioavailability 18% lower (95% CI 2, 29%) in CYP3A5 expressers compared with non-expressers. An Emax model described decreasing tacrolimus bioavailability with increasing prednisolone dose. The theory-based model was superior to the empirical models during external evaluation displaying a median prediction error of −1.2% (95% CI −3.0, 0.1%). Based on simulation, Bayesian forecasting led to 65% (95% CI 62, 68%) of patients achieving a tacrolimus average steady-state concentration within a suggested acceptable range. CONCLUSION: A theory-based population pharmacokinetic model was superior to two empirical models for prediction of tacrolimus concentrations and seemed suitable for Bayesian prediction of tacrolimus doses early after kidney transplantation.

Effects of combinational CYP3A5 6986A>G polymorphism in graft liver and native intestine on the pharmacokinetics of tacrolimus in liver transplant patients: a meta-analysis.

BACKGROUND: Many studies have reported reduced tacrolimus dose-adjusted exposure in individuals expressing the CYP3A5*1 allele. A meta-analyses of the current data may help characterize the extent of impact this polymorphism has on tacrolimus pharmacokinetics in adult liver transplant recipients and whether donor or recipient genotype is the most influential factor. METHODS: Structured searches, of studies that evaluated the association between CYP3A5*1 allele and tacrolimus pharmacokinetics in adult liver transplant recipients, were conducted using Embase and Medline. A meta-analysis comparing tacrolimus daily dose, trough concentrations (C0), and dose-adjusted trough concentrations (C0/dose) across the donor and recipient genotype pairs was conducted using a random effects model. RESULTS: Eight studies, involving a total of 694 adult liver transplant recipients, were included. Dose-adjusted tacrolimus trough concentrations were significantly lower in those in whom the donor or recipient expressed a *1 allele compared with those in whom neither the donor nor recipient expressed this allele at 7 days and 2, 3, 6, and 12 months after transplant [standardized mean differences between expressers and nonexpressers of -1.98, -2.12, -2.39, -3.68, and -3.26 (ng/mL)/(mg·kg·d), respectively]. CONCLUSIONS: Results of the meta-analysis demonstrated that, in adult liver transplant patients, CYP3A5 expression in either the donor or recipient resulted in a need for a higher mean tacrolimus daily dose to achieve the target drug exposure. In the immediate posttransplant period, recipient expression of a CYP3A5*1 allele seemed to have the greatest influence on tacrolimus pharmacokinetics with donor expression of a CYP3A5*1 allelle possibly becoming more important with increasing time after transplant.

Population pharmacokinetics of tacrolimus in adult kidney transplant patients: impact of CYP3A5 genotype on starting dose.

OBJECTIVES: The aims of this study were to develop a population pharmacokinetic model of tacrolimus in adult kidney transplant recipients, to use this model to compare cytochrome P450 3A5 (CYP3A5) genotype-based initial dosing of tacrolimus with standard per-kilogram-based dosing, and to predict the best starting dose of tacrolimus based on patient genotype to achieve a trough concentration between 6 and 10 µg/L by day 5 posttransplantation. METHODS: Population analysis was performed using the software program NONMEM. Tacrolimus dosing regimens were compared by predicting tacrolimus trough concentrations in a simulated data set by running NONMEM with population parameters fixed at the final model estimates. Data from 173 patients with 1554 tacrolimus concentration-time measurements were modeled. RESULTS: Tacrolimus disposition was well described by a 2-compartment model with first-order elimination and first-order absorption after a lag time. Patient CYP3A5 genotype (rs776746), weight, hematocrit, and postoperative day were identified as significant covariates effecting tacrolimus apparent oral clearance (CL/F), with higher CL/F in CYP3A5*1 allele carriers, heavier patients, patients with low hematocrit, and in the immediate posttransplantation period. Typical population estimates for tacrolimus CL/F in CYP3A5*1 allele carriers and noncarriers were 40.8 and 25.5 L/h, respectively. CONCLUSIONS: In patients carrying the CYP3A5*1 allele, a per-kilogram dose of 0.075 mg/kg twice daily seemed too much low with approximately 65% of simulated subjects predicted to achieve a trough below 6 µg/L at day 5 posttransplantation. To reduce the risk of under immunosuppression in the immediate posttransplantation period, carriers of a CYP3A5*1 allele are likely to benefit from a tacrolimus starting dose of either 10 mg or 0.115 mg/kg twice daily.

Pharmacology and toxicology of mycophenolate in organ transplant recipients: an update.

This review aims to provide an update of the literature on the pharmacology and toxicology of mycophenolate in solid organ transplant recipients. Mycophenolate is now the antimetabolite of choice in immunosuppressant regimens in transplant recipients. The active drug moiety mycophenolic acid (MPA) is available as an ester pro-drug and an enteric-coated sodium salt. MPA is a competitive, selective and reversible inhibitor of inosine-5'-monophosphate dehydrogenase (IMPDH), an important rate-limiting enzyme in purine synthesis. MPA suppresses T and B lymphocyte proliferation; it also decreases expression of glycoproteins and adhesion molecules responsible for recruiting monocytes and lymphocytes to sites of inflammation and graft rejection; and may destroy activated lymphocytes by induction of a necrotic signal. Improved long-term allograft survival has been demonstrated for MPA and may be due to inhibition of monocyte chemoattractant protein 1 or fibroblast proliferation. Recent research also suggested a differential effect of mycophenolate on the regulatory T cell/helper T cell balance which could potentially encourage immune tolerance. Lower exposure to calcineurin inhibitors (renal sparing) appears to be possible with concomitant use of MPA in renal transplant recipients without undue risk of rejection. MPA displays large between- and within-subject pharmacokinetic variability. At least three studies have now reported that MPA exhibits nonlinear pharmacokinetics, with bioavailability decreasing significantly with increasing doses, perhaps due to saturable absorption processes or saturable enterohepatic recirculation. The role of therapeutic drug monitoring (TDM) is still controversial and the ability of routine MPA TDM to improve long-term graft survival and patient outcomes is largely unknown. MPA monitoring may be more important in high-immunological recipients, those on calcineurin-inhibitor-sparing regimens and in whom unexpected rejection or infections have occurred. The majority of pharmacodynamic data on MPA has been obtained in patients receiving MMF therapy in the first year after kidney transplantation. Low MPA area under the concentration time from 0 to 12 h post-dose (AUC0-12) is associated with increased incidence of biopsy-proven acute rejection although AUC0-12 optimal cut-off values vary across study populations. IMPDH monitoring to identify individuals at increased risk of rejection shows some promise but is still in the experimental stage. A relationship between MPA exposure and adverse events was identified in some but not all studies. Genetic variants within genes involved in MPA metabolism (UGT1A9, UGT1A8, UGT2B7), cellular transportation (SLCOB1, SLCO1B3, ABCC2) and targets (IMPDH) have been reported to effect MPA pharmacokinetics and/or response in some studies; however, larger studies across different ethnic groups that take into account genetic linkage and drug interactions that can alter a patient's phenotype are needed before any clinical recommendations based on patient genotype can be formulated. There is little data on the pharmacology and toxicology of MPA in older and paediatric transplant recipients.