Dried blood spot (DBS) sampling for the purpose of therapeutic drug monitoring can be an attractive alternative for conventional blood sampling, especially in children. This study aimed to compare all costs involved in conventional sampling versus DBS home sampling in two pediatric populations: renal transplant patients and hemato-oncology patients. Total costs were computed from a societal perspective by adding up healthcare cost, patient related costs and costs related to loss of productivity of the caregiver. Switching to DBS home sampling was associated with a cost reduction of 43% for hemato-oncology patients (€277 to €158) and 61% for nephrology patients (€259 to €102) from a societal perspective (total costs) per blood draw. From a healthcare perspective, costs reduced with 7% for hemato-oncology patients and with 21% for nephrology patients. Total savings depend on the number of hospital visits that can be avoided by using home sampling instead of conventional sampling.

A DBS assay was developed for tacrolimus and MPA. Tacrolimus venous concentrations could be adequately predicted from DBS. DBS analysis of MPA seemed to be a semiquantitative measurement at the most when compared with conventional plasma analysis, considering the high variability between observed and predicted concentrations. Next, home-based DBS sampling of tacrolimus for the purpose of therapeutic drug monitoring will be implemented into routine clinical care.

Background and ObjectivesCaspofungin is an echinocandin antifungal agent used as first-line therapy for the treatment of invasive candidiasis. The maintenance dose is adapted to body weight (BW) or liver function (Child-Pugh score B or C). We aimed to study the pharmacokinetics of caspofungin and assess pharmacokinetic target attainment for various dosing strategies.MethodsCaspofungin pharmacokinetic data from 21 intensive care unit (ICU) patients was available. A population pharmacokinetic model was developed. Various dosing regimens (loading dose/maintenance dose) were simulated: licensed regimens (I) 70/50 mg (for BW <80 kg) or 70/70 mg (for BW >80 kg); and (II) 70/35 mg (for Child-Pugh score B); and adapted regimens (III) 100/50 mg (for Child-Pugh score B); (IV) 100/70 mg; and (V) 100/100 mg. Target attainment based on a preclinical pharmacokinetic target for Candida albicans was assessed for relevant minimal inhibitory concentrations (MICs).ResultsA two-compartment model best fitted the data. Clearance was 0.55 L/h and the apparent volumes of distribution in the central and peripheral compartments were 8.9 and 5.0 L, respectively. The median area under the plasma concentration–time curve from time zero to 24 h on day 14 for regimens I–V were 105, 65, 93, 130, and 186 mg·h/L, respectively. Pharmacokinetic target attainment was 100 % (MIC 0.03 µg/mL) irrespective of dosing regimen but decreased to (I) 47 %, (II) 14 %, (III) 36 %, (IV) 69 %, and (V) 94 % for MIC 0.125 µg/mL.ConclusionThe caspofungin maintenance dose should not be reduced in non-cirrhotic ICU patients based on the Child-Pugh score if this classification is driven by hypoalbuminemia as it results in significantly lower exposure. A higher maintenance dose of 70 mg in ICU patients results in target attainment of >90 % of the ICU patients with species with an MIC of up to 0.125 µg/mL.

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Title: Population pharmacokinetics and genetics of oral meltdose tacrolimus (Envarsus ® ) in stable adult liver transplant recipients Lisa C Martial(1*); Maaike Biewenga(2*); Bastian N Ruijter(2); Ron Keizer (3); Jesse J Swen(1); Bart van Hoek(2**); Dirk Jan AR Moes(1**).

ObjectiveTo study the pharmacokinetics of micafungin in intensive care patients and assess pharmacokinetic (PK) target attainment for various dosing strategies.MethodsMicafungin PK data from 20 intensive care unit patients were available. A population-PK model was developed. Various dosing regimens were simulated: licensed regimens (I) 100 mg daily; (II) 100 mg daily with 200 mg from day 5; and adapted regimens 200 mg on day 1 followed by (III) 100 mg daily; (IV) 150 mg daily; and (V) 200 mg daily. Target attainment based on a clinical PK target for Candida as well as non-Candida parapsilosis infections was assessed for relevant minimum inhibitory concentrations [MICs] (Clinical and Laboratory Standards Institute). Parameter uncertainty was taken into account in simulations.ResultsA two-compartment model best fitted the data. Clearance was 1.10 (root square error 8%) L/h and V 1 and V 2 were 17.6 (root square error 14%) and 3.63 (root square error 8%) L, respectively. Median area under the concentration–time curve over 24 h (interquartile range) on day 14 for regimens I–V were 91 (67–122), 183 (135–244), 91 (67–122), 137 (101–183) and 183 (135–244) mg h/L, respectively, for a typical patient of 70 kg. For the MIC/area under the concentration–time curve >3000 target (all Candida spp.), PK target attainment was >91% on day 14 (MIC 0.016 mg/L epidemiological cut-off) for all of the dosing regimens but decreased to (I) 44%, (II) 91%, (III) 44%, (IV) 78% and (V) 91% for MIC 0.032 mg/L. For the MIC/area under the concentration–time curve >5000 target (non-C. parapsilosis spp.), PK target attainment varied between 62 and 96% on day 14 for MIC 0.016.ConclusionsThe licensed micafungin maintenance dose results in adequate exposure based on our simulations with a clinical PK target for Candida infections but only 62% of patients reach the target for non-C. parapsilosis. In the case of pathogens with an attenuated micafungin MIC, patients may benefit from dose escalation to 200 mg daily. This encourages future study.Electronic supplementary materialThe online version of this article (doi:10.1007/s40262-017-0509-5) contains supplementary material, which is available to authorized users.

MPA is an immunosuppressive agent used to prevent graft rejection after renal transplantation. MPA shows considerable inter- and intraindividual variability in exposure in children and has a defined therapeutic window, and TDM is applied to individualize therapy. We aimed to study the exposure to MPA measured as the AUC in pediatric renal transplant patients, to identify factors influencing exposure and to assess target attainment. Children transplanted between 1998 and 2014 in a single center were included. Two groups were identified: Group 1 (AUC <3 wk post-transplantation) and Group 2 (AUC >18 months post-transplantation). Therapeutic targets were set at: AUC0-12h of 30-60 mg h/L. A total of 39 children were included in Group 1 (median age 13.3 yr) vs. 14 in Group 2 (median age 13.4 yr). AUC0-12h was 29.7 mg h/L in Group 1 and 56.6 mg h/L in Group 2, despite a lower dosage in Group 2 (584 and 426 mg/m(2) , respectively). About 46% of patients reached the target AUC0-12h in Group 1. Time since transplantation and serum creatinine were significantly associated with MPA exposure (p < 0.001), explaining 36% of the variability. Individualization of the mycophenolate dose by more intense and more early TDM could improve target attainment.

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