Impact of a Bayesian Individualization of Cyclosporine Dosage Regimen for Children Undergoing Allogeneic Hematopoietic Cell Transplantation: A Cost-Effectiveness Analysis

BACKGROUND

Cyclosporine A (CsA) is the main drug used to prevent graft-versus-host disease in patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT). CsA therapeutic drug monitoring (TDM) has been performed for ages, with studies revealing clinical benefits, but failing to examine its economic impact. In this article, the main objective was to evaluate the economic impact of the CsA TDM strategy, based on a Bayesian approach, by assessing costs related to its clinical impact. Furthermore, TDM effectiveness was analyzed for pharmacokinetics and clinical outcomes.

METHODS

A cost-effective, nonrandomized, retrospective, single-center study compared 2 CsA monitoring and dose adaptation strategies in pediatric patients undergoing HSCT. From 2014 to 2016, CsA TDM was performed using a population pharmacokinetics model-coupled Bayesian approach by a pharmacist ["pharmacist-assisted individualization" (PAI)]. From 2017 to 2018, CsA TDM was performed by the clinician without a Bayesian approach (non-PAI group). HSCT costs were evaluated from the French National Insurance perspective. Economic and clinical outcomes were assessed by measuring incremental cost-effectiveness ratios.

RESULTS

The study included 144 patients: 90 and 54 patients in PAI and non-PAI groups, respectively. Both groups were comparable for sociodemographic and clinical characteristics. The mean total cost per patient was significantly lower (P < 0.01) in the PAI group (€85,947) than in the non-PAI group (€100,435). Multivariate analysis revealed that TDM based on the Bayesian approach was a protective factor (odds ratio = 0.86) for severe acute graft-versus-host disease. We noted that pharmacist-based TDM was the dominant strategy. Bayesian method-based TDM allowed an increase in the percentage of target attainment at any period post-HSCT.

CONCLUSIONS

CsA TDM with a Bayesian approach is a cost-effective procedure, and highlighted clinical benefits encourage the development of new TDM strategies for HSCT.

A Model for Predicting the Interindividual Variability of Drug-Drug Interactions

Pharmacokinetic drug-drug interactions are frequently characterized and quantified by an AUC ratio (Rauc). The typical value of the AUC ratio in case of cytochrome-mediated interactions may be predicted by several approaches, based on in vitro or in vivo data. Prediction of the interindividual variability of Rauc would help to anticipate more completely the consequences of a drug-drug interaction. We propose and evaluate a simple approach for predicting the standard deviation (sd) of Ln(Rauc), a metric close to the interindividual coefficient of variation of Rauc. First, a model was derived to link sd(Ln Rauc) with the substrate fraction metabolized by each cytochrome and the potency of the interactors, in case of induction or inhibition. Second, the parameters involved in these equations were estimated by a Bayesian hierarchical model, using the data from 56 interaction studies retrieved from the literature. Third, the model was evaluated by several metrics based on the fold prediction error (PE) of sd(Ln Rauc). The median PE was 0.998 (the ideal value is 1) and the interquartile range was 0.96-1.03. The PE was in the acceptable interval (0.5 to 2) in 52 cases out of 56. Fourth, a surface plot of sd(Ln Rauc) as a function of the characteristics of the substrate and the interactor has been built. The minimal value of sd(Ln Rauc) was about 0.08 (obtained for Rauc = 1) while the maximal value, 0.7, was obtained for interactions involving highly metabolized substrates with strong interactors.

Should busulfan therapeutic range be narrowed in pediatrics? Experience from a large cohort of hematopoietic stem cell transplant children

Busulfan, the corner stone of hematopoietic stem cell transplantation regimens, has a narrow therapeutic window. Therapeutic drug monitoring (TDM)-guided dosing to reach the conventional area under the concentration-time curve (AUC) target range of 900-1500 μmol min/L is associated with better outcomes. We report our experience with busulfan TDM in a large cohort of children. The aims were to investigate the relevance of using a more restricted therapeutic range and investigate the association between busulfan therapeutic range and clinical outcome. This study includes 138 children receiving 16 doses of intravenous busulfan, with the first dose assigned based on weight and doses adjusted to a local AUC target range of 980-1250 μmol min/L. Busulfan TDM combined with model-based dose adjustment was associated with an increased probability of AUC target attainment, for both target range: 90.8% versus 74.8% for the conventional target range and 66.2% versus 43.9% for the local target range (P<0.001). The median follow-up was 56.2 months. Event-free survival was 88.5%, overall survival was 91.5% and veno-occlusive disease occurred in 18.3% of patients. No difference was observed for clinical outcomes depending on the selected target range. Pharmacokinetic monitoring and individualization of busulfan dosage regimen are useful in improving target attainment, but using a restricted target range has no impact on clinical outcomes.

High methotrexate exposure and toxicity in children with t(9;22) positive acute lymphoblastic leukaemia treated with imatinib

WHAT IS KNOWN AND OBJECTIVE

Although there is one report on the possible reduced clearance of methotrexate in an adult patient when given concomitantly with imatinib, there is little information on the possible pharmacokinetic interaction. We report on three cases of delayed elimination of methotrexate in children with chromosome Philadelphia-positive acute lymphoblastic leukaemia treated concomitantly with imatinib.

CASE SUMMARY

Three patients, aged 9-17 years, presented with high methotrexate blood levels following co-administration of imatinib and high-dose methotrexate. Two patients presented with clinical symptoms (nausea, epigastric pain and mucositis, acute renal failure, liver cytolysis). One patient required extra supplementary folinic acid doses than used in the standard protocol and one child required the use of carboxypeptidase-G2.

WHAT IS NEW AND CONCLUSION

There is an apparent pharmacokinetic interaction between imatinib and methotrexate in children. Several mechanisms could explain this interaction, including competition for BCRP or ABCB transporters. Temporary withdrawal of imatinib may be necessary for preventing severe methotrexate-related adverse events.

Cytomegalovirus infection in pediatric allogenic hematopoietic stem cell transplantation. A single center experience

We report a retrospective analysis of Cytomegalovirus (CMV) infection: incidence, recurrence, resistance, and subsequent disease of 81 children who underwent allogenic hematopoietic stem cell transplantation (HSCT). The recipient and/or donor's CMV serology was positive prior to transplant [recipient (R+) and/or donor (D+)]. CMV was monitored by RT-PCR starting from the first week post transplant. Forty patients showed CMV infection (49, 5%). Of them 10 manifested CMV disease leading to four deaths. In univariate analysis, factors associated with CMV infection were CMV R+ P < .01, CMV R+/D+ pair P < .01, nonbone marrow (BM) stem cell source P < .05, nonirradiation conditioning regimen P < .05, Antithymocyte globulin (ATG) P < .01. Factors associated with CMV resistance were: >1 HLA allele mismatch P < .05, CMV R +/D-pair P < .01, CMV D-P < .01, non-BM P < .05, nongenoidentical transplant P < .01. CMV disease was influenced by >1 HLA allele mismatch (P < .001), non-BM (P < .01). On multivariate analysis, CMV R+/D- (P < .05), corticosteroids ≥2 mg/kg P < .01, ATG P < .01 and non-BM (P < .05) were independent factors for CMV infection. CMV R+ transplant is associated with more CMV infection and resistance to preemptive treatment. Prolonged immune suppression (IS) worsens outcome of CMV infection and should be shortened whenever possible.

[Assessment of adherence to Afssaps guidelines for the prescription of antifungals in pediatric hemato-oncology]

OBJECTIVE

This study had for aim to identify factors limiting the implementation of clinical guidelines related to the use of expensive antifungal drugs in pediatric hemato-oncology.

DESIGN

A retrospective study was conducted in a Lyon teaching hospital (France), from February to December 2008. The compliance of antifungal prescription to French guidelines was assessed. Audit findings were interpreted using both semi-directed interviews of six prescribers (qualitative approach) and statistical analysis of prescriptions (quantitative approach).

RESULTS

Fifty antifungal prescriptions were studied. The compliance with clinical guidelines reached 66% (CI 95% 52-80%). The semi-directed interviews revealed that five issues may have influenced the adherence of prescribers with recommended practices: the guidelines, the molecule, the prescriber, the child, and practice settings. The statistical analysis did not reveal any link between the prescriber's activities or his department and the compliance with guidelines. A significant association was found between the documentation of infection and the non-conformity of antifungal prescriptions (p=0.02).

CONCLUSIONS

This study, combining qualitative and quantitative assessments, addressed potential issues related to the implementation of guidelines in specific patient groups or to their adaptation in the context of pediatric hematology-oncology. Harmonization of practices related to the widespread use of antifungal associations is required.

The use of pharmacokinetic models in paediatric onco-haematology: effects on clinical outcome through the examples of busulfan and cyclosporine

Overall survival after allogeneic haematopoietic stem cell transplantation (HSCT) is reduced by the high rate of transplantation-related mortality (TRM), especially because of liver veno-occlusive disease (VOD) or acute graft-vs.-host disease (GVHD) because of the toxicity or inefficacy of busulfan and cyclosporine (CsA), respectively. Results of clinical outcome of previous studies performed to optimize busulfan and CsA therapy by controlling their pharmacokinetic variability by means of maximum a posteriori (MAP) Bayesian individualization of both drugs are presented. The 90-day VOD-free survival was significantly higher in patients with individualized busulfan doses: 97% vs. 76%. Monitoring CsA trough blood concentrations allowed us to obtain a successful GVHD outcome (mild or moderate GVHD and graft vs. leukaemia effect (GVL) in malignant diseases and no GVHD (in non-malignant ones) in the majority of our patients. Severe GVHD occurred in <5% of patients. TRM in children can be significantly decreased by using population pharmacokinetic models and MAP Bayesian individualization of dose regimens for drugs such as CsA and busulfan.

Influence of Underlying Disease on Busulfan Disposition in Pediatric Bone Marrow Transplant Recipients: A Nonparametric Population Pharmacokinetic Study

Busulfan is an alkylating agent used in a conditioning regimen prior to bone marrow transplantation. Busulfan has a narrow therapeutic index, giving rise to major liver toxicity (veno-occlusive disease), and a wide interpatient and intrapatient pharmacokinetic variability. This report presents the results of a population pharmacokinetic analysis leading to models based on underlying diseases requiring bone marrow transplantation. One hundred children received oral busulfan-based conditioning regimens between March 1998 and February 2006. Busulfan pharmacokinetic parameter estimates (Ka, first order absorption rate constant; Vs, volume of distribution related to the body weight; and Cl/F, apparent clearance) were estimated by using the nonparametric adaptative grid (NPAG) algorithm in patients divided into four groups according to initial diagnosis: metabolic diseases, hemoglobinopathies, hematological malignancies, and immune deficiencies. Ka and Vs did no differ significantly in the four subgroups. Cl/F and areas under the plasma concentration curve were significantly different in the four groups. Cl/F was significantly higher in the hemoglobinopathies group (P = 0.002), with a mean value of 7.78 L . h, whereas the immune deficiencies group was characterized by the lowest Cl/F (3.59 L . h). Interindividual variability was shown by high interindividual parameter percent coefficients of variation (CV%) but, nevertheless, with less diversity in the population parameter distributions for Vs in the three subgroups-metabolic diseases, hemoglobinopathies, and malignant diseases-and in Cl/F for patients with hemoglobinopathies. The fit was good for busulfan concentration predictions based on Bayesian individual posterior values, with little bias and good precision. In comparison with the overall population, the only model of subgroup presenting a greater precision was patients with hemoglobinopathies (P = 0.002). Use of these more specific models of a given disease may well result in more accurate individualization of busulfan dose regimens, especially in very sparse blood sampling situations.

Un cas d'encéphalite à herpès virus humain de type 6 après transplantation de moelle osseuse

Human herpesvirus 6 (HHV-6) encephalitis may induce neurological sequelae and death; the diagnosis is difficult because of an initially poor symptomatology and of the absence of specific biochemical, electric and radiological signs. We report on a 7-year-old boy with relapsed acute lymphoblastic leukaemia, who developed HHV-6 encephalitis after bone marrow transplantation; the patient recovered after treatment with ganciclovir.

Low incidence of sepsis due to viridans streptococci in a ten-year retrospective study of pediatric acute myeloid leukemia

BACKGROUND

Infections remain an important cause of morbidity and mortality in children with acute myeloid leukemia (AML), and particularly viridans group streptococci (VGS) sepsis. The present study, conducted between 1993 and 2003 in children with AML, sought to assess the frequency and characteristics of infectious complications (ICs), the incidence of VGS sepsis, the interest of preventive decontamination, and a possible cytarabine dose-effect on the occurrence of ICs.

METHODS

Medical charts of 78 children treated according to the EORTC 58921 clinical trial were analyzed retrospectively. Patients were isolated in laminar air flow rooms, received non-absorbable gut decontamination, gum decontamination with vancomycin mouthwash, and trimethoprim-sulfamethoxasole. ICs were categorized as microbiologically documented infections (MDI), clinically documented infections (CDI), or fever of unknown origin (FUO).

RESULTS

Overall, 268 ICs occurred: 57.5% FUO, 8.5% CDI, and 34% MDI. Bloodstream infections occurred in 58 febrile episodes: Gram-positive bacteria represented 83% of the pathogens including 66.1% Staphylococcus species and 8.5% Streptococcus species (6.8% VGS), Gram-negative bacteria represented 13.5% of the pathogens and yeasts 3.5%. Five patients died of infection (6.4%). None died from bacterial infection and no case of VGS sepsis required intensive care. Invasive fungal infection was proven in four patients. Number of ICs was significantly different according to gum and gut decontamination status, and according to the cytarabine dose during the first intensification. No resistant strains were detected in spite of the use of local antibiotics.

CONCLUSION

The low rate of VGS and enterobacteriaceae sepsis was probably due to the effective decontamination. Our supportive care strategy could potentially help enhance overall survival in children with AML.

Efficacy and plasma levels of ropivacaine for children: controlled regional analgesia following lower limb surgery

BACKGROUND

Continuous regional analgesia (CRA) is considered a safe and efficacious technique for postoperative pain relief in children after lower limb surgery. We recently evaluated the feasibility of patient-controlled regional analgesia (PCRA) in a similar acute pain situation and we concluded that PCRA might be advantageous over CRA in terms of lower costs, risk of systemic toxicity while producing similarly adequate analgesia. We therefore prospectively compared both techniques in the paediatric population.

METHODS

In total, 30 children undergoing lower limb orthopaedic surgery were randomized to receive PCRA or CRA with ropivacaine 0.2%. Visual analogue scale scores, rescue analgesia, overall satisfaction, motor blockade and plasma ropivacaine concentrations were recorded for 48 h.

RESULTS

Adequate analgesia was achieved with both techniques. No significant difference was noted for rescue analgesia, overall satisfaction and motor blockade. In contrast, children in the PCRA group received significantly less local anaesthetics than those in the CRA group. In addition, total plasma concentrations of ropivacaine were significantly reduced in the PCRA group as compared with the CRA group during the 48 h postoperative period.

CONCLUSIONS

Both techniques are efficacious and satisfactory. However, PCRA with ropivacaine 0.2% can provide adequate postoperative analgesia for paediatric orthopaedic procedures with smaller doses of ropivacaine than CRA.

Antileukemic and long-term effects of two regimens with or without TBI in allogeneic bone marrow transplantation for childhood acute lymphoblastic leukemia

Between September 1986 and June 1997, 24 children with high-risk ALL in CR1 were allografted after TAM (fractionated TBI, high-dose Ara-C, and melphalan; n = 10) or BAM protocol (busulfan, high-dose Ara-C, and melphalan; n = 14). The EFS for transplants from sibling donors was 33% with TAM and 62% with BAM (P = 0.148). The probability of acute GvHD was 70% with TAM and 15% with BAM (P = 0.003). Four of 17 evaluable patients relapsed: one after TAM and three after BAM. In all, 46 other children transplanted in CR beyond CR1 were studied for sequelae. Long-term side effects were more frequent in TAM vs BAM. In children with ALL, busulfan may be a good alternative to TBI to improve the quality of life.

[Busulfan and cycosporin in bone graft children]

Most drugs exhibit both inter- and intra-individual pharmacokinetic and pharmacodynamic variability. This variability explains the different responses observed in patients exposed to standard doses and must be taken into consideration when the therapeutic window is narrow. Population pharmacokinetics provides mean (or median) values of pharmacokinetic parameters as well as the distribution pattern and the statistical relationship with covariables in a group of individuals presenting common characteristics. Among the different methods developed for population pharmacokinetics, the data pool method, as well as the two-step and one-step methods (NONMEM and NPEM) are attractive. Population models can then be developed using bayesian logistics to obtain an estimation of the pharmacokinetic parameters of a given patient and predict the most adapted dose in light of the therapeutic target (residual serum concentration, mean concentration.). Busulfan is an alkylizing agent used instead of radiotherapy for pre-graft preparation before bone marrow grafts in children. This compound requires dose monitoring because of its narrow therapeutic window: under-dosing raises the risk of graft rejection; inversely over-dosing can cause potentially fatal complications such as occlusive venous disease. Interindividual variability is characteristic of busulfan kinetics. Several factors can explain part of this variability: age, underlying disease, changes in liver function, drug bioavailability, chronobiology. The short treatments used (most protocols have 16 doses given in four days) require rapid monitoring to propose effective adjustments. In this context, use of bayesian logistics to estimate the patient's pharmokinetic parameters is very useful for correct dosing. This type of monitoring could also be used for other compounds such as cyclosporine, with a narrow therapeutic window.

Clinical and pharmacological risk factors for acute graft-versus-host disease after paediatric bone marrow transplantation from matched-sibling or unrelated donors

The aim of this study was to identify the risk factors for acute graft-versus-host disease (aGVHD) in children transplanted from a matched-sibling donor (MSD) or an unrelated donor (UD). In all, 87 children consecutively underwent allogeneic bone marrow transplantation (BMT) from MSD (n=36), and UD (n=51). GVHD prophylaxis included CsA alone (n=33) or with MTX (n=51). ATG was added in UD-BMT and thalassemic recipients. CsA whole-blood concentrations were measured by EMIT and the dosing regimen was monitored by Bayesian pharmacokinetic modelling. Trough blood concentration (TBC) during the first 2 weeks post transplantation was lower in children who developed grade II-IV aGVHD than those developing no GVHD or only grade I (57+/-9 vs 94+/-8 ng/ml, P=0.007), whereas peak blood concentration and area under concentration curve vs time were similar in both groups. TBC <85 ng/ml and 'use of MTX' were associated with aGVHD in MSD-SCT (P=0.003 and 0.007, respectively) as well as in UD-SCT (P=0.006 and 0.003). Donor age >or=8 years was significant only in MSD-BMT. Our results have shown the significant decisive role of pharmacological factors such as CSA TBC or use of MTX in the occurrence of GVHD in MSD as well as in UD paediatric BMT.

Relationship between CsA trough blood concentration and severity of acute graft-versus-host disease after paediatric stem cell transplantation from matched-sibling or unrelated donors

In order to determine optimal CsA trough blood concentrations (TBC) in the early post transplantation period, we analysed relationships between TBC and acute graft-versus-host disease (aGVHD) in paediatric SCT. A total of 94 children consecutively underwent allogeneic stem cell transplantation (SCT) from: matched-sibling (MSD) (n=36), mismatched-related (MMRD) (n=3) and unrelated donors (UD) (n=55). GVHD prophylaxis usually included CsA alone or with methotrexate. Antithymocyte globulin was added in UD-SCT. TBC during the first weeks of post transplantation were estimated retrospectively by a Bayesian pharmacokinetic method and statistically associated with aGVHD. In MSD-SCT, the mean TBC during the first 2 weeks post transplantation were 42+/-10 and 90+/-7 ng/ml, respectively, in patients with grade II-IV and 0-I aGVHD (P=0.001). In SCT from UD and MMRD, TBC were 73+/-4 vs 95+/-8 ng/ml (P=0.284). For TBC >85 ng/ml, no patient developed grade II-IV aGVHD, 10 developed mild aGVHD and 30 had no aGVHD. For TBC <65 ng/ml, 7/11 patients receiving an MSD-SCT and 4/18 receiving an UD- or MMRD-SCT developed grade II-IV aGVHD. The mean TBC corresponding to each grade were: no GVHD: 101+/-10 ng/ml, mild: 77+/-11 ng/ml, moderate: 61+/-13 ng/ml, severe: 56+/-15 ng/ml (P <0.001). These results reveal a strong relationship between TBC during the early post transplantation period and the severity of aGVHD in paediatric SCT.

Outcome of 27 patients with Hurler's syndrome transplanted from either related or unrelated haematopoietic stem cell sources

Over the last 15 years, we have performed a total of 30 haematopoietic stem cell transplants on 27 children suffering from Hurler's syndrome. These children were of median age 11 months at the time of diagnosis and 25 months at the time of transplantation. The phenotype was severe in 21 cases (78%). The donor was familial in 13 cases: nine genotypically identical, one phenotypically identical father and three HLA-mismatched donors. Unrelated donors were selected in 17 cases: four phenotypically identical and 13 with 1-4 HLA mismatches. The conditioning regimen generally consisted of busulphan 600 mg/m(2) plus cyclophosphamide (Endoxan) 260 mg/kg and cyclosporin with methotrexate for GvHD prophylaxis. Rabbit anti-thymocyte globulin (Thymoglobuline) was given for all unrelated or familial mismatched transplantations. The median nucleated cell dose infused was 6.00 x 10(8) TNC/kg. No bone marrow (apart from one) was T cell depleted. For first transplants, engraftment was observed in 23/27 patients (pts) (85%). Primary graft failure was observed in 4/27 patients (16%), two were retransplanted from an unrelated donor, one with success. Four patients have died. The primary cause of death was infection in three cases (TRM : 11%) and disease progression in one case, after primary graft failure. Of the 23 living patients, two have disease progression after graft failure and 21 (78%) have functional grafts with a favourable long-term outcome after a median follow-up of 4.7 years, having either full or mixed chimaerism. Among surviving patients with functional grafts, 13 (62%) were transplanted from unrelated donors of whom 10 (77 %) had HLA disparities. There was a remarkably low incidence of GvHD. In our experience, haematopoietic stem cell transplantation using an HLA-matched familial donor or an HLA-matched or -mismatched unrelated donor without T cell depletion or irradiation can achieve a favourable outcome in Hurler's syndrome, with improved cognitive function, but with a limited effect on the corneas and skeleton.

Simple and rapid high-performance liquid chromatographic method for nelfinavir, M8 nelfinavir metabolite, ritonavir and saquinavir assay in plasma

A simple reversed-phase liquid chromatographic method has been developed to determine protease inhibitors concentrations in plasma. Plasma samples (250 micro l) containing protease inhibitors were prepared by a simple deproteinization (recovery: 92, 91, 91 and 90.5% for ritonavir, saquinavir, nelfinavir and M8 nelfinavir metabolite, respectively). Chromatography was accomplished using a Hypersil octadecylsilyl column (100 x 4.6 mm I.D.) and a mobile phase composed of acetonitrile, tetrahydrofuran and dihydrogenophosphate buffer (pH 4) (32:10:58, v/v). Ultraviolet detection at 210 nm was used. The limit of detection was 200 ng/ml for ritonavir, saquinavir, nelfinavir and M8 nelfinavir metabolite. Calibration curves were linear up to 20000 ng/ml, with correlation coefficients better than 0.997 for all compounds. Intra- and inter-day coefficients of variation of the assay were <or=6% for all compounds. This method was used to analyse protease inhibitors plasma concentrations after oral administration within the framework of therapeutic drug monitoring and pharmacokinetic studies in AIDS patients.

Cyclosporin A inhibits dendritic cell maturation promoted by TNF-alpha or LPS but not by double-stranded RNA or CD40L

Here, we investigated the influence of cyclosporin A (CsA) on dendritic cell (DC) generation. With this aim, human DC were propagated from monocytes in serum-free medium with granulocyte macrophage-colony stimulating factor and interleukin-4. DC were then exposed to tumor necrosis factor alpha (TNF-alpha) for maturation. Our results show that CsA does not impair commitment of monocytes into DC, as assessed by loss of CD14 and increase of CD40 and CD1a. However, TNF-alpha-induced DC maturation was affected, as CsA-treated DC expressed lower levels of human leukocyte antigen and costimulatory molecules but sustained levels of CD1a, and less DC expressed DC-lysosomal-associated-membrane-protein (LAMP) and CD83. Accordingly, CsA inhibited the allostimulatory and accessory cell functions of DC. Surprisingly, when other maturation stimuli were used, we observed that CsA significantly inhibited maturation induced by lipopolysaccharides but not by polyribocytidylic acid or CD40 ligand, as assessed by DC phenotype and functions. Therefore, our results indicate that CsA may differentially affect DC maturation.

[Anaphylactic shock associated with ceftriaxone therapy in a newborn]

CASE REPORT

During an hospitalization, a ten-day-old newborn infant was treated with ceftriaxone (Rocephine i.v., 390 mg/day) for an infection secondary to the presence of an umbilical catheter. A few minutes after the end of the fifth injection, the infant presented with cyanosis, initially localized at the perfusion site, then generalized, a tachycardia followed by acute circulatory failure with arterial hypotension and finally a multiple organe failure with coagulation, kidney and liver dysfunction. The infant received classical resuscitation treatment and recovered without short term sequelae. The time of onset was in favour of drug-induced accident. A postnatal sensitization during previous injections might have occurred, although the latency of immediate hypersensitivity reactions after a first sensitizing contact is usually longer. A sensitization in utero or via breast feeding was ruled out due to the absence of maternal exposure to ceftriaxone. The absence of urticaria and bronchospasm, and the initial localization of cyanosis were not in favour of a classic allergic disease. An other cause, toxic or infectious cannot be ruled out.

[A new tool for evaluation of medication errors applied to pediatric hematology]

This study was conducted in a haematological paediatric department and was aimed at evaluating drug medication errors. Their frequency was studied, but also and mainly their degree of severity and preventability. Only adverse drug events that were identified as possibly due to pharmacological properties of drugs or medication errors were collected. An original method was used, based on a multidimensional mathematical tool, called Factorial Analysis of Multiple Correspondences (FAMC), in order to assess the grade of severity and preventability for each adverse drug event. A total of 155 adverse drug events were detected for 34 out of 52 patients hospitalized during the study period. The prevalence rate was 65 per cent and among these adverse drug events, 16 per cent were serious and 53 per cent were avoidable. Apart from the fact that the FAMC helped to determine the grade of preventability, FAMC allowed one to demonstrate that allergy and medication errors were the most avoidable adverse drug events. In this way the method used was validated. This study permitted the assessment of drug medication errors in this department and helped to choose the priorities for the management of preventive actions.

Improved clinical outcome of paediatric bone marrow recipients using a test dose and Bayesian pharmacokinetic individualization of busulfan dosage regimens

In order to control busulfan pharmacokinetic variability and toxicity, a specific monitoring protocol was instituted in our bone marrow transplant BMT paediatric patients including a test dose, daily Bayesian forecasting of busulfan plasma levels, and Bayesian individualization of busulfan dosage regimens. Twenty-nine children received BMT after a busulfan-based conditioning regimen. Individual pharmacokinetic parameters were obtained following a 0.5 mg*kg test dose and were used for daily individualization of dosage regimens during the subsequent 4-day course of treatment. Doses were adjusted to reach a target mean AUC per 6 h between 4 and 6 microg.h.ml(+1). Plasma busulfan assays were performed by liquid chromatography. Pharmacokinetic analysis used the USC*PACK software. The performance of the test dose to predict AUC during the busulfan regimen was evaluated. Incidence of toxicity, chimerism and relapse, overall Kaplan-Meier survival, and VOD-free survival were compared after matching our patients (group A) with patients conditioned by using standard doses of busulfan (group B). Busulfan doses were decreased in 69% of patients compared to conventional doses. Expected AUC was significantly correlated with observed AUC and predictability of the test dose was 101.9 +/- 17.9%. Incidence of VOD in group A was 3.4% vs 24.1% in group B, while the incidence of stomatitis was similar. Engraftment was successful in all patients in group A. The rate of full engraftment at 3 months post-BMT was higher in group A (P = 0.012). Long-term overall survival did not differ between the two groups, in contrast to the 90-day survival. VOD-free survival was higher in group A (P = 0.026). Pharmacokinetic monitoring and individualization of busulfan dosage regimen are useful in improving clinical outcome and reducing early mortality in paediatric bone marrow transplant recipients.

Population pharmacokinetics of amikacin at birth and interindividual variability in renal maturation

OBJECTIVE

Pharmacokinetic (PK) interindividual variability in amikacin has been shown to be wide in neonates. This study evaluated the evolution of this variability with gestational age (GA) at birth in relation to renal maturation.

METHODS

Population PK values of amikacin were studied in 131 newborns (postnatal age 1 day, GA 24-41 weeks) divided into 16 groups, defined by GA, from 24 to 41 weeks (with a mean of 8.2 infants per group). PK variables were Kel/Vol, Ks/Vs, Cl/Vol. Cls/ where: Kel = Kslope x GA + Kintercept, Cl = Clslope x GA + Clintercept, and Vol = Vs x body weight. Ki and Cli were held as constants. The nonparametric distribution of the probability density function (PDF) was obtained, as were mean, median, and SD values of each PK variable for each GA group.

RESULTS

Amikacin elimination increased linearly with GA, showing that GA is a good covariate of renal elimination. Amikacin volume of distribution increased with body weight up to a GA of about 38 weeks and then decreased for highest GA values. However, the PDF for the individual GA groups showed a multimodal PK distribution. Kel, Vol, Vs, Cl, and Cl, standard deviations increased linearly with GA, showing differential renal maturation. The higher the GA, the more interindividual PK variability increased.

CONCLUSIONS

These results show that amikacin elimination and the volume of distribution are dependent upon GA, and that differential renal maturation in neonates is responsible for the wider PK interindividual variability with high GA. Dosage regimens of amikacin and other aminoglycosides should be revised in newborns with high GA. Bayesian adaptive control of therapeutics might be particularly indicated to obtain efficacy for each neonate as early as the first dose.

Once-a-day individualized amikacin dosing for suspected infection at birth based on population pharmacokinetic models

Amikacin is widely used in the treatment of suspected or confirmed neonatal infections. However, dosage regimens are not well defined in this group of patients because of a wide inter-individual pharmacokinetic variability. An individualized goal-oriented amikacin dosage design was applied using population pharmacokinetic data. A dosing chart was developed for neonates during the first 2 days of life, by using population pharmacokinetic parameter values and USCPACK software. This dosing chart based on gestational age (GA) and body weight gives a once-a-day amikacin dosage regimen involving an injection every 24 h. Validation was performed in 57 neonates less than 2 days old, divided into three GA groups and prospectively treated using the dosing chart. Target peak serum levels of amikacin were obtained in 62-80% of patients after the first dose and in 80-100% after the second dose, and trough concentrations were obtained in 100%. This study has confirmed the need for individualization of amikacin dosage regimens in neonates.

Comparison of nonlinear mixed-effect and non-parametric expectation maximisation modelling for Bayesian estimation of carboplatin clearance in children

OBJECTIVE

The pharmacodynamic-pharmacokinetic relationships for carboplatin involve the area under the curve of ultrafiltrable plasma concentrations versus time (AUC). The objective of the study was to compare two specific population pharmacokinetic methodologies, nonlinear mixed-effect model (NONMEM) and non-parametric expectation maximisation (NPEM), when they are applied to sparse carboplatin pharmacokinetic data in order to obtain an individual value for carboplatin clearance by Bayesian estimation.

METHODS

The data from 117 patients (from 1 month to 18 years old) were available. For 20 patients randomly selected, the carboplatin clearance obtained by Bayesian estimation using two plasma ultrafiltrable concentrations was compared with that obtained by individual analysis using all concentrations.

RESULTS

Both methodologies were unbiased with mean relative percentage errors (95%CI) of -1.9% ( 7.8; +4.1%) and +6.4% (-2.1; +14.9%) for NONMEM and NPEM, respectively. A comparison of precision between the two methods showed that they were not significantly different (12.5% for NONMEM, and 18.9% for NPEM), but the percentage error ranged between -21% and + 19% for NONMEM, and -35% and + 42% for NPEM. A NONMEM analysis was also performed with all the data available (117 children) in order to update an equation describing the relationship between carboplatin clearance and the patients' covariates. The best relationship corresponded to the equation: clearance (ml/min) = [4.47 x body weight x (1 -0.22 x Np)/(l + 0.0156 x Scr)] +6.4, with body weight in kilograms and where Scr is serum creatinine in micromoles per litre and Np= 1 or 0 for unilateral nephrectomy or not, respectively.

CONCLUSION

These methodologies may be useful for dose individualisation and drug monitoring of carboplatin in paediatric patients. Since the mode of administration of carboplatin in paediatric practice in some protocols is daily 1-h i.v. infusion repeated up to five times, dose individualisation may be performed from the clearance observed after the first administration, given an overall target AUC.

New sensitive assay of vancomycin in human plasma using high-performance liquid chromatography and electrochemical detection

A method using reversed-phase high-performance liquid chromatography with electrochemical detection for the analysis of vancomycin in human plasma was developed. Chromatographic conditions included an octadecyl column, a mobile phase of acetonitrile-sodium phosphate buffer (pH 7) (12:88), a total run time of 12 min, and coulometric electrochemical detection at +700 mV. Linear detector response was found in the range 5-100 microg ml(-1) after a 1:80 dilution or from 0.5 to 50 microg ml(-1) after a 1:20 dilution of the samples. In both cases the correlation coefficient (r) of the calibration curve standard was better than 0.995. Vancomycin determination was based on a denaturation of plasma proteins with methanol, then a dilution with mobile phase was performed. Recovery of vancomycin from plasma was 103.1+/-3.9%, and no interference from commonly used drugs or endogenous compounds was observed. A significant correlation was shown with the EMIT assay (r=0.92, P<0.001) using clinical samples from children. This HPLC technique is simple, sensitive, rapid, precise, selective and requires only 100 microl of plasma for completion.

Rapid and sensitive high-performance liquid chromatographic method for busulfan assay in plasma

A reversed-phase liquid chromatographic method with ultraviolet detection has been developed to determine busulfan concentrations in plasma of children undergoing bone marrow transplantation. Plasma samples (200 microl) containing busulfan and 1,6-bis(methanesulfonyloxy)hexane as an internal standard were prepared by a simple derivatization method with diethyldithiocarbamate followed by extraction with ethyl acetate and solid-phase purification on C8 columns conditioned with methanol and water and eluted with acetonitrile (recovery 99%). Chromatography was accomplished using a Hypersil octadecylsilyl column (10 cm x 4.6 mm I.D.) and a mobile phase of acetonitrile, tetrahydrofuran and distilled water (65:5:30, v/v). The limit of detection was 25 ng/ml (signal-to-noise ratio of 5). Calibration curves were linear up to 25,000 ng/ml. Intra-day and inter-day coefficients of variation of the assay were < or =5%. This method was used to analyse busulfan plasma concentrations after oral administration within the framework of therapeutic drug monitoring and pharmacokinetic studies in children.

Diurnal changes in the pharmacokinetic behavior of amikacin

This retrospective study evaluated possible differences in the pharmacokinetic behavior of amikacin between the morning (AM) and evening (PM). Of 634 patients receiving amikacin therapy, 17 received a dose every 12 hours (an i.v. infusion at 8:00 AM and 8:00 PM) with amikacin serum levels obtained after both the AM and PM infusions. Pharmacokinetic parameter values were estimated by the nonparametric EM algorithm (USC*PACK clinical software) for a one-compartment model. All patient data were analyzed in three ways. The parameter values were estimated by fitting the model first only to the serum levels drawn following the AM dose; second, only to the data following the PM dose; and third, to all serum levels (AM + PM). Parameter values found were (mean, median, SD respectively): AM: Kel = 0.181114 h(-1), 0.224460 h(-1), 0.058820 h(-1); Vol = 23.657507 L; 23.376231 L; 1.353253 L; Cl = 4.326720 L x h(-1), 5.303726 L x h(-1), 1.447731 L x h(-1); PM: Kel = 0.110151 h(-1); 0.121295 h(-1); 0.016860 h(-1); Vol = 28.948043 L; 24.091703 L; 9.266628 L; Cl = 3.081761 L x h(-1), 2.810615 L x h(-1); 0.705874 L x h(-1); AM + PM: Kel = 0.165321 h(-1); 0.131796 h(-1); 0.075425 h(-1); Vol = 25.479043 L; 26.187970 L; 5.367054 L. These findings are in agreement with the known diurnal rhythm of glomerular filtration rate. Because pharmacokinetic parameter values are most often estimated using AM data, this may lead to an overevaluation of these values compared with PM or to values for the entire day. The resulting drug regimens may therefore be overestimated regarding the elimination rate constant and underestimated regarding the volume of distribution.

[Can we use a Bayesian method to build a pharmacokinetic population in two steps?]

The aim of this study is to evaluate the use of a pharmacokinetic population model built by the two-stage method and individual parameters determined by a Bayesian estimation instead of nonlinear regression. We performed a retrospective analysis on 32 patient files (mean age: 82 years). First, we analysed prediction of amikacin serum levels for the Bayesian method (MAP) and nonlinear regression (MLS). Second, we compared pharmacokinetic parameter values for each patient with MAP and MLS methods for a one- or two-compartment model. For the one-compartment model, no difference in prediction performance was found (correlation coefficient: rMLS = 0.911, rMAP = 0.903, p > 0.05; precision: pMLS = 134.3, pMAP = 147, p > 0.05). A significant difference was observed only for systematic error (eMLS = -4.47, eMAP = -3.34, p < 0.05). For a two-compartment model, the Bayesian method was better for long-term prediction: 4-8 days (rMLS = 0.877, rMAP = 0.886, p > 0.05; eMLS = 5.26, eMAP = 0.04, p < 0.01; pMLS = 441.7, pMAP = 149, p < 0.05). The comparison of MAP and MLS estimated pharmacokinetic parameter values for a one-compartment model showed that the Bayesian method used to built a pharmacokinetic population in two stages does not influence pharmacokinetic parameter estimation (p > 0.05 for Vd, Kslope, Kel and t1/2). We conclude that we can use a Bayesian method to build a pharmacokinetic population in two steps in order to perform adaptative control of a drug-dosage regimen.

Assessment of acyclovir intraindividual pharmacokinetic variability during continuous hemofiltration, continuous hemodiafiltration, and continuous hemodialysis

The use of intravenous acyclovir can be particularly complicated in pediatric patients with evolving renal impairment, because of intraindividual pharmacokinetic variability linked to the patient's clinical condition. The objective of this study was to use therapeutic drug monitoring data to assess acyclovir intraindividual pharmacokinetic variability during several types of renal replacement therapy. Bayesian adaptive control of acyclovir dosage regimen was performed in a pediatric patient with bone marrow transplant who developed severe renal impairment. Acyclovir pharmacokinetic parameter values corresponding to the different techniques and periods of renal replacement therapy were estimated using USCPACK PC Clinical Programs and therapeutic drug monitoring data. Results showed a wide intraindividual pharmacokinetic variability during CAVH, CAVHDF, and CVVHD, reflecting not only the performance of each dialysis technique but also the difficulty in making use of each one. The acyclovir elimination rate constant was higher during CVVHD compared to CAVH or CAVHDF. Bayesian method appears to be valuable in assessing intraindividual pharmacokinetic variability, as it allows the clinician to deal with sparse routine patient data.

[Renal differential aging processes and ofloxacin pharmacokinetics in the elderly]

Ageing generates an important inter- and intra-individual variability in drug pharmacokinetics. The increasing frequency of ofloxacin adverse effects in elderly patients results from increased ofloxacin plasma levels about two or threefold over normal concentrations. A retrospective study of ofloxacin population pharmacokinetics in 17 elderly patients (83.6 +/- 6.8 years) shows the existence of three subgroups according to ofloxacin total clearance [group 1: 1.44 l/h, group 2: 4.37 l/h and group 3: 15.08 l/h] reflecting the important inter-individual variability. No correlation between this clearance and creatinine clearance, nor between this clearance and age, could be established, showing the limits of traditional drug monitoring in the elderly. Ofloxacin pharmacokinetic parameters estimated by the non-parametric software NPEM2 in the 17 elderly patients (absorption rate constant, Ka: 2.668 +/- 1.256 h-1; apparent volume of distribution related to weight, Vs: 1.272 +/- 0.778 l/kg; elimination rate constant, Ks: 0.265 +/- 0.247 10(-3) min/ml/h) are clearly different from those estimated in young adults. These results show the limits of classic drug monitoring in the elderly, and also the interest of adaptive control of a drug regimen.

Comparisons between antimicrobial pharmacodynamic indices and bacterial killing as described by using the Zhi model

Various suggestions have been made for empirical pharmacodynamic indices of antibiotic effectiveness, such as areas under the drug concentration-time curve in serum (AUC), AUC > MIC, AUC/MIC, area under the inhibitory curve (AUIC), AUC above MIC, and time above MIC (T > MIC). In addition, bacterial growth and killing models, such as the Zhi model, have been developed. The goal of the present study was to compare the empirical behavior of the Zhi model of bacterial growth and killing with the other empirical pharmacodynamic indices described above by using simulated clinical data analyzed with the USC*PACK PC clinical programs for adaptive control of drug therapy, with one model describing a concentration-dependent antibiotic (tobramycin) and another describing a concentration-independent antibiotic (ticarcillin). The computed relative number of CFU was plotted against each pharmacodynamic index, with each axis parameterized over time. We assumed that a good pharmacodynamic index should present a clear and continuous relationship between the time course of its values and the time course of the bacterial killing as seen with the Zhi model. Preliminary work showed that some pharmacodynamic indices were very similar. A good sensitivity to the change in the values of the MIC was shown for AUC/MIC and also for T > MIC. In addition, the time courses of some other pharmacodynamic indices were very similar. Since AUC/MIC is easily calculated and shows more sensitivity, it appeared to be the best of the indices mentioned above for the concentration-dependent drug, because it incorporated and used the MIC the best. T > MIC appeared to be the best index for a concentration-independent drug. We also propose a new composite index, weighted AUC (WAUC), which appears to be useful for both concentration-dependent and concentration-independent drugs.

[Non-parametric estimation of pharmacokinetic parameters of amikacin in patients with non-insulin-dependent diabetes mellitus]

To establish a reference for MAP Bayesian adaptive control of amikacin therapy in non-insulin-dependent diabetic patients, 30 patients (age: 63.5 +/- 10.1 years) were studied. Weight (84.2 +/- 15.4 kg) and body mass index (28.0 +/- 4.3 kg/m2 for males and 30.5 +/- 6.4 kg/m2 for females) were stable during treatment. Creatinine clearance (CCr) was 70.3 +/- 27.2 ml/min/1.73 m2 before treatment and 69.6 +/- 24.3 ml/min/1.73 m2 (NS) at the end of treatment (2 to 15 days). 129 serum concentrations were drawn (4.8 +/- 2.6 levels per patient). The one-compartment model was parameterized as having Vs (l.kg-1) and Kslope (min/ml.h) for each unit of CCr (Kel = Kintercept + Kslope x CCr). The non-renal Kintercept was fixed at 0.00693 h-1. The NPEM computes the joint probability densities. The mean, median, and SD were respectively: Vs = 0.3574, 0.3654, 0.0825 l.kg-1; Kslope = 0.0026, 0.0027, 0.0007 min/ml.h. For the a priori first doses determination, precision is higher with the new population. No difference in adaptive control was observed. In additive, the full joint density probability should be used to develop stochastic multiple model linear quadratic (MMLQ) adaptive control strategies.

High-performance liquid chromatographic determination of ganciclovir nucleotides in human myocardial tissue

A method for the analysis of ganciclovir nucleotides in myocardial tissues was developed. The antiviral effect of ganciclovir is attributed to intracellular ganciclovir nucleotides. The procedure is based on perchloric acid deproteinization and enzymatic hydrolysis of the ganciclovir nucleotides to ganciclovir. Then, the parent drug was analyzed on a Hypersil ODS column using potassium dihydrogenphosphate buffer as mobile phase. The mean analytical recovery of ganciclovir from myocardial tissue was 101 +/- 2% and the detection limit was 2 pmol. The sample treatment procedure described is simple and presents a suitable analytical tool for the investigation of the ganciclovir nucleotides pool in tissues.

Clinical use of ganciclovir during renal failure and continuous hemodialysis

OBJECTIVE

Data is scarce concerning ganciclovir, used in CMV-related diseases in transplant patient with renal failure, especially when dialysis is necessary.

DESIGN

Prospective trial.

SETTING

Intensive care unit in a university hospital, and pharmacy laboratory.

PATIENTS

pharmacokinetics were obtained in 3 patients undergoing continuous veno-venous hemodialysis (CVVHD) (PAN 69).

INTERVENTIONS

HPLC measurements of plasmatic and ultrafiltrated ganciclovir were determined at 17 times intervals after a 5 mg/kg every 48 h dosage.

RESULTS

Peak and trough concentrations were respectively 16.1 +/- 2.4 and 5.5 +/- 0.5 mg/l, sieving coefficient 0.75-0.95, and volume of distribution at steady state 0.64 +/- 0.09 l/kg, half life (beta phase) 18.6 +/- 1.8 h. No direct toxicity, or CMV-related death occurred.

CONCLUSION

Plasma concentrations were higher than the ID 90. A dosage of 5 mg/kg/48 h of ganciclovir could be used during CVVHD, and ideally adjusted to monitoring of plasma drug levels.

Pharmacokinetics of ganciclovir in heart transplant patients undergoing continuous venovenous hemodialysis

The pharmacokinetics of ganciclovir in patients with severe renal dysfunction is poorly defined. In this paper, we report the pharmacokinetics of ganciclovir in three anuric heart transplant patients under continuous venovenous hemodialysis (CVVHD). Ganciclovir was administered at a dose of 5 mg/kg every 48 h for at least 9 days. Samples from the arterial and venous blood lines and from ultrafiltrate were collected to calculate pharmacokinetic parameters, clearance of ultrafiltration, and sieving coefficient. Ganciclovir concentrations were determined by high-performance liquid chromatography. Pharmacokinetic parameters (mean +/- SD) were the following: t1/2 beta 18.9 +/- 2.2 h, Cl 0.42 +/- 0.08 ml/min/kg, Vdss 0.68 +/- 0.10 L/kg. At the steady state the clearance of ultrafiltration was 12.9 +/- 1.9 ml/min (or 130 L/week) and the sieving coefficient was 0.84 +/- 0.08 with an average fraction of 89.7 +/- 10.6% of the administered dose removed by CVVHD. These results show that CVVHD is highly effective in removing ganciclovir from plasma. Furthermore, CVVHD appears more effective than intermittent hemodialysis. These data should be taken into account to optimize dosage adjustment of ganciclovir in patients under CVVHD, and until guidelines are available, careful monitoring of drug concentrations is recommended.

Modified high-performance liquid chromatographic method for the determination of ganciclovir in plasma from patients with severe renal impairment

Using the rapid and sensitive high-performance liquid chromatographic (HPLC) method previously described for the analysis of ganciclovir in plasma, we have observed an interfering peak which co-elutes with the peak of ganciclovir in plasma samples from heart-transplant patients with severe renal insufficiency. A slight modification of this method allows the separation of the two peaks. The modified HPLC method, presented in this paper, is suitable for the accurate determination of ganciclovir in plasma from patients with severe renal impairment.