A simple extemporaneous oral suspension of aprepitant yields sufficient pharmacokinetic exposure in children.

INTRODUCTION: Aprepitant is used for the treatment of chemotherapy induced nausea and vomiting. A liquid formulation is needed for treatment of young children. However, the commercial (powder for) suspension was not available worldwide for a prolonged period of time and, therefore, a 10 mg/mL aprepitant oral suspension was extemporarily prepared to prevent suboptimal antiemetic treatment. The current pharmacokinetic study was developed to investigate whether this extemporaneous oral suspension offers an appropriate treatment option. METHODS: From 49 pediatric patients (0.7-17.9 years) 235 plasma concentrations were collected. Patients were either treated with our extemporaneous oral suspension (n = 26; 53%), commercially available capsules (n = 18; 37%), or the intravenous prodrug formulation of aprepitant (fosaprepitant, n = 5; 10%). Pharmacokinetic analyses were performed using nonlinear mixed effects modelling. RESULTS: A one-compartment model adequately described the pharmacokinetics of aprepitant in children. The bioavailability of the extemporaneous oral suspension was not significantly different to that of the capsules (P = 0.26). The observed bioavailability throughout the total population was 83% (95% CI 69%-97%). The absorption of the extemporaneous oral suspension was 39.4% (95%CI 19.5-57.4%) faster than that of capsules (mean absorption time of 1.78 h (95%CI 1.32-2.35), but was comparable to that of the commercial oral suspension. The median area under the curve after (fos)aprepitant was 22.2 mg/L*h (range 8.9-50.3 mg/L*h) on day 1. CONCLUSION: Our extemporaneous oral suspension is an adequate alternative for the commercially (un)available oral suspension in young children. An adequate exposure to aprepitant in children was yielded and the bioavailability of the extemporaneous suspension was comparable to capsules.

Practical Recommendations for the Manipulation of Kinase Inhibitor Formulations to Age-Appropriate Dosage Forms.

Over 75 kinase inhibitors (KIs) have been approved for the treatment of various cancers. KIs are orally administrated but mostly lack pediatric age-appropriate dosage forms or instructions for dose manipulation. This is highly problematic for clinical practice in pediatric oncology, as flexible oral formulations are essential to individually set dosages and to adjust it to a child's swallowability. Most KIs are poorly soluble, categorized in Biopharmaceutics Classification System (BCS) class II or IV, and improperly manipulating the KI formulation can alter pharmacokinetics and jeopardize KI drug safety and efficacy. Therefore, the goals of this review were to provide practical recommendations for manipulating the formulation of the 15 most frequently used KIs in pediatric oncology (i.e., bosutinib, cabozantinib, cobimetinib, crizotinib, dabrafenib, dasatinib, entrectinib, imatinib, larotrectinib, nilotinib, ponatinib, ruxolitinib, selumetinib, sunitinib and trametinib) based on available literature studies and fundamental drug characteristics and to establish a decision tool that supports decisions regarding formulation manipulation of solid oral dosages of KIs that have been or will be licensed (for adult and/or pediatric cancers) but are not included in this review.

Modelling Tools to Characterize Acetaminophen Pharmacokinetics in the Pregnant Population.

This review describes acetaminophen pharmacokinetics (PK) throughout pregnancy, as analyzed by three methods (non-compartmental analyses (NCA), population PK, and physiologically based PK (PBPK) modelling). Eighteen studies using NCA were reported in the scientific literature. These studies reported an increase in the volume of distribution (3.5-60.7%) and an increase in the clearance (36.8-84.4%) of acetaminophen in pregnant women compared to non-pregnant women. Only two studies using population PK modelling as a technique were available in the literature. The largest difference in acetaminophen clearance (203%) was observed in women at delivery compared to non-pregnant women. One study using the PBPK technique was found in the literature. This study focused on the formation of metabolites, and the toxic metabolite N-acetyl-p-benzoquinone imine was the highest in the first trimester, followed by the second and third trimester, compared with non-pregnant women. In conclusion, this review gave an overview on acetaminophen PK changes in pregnancy. Also, knowledge gaps, such as fetal and placenta PK parameters, have been identified, which should be explored further before dosing adjustments can be suggested on an evidence-based basis.

Supplementation of vitamins, trace elements and electrolytes in the PEPaNIC Randomised Controlled Trial: Composition and preparation of the prescription.

BACKGROUND AND AIMS: Following the results of the paediatric early versus late parenteral nutrition in critical illness (PEPaNIC) multicentre, randomised, controlled trial, the new ESPGHAN/ESPEN/ESPR/CSPEN and ESPNIC guidelines recommend to consider withholding parenteral macronutrients for 1 week, while providing micronutrients, in critically ill children if enteral nutrition is insufficient. Critically ill children are suspected to be vulnerable to micronutrient deficiencies due to inadequate enteral nutrition, increased body's demands and excessive losses. Hitherto, micronutrient requirements in PICU are estimated based on recommended daily intakes for healthy children and expert opinion. We aimed to provide an overview of the current practice of micronutrient administration and practical considerations in the three participating centres of the PEPaNIC study, and compare these therapies with the recommendations in the new ESPGHAN/ESPEN/ESPR/CSPEN guidelines. METHODS: We describe the current composition and preparation of the prescribed parenteral micronutrients (consisting of vitamins, trace elements and electrolytes) in the three centres (Leuven, Rotterdam and Edmonton) that participated in the PEPaNIC RCT, and compare this per micronutrient with the ESPGHAN/ESPEN/ESPR/CSPEN guidelines recommendations. RESULTS: The three centres use a different micronutrient supplementation protocol during the first week of critical illness in children, with substantial differences regarding the amounts administered. Leuven administers commercial vitamins, trace elements and electrolytes in separate infusions both in 4 h. Rotterdam provides commercial vitamins and trace elements simultaneously via 8-h infusion and electrolytes continuously over 24 h. Lastly, Edmonton administers commercial vitamins and institutionally prepared trace elements solutions in 1 h and electrolytes on demand. Comparison with the ESPGHAN/ESPEN/ESPR/CSPEN guidelines yields in differences between the recommendations and the administered amounts, which are most substantial for vitamins. CONCLUSION: The practice of intravenous micronutrient administration differs substantially between the three PEPaNIC centres and in comparison with the current guideline recommendations. This deviation is at least partially explained by the inability to provide all recommended amounts with the currently available commercial products and by the lack of strong evidence supporting these recommendations.

Pharmacogenomics as a Tool to Limit Acute and Long-Term Adverse Effects of Chemotherapeutics: An Update in Pediatric Oncology.

In the past decades, new cancer treatments have been introduced in pediatric oncology leading to improvement in clinical outcomes and survival rates. However, due to inter-individual differences, some children experience severe chemotherapy-induced toxicities or a poor clinical outcome. An explanation for the diversity in response to chemotherapy is genetic variation, leading to differences in expression and activity of metabolizing and transport enzymes as well as drug targets. Pharmacogenetic testing has emerged as a promising tool to predict and limit acute and long-term adverse effects in patients. However, in pediatric oncology, limited number of patients and a considerable diversity in study results complicate the interpretation of test results and its clinical relevance. With this review, we provide an overview of new developments over the past four years regarding relevant polymorphisms related to toxicity in pediatric oncology. The following chemotherapeutics and associated toxicities are discussed: alkylating agents, anthracyclines, asparaginase, methotrexate, platinum compounds, steroids, thiopurines, topoisomerase inhibitors, and vinca alkaloids. Our review identifies several questions regarding the role of genetic variants in chemotherapy-induced toxicities. Ambiguities in the literature stem from small population sizes, differences in (statistical) interpretation and variations in sequencing technologies as well as different clinical outcome definitions. Standardization of clinical outcome data and toxicity definitions within electronic health records combined with the increased availability of genomic sequence techniques in clinical practice will help to validate these models in upcoming years.

Use of amlodipine oral solution for the treatment of hypertension in children.

Background Amlodipine is a widely used antihypertensive agent for the treatment of paediatric hypertension, but the commercially available tablets are not suitable to treat young patients, who need lower, flexible dosages and a liquid formulation. Objective To determine the pharmacokinetic properties of amlodipine and the acceptability of a standardised, extemporaneous oral solution. Method A newly developed liquid formulation of amlodipine was administered to hypertensive children between the age of 6 months and 11 years. Using a limited sampling strategy, population PK analysis was performed using nonlinear mixed effects modelling. Results Nine children, with a median age of 2.9 years (IQR 1.8-8.4), receiving stable amlodipine therapy in a median dose of 0.15 mg kg-1 day-1 (IQR 0.11-0.18), were switched to study medication. The population pharmacokinetic model was able to accurately predict the clearance of amlodipine in the study population. Based on the final model, clearance was reduced by 31.2% (RSE: 10%) in females. Patient reported outcomes on taste from a five-point hedonic scale were available for five patients, who scored the taste from positive to slightly negative. Conclusion The results from the PK study and the acceptability assessment show that the amlodipine oral solution presented in this study offers an appropriate treatment option for young children.

Pharmacokinetic Targets for Therapeutic Drug Monitoring of Small Molecule Kinase Inhibitors in Pediatric Oncology.

In recent years new targeted small molecule kinase inhibitors have become available for pediatric patients with cancer. Relationships between drug exposure and treatment response have been established for several of these drugs in adults. Following these exposure-response relationships, pharmacokinetic (PK) target minimum plasma rug concentration at the end of a dosing interval (Cmin ) values to guide therapeutic drug monitoring (TDM) in adults have been proposed. Despite the fact that variability in PK may be even larger in pediatric patients, TDM is only sparsely applied in pediatric oncology. Based on knowledge of the PK, mechanism of action, molecular driver, and pathophysiology of the disease, we bridge available data on the exposure-efficacy relationship from adults to children and propose target Cmin values to guide TDM for the pediatric population. Dose adjustments in individual pediatric patients can be based on these targets. Nevertheless, further research should be performed to validate these targets.

Potential prediction of formulation performance in paediatric patients using biopharmaceutical tools and simulation of clinically relevant administration scenarios of nifedipine and lorazepam.

AIMS: This study explores the impact of paediatric patient related factors and choice of formulation on the dissolution characteristics of nifedipine and lorazepam, 2 drug substances regularly applied in very young patients and in compounded formulations. METHODS: Dissolution experiments were designed to reflect clinical practice in a paediatric hospital, with respect to dosage forms, feeding regimens and methods of administration. Solubility studies addressed the influence of age and prandial state. Drug solubility and dissolution experiments were conducted in biorelevant media and adapted age-specific (neonate and infant) media. Dissolution studies were performed with the mini-paddle apparatus and the flow-through cell apparatus. RESULTS: Dissolution of nifedipine formulations was not affected by age-related changes of the fasted state simulated gastrointestinal fluids, and by disintegration of the formulation before administration. However, a significant difference in nifedipine's dissolution rate from commercial tablets and compounded capsules was observed. The dissolution of lorazepam tablets was affected by fasted- vs fed-state media, but it was deemed less likely to be clinically relevant. The significant effect of fed-state media on nifedipine's solubility was considered to have possible clinical relevance since very young patients are almost continuously in a fed state. CONCLUSION: The in vitro results obtained from these studies reveal the potential of biorelevant solubility and dissolution studies reflecting clinical practice to predict drug performance in paediatric patients.

Impact of dose adaptations following voriconazole therapeutic drug monitoring in pediatric patients.

Voriconazole is the mainstay of treatment for invasive aspergillosis in immunocompromised pediatric patients. Although Therapeutic Drug Monitoring (TDM) of voriconazole is recommended, it remains unknown if TDM-based dose adaptations result in target attainment. Patients <19 years from two pediatric hematologic-oncology wards were retrospectively identified based on unexplained high voriconazole trough concentrations (Cmin > 6 mg/l). Patient demographics, clinical characteristics, treatment, voriconazole dosing information, voriconazole Cmin before and after adjustment based on TDM were obtained. Twenty-one patients, median (range) age 7.0 (1.2-18.5) years, were identified in two centers. First Cmin (3.1 mg/l [0.1-13.5]) was obtained after 3 days (1-27) of treatment. The median of all Cmin (n = 485, median 11 per patient) was 2.16 mg/l (0.0 (undetectable)-28.0), with 24.1% of Cmin < 1 mg/l, 48.9% 1-4 mg/l, 9.3% 4-6 mg/l, and 17.7% > 6 mg/l. Intrapatient variability was large (94.1% for IV, 88.5% for PO). Dose increases at Cmin < 1 mg/l resulted in an increased Cmin in 76.4%, with 60% between 1 and 4 mg/l. Dose decreases at Cmin > 6 mg/l resulted in a decreased Cmin in 80%, with 51% between 1 and 4 mg/l. Overall, in 45% of the cases (33 out of 55 and 12 out of 45) therapeutic targets were attained after dose adjustment. Fifty-five percent of initial Cmin was outside the therapeutic target of 1-4 mg/l, with multiple dose adaptations required to achieve therapeutic concentrations. Only 60% and 51% of dose adaptations following sub- and supra-therapeutic Cmin, respectively, did result in target attainment. Intensive and continuous TDM of voriconazole is a prerequisite for ensuring adequate exposure in pediatric patients.

Manipulation of oral medication for children by parents and nurses occurs frequently and is often not supported by instructions.

AIM: Due to a lack of age-appropriate formulations, administration of drugs to children remains a challenge. This study aimed to identify the problems experienced in both the outpatient setting and the clinical setting. METHODS: Between June 2017 and January 2018, we performed a cross-sectional, prospective study at the Sophia Children's Hospital, The Netherlands. The study comprised of a structured interview on drug manipulations with parents visiting the outpatient clinic, and an observational study of drug manipulations by nurses at the wards. RESULTS: A total of 201 questionnaires were collected, accounting for 571 drugs and 169 manipulations (30%). Drug substances that were most often mentioned as manipulated were macrogol (n = 23), esomeprazole (n = 15), paracetamol (n = 8), methylphenidate (n = 7) and melatonin (n = 7). Of all manipulated medicines, 93/169 (55%) were manipulated according to the instructions or recommendations of the Summary of Product Characteristics (SmPC) or patient information leaflet. During the observational study, manipulation was performed by 21/35 of observed nurses (60%), of whom 11 deviated from the hospital protocol for manipulation or SmPC (52%). CONCLUSION: Manipulation was a widely used method to administer drugs to children. Validated information regarding manipulation of drugs for both parents and nursing staff is needed.

Oral lorazepam can be substituted for intravenous midazolam when weaning paediatric intensive care patients off sedation.

AIM: Intravenous sedatives used in the paediatric intensive care unit (PICU) need to be tapered after prolonged use to prevent iatrogenic withdrawal syndrome (IWS). We evaluated the occurrence of IWS and the levels of sedation before and after conversion from intravenous midazolam to oral lorazepam. METHODS: This was a retrospective, observational, single cohort study of children under the age of 18 admitted to the PICU of the Erasmus MC-Sophia Children's Hospital, Rotterdam, The Netherlands, between January 2013 and December 2014. The outcome parameters were the Sophia Observation withdrawal Symptoms (SOS) scale scores and COMFORT Behaviour scale scores before and after conversion. RESULTS: Of the 79 patients who were weaned, 32 and 39 had before and after SOS scores and 77 had COMFORT-B scores. IWS was reported in 15 of 79 patients (19.0%) during the 48 hours before the start of lorazepam and 17 of 79 patients (21.5%) during the 48 hours after treatment started. Oversedation was seen in 16 of 79 patients (20.3%) during the 24 hours before substitution and in 30 of 79 patients (38.0%) during the 24 hours after substitution. CONCLUSION: The weaning protocol was not able to prevent IWS in all patients, but converting from intravenous midazolam to oral lorazepam did not increase the incidence.

Personalized Medicine in Pediatrics: The Clinical Potential of Orodispersible Films.

Children frequently receive medicines that are designed for adults. The dose of commercially available products is adapted, mostly based on the child's bodyweight, thereby neglecting differences in pharmacokinetic and pharmacodynamics parameters. If commercial products are unsuitable for administration to children or are unavailable, extemporaneous pharmacy preparations are a good alternative. For this particular population, orodispersible films (ODFs) can be a highly attractive dosage form for the oral administration of drugs. ODFs are relatively easy to prepare in a hospital setting, create dose flexibility, and may suit an individual approach, especially for patients having difficulties in swallowing tablets or being fluid restricted. In this article, various aspects related to pharmacy preparations, clinical application, and preparation of ODFs for pediatric patients are highlighted and discussed.

Insufficient Sedation and Severe Side Effects after Fast Administration of Remifentanil during INSURE in Preterm Newborns.

BACKGROUND: Neonatal intubation is stressful and should be performed with premedication. In the case of an INSURE (intubation/surfactant/extubation) procedure a short duration of action of the premedication used is needed to facilitate fast extubation. Given its pharmacological profile, remifentanil seems a suitable candidate. OBJECTIVES: The aim here was to evaluate the effect and side effects of remifentanil as a premedication for preterm neonates undergoing INSURE. METHODS: A prospective, single-center study in a level III neonatal intensive care unit was conducted. The quality of sedation was assessed in preterm infants receiving remifentanil prior to intubation for the INSURE procedure. Intravenous remifentanil was administered quickly and followed by a saline flush in approximately 30 s. The quality of sedation was defined by a combination of adequate sedation score, good intubation conditions and absence of side effects. RESULTS: The study was terminated after the inclusion of 14 patients because of the high rate of side effects and the poor intubation conditions. Adequate sedation was achieved in only 2 patients (14%). Six patients (43%) needed additional propofol to obtain adequate sedation. Chest wall rigidity occurred in 6 patients (43%). CONCLUSIONS: The rapid administration of remifentanil provides insufficient sedation and is associated with a high risk of chest wall rigidity in preterm neonates.

Necrotising enterocolitis and mortality in preterm infants after introduction of probiotics: a quasi-experimental study.

Evidence on the clinical effectiveness of probiotics in the prevention of necrotising enterocolitis (NEC) in preterm infants is conflicting and cohort studies lacked adjustment for time trend and feeding type. This study investigated the association between the introduction of routine probiotics (Lactobacillus acidophilus and Bifidobacterium bifidum; Infloran(®)) on the primary outcome 'NEC or death'. Preterm infants (gestational age <32 weeks or birth weight <1500 gram) admitted before (Jan 2008-Sep 2012; n = 1288) and after (Oct 2012-Dec 2014; n = 673) introduction of probiotics were compared. Interrupted time series logistic regression models were adjusted for confounders, effect modification by feeding type, seasonality and underlying temporal trends. Unadjusted and adjusted analyses showed no difference in 'NEC or death' between the two periods. The overall incidence of NEC declined from 7.8% to 5.1% (OR 0.63, 95% CI 0.42-0.93, p = 0.02), which was not statistically significant in the adjusted models. Introduction of probiotics was associated with a reduced adjusted odds for 'NEC or sepsis or death' in exclusively breastmilk-fed infants (OR 0.43, 95% CI 0.21-0.93, p = 0.03) only. We conclude that introduction of probiotics was not associated with a reduction in 'NEC or death' and that type of feeding seems to modify the effects of probiotics.

Bioequivalence study of an extemporaneously prepared oral solution of amlodipine suitable for use in pediatric patients compared to commercial tablets.

OBJECTIVE: Amlodipine, a long-acting dihydropyridine calcium channel blocker, is frequently prescribed to pediatric patients. To date, no suitable pediatric formulation has been available. In this study, an amlodipine oral solution was developed and tested for bioequivalence to tablets in healthy adult volunteers. METHODS: This study was designed as an open-label, single-dose, twosequence, two-period, crossover trial to assess the bioequivalence of a newly developed amlodipine besylate oral solution 0.5 mg/mL compared to Norvasc® 5 mg tablets. 13 adult subjects (mean [standard deviation] age of 23.2 [3.6] years, weight 71.5 [7.7] kg) were included and blood samples were collected for 72 hours. Amlodipine plasma levels were determined using a validated UPLC-MS/MS assay. Non-compartmental pharmacokinetic parameters were compared between the formulations according to European Medicines Agency (EMA) bioequivalence guidelines. RESULTS: The 90% confidence intervals of the test/reference ratios of the geometric means for the primary pharmacokinetic parameters AUC(0-72) (88.24 - 104.37%) and C(max) (99.00 - 121.40%) were within the acceptance range of 80.00 - 125.00% for bioequivalence. Mean (SD) AUC(0-72) was 102.7 (26.8) (26.8) µg × h/L for the solution and 108.2 (30.6) µg × h/L for the tablet. Mean (SD) Cmax of the solution was 3.11(1.06) µg/L with a median (IQR) t(max) of 4.0 (2.6 - 7.5) hours. Mean (SD) C(max) of the tablet was 2.91 (0.84) µg/L with a median (IQR) tmax of 6.0 (4.0 - 14.0) hours. Intrasubject coefficients of variation were 10.2% (AUC(0-72)) and 12.4% (C(max)). CONCLUSIONS: The formulations are bioequivalent according to EMA guidelines. This warrants further study of our novel amlodipine oral solution in pediatric patients.

Ketanserin versus dihydralazine for the treatment of severe hypertension in early-onset preeclampsia: a double blind randomized controlled trial.

OBJECTIVE: Determine the definitive position of ketanserin and dihydralazine for treatment of severe hypertension in pregnancy. STUDY DESIGN: A single centre double blind randomized controlled trial was performed at the obstetrical tertiary high care unit of the University Medical Centre in Rotterdam, the Netherlands. Women with severe hypertension in pregnancy (diastolic blood pressure (DBP)≥110mmHg), and significant proteinuria (≥300mg/24h), and gestational age≤32 weeks were eligible for the study. All patients (n=30) received two infusions (double dummy technique): one contained the active ingredient (ketanserin or dihydralazine), the other was used for placebo. Nicardipine was used as rescue medication. The main outcome measures were persistent severe hypertension (DBP>100mmHg>120min) despite maximum dosage of study medication and prolongation of pregnancy. RESULTS: Dihydralazine was significantly more effective in lowering blood pressure than ketanserin. No significant difference in prolongation of pregnancy was seen between the two groups. After 30 inclusions, the study was stopped because of the high rate of persistent hypertension using ketanserin and the high rate of maternal side effects using dihydralazine and the apparent succesful use of the rescue drug nicardipine. CONCLUSIONS: Our results do not support the use of either dihydralazine or ketanserin for the treatment of severe hypertension in pregnancy. Future research is needed to compare nicardipine with other antihypertensive drugs currently in use for treatment of severe hypertension in pregnancy.

Development and Validation of an HPLC-UV Assay to Quantify Plasma Levels of Sulfametrol: A Preferential Antibiotic in Children.

BACKGROUND: Sulfonamides in combination with trimethoprim are frequently used antibiotics. They work synergistic. In infections with Pneumocystis jiroveci or Stenotrophomonas maltophilia, higher dosages are indicated than in other infections. Therapeutic drug monitoring (TDM) is warranted to assure the efficacy while limiting toxicity. Although trimethoprim in combination with sulfamethoxazole is the most common combination with established TDM target concentrations, the intravenous formulation is not suited for children because of its additives ethanol and propylene glycol to increase solubility. An alternative can be sulfametrol in combination with trimethoprim. When sulfametrol was introduced in the hospital, there was a need for a TDM method for sulfametrol. METHODS: A High Pressure Liquid Chromatography-Ultraviolet (HPLC-UV) detection method for sulfametrol determination in plasma was developed and validated according to the International Conference on Harmonization guidelines. Linearity, limit of detection, lower limit of quantification, recovery, process efficiency, selectivity, within-run precision, between-run precision, and sample stability were tested. RESULTS: All tested parameters met the required criteria. For linearity, r was 0.9948, lower limit of quantification was 10 mg/L, and limit of detection was 6 mg/L. Recovery was 100.4% and process efficiency 94.4%. Selectivity was met with no interfering peaks at the retention time of 4.2 minutes. Between-run precision and within-run precision were evaluated by replicating quality control levels, resulting in a within-run relative average standard deviation of 0.8% and a between-run relative standard deviation of 2.3%. Recovery of the samples after storing 8 days was 101.9% and recovery of already tested vials was 98.8% after 48 hours. CONCLUSIONS: In conclusion, an HPLC-UV method for sulfametrol determination in human plasma was developed and validated. The method is fast, accurate, reproducible, and has a short analysis time. It is now being used in routine TDM in our clinic.

Pediatric microdose study of [(14)C]paracetamol to study drug metabolism using accelerated mass spectrometry: proof of concept.

BACKGROUND: Pediatric drug development is hampered by practical, ethical, and scientific challenges. Microdosing is a promising new method to obtain pharmacokinetic data in children with minimal burden and minimal risk. The use of a labeled oral microdose offers the added benefit to study intestinal and hepatic drug disposition in children already receiving an intravenous therapeutic drug dose for clinical reasons. OBJECTIVE: The objective of this study was to present pilot data of an oral [(14)C]paracetamol [acetaminophen (AAP)] microdosing study as proof of concept to study developmental pharmacokinetics in children. METHODS: In an open-label microdose pharmacokinetic pilot study, infants (0-6 years of age) received a single oral [(14)C]AAP microdose (3.3 ng/kg, 60 Bq/kg) in addition to intravenous therapeutic doses of AAP (15 mg/kg intravenous every 6 h). Blood samples were taken from an indwelling catheter. AAP blood concentrations were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and [(14)C]AAP and metabolites ([(14)C]AAP-Glu and [(14)C]AAP-4Sul) were measured by accelerator mass spectrometry. RESULTS: Ten infants (aged 0.1-83.1 months) were included; one was excluded as he vomited shortly after administration. In nine patients, [(14)C]AAP and metabolites in blood samples were detectable at expected concentrations: median (range) maximum concentration (C max) [(14)C]AAP 1.68 (0.75-4.76) ng/L, [(14)C]AAP-Glu 0.88 (0.34-1.55) ng/L, and [(14)C]AAP-4Sul 0.81 (0.29-2.10) ng/L. Dose-normalized oral [(14)C]AAP C max approached median intravenous average concentrations (C av): 8.41 mg/L (3.75-23.78 mg/L) and 8.87 mg/L (3.45-12.9 mg/L), respectively. CONCLUSIONS: We demonstrate the feasibility of using a [(14)C]labeled microdose to study AAP pharmacokinetics, including metabolite disposition, in young children.