Ganesh Moorthy

Fluconazole Loading Dose Pharmacokinetics and Safety in Infants

Background: Invasive candidiasis is a leading cause of morbidity and mortality in critically ill infants. Prompt administration of fluconazole and achievement of the therapeutic target (area under the curve 0 to 24 hours >400 mg*h/L) improve outcomes in candidemic patients. A loading dose of fluconazole is advised for older patients but has not been evaluated in infants. We sought to determine the pharmacokinetics and safety of a fluconazole loading dose in infants at risk for invasive fungal infection. Methods: We enrolled 10 hospitalized infants <60 days old with suspected systemic fungal infection in this open-label study; 9 received a 25-mg/kg fluconazole loading dose followed by a maintenance dose of 12 mg/kg every 24 hours for 4 additional days. Plasma samples were obtained following the loading and steady-state doses (doses 3–5). We used a 1-compartment model to fit the data to estimate pharmacokinetic indices. Results: Data from 57 drug concentrations obtained from 8 infants (median postnatal age, 16 days [interquartile range, 13–32] and median gestational age, 37 weeks [35–38]) showed that the median fluconazole area under the curve 0 to 24 hours (mg*h/L) in this population was 479 (347–496). Of the 8 infants who received the loading dose, 5 (63%) achieved the therapeutic target on the first day of dosing, and all infants achieved a fluconazole 24-hour trough concentration >8 &mgr;g/mL. No adverse events were thought to be related to fluconazole therapy. Conclusions: A loading dose of fluconazole (25 mg/kg) was safe in this small cohort of young infants and achieved the therapeutic target more rapidly than traditional dosing.

Pharmacokinetics and safety of fluconazole in young infants supported with extracorporeal membrane oxygenation.

Background: Candida infections are a leading cause of infectious disease–related death in infants supported with extracorporeal membrane oxygenation (ECMO). The ECMO circuit can alter drug pharmacokinetics; thus, standard fluconazole dosing in children on ECMO may result in suboptimal drug exposure. This study determined the pharmacokinetics of fluconazole in infants on ECMO. Methods: Infants <120 days of age received either intravenous fluconazole prophylaxis (25 mg/kg once a week) or treatment (12 mg/kg daily) while on ECMO. Paired plasma samples were collected preoxygenator and postoxygenator around doses 1 and 2 to calculate pharmacokinetic indices and describe oxygenator extraction. A 1-compartment model was fit to the data using nonlinear regression. Surrogate pharmacodynamic targets for efficacy were evaluated. Results: Ten infants were enrolled. After dose 1 (n = 9), the median clearance was 17 mL/kg/h, the median volume of distribution was 1.5 L/kg and the median exposure in the first 24 hours (area under the curve from 0 to 24 hours) was 322 h × mg/L. After multiple doses (n = 7), the median clearance was 22 mL/kg/h, the median volume of distribution was 1.9 L/kg and the area under the curve from 0 to 24 hours was 352 h × mg/L. After dose 1, 78% of infants achieved the prophylaxis target, whereas only 11% achieved the therapeutic target. Oxygenator extraction of fluconazole was minimal (–2.0%, standard deviation 15.0), and extraction was not correlated with age of the ECMO circuit (&rgr;= –0.05). There were no adverse events related to fluconazole. Conclusions: Infants on ECMO had higher volume of distribution but similar clearance when compared with historical controls not on ECMO. In infants on ECMO, a fluconazole dose of 25 mg/kg weekly provides adequate exposure for prophylaxis against Candida infections. However, higher doses may be needed for treatment.

Skeletal muscle and plasma concentrations of cefazolin during cardiac surgery in infants

OBJECTIVE To describe the pharmacokinetics and tissue disposition of prophylactic cefazolin into skeletal muscle in a pediatric population undergoing cardiac surgery. METHODS The subjects included 12 children, with a median age of 146 days (interquartile range, 136-174) and median weight of 5.5 kg (interquartile range, 5.2-7.3) undergoing cardiac surgery and requiring cardiopulmonary bypass with or without deep hypothermic circulatory arrest. Institutional cefazolin at standard doses of 25 mg/kg before incision and 25 mg/kg in the bypass prime solution were administered. Serial plasma and skeletal muscle microdialysis samples were obtained intraoperatively and the unbound cefazolin concentrations measured. Noncompartmental pharmacokinetic analyses were performed and the tissue disposition evaluated. RESULTS After the first dose of cefazolin, the skeletal muscle concentrations peaked at a median microdialysis collection interval of 30 to 38.5 minutes. After the second dose, the peak concentrations were delayed a median of 94 minutes in subjects undergoing deep hypothermic circulatory arrest. Skeletal muscle exposure to cefazolin measured by the area under concentration time curve 0-last measurement was less in the subjects who underwent deep hypothermic circulatory arrest than in those who received cardiopulmonary bypass alone (P = .04). The skeletal muscle concentrations of cefazolin exceeded the goal concentrations for methicillin-sensitive Staphylococcus aureus prophylaxis; however, the goal concentrations for gram-negative pathogens associated with surgical site infections were achieved only 42.1% to 84.2% and 0% to 11.2% of the intraoperative time in subjects undergoing cardiopulmonary bypass alone or deep hypothermic circulatory arrest, respectively. CONCLUSIONS This cefazolin dosing strategy resulted in skeletal muscle concentrations that are likely not effective for surgical prophylaxis against gram-negative pathogens but are effective against methicillin-sensitive S aureus in infants undergoing cardiac surgery.

Urine assay for tenofovir to monitor adherence in real time to tenofovir disoproxil fumarate/emtricitabine as pre‐exposure prophylaxis

Tenofovir disoproxil fumarate/emtricitabine (TDF/FTC) is approved for pre‐exposure prophylaxis (PrEP) against HIV infection. Adherence is critical for the success of PrEP, but current adherence measurements are inadequate for real‐time adherence monitoring. We developed and validated a urine assay to measure tenofovir (TFV) to objectively monitor adherence to PrEP.

A sensitive and selective liquid chromatography/tandem mass spectrometry method for quantitative analysis of efavirenz in human plasma.

A selective and a highly sensitive method for the determination of the non-nucleoside reverse transcriptase inhibitor (NNRTI), efavirenz, in human plasma has been developed and fully validated based on high performance liquid chromatography tandem mass spectrometry (LC–MS/MS). Sample preparation involved protein precipitation followed by one to one dilution with water. The analyte, efavirenz was separated by high performance liquid chromatography and detected with tandem mass spectrometry in negative ionization mode with multiple reaction monitoring. Efavirenz and 13C6-efavirenz (Internal Standard), respectively, were detected via the following MRM transitions: m/z 314.20243.90 and m/z 320.20249.90. A gradient program was used to elute the analytes using 0.1% formic acid in water and 0.1% formic acid in acetonitrile as mobile phase solvents, at a flow-rate of 0.3 mL/min. The total run time was 5 min and the retention times for the internal standard (13C6-efavirenz) and efavirenz was approximately 2.6 min. The calibration curves showed linearity (coefficient of regression, r>0.99) over the concentration range of 1.0–2,500 ng/mL. The intraday precision based on the standard deviation of replicates of lower limit of quantification (LLOQ) was 9.24% and for quality control (QC) samples ranged from 2.41% to 6.42% and with accuracy from 112% and 100–111% for LLOQ and QC samples. The inter day precision was 12.3% and 3.03–9.18% for LLOQ and quality controls samples, and the accuracy was 108% and 95.2–108% for LLOQ and QC samples. Stability studies showed that efavirenz was stable during the expected conditions for sample preparation and storage. The lower limit of quantification for efavirenz was 1 ng/mL. The analytical method showed excellent sensitivity, precision, and accuracy. This method is robust and is being successfully applied for therapeutic drug monitoring and pharmacokinetic studies in HIV-infected patients.

CYP2B6 genotypes and early efavirenz-based HIV treatment outcomes in Botswana

Objectives: To determine the association between cytochrome p450 2B6 genotypes and efavirenz-based HIV treatment outcomes. Design: Observational cohort study of HIV-infected adults initiating efavirenz-based regimens in Botswana. Methods: The primary endpoint was a composite of death or loss to care or HIV RNA more than 25 copies/ml at 6 months. CYP2B6 516G>T and 983T>C genotyping was done with Taqman Open Array platform. Adverse experiences were measured by using the Subject Experience Questionnaire. Metabolism alleles were included in logistic regression models of the composite endpoint. Results: A total of 801 individuals included 406 (51%) men, median age 37 years, median baseline CD4+ cell count 195 cells/&mgr;l, and plasma HIV RNA 4.9 log10 copies/ml. 288 (36%) reached the endpoint, including 34 (4%) deaths, 151 (19%) lost to care, 11 (1%) lost to the study, but alive and in care, and 92 (11%) with plasma HIV RNA more than 25 copies/ml. Metabolism variant alleles were common with 396 (49%) intermediate and 192 (24%) slow metabolizers. There were no statistically significant associations between metabolism and treatment endpoints. However, slower metabolism was associated with fewer adverse experiences. Conclusion: Slow metabolism alleles were associated with lower efavirenz clearance but not any of the treatment endpoints. Slow efavirenz metabolism did not exacerbate central nervous system toxicity. These results should allay concern that slow efavirenz metabolism adversely impacts individuals in sub-Saharan African settings in which these alleles are common.

Modeling and Simulation Approach to Support Dosing and Study Design Requirements for Treating HIV-Related Neuropsychiatric Disease with the NK1-R Antagonist Aprepitant

Psychiatric illness is common in HIV-infected patients and underlines the importance for screening not only for cognitive impairment but also for co-morbid mental disease. The rationale for combining immunomodulatory neurokinin- 1 receptor (NK1-R) antagonists with combined antiretroviral therapy (cART) is based on multimodal pharmacologic mechanisms. The NK1-R antagonist aprepitants potential utility as a drug for depression is complicated by >99.9% protein binding and both enzyme inhibition and induction of CYP3A4. A population-based PK model developed from a pilot Phase 1B trial in 19 HIV-infected patients (125 or 250 mg/d aprepitant for 2 weeks) was modified to account for enzyme induction and impact of an exposure enhancer on CYP3A4 metabolism. Likelihood of clinical success in depression was assessed based on achievement of target trough plasma concentration and evaluated using Monte Carlo simulation. Scenarios were generated for varying daily dose (375, 625, 750 and 875 mg), pharmacokinetic variability, exposure enhancement (EE), duration (2 and 6 months) and sample size (n=12 and 24/arm). Daily dosing of ≥ 625 mg with EE yielded desirable troughs (based on in vitro infectivity experiments) of > 2.65 ug/mL for the majority of virtual patients simulated. Results are dependent on the degree of exposure enhancement and extent of enzyme induction. Actual threshold exposure requirements for aprepitant in HIV-associated depression are unknown though preclinical evidence supports trough levels > 2.65 ug/mL. If 100% NK1r blockage is necessary for efficacy, doses of 875 mg (625 mg with EE) or higher may be required. The benefit of aprepitant on innate immunity(natural killer cells) and absence of negative effects onex vivo neutrophil chemotaxis alleviates concerns regarding drug dependent inhibition (DDI)-mediated infection risk.

A sensitive and selective liquid chromatography/tandem mass spectrometry method for determination of MLN8237 in human plasma

We describe a selective and a highly sensitive high-performance liquid chromatography-electron spray ionization-collision induced dissociation-tandem mass spectrometry (HPLC-ESI-CID-MS/MS) assay for the Aurora A kinase inhibitor MLN8237 in human plasma. The intra-day precision based on the standard deviation of replicates of quality control samples ranged from 0.2 to 4% and with accuracy ranging from 96 to 102%. The inter-day precision ranged from 0.5 to 7% and the accuracy ranged from 93 to 105%. Stability studies showed that MLN8237 was stable both during the expected conditions for sample preparation and storage. The lower limit of quantification for MLN8237 was 5 ng/mL. The analytical method showed excellent sensitivity, precision, and accuracy. This method is robust and is being successfully employed in a Childrens Oncology Group Phase 1 Consortium study of MLN8237 in children with cancer.

Skeletal muscle and plasma concentrations of cefazolin during complex paediatric spinal surgery

BACKGROUND Surgical site infections (SSIs) can have devastating consequences for children who undergo spinal instrumentation. Prospective evaluations of prophylactic cefazolin in this population are limited. The purpose of this study was to describe the pharmacokinetics and skeletal muscle disposition of prophylactic cefazolin in a paediatric population undergoing complex spinal surgery. METHODS This prospective pharmacokinetic study included 17 children with adolescent idiopathic scoliosis undergoing posterior spinal fusion, with a median age of 13.8 [interquartile range (IQR) 13.4-15.4] yr and a median weight of 60.6 (IQR 50.8-66.0) kg. A dosing strategy consistent with published guidelines was used. Serial plasma and skeletal muscle microdialysis samples were obtained during the operative procedure and unbound cefazolin concentrations measured. Non-compartmental pharmacokinetic analyses were performed. The amount of time that the concentration of unbound cefazolin exceeded the minimal inhibitory concentration for bacterial growth for selected SSI pathogens was calculated. RESULTS Skeletal muscle concentrations peaked at a median of 37.6 (IQR 26.8-40.0) µg ml(-1) within 30-60 min after the first cefazolin 30 mg kg(-1) dose. For patients who received a second 30 mg kg(-1) dose, the peak concentrations reached a median of 40.5 (IQR 30.8-45.7) µg ml(-1) within 30-60 min. The target cefazolin concentrations for SSI prophylaxis for meticillin-sensitive Staphylococcus aureus (MSSA) and Gram-negative pathogens were exceeded in skeletal muscle 98.9 and 58.3% of the intraoperative time, respectively. CONCLUSIONS For children with adolescent idiopathic scoliosis undergoing posterior spinal fusion, the cefazolin dosing strategy used in this study resulted in skeletal muscle concentrations that were likely not to be effective for intraoperative SSI prophylaxis against Gram-negative pathogens.

Fasoracetam in adolescents with ADHD and glutamatergic gene network variants disrupting mGluR neurotransmitter signaling

The glutamatergic neurotransmitter system may play an important role in attention-deficit hyperactivity disorder (ADHD). This 5-week, open-label, single-blind, placebo-controlled study reports the safety, pharmacokinetics and responsiveness of the metabotropic glutamate receptor (mGluR) activator fasoracetam (NFC-1), in 30 adolescents, age 12–17 years with ADHD, harboring mutations in mGluR network genes. Mutation status was double-blinded. A single-dose pharmacokinetic profiling from 50–800 mg was followed by a single-blind placebo at week 1 and subsequent symptom-driven dose advancement up to 400 mg BID for 4 weeks. NFC-1 treatment resulted in significant improvement. Mean Clinical Global Impressions-Improvement (CGI-I) and Severity (CGI-S) scores were, respectively, 3.79 at baseline vs. 2.33 at week 5 (P < 0.001) and 4.83 at baseline vs. 3.86 at week 5 (P < 0.001). Parental Vanderbilt scores showed significant improvement for subjects with mGluR Tier 1 variants (P < 0.035). There were no differences in the incidence of adverse events between placebo week and weeks on active drug. The trial is registered at https://clinicaltrials.gov/ct2/show/study/NCT02286817.Stimulant drugs are most commonly used to treat ADHD. Here, the authors demonstrate that in adolescents with ADHD who also have genetic variation in genes impacting metabotropic glutamate signaling, the non-stimulant mGluR activator fasoracetam is well tolerated and may be beneficial in alleviating symptoms of this disease.