Use of physiologically‐based pharmacokinetic modeling to inform dosing of the opioid analgesics fentanyl and methadone in children with obesity

Obesity is an increasingly alarming public health threat, with nearly 20% of children classified as obese in the United States today. Children with obesity are commonly prescribed the opioids fentanyl and methadone, and accurate dosing is critical to reducing the risk of serious adverse events associated with overexposure. However, pharmacokinetic studies in children with obesity are challenging to conduct, so there is limited information to guide fentanyl and methadone dosing in these children. To address this clinical knowledge gap, physiologically‐based pharmacokinetic models of fentanyl and methadone were developed in adults and scaled to children with and without obesity to explore the interplay of obesity, age, and pharmacogenomics. These models included key obesity‐induced changes in physiology and pharmacogenomic effects. Model predictions captured observed concentrations in children with obesity well, with an overall average fold error of 0.72 and 1.08 for fentanyl and methadone, respectively. Model simulations support a reduced fentanyl dose (1 vs. 2 μg/kg/h) starting at an earlier age (6 years) in virtual children with obesity, highlighting the importance of considering both age and obesity status when selecting an infusion rate most likely to achieve steady‐state concentrations within the target range. Methadone dosing simulations highlight the importance of considering genotype in addition to obesity status when possible, as cytochrome P450 (CYP)2B6*6/*6 virtual children with obesity required half the dose to match the exposure of wildtype children without obesity. This physiologically‐based pharmacokinetic modeling approach can be applied to explore dosing of other critical drugs in children with obesity.

Results of a phase I study of bevacizumab (BV), everolimus (EV), and erlotinib (E) in patients with advanced solid tumors

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Background: BV inhibits vascular endothelial growth factor (VEGF). EV is an mTOR (mammalian target of rapamycin) inhibitor. E inhibits epidermal growth factor receptor (EGFR) tyrosine kinase. VEGF, mTOR, and EGFR inhibitors have anti-tumor and anti-angiogenesis effects alone and in combination in preclinical models. As a combination targeted therapy, we evaluated BV + EV + E in a phase I, pharmacokinetic (PK), biomarker study. Methods: Cycle length was 28 days. Doses: BV 10mg/kg IV q14d. EV 5mg PO QD, escalating to 10mg QD. Once the recommended phase II dose (RPTD) of BV + EV was reached, E was added, starting at 75 mg PO QD. DLT was defined as any treatment-related grade 4 heme or grade 3/4 non-heme event in Cycle 1. Results: 34 pts have been enrolled (18 F, 16 M), 28 evaluable for DLT, 24 for efficacy. Median age is 58y (range 29–73). Dose level 1 (BV 10mg/EV 5mg) had no DLT’s. Dose level 2 (BV 10mg/EV 10mg) had no DLT’s and the cohort was expanded to 13 evaluable pts. E (75mg) was added to BV 10mg/ EV 10mg. 2/6 patients had DLT (grade 3 mucositis and grade 3 rash). The doses were adjusted to BV 5mg/EV 5mg/E 75mg. 3 patients had no DLT and this dose is the MTD and RPTD for the 3-drug combination. 20 more patients are being enrolled at the RPTD for biomarker studies. Other grade ¾ toxicity included: nephrotic syndrome, cardiac ischemia, ventricular thrombus, portacath thrombosis, and bowel perforation. 2 patients had PR: 1 renal and 1 osteosarcoma. 16/24 pts had SD (10–112+ weeks). 5/6 patients with colorectal cancer (CRC) previously progressing on BV had SD (16+ - 112 weeks). One CRC patient had 19% radiologic decrease. Conclusions: BV + EV + E preliminary clinical activity (notably in refractory CRC) and class-related side effects were seen. The MTD is BV 5mg/kg IV q14d + EV 5mg PO QD + E 75mg PO QD. Updated data will be presented.

No significant financial relationships to disclose.

Preliminary results of a phase I study of bevacizumab (BV) in combination with everolimus (E) in patients with advanced solid tumors

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Background: BV is a potent inhibitor of vascular endothelial growth factor (VEGF) with broad clinical activity. E is an mTOR (mammalian target of rapamycin) inhibitor in development for cancer and solid organ transplant therapy. VEGF and mTOR inhibitors have anti-tumor and anti-angiogenesis effects alone and in combination in preclinical models. As a combination anti-angiogenesis therapy, we evaluated BV + E in a phase I, pharmacokinetic (PK), biomarker study. Methods: BV was dosed at 10mg/kg IV q14d. E was dosed at 5mg PO QD, escalating to 10mg QD. Cycle length was 28 days. DLT was defined as any grade 4 heme or grade 3/4 non-heme event in Cycle 1 related to treatment. Pts had advanced solid tumors, adequate organ function, and no increased risks for class-related toxicities. Serial blood samples were collected for PK studies of E. Dermal wound angiogenesis assays were performed pre and on treatment for phospho VEGFR2, AKT, mTOR, and S6K. Results: 14 pts have been enrolled (8 F, 6 M), 12 evaluable for toxicity, 14 for efficacy. Median age is 58y (range 29–73). At dose level 1 (BV 10mg/E 5mg) there were no DLT’s in 5 pts. At dose level 2 (BV 10mg/E 10mg), no DLT’s were noted in the initial 3 pts and the cohort was expanded to 9 pts. Side effects were primarily grade 1–2: pain (10/14), mucositis (9/14), anorexia (8/14), rash (7/14), bleeding (7/14), hyperlipidemia (6/14), fatigue (6/14), and HTN (4/14). 1 pt had a myocardial infarction at day 72 and one pt developed nephrotic syndrome at day 70. 7/14 pts had stable disease as best response (70–278d). Conclusions: BV + E is generally well-tolerated. Preliminary clinical activity and class-related side effects were noted. The recommended phase II dose is BV 10mg/kg IV q14d and E 10mg PO QD.

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Cloning and DNA sequencing of the fbc operon encoding the cytochrome bc1 complex from Rhodobacter sphaeroides. Characterization of fbc deletion mutants and complementation by a site-specific mutational variant

The ubiquinol: cytochrome-c oxidoreductase (cytochrome bc1 complex) is a central component of the mitochondrial respiratory chain as well as the respiratory and/or photosynthetic systems of numerous prokaryotic organisms. In Rhodobacter sphaeroides, the bc1 complex has a dual function. When the cells are grown photosynthetically, the bc1 complex is present in the intracytoplasmic membrane and is a critical component of the cyclic electron transport system. When the cells are grown in the dark in the presence of oxygen, the same bc1 complex is a necessary component of the cytochrome-c2-dependent respiratory chain. The fact that the bc1 complex from R. sphaeroides has been extensively studied, plus the ability to manipulate this organism genetically, makes this an ideal system for using site-directed mutagenesis to address questions relating to the structure and function of the bc1 complex. In the current work, the cloning and complete sequence of the fbc operon from R. sphaeroides is reported. As in other bacteria, this operon contains three genes, encoding the Rieske 2Fe-2S subunit, the cytochrome b subunit, and the cytochrome c1 subunit. Recombination techniques were used to delete the entire fbc operon from the chromosome. The resulting strain cannot grow photosynthetically, but can grow aerobically utilizing a quinol oxidase. Photosynthetic growth is restored by providing fbc operon on a plasmid, and the reappearance of the protein subunits and the spectroscopic features due to the bc1 complex are also demonstrated. Finally, a mutation is introduced within the gene encoding the cytochrome b subunit which is predicted to confer resistance to the inhibitor myxothiazol. It is shown that the resulting strain contains a functional bc1 complex which, as expected, is resistant to the inhibitor. Hence, this system is suitable for the detailed characterization of the bc1 complex, combining site-directed mutagenesis with the biochemical and biophysical techniques which have been previously developed for the study of photosynthetic bacteria.