Population Pharmacokinetics and Exposure-Response Analysis for the Phase 3 COSMIC-311 Trial of Cabozantinib for Radioiodine-Refractory Differentiated Thyroid Cancer.

BACKGROUND AND OBJECTIVE: In the USA, cabozantinib was approved for the treatment of patients aged ≥ 12 years with radioiodine-refractory differentiated thyroid cancer (DTC) who progressed on prior vascular endothelial growth factor (VEGFR)-targeted therapy based on the Phase 3 COSMIC-311 trial, which evaluated cabozantinib 60 mg/day versus placebo. Approved dosing is 60 mg/day for adults and for pediatric patients aged ≥ 12 years with body surface area (BSA) ≥ 1.2 m2, and 40 mg/day for pediatric patients aged ≥ 12 years with BSA < 1.2 m2. This report describes a population pharmacokinetic (PopPK) and exposure-response analysis of COSMIC-311. METHODS: A PopPK model was developed using concentration-time data from COSMIC-311 and 6 other cabozantinib studies. The final (full) PopPK model was used to simulate the effect of sex, body weight, race, and patient population. For exposure-response analysis, derived datasets from COSMIC-311 were constructed for time-to-event analyses of progression-free survival (PFS) and safety endpoints. RESULTS: The PopPK analysis included 4746 cabozantinib PK samples from 1745 patients and healthy volunteers. Body weight had minimal impact on cabozantinib exposure but increasing body weight was associated with increased apparent volume of distribution. Based on model-based simulation, adolescents < 40 kg had higher maximum plasma concentration at steady state of cabozantinib 60 mg/day compared to adults. Allometric scaling simulation in adolescents < 40 kg demonstrated higher exposure with 60 mg/day relative to adults receiving the same dose, while exposure with 40 mg/day in adolescents < 40 kg was similar to 60 mg/day in adults. The exposure-response analysis included 115 patients. There was no clear relationship between PFS or dose modification and cabozantinib exposure. A statistically significant relationship was demonstrated for cabozantinib exposure and hypertension (Grade ≥ 3) and fatigue/asthenia (Grade ≥ 3). CONCLUSIONS: These results support the dosing strategy implemented in COSMIC-311 and the BSA-based label recommendations for adolescents. The cabozantinib dose should be reduced to manage adverse events as indicated.

Population Pharmacokinetics and Target Attainment of Ertapenem in Plasma and Tissue Assessed via Microdialysis in Morbidly Obese Patients after Laparoscopic Visceral Surgery.

Ertapenem provides broad-spectrum activity against many pathogens, and its use is relevant for the prophylaxis and treatment of infections in morbidly obese patients undergoing surgery. However, its pharmacokinetics and tissue penetration in these patients are not well defined. We assessed the population pharmacokinetics and target attainment for ertapenem in the plasma, subcutaneous tissue, and peritoneal fluid of morbidly obese patients. Six female patients (body mass index, 43.7 to 55.9 kg/m2) received 1,000 mg ertapenem as 15-min infusions at 0 and 26 h. On day 2, the unbound ertapenem concentrations in plasma, subcutaneous tissue, and peritoneal fluid were measured by microdialysis; total plasma concentrations were additionally quantified. The probability of attaining a target of an unbound ertapenem concentration above the MIC for at least 40% of the dosing interval was predicted via Monte Carlo simulations. The population pharmacokinetic model contained two disposition compartments and simultaneously described all concentrations. For unbound ertapenem, total clearance was 12.3 liters/h (coefficient of variation, 21.6% for between-patient variability) and the volume of distribution at steady state was 57.8 liters in patients with a 53-kg fat-free mass. The area under the concentration-time curve (AUC) for ertapenem was 49% lower in subcutaneous tissue and 25% lower in peritoneal fluid than the unbound AUC in plasma. Tissue penetration was rapid (equilibration half-life, <15 min) and was variable in subcutaneous tissue. Short-term ertapenem infusions (1,000 mg every 24 h) achieved robust (>90%) target attainment probabilities for MICs of up to 1 mg/liter in plasma, 0.25 to 0.5 mg/liter in subcutaneous tissue, and 0.5 mg/liter in peritoneal fluid. Ertapenem presents an attractive choice for many pathogens relevant to morbidly obese patients undergoing surgery. (This study has been registered at ClinicalTrials.gov under identifier NCT01407965.).

Emergence of polymyxin B resistance influences pathogenicity in Pseudomonas aeruginosa mutators.

The interplay between polymyxin B pharmacodynamics and pathogenicity was examined in Pseudomonas aeruginosa PAO1 and isogenic DNA repair-deficient mutators (mutM and mutS strains). Against mutS mutators, polymyxin B initial killing was concentration dependent, with >99.9% bacterial reduction at 2 h followed by regrowth and resistance. The pre- versus postexposed strains were inoculated real time into Galleria mellonella waxworms, resulting in increased median survival times from 20 h to 23 h (P < 0.001). Emergence of resistance in mutS P. aeruginosa resulted in attenuation of virulence.