Morphomics-informed population pharmacokinetic and physiologically-based pharmacokinetic modeling to optimize cefazolin surgical prophylaxis.

INTRODUCTION: Cefazolin is the leading antibiotic used to prevent surgical site infections worldwide. Consensus guidelines recommend adjustment of the cefazolin dose above and below 120 kg without regard to body composition. Algorithms exist to repurpose radiologic data into body composition (morphomics) and inform dosing decisions in obesity. OBJECTIVES: To compare the current standard of body weight to morphomic measurements as covariates of cefazolin pharmacokinetics and aid dose stratification of cefazolin in patients with obesity undergoing colorectal surgery. METHODS: This prospective study measured cefazolin plasma, fat, and colon tissue concentrations in colorectal surgery patients in order to develop a morphomics-informed population pharmacokinetic (PopPK) model to guide dose adjustments. A physiologically-based pharmacokinetic (PBPK) model was also constructed to inform tissue partitioning in morbidly obese patients (n = 21, body mass index ≥35 kg/m2 with one or more co-morbid conditions). RESULTS: Morphomics and pharmacokinetic data were available in 58 patients with a median [min, max] weight and age of 95.9 [68.5, 148.8] kg and 55 [25, 79] years, respectively. The plasma-to-subcutaneous fat partition coefficient was predicted to be 0.072 and 0.060 by the PopPK and PBPK models, respectively. The estimated creatinine clearance (eCLcr ) and body depth at the third lumbar vertebra (body depth_L3) were identified as covariates of cefazolin exposure. The probability of maintaining subcutaneous fat concentrations above 2 µg/mL for 100% of a 4-h surgical period was below 90% when eCLcr ≥105 mL/min and body depth_L3 ≥ 300 mm and less sensitive to the rate of infusion between 5 and 60 min. CONCLUSIONS: Kidney function and morphomics were more informative than body weight as covariates of cefazolin target site exposure. Data from more diverse populations, consensus on target cefazolin exposure, and comparative studies are needed before a change in practice can be implemented.

Pharmacokinetics of Polymyxin B in Hospitalized Adults with Cystic Fibrosis.

The optimal polymyxin B dosage needed to achieve an efficacy target of 50 to 100 mg · h/liter when treating multidrug-resistant bacterial infections in adult cystic fibrosis (CF) patients is unclear. The pharmacokinetics of intravenous polymyxin B were evaluated to better inform dosing. This was a prospective, observational pharmacokinetic (PK) study of nine CF adults receiving intravenous polymyxin B as part of usual clinical care. Doses preceding PK sampling ranged from 50 to 100 mg every 12 h. Five PK samples were collected following the fourth or fifth dose and concentrations of polymyxin subcomponents B1 and B2 were quantified using liquid chromatography mass spectrometry (LC-MS). Population PK (NONMEM software) analysis was performed using pooled polymyxin B1+B2 concentrations. Participants were Caucasian, predominantly male, with mean age and weight of 31 years (range 21 to 57 years) and 58.0 kg (range 38.3 to 70.4 kg), respectively. A 1-compartment zero-order infusion and linear elimination model adequately described the data with estimated clearance and volume of distribution being 2.09 liters/h and 12.7 liters, respectively, corresponding to a 4.1 h mean half-life (t1/2). Although body weight was observed to influence the volume of distribution, a fixed dose of 75 mg every 12 h was predicted to achieve the target steady-state exposure. Neurotoxicities were reported in all patients, with acute kidney injury events in two patients. These events resolved within 2 to 4 days after discontinuing polymyxin B. Fixed maintenance dosing of polymyxin B without loading is predicted to achieve the targeted therapeutic exposure in CF adults. Treatment-limiting neurotoxicities are very common in this population.