Comparative Plasma Pharmacokinetics of Ceftriaxone and Ertapenem in Normoalbuminemia, Hypoalbuminemia, and Albumin Replacement in a Sheep Model

Optimal concentrations of unbound antimicrobials are essential for a maximum microbiological effect. Although hypoalbuminemia and albumin fluid resuscitation are common in critical care, the effects of different albumin concentrations on the unbound concentrations of highly protein-bound antimicrobials are not known. The aim of this study was to compare the effects of different albumin states on total and unbound concentrations of ertapenem and ceftriaxone using an ovine model. The study design was a prospective, three-phase intervention observational study. The subjects were healthy Merino sheep. Eight sheep were subjected to three experimental phases: normoalbuminemia, hypoalbuminemia using plasmapheresis, and albumin replacement using a 25% albumin solution. In each phase, ceftriaxone at 40 mg/kg of body weight and ertapenem at 15 mg/kg were given intravenously. Blood samples were collected at predefined intervals and analyzed using an ultrahigh-performance liquid chromatography-tandem mass spectrometry method. Pharmacokinetic parameters such as the area under the curve from 0 to 24 h (AUC 0-24 ), plasma clearance (CL), and apparent volume of distribution in the terminal phase ( V ) were estimated and compared between the phases. The protein and albumin concentrations were significantly different between phases. Hypoalbuminemia resulted in a significantly lower AUC 0-24 and higher CL of total and unbound concentrations of ceftriaxone than in the other phases, whereas albumin replacement led to higher AUC 0-24 and lower CL than in the other phases for both drugs. The V values for total drug concentrations for both drugs were significantly lower with albumin replacement. For highly protein-bound drugs such as ceftriaxone and ertapenem, both hypoalbuminemia and albumin replacement may affect unbound drug exposure.