Clearance of Amlodipine, Fentanyl, Fluconazole, Methylprednisolone, and Midazolam by Continuous Renal Replacement Circuits

Critically ill pediatric patients on continuous renal replacement therapy (CRRT) have high mortality rates ranging from 30% to 70%, due in part to altered drug exposure from drug-CRRT circuit interactions. Drug loss within CRRT circuits can occur through both clearance by the hemofilter and adsorption to circuit components. Although these interactions are known to exist, their impact on the pharmacokinetics of most drugs is unknown, resulting in limited drug dosing guidance and increased risk for suboptimal drug exposure. In this study, we administered amlodipine, fentanyl, fluconazole, methylprednisolone, and midazolam individually and in combination with ex vivo, closed-loop, blood-primed CRRT circuits to quantify drug-circuit interactions. Circuits were dosed to drug-specific therapeutic concentrations, and drug concentrations in both plasma and effluent were measured over time. For all drugs administered individually, variable extraction by the CRRT circuit was observed (mean plasma recovery 0.4-49%). For drugs coadministered into a circuit, significant decreases in extraction and increases in drug recovery (2.5-109%) were found, suggesting dosing adjustments may be needed. This study highlights the need for additional studies of drug coadministration within CRRT circuits to describe complex drug-circuit and drug-drug interactions to provide dosing guidance in pediatric CRRT patients.

The Impact of Suboptimal 25-Hydroxyvitamin D Levels and Cholecalciferol Replacement on the Pharmacokinetics of Oral Midazolam in Control Subjects and Patients With Chronic Kidney Disease

The aim of this study was to investigate the impact of suboptimal 25-hydroxyvitamin D (25-VitD) and cholecalciferol (VitD3 ) supplementation on the pharmacokinetics of oral midazolam (MDZ) in control subjects and subjects with chronic kidney disease (CKD). Subjects with CKD (n = 14) and controls (n = 5) with suboptimal 25-VitD levels (<30 ng/mL) were enrolled in a 2-phase study. In phase 1 (suboptimal), subjects were administered a single oral dose of VitD3 (5000 IU) and MDZ (2 mg). In phase 2 (replete) subjects who achieved 25-VitD repletion after receiving up to 16 weeks of daily cholecalciferol were given the identical single oral doses of VitD3 and MDZ as in phase 1. Concentrations of MDZ and metabolites, 1'-hydroxymidazolam (1'-OHMDZ), and 1'-OHMDZ glucuronide (1'-OHMDZ-G) were measured by liquid chromatography-tandem mass spectrometry and pharmacokinetic analysis was performed. Under suboptimal 25-VitD, reductions in MDZ clearance and renal clearance of 47% and 87%, respectively, and a 72% reduction in renal clearance of 1'-OHMDZ-G were observed in CKD vs controls. In phase 1 versus phase 2, MDZ clearance increased in all control subjects, with a median (interquartile range) increase of 10.5 (0.62-16.7) L/h. No changes in MDZ pharmacokinetics were observed in subjects with CKD between phases 1 and 2. The effects of 25-VitD repletion on MDZ disposition was largely observed in subjects without kidney disease. Impaired MDZ metabolism and/or excretion alterations due to CKD in a suboptimal 25-VitD state may not be reversed by cholecalciferol therapy. Suboptimal 25-VitD may augment the reductions in MDZ and 1'-OHMDZ-G clearance values observed in patients with CKD.