Microdosing as a Potential Tool to Enhance Clinical Development of Novel Antibiotics: A Tissue and Plasma PK Feasibility Study with Ciprofloxacin

A single intravenous microdose of radiolabeled ciprofloxacin (1.1 µg) can accurately predict the drug's pharmacokinetics in plasma and subcutaneous tissue but not in epithelial lining fluid. Healthy volunteers received the microdose either with or without a prior therapeutic dose (400 mg). The dose-adjusted area under the concentration–time curve in plasma and subcutaneous tissue was similar between the microdose and therapeutic dose, with ratios within 0.8 to 1.1. Penetration into subcutaneous tissue was comparable across conditions, with tissue-to-plasma ratios of 0.44, 0.44, and 0.38. However, microdose penetration into epithelial lining fluid was highly variable and did not predict therapeutic-dose penetration. Microdosing with microdialysis may aid antimicrobial drug development but requires further study for pulmonary assessments.

Study at a glance

Abstract

Background and Objective In microdose studies, drug pharmacokinetics is measured in humans after administration of subtherapeutic doses. While previous microdose studies focused primarily on plasma pharmacokinetics, we set out to evaluate the feasibility of microdosing for a pharmacokinetic assessment in subcutaneous tissue and epithelial lining fluid. Methods Healthy subjects received a single intravenous bolus injection of a microdose of [ 14 C]ciprofloxacin (1.1 µg, 7 kBq) with (cohort A, n = 9) or without (cohort B, n = 9) a prior intravenous infusion of a therapeutic dose of unlabeled ciprofloxacin (400 mg). Microdialysis and bronchoalveolar lavage were applied for determination of subcutaneous and intrapulmonary drug concentrations. Microdose [ 14 C]ciprofloxacin was quantified by accelerator mass spectrometry and therapeutic-dose ciprofloxacin by liquid chromatography–tandem mass spectrometry. Results The pharmacokinetics of therapeutic-dose ciprofloxacin (cohort A) in plasma, subcutaneous tissue, and epithelial lining fluid was in accordance with previous data. In plasma and subcutaneous tissue, the dose-adjusted area under the concentration–time curve of microdose ciprofloxacin was similar in cohorts A and B and within an 0.8-fold to 1.1-fold range of the area under the concentration–time curve of therapeutic-dose ciprofloxacin. Penetration of microdose ciprofloxacin into subcutaneous tissue was similar in cohorts A and B and comparable to that of therapeutic-dose ciprofloxacin with subcutaneous tissue-to-plasma area under the concentration–time curve ratios of 0.44, 0.44, and 0.38, respectively. Penetration of microdose ciprofloxacin into epithelial lining fluid was highly variable and failed to predict the epithelial lining fluid penetration of therapeutic-dose ciprofloxacin. Conclusions Our study confirms the feasibility of microdosing for pharmacokinetic measurements in plasma and subcutaneous tissue. Microdosing combined with microdialysis is a potentially useful tool in clinical antimicrobial drug development, but its applicability for the assessment of pulmonary pharmacokinetics with bronchoalveolar lavage requires further studies. Clinical Trial Registration ClinicalTrials.gov NCT03177720 (registered 6 June, 2017).