Pharmacokinetics and Pharmacodynamics of Nebulized and Intratracheal Milrinone in a Swine Model of Hypercapnia Pulmonary Hypertension

Objectives: Milrinone pulmonary administration is used currently for the treatment of pulmonary hypertension. Several methods are available: simple jet nebulization, vibrating mesh nebulization, intratracheal instillation, and intratracheal atomization. The aim of this study was to explore the concentration-effect relationship of milrinone for each of these methods.

Design: Observational open-label pharmacokinetic/pharmacodynamics cohort study.

Setting: Single-center, hospital animal laboratory.

Participants: Twelve swine.

Interventions: After hypercapnia pulmonary hypertension, swine were administered equivalent inhaled milrinone doses of 15 or 50 µg/kg through simple jet nebulization, vibrating mesh nebulization, intratracheal instillation, and intratracheal atomization.

Measurements and main results: Blood and urine samples were taken up to 360 minutes postadministration. The ratio of mean systemic arterial pressure to mean pulmonary arterial pressure was monitored continuously. Right heart echographies were taken before and after hypercapnia and after drug administration. Mean elimination half-lives were similar for the 4 administrations. Mean percent changes in the ratio were of 37 (60%), 18 (31%), 17 (36%), and 20 (20%), for simple jet nebulization, vibrating mesh nebulization, intratracheal instillation, and intratracheal atomization, respectively. Mean maximum plasma concentrations for intratracheal administrations were reached at 8 and 45 min for atomization and instillation, respectively. Significant increases in right atrial diameter and right ventricular end-diastolic area were witnessed during pulmonary hypertension as well as a return to baseline values after milrinone administration.

Conclusions: The intratracheal methods, particularly intratracheal atomization, showed less hemodynamic effect than nebulizations and, in the case of intratracheal instillation, unpredictable drug exposure. Nebulization methods on the other hand, especially simple jet nebulization, suggest better efficacy and sensitivity but are less fit for emergency situations.