Doxapram-mediated Increase in Cardiac Output Reduces Opioid Plasma Concentrations: A Pharmacokinetic/Pharmacodynamic-Pharmacokinetic/Pharmacodynamic Modeling Study in Healthy Volunteers.

Doxapram is an analeptic that induces ventilatory stimulation and increases blood pressure and cardiac output (CO). Its mechanism of action is the blockade of background K+ -channels expressed on type 1 carotid body cells. In the randomized controlled trial, the authors explored the role of the increase in CO by doxapram (plasma concentration (Cp) 1,000-3,500 ng/mL) on the pharmacokinetics (PKs) and pharmacodynamics (PDs) of the potent opioid alfentanil (Cp 100-200 ng/mL). Population PK-PD analyses were performed on the doxapram PK-CO data and the alfentanil PK-antinociception data. The analyses showed that the doxapram-induced increase in CO explained the increase in alfentanil distribution and elimination clearances causing a significant reduction in plasma alfentanil Cp and antinociception. This novel approach in which one PK-PD model effectively drives another PK-PD model highlights the importance of physiological influences on PK and PD of a potent opioid with rapid onset of effect and low clinical margin of safety.