Milrinone attenuates the negative inotropic effects of landiolol in halothane-anesthetized dogs

Background: Clinical use of high dose beta-blocker therapy is limited by excessive negative inotropic effects. Previous studies suggest that milrinone may be of utility in limiting the inotropic but not the chronotropic effects of beta blockers. We examined the hemodynamic effects of co-administration of a new potent selective betal blocker, landiolol, and milrinone in halothane-anesthetized dogs. Methods: Eighteen adult mongrel dogs were anesthetized with 1.2 MAC halothane. Hemodynamic measurements were made at baseline, 30 min after starting the milrinone (0.5 mug.kg(-1).min(-1)) or normal saline infusion (n = 9 in each), then 30 min after each change in the dose of landiolol infusion. The tested doses of landiolol were 10, 100, and 1000 mug.kg(-1).min(-1). Results: Landiolol (greater than or equal to = 10 mug.kg(-1).min(-1)) has significant and comparable negative chronotropic effects in both groups of dogs. While it also has significant negative inotropic effects in both groups, such effects are significantly attenuated in the dogs treated with milrinone. Conclusion: Milrinone is effective to attenuate the negative inotropic effects of landiolol in halothane-anesthetized dogs.