Acute effects of escalating doses of amiodarone in isolated guinea pig hearts

Kinetic analysis of myocardial uptake and negative inotropic effect of amiodarone in rat heart

The distribution kinetics of the highly lipophilic antiarrhythmic agent amiodarone is not well understood. The purpose of the present investigation was to develop a pharmacokinetic-pharmacodynamic (PK/PD) model to describe cardiac uptake and the negative inotropic effect of amiodarone in the isolated perfused rat heart. Amiodarone (10 microM) was infused for 15 min to 6 hearts. The time course of outflow concentration and left ventricular developed pressure were measured and analyzed by the model. The uptake of amiodarone by the heart was flow limited and characterized by an extremely high partition coefficient with a predicted tissue washout half-live of 17 h. Only 36.8% of input amount to heart recovered within 45 min after start of the 15 min infusion. The negative inotropic effect was delayed with a time constant of 11 min and the maximal decrease in left ventricular developed pressure was described by a sigmoid E(max) model with an E(max) of 37.7% and an EC(50) of 0.53 microM. Our results suggest a rapid tissue uptake and a moderate negative inotropic effect of amiodarone after intravenous injection.

Sensitivity and specificity of isolated perfused guinea pig heart to test for drug-induced lengthening of QTc

INTRODUCTION

The purpose of this study was to determine the sensitivity and specificity for predicting the liability of a compound to lengthen QTc using isolated, perfused guinea pig hearts (Langendorff preparation).

METHODS

QTc (Fridericia correction) was calculated from bipolar transventricular electrograms. Hearts were exposed to escalating concentrations of 26 compounds thought to lengthen, and 13 compounds thought not to lengthen, QTc in humans.

RESULTS

In this preparation, QTc was found to lengthen in 26 of 26 compounds thought to be positive (sensitivity 1.00) and not to lengthen or to lengthen insignificantly in 13 of 13 compounds thought to be negative (specificity 1.0) in man. Probucol and ontazolast could not be studied because of limited solubility. Successful experiments were conducted on over 98% of guinea pigs anesthetized.

DISCUSSION

We believe that the isolated perfused guinea pig heart is an in vitro preparation that could be utilized early in preclinical testing for identifying a liability to lengthen QTc in humans, but we do not believe--as is true also for other in vitro methods--that the concentration at which the liability is demonstrated in vitro necessarily predicts the concentration at which a liability exists in man.