Possible Interaction: Propranolol and Quinidine

“In order to estimate the pharmacodynamic action of the pharmacokinetic interaction, the change in the heart rate during treadmill … testing was studied in group A. A significant inhibition of exercise-induced tachycardia was observed after administration of propranolol alone, but … combination with quinidine an even greater suppression was evident.”

“ Quinidine induced a significant rise in the plasma concentrations of propranolol , and the area under the propranolol concentration-time curves (AUC) was also increased about 3-fold in both groups, indicative of an alteration of propranolol pharmacokinetics.”

“These results indicate that the coadministration of propranolol and quinidine provides not only the potentiation of quinidine action by propranolol, which has been reported, but also the enhancement of propranolol action by quinidine, due to an increased plasma concentration of propranolol.”

“Inhibition studies showed that quinidine inhibited approximately 55% of propranolol 4-hydroxylation and furaphylline (CYP1A2-selective inhibitor) inhibited about 45% of propranolol 4-hydroxylation.”

“ Quinidine , a specific inhibitor of CYP2D6, inhibited propranolol 4- and 5-hydroxylase activities selectively and in a concentration-dependent manner.”

“ Quinidine differentially affected the metabolism of (+)‐propranolol and (−)‐propranolol, resulting in an increase of 176.6% ± 45.5% and 100.4% ± 25.5% in the area under the plasma concentration—time curve of (+)‐propranolol and (−)‐propranolol, respectively (p < 0.05).”

“The combination of propranolol and quinidine resulted in increased ß‐blockade measured by reduction in exercise heart rate and prolongation of the QTc and PR intervals.”

“The increased concentration of propranolol produced by quinidine results in increased β‐blockade.”

“The metabolism of propranolol by the 4‐hydroxylation pathway was almost abolished by quinidine , resulting in a fall in the partial metabolic clearance by this pathway from 678 ± 246 to 56 ± 11 ml/min (p < 0.05).”

“We conclude that quinidine stereoselectively inhibits the metabolism of propranolol through inhibition of the debrisoquin isozyme.”

“Physicians should be alerted to the possibility of orthostatic hypotension when the alpha blocking effects of quinidine are combined with a beta blocking agent such as propranolol.”

“In 8 additional patients no single drug tested was effective, and quinidine in combination with either mexiletine (7 patients) or propranolol (1 patient) prevented the initiation of VT during electrophysiologic testing.”

“Therefore in patients receiving propranolol, quinidine levels may be higher than expected shortly after dosage, and therefore a potential for transient toxicity exists in these patients.”

“The additive antiarrhythmic action of combined propranolol and quinidine therapy may be helpful in managing CAM.”

“Treatment or prevention of various cardiac arrhythmias was attempted by the combined use of propranolol and quinidine in small doses, in 22I patient trials.”

“Combined treatment with propranolol plus quinidine produced conversion to sinus rhythm in 65% of the cases of atrial fibrillation and maintained that rhythm once it had been reestablished for at least”