Quinidine

Endpoint summary

Description of key information

Quinidine is almost completely absorbed from the gastrointestinal tract. About 70 to 80 % of the plasma quinidine is bound to proteins. 50 to 90 % of quinidine is metabolized in the liver by hydroxylation and metabolic products. Up to 50 % of a dose of quinidine is excreted in urine within 24 hours after administration. Approximately 1 to 3 % is excreted in the feces via the bile.  The half-life of quinidine in plasma is about 5 to 8 hours.

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Absorption rate - oral (%):

80

Additional information

According to the peer-reviewed database, HSDB, oral absorption of quinidine is the most frequent cause of intoxication. Quinidine is almost completely absorbed from the gastrointestinal tract. However, because of hepatic first-pass effect, the absolute bioavailability is about 70 to 80% of the ingested dose and may vary between patients and preparations. The time to plasma peak concentration is 1 to 3 hours for quinidine sulphate, 3 to 6 hours for quinidine gluconate and about 6 hours for quinidine polygalacturonate. Sustained-release quinidine is absorbed continuously over 8 to 12 hours. Absorption of quinidine after intramuscular injection may be erratic and unpredictable with incomplete absorption of the administered dose, probably due to precipitation of drug at the site of injection. About 70 to 80% of the drug is bound to plasma protein. Plasma protein binding is decreased in patients with chronic liver disease. The quinidine concentrations in liver are 10 to 30 times higher than those in plasma. Skeletal and cardiac muscle, brain and other tissues contain intermediate amounts. The red cell plasma partition ratio is 0.82. The half-life is about 6 to 7 hours. It is increased in chronic liver disease and in the elderly. It does not appear to be altered in congestive heart failure or renal failure. 50 to 90% of quinidine is metabolized in the liver to hydroxylated products. Metabolites include 3-hydroxyquinidine, 2 oxoquinidinone, 0-desmethylquinidine, quinidine-N-oxide. The principal metabolite is 3 hydroxyquinidine which exerts similar effects to quinidine and may account for part of the observed antiarrhythmic effects. The elimination kinetics of hydroxyquinidine appear to be similar to those of quinidine. The amount excreted unchanged in urine is variable but is about 17% of an administered dose. Up to 50% of a dose of quinidine (unchanged + metabolites) is excreted in urine within 24 hours after administration. Renal excretion is dependent upon the pH of the urine. 50 to 90% of a dose of quinidine is metabolized in the liver. Approximately 1 to 3% is excreted in the feces via the bile. Quinidine is excreted in breast milk. In the study published by Amlie, 1979 the pharmacokinetic of quinidine was determined. Quinidine showed an absolute bioavailability of 78.4 %. The median AUC was about 66.3 µmol/L *h and the peak plasma concentrations was about 3.19 µmol/L. The half-life of quinidine is in the range of 5-8 hours.