tabolism are 42%, 41%, and 17%, respectively, but with considerable variability between individuals. The 4 major metabolites are propranolol glucuronide, naphthyloxylactic acid, and glucuronic acid and sulfate conjugates of 4-hydroxy propranolol.
In vitro studies have indicated that the aromatic hydroxylation of propranolol is catalyzed mainly by polymorphic CYP2D6. Side-chain oxidation is mediated mainly by CYP1A2 and to some extent by CYP2D6. 4-hydroxy propranolol is a weak inhibitor of CYP2D6.
Propranolol is also a substrate for CYP2C19 and a substrate for the intestinal efflux transporter, p-glycoprotein (p-gp). Studies suggest however that p-gp is not dose-limiting for intestinal absorption of propranolol in the usual therapeutic dose range.
In healthy subjects, no difference was observed between CYP2D6 extensive metabolizers (EMs) and poor metabolizers (PMs) with respect to oral clearance or elimination half-life. Partial clearance to 4-hydroxy propranolol was significantly higher and to naphthyloxylactic acid was significantly lower in EMs than PMs.
In normal subjects receiving oral doses of racemic propranolol, S-enantiomer concentrations exceeded those of the R-enantiomer by 40 to 90% as a result of stereoselective hepatic metabolism.
The elimination half-life of propranolol was approximately 8 hours.
12.6 Specific Populations
Pediatric: The pharmacokinetics of INNOPRAN XL have not been investigated in patients younger than 18 years of age.
Geriatric: The pharmacokinetics of INNOPRAN XL have not been investigated in patients older than 65 years. In a study of 12 elderly (62 to 79 years old) and 12 young (25 to 33 years old) healthy subjects administered immediate-release propranolol, the clearance of the S-enantiomer of propranolol was decreased in the elderly. Additionally, the half-lives of both R- and S-propranolol were prolonged in the elderly compared with the young (11 hours versus 5 hours).
Gender: In a dose-proportionality study, the pharmacokinetics of INNOPRAN XL were eva luated in 22 male and 14 female healthy volunteers. Following single doses under fasting conditions, the mean AUC and Cmax were about 49% and 16% higher for females across the dosage range. The mean elimination half-life was longer in females than in males (11 hours versus 7.5 hours).
Race: A study conducted in 12 white and 13 African-American male subjects taking immediate-release propranolol showed, that at steady state, the clearance of R- and S-propranolol were about 76% and 53% higher in African-Americans than in whites, respectively.
Renal Impairment: The pharmacokinetics of propranolol after administration of INNOPRAN XL have not been eva luated in patients with renal impairment. In a study conducted in 5 patients with chronic renal failure, 6 patients on regular dialysis, and 5 healthy subjects, who received a single oral dose of 40 mg of propranolol, the peak plasma concentrations (Cmax) of propranolol in the chronic renal failure group were 3- to 5-fold (161±41 ng/mL) those observed in the dialysis patients (47±9 ng/mL) and in the healthy subjects (26±1 ng/mL). Propranolol plasma clearance was also reduced in the patients with chronic renal failure.
Chronic renal failure has been associated with a decrease in drug metabolism via down regulation of hepatic cytochrome P450 activity. &nb
