INNOPRAN XL

INNOPRAN XL- propranolol hydrochloride capsule, extended release
GlaxoSmithKline LLC

DESCRIPTION

INNOPRAN XL (propranolol hydrochloride) is a nonselective, beta-adrenergic receptor-blocking agent for oral administration, available as an extended release product. INNOPRAN XL is available as 80-mg and 120-mg capsules which contain sustained-release beads. Each of the beads contains propranolol hydrochloride and is coated with dual membranes. These membranes are designed to retard release of propranolol hydrochloride for several hours after ingestion followed by the sustained release of propranolol.

The active ingredient in INNOPRAN XL is a synthetic beta-adrenergic receptor-blocking agent chemically described as 1-(Isopropylamino)-3-(1-naphthyloxy)-2-propanol hydrochloride. Its structural formula is:

propranolol hydrochloride chemical structure
(click image for full-size original)

Propranolol hydrochloride is a stable, white, crystalline solid, which is readily soluble in water and ethanol. Its molecular weight is 295.81. Each capsule for oral administration contains sugar spheres, ethylcellulose, povidone, hypromellose phthalate, diethyl phthalate, hypromellose, polyethylene glycol, gelatin, titanium dioxide, and black iron oxide. In addition, INNOPRAN XL 120 mg capsules contain yellow iron oxide.

CLINICAL PHARMACOLOGY

General

Propranolol is a nonselective, beta-adrenergic receptor-blocking agent possessing no other autonomic nervous system activity. It specifically competes with beta-adrenergic receptor-stimulating agents for available receptor sites. When access to beta-receptor sites is blocked by propranolol, chronotropic, inotropic, and vasodilator responses to beta-adrenergic stimulation are decreased proportionately. At dosages greater than required for beta blockade, propranolol also exerts a quinidine-like or anesthetic-like membrane action, which affects the cardiac action potential. The significance of the membrane action in the treatment of arrhythmias is uncertain.

Mechanism of Action

The mechanism of the antihypertensive effect of propranolol has not been established. Among factors that contribute to the antihypertensive action are: (1) decreased cardiac output, (2) inhibition of renin release by the kidneys, and (3) diminution of tonic sympathetic nerve outflow from vasomotor centers in the brain. Although total peripheral resistance may increase initially, it readjusts to or below the pretreatment level with chronic use of propranolol. Effects of propranolol on plasma volume appear to be minor and somewhat variable.

Pharmacokinetics and Drug Metabolism

Absorption

Propranolol is highly lipophilic and is almost completely absorbed after oral administration. However, it undergoes high first-pass metabolism by the liver and on average, only about 25% of propranolol reaches the systemic circulation.

A single-dose, food-effect study in 36 healthy subjects showed that a high fat meal administered with INNOPRAN XL at 10 p.m., increased the lag time from 3 to 5 hours and the time to reach the maximum concentration from 11.5 to 15.4 hours, under fed conditions, with no effect on the AUC (see DOSAGE AND ADMINISTRATION).

Following multiple-dose administration of INNOPRAN XL at 10 p.m. under fasting conditions, the steady state lag time was between 4 and 5 hours and propranolol peak plasma concentrations were reached approximately 12 to 14 hours after dosing. Propranolol trough levels were achieved 24 to 27 hours after dosing, and persisted for 3 to 5 hours after the next dose. The elimination half-life of propranolol was approximately 8 hours.

The plasma levels of propranolol showed dose-proportional increases after single and multiple administration of 80-, 120-, and 160-mg of INNOPRAN XL.

At steady state, the bioavailability of a 160-mg dose of INNOPRAN XL and propranolol hydrochloride long-acting capsules did not differ significantly.

Distribution

Approximately 90% of circulating propranolol is bound to plasma proteins (albumin and alpha1 acid glycoprotein). The binding is enantiomer-selective. The S-isomer is preferentially bound to alpha1 glycoprotein and the R-isomer preferentially bound to albumin. The volume of distribution of propranolol is approximately 4 liters.

Metabolism and Elimination

Propranolol is extensively metabolized with most metabolites appearing in the urine. Propranolol is metabolized through 3 primary routes: Aromatic hydroxylation (mainly 4-hydroxylation), N-dealkylation followed by further side-chain oxidation, and direct glucuronidation. It has been estimated that the percentage contributions of these routes to total metabolism 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.

Enantiomers

Of the 2 enantiomers of propranolol, the S-enantiomer blocks beta adrenergic receptors. 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.

Special 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, 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 evaluated 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 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 Insufficiency

The pharmacokinetics of INNOPRAN XL have not been evaluated in patients with renal insufficiency. 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 2- to 3-fold higher (161±41 ng/mL) than 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.

Propranolol is not significantly dialyzable.

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