PROPRANOLOL HYDROCHLORIDE- propranolol hydrochloride injection
West-Ward Pharmaceuticals Corp
Propranolol Hydrochloride, USP is a synthetic beta-adrenergic receptor blocking agent chemically described as (+)-1-(isopropylamino)-3-(1-naphthyloxy)-2-propanol hydrochloride. Its structural formula is:
C16 H21 NO2 •HCl
Propranolol Hydrochloride, USP is a stable, white, crystalline solid which is readily soluble in water and ethanol. Its molecular weight is 295.80.
Propranolol Hydrochloride Injection, USP is available as a sterile injectable solution for intravenous administration. Each mL contains 1 mg of Propranolol Hydrochloride, USP in Water for Injection, USP. The pH is adjusted with anhydrous Citric Acid, USP.
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 doses 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.
The effects of propranolol are due to selective blockade of beta-adrenergic receptors, leaving alpha-adrenergic responses intact. There are two well-characterized subtypes of beta receptors (beta1 and beta2 ); propranolol interacts with both subtypes equally. Beta1 -adrenergic receptors are found primarily in the heart. Blockade of cardiac beta1 -adrenergic receptors leads to a decrease in the activity of both normal and ectopic pacemaker cells and a decrease in A-V nodal conduction velocity. All of these actions can contribute to antiarrhythmic activity and control of ventricular rate during arrhythmias. Blockade of cardiac beta1 ‑adrenergic receptors also decreases the myocardial force of contraction and may provoke cardiac decompensation in patients with minimal cardiac reserve.
Beta2 -adrenergic receptors are found predominantly in smooth muscle–vascular, bronchial, gastrointestinal and genitourinary. Blockade of these receptors results in constriction. Clinically, propranolol may exacerbate respiratory symptoms in patients with obstructive pulmonary diseases such as asthma and emphysema (see CONTRAINDICATIONS and WARNINGS).
Propranolol’s beta blocking effects are attributable to its S(-) enantiomer.
Propranolol has a distribution half-life (T½ alpha) of 5-10 minutes and a volume of distribution of about 4 to 5 L/kg. Approximately 90% of circulating propranolol is bound to plasma proteins. The binding is enantiomer-selective. The S-isomer is preferentially bound to alpha1 glycoprotein and the R-isomer is preferentially bound to albumin.
The elimination half-life (T½ beta) is between 2 and 5.5 hours. Propranolol is extensively metabolized with most metabolites appearing in the urine. The major metabolites include propranolol glucuronide, naphthyloxylactic acid, and glucuronic acid and sulfate conjugates of 4-hydroxy propranolol. Following single-dose intravenous administration, side-chain oxidative products account for approximately 40% of the metabolites, direct conjugation products account for approximately 45-50% of metabolites, and ring oxidative products account for approximately 10-15% of metabolites. Of these, only the primary ring oxidative product (4-hydroxypropranolol) possesses beta-adrenergic receptor blocking activity.
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.
As propranolol concentration increases, so does its beta-blocking effect, as evidenced by a reduction in exercise-induced tachycardia (n = 6 normal volunteers).
The pharmacokinetics of propranolol have not been investigated in patients under 18 years of age. Propranolol injection is not recommended for treatment of cardiac arrhythmias in pediatric patients.
Elevated propranolol plasma concentrations, a longer mean elimination half-life (254 vs. 152 minutes), and decreased systemic clearance (8 vs. 13 mL/kg/min) have been observed in elderly subjects when compared to young subjects. However, the apparent volume of distribution seems to be similar in elderly and young subjects. These findings suggest that dose adjustment of propranolol injection may be required for elderly patients (see PRECAUTIONS).
Intravenously administered propranolol was evaluated in 5 women and 6 men. When adjusted for weight, there were no gender-related differences in elimination half-life, volume of distribution, protein binding, or systemic clearance.
In a study of intravenously administered propranolol, obese subjects had a higher AUC (161 versus 109 hr·mcg/L) and lower total clearance than did non-obese subjects. Propranolol plasma protein binding was similar in both groups.
The pharmacokinetics of propranolol and its metabolites were evaluated in 15 subjects with varying degrees of renal function after propranolol administration via the intravenous and oral routes. When compared with normal subjects, an increase in fecal excretion of propranolol conjugates was observed in patients with increased renal impairment. Propranolol was also evaluated in 5 patients with chronic renal failure, 6 patients on regular dialysis, and 5 healthy subjects, following 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 ng/mL) than those observed in the dialysis patients (47 ng/mL) and in the healthy subjects (26 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 downregulation of hepatic cytochrome P-450 activity.
Propranolol is extensively metabolized by the liver. In a study conducted in 6 normal subjects and 20 patients with chronic liver disease, including hepatic cirrhosis, 40 mg of R-propranolol was administered intravenously. Compared to normal subjects, patients with chronic liver disease had decreased clearance of propranolol, increased volume of distribution, decreased protein-binding, and considerable variation in half-life. Caution should be exercised when propranolol is used in this population. Consideration should be given to lowering the dose of intravenous propranolol in patients with hepatic insufficiency (see PRECAUTIONS).
No pharmacokinetic changes were observed in hyperthyroid or hypothyroid patients when compared to their corresponding euthyroid state. Dosage adjustment does not seem necessary in either patient population based on pharmacokinetic findings.
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