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 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.
Mechanism of Action
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 (beta 1
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.
Pharmacokinetics And Drug MetabolismDistribution
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.
Metabolism and Elimination
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.
Pharmacodynamics
As propranolol concentration increases, so does its beta-blocking
effect, as evidenced by a reduction in exercise-induced tachycardia (n=6 normal
volunteers).
Special PopulationsPediatric
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.
Geriatric
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).
Gender
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.
Obesity
In a study of intravenously administered propranolol, obese
subjects had a higher AUC (161 versus 109 hr•µg/L) and lower total clearance
than did non-obese subjects. Propranolol plasma protein binding was similar in
both groups.
Renal Insufficiency
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 P450 activity.
Hepatic Insufficiency
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).
Thyroid Dysfunction
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.
Drug InteractionsInteractions with Substrates, Inhibitors or Inducers
of Cytochrome P-450 Enzymes
Because propranolol’s metabolism involves multiple pathways in
the cytochrome P-450 system (CYP2D6, 1A2, 2C19), administration of propranolol
with drugs that are metabolized by, or affect the activity (induction or
inhibition) of one or more of these pathways may lead to clinically relevant
drug interactions (see PRECAUTIONS, Drug
Interactions).
Substrates or Inhibitors of CYP2D6
Blood levels of propranolol may be increased by administration of
propranolol with substrates or inhibitors of CYP2D6, such as amiodarone,
cimetidine, delavirdine, fluoxetine, paroxetine, quinidine, and ritonavir. No
interactions were observed with either ranitidine or lansoprazole.
Substrates or Inhibitors of CYP1A2
Blood levels of propranolol may be increased by administration of
propranolol with substrates or inhibitors of CYP1A2, such as imipramine,
cimetidine, ciprofloxacin, fluvoxamine, isoniazid, ritonavir, theophylline,
zileuton, zolmitriptan, and rizatriptan.
Substrates or Inhibitors of CYP2C19
Blood levels of propranolol may be increased by administration of
propranolol with substrates or inhibitors of CYP2C19, such as fluconazole,
cimetidine, fluoxetine, fluvoxamine, teniposide, and tolbutamide. No interaction
was observed with omeprazole.
Inducers of Hepatic Drug Metabolism
Blood levels of propranolol may be decreased by administration of
propranolol with inducers such as rifampin and ethanol. Cigarette smoking also
induces hepatic metabolism and has been shown to increase up to 100% the
clearance of propranolol, resulting in decreased plasma concentrations.
Cardiovascular DrugsAntiarrhythmics
The AUC of propafenone is increased by more than 200% with
co-administration of propranolol.
The metabolism of propranolol is reduced by co-administration of quinidine,
leading to a 2- to 3-fold increased blood concentrations and greater
beta-blockade.
The metabolism of lidocaine is inhibited by co-administration of propranolol,
resulting in a 25% increase in lidocaine concentrations.
Calcium Channel Blockers
The mean Cmax and AUC of propranolol are
increased respectively, by 50% and 30% by co-administration of nisoldipine and
by 80% and 47%, by co-administration of nicardipine.
The mean values of Cmax and AUC of nifedipine are
increased by 64% and 79%, respectively, by co-administration of propranolol.
Propranolol does not affect the pharmacokinetics of verapamil and
norverapamil. Verapamil does not affect the pharmacokinetics of
propranolol.
Non-Cardiovascular DrugsMigraine Drugs
Administration of zolmitriptan or rizatriptan with propranolol
resulted in increased concentrations of zolmitriptan (AUC increased by 56% and
Cmax by 37%) or rizatriptan (the AUC and Cmax were increased by 67% and 75%, respectively).
Theophylline
Co-administration of theophylline with propranolol decreases
theophylline clearance by 33% to 52%.
Benzodiazepines
Propranolol can inhibit the metabolism of diazepam, resulting in
increased concentrations of diazepam and its metabolites. Diazepam does not
alter the pharmacokinetics of propranolol.
The pharmacokinetics of oxazepam, triazolam, lorazepam, and alprazolam are
not affected by co-administration of propranolol.
Neuroleptic Drugs
Co-administration of propranolol at doses greater than or equal
to 160 mg/day resulted in increased thioridazine plasma concentrations ranging
from 50% to 370% and increased thioridazine metabolites concentrations ranging
from 33% to 210%.
Co-administration of chlorpromazine with propranolol resulted in increased
plasma levels of both drugs (70% increase in propranolol concentrations).
Anti-Ulcer Drugs
Co-administration of propranolol with cimetidine, a non-specific
CYP450 inhibitor, increased propranolol concentrations by about 40%.
Co-administration with aluminum hydroxide gel (1200 mg) resulted in a 50%
decrease in propranolol concentrations.
Co-administration of metoclopramide with propranolol did not have a
significant effect on propranolol’s pharmacokinetics.
Lipid Lowering Drugs
Co-administration of cholesteramine or colestipol with
propranolol resulted in up to 50% decrease in propranolol concentrations.
Co-administration of propranolol with lovastatin or pravastatin decreased 20%
to 25% the AUC of both, but did not alter their pharmacodynamics. Propranolol
did not have an effect on the pharmacokinetics of fluvastatin.
Warfarin
Concomitant administration of propranolol and warfarin has been
shown to increase warfarin bioavailability and increase prothrombin time.