Interactions 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), coadministration with drugs that are metabolized by, or effect the activity (induction or inhibition) of one or more of these pathways may lead to clinically relevant drug interactions (see Drug Interactions under PRECAUTIONS).
Substrates or Inhibitors of CYP2D6
Blood levels and/ or toxicity of propranolol may be increased by coadministration with substrates or inhibitors of CYP2D6, such as amiodarone, cimetidine, delavudin, fluoxetine, paroxetine, quinidine, and ritonavir. No interactions were observed with either ranitidine or lansoprazole.
Substrates or Inhibitors of CYP1A2
Blood levels and/ or toxicity of propranolol may be increased by coadministration 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 and/ or toxicity of propranolol may be increased by coadministration with substrates or inhibitors of CYP2C19, such as fluconazole, cimetidine, fluoxetine, fluvoxamine, tenioposide, and tolbutamide. No interaction was observed with omeprazole.
Inducers of Hepatic Drug Metabolism
Blood levels of propranolol may be decreased by coadministration with inducers such as rifampin, ethanol, phenytoin, and phenobarbital. Cigarette smoking also induces hepatic metabolism and has been shown to increase up to 77% the clearance of propranolol, resulting in decreased plasma concentrations.
Cardiovascular Drugs
Antiarrhythmics
The AUC of propafenone is increased by more than 200% by coadministration of propranolol.
The metabolism of propranolol is reduced by coadministration of quinidine, leading to a two-three fold increased blood concentration and greater degrees of clinical beta-blockade.
The metabolism of lidocaine is inhibited by coadministration 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 coadministration of nisoldipine and by 80% and 47%, by coadministration of nicardipine.
The mean Cmax and AUC of nifedipine are increased by 64% and 79%, respectively, by coadministration of propranolol.
Propranolol does not affect the pharmacokinetics of verapamil and norverapamil. Verapamil does not affect the pharmacokinetics of propranolol.
Non-Cardiovascular Drugs
Migraine 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
Coadministration of theophylline with propranolol decreases theophylline oral clearance by 30% 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 coadministration of propranolol.
Neuroleptic Drugs
Coadministration of long-acting propranolol at doses greater than or equal to 160mg/day resulted in increased thioridazine plasma concentrations ranging from 55% to 369% and increased thioridazine metabolite (mesoridazine) concentrations ranging from 33% to 209%.
Coadministration of chlorpromazine with propranolol resulted in a 70% increase in propranolol plasma level.
Anti-Ulcer Drugs
Coadministration of propranolol with cimetidine, a non-specific CYP450 inhibitor, increased propranolol AUC and Cmax by 46% and 35%, respectively. Coadministration with aluminum hydroxide gel (1200 mg) may result in a decrease in propranolol concentrations.
Coadministration of metoclopramide with the long-acting propranolol did not have a significant effect on propranolol’s pharmacokinetics.
Lipid Lowering Drugs
Coadministration of cholestyramine or colestipol with propranolol resulted in up to 50% decrease in propranolol concentrations.
Coadministration of propranolol with lovastatin or pravastatin, decreased 18% to 23% 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.
Alcohol
Concomitant use of alcohol may increase plasma levels of propranolol.
Caution should be exercised when propranolol hydrochloride tablets are administered with drugs that have an effect on CYP2D6, 1A2, or 2C19 metabolic pathways. Coadministration of such drugs with propranolol may lead to clinically relevant drug interactions and changes on its efficacy and/or toxicity (see Drug Interactions in PHARMACOKINETICS AND DRUG METABOLISM).
Cardiovascular Drugs
Antiarrhythmics
Propafenone has negative inotropic and beta-blocking properties that can be additive to those of propranolol.
Quinidine increases the concentration of propranolol and produces greater degrees of clinical beta-blockade and may cause postural hypotension.
Amiodarone is an antiarrhythmic agent with negative chronotropic properties that may be additive to those seen with β-blockers such as propranolol.
The clearance of lidocaine is reduced with administration of propranolol. Lidocaine toxicity has been reported following coadministration with propranolol.
Caution should be exercised when administering propranolol hydrochloride tablets with drugs that slow A-V nodal conduction, e.g. digitalis, lidocaine and calcium channel blockers.
Digitalis Glycosides
Both digitalis glycosides and beta-blockers slow atrioventricular conduction and decrease heart rate. Concomitant use can increase the risk of bradycardia.
Calcium Channel Blockers
Caution should be exercised when patients receiving a beta-blocker are administered a calcium-channel-blocking drug with negative inotropic and/or chronotropic effects. Both agents may depress myocardial contractility or atrioventricular conduction.
There have been reports of significant bradycardia, heart failure, and cardiovascular collapse with concurrent use of verapamil and beta-blockers.
Coadministration of propranolol and diltiazem in patients with cardiac disease has been associated with bradycardia, hypotension, high degree heart block, and heart failure.
ACE Inhibitors
When combined with beta-blockers, ACE inhibitors can cause hypotension, particularly in the setting of acute myocardial infarction.
The antihypertensive effects of clonidine may be antagonized by beta-blockers. Propranolol hydrochloride tablets should be administered cautiously to patients withdrawing from clonidine.
Alpha Blockers
Prazosin has been associated with prolongation of first dose hypotension in the presence of beta-blockers.
Postural hypotension has been reported in patients taking both beta-blockers and terazosin or doxazosin.
Reserpine
Patients receiving catecholamine-depleting drugs, such as reserpine, should be closely observed for excessive reduction of resting sympathetic nervous activity, which may result in hypotension, marked bradycardia, vertigo, syncopal attacks, or orthostatic hypotension.
Inotropic Agents
Patients on long term therapy with propranolol may experience uncontrolled hypertension if administered epinephrine as a consequence of unopposed alpha-receptor stimulation. Epinephrine is therefore not indicated in the treatment of propranolol overdose (see OVERDOSAGE).
Isoproterenol and Dobutamine
Propranolol is a competitive inhibitor of beta-receptor agonists, and its effects can be reversed by administration of such agents, e.g., dobutamine or isoproterenol. Also, propranolol may reduce sensitivity to dobutamine stress echocardiography in patients undergoing evaluation for myocardial ischemia.