Hypoglycaemic agents: Tachycardia associated with hypoglycaemia may be modified by propranolol. Use of propranolol alongside hypoglycaemic therapy in diabetic patients should be with caution since it may prolong the hypoglycaemic response to insulin (see section 4.3 and 4.4).
Anti-arrhythmics: Class I anti-arrhythmic drugs (e.g. disopyramide and flecainide) may have a potentiating effect on atrial-conduction time and induce negative inotropic effect. Concomitant use with class III anti-arrhythmic drugs (e.g. amiodarone) increases the risk of bradycardia, AV block and myocardial depression.
Calcium Channel Blockers: Combined use of beta-adrenoceptor blocking drugs and calcium channel blockers with negative inotropic effects (eg, verapamil, diltiazem) can lead to an exaggeration of these effects particularly in patients with impaired ventricular function and/or SA or AV conduction abnormalities. This may result in severe hypotension, bradycardia and cardiac failure. Neither drug should be administered intravenously within 48 hours of discontinuing the other.
Dihydropyridines: Concomitant therapy with dihydropyridines e.g. nifedipine, may increase the risk of hypotension, and cardiac failure may occur in patients with latent cardiac insufficiency.
Digitalis Glycosides: These preparations in association with beta-adrenoceptor blocking drugs may increase atrio-ventricular conduction time.
Drugs with hypotensive effects: Dynamic interactions between propranolol and other drugs with hypotensive effects are to be expected. Reactions are sometimes severe and careful monitoring is advised in co-administration of propranolol with other drugs including ACE inhibitors, diuretics, angiotensin II receptor antagonists, vasodilator antihypertensives, diazoxide, adrenergic neurone blockers, alpha blockers, moxisylyte, moxonidine, nitrates and methyldopa.
Anaesthesia: Caution must be exercised when using anaesthetic agents with propranolol. The anaesthetist should be informed and the choice of anaesthetic should be the agent with as little negative inotropic activity as possible. Use of beta-adrenoceptor blocking drugs with anaesthetic drugs may result in attenuation of the reflex tachycardia and increase the risk of hypotension. Anaesthetic agents causing myocardial depression are best avoided.
Lidocaine / Bupivacaine: Administration of propranolol during infusion of lidocaine may increase the plasma concentration of lidocaine by approximately 30%. Patients already receiving propranolol tend to have higher lidocaine levels than controls. The combination should be avoided. There is an increased risk of bupivacaine toxicity when used with propranolol.
Neostigmine and other anticholinesterases: Propranolol reduces the efficacy of these compounds in treatment of myasthenia gravis.
Sympathomimetic Agents and Parenteral Adrenaline: Concomitant use of sympathomimetic agents e.g. adrenaline and dobutamine, may counteract the effect of beta-adrenoceptor blocking drugs. Caution should be taken in the parenteral administration of preparations containing adrenaline to people taking beta-adrenoceptor blocking drugs as, in rare cases, vasoconstriction, hypertension and bradycardia may result.
Muscle relaxants (e.g. baclofen): Concomitant use may result in a fall in blood pressure. Tizanidine may also result in bradycardia.
Antidepressants, anxiolytics and hypnotics: Plasma levels of propranolol can be increased by fluvoxamine. Anxiolytics, hypnotics and MAOIs when given with propranolol may have an enhanced hypotensive effect. Propranolol may increase plasma concentration of imipramine. Barbiturates may reduce the plasma concentration of propranolol.
Chlorpromazine: Concomitant administration with propranolol may result in an increase in plasma levels of both drugs. This may lead to an enhanced antipsychotic effect for chlorpromazine and an increased antihypertensive effect for propranolol.
Corticosteroids: Can antagonise the effects of beta-blockers.
Ergotamine: Caution should be exercised if ergotamine, dihydroergotamine or related compounds are given in combination with propranolol since vasospastic reactions have been reported in a few patients.
Prostaglandin Synthetase Inhibiting Drugs: Concomitant use of these e.g. ibuprofen or indomethacin, may decrease the hypotensive effects of propranolol.
Mefloquine: May lead to an increased risk of bradycardia.
Cimetidine, hydralazine: Concomitant use of cimetidine and hydralazine will increase the plasma level of propranolol.
Beta-blockers may exacerbate the rebound hypertension which can follow the withdrawal of clonidine. If the two drugs are co-administered, the betablocker should be withdrawn several days before discontinuing clonidine. If replacing clonidine by beta-blocker therapy, the introduction of betablockers should be delayed for several days after clonidine administration has stopped.
Alcohol (ethanol): Coadministration with alcohol may increase plasma propranolol levels (by enzyme inhibition), where as chronic use of alcohol may lower propranolol levels (by enzyme induction). Alcohol can have variable effects on the hypotensive action of propranolol.
Dopaminergics (e.g. Levodopa), Aldesleukin, Prostaglandins (alprostadil): May have an enhanced hypotensive effect when used concomitantly with propranolol.
Oestrogens: May antagonise the hypotensive effect of propranolol.
5HT1 agonists: Simultaneous administration of rizatriptan and propranolol can cause an increased rizatriptan AUC and Cmax by approximately 70-80%. The increased rizatriptan exposure is presumed to be caused by inhibition of first-passage metabolism of rizatriptan through inhibition of monoamine oxidase-A. If both drugs are to be used, a rizatriptan dose of 5 mg has been recommended.
Pharmacokinetic studies have shown that the following agents may interact with propranolol due to effects on enzyme systems in the liver which metabolise propranolol and these agents: quinidine, propafenone, rifampicin, theophylline, warfarin, thioridazine and dihydropyridine calcium channel blockers such as nifedipine, nisoldipine, nicardipine, isradipine and lacidipine. Owing to the fact that blood concentrations of either agent may be affected, dosage adjustments may be needed according to clinical judgement. (See also the interaction above concerning the concomitant therapy with dihydropyridine calcium channel blockers).