Care should be taken when prescribing beta-adrenoceptor blocking drugs with Class I anti-arrhythmic drugs (e.g. disopyramide) and amiodarone, as they may have potentiating effect on atrial-conduction time and induce negative inotropic effect.
Digitalis glycosides, in association with beta-blockers could increase the atrio-ventricular conduction time.
There is an increased risk of myocardial depression and bradycardia, there is also an increased risk of lidocaine toxicity. The antidysrhythmic propafenone increases plasma concentration of propranolol.
Beta-adrenoceptor blocking drugs should be used with caution in combination with calcium channel blockers such as verapamil or diltiazem in patients with impaired ventricular function and /or sino-atrial or atrio-ventricular conduction abnormalities. This could result in severe hypotension, bradycardia and cardiac failure. These should not be given to patients with conduction abnormalities. Beta-blockers or calcium channel blockers should not be given intravenously within 48 hours of discontinuing either one or the other.
Use with nifedipine or other dihydropyridines may cause an increased risk of hypotension, and heart failure may occur in patients with undiscovered cardiac insufficiency.
Propranolol modifies the tachycardia of hypoglycaemia and care should be taken when treating diabetic patients with Bedranol* SR whether or not they are also taking hypoglycaemic agents. Propranolol may prolong the hypoglycaemic response to insulin.
Use of adrenaline or other sympathomimetics with propranolol may counteract the effect of propranolol. Care should be taken in giving parenteral administration of adrenaline to patients taking beta-blocking drugs as, rarely, vasoconstriction, hypertension and bradycardia may result.
Rebound hypertension which can follow after withdrawal of clonidine may be exacerbated by beta-blockers. Therefore, if the patient is transferring from clonidine to propranolol, the latter treatment should be started several days after clonidine has been stopped. If Bedranol* SR and clonidine are given together, clonidine should be discontinued several days after stopping treatment with Bedranol* SR.
Digitoxin or digoxin taken at the same time as beta-blockers can increase atrioventricular conduction time.
Ergotamine, dihydroergotamine or related compounds given with propranolol have resulted in reports of vasospastic reactions in some patients.
The hypotensive effects of propranolol may be decreased if the patient also takes prostaglandin synthetase inhibitors, eg ibuprofen or indometacin.
If propranolol is taken with chlorpromazine, plasma levels of both agents may be increased, leading to enhanced antipsychotic and elevated antihypertensive effects.
Concomitant administration of rifampicin with propranolol may result in reduced plasma concentrations of propranolol. Thyroxine taken at the same time as propranolol also has this effect.
Cimetidine taken at the same time as propranolol will increase propranolol plasma levels. Fluvoxamine taken with propranolol also has this effect.
Alcohol enhances hypotensive effect, and may increase the plasma levels of propranolol.
Propranolol may affect lidocaine infusion by increasing the plasma concentration of lidocaine by approximately a third and therefore this should be avoided.
ACE inhibitors and Angiotensin-II Antagonists taken at the same time as propranolol may result in enhanced hypotensive effects. Aldesleukin and Alprostadil also has this effect.
Concomitant administration of corticosteroid may result in antagonism of hypotensive effect.
Propranolol may increase plasma concentration of rizatriptan when taken concomitantly.
Beta blockers including propranolol when taken with moxisylyte may result in severe postural hypotension
Concomitant administration of muscle relaxants may result in enhanced hypotensive effect.
Oestrogen and progestrogens, as used in the contraceptive pill, when taken with propranolol may antagonise the hypotensive effect.
The manufacturer of tropisetron advises caution for the co-administration with propranolol.
The concomitant administration of xamoterol with propranolol may result in a reduction in the beta-blockade.
Parasympathomimetics when used with propranolol increase the possibility of arrhythmias.
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-blockers 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.
Interference with laboratory tests: Propranolol has been reported to interfere with the estimation of serum bilirubin by the diazo method and with the determination of catecholamines by methods using fluorescence.
Pharmacodynamic studies have shown the following agents may interact with propranolol due to the effects on enzyme systems in the liver, which metabolise propranolol and the following agents: quinidine, propafenone, rifampicin, theophylline, warfarin, thioridazine, dihydropyridine, calcium channel blockers (e.g. nifedipine, nisoldipine, isradipine and lacidipine). Due 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 concomitant therapy with dihydropyridine calcium channel blockers).