Combigan Drug Interactions

No interaction studies have been performed with COMBIGAN. Although specific drug interactions studies have not been conducted with COMBIGAN, the theoretical possibility of an additive or potentiating effect with CNS depressants (alcohol, barbiturates, opiates, sedatives, or anaesthetics) should be considered.
There is potential for additive effects resulting in hypotension, and/or marked bradycardia when eye drops with timolol are administered concomitantly with oral calcium-channel blockers, guanethidine, beta-blocking agents, antiarrhythmics (including amiodarone), digitalis glycosides or parasympathomimetics. After the application of brimonidine, very rare (<1 in 10,000) cases of hypotension have been reported. Caution is therefore advised when using COMBIGAN with systemic antihypertensives.
Although timolol has little or no effect on the size of the pupil, mydriasis has occasionally been reported when timolol has been used with mydriatic agents such as adrenaline.
Beta-blockers may increase the hypoglycaemic effect of antidiabetic agents. Beta-blockers can mask the sign and symptoms of hypoglycaemia.
The hypertensive reaction to sudden withdrawal of clonidine can be potentiated when taking beta-blockers. Potentiated systemic beta-blockade (e.g. decreased heart rate, depression) has been reported during combined treatment with quinidine and timolol, possibly because quinidine inhibits the metabolism of timolol via the P450 enzyme, CYP2D6.
Tricyclic antidepressants have been reported to blunt the hypotensive effect of systemic clonidine. It is not known whether the concurrent use of these agents with COMBIGAN in humans can lead to resulting interference with the IOP lowering effect. No data on the level of circulating catecholamines after COMBIGAN administration are available. Caution, however, is advised in patients taking tricyclic antidepressants which can affect the metabolism and uptake of circulating amines e.g. chlorpromazine, methylphenidate, reserpine. Concomitant administration of MAO inhibitors is contraindicated (see Contraindications). Patients who have been receiving MAOI therapy should wait 14 days after discontinuation before commencing treatment with COMBIGAN.
Caution is advised when initiating (or changing the dose of) a concomitant systemic agent (irrespective of pharmaceutical form) which may interact which α-adrenergic agonists or interfere with their activity i.e. agonists or antagonists of the adrenergic receptor (e.g. isoprenaline, prazosin).
Although specific drug interactions studies have not been conducted with COMBIGAN, the theoretical possibility of an additive IOP lowering effect with prostamides, prostaglandins, carbonic anhydrase inhibitors and pilocarpine should be considered.
Patients who are receiving a systemic (e.g., oral or intravenous) beta-adrenergic blocking agent and COMBIGAN should be observed for potential additive effects of beta-blockade, both systemic and on intraocular pressure.