Drug Interactions between bromocriptine and timolol ophthalmic

MONITOR: Several case reports have suggested that beta-blockers may potentiate the vasoconstrictive action of ergot alkaloids. The exact mechanism of interaction is unknown, but may involve blockade of beta-2-mediated (i.e., sympathetic) vasodilatation. In addition, beta-1 blockade reduces cardiac output, which can diminish blood flow and exacerbate ergot-induced vasospasm. Peripheral ischemia, hypertension with chest pain, gangrene resulting in surgical amputation, and migraine exacerbation have been described in suspected cases of the interaction. Reported cases have involved the noncardioselective beta-blockers, propranolol and oxprenolol. However, a theoretical risk also exists with cardioselective beta-blockers, since beta-1 selectivity is not absolute and may be lost with larger doses. The interaction may also occur with beta-blocker ophthalmic preparations, since they may be systemically absorbed and can produce clinically significant systemic effects even at low or undetectable plasma levels. In any case, the interaction appears to be rare, and patients have taken both drugs without adverse effects.

MANAGEMENT: Except for increased awareness of the interaction, no specific intervention appears to be necessary. Patients should be advised to seek immediate medical attention if they experience potential symptoms of ischemia such as coldness, pallor, cyanosis, numbness, tingling, or pain in the extremities; muscle weakness; severe or worsening headache; visual disturbances; severe abdominal pain; chest pain; and shortness of breath.