Cross tolerance between two dopaminergic ergot derivatives--bromocriptine and lergotrile.

1. When initially given to patients with idiopathic parkinsonism, lergotrile induced marked supine arterial hypotension. Tolerance to this hypotensive effect developed and larger doses of lergotrile were administered without this adverse effect. 2. Cross tolerance occurred between lergotrile and a structurally related ergot derivative, bromocriptine. A high dose of lergotrile given to patients who had been on long term bromocriptine therapy did not induce any significant hypotension when compared to placebo whereas hypotension still occurred when lergotrile was given after previous treatment with levodopa.