New strategies with dopaminergic drugs: modified formulations of levodopa and novel agonists.

Most new pharmacological therapies in Parkinson's disease focus on the dopaminergic system. Drugs that enhance dopaminergic function fall into three primary categories: amino acid precursors to dopamine, agonists that stimulate dopamine receptors, and enzyme antagonists that prevent the metabolism of dopamine and hence permit more or prolonged neurotransmitter activity; the first two are discussed below. Within the first category, levodopa is the amino acid precursor to dopamine, and a number of modifications in its formulation have been developed to enhance dopaminergic activity. In the area of agonists, new agents pramipexole, ropinerole, and cabergoline have recently been developed to complement the currently available bromocriptine and pergolide, and these new drugs may be released in the United States.