Comparative tolerability of the newer generation antiparkinsonian agents

In recent years, the treatment of Parkinson's disease has undergone an immense amount of research, resulting in the development of multiple new medications. This has largely been fuelled by dissatisfaction over the development of motor complications secondary to long term levodopa therapy. Different treatment approaches are applied depending on the stage of Parkinson's disease. In early and mild Parkinson's disease, selegiline offers a limited symptomatic effect. Its neuroprotective effect, although at present theoretical, has questionable clinical relevance. Increased mortality associated with selegiline has been reported, although a meta-analysis of 5 different trials did not support this finding. The newer, non-ergoline dopamine agonists, pramipexole and ropinirole, have undergone extensive studies to evaluate their efficacy as monotherapy in early Parkinson's disease. These newer agonists are ideal initial symptomatic medications, primarily because they delay the onset of levodopa-induced motor fluctuations. Efficacy of the newer dopamine agonists in advanced disease seems to be comparable to that of the older agents, bromocriptine and pergolide. Adverse effects can be reduced by starting the medication at a very low dose and then slowly titrating upward. Catechol-O-methyl transferase (COMT) inhibitors are indicated for the treatment of motor fluctuations in advanced disease, particularly the 'wearing-off' phenomenon. Tolcapone, a peripheral and central COMT inhibitor, appears to be quite effective, producing a 47% reduction in 'off' time. Unfortunately, 3 deaths have been observed, which are presumably secondary to tolcapone therapy. The drug has been withdrawn in many countries, and liver enzyme testing is mandatory in the US. Entacapone, a purely peripheral COMT inhibitor with a lower potency than tolcapone, has also proved to be effective and has not been associated with liver damage, obviating the need for testing.