European Journal of Neurology [2011] Dec 5 [Epub ahead of print] (D.Nyholm, A.Johansson, H.Lennernäs, H. Askmark)
Duodopa is a combination of L-dopa and carbidopa in the form of a gel. It is administered throughout the day using a portable pump directly into the small intestine through a surgically placed tube. This ensures a flow of L-dopa that can be adjusted according to the person's needs. It enables more consistent plasma concentrations of L-dopa. The side effects of Duodopa are similar to those observed with oral administration of L-dopa and carbidopa. COMT inhibitors (Catechol-O-methyltransferase inhibitors) may be used to decrease the need for L-dopa, because they reduce its breakdown. COMT inhibitors have already been successfully used orally as Stalevo, which is a combination of L-dopa and carbidopa (the same as Sinemet), plus a COMT inhibitor (Entacapone). So researchers have investigated whether COMT inhibitors can also be taken orally in order to reduce the L-dopa requirement used with Duodopa. Both major COMT inhibitors (entacapone and tolcapone) were tested. The additional oral use of either of the COMT inhibitors was found to reduce the need of L-dopa by 20%. They did this without altering plasma L-dopa concentrations, reducing symptoms, or by reducing "off" time.