Motor fluctuations in parkinsonian patients can be reduced by intraduodenal infusion of levodopa. Between 1991 and 1998 continuous daytime administration of levodopa through a transabdominal port has been used in 28 very advanced patients over a total period of 1045 months. A stable suspension of levodopa and carbidopa (Duodopa) has been developed. Patients were characterized by early onset, long history of disease and levodopa therapy. The reason for infusion was in all cases related to on-off fluctuations. All patients experienced a general improvement after the introduction of continuous treatment. There have been no severe complications. Six patients have taken the decision to curtail their treatment. The mean daily levodopa consumption has been slightly reduced on infusion as compared to oral therapy. Nine of the first group of patients participating in the new therapy have been regularly evaluated by means of rating scales and movement analyses. Short-term results have already been published and a follow-up showing continued positive effect after 4-7 years of continuous duodenal infusion is presented.

Positron emission tomography (PET) seems to be a valuable method for the understanding of intestinal absorption mechanisms, for simultaneous quantitation of absorption rate and distribution kinetics to the tissues of interest after oral drug delivery. PET was evaluated in three Rhesus monkeys for quantitation of the absorption rate from the gastrointestinal tract and the distribution kinetics into different organs. To obtain optimal standardized conditions for the measurement of absorption the drug was administered via a naso–duodenal catheter directly to the absorption site in the proximal small intestine. l-DOPA was used as study drug given in a suspension together with carbidopa and the radiomarker l-[β-11C]DOPA. The l-DOPA suspension was given into the duodenum without and after administration of a suspension of six l-amino acids (120 mM) in order to investigate any interaction on the intestinal absorption and distribution of l-DOPA into the liver and brain tissue. Intestinal absorption was in general minor during the first study period and higher together with administered l-amino acids. The somewhat contradictory result with increased absorption when amino acids were present in the intestinal lumen, may be a consequence of increased intestinal motility initiated by the nutrient load.

The mechanisms controlling rates and routes for intestinal absorption of nutrients and small compounds are still not fully clarified. In the present study we aimed to investigate the effect of solvent drag on intestinal permeability of compounds with different molecular sizes in humans and rats. The effective intestinal permeabilities ( P eff ) of hydrophilic compounds (MW 60–4000) were determined in the single‐pass perfused jejunum in humans in vivo and rats in situ under iso‐ and hypotonic conditions. The transport mechanism(s) of water and the importance of the solvent drag effect were investigated by the use of D 2 O. This is the first report in humans establishing the relation between in vivo measured jejunal P eff and molecular size for hydrophilic compounds. In addition, in rats we also found a molecular‐size selectivity for hydrophilic compounds similar to man. The jejunal P eff of water and urea (MW 60) in both species were several times higher than predicted from their physicochemical properties. In humans, the jejunal absorption of urea and creatinine (MW 113) was increased by solvent drag, while no effect was found for the other investigated compounds. In rats, P eff for urea and creatinine were unaffected. In conclusion, it is still unclear if solvent drag occurs mainly through the para‐ or transcellular route, although, results from this study further add to our earlier reports suggesting that the transcellular route is most important from a quantitative point of view regardless of physicochemical properties of the transported compounds.

OBJECTIVE:To evaluate the effects of continuous duodenal infusion of levodopa over time on the disabling fluctuations in motor performance in advanced parkinsonian patients. It has earlier been demonstrated that these fluctuations can be reduced by keeping the plasma concentration of levodopa constant.MATERIAL AND METHODS:In view of the low water solubility of levodopa a stable dispersion of the drug was developed and used for continuous intraduodenal infusion in patients with advanced Parkinson's disease. Nine patients were evaluated with respect to an optimal oral treatment, during nasoduodenal infusion by a portable pump and then followed for 6 months to 2 1/2 years when treated via transabdominal infusion. Upon each test occasion, over 2 non-consecutive days, objective movement analysis by means of an opto-electronic system was applied every 15-20 min and video recordings performed twice every h. On several test occasions plasma levodopa concentrations were analysed every 15 min.RESULTS:The patients showed improvement and decreased variance of their motor function. In the 2 patients followed over a period of 2 1/2 years levodopa plasma concentration showed reduced fluctuations on infusion and the levodopa consumption as well as mean levodopa plasma concentration decreased.CONCLUSION:Continuous duodenal infusion of levodopa is an alternative treatment strategy for patients with advanced Parkinson's disease when conventional therapy has failed.

Food ingestion can influence the absorption of levodopa in the intestine and thereby contribute to fluctuations of motor functions in Parkinson patients. Obstruction of the active transport of levodopa by amino acids can be one factor. Paracellular drug absorption, a route proposed to be influenced by net transport of water across the intestinal epithelium, might occur for a small and hydrophilic drug such as levodopa. In the present study we studied how luminal L-leucine (60 mmol/L), alone or combined with hypotonicity, might stimulate net water absorption, and levodopa uptake in the human small intestine, since this possibly can contribute to the variable intestinal absorption of levodopa. The Loc-I-Gut perfusion technique was used in 10 healthy volunteers to study the effects of induced net fluid absorption on the small intestinal absorption of levodopa (2.5 mmol/L). An induced net fluid absorption was observed only when L-leucine was combined with a hypoosmolar perfusion solution. However, this did not enhance the intestinal permeability of levodopa. In conclusion, we suggest that the variability in the absorption of levodopa in Parkinson’s disease cannot be explained by differences in transmucosal water flux in the human small intestine.

1. A new method for perfusing a 10 cm segment of jejunum in humans has been used in seven subjects to study the effect of the amino acid L-leucine (40 mM) on the intestinal absorption of levodopa (2.5 mM). The tube contains six channels and has two inflatable balloons, which enable a perfusion of a closed and defined segment of the proximal small intestine. 2. L-leucine decreased the intestinal absorption of levodopa from 40 +/- 19 to 21 +/- 15% but was without effect on the absorption of antipyrine, benserazide and D-glucose. 3. We confirm that levodopa is absorbed by the active transport system normally responsible for the absorption of large neutral amino acids (LNAA) in humans. Oral absorption by passive diffusion, probably by the paracellular route, might also occur for levodopa in the proximal part of the small intestine.

Assuming the presence of clinically significant cholinergic hypofunction in amyotrophic lateral scleroses (ALS), seven patients with ALS were treated with 100–200 mg tetrahydroaminoacridine (THA) together with 11 g lecithin daily for up to 7 weeks. In a separate experiment pharmacokinetics and effects on muscle strength and neurophysiological parameters were studied following the injection of 30 mg THA intravenously. Following the injection of THA an increase in muscle strength was observed in two patients. There were no consistent pharmacokinetic differences that could explain the effect on intravenous THA on muscle strength in these two patients. The plasma clearance of THA was high and the oral bioavailability low with large interindividual differences (6–36%). No beneficial effect was seen during oral medication and side-effects were common. There were no conclusive changes observed regarding neurophysiological parameters after drug administration. THA has probably no place in the treatment of ALS.