Pharmacodynamic modelling of levodopa, 3-O-methyldopa and their effects: an application of the Dixon equation.
The modified Dixon equation was applied to describe the relationship between levodopa, 3-O-methyldopa (3OMD) concentrations and tapping test in 16 patients with Parkinson's disease treated with controlled release levodopa/carbidopa association. The sigmoid equation was also used to describe the relationship between levodopa and tapping test, and the results were compared to those obtained using the Dixon equation. Graphically, the fittings using the Dixon equation can be constructed in a three-dimensional space, whereas the fittings using the sigmoid equation can be constructed in a two-dimensional plane. The results show that the fittings in the three-dimensional space are slightly better than those in the two-dimensional plane. The advantage of the Dixon equation over the sigmoid equation is that the Dixon equation can take 3OMD into consideration for pharmacodynamic modelling.
Wu
G
G
Institute of Clinical Pharmacology and Toxicology, Medical School, University of Udine, P.le S. Maria della Misericordia, Udine, 33100, Italy.
Furlanut
M
M
D000368:Aged; D004347:Drug Interactions; D005260:Female; D006801:Humans; D007980:Levodopa / Q000493:pharmacokinetics / Q000494:pharmacology*; D008297:Male; D015233:Models, Statistical; D010300:Parkinson Disease / Q000188:drug therapy / Q000378:metabolism*; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology
D014443:Tyrosine; D007980:Levodopa; C008404:3-methoxytyrosine